AJP - Regu Fuel your research with LabChart
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Am J Physiol Regul Integr Comp Physiol 288: R1279-R1287, 2005. First published December 16, 2004; doi:10.1152/ajpregu.00560.2004
0363-6119/05 $8.00
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
288/5/R1279    most recent
00560.2004v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chen, K.
Right arrow Articles by Rose, J. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chen, K.
Right arrow Articles by Rose, J. C.

DEVELOPMENTAL PHYSIOLOGY AND PREGNANCY

The effect of hypothalamo-pituitary disconnection on the renin-angiotensin system in the late-gestation fetal sheep

Kai Chen,1 Luke C. Carey,1 Jingfang Liu,1 Nancy K. Valego,2 Stephen B. Tatter,3 and James C. Rose1,2

Departments of 1Obstetrics/Gynecology, 2Physiology/Pharmacology, and 3Neurosurgery, Wake Forest University School of Medicine, Winston-Salem, North Carolina

Submitted 16 August 2004 ; accepted in final form 11 December 2004


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
The activity of the renin-angiotensin system (RAS) increases significantly in the late-gestation fetal sheep. Fetal cortisol is also increased during this time, and it is thought that the increase in cortisol may modulate the RAS changes. Previous studies have examined the effects of cortisol infusion on RAS activity, but the effects of blocking the peripartum increase in cortisol concentrations on the developmental changes in the RAS are not known. Therefore, we utilized the technique of hypothalamic-pituitary disconnection (HPD), which prevents the cortisol surge from occurring, to investigate the importance of the late-gestation increase in cortisol on the ontogenic changes in RAS activity. HPD of fetal sheep was performed at 120 days of gestational age (dGA), and fetuses were delivered between 135 and 139 dGA. Control fetuses were sham operated. HPD blocked the late-gestation cortisol increase but did not alter renal renin mRNA, renal renin or prorenin protein content, nor plasma renin levels compared with sham operated. However, HPD fetuses had increased ANG II receptor subtype 1 (AT1) mRNA and protein expression in the kidney and lungs. ANG II receptor subtype 2 (AT2) expression was not altered in these tissues at either mRNA or protein level. HPD did not change AT1 or AT2 mRNA in the left ventricle but did result in decreased protein levels for both receptors. These studies demonstrate that blockade of the naturally occurring increase in fetal cortisol concentration in late gestation is associated with tissue-specific alterations in expression of AT1 and AT2 receptors. These changes may impact on fetal tissue maturation and hence have consequences in postnatal life.

ovine fetus; cortisol

PREVIOUS STUDIES INDICATE that all components of the renin-angiotensin system (RAS) in fetal sheep are detectable in the kidney at 0.27 of gestation (65). It has also been demonstrated that renin, angiotensinogen, ANG I, and ANG II are present in the fetal circulation (18, 41). During fetal development, both activity and function of the RAS change significantly. Human and animal studies reveal that renal renin mRNA and protein levels peak during the perinatal period , while there is an overall increase in RAS activity on parturition (7, 11, 20, 39, 64). It has also been noted in the sheep and horse fetus that plasma angiotensin converting enzyme (ACE) concentrations (15, 16, 37) and ANG II levels (44) significantly increase close to term.

ANG II exerts its effects via specific receptors, classified, on the basis of selective antagonism by peptidic and nonpeptidic ligands, as type 1 (AT1) and type 2 (AT2) (9, 57). It is apparent that the expression of both ANG II receptor subtypes is developmentally regulated (19, 54, 60). In the fetal sheep, renal AT1 mRNA expression is low during the first half of pregnancy but significantly elevated in the last third of gestation (42, 66). In contrast, AT2 receptor expression is maximal by the middle of gestation and then declines thereafter to almost undetectable levels close to parturition (17, 42, 66). Interestingly, it has been noted that functionality of the fetal RAS alters with these ontogenic changes in receptor subtype expression. In early gestation, the fetal RAS plays a major role in promoting cellular growth and organ differentiation (14, 19, 38, 40), while in late gestation it modulates fetal blood pressure and fluid and electrolyte homeostasis (41, 44, 45). The mechanisms regulating these changes are not clear.

In late gestation, activity of the fetal hypothalamo-pituitary adrenal (HPA) axis also increases significantly, culminating in a cortisol surge close to term. To this extent, it has been demonstrated that glucocorticoids induce enzyme activity in many fetal tissues in preparation for delivery and extrauterine life (15). For example, in the sheep and horse fetus, the increase in plasma angiotensin converting enzyme (ACE) concentration near term closely parallels the prepartum rise in plasma cortisol levels (16, 37). Previous studies also suggest that cortisol may play an important role in regulating fetal RAS activity in late gestation (15), but the effects of cortisol infusion on renin levels in late gestation are controversial. Both decreases (52, 69) and increases have been noted (15). Although the data are limited to mRNA levels, cortisol infusions have also been reported to decrease AT1 (52) and have no effect on AT2 receptor expression in the sheep fetus (42). The effects of decreased cortisol concentrations on RAS activity in the late-gestation sheep fetus have not been examined.

Disconnecting the hypothalamus from the pituitary (hypothalamic-pituitary disconnection, HPD) results in retarded HPA axis development and resultant activity. Most notably, following HPD there is no surge in fetal plasma cortisol concentrations in late gestation (2, 3, 12, 72). With this in mind, the present study was designed to examine the importance of endogenous cortisol in regulating the fetal sheep RAS in late gestation, specifically by assessing how blocking the naturally occurring increase in cortisol levels close to term affects plasma and renal renin and prorenin concentrations, and AT1 and AT2 receptor expression in kidney, heart, and lung. We chose these particular tissues as the RAS is purported to play developmental and/or functional roles in all (5, 49, 53–55).


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 
Animal preparation and surgical procedures. Cross-bred pregnant ewes with known insemination dates were obtained from a local supplier. All procedures were approved by the Wake Forest University School of Medicine Institutional Animal Care and Use Committee. Ewes were housed in individual pens with food and water provided ad libitum. After 5 days of acclimatization, surgery was performed. After surgery, ewes were returned to their pens where they remained until the fetuses were delivered. A total of 10 fetuses were used: 5 HPD (3 male, 2 female) and 5 controls (3 male, 2 female).

Surgical preparation. Surgeries were performed at ~120 days of gestational age (dGA). Polyvinyl catheters previously filled with sterile saline were inserted into the fetal femoral arteries and veins and advanced to the descending aorta and inferior vena cava, and HPD was performed as described by Antolovich et al. (1), with slight modifications (72).

Catheters from the fetus and maternal arterial and venous catheters were exteriorized through a small incision in the maternal flank, placed into a sterile glove and protected by netting placed around the ewe's abdomen. When a control operation was performed, all steps of the surgery were done except the median eminence and pituitary stalk were not separated, the median eminence tissue was not removed, and a piece of latex glove was placed near the intact pituitary stalk. Gentamicin and ampicillin were administered to the ewe at the time of surgery and for the next 3 days through the maternal venous catheter. Blood samples were taken from both ewe and fetus every other day to assess fetal and maternal health via blood gas and pH measurements. Fetal plasma samples were collected following 3 days of postsurgery recovery, and just prior to necropsy for measurement of cortisol. Thyroxine (T4) and triiodothyronine (T3) were measured immediately before necropsy. Fetuses were delivered by cesarean section between 135 and 139 dGA, and tissues (kidney, heart, and lung) were collected, processed, and stored at –80°C until required for assay. Completeness of HPD was confirmed by both visual examination at the time of necropsy and by measuring plasma cortisol concentrations.

Cortisol, T4, and T3 measurement. Cortisol was measured by radioimmunoassay (RIA) using a kit from Diagnostic Systems Laboratories (Webster, TX) that measures total cortisol. This assay has been validated for measuring fetal cortisol levels. The minimum detectable amount of cortisol was 0.6 ng/ml. Coefficients of variation were 4.2% intra-assay and 7.0% interassay.

T4 was measured by RIA using a kit from ICN Pharmaceuticals (Costa Mesa, CA) that measures total T4. The minimum detectable amount of T4 was 0.76 ng/dl. Coefficients of variation were 5.3% intra-assay and 7.9% interassay. T3 was measured by enzyme immunoassay assay using a kit from Diagnostic Systems Laboratories. The minimum detectable amount of T3 was 0.4 ng/dl. Coefficients of variation were 5.7% intra-assay and 6.7% interassay.

Plasma active renin measurement. Plasma active renin concentration (ARC) was measured as a function of the amount of ANG I generated from angiotensinogen. To measure renin concentration independent of endogenous angiotensinogen, the method was slightly modified from that described for renin activity. Excess renin substrate (0.5 ml of adult nephrectomized sheep plasma) was added to each aliquot (0.1 ml) of plasma along with the enzyme inhibitors, dimercaprol, 8-hydroxyquinoline, and maleate buffer (pH 6.0, to ensure a constant pH at the optimum for renin activity). One milliliter of this mixture was then incubated at 37°C while the rest was maintained at 4°C for 1 h. The ANG I generated was measured by RIA kit (PerkinElmer Life and Analytical Sciences, Boston, MA). All samples from an animal were analyzed simultaneously and in duplicate, and all assays included samples from control and HPD animals. Results are expressed as nanograms ANG I per milliliter plasma per hour of incubation.

Tissue ARC measurement. Approximately 100 mg of renal cortex was homogenized on ice for 45 s in 4 ml of saline, the homogenate was centrifuged at 2,100 g for 10 min, and the resultant supernatant was collected. An aliquot was taken for protein determination, while the remainder was frozen at –80 °C until time of assay. For the assay, samples were diluted with saline containing 5.2 mM BAL (2,3-dimercapto-1-propanol), 0.59 mM 8-hydroxyquinoline, and 10 mM disodium EDTA. ARC was determined as for plasma and is expressed as nanograms per milligram of protein per hour of incubation.

Renal prorenin concentration measurement. Prorenin concentrations were determined by measuring active renin before and after treatment of kidney homogenate with bovine pancreatic trypsin at a concentration determined to yield maximum renin activation. Each lot of trypsin was tested by constructing a dose-response curve with pooled plasma or kidney homogenate. Once the optimal dose of trypsin was established for each, this dose was used for subsequent assays. Trypsin activation was at 4°C and pH 7.3 for 0.5 h. The activation was stopped by addition of trypsin inhibitor at room temperature for 15 min. The total renin concentration represented the sum of active and prorenin.

RNA extraction. Total tissue RNA was extracted using standard procedures recommended by the manufacturer of Trizol (Gibco BRL, Carlsbad, CA). Briefly, tissues were homogenized in Trizol reagent (50 mg tissue/1 ml Trizol) using a high-speed polytron for 30–60 s. Chloroform was added (0.2 ml/1 ml Trizol), and the mixture was incubated at room temperature for 5 min, before centrifugation at 12,000 g for 15 min at 4°C. The aqueous phase was transferred to a fresh tube, and the RNA was precipitated by the addition of isopropanol (0.5 ml/1 ml Trizol) and recentrifuged at 7,500 g at 4°C for 5 min. The isopropanol was removed, and the RNA pellets were allowed to air dry and then redissolved in RNase-free water. RNA concentrations were determined by absorbance at 260 nm in a spectrophotometer. The integrity of all RNA samples was determined by electrophoresis on a 1.0% agarose gel containing 6.6% formaldehyde.

Synthesis of antisense RNA probes. The probe used for sheep renin mRNA was partial sheep renin cDNA from coordinates 117–983 cloned into pGEM-T easy (Promega. Madison, WI) and cut with the restriction enzyme EcoR1 to linearize the plasmid in preparation for in vitro transcription. The probe used for sheep AT1 mRNA was partial sheep AT1 cDNA from coordinates 114–783 cloned into pGEM-T easy (Promega. Madison, WI) and cut with the restriction enzyme SpeI to linearize the plasmid in preparation for in vitro transcription. The probe used for sheep AT2 mRNA was partial sheep AT2 cDNA from coordinates 142–921 cloned into pT7/T3 U18 (Ambion, Austin, TX) and cut with the restriction enzyme Hind III to linearize the plasmid in preparation for in vitro transcription.

In vitro transcription was performed by adding the following items in this order {4 µl 5x transcription buffer, 2 µl 100 mM dithiothreitol, 1 µl RNasin RNase inhibitor, 4 µl ATP, GTP, and CTP mix (25 mM each), 2.4 µl 100 µM UTP, 5 µl [{alpha}-32P]UTP (3,000 Ci/ mmol; Perkin-Elmer, Boston, MA), and 1 µl SP6 (for renin) or T7 (for AT1 and AT2) polymerase} and incubating for 2 h at room temperature. One microliter RQ1 RNase-free DNase was added, and the reaction was incubated for an additional 15 min at 37°C to remove the DNA template. Unincorporated nucleotides were removed by G-50 Sephadex column chromatography (Roche Molecular Biochemicals, Indianapolis. IN). One microliter of the purified probe was placed into a scintillation vial to determine counts per minute. Sense strand RNA used for the standard was synthesized with linearized plasmid by in vitro transcription similar to the above; however, [{alpha}-32P]UTP and 100 µM UTP were replaced with 25 mM UTP.

RNase protection assay. Renin, AT1 and AT2 mRNAs were quantified by RNase protection assay (RPA; RPA kit III; Ambion). Briefly, 20 µg total tissue RNA was mixed with 10 µl hybridization buffer and 100,000 cpm of the renin, AT1, or AT2 probe. Samples were then heated at 95°C for 4 min and placed in a 48°C water bath for overnight hybridization. RNaseA/T1 (1:150 dilution in RNase digestion buffer) was then added to the samples to digest unhybridized probe and RNA. Digestion was stopped, and the hybridized RNA was precipitated by adding RNase inactivation/precipitation buffer and incubating for 30 min at –20 °C. Hybridized RNA was pelleted by centrifugation at 14,000 g for 15 min. Samples were then run on a 5% polyacrylamide/8 M urea denaturing gel at 250 V for 1 h. Gels were then exposed to film (Biomax-MR, Kodak, Cealex, France) with an intensifying screen.

Immunoblotting. Western blot analysis for AT1 and AT2 was performed as previously described (51). Briefly, tissue samples were homogenized in 50 mM Tris, 10 mM EDTA, 150 mM NaCl, 0.1% (vol/vol) Tween-20, 0.1% (vol/vol) 2-mercaptoethanol, 0.1 mM phenylmethysulfonyl fluoride, 5 µg/ml leupeptin, and 5 µg/ml aprotinin, pH 7.5, and sonicated on ice for 15–20 s. One-milliliter aliquots were centrifuged in a microfuge at 12,000 g for 3 min, at 4 °C. The pellet was discarded, and samples of supernatant were diluted in a sample buffer. Protein concentrations of samples harvested from HPD and control animals were determined using a modified Bradford method. A standard curve was produced with known concentration of bovine albumin, and the protein concentrations of samples were determined by comparing their optical density (OD) 595-nm values with values from the standard curve. Both AT1 and AT2 receptor-specific polyclonal antibodies (Santa Cruz Biotechnology, CA) have been used to detect the ovine AT1 and AT2 receptors, respectively (51). Forty micrograms of protein per lane were electrophoresed on a 12% polyacrylamide gel containing SDS for 1.5 h and then blotted onto a polyvinylidene fluoride membrane (Immobilon, Millipore, Marlborough, MA) by semidry electroblotting. The blot was blocked overnight at 4°C with 6% nonfat milk in 0.05% Tween-20 Tris-buffered saline (TTBS) and then incubated with the primary antibody using a 1:2,000 (AT1) or 1:6,000 (AT2) dilution in 6% dry milk/TTBS for 2 h at room temperature. Blots were then rinsed, washed, and incubated with a 1:4,000 dilution of monkey anti-rabbit horseradish peroxidase-conjugated antibody in 6% dry milk/TTBS for 1 h at room temperature. Binding of the secondary antibody was detected using a chemiluminescent system consisting of horseradish peroxidase-hydrogen peroxide oxidation of luminol (ECL plus, Amersham, Arlington Heights, IL). Blots were then exposed to film for 5–10 min before densitometric analysis.

Densitometry. Films were scanned and analyzed using Quantity One software (PDI Imageware Systems, San Diego, CA). Sense RNA standards were used to calibrate the system for RPA data. Data were converted from optical density readings to picrograms mRNA per 10 µg total RNA for RPA data. Western blot data are reported in OD units.

Data analysis. Data pertaining to renal renin mRNA, and renal active and prorenin levels were compared by Student's t-test. All other evaluations were made using two-way ANOVA, followed by Newman-Keuls multiple comparison test. Results are expressed as means ± SE, with P < 0.05 considered significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 REFERENCES
 
Fetal plasma cortisol, T4 and T3 levels, and fetal health. Plasma cortisol concentrations were not different between HPD and sham-operated fetuses at 120–125 dGA. However, by 135–139 dGA, plasma cortisol concentrations were significantly elevated in control fetuses but not HPD fetuses, where 120–125 dGA levels were maintained (Fig. 1). Fetal health, as assessed by arterial blood gas and pH measurements, was normal throughout the duration of the study in both HPD and control fetuses (Table 1). Although PO2 levels in the HPD group exhibited a modest decline during gestation, the values remained in the normal range and were not different from those in the control group.



View larger version (14K):
[in this window]
[in a new window]
  		Fig. 1. Plasma cortisol concentrations in sham-operated (A) and hypothalmo-pituitary disconnection (HPD) fetuses (B) during late gestation. *P < 0.05, 120–125 days vs. 135–139 days; n = 8.

 

View this table:
[in this window]
[in a new window]
  		Table 1. Fetal arterial blood gases and pH throughout the experiment

 
T4 and T3 concentrations were not different between HPD (95.12 ± 22.88 and 0.50 ± 0.07 ng/ml) and sham-operated fetuses (87.22 ± 14.01 and 0.36 ± 0.07 ng/ml).

Effect of HPD on plasma and renal renin. HPD did not alter renal renin mRNA expression, where levels in kidney cortex were 5.83 ± 1.89 pg and 5.76 ± 1.86 pg/20 µg total RNA in control and HPD fetuses, respectively. HPD also had no effect on renal active renin (1,778.6 ± 301.8 in HPD vs. 1,919.3 ± 250.2 ng ANG I released·mg protein–1·h–1 in controls) and prorenin content (420.4 ± 76.8 HPD vs. 323.1 ± 69.7 ng ANG I released·mg protein–1·h–1 in controls). Plasma renin concentrations in both HPD and control fetuses significantly increased in late gestation (Fig. 2). The active renin to prorenin ratio in renal cortical tissue tended to decrease in HPD fetuses (4.6 ± 0.6 vs. 7.0 ± 1.2 in controls, P = 0.056) (Fig. 3).



View larger version (30K):
[in this window]
[in a new window]
  		Fig. 2. Plasma renin concentrations (PRC) in sham-operated (A) and HPD fetuses (B). *P < 0.05, 120–125 days vs. 135–139 days; n = 8.

 


View larger version (19K):
[in this window]
[in a new window]
  		Fig. 3. Active renin/prorenin ratio in the renal cortex of HPD and sham-operated fetuses. *P = 0.056, sham operated vs. HPD; n = 7.

 
The renin mRNA levels in lung and cardiac ventricular tissue were barely detectable by RPA and hence are not reported.

Effect of HPD on ANG II subtype receptors. AT1 and AT2 mRNA were expressed in all collected tissues (Fig. 4). AT1 mRNA expression was significantly higher than AT2 mRNA expression in all tissues. AT1 mRNA levels in the kidney and lung were higher than that in left ventricle. HPD increased the AT1 mRNA level in the kidney and the lung but had no effect on AT1 mRNA expression in the left ventricle. Expression of AT2 mRNA was greatest in the left ventricle, followed by the lung and kidney. In contrast to AT1 mRNA, HPD had no effect on AT2 mRNA expression in all collected tissues.



View larger version (36K):
[in this window]
[in a new window]
  		Fig. 4. AT1 (A) and AT2 (B) mRNA expression in kidney, lung, and left ventricle of HPD and sham-operated fetuses. # P < 0.001, AT1 mRNA vs. AT2 mRNA; + P < 0.05, AT1 mRNA in kidney and lung vs. that in left ventricle; *P < 0.05, AT2 mRNA in lung and left ventricle vs. that in kidney; $ P < 0.05, HPD vs sham.

 
Using the AT1 receptor antibody, we detected bands of the expected sizes in all three tissues, with the major band at 67 kDa, as previously reported (32). HPD significantly increased AT1 protein levels in the kidneys and lung but was associated with decreased levels in the left ventricle (Fig. 5). AT2 protein was also present in these tissues. Both the band at 44 kDa (considered to be the primary band expressed in fetal kidney) and the band at 78 kDa (the primary band in adult adrenal and fetal arteries) (51) were found in our study. HPD did not affect protein amount in any tissue at the 44-kDa band, while at the 78-kDa band, AT2 levels were decreased in the left ventricle following HPD and unchanged in the lung and kidney (Fig. 6).



View larger version (26K):
[in this window]
[in a new window]
  		Fig. 5. Effect of HPD on AT1 protein expression in kidney (A), lung (B), and left ventricle (C) of HPD and sham-operated fetuses. *P < 0.05, HPD vs. sham-operated fetuses.

 


View larger version (28K):
[in this window]
[in a new window]
  		Fig. 6. Effect of HPD on AT2 protein expression in kidney, lung and left ventricle at both 78-kDa and 44-kDa band. *P < 0.05 vs. sham-operated fetuses.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 REFERENCES
 
The purpose of the present study was to determine if the naturally occurring increase in fetal plasma glucocorticoid levels close to term is responsible for some of the developmental changes observed in the RAS (7, 11, 15, 16, 20, 39, 44, 64). To study this issue, we utilized the ovine fetus in which hypothalamic communication with the pituitary was interrupted, as this manipulation abolishes the peripartum increase in fetal plasma cortisol but leaves the fetal adrenals intact. An alternative approach for blocking the prepartum elevation in plasma cortisol is fetal adrenalectomy. However, that procedure also removes a source of aldosterone and catecholamines from the circulation. Thus to avoid problematic and likely confounding issues related to replacement of these hormones, HPD was utilized. We found that HPD, while preventing the late-gestational plasma cortisol surge, did not influence renal renin mRNA expression, renal renin content, or plasma renin concentration. It seems therefore that the increases in renal renin expression and plasma renin concentrations close to term in fetal sheep are not regulated by heightened cortisol levels. In contrast, blockade of the increase in fetal plasma cortisol did alter the expression of angiotensin receptor subtypes in a tissue-specific fashion. Thus the data suggest that the natural increase in cortisol in late gestation may be an important modulator of the effects of angiotensin in the period immediately preceding the transition from fetal to newborn life.

Close to term, glucocorticoids are known to induce enzyme activity in many fetal tissues in preparation for delivery and extrauterine life (16), and it has been suggested that the heightened RAS activity close to parturition may be modulated by changing plasma cortisol concentrations (15). However, there are conflicting observations in the literature concerning the effect of cortisol on renin secretion and expression, with some laboratories reporting that infusions of the steroid suppress renin (52, 69) while others note either increases or no significant change (8, 15, 68). The explanation for these different effects is not known but may relate to the gestational age when the studies were conducted, the dose of steroid given, the duration of the exposure to steroid, or a combination of these variables. However, the lack of any effect on renal renin expression and plasma renin concentration caused by blocking the age-related increase in fetal plasma cortisol demonstrates that the peripartum elevation in glucocorticoids is not a prerequisite for the maturational increase in renin secretion. Indeed, in both control and HPD animals, plasma renin concentrations were similar shortly after surgery, and the renin concentration increased in parallel as gestation progressed. This pattern is similar to what has been reported previously (39) and is consistent with the increased renal renin expression in the fetal kidney in late gestation (7). The lack of effect of elevated levels of endogenous glucocorticoids on plasma renin levels in the fetus is consistent with similar observations in adult dogs with hypercortisolemia. Plasma renin activity in these animals is not different from those in normal dogs (26).

There is some evidence that renin processing in the fetal kidney is influenced by the absence of the rise in fetal plasma cortisol. A small decline in the active renin concentration and increase in the prorenin concentration in the kidney of HPD animals resulted in a small decrease in the active renin-to-prorenin ratio (P = 0.056) compared with the ratio in intact animals. This suggests that the prenatal increase in fetal plasma cortisol may enhance the processing of prorenin to renin. While a number of enzymes have been implicated in this processing (10, 23, 61, 62), the influence of glucocorticoids on the conversion has not been systematically investigated. Additional work in this area is needed to firmly establish a role for the prenatal increase in fetal plasma cortisol in regulating the posttranslational processing of renin.

Renal AT1 mRNA expression is known to increase rapidly close to term and then decrease postpartum (42, 43). The fact that this increase parallels the cortisol surge suggests that cortisol may play a regulatory role. If this were the case, then HPD, in preventing the cortisol surge, would also inhibit the normal increase in AT1 receptor mRNA expression. Somewhat surprisingly, in the present studies, HPD significantly elevated AT1 mRNA levels and the corresponding protein levels in kidney and lung. Our findings therefore imply that the renal AT1 increase in late gestation is not positively regulated by cortisol. On the contrary, it would appear that cortisol acts to prevent renal AT1 receptor overexpression during this period of development.

The effect of cortisol on renal AT1 receptor expression appears to vary depending on the age at exposure. Exposure to increased cortisol levels in early gestation (~27 dGA) tends to upregulate renal AT1 expression (34), while treatment in later gestation (120 dGA) depresses AT1 mRNA expression in fetal sheep (52). Our findings are supportive of the late-gestation observations, in that by preventing the normal increase in cortisol concentrations we demonstrated uninhibited/increased renal AT1 receptor expression in HPD fetuses. It is apparent that the effect of cortisol on renal AT1 expression is developmentally regulated.

The differential effects of cortisol on renal AT1 receptor expression in early and late gestation suggest that receptor function may change as the fetus develops. In early and midgestation, before nephrogenesis is complete, ANG II is known to act via the AT1 receptor (67) as a renal growth factor, stimulating proliferation in mesangial (40) and medullary interstitial cells (31). Interestingly, overexpression of the AT1 receptor during this time results in increased kidney weight at birth, thus further emphasizing the importance of the receptor in renal development (58). In later gestation, the role of the AT1 receptor changes to that of mediating salt and water excretion by the metanephrons, thereby maintaining volume in fetal fluid compartments and ensuring normal growth and development over the last third of pregnancy (65).

It has been demonstrated that the cardiac AT1 receptor is important in mediating cardiac function and growth during the perinatal period (4, 47, 48). During fetal life, the cardiac inotropic, chronotropic, and growth-promoting effects of ANG II appear to be mediated by the cardiac AT1 receptor (47, 48). Blockade of the AT1 receptor with losartan attenuates the rapid growth of the left ventricle that normally occurs in the first 3 days of life in newborn piglets (4). The effects of cortisol infusions on cardiac AT1 receptor mRNA expression have been described. Cortisol infusion at ~120 dGA significantly increases cardiac AT1 receptor expression (52). Cortisol also significantly increases the heart-to-body weight ratio, but not the kidney- or lung-to-body weight ratios in fetal sheep and rats, as well as in preterm infants (13, 27, 56). Our studies in fetal sheep show that the HPD-mediated lower cortisol levels are associated with significantly decreased cardiac AT1 receptor protein expression. This finding is consistent with those from previous studies and indicates that the inhibited fetal cardiovascular function associated with low cortisol levels may be due in part to decreased cardiac AT1 receptor expression.

The relationship between fetal lung maturation and AT1 receptor expression is, however, not so clear. It has been demonstrated that fetal sheep lung AT1 receptor mRNA levels are elevated following maternal malnutrition in early gestation, suggesting that the associated cortisol increase may be the driving factor (58). In contrast, our data (where cortisol concentrations were manipulated in late gestation) imply that lower fetal cortisol concentrations promote lung AT1 expression. These different findings imply that fetal lung AT1 receptor expression is also developmentally regulated.

In contrast to AT1, the function of the tissue AT2 receptor is not clear. In the kidney, there is evidence that the AT2 receptor may play an important role in nephrogenesis. This is suggested by the observation that AT2 receptor expression is high in interstitial cells of the cortex, and in the macula densa during the nephrogenic period (6), and by the finding that expression is very low in the third trimester, when nephrogenesis is complete (17). With respect to the effects of glucocorticoids on AT2 expression, it has been demonstrated that exposure to dexamethasone in early gestation (26 and 28 days of gestation) increases levels in the macula densa (34), while a late gestation (130 dGA) infusion of cortisol has no effect (52). Our observation that the lower cortisol concentrations in HPD fetuses did not effect renal AT2 expression close to term is in keeping with the theory that cortisol-induced changes in AT2 receptors play an important role in regulating kidney development in early to middle, but not in late, gestation when the organ has attained functionality.

The AT2 receptor is also thought to be an important factor in cell proliferation and differentiation and tissue remodeling and repair (25, 36, 63). Thus, in the present study, the tendency for AT2 expression to be higher in HPD fetal lungs might be indicative of lung immaturity, instigated by the lower prevailing plasma cortisol concentrations.

Cardiac AT2 protein was detected as two bands, at 44 and 78 kDa. In sheep, the 44-kDa band has been reported to predominate in the fetal kidney, while the larger band is more evident in the mature fetal arteries and adult adrenal (51). The finding that AT2 protein was unchanged by HPD at the 44-kDa band, but decreased at the 78-kDa band, suggests that hearts from HPD fetuses were less mature than those from control counterparts and implicates the lack of cortisol as a mediating factor.

Changes in mRNA expression do not always translate to the protein level and vice versa. In the present study, neither AT1 nor AT2 receptor mRNA expression in left ventricle was altered by HPD; however, patterns of protein expression were. A study in sheep by Moritz and colleagues (34) demonstrated that AT1 mRNA was elevated following dexamethasone treatment, while there was no corresponding change in protein levels. Posttranscriptional regulation of the AT1 receptor may result in changes in mRNA expression that do not directly reflect changes in cell surface receptor number (73). In this situation, it is critical that expression of both mRNA and protein is quantified to facilitate complete interpretation of data.

We recognize that HPD, in addition to preventing the cortisol surge, may also affect other hormones and physiological parameters that could influence the RAS. For instance, with respect to fetal blood pressure, any HPD-associated decrease should result in increased renal and plasma renin concentrations, changes that were not observed in our study. Thyroid hormones have also been implicated in regulating renin and angiotensin receptor expression (28–30, 33, 59). However, in the present study we measured both T4 and T3 concentrations and found there to be no difference between HPD and sham-operated fetuses. Similarly, vasopressin and oxytocin have been shown to affect renin secretion in adult animals (24, 50). Because the concentration of these peptides is low in fetal sheep (35, 46), it seems unlikely that any further reduction possibly caused by HPD would alter renin secretion, and no differences in plasma renin concentration were found in the HPD animals compared with the sham-operated fetuses. Another hormone with possible effects on the RAS is growth hormone (GH). GH treatment in humans has been demonstrated to activate the RAS (22), and in rat astrocytes and GH-deficient rats increase AT1 mRNA expression and ANG II receptor density, respectively (70, 71). The effect of HPD on plasma GH concentrations in the fetal sheep has not been examined; however, evidence in adult animals suggests no significant effects are apparent (21). Thus there does not appear to be compelling evidence suggesting that other variables potentially altered by HPD would significantly influence the RAS in fetal sheep.

In summary, our studies demonstrate that HPD-induced lower plasma cortisol concentrations in fetal sheep are associated with tissue-specific alterations in expression of the AT1 and AT2 receptors at the mRNA and corresponding protein levels in kidney and lung. In contrast, HPD did not alter the peripartum increase in renin expression. These changes may influence fetal tissue maturation and hence have consequences in neonatal life. The importance of the naturally occurring increase in cortisol in regulating aspects of RAS development is emphasized by our findings.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
REFERENCES
 
This work was supported by National Institutes of Health Grants HD-11210 and HD-17644.


   ACKNOWLEDGMENTS
 
We acknowledge the helpful discussions with Dr. Jorge Figueroa.


   FOOTNOTES
 

Address for reprint requests and other correspondence: J. C. Rose, Dept. of Obstetrics and Gynecology, Wake Forest Univ. School of Medicine, Winston-Salem, NC 27157-1066 (E-mail: jimrose{at}wfubmc.edu

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 REFERENCES
 

  1. AntolovichGC, Clarke IJ, McMillen IC, Perry RA, Robinson PM, Silver M, and Young R. Hypothalamo-pituitary disconnection in the fetal sheep. Neuroendocrinology 51: 1–9, 1990.
  2. AntolovichGC, McMillen IC, Robinson PM, Silver M, Young IR, and Perry RA. Effect of cortisol infusion on the pituitary-adrenal axis of the hypothalamo-pituitary-disconnected fetal sheep. Neuroendocrinology 56: 312–319, 1992.
  3. AntolovichGC, McMillen IC, Robinson PM, Silver M, Young IR, and Perry RA. The effect of hypothalamo-pituitary disconnection on the functional and morphologic development of the pituitary-adrenal axis in the fetal sheep in the last third of gestation. Neuroendocrinology 54: 254–261, 1991.
  4. BeinlichCJ, White GJ, Baker KM, and Morgan HE. Angiotensin II and left ventricular growth in newborn pig heart. J Mol Cell Cardiol 23: 1031–1038, 1991.
  5. BurrellJH, Hegarty BD, McMullen JR, and Lumbers ER. Effects of gestation on ovine fetal and maternal angiotensin receptor subtypes in the heart and major blood vessels. Exp Physiol 86: 71–82, 2001.
  6. ButkusA, Albiston A, Alcorn D, Giles M, McCausland J, Moritz K, Zhuo J, and Wintour EM. Ontogeny of angiotensin II receptors, types 1 and 2, in ovine mesonephros and metanephros. Kidney Int 52: 628–636, 1997.
  7. CarboneGM, Sheikh AU, Rogers S, Brewer G, and Rose JC. Developmental changes in renin gene expression in ovine kidney cortex. Am J Physiol Regul Integr Comp Physiol 264: R591–R596, 1993.
  8. CarboneGM, Sheikh AU, Zehnder T, and Rose JC. Effect of chronic infusion of cortisol on renin gene expression and renin response to hemorrhage in fetal lambs. Pediatr Res 37: 316–320, 1995.
  9. ChiuAT, Herblin WF, McCall DE, Ardecky RJ, Carini DJ, Duncia JV, Pease LJ, Wong PC, Wexler RR, Johnson AL, and Timmermans P. Identification of angiotensin II receptor subtypes. Biochem Biophys Res Commun 165: 196–203, 1989.
  10. DasSK, Chatterjee D, and Uddin M. Induction of pro-renin converting enzyme mk9 by thyroid hormone in the guinea-pig liver. Biochem Biophys Res Commun 293: 412–415, 2002.
  11. DavidsonD. Circulating vasoactive substances and hemodynamic adjustments at birth in lambs. J Appl Physiol 63: 676–684, 1987.
  12. DeaytonJM, Young IR, Hollingworth SA, White A, Crosby SR, and Thorburn GD. Effect of late hypothalamo-pituitary disconnection on the development of the HPA axis in the ovine fetus and the initiation of parturition. J Neuroendocrinol 6: 25–31, 1994.
  13. EvansN. Cardiovascular effects of dexamethasone in the preterm infant. Arch Dis Child Fetal Neonatal Ed 70: 25–30, 1994.
  14. FogoA, Yoshida Y, Yared A, and Ichikawa I. Importance of angiogenic action of angiotensin II in the glomerular growth of maturing kidneys. Kidney Int 38: 1068–1074, 1990.
  15. ForheadAJ, Broughton Pipkin F, and Fowden AL. Effect of cortisol on blood pressure and the renin-angiotensin system in fetal sheep during late gestation. J Physiol 526: 167–176, 2000.
  16. ForheadAJ, Melvin R, Balouzet V, and Fowden AL. Developmental changes in plasma angiotensin-converting enzyme concentration in fetal and neonatal lambs. Reprod Fertil Dev 10: 393–398, 1998.
  17. GimonetV, Bussieres L, Medjebeur AA, Gasser B, Lelongt B, and Laborde K. Nephrogenesis and angiotensin II receptor subtypes gene expression in the fetal lamb. Am J Physiol Renal Physiol 274: F1062–F1069, 1998.
  18. GomezRA and Robillard JE. Developmental aspects of the renal responses to hemorrhage during converting-enzyme inhibition in fetal lambs. Circ Res 54: 301–312, 1984.
  19. GradyEF, Sechi LA, Griffin CA, Schambelan M, and Kalinyak JE. Expression of AT2 receptors in the developing rat fetus. J Clin Invest 88: 921–033, 1991.
  20. GuilleryEN. The renin-angiotensin system and blood pressure regulation during infancy and childhood. In: The Pediatric Clinics of North America: Childhood Hypertension, edited by AP R. Philadelphia, PA: Saunders, 1993, p. 61–67.
  21. HamernikDL, Crowder ME, Nilson JH, and Nett TM. Measurement of messenger ribonucleic acid for luteinizing hormone beta-subunit, alpha-subunit, growth hormone, and prolactin after hypothalamic pituitary disconnection in ovariectomized ewes. Endocrinology 119: 2704–2710, 1986.
  22. HanukogluA, Belutserkovsky O, and Phillip M. Growth hormone activates renin-aldosterone system in children with idiopathic short stature and in a pseudohypoaldosteronism patient with a mutation in epithelial sodium channel alpha subunit. J Steroid Biochem Mol Biol 77: 49–57, 2001.
  23. HirotaN, Ichihara A, Koura Y, Hayashi M, and Saruta T. Phospholipase D contributes to transmural pressure control of prorenin processing in juxtaglomerular cell. Hypertension 39: 363–367, 2002.
  24. HuangW, Sjoquist M, Skott O, Stricker EM, and Sved AF. Oxytocin-induced renin secretion in conscious rats. Am J Physiol Regul Integr Comp Physiol 278: R226–R230, 2000.
  25. JaniakP, Pillon A, Prost JF, and Vilaine JP. Role of angiotensin subtype 2 receptor in neointima formation after vascular injury. Hypertension 20: 737–745, 1992.
  26. JavadiS, Kooistra HS, Mol JA, Boer P, Boer WH, and Rijnberk A. Plasma aldosterone concentrations and plasma renin activity in healthy dogs and dogs with hyperadrenocorticism. Vet Rec 153: 521–525, 2003.
  27. JensenEC, Gallaher BW, Breier BH, and Harding JE. The effect of a chronic maternal cortisol infusion on the late-gestation fetal sheep. J Endocrinol 174: 27–36, 2002.
  28. KarenP and Morris BJ. Stimulation by thyroid hormone of renin mRNA in mouse submandibular gland. Am J Physiol Endocrinol Metab 251: E290–E293, 1986.
  29. KoboriH, Hayashi M, and Saruta T. Thyroid hormone stimulates renin gene expression through the thyroid hormone response element. Hypertension 37: 99–104, 2001.
  30. MarchantC, Brown L, and Sernia C. Renin-angiotensin system in thyroid dysfunction in rats. J Cardiovasc Pharmacol 22: 449–455, 1993.
  31. MaricC, Aldred GP, Antoine AM, Dean RG, Eitle E, Mendelsohn FA, Williams DA, Harris PJ, and Alcorn D. Effects of angiotensin II on cultured rat renomedullary interstitial cells are mediated by AT1A receptors. Am J Physiol Renal Fluid Electrolyte Physiol 271: F1020–F1028, 1996.
  32. MarreroMB, Schieffer B, Paxton WG, Heerdt L, Berk BC, Delafontaine P, and Bernstein KE. Direct stimulation of Jak/STAT pathway by the angiotensin II AT1 receptor. Nature 375: 247–250, 1995.
  33. MatillaMJ, Montiel M, and Jimenez E. Angiotensin II (AII) and adrenal gland AII receptors in rats with congenital hypothyroidism. J Endocrinol 137: 231–238, 1993.
  34. MoritzKM, Johnson K, Douglas-Denton R, Wintour EM, and Dodic M. Maternal glucocorticoid treatment programs alterations in the renin-angiotensin system of the ovine fetal kidney. Endocrinology 143: 4455–4463, 2002.
  35. MorrisM, Castro M, and Rose JC. Alterations in oxytocin prohormone processing during early development in the fetal sheep. Am J Physiol Regul Integr Comp Physiol 263: R738–R740, 1992.
  36. NakajimaM, Hutchinson HG, Fujinaga M, Hayashida W, Morishita R, Zhang L, Horiuchi M, Pratt RE, and Dzau VJ. The angiotensin II type 2 (AT2) receptor antagonizes the growth effects of the AT1 receptor: gain-of-function study using gene transfer. Proc Natl Acad Sci USA 92: 10663–10667, 1995.
  37. O'ConnorSJ, Fowden AL, Holdstock N, Giussani DA, and Forhead AJ. Developmental changes in pulmonary and renal angiotensin-converting enzyme concentration in fetal and neonatal horses. Reprod Fertil Dev 14: 413–417, 2002.
  38. PrydePG, Sedman AB, Nugent CE, and Barr M Jr. Angiotensin-converting enzyme inhibitor fetopathy. J Am Soc Nephrol 3: 1575–1582, 1993.
  39. RawashdehNM, Rose JC, and Kerr DR. Age-dependent differences in active and inactive renin in the lamb fetus. Biol Neonate 60: 243–248, 1991.
  40. RayPE, Aguilera G, Kopp JB, Horikoshi S, and Klotman PE. Angiotensin II receptor-mediated proliferation of cultured human fetal mesangial cells. Kidney Int 40: 764–771, 1991.
  41. RobillardJE and Nakamura KT. Neurohormonal regulation of renal function during development. Am J Physiol Renal Fluid Electrolyte Physiol 254: F771–F779, 1988.
  42. RobillardJE, Page WV, Mathews MS, Schutte BC, Nuyt AM, and Segar JL. Differential gene expression and regulation of renal angiotensin II receptor subtypes (AT1 and AT2) during fetal life in sheep. Pediatr Res 38: 896–904, 1995.
  43. RobillardJE, Schutte BC, Page WV, Fedderson JA, Porter CC, and Segar JL. Ontogenic changes and regulation of renal angiotensin II type 1 receptor gene expression during fetal and newborn life. Pediatr Res 36: 755–762, 1994.
  44. RobillardJE, Weismann DN, Gomez RA, Ayres NA, Lawton WJ, and VanOrden DE. Renal and adrenal responses to converting-enzyme inhibition in fetal and newborn life. Am J Physiol Regul Integr Comp Physiol 244: R249–R256, 1983.
  45. RobillardJE. Developmental aspects of renal function during fetal life. In: Pediatric Kidney Disease, edited by Edelmann CM BJMSSATLB. Boston: Little, Brown, 1992, p. 3–18.
  46. RoseJC, Meis PJ, and Morris M. Ontogeny of endocrine (ACTH, vasopressin, cortisol) responses to hypotension in lamb fetuses. Am J Physiol Endocrinol Metab 240: E656–E661, 1981.
  47. SadoshimaJ and Izumo S. Molecular characterization of angiotensin II-induced hypertrophy of cardiac myocytes and hyperplasia of cardiac fibroblasts. Critical role of the AT1 receptor subtype. Circ Res 73: 413–423, 1993.
  48. SchunkertH, Sadoshima J, Cornelius T, Kagaya Y, Weinberg EO, Izumo S, Riegger G, and Lorell BH. Angiotensin II-induced growth responses in isolated adult rat hearts. Evidence for load-independent induction of cardiac protein synthesis by angiotensin II. Circ Res 76: 489–497, 1995.
  49. SchutzS, Le Moullec JM, Corvol P, and Gasc JM. Early expression of all the components of the renin-angiotensin-system in human development. Am J Pathol 149: 2067–2079, 1996.
  50. SchwartzJ and Reid IA. Role of the vasoconstrictor and antidiuretic activities of vasopressin in inhibition of renin secretion in conscious dogs. Am J Physiol Renal Fluid Electrolyte Physiol 250: F92–F96, 1986.
  51. SegarJL, Barna TJ, Acarregui MJ, and Lamb FS. Responses of fetal ovine systemic and umbilical arteries to angiotensin II. Pediatr Res 49: 826–833, 2001.
  52. SegarJL, Bedell K, Page WV, Mazursky JE, Nuyt AM, and Robillard JE. Effect of cortisol on gene expression of the renin-angiotensin system in fetal sheep. Pediatr Res 37: 741–746, 1995.
  53. ShanmugamS, Lenkei ZG, Gasc JM, Corvol PL, and Llorens-Cortes CM. Ontogeny of angiotensin II type 2 (AT2) receptor mRNA in the rat. Kidney Int 47: 1095–1100, 1995.
  54. ShanmugamS, Monnot C, Corvol P, and Gasc JM. Distribution of type 1 angiotensin II receptor subtype messenger RNAs in the rat fetus. Hypertension 23: 137–141, 1994.
  55. ShanmugamS and Sandberg K. Ontogeny of angiotensin II receptors. Cell Biol Int 20: 169–176, 1996.
  56. SicardRE and Werner JC. Dexamethasone induces a transient relative cardiomegaly in neonatal rats. Pediatr Res 31: 359–363, 1992.
  57. SmithRD, Chiu AT, Wong PC, Herblin WF, and Timmermans PB. Pharmacology of nonpeptide angiotensin II receptor antagonists. Annu Rev Pharmacol Toxicol 32: 135–165, 1992.
  58. TowernAT, Bertram C, and Whorwood CB. The intra-uterine environment programmes hypertension (Abstract). In: Proceedings of the Fetal and Neonatal Physiological Society. 27th Annual Meeting, University of Southampton, Southampton, UK, 2000, 2000, p. 35.
  59. TronikD and Rougeon F. Thyroxine and testosterone transcriptionally regulate renin gene expression in the submaxillary gland of normal and transgenic mice carrying extra copies of the Ren2 gene. FEBS Lett 234: 336–340, 1988.
  60. Tufro-McReddieA, Harrison JK, Everett AD, and Gomez RA. Ontogeny of type 1 angiotensin II receptor gene expression in the rat. J Clin Invest 91: 530–537, 1993.
  61. UddinM, Polley-Mandal M, and Beg OU. Kallikrein-like prorenin-converting enzymes in inbred hypertensive mice. Biochem Biophys Res Commun 304: 724–728, 2003.
  62. VincentP, Adler C, Avila C, Guardia C, and De Vito E. Prorenins activation by an enzyme from rat plasma (PreR-Co). Comp Biochem Physiol B Biochem Mol Biol 131: 201–207, 2002.
  63. ViswanathanM and Saavedra JM. Expression of angiotensin II AT2 receptors in the rat skin during experimental wound healing. Peptides 13: 783–786, 1992.
  64. WangJ, Perez FM, and Rose JC. Developmental changes in renin-containing cells from the ovine fetal kidney. J Soc Gynecol Investig 4: 191–196, 1997.
  65. WintourEM, Alcorn D, Albiston A, Boon WC, Butkus A, Earnest L, Moritz K, and Shandley L. The renin-angiotensin system and the development of the kidney and adrenal in sheep. Clin Exp Pharmacol Physiol Suppl 25: 97–100, 1998.
  66. WintourEM, Moritz K, Butkus A, Baird R, Albiston A, and Tenis N. Ontogeny and regulation of the AT1 and AT2 receptors in the ovine fetal adrenal gland. Mol Cell Endocrinol 157: 161–170, 1999.
  67. WolfG and Neilson EG. Angiotensin II as a renal growth factor. J Am Soc Nephrol 3: 1531–1540, 1993.
  68. WoodCE. Sensitivity of cortisol-induced inhibition of ACTH and renin in fetal sheep. Am J Physiol Regul Integr Comp Physiol 250: R795–R802, 1986.
  69. WoodCE, Keil LC, and Rudolph AM. Physiological inhibition of ovine fetal plasma renin activity by cortisol. Endocrinology 115: 1792–1796, 1984.
  70. WyseB and Sernia C. Growth hormone regulates AT-1a angiotensin receptors in astrocytes. Endocrinology 138: 4176–4180, 1997.
  71. WyseB, Waters M, and Sernia C. Stimulation of the renin-angiotensin system by growth hormone in Lewis dwarf rats. Am J Physiol Endocrinol Metab 265: E332–E339, 1993.
  72. YoungSF, Tatter SB, Valego NK, Figueroa JP, Thompson J, and Rose JC. The role of hypothalamic input on corticotroph maturation in fetal sheep. Am J Physiol Regul Integr Comp Physiol 284: R1621–R1630, 2003.
  73. ZhengW, Ji H, Szabo Z, Brown PR, Yoo SE, and Sandberg K. Coordinate regulation of canine glomeruli and adrenal angiotensin receptors by dietary sodium manipulation. Kidney Int 59: 1881–90, 2001.




This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
288/5/R1279    most recent
00560.2004v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via ISI Web of Science (1)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Chen, K.
Right arrow Articles by Rose, J. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Chen, K.
Right arrow Articles by Rose, J. C.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Visit Other APS Journals Online
Copyright © 2005 by the American Physiological Society.