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Am J Physiol Regul Integr Comp Physiol 283: R732-R738, 2002; doi:10.1152/ajpregu.00346.2001
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Vol. 283, Issue 3, R732-R738, September 2002

Superoxide dismutase and oxidative stress in Dahl salt-sensitive and -resistant rats

Shumei Meng, L. Jackson Roberts II, Garrick W. Cason, Travis S. Curry, and R. Davis Manning Jr.

Department of Physiology and Biophysics, University of Mississippi Medical Center, Jackson, Mississippi 39216; and Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The roles of oxidative stress and renal superoxide dismutase (SOD) levels and their association with renal damage were studied in Dahl salt-sensitive (S) and salt-resistant (R)/Rapp strain rats during changes in Na intake. After 3 wk of a high (8%)-Na diet in S rats, renal medullary Cu/Zn SOD was 56% lower and Mn SOD was 81% lower than in R high Na-fed rats. After 1, 2, and 3 wk of high Na, urinary excretion of F2-isoprostanes, an index of oxidative stress, was significantly greater in S rats compared with R rats. Plasma F2-isoprostane concentration increased in the 2-wk S high Na-fed group. After 3 wk, renal cortical and medullary superoxide production was significantly increased in Dahl S rats on high Na intake, and urinary protein excretion, an index of renal damage, was 273 ± 32 mg/d in S high Na-fed rats and 35 ± 4 mg/d in R high Na-fed rats (P < 0.05). In conclusion, salt-sensitive hypertension in the S rat is accompanied by marked decreases in renal medullary SOD and greater renal oxidative stress and renal damage than in R rats.

urinary protein excretion; isoprostane; dietary sodium; renal damage


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

IN HUMAN HYPERTENSION, reactive oxygen species such as superoxide ions (O<UP><SUB>2</SUB><SUP>−</SUP></UP>·), hydroxyl radicals, and hydrogen peroxide (H2O2) contribute to the pathogenesis of hypertension and exacerbate renal damage. O<UP><SUB>2</SUB><SUP>−</SUP></UP>· and H2O2 produced by leukocytes and plasma levels of lipid peroxides were increased in patients with uncontrolled hypertension (17). Blood pressure reduction in these patients decreased free radical production and lipid peroxides to normal (17).

Animal models of hypertension also have increased oxidative stress. The spontaneous hypertensive rat (SHR) is characterized by increased production of O<UP><SUB>2</SUB><SUP>−</SUP></UP>· in mesenteric arterioles (22, 23). Recently, Schnackenberg and Wilcox (20) showed that oral administration of 4-hydroxyl-2,2,6,6-tetramethyl piperidine-1-oxyl (Tempol), a superoxide dismutase (SOD) mimetic, for 14 days reduced mean arterial pressure (MAP) in the SHR. In this study, Tempol significantly decreased urinary excretion of F2-isoprostanes (20), which have been shown to be an index of oxidative stress in multiple pathological conditions (16). Oxidative stress may be increased in the Dahl salt-sensitive (S) rat, because vitamin E administration prevented renal and arterial injuries in S rats (1). However, the role of oxidative stress in Dahl salt-sensitive hypertension is not clear. In addition, the relationship between oxidative stress and renal damage in the S rat is not well understood.

Oxidative stress can be increased during hypertension by an increased production of reactive oxygen species such as O<UP><SUB>2</SUB><SUP>−</SUP></UP>· or by a decrease in antioxidant enzymes such as SOD. The activity of SOD is decreased in patients with essential hypertension and experimental hypertension. SOD activity in erythrocytes (19) and neutrophils (4) is decreased in essential hypertension. Myocardial SOD activity is decreased in the SHR (5), and blood SOD activity is decreased in the Isiah stress-sensitive hypertensive rat (28). However, whether SOD is altered in S rats has not been determined.

Our goal was to test the hypothesis that renal oxidative stress is increased in the S rat during increased Na intake, and renal levels of SOD are decreased compared with the Dahl salt-resistant (R) rat. Studies were conducted in Dahl R and S/Rapp strain rats during either low or high Na intake for 1 to 3 wk. Oxidative stress was characterized by measuring O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production in the renal cortex and medulla and urine and plasma F2-isoprostanes, and renal tissue Cu/Zn SOD and Mn SOD were determined to assess the level of this antioxidant enzyme in the kidney. Renal damage was assessed by measuring urinary protein excretion.


    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Animal protocol. Experiments were conducted in 59 R and 61 S male rats, Rapp strain (Harlan, Indianapolis, IN) at an age of 7-8 wk. The project had the approval of the local Institutional Animal Committee. The rats were placed on either a low-Na (0.03%) or a high-Na (8%) diet for 1-3 wk. Rats were housed in a temperature-controlled room with a 12:12-h light-dark cycle.

The first group of R and S rats was subjected to the specified Na diet for 1, 2, or 3 wk, and a 24-h urine sample was collected for analysis of urine F2-isoprostanes and protein. The Bradford (BioRad, Richmond, CA) method was used to measure urine protein concentration. The next day, rats were anesthetized with isoflurane, a laparotomy was performed, and blood was withdrawn from the aorta for analysis of plasma F2-isoprostanes. All samples were stored at -80°C until processing. Urine and plasma F2-isoprostane concentrations were measured with a gas chromatography, negative ion-chemical ionization mass spectrometry method (16).

Tissue preparation and Western blotting. After 3 wk on the specified Na diet, a second group of R and S rats was anesthetized with isoflurane, and kidneys were perfused through the aorta with 0.1 M phosphate-buffered saline containing 2% heparin (1,000 U/ml). The renal cortex and medulla were dissected out and were snap-frozen in liquid nitrogen and stored at -80°C until processing. Renal cortical and medullary Cu/Zn SOD and Mn SOD protein were determined by Western blotting. There are three isoforms of SOD that localize in the cytosol (Cu/Zn SOD), the mitochondria (Mn SOD), or the extracellular space (ecSOD). Carlsson et al. (6) found that rat ecSOD is a dimer and has low affinity for heparin. Therefore, ecSOD content is very low in rat tissues (6), so the protein expression of this SOD was not measured in this study.

Frozen kidney sections were homogenized in 20 mM HEPES buffer (pH 7.5) containing protease inhibitors (100 µM pepstatin A, 1 mM phenanthroline, 100 µg/ml aprotinin, 100 µg/ml leupeptin, 1 mM E-64, and 10 mM EDTA). Protein concentration was determined with the Lowry method. Equal amounts of protein from each sample were electrophoresed with a 4% polyacrylamide stacking gel and a 15% resolving gel. Separated proteins were transferred to nitrocellulose membranes and were incubated with the sheep anti-SOD antibody (Biodesign, Saco, ME). Membranes were washed and incubated with peroxidase-conjugated donkey anti-sheep/goat IgG (Biodesign). SOD protein was detected by chemiluminescence (ECL Plus kit, Amersham, Piscataway, NJ), quantified by densitometry (BioRad), and normalized relative to actin. Cross-gel comparisons were done using a common control.

Chemiluminescence measurement of O<UP><SUB>2</SUB><SUP><UP>−</UP></SUP></UP>· production in renal tissues. Chemiluminescence of tissue in 5 µM lucigenin (bis-N-methylacridinium nitrate) was detected using a scintillation counter (Beckman LS 6500) in the out-of-coincidence mode with a single active photonmutiplier tube (15). The validity of measuring oxygen free radical production with 5 µM lucigenin has been confirmed with electron spin resonance methods (11, 21). Renal cortical and medullary tissues were dissected out on dry ice, homogenized in lysis buffer (PBS containing: 1% NP40, 0.5% sodium deoxycholate, 0.1% SDS, 1 mM PMSF, and 10 U/ml aprotinin, 10 mM sodium orthovanadate), and the mixture was centrifuged. The supernatant was aspirated and kept on ice for free radical measurement. After 5 min of dark adaptation, 20 counts of 0.5 min each were made and only the last five counts were averaged and blank values were subtracted. The amounts of protein in the renal tissues were quantified with the Lowry assay. The final readings were expressed as counts per minute per milligram protein.

Data analysis. Statistics were performed by first using a two-way analysis of variance and a Fisher least-significant difference test for post hoc analysis at each experimental time point. Data were considered to be statistically different if P < 0.05. All data are expressed as means ± SE.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Urine and plasma F2-isoprostane responses to a high- or low-sodium diet. Figure 1 indicates that urine F2-isoprostane excretion, an index of oxidative stress in multiple pathological conditions (16), significantly increased throughout the experiment in S rats on a high-Na diet compared with R rats on a high-Na diet. Also, throughout the experiment, urinary F2-isoprostane excretion significantly increased in R high Na-fed and S high Na-fed rats compared with low Na-fed rats of the same strain at the same experimental time. Except for week 1, urinary isoprostane excretion during low Na intake was not significantly different between R and S rats. At 3 wk, the urinary excretion of isoprostanes was 31.4 ± 7.4 ng/day in S high Na-fed rats compared with 22.0 ± 2.8 ng/day in R high Na-fed rats (P < 0.05). Urine concentrations of isoprostane (ng/ml) at 1, 2, and 3 wk were 0.36 ± 0.04, 0.31 ± 0.03, and 0.40 ± 0.05 for R high Na-fed rats; 0.86 ± 0.19, 0.89 ± 0.10, and 0.98 ± 0.14 for R low Na-fed rats; 0.36 ± 0.05, 0.36 ± 0.02, and 0.37 ± 0.35 for S high Na-fed rats; and 0.81 ± 0.24, 0.88 ± 0.23, and 0.89 ± 0.12 for S low Na-fed rats.


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  		Fig. 1.   Urine F2-isoprostane excretion in Dahl salt-sensitive (S) and salt-resistant (R) rats on low (A)- or high (B)-sodium intake for 1, 2, or 3 wk. dagger P < 0.05 compared with R rats on the same Na intake at the same experimental time.

Plasma F2-isoprostanes, an index of oxidative stress, are shown for R and S rats in Fig. 2. The average value for plasma F2-isoprostane concentration in the 2-wk S high Na-fed group was 0.65 ± 0.22 ng/ml, which was significantly greater than the value in the 2-wk R high Na-fed group (0.23 ± 0.03 ng/ml; P < 0.05).


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  		Fig. 2.   Plasma F2-isoprostane concentration in S and R rats on low (A)- or high (B)-sodium intake for 1, 2, or 3 wk. dagger P < 0.05 compared with R rats on the same Na intake at the same experimental time.

Renal cortical and medullary O<UP><SUB>2</SUB><SUP><UP>−</UP></SUP></UP>· production responses to a high- or low-sodium diet. Figure 3A shows that renal cortical O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production significantly increased in S rats after 3 wk of high-Na intake, and the value was 68.7 ± 4.9 cpm/mg protein. Figure 3B shows that renal medullary O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production also significantly increased in S high Na-fed rats compared with R rats on either low- or high-Na intake . The highest renal medullary O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production occurred in S rats on high-Na intake, and the value was 37.3 ± 1.3 cpm/mg protein.


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  		Fig. 3.   Renal cortical (A) and medullary (B) superoxide (O<UP><SUB>2</SUB><SUP>−</SUP></UP>·) production in S and R rats on low- and high-sodium intake for 3 wk. dagger P < 0.05 compared with S low Na-fed rats in the same type of tissue. *P < 0.05 compared with S high Na-fed rats in the same type of tissue.

Renal cortical and medullary Cu/Zn SOD and Mn SOD responses to a high- or low-sodium diet. Figure 4 shows that renal cortical Cu/Zn SOD were not significantly different in the R and S high and low Na-fed groups in samples taken 3 wk after initiation of the Na diet. However, renal medullary Cu/Zn SOD was significantly lower in both the S high Na-fed and S low Na-fed groups compared with the R high Na-fed and R low Na-fed groups.


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  		Fig. 4.   Renal cortical (A) and medullary (B) Cu/Zn SOD expression in S and R rats on low- or high-sodium intake for 3 wk. Dens, densitometric. Insets show a representative Western blot of renal cortical and medullary copper/zinc (Cu/Zn) SOD, respectively. SOD protein shown in the insets corresponds to the groups immediately below in the bar graphs. dagger P < 0.05 compared with S low Na-fed rats in the same type of tissue. *P < 0.05 compared with S high Na-fed rats in the same type of tissue. N = 7 for each group.

Figure 5 indicates that in kidney samples taken 3 wk after initiation of the Na diet, the renal cortical Mn SOD was significantly lower in the S high Na-fed and S low Na-fed groups compared with the R high Na-fed group. Renal medullary Mn SOD was also significantly lower in both the S high Na-fed and S low Na-fed groups compared with the R high Na-fed group. The R high Na-fed group had a value of medullary Mn SOD of 22.7 ± 2.0 (densitometric units) compared with a value of 4.4 ± 1.1 (P < 0.05) in the S high Na-fed group (P < 0.05). In addition, the S high Na-fed group had a lower value of medullary Mn SOD than the S low Na-fed group (P < 0.05).


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  		Fig. 5.   Renal cortical (A) and medullary (B) Mn SOD expression in S and R rats on low- or high-sodium intake for 3 wk. Insets show a representative Western blot of renal cortical and medullary manganese (Mn) SOD, respectively. SOD protein shown in the inset corresponds to the groups immediately below in the bar graphs. dagger P < 0.05 compared with S low Na-fed rats in the same type of tissue. *P < 0.05 compared with S high Na-fed rats in the same type of tissue. N = 7 for each group.

Urinary protein excretion responses to a high- or low-sodium diet. Figure 6 shows that urinary protein excretion increased significantly at 1, 2, and 3 wk in S high Na-fed rats compared with the R high Na-fed group. Also, throughout the experiment, S high Na-fed rats also demonstrated a greater protein excretion than the S low Na-fed group. At 3 wk, the maximum value of urinary protein excretion in the S high Na-fed rats was 273 ± 32 mg/day, which was greater than the value of 35 ± 4 mg/day in the R high Na-fed rats at 3 wk (P < 0.05).


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  		Fig. 6.   Urinary protein excretion in S and R rats on low (A)- or high (B)-sodium intake for 1, 2, or 3 wk. dagger P < 0.05 compared with R rats on the same Na intake at the same experimental time.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

A major new finding in this study is that during a 3-wk increase in dietary Na in the S rat, renal oxidative stress increased and renal medullary Cu/Zn and Mn SOD levels decreased compared with the R rat. Increased renal O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production occurred in S rats in the renal cortex during high-Na intake and in the renal medulla during either high- or low-Na intake. Increased oxidative stress was also evidenced by significant increases in urinary excretion of F2-isoprostanes throughout the experiment and plasma F2-isoprostanes after 2 wk of high-Na intake. After 3 wk on high Na, the S rat experienced a 56% reduction in renal medullary Cu/Zn SOD levels and an 81% reduction in medullary Mn SOD levels compared with R high Na-fed rats. Therefore, the ability of SOD to inactivate O<UP><SUB>2</SUB><SUP>−</SUP></UP>· in the renal medulla is markedly decreased in S rats. Indeed, this area of the kidney experienced a significant increase in O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production. Also, urinary F2-isoprostane excretion increased in S rats after 1, 2, and 3 wk of high-Na intake, and this was associated with large increases in urinary protein excretion. Renal medullary Mn SOD in S rats was sodium sensitive, and significantly lower values occurred during high-Na intake compared with low-Na intake.

Changes in oxidative stress in S rats in the present experiment may have preceded major changes in arterial pressure and urinary protein excretion. Urinary isoprostane excretion in high Na-fed S rats reached a maximum value after 7 days of high Na, but arterial pressure of high Na-fed S rats in another study from our laboratory (14) reached significance for the first time on that day and had a value of 104 ± 4 mmHg. The maximum arterial pressure of 140 ± 3 mmHg was not reached until day 21 of high Na. After 7 days of high Na in S rats in the present experiment, urinary protein excretion was 94 ± 11 mg/day but increased to 273 ± 32 mg/day after 3 wk of high Na. Therefore, urinary isoprostane excretion reached a maximum after only 1 wk of high Na, and arterial pressure and urinary protein excretion continued to increase during the 3-wk period of high-Na intake. In another study from our laboratory, the increases in MAP and urinary protein excretion in S rats on high-Na intake for 3 wk were significantly blunted by long-term intravenous infusion of Tempol (14). This suggests that oxidative stress may contribute to the temporal increases in arterial pressure and renal damage in S rats on high-Na intake.

Increased oxidative stress can be caused by an increase in O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production due to increased oxidase activity or by a decrease in antioxidant levels. The oxidases that could have led to the increased oxidative stress in this study were not determined, but the data indicate that a decrease in renal medullary and cortical SOD levels could have contributed to the higher oxidative stress in high Na-fed S rats. Several studies have shown that SOD activity is decreased in hypertensive humans and experimental animals (4, 19, 28). The SHR had a lower myocardial SOD activity compared with the Wistar-Kyoto (WKY) rat, and antihypertensive treatment of the SHR caused increases in Mn SOD and Cu/Zn SOD activity(5). These studies agree with the present study, because the S high Na-fed rats had lower levels of Cu/Zn SOD and Mn SOD in the renal medulla compared with R rats on low or high Na. After 3 wk on low-Na intake, S rats demonstrated a decrease in renal Mn SOD and Cu/Zn SOD protein expression even during low-Na intake, and these rats had an increased renal medullary and cortical O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production compared with R rats. At this time, urinary protein excretion, an index of renal damage, was significantly increased in the low Na-fed S rats, but the urinary isoprostane excretion was elevated significantly only in the 1-wk group. The S high Na-fed rats had an even lower medullary Mn SOD than the low Na-fed S rats. This suggests that the S rat on low-Na intake may have a deficient production or stability in renal medullary Mn SOD and Cu/Zn SOD and that salt-induced hypertension is associated with a further decrease in medullary Mn SOD protein expression.

Mn SOD is found in the mitochondria, and mitochondrial respiration is very high in renal tubules because of active transport mechanisms. This may increase leakage of O<UP><SUB>2</SUB><SUP>−</SUP></UP>·, and because Mn SOD levels in the S high Na-fed rats are decreased in the renal medulla, O<UP><SUB>2</SUB><SUP>−</SUP></UP>· levels could increase, thus inactivating nitric oxide (NO) (12). Cu/Zn SOD levels are also decreased in the renal medulla of S rats, which could also increase O<UP><SUB>2</SUB><SUP>−</SUP></UP>· concentrations in the kidney. Thus these decreases in renal medullary SOD could lead to increased medullary O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production, which could exacerbate the hypertension in S rats on high-Na intake.

Oxidative stress may have significant effects in human and experimental hypertension. Serum thiols and ascorbic acid were reduced in patients with hypertension, indicating an increased consumption of these antioxidants. Administration of vitamin C or other antioxidants decreased arterial pressure in these patients (7, 8) and improved the attenuated endothelial-dependent vasodilation in patients with essential hypertension (25). The SHR has high oxidative stress as indicated by elevated O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production in mesenteric arterioles (23) and a reduction of arterial pressure in the SHR but not in the WKY rat using the SOD mimetic Tempol (20). The S rat may also have high oxidative stress as evidenced by increased O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production in the mesentery and a high plasma H2O2 concentration (24). Also, vitamin E administration improved renal and arterial injuries in S rats (1). These studies confirm our results in the present study that increased oxidative stress is associated with renal damage in the S rat.

Hayakawa and Raij (9) showed that in the S rat on a high-Na diet, there are parallel increases in urinary protein excretion, the glomerular injury score, and the tubulointerstitial injury score. Tubulointerstitial damage, which is highly correlated with the progression of renal disease, was more severe in the juxtamedullary and medullary regions (9). Therefore, although we only measured urinary protein excretion, which is due to glomerular damage, it is likely that medullary damage also occurred.

We measured arterial pressure in several groups of R and S rats, and the S rats but not R rats increase their MAP in a salt-sensitive fashion. Our studies showed that R rats remain normotensive on a high-Na diet (27) and S rats experience up to a 50-mmHg increase in MAP over 3 wk of a high-Na diet (14). During this period of time, the high Na-fed S rats also experienced an increase in glomerulosclerosis and glomerular cross-sectional area. These increases in MAP and glomerular damage in high Na-fed S rats were significantly blunted by long-term intravenous infusion of Tempol (14), an SOD mimetic. This further supports our hypothesis that a lack of SOD in S rats contributes to renal damage and suggests that oxidative stress may contribute to the temporal increases in arterial pressure and renal damage in S rats on high-Na intake.

Several recent studies suggest that high-Na intake in normotensive rats can increase oxidative stress. Sprague-Dawley (SD) rats were fed a low- or high-Na diet, and arteriolar and venular O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production increased in the high Na-fed group (10). The O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production decreased in high Na-fed rats treated with Tempol + catalase or SOD + catalase (10). These rats did not develop hypertension during high Na feeding, indicating that the increased O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production was due to the high-Na diet but not hypertension. Other studies have shown that increased O<UP><SUB>2</SUB><SUP>−</SUP></UP>· could inactivate NO in SD rats on a high-Na intake, because the vasodilatory responses to NO agonists were markedly decreased in pial arterioles (13) and skeletal muscle resistance arterioles (12).

The above studies indicate that a high-Na diet even in normotensive rats can cause a release of O<UP><SUB>2</SUB><SUP>−</SUP></UP>· (2, 3, 10, 12, 13) and that a further increase in O<UP><SUB>2</SUB><SUP>−</SUP></UP>· may occur if a high-Na diet causes hypertension (12). In fact, this agrees with the present study, because a high-Na diet given to the highly salt-resistant R rat caused an increase in urinary F2-isoprostane excretion. However, neither renal medullary nor cortical O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production increased in the R rat on high-Na intake compared with low Na-fed R rats. This suggests that the increase in urinary isoprostanes may be caused by extrarenal increases in oxidative stress. When the highly salt-sensitive S rat was given a high-Na diet in the present study, urinary F2-isoprostane excretion increased even more than in the R rats. The decrease in renal SOD in the high Na-fed Dahl S rats could have contributed to this increased oxidative stress.

Release of O<UP><SUB>2</SUB><SUP>−</SUP></UP>· can have detrimental effects, including DNA destruction, protein aggregation, and lipid peroxidation, which can cause renal damage. F2-isoprostanes are generated in a bound form when O<UP><SUB>2</SUB><SUP>−</SUP></UP>· react with arachidonic acid in phospholipids, and they are subsequently released in a free form that are excreted in the urine (18). F2-isoprostanes have been used as a marker of oxidative stress in vivo (16). Elevated renal excretion of F2-isoprostanes have been reported in renal ischemia-reperfusion injury (26) and during hypertension in the SHR (20). Treatment of the SHR with Tempol decreased the F2-isoprostane excretion and arterial pressure significantly (20).

Urinary excretion of F2-isoprostanes in the present experiment could have been increased in response to an increase in glomerular filtration rate (GFR) in the R and S high Na-fed rats. However, we previously showed that GFR is not different in high Na-fed R and S rats, and the increase in GFR in both groups compared with low Na-fed R and S rats is only 15% (27). Therefore, the increases in urinary F2-isoprostane excretion in high Na-fed R and S rats are not likely due to an increase in GFR.

In conclusion, oxidative stress increased in S rats on high-Na intake as evidenced by increased renal cortical and medullary O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production and increased plasma F2-isoprostanes and urinary excretion of F2-isoprostanes. After 3 wk on high Na, the S rats experienced an 81% reduction in Mn SOD levels and a 56% reduction in Cu/Zn SOD levels in the renal medulla compared with R rats. The Mn SOD levels of S rats were also decreased in the cortex. Therefore, the ability of SOD to inactivate O<UP><SUB>2</SUB><SUP>−</SUP></UP>· is likely decreased in the kidney. R rats on high-Na intake also experienced an increase in urinary F2-isoprostane excretion but no increase in either renal cortical or medullary O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production, which may reflect an increase in extrarenal oxidative stress. Compared with the R high Na-fed rats, the high Na-fed S rats showed an increase in renal O<UP><SUB>2</SUB><SUP>−</SUP></UP>· production, significantly greater increase in urinary F2-isoprostane excretion, markedly lower renal SOD levels, and increased renal damage as evidenced by marked elevations in urinary protein excretion. A high-Na diet may increase renal oxidative stress in the S rat, which is accompanied by low renal SOD and is associated with severe renal damage.


    ACKNOWLEDGEMENTS

This research was supported by Grant HL-51971 from the National Heart, Lung, and Blood Institute and National Institutes of Health Grants GM-42056, GM-15431, DK-26657, and CA-68485.


    FOOTNOTES

Address for reprint requests and other correspondence: R. D. Manning Jr., Dept. of Physiology and Biophysics, 2500 North State St., Jackson, MS 39216.

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.

10.1152/ajpregu.00346.2001

Received 15 June 2001; accepted in final form 10 June 2002.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Atarashi, K, Ishiyama A, Takagi M, Minami M, Kimura K, Goto A, and Omata M. Vitamin E ameliorates the renal injury of Dahl Salt-sensitive rats. Am J Hypertens 10: 116s-119s, 1997.

2.   Boegehold, MA. Effect of dietary salt on arterial nitric oxide in striated muscle of normotensive rats. Am J Physiol Heart Circ Physiol 264: H1810-H1816, 1993[Abstract/Free Full Text].

3.   Boegehold, MA. Flow-dependent arteriolar dilation in normotensive rats fed low- or high-salt diets. Am J Physiol Heart Circ Physiol 269: H1407-H1414, 1995[Abstract/Free Full Text].

4.   Buczynski, A, Wachowic ZB, Kedziora-Kornatowska K, Tkaczewski W, and Kedziora J. Changes in antioxidant enzymes activities, aggregability and malonyl dialdehyde concentration in blood platelets from patients with coronary heart disease. Atherosclerosis 100: 223-228, 1993[ISI][Medline].

5.   Cabell, KS, Ma L, and Johnson P. Effects of antihypertensive drugs on rat tissue antioxidant enzyme activities and lipid peroxidation levels. Biochem Pharmacol 54: 133-141, 1997[ISI][Medline].

6.   Carlsson, LM, Marklund SL, and Edlund T. The rat extracellular superoxide dismutase dimer is converted to a tetramer by the exchange of a single amino acid. Proc Natl Acad Sci USA 93: 5219-5222, 1996[Abstract/Free Full Text].

7.   Ceriello, A, Giugliano D, Quatraro A, and Lefebvre PJ. Anti-oxidants show anti-hypertensive effect in diabetic and hypertensive subjects. Clin Sci (Colch) 81: 739-742, 1991.

8.   Galley, HF, Thornton J, Howdle PD, Walker BE, and Webster NR. Combination oral antioxidant supplementation reduce blood pressure. Clin Sci (Colch) 92: 361-365, 1997.

9.   Hayakawa, H, and Raij L. Nitric oxide synthase activity and renal injury in genetic hypertension. Hypertension 31: 266-270, 1998[Abstract/Free Full Text].

10.   Lenda, DM, Sauls BA, and Boegehold MA. Reactive oxygen species may contribute to reduced endothelium-dependent dilation in rats fed high salt. Am J Physiol Heart Circ Physiol 279: H7-H14, 2000[Abstract/Free Full Text].

11.   Li, Y, Zhu H, Kuppusamy P, Roubaud V, Zweier JL, and Trush MA. Validation of lucigenin (bis-N-methylacridinium) as a chemilumigenic probe for detecting superoxide anion radical production by enzymatic and cellular systems. J Biol Chem 273: 2015-2023, 1998[Abstract/Free Full Text].

12.   Liu, Y, Fredricks KT, Roman RJ, and Lombard JH. Response of resistance arteries to reduced PO2 and vasodilation during hypertension and elevated salt intake. Am J Physiol Heart Circ Physiol 273: H869-H877, 1997[Abstract/Free Full Text].

13.   Liu, Y, Rusch NJ, and Lombard JH. Loss of endothelium and receptor-mediated dilation in pial arterioles of rats fed a short-term high salt diet. Hypertension 33: 686-688, 1999[Abstract/Free Full Text].

14.   Meng, S, Cason GW, Racusen LC, and Manning RD, Jr. The role of oxidative stress in Dahl salt-sensitive hypertension (Abstract). Hypertension 36: 686, 2000.

15.   Mohazzab-HKM, Kaminski PM, Fayngersh RP, and Wolin MS. Oxygen-elicited responses in calf coronary arteries: role of H2O2 production via NADH-derived superoxide. Am J Physiol Heart Circ Physiol 270: H1044-H1053, 1996[Abstract/Free Full Text].

16.   Morrow, JD, and Roberts LJ II. Mass spectrometry of prostanoids: F2-isoprostanes produced by non-cyclooxygenase free radical catalyzed mechanism. Methods Enzymol 233: 163-174, 1994[ISI][Medline].

17.   Prabha, PS, Das UN, Koratkar R, Sagar PS, and Ramesh G. Free radical generation, lipid peroxidation and essential fatty acids in uncontrolled essential hypertension. Prostaglandins Leukot Essent Fatty Acids 41: 27-33, 1990[ISI][Medline].

18.   Roberts, LJ II, and Morrow JD. The generation and actions of isoprostanes. Biochim Biophys Acta 1345: 121-135, 1997[Medline].

19.   Russo, C, Olivieri O, Girelli D, Faccini G, Zenari ML, Lombardi S, and Corrocher R. Anti-oxidant status of lipid peroxidation in patients with essential hypertension. J Hypertens 16: 1267-1271, 1998[ISI][Medline].

20.   Schnackenberg, CG, and Wilcox CS. Two-week administration of Tempol attenuates both hypertension and renal excretion of 8-Iso prostaglandin f2alpha. Hypertension 33: 424-428, 1999[Abstract/Free Full Text].

21.   Skatchkov, MP, Sperling D, Hink U, Mulsch A, Harrison DG, Sindermann I, Meinertz T, and Munzel T. Validation of lucigenin as a chemiluminescent probe to monitor vascular superoxide as well as basal vascular nitric oxide production. Biochem Biophys Res Commun 254: 319-324, 1999[ISI][Medline].

22.   Suzuki, H, DeLano FA, Parks DA, Jamshidi N, Granger DN, Ishii H, Suematsu M, Zweifach BW, and Schmid-Schonbein GW. Xanthine oxidase activity associated with arterial blood pressure in spontaneously hypertensive rats. Proc Natl Acad Sci USA 95: 4754-4759, 1998[Abstract/Free Full Text].

23.   Suzuki, H, Swei A, Zweifach BW, and Schmid-Schonbein GW. In vivo evidence for microvascular oxidative stress in spontaneously hypertensive rats: hydro-ethidine microfluorography. Hypertension 25: 1083-1089, 1995[Abstract/Free Full Text].

24.   Swei, A, Lacy F, DeLano FA, and Schmid-Schonbein GW. Oxidative stress in the Dahl hypertensive rat. Hypertension 30: 1628-1633, 1997[Abstract/Free Full Text].

25.   Taddei, S, Virdis A, Ghiadoni L, Magagna A, and Salvetti A. Vitamin C improves endothelium-dependent vasodilation by restoring nitric oxide activity in essential hypertension. Circulation 97: 2222-2229, 1998[Abstract/Free Full Text].

26.   Takahashi, K, Nammour TM, Fukunaga M, Ebert J, Morrow JD, Roberts LJ, II, Hoover RL, and Badr KF. Glomerular actions of a free radical-generated novel prostaglandin, 8-epi-prostaglandin F2a, in the rat. Evidence for interaction with thromboxane A2 receptors. J Clin Invest 90: 136-141, 1992[ISI][Medline].

27.   Tan, DY, Meng S, and Manning RD, Jr. Role of neuronal nitric oxide synthase in Dahl salt-sensitive hypertension. Hypertension 33: 456-461, 1999[Abstract/Free Full Text].

28.   Yelinova, VI, Khramtsov VV, and Markel AL. Manifestation of oxidative stress in the pathogenesis of arterial hypertension in ISIAH rats. Biochem Biophys Res Commun 263: 450-453, 1999[ISI][Medline].

Am J Physiol Regul Integr Comp Physiol 283(3):R732-R738
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