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The Second Department of Internal Medicine, Gunma University School of Medicine, Maebashi, 371-8511 Japan
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ABSTRACT |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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The degree of involvement of the renin-angiotensin system in
endothelial dysfunction was investigated by using a one-kidney, one-clip (1K,1C) model of renal hypertension. Male Wistar rats received
0.02% enalapril, 0.02% losartan, or tap water for 1 day before and
for 48 h after the induction of renal artery stenosis or sham
operation. The aorta of 1K,1C rats showed increased contraction and
decreased relaxation responses produced by norepinephrine and
acetylcholine, respectively, vs. control responses. Exposure to
10
5 mol/l
NG-monomethyl-L-arginine
acetate augmented the contractile responses to norepinephrine to a
greater extent in control rats than in the 1K,1C rats. The increased
contraction and decreased relaxation responses to these agonists in the
1K,1C rats were normalized by enalapril or losartan. The addition of
HOE-140 to the bath did not alter these normalized responses. Results
suggest that angiotensin II causes endothelial dysfunction and reduces
nitric oxide levels in 1K,1C rats. Such endothelial dysfunction
enhanced the norepinephrine-induced contraction during the early-stage hypertension in 1K,1C rats.
acetylcholine; sodium nitroprusside; bradykinin
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INTRODUCTION |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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AN INCREASED REACTIVITY to pressor agents is seen in patients with hypertension (2, 6) as well as in experimental models of hypertension (9, 11, 25). The mechanism underlying this phenomenon has not been elucidated clearly, but Folkow et al. (3) have proposed that an increased reactivity to pressor agents results from a thickening of the vascular wall or medial hypertrophy. However, other researchers contend that the enhanced pressor response is not fully explained by such a mechanism (9, 20). For instance, Prewitt et al. (20) failed to find any thickening of the resistance vessels in rats with one-kidney, one clip (1K,1C) renal hypertension. It has also been reported that an enhanced pressor response to norepinephrine can be detected in rabbits with renal artery stenosis at an early stage, even before the onset of hypertension (9). These findings suggest that the pressor response may be enhanced by changes in vascular reactivity even in the absence of thickening of the vascular wall.
Recent studies show that the vascular response to vasoactive agents is regulated by endothelial cells (12, 16, 26). Endothelium-derived relaxing factor was first described by Furchgott and Zawadzki (4) in 1980, and was subsequently identified as nitric oxide (NO) (19). NO is synthesized from L-arginine and O2 by NO synthase (19) and acts on such adjacent target cells as smooth muscle cells to induce relaxation of smooth muscle (22). The intravenous administration of NG-monomethyl-L-arginine acetate (L-NMMA), an analog of L-arginine, has been shown to selectively inhibit NO synthase and to increase the blood pressure (23). Studies using aortic preparations have shown that endothelium-dependent responses are reduced in various models of hypertension (12, 17, 26). In a previous study, we demonstrated that impairment of NO synthesis or a reduction in NO release could explain the enhanced vasoconstrictor response to norepinephrine before the occurrence of vascular wall thickening during the very early stages of 1K,1C renal hypertension in rats (8). Rubbing the endothelium augmented the contractile responses to norepinephrine to a greater extent in control rats than in the 1K,1C rats; therefore, the response of the groups did not differ significantly (8). We also demonstrated that angiotensin-converting enzyme (ACE) inhibitors can prevent or reverse endothelial dysfunction in this model (8). Other investigators have also reported that ACE inhibitors improve endothelial function (1, 15).
ACE inhibitors reduce the formation of angiotensin II and prevent the degradation of bradykinin, an endothelium-dependent vasorelaxant that stimulates NO release. In the present study, we investigated the involvement of the renin-angiotensin system and the kinin-kallikrein system in endothelial dysfunction during the early stage of hypertension in the 1K,1C rat model to determine whether angiotensin II interferes with the action of NO. For this purpose, we evaluated the ability of an angiotensin II type 1A receptor antagonist (losartan) and a bradykinin B2 receptor antagonist (HOE-140) to restore the endothelial function in this model.
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MATERIALS AND METHODS |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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All procedures were approved by the Animal Care and Use Committee of Gunma University School of Medicine and were performed in accordance with the Guide for the Care and Use of Laboratory Animals of the National Research Council (revised 1996). Male Wistar rats aged 15-16 wk (Imai, Saitama, Japan) were anesthetized with ethyl ether. After an incision was made in each flank, a silver clip of 0.45 mm in diameter was placed on the right renal artery; the left kidney was removed. Control rats were similarly treated, except that no clip was applied (sham-operated rats). A prophylactic antibiotic (carumonam, 30 mg/kg im) was injected after the operation. Systolic blood pressure was measured by using the tail-cuff method (model UR5000; Ueda, Tokyo, Japan). In preliminary studies conducted in 8 rats, the plasma levels of angiotensin II were significantly higher in 1K,1C (1,245 ± 72 pg/ml) than in control (462 ± 83 pg/ml) rats 48 h after the induction of renal artery stenosis or the sham operation. We also observed that systolic blood pressure rose from 130 ± 7 mmHg to 223 ± 43 mmHg 4 wk after the placement of a clip of this size in six rats.
Forty-eight hours after the induction of renal artery stenosis or the sham operation, the rats were anesthetized with an intraperitoneal injection of pentobarbital sodium (50 mg/kg). After the descending thoracic aorta was carefully excised, one or two cylindrical segments 3 mm long were cut from the aorta. The number of aortic rings obtained from each rat depended on the experimental protocol (described below).
The tissue preparation was bathed in 10 ml of Krebs bicarbonate
solution aerated with a mixture of 95%
O2 and 5%
CO2 and maintained at 37°C.
The composition of the Krebs bicarbonate solution was 120 mmol/l NaCl,
5.2 mmol/l KCl, 2.4 mmol/l CaCl2,
1.2 mmol/l MgSO4, 25 mmol/l
NaHCO3, 0.03 mmol/l
Na2-EDTA, and 11 mmol/l dextrose (pH 7.4). The arterial rings were suspended under 2 g of tension. The
force of isometric contraction was measured by using a
force-displacement transducer (model UR-50GR; Minebea, Nagano, Japan).
Each drug was progressively added from a low to high concentration to
the bath in a volume of 0.1 ml to achieve the final concentration indicated in the protocol. In all cases, 100 µl of
105 mol/l norepinephrine
was initially applied to the bath to preconstrict the aortic strip. The
concentration of norepinephrine in the final bath was
107 mol/l. When the
contraction had reached its maximum after ~2 min, the aorta was
relaxed using 107 mol/l
acetylcholine to confirm that the endothelium was intact. The bath
solution was then washed out with Krebs bicarbonate solution and
allowed to equilibrate for an additional 30 min. The arteries were not
treated with indomethacin.
Experiment 1: Alteration of Vasoconstrictor and Vasodilator Responses to Norepinephrine and Acetylcholine
Experiment 1A: Effect of NO synthesis inhibition with
L-NMMA on norepinephrine-induced
vasoconstriction.
The dose-related vasoconstrictor response to norepinephrine was
evaluated in 1K,1C and sham-operated rats. To evaluate the influence of
endothelium-derived NO on norepinephrine-induced vasoconstriction, one
of the two aortic preparations from each 1K,1C or sham-operated rat was
equilibrated in Krebs bicarbonate solution with
105 mol/l
L-NMMA for 30 min. As a control,
another strip was incubated in Krebs bicarbonate solution without
L-NMMA. The dose response for
the contractions observed in the presence of
1010-106
mol/l norepinephrine was then determined.
5 mol/l
L-NMMA for 30 min. Another strip
was incubated in Krebs bicarbonate solution without
L-NMMA as a control. The rings
were then preconstricted by adding
107 mol/l norepinephrine.
After contraction had reached a plateau, the relaxation responses
produced by
1010-105
mol/l acetylcholine were recorded.
Experiment 1C: Confirmation of intact vasodilator
response to sodium nitroprusside. To verify that
responsiveness of the vascular smooth muscle to NO is intact, the
dose-related vasodilator response to sodium nitroprusside was evaluated
in 1K,1C or sham-operated rat. One aortic preparation from each 1K,1C
or sham-operated rat was equilibrated in Krebs bicarbonate solution for
30 min. The rings were then preconstricted by adding
107 mol/l norepinephrine.
After contraction had reached a plateau, the relaxation responses
produced by
1010-105
mol/l sodium nitroprusside were recorded.
Experiment 2: Involvement of the Renin-Angiotensin System in Endothelial Function and Evaluation of Vasomotor Tone
We tested the effectiveness of angiotensin-converting enzyme (ACE) inhibition with enalapril and angiotensin II antagonism with losartan in a preliminary study. For 3 days, three concentrations of enalapril (0.01, 0.02, and 0.05%) or of losartan (0.002, 0.01, and 0.02%) were added to the drinking water of normal Wistar rats (200-250 g, n = 6 in each group). The animals were anesthetized with pentobarbital sodium (50 mg/kg), and the carotid artery and jugular vein were cannulated. The increase in mean arterial pressure in response to intravenous angiotensin I, 200 ng · kg1 · min1,
was suppressed by the ACE inhibitor, being 28 ± 4, 19 ± 5, and 11 ± 4 mmHg at enalapril doses of 0.01, 0.02, and 0.05%,
respectively. However, the increase in mean arterial pressure in
response to angiotensin II, 200 ng · kg1 · min1,
was unaffected with each increase in dose of enalapril. From these
results, we selected a dose of enalapril of 0.02% to inhibit ACE
activity. The increase in mean arterial pressure in response to
intravenous angiotensin II, 200 ng · kg1 · min1,
was suppressed by losartan, being 20 ± 9, 8 ± 3, and 3 ± 1 mmHg at doses of 0.002, 0.01, and 0.02%, respectively. We therefore selected a dose of losartan of 0.02%.
Experiment 2A: Effect of ACE inhibition with enalapril
on vasoconstriction induced by norepinephrine. Rats
were divided into four groups, two groups with renal artery stenosis
and two sham-operated groups, with or without 0.02% enalapril in the
drinking water (~100
mg · kg1 · day1).
In each group, the experiment was begun the day before the induction of
renal artery stenosis or sham operation and continued for 48 h after
surgery. One aortic ring preparation was obtained from each rat. The
dose response of isometric contraction in the presence of
1010-106
mol/l norepinephrine was determined.
Experiment 2B: Effect of ACE inhibition with enalapril
on vasodilation induced by acetylcholine. We evaluated
the effect of ACE inhibition with enalapril on the vasodilation induced
by acetylcholine. As in expt 2A, rats
were divided into four groups. One aortic ring preparation from each
rat was preconstricted by adding
107 mol/l norepinephrine to
the bath. After the contraction had reached a plateau, 100 µl
acetylcholine was progressively applied to the bath as in
expt 1C.
Experiment 2C: Effect of angiotensin II type 1A
receptor antagonism with losartan on vasoconstriction induced by
norepinephrine. We also studied the effect of the
angiotensin II type 1A receptor antagonist losartan on the
vasoconstriction induced by norepinephrine. The same protocol as used
in expt 2A was followed, but with
losartan instead of enalapril. Losartan was administered in the
drinking water at a concentration of 0.02% (~100
mg · kg1 · day1).
Experiment 2D: Effect of angiotensin II type 1A receptor antagonism with losartan on vasodilation induced by acetylcholine. The same protocol as in expt 2B was followed, with losartan used instead of enalapril. Losartan was given in the drinking water as in expt 2C. One aortic ring preparation was obtained from each rat, and the dose-response curve for the vasodilator responses to acetylcholine was determined as in expt 1C.
Experiment 3: Effect of Bradykinin B2 Receptor Antagonism With HOE-140 on Restoration of Endothelial Function After ACE Inhibition
Preliminarily, we tested the effectiveness of the bradykinin B2 receptor antagonism produced by HOE-140. Aortic rings from normal Wistar rats were equilibrated in Krebs bicarbonate solution with three concentrations of HOE-140 (109,
107, and
105 mol/l, final bath
concentrations) or without HOE-140 for 30 min (n = 5 in each group). The rings
were then preconstricted by adding 107 mol/l norepinephrine.
The vasodilatory responses to
1011-106
mol/l bradykinin were abolished by
105 and
107 mol/l HOE-140. In the
present study, we selected a dose of
105 mol/l for HOE-140.
Experiment 3A: Effect of bradykinin B2
receptor antagonism on vasoconstriction induced by norepinephrine.
Rats were divided into four groups: two groups with renal artery
stenosis and two sham-operated groups, with or without 0.02% enalapril
in the drinking water. One aortic ring preparation was obtained from
each rat. Aortic rings from 1K,1C and control rats given enalapril were
equilibrated in Krebs bicarbonate solution containing
105 mol/l HOE-140 for 30 min. Aortic rings from 1K,1C and control rats given tap water were
incubated in Krebs bicarbonate solution without HOE 140. The
dose-response curves for the contractile responses to norepinephrine
were then determined for each aortic preparation as in
expt 2A.
Experiment 3B: Effect of bradykinin B2
receptor antagonism with HOE-140 on vasodilation induced by
acetylcholine.
The same protocol as in expt 3A was
performed in four groups of rats treated with or without enalapril. One
aortic ring preparation was obtained from each rat. Aortic rings from
1K,1C and control rats given enalapril were equilibrated in Krebs
bicarbonate solution containing
105 mol/l HOE-140 for 30 min as in expt 3A. Aortic rings from
1K,1C and control rats given tap water were incubated in Krebs
bicarbonate solution without HOE-140. The dose-response curves for the
vasodilatory responses to acetylcholine were then determined.
Drug Administration
Acetylcholine (Sigma Chemical, St. Louis, MO) and L-NMMA (Calbiochem, La Jolla, CA) were dissolved in saline, frozen, and stored at
20°C for
no more than 6 wk. Norepinephrine was a gift of Sankyo Pharmaceutical,
Tokyo, Japan. These drugs were subsequently diluted with Krebs
bicarbonate solution to the desired concentrations. Enalapril and
losartan were dissolved daily in the drinking water. Enalapril and
losartan were both kindly donated by Banyu Pharmaceutical, Tokyo,
Japan. HOE-140 was kindly donated by Hekist Pharmaceutical, Tokyo, Japan.
Data Analysis
In each experimental group, n refers to the number of animals from which the aortas were taken. Responses to norepinephrine or acetylcholine were expressed according to the method of Konishi and Su (12) and our previous study (8). For vasoconstriction, the maximal response was taken to be the maximal force (mg) of the norepinephrine-induced vasoconstriction observed in the dose-response curve for each aortic preparation. The negative logarithm of the concentrations of norepinephrine that produced the half-maximal response was referred to as pD2. For vasodilation, the negative logarithm of the concentrations of acetylcholine that produced the half-maximal response to the drug was used and was referred to as pD2. The putative maximal vasodilator response was taken to be the level that preceded the preconstriction induced by norepinephrine. The response to each dose was expressed as a percent of the putative maximal vasodilation. Data are expressed as means ± SE. Differences among data sets were evaluated by performing an ANOVA, followed by Duncan's multiple-range test. A level of P < 0.05 was accepted as statistically significant.| |
RESULTS |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Table 1 summarizes the body weights, systolic blood pressures, and heart rates of the six groups of rats studied. There was no significant difference in body weight among the groups on the day on which the aortic ring preparations were obtained. The systolic blood pressures and heart rates did not differ among the groups before the induction of renal artery stenosis or sham operation. However, the systolic blood pressures rose slightly (P < 0.05) in the 1K,1C rats 48 h after renal artery stenosis as compared with the sham-operated rats. Treatment with enalapril and losartan prevented the rise in systolic blood pressure in the 1K,1C rats. The presence of renal artery stenosis or the administration of enalapril or losartan did not significantly affect the heart rate.
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Experiment 1: Alteration of Vasoconstrictor and Vasodilator Responses to Norepinephrine and Acetylcholine
The isometric contraction of the aortic ring in response to norepinephrine was exaggerated in 1K,1C compared with control rats (Figs. 1A and 3). The pD2 was significantly higher in the 1K,1C rats than in control rats (P < 0.05) (Table 2; expt 1A and Table 3). After treatment with L-NMMA, the pD2 and maximal response increased significantly in both groups (P < 0.05). However, these increases were more pronounced in the control rats, and the difference in the vasoconstrictor response to norepinephrine between the two groups was diminished (Fig. 1A and Table 2, expt 1A).
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The cumulative addition of acetylcholine produced endothelium- and
concentration-dependent relaxations of aortic rings that were
precontracted with norepinephrine
(107 mol/l). The relaxation
induced by acetylcholine was significantly reduced in 1K,1C rats
compared with control rats (P < 0.05) (Figs. 1B and 3). In addition,
the pD2 and maximal response
values in 1K,1C rats were significantly smaller than the control values (P < 0.05) (Table 2,
expt 1B, and Table
4).
L-NMMA abolished the
vasodilatory responses to acetylcholine in both groups (Fig. 1B and Table 2, expt
1B). No significant difference was observed in the
response between the groups after treatment with
L-NMMA (Fig.
1B and Table 2, expt
1B).
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The cumulative addition of sodium nitroprusside produced
concentration-dependent relaxations of aortic rings that were
preconstricted with norepinephrine
(107 mol/l). No significant
difference was observed in the response between 1K,1C and control rats
(Fig. 1C and Table 2,
expt 1C).
Experiment 2: Involvement of the Renin-Angiotensin System in Endothelial Function and the Evaluation of Vasomotor Tone
Treatment with enalapril (Fig. 2A) and losartan (Fig. 2B) produced a rightward shift of the norepinephrine-induced vasoconstriction in 1K,1C rats but did not alter the response in control rats. Both the pD2 and the maximal response were decreased significantly following enalapril or losartan in 1K,1C (P < 0.05) (Table 3, expts 2A and 2C). There was no significant difference in either the pD2 or the maximal response between 1K,1C and control after treatment with enalapril or losartan (Table 3, expts 2A and 2C).
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Figure 3 and Table 4 show the effect of the oral administration of enalapril and losartan on acetylcholine-induced vasodilation in control and 1K,1C rats. The relaxation was augmented by enalapril (Fig. 3A) and losartan (Fig. 3B) in 1K,1C rats, with a significant shift of the dose-response curves toward the left (P < 0.05) (Table 4, expts 2B and 2D). In contrast to 1K,1C rats, neither enalapril nor losartan altered the dose-response curve in control rats (Table 4, expts 2B and 2D). There was no significant difference between the 1K,1C and control rats in the acetylcholine-induced vasodilation after treatment with enalapril or losartan.
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Experiment 3: Effect of Bradykinin B2 Receptor Antagonism With HOE-140 on the Restoration of Endothelial Function After ACE Inhibition
Figure 2C shows the effect of HOE-140 on norepinephrine-induced vasoconstriction in control and 1K,1C rats treated with enalapril. The addition of HOE-140 to the bath did not alter the normalized contractile response of the aorta to norepinephrine in 1K,1C rats treated with enalapril. There was no significant difference in pD2 or in the maximal constriction between the control and the 1K,1C rats treated with enalapril plus HOE-140 (Table 3, expt 3A).Figure 3C shows the effect of HOE-140 on the acetylcholine-induced vasodilation in control and 1K,1C rats treated with enalapril. The addition of HOE-140 to the bath did not alter the normalized relaxation responses of the aorta to acetylcholine in 1K,1C rats treated with enalapril. There was no significant difference in either the pD2 or the maximal dilatation between the control and the 1K,1C rats treated with enalapril plus HOE-140 (Table 4, expt 3B).
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DISCUSSION |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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The present study showed an enhanced vasoconstrictor response to norepinephrine and a depressed endothelium-dependent relaxation response to acetylcholine in aortic rings studied during the early-stage hypertension in 1K,1C rats. After treatment with L-NMMA, the difference between the 1K,1C rats and the control rats in the norepinephrine-induced vasoconstriction was diminished. L-NMMA also abolished the vasodilator response to acetylcholine in the control and 1K,1C rats. The oral administration of enalapril or losartan normalized the vasoconstrictor and vasodilator responses to the control level in 1K,1C rats. These normalized responses to norepinephrine or acetylcholine by enalapril in 1K,1C rats were unaffected by coincubating the preparations with the bradykinin B2 receptor antagonist HOE-140. These data indicate that angiotensin II disturbs endothelial function in 1K,1C rats.
Exaggerated pressor responses have been reported in hypertensive patients (2, 6) as well as in animal models of hypertension (9, 11, 25). Our group (11) as well as others (9) have reported that the pressor response to norepinephrine is enhanced in prehypertensive 1K,1C rats and rabbits even before the onset of hypertension. These enhanced vascular contractile and pressor responses to vasoconstrictors may contribute to the initiation and maintenance of hypertension. This early stage of experimental hypertension is important, especially because such structural alterations as vascular wall hypertrophy, which could be one of the mechanisms leading to an enhanced pressor response (3), are not considered to occur, although an increase in the wall cross-sectional area (medial hypertrophy) of resistance vessels has not been demonstrated (20) in the early or the chronic stages of hypertension in 1K,1C rats.
We previously demonstrated that the aorta exhibits a significantly exaggerated contractile response to norepinephrine during early-stage hypertension in 1K,1C rats and that endothelial dysfunction contributes to this exaggerated response (8). In those experiments, the ACE inhibitors captopril and enalapril restored the endothelial function in 1K,1C rats. The renin-angiotensin system is activated during early-stage hypertension in 1K,1C rats, although its activity is not considered to be enhanced during the chronic stage. The present study evaluated the agonist-induced vasoconstrictor and vasodilator responses of aortic ring preparations 48 h after the induction of renal artery stenosis or a sham operation. We evaluated the effects of an angiotensin II type 1A receptor antagonist on these responses in the present study. Systolic blood pressure was slightly higher in the 1K,1C rats than in the controls; however, endothelial dysfunction was already present, as documented by the acetylcholine-induced vasodilation observed at this early stage of renal hypertension. These observations suggest that neurohumoral factors, rather than hemodynamic factors, may contribute to the endothelial dysfunction in this model. An important finding of the present study was that not only ACE inhibitors but also the angiotensin II type 1A receptor antagonist losartan restored endothelial function, indicating a close association between endothelial dysfunction and the renin-angiotensin system. The normalized responses to norepinephrine or acetylcholine by enalapril in 1K,1C rats were unaffected by coincubating the preparations with the bradykinin B2 receptor antagonist HOE-140.
ACE inhibitors reduce the formation of angiotensin II and prevent the degradation of bradykinin, an endothelium-dependent relaxant that works by stimulating NO release (5, 13). It has therefore been suggested that part of the antihypertensive action and thus the vascular protective capacity of the ACE inhibitors may be mediated by bradykinin and NO. If true, the improvement in endothelial function produced by the ACE inhibitor used in the present study could also be partly explained by an increase in the bradykinin level. However, intact endothelium is required for the release of NO by bradykinin, and the vasorelaxant response to bradykinin is reportedly reduced in 1K,1C rats (18). Because endothelial function was also improved by the angiotensin II type 1A receptor antagonist losartan, the inhibition of the renin-angiotensin system is of principal importance for the improvement of endothelial function. The normalized response to norepinephrine or acetylcholine produced by enalapril in 1K,1C rats was unaffected by coincubating the preparations with a bradykinin B2 receptor antagonist. This finding also suggests that angiotensin II is involved in endothelial dysfunction. Although receptors for angiotensin II include types 1A, 1B, and 2 (10), the response to losartan suggests that only the type 1A receptor is mainly involved in the endothelial cell damage and inhibition of NO production.
In conclusion, the present study demonstrated that an enhanced vascular response to norepinephrine was present during the early-stage hypertension in 1K,1C rats. Vascular endothelial dysfunction in these rats was normalized to the control levels by treatment with an ACE inhibitor or an angiotensin II type 1A receptor antagonist. The addition of bradykinin B2 receptor antagonist did not alter the normalized endothelial function. The enhancement of norepinephrine-induced vascular contraction was caused by a reduction in NO release due to endothelial dysfunction in which the renin-angiotensin system was demonstrated to be involved. These findings suggest that angiotensin II impairs endothelial function during the early-stage hypertension in this model.
Perspectives
The renin-angiotensin system has long been implicated in the vascular injury produced by hypertension (14). Laragh et al. (14) reported that such vascular dysfunction is more severe in high-renin essential hypertension than in low-renin essential hypertension. The reversal of endothelial dysfunction in 1K,1C rats by enalapril and losartan in the present study indicates that the endothelial dysfunction, which is involved in the development and progression of hypertension and damage to target organs, could be caused by an increase in the activity of the renin-angiotensin system. It has become evident over the past two years that the NADH/reduced NADP (NADPH) oxidases are the most important source of superoxide in the endothelial cells and vascular smooth muscle cells (21). Superoxide anions reportedly inactivate NO by promoting its breakdown and shortening its half-life (24). A recent study by Griending et al. (7) showed that angiotensin II activates an NADH/NADPH oxidase in cultured vascular smooth muscle cells. Rajagopalan et al. (21) demonstrated that angiotensin II can exert this effect in vivo. They concluded that angiotensin II-mediated hypertension in the rat increases the vascular production of superoxide via the activation of membrane NADH/NADPH oxidase (7, 21). They suggest that conditions in which circulating or local levels of angiotensin II are elevated may activate vascular oxidase to cause vascular disease, independent of the elevation of blood pressure. It is thus suggested that the angiotensin II type 1A receptor plays a role in vascular endothelial dysfunction and reducing the release of NO in 1K,1C rats.| |
ACKNOWLEDGEMENTS |
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The authors are grateful to Shizuko Saiki for exellent technical help.
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FOOTNOTES |
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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. §1734 solely to indicate this fact.
Address reprint requests to T. Nakamura.
Received 5 May 1998; accepted in final form 24 August 1998.
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REFERENCES |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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