Effects of captopril on acute phase in two-kidney Goldblatt hypertensive rats and spontaneously hypertensive rats]

Effects of continuous oral administration of captopril were investigated on acute phase in two-kidney Goldblatt hypertensive (2 KGH) rats and spontaneously hypertensive rats (SHR). Systolic blood pressure gradually rose throughout the experimental period of 7, 14, 21 and 28 days in both 2 KGH rats and SHR. These gradual increases of systolic blood pressure were reduced by administration of captopril in both rats. Plasma renin activity were markedly increased throughout the experimental period in both rats treated with captopril, and were modestly increased in 2 KGH rats. In contrast, those changes in plasma renin activity were not obvious in SHR. In 2 KGH rats, juxtaglomerular index (JGI) and juxtaglomerular cell count (JGCC) of the clipped kidneys increased whereas JGI of the opposite kidneys decreased. In contrast, those changes in JGI and JGCC were not obvius in SHR. On the other hand, JGI and JGCC of the clipped kidneys increased in 2 KGH rats treated with captopril and those of the both kidneys increased in SHR treated with captopril. These results suggested that juxtaglomerular cells were related to the development of hypertension in 2 KGH rats, but were not clear in SHR. And these results were found that captopril showed antihypertensive effects, in spite of rises in JGI and JGCC of both 2 KGH rats and SHR.     

Effect of elevated blood pressure, renin and aldosterone on renal sodium handling in two-kidney Goldblatt hypertensive rats

The effect of elevated blood pressure, renin and aldosterone on renal Na+ retention in two-kidney Goldblatt hypertensive rats were investigated. The technique involved retrograde perfusion from the renal veins via the kidneys, and then through the renal arteries and dorsal aorta. Sodium retention in the stenosed kidney of 7 and 30-60 days post-stenosis hypertensive rats was 82 and 70% higher than in normotensive sham-operated rats respectively. Sodium rention in the clipped kidney, 1 day post-stenosis, was insignificant. However, the contralateral kidney of the 1 day post-stenosis rats retained 27% more Na+. The 1 and 7 days post-stenosis rats had higher plasma aldosterone concentrations than controls, while the 30-60 days post-stenosis rats showed lower levels. The plasma renin activity of the 1 day post-stenosis rats showed 65% higher activity than the sham controls with no significant change in the 30-60 days post-stenosis. Therefore Na+ retention may be mediated by aldosterone in the 7 days post-stenosis rats. Natriuresis in the non-stenosed kidneys of both the 7 and 30-60 days post-stenosis rats may be modulated by an increase in filtration rate due to hypertrophy.     

Correlation of the fibrinogen level with blood pressure and plasma renin activity in rats with early Goldblatt hypertension

Goldblatt hypertension was induced in rats by constricting the renal artery on one side. In one group of animals the contralateral kidney remained untouched (two-kidney hypertension), while in the other it was removed (one-kidney hypertension). In the two-kidney hypertension group, renin activity was higher than in the control animals, the fibrinogen was normal both in arterial and venous blood while in one-kidney hypertension the PRA was normal, but the fibrinogen was increased. A close significant correlation could be demonstrated between blood pressure and fibrinogen.     

Acute antihypertensive synergism of angiotensin-converting enzyme inhibitors and diuretics

In spontaneously hypertensive rats (SHR), after 1 day of dosing with an angiotensin-converting enzyme (ACE) inhibitor (captopril or enalapril) plus a diuretic (hydrochlorothiazide), a synergistic antihypertensive effect was observed when a second dose of the combination or ACE inhibitor alone but not the diuretic alone was given the next day. Bilateral ureteral ligation did not prevent the synergism, which indicates that diuresis per se was not the mechanism. Vascular responses to various agonists did not differ in SHR given ACE inhibitor or ACE inhibitor plus diuretic. SHR given combination treatment had higher and more prolonged increases in plasma renin activity. Aprotinin or indomethacin did not alter the synergism, which suggests that endogenous kinins and prostaglandins did not play a role. These data suggest that the mechanism for the synergistic antihypertensive effect resulted from the combination treatment's shifting the blood pressure regulation system to be renin dependent and responding more to drugs affecting the renin-angiotensin system (RAS). Evidence was presented that the RAS can be shifted rapidly to assume a greater role in blood pressure regulation in SHR as well as in normotensive and two-kidney, one-clip Goldblatt renal hypertensive dogs by restricting sodium intake. The data may partly explain the various degrees of antihypertensive responsiveness of essential hypertensive patients to ACE inhibitors.     

Effect of enalapril (MK-421), an orally active angiotensin I converting enzyme inhibitor, on blood pressure, active and inactive plasma renin, urinary prostaglandin E2, and kallikrein excretion in conscious rats

The angiotensin I converting enzyme (ACE) inhibitor enalapril (MK-421), at a dose of 1 mg/kg or more by gavage twice daily, effectively inhibited the pressor response to angiotensin I for more than 12 h and less than 24 h. Plasma renin activity (PRA) did not change after 2 or 4 days of treatment at 1 mg/kg twice daily despite effective ACE inhibition, whereas it rose significantly at 10 mg/kg twice daily. Blood pressure fell significantly and heart rate increased in rats treated with 10 mg/kg of enalapril twice daily, a response which was abolished by concomitant angiotensin II infusion. However, infusion of angiotensin II did not prevent the rise in plasma renin. Enalapril treatment did not change urinary immunoreactive prostaglandin E2 (PGE2) excretion and indomethacin did not modify plasma renin activity of enalapril-treated rats. Propranolol significantly reduced the rise in plasma renin in rats receiving enalapril. None of these findings could be explained by changes in the ratio of active and inactive renin. Water diuresis, without natriuresis and with a decrease in potassium urinary excretion, occurred with the higher dose of enalapril. Enalapril did not potentiate the elevation of PRA in two-kidney one-clip Goldblatt hypertensive rats. In conclusion, enalapril produced renin secretion, which was in part beta-adrenergically mediated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma active and acid-activatable renin during the development of one-kidney, one-clip and two-kidney, one-clip hypertension in the rabbit.

Systolic blood pressure in the central ear artery of eight rabbits increased by 21 mmHg (1 mmHg = 133.32 Pa) over 40 days following renal artery clipping and contralateral nephrectomy (one-kidney, one-clip). Plasma active and acid-activatable (pH 2.8) renin did not change significantly. Similar data were obtained from a group of 12 rabbits following renal artery clipping alone (two-kidney, one-clip) except that blood pressure in this group increased for 26 days but then declined until 40 days. Two animals with one-kidney, one-clip hypertension and three rabbits with two-kidney, one-clip hypertension had large increases in plasma active and inactive renin levels, which followed a more exaggerated rise in blood pressure than in the previous two groups. Forty days after unilateral renal artery clipping, the unclipped kidney was removed in 10 animals with two-kidney, one-clip hypertension. A further increase in blood pressure (+29%) occurred in seven of the animals but no change in plasma active or inactive renin. Results were compared with two groups of control animals, a unilateral nephrectomy group and a laparotomy group. None of the surgical procedures used produced a consistent pattern of change in the relative amounts of active and inactive renin in plasma. No marked changes in sodium, potassium, or water balance occurred in any group of animals.     

Correlation between juxtaglomerular index, kidney renin content and plasma renin concentration in the rat.

The correlation between juxtaglomerular index, kidney renin content, and plasma renin concentration has been investigated in rats. The results indicate that renin exists in two forms. When determining the renin content of the kidney, the renin actually present in the modified smooth muscle cells of the juxtaglomerular apparatus is measured; this is called bound renin. The amount of bound renin is derived from the total of granular and subgranular renin in the modified smooth muscle cells. Since JGI and KRCont show a significant positive correlation in untreated adult rats, it is assumed that in such animals the ratio of granular and subgranular renin is constant. Since no correlation could be demonstrated between kidney renin content and PRC in untreated adult rats, and JGI and KRCont did not change parallel with the increase of PRC in numerous experimental conditions, it is assumed that part of the renin synthetized in the JG cells is secreted directly, without passing the process of condensation into membrane bound granules. This mobile renin does not significantly affect the renin content and the JGI of the kidney. Under physiological circumstances, most of the produced renin seems to mature to granules in the modified smooth muscle cells before being secreted. When renin production and release increased, maturation to granules may be inhibited, a significant part of the produced renin released by direct secretion, and the subgranular, immature renin may also be secreted.     

Antihypertensive effect of total flavonoid fraction of Astragalus complanatus in hypertensive rats

The purpose of the present study was to quantify the antihypertensive effect of the total flavonoid (TF), extracted from the seed of Astragalus complanatus R. Brown, and to observe its effect on the renin-angiotensin system (RAS) in both renal hypertensive rats (RHR) and spontaneously hypertensive rats (SHR). RHR were created by the two-kidney one clip (2K1C) method. Systolic blood pressure was measured in conscious rats by the tail-cuff method. Plasma angiotensin II (AngII) and plasma renin activity (PRA) were measured with radioimmunoassay at 60 min after drug administration. The effects of TF on cardiac hemodynamics were also recorded in anesthetized RHR and SHR. TF was given by oral administration in low dose (100 mg/kg) and high dose (200 mg/kg) respectively. Compared to pre-administration control, TF induced an obvious decrease in systolic blood pressure in conscious normotensive Wistar rat, RHR and SHR. In the three groups the systolic blood pressure reached the lowest value at 60 min after TF. TF also induced a significant decrease in blood pressure in anesthetized RHR and SHR. At 60 min after treatment of TF, mean arterial pressure in high dose group (200 mg/kg) was decreased by 17% in RHR and by 17% in SHR respectively (P < 0.01). The depressor effect of TF lasted for at least 60 min. Cardiac output, heart rate and +/- dp/dtmax did not change. Conversely, total peripheral resistance was significantly decreased. The decrease in plasma AngII was found in both RHR and SHR. On the contrary, PRA increased at the same time. These findings suggested that TF is effective in reducing blood pressure in both RHR and SHR. The antihypertensive action of TF was attributed to a decrease in TPR secondary to a decrease in plasma concentration of AngII caused by TF.     

Enzymuria (the output of gamma-glutamyl-transpeptidase and of N-acetyl-beta-D-glucosaminidase) in the course of experimental renovascular hypertension

The urinary output of gamma-glutamyl-transpeptidase (gamma GT) and of N-acetyl-beta-D-glucosaminidase (NAG) was studied with "two-kidney Goldblatt hypertension' 3-6, 16-19 and 30-33 weeks after eliciting high blood pressure. gamma GT excretion rate of normotensive males was higher than that of females, while the activity of the renal tissue was on the same level. gamma GT output of hypertensive males was elevated in the early and in the middle stages of the disease, it was subnormal in the late stage. In females gamma GT output increased in animals with excessively high blood pressure (less than 200 mm Hg) only. gamma GT output correlated with the tissue activity in males only. In all animals there was an inverse, linear correlation between tissue gamma GT activity and the hydroxyproline content. The pattern of the NAG output was similar to that of gamma GT, however, excretion of NAG showed no sex differences and remained high in the late stage of the disease, too. Nephrosclerosis was less pronounced in female Goldblatt rats than in males.     

High salt intake attenuates the development of hypertension in two-kidney, one-clip Goldblatt rats.

Effects of high salt intake on the early onset of hypertension were examined in two-kidney, one-clip rats. They were divided into high salt and control groups which were supplied with 1.0% NaCl and tap water, respectively, as a drinking solution for 12 days after clipping the left renal artery. The high salt group showed a lower plasma renin concentration and a higher plasma atrial natriuretic peptide (ANP) along with an attenuation of the magnitude of early hypertension, as compared with the control group. A significant positive correlation between blood pressure and plasma renin concentration and an inverse correlation between plasma renin concentration and ANP were shown. Cortical renal renin content was comparable between the two groups. In another two groups of sham-clipped rats, the high salt group did not differ from the tap water-drinking group in any of the parameters examined, except that ANP was significantly higher. These results demonstrate that high salt intake attenuates the developmental phase of hypertension in two-kidney, one-clip rats by increasing the ANP and suppressing the release of renin.     

Loss of Prolyl Carboxypeptidase in Two-Kidney,One-Clip Goldblatt Hypertensive Mice

It is well documented that angiotensin (Ang) II contributes to kidney disease progression. The protease prolyl carboxypeptidase (PRCP) is highly expressed in the kidney and may be renoprotective by degrading Ang II to Ang-(1-7). The aim of the study was to investigate whether renal PRCP protein expression and activity are altered in two-kidney, one-clip (2K1C) Goldblatt hypertensive mice. Left renal artery was constricted by using 0.12 mm silver clips. Blood pressure was measured using telemetry over the eleven weeks of study period and revealed an immediate increase in 2K1C animals during the first week of clip placement which was followed by a gradual decrease to baseline blood pressure. Similarly, urinary albumin excretion was significantly increased one week after 2K1C and returned to baseline levels during the following weeks. At 2 weeks and at the end of the study, renal pathologies were exacerbated in the 2K1C model as revealed by a significant increase in mesangial expansion and renal fibrosis. Renal PRCP expression and activity were significantly reduced in clipped kidneys. Immunofluorescence revealed the loss of renal tubular PRCP but not glomerular PRCP. In contrast, expression of prolyl endopeptidase, another enzyme capable of converting Ang II into Ang-(1-7), was not affected, while angiotensin converting enzyme was elevated in unclipped kidneys and renin was increased in clipped kidneys. Results suggest that PRCP is suppressed in 2K1C and that this downregulation may attenuate renoprotective effects via impaired Ang II degradation by PRCP.     

Antihypertensive profile of the angiotensin-converting enzyme inhibitors CI-906 and CI-907

CI-906 and CI-907, new orally active nonsulfhydryl angiotensin-converting enzyme inhibitors, were examined for antihypertensive effects in unanesthetized hypertensive rats and dogs. In two-kidney, one-clip Goldblatt hypertensive rats, single oral daily doses (0.03-30 mg/kg) produced dose-dependent decreases in blood pressure; a single 3 mg/kg oral dose lowered blood pressure to normotensive levels. In spontaneously hypertensive rats, 30 mg/(kg X day) orally administered for 5 consecutive days achieved the same blood pressure decrease as that obtained on the first day in the renal hypertensive rats. In diuretic-pretreated renal hypertensive dogs, a 10 mg/kg oral dose decreased blood pressure by 25%. No adverse side effects were observed with CI-906 and CI-907 in any of the conscious animals. These studies indicate that CI-906 and CI-907 are potent, orally active antihypertensive agents without any apparent limiting side effects.     

The renin-angiotensin system in rats made hypertensive by ligation of the kidney poles (38584).

The renin-angiotensin system was studied in experimental renal hypertension produced by ligation of the poles of the left kidney followed by contralateral nephrectomy. Plasma renin concentration of renin substrate was lower and that of angiotensin I converting enzyme was higher in hypertensive animals. The juxtaglomerular index decreased in the medial zone of the kidney, while heavily granulated areas appeared in the poles. Ligated kidneys of rats that remained normotensive showed juxtaglomerular indices intermediate between the control and the hypertensive rats. Differences in renal renin content between the groups correspond to those for the juxtaglomerular index, but were smaller. No differences between the experimental groups were observed in iso-renin content in the brain; however in all animals with ligated kidney poles, hypertensive or normotensive, there was a tendency for iso-renin in the adrenals, left ventricular myocardium, and especially aorta to be lower than in controls.     

Effect of valsartan on angiotensin II- and vasopressin-degrading activities in the kidney of normotensive and hypertensive rats.

Valsartan, a selective antagonist of angiotensin II at the AT(1) receptor subtype, is an efficacious, orally active, blood pressure-lowering agent used in hypertensive patients. Given that aminopeptidases (APs) play a major role in the metabolism of local peptides involved in blood pressure control, studying them helped us to understand cardiovascular control. We studied the effect of valsartan on angiotensin II- (GluAP) and vasopressin- (CysAP) degrading activities in the kidney in the rat model of renovascular hypertension, Goldblatt two-kidney one-clip. GluAP and CysAP in renal cortex and medulla exhibited different responses to hypertension and valsartan treatment. In the renal cortex, GluAP decreased in clipped and non-clipped kidneys of hypertensive animals. However, while hypertension did not affect GluAP in the clipped kidney medulla, the non-clipped kidney exhibited an increase in soluble and a decrease in membrane-bound activity. Valsartan decreased soluble GluAP in the medulla of normotensive and hypertensive animals. In the renal cortex, CysAP activity was mainly downregulated following hypertension. Valsartan decreased soluble CysAP activity in sham-operated, but not in hypertensive animals. The renal medulla showed a significant valsartan-related decreased activity in clipped and non-clipped kidneys of both sham-operated and hypertensive animals. These results suggest a functional relationship between the AT(1) receptor and vasopressin-degrading activity.     

Adrenal and vascular renin-like activity in chronic 'two-kidney, one-clip' hypertensive rats

In order to study the vascular and adrenal renin angiotensin system in the chronic phase (4 months after clipping) of 'two-kidney, one-clip' hypertension in rats, systolic blood pressure, plasma renin activity, and tissue renin-like activity in both aorta and adrenal have been measured. Renin activity in adrenal gland was studied in both the zona glomerulosa (GLO) and the remainder of the gland. Results showed an increase in vascular renin activity in chronic hypertensive rats. Moreover it was found that GLO of hypertensive rats presented a significant increase in renin-like activity compared with controls (349.43 +/- 43.86 versus 167 +/- 34.25 ng AI/g/20 h, p less than 0.01) and the fasciculata-reticular-medullar (FRM) portion also showed greater renin activity (345.16 +/- 64.36 versus 57.90 +/- 4.83 ng AI/g/20 h, p less than 0.01). The higher levels of vascular and FRM renin-like activity in chronic renal hypertension are probably a consequence of plasma renin increase. This hypothesis is supported by the fact that bilateral nephrectomy in normal rats induces a significant decrease in plasma renin activity and both aortic and FRM renin-like activity. On the other hand the GLO renin-like activity could depend on both plasma renin and local synthesis since bilateral nephrectomy induces an increase in the renin-like activity in this tissue. These data support the idea that aortic and FRM renin are, at least in part, due to plasma renin uptake and GLO renin is an autonomic system.     

Tissue-specific regulation of renin-binding protein gene expression in rats.

Rat gene for renin-binding protein (RnBP) was shown to be expressed in the kidney, adrenal gland, brain, lung, spleen, ovary, testis, and heart. On sodium depletion and captopril administration, the rat showed a marked increase in the adrenal RnBP mRNA level and a slight decrease in the kidney RnBP mRNA level. In two-kidney, one clip hypertensive rats, the RnBP mRNA levels of the clipped and contralateral kidneys were unchanged and also its adrenal mRNA level was maintained at the control level. The recombinant rat RnBP was synthesized in Escherichia coli cells and purified to apparent homogeneity. The RnBP existed as a homodimer and formed a heterodimer with rat renin to inhibit renin activity extensively. Intravenous injection of the RnBP into rats resulted in a rapid and strong inhibition of plasma renin activity, which persisted at least for 2 h. These results suggest that the expression of RnBP gene in the kidney and adrenal gland is regulated independently, and the function of RnBP is related to electrolyte homeostasis, probably through the interaction with renin.     

Pharmacological properties of the converting enzyme inhibitor, enalapril maleate (MK-421)

Enalapril maleate (MK-421), an ethyl ester, is an angiotensin-converting enzyme (ACE) inhibitor from a novel series of substituted N-carboxymethyldipeptides. The parent diacid (MK-422) N-[(S)-1-carboxy-3-phenylpropyl]-L-Ala-L-Pro of MK-421 inhibited hog plasma ACE with an I50 of 1.2 nM. Because deesterification occurs slowly or not at all in vitro, the in vitro I50 for enalapril was 1200 nM. However, both enalapril and MK-422 were potent inhibitors of ACE by the i.v. and oral routes in rats and dogs. In rats with experimental hypertension, enalapril was most potent in those models in which the renin-angiotensin system plays a dominant role (salt restriction, two-kidney Grollman) and in models rendered renin dependent by diuretics, although blood pressure reduction did occur in low or normal renin models such as spontaneously hypertensive rats, in which inhibition of ACE as measured by the blockade of angiotensin I pressor responses bore little temporal relationship to the later fall in blood pressure after enalapril.     

Effect of apocynin treatment on renal expression of COX-2, NOS1, and renin in Wistar-Kyoto and spontaneously hypertensive rats

Macula densa (MD) cells of the juxtaglomerular apparatus (JGA) synthesize type 1 nitric oxide synthase (NOS1) and type 2 cyclooxygenase (COX-2). Both nitric oxide (NO) and prostaglandins have been considered to mediate or modulate the control of renin secretion. Reactive oxygen species (ROS) produced locally by NADPH oxidase may influence NO bioavailability. We have tested the hypothesis that in hypertension elevated ROS levels may modify the expression of NOS1 and COX-2 in the JGA, thereby interacting with juxtaglomerular signaling. To this end, spontaneously hypertensive rats (SHR) and Wistar-Kyoto control rats (WKY) received the specific NADPH oxidase inhibitor, apocynin, during 3 wk. Renal functional and histochemical parameters, plasma renin activity (PRA), and as a measure of ROS activity, urinary isoprostane excretion (IP) were evaluated. Compared with WKY, IP levels in untreated SHR were 2.2-fold increased, and NOS1 immunoreactiviy (IR) of JGA 1.5-fold increased, whereas COX-2 IR was reduced to 35%, renin IR to 51%, and PRA to 7%. Apocynin treatment reduced IP levels in SHR to 52%, NOS1 IR to 69%, and renin IR to 62% of untreated SHR, whereas renin mRNA, COX-2 IR, glomerular filtration rate, PRA, and systolic blood pressure remained unchanged. WKY revealed no changes under apocynin treatment. These data show that NADPH oxidase is an important contributor to elevated levels of ROS in hypertension. Upregulation of MD NOS1 in SHR may have the potential of blunting the functional impact of ROS at the level of bioavailable NO. Downregulated COX-2 and renin levels in SHR are apparently unrelated to oxidative stress, since apocynin treatment had no effect on these parameters.     

Targeted activation of transcription in vivo through hairpin-triplex forming oligonucleotide in Saccharomyces cerevisiae

The aims of the present study were to analyse the effects of an oral daily dose (10 mg/kg) of the dietary flavonoid quercetin for five weeks in two-kidney, one-clip (2K1C) Goldblatt (GB) hypertensive rats. The evolution of systolic blood pressure was followed by weekly measurements, and morphological variables, proteinuria, plasma nitrates plus nitrites (NO_x) and thiobarbituric acid reactive substances (TBARS), liver oxidative stress markers and endothelial function were determined at the end of the experimental period. Quercetin treatment reduced systolic blood pressure of GB rats, producing no effect in control animals. It also reduced cardiac hypertrophy and proteinuria developed in GB hypertensive rats. Decreased endothelium-dependent relaxation to acetylcholine of aortic rings from GB rats was improved by chronic quercetin treatment, as well as increased endothelium-dependent vasoconstrictor response to acetylcholine and overproduction of TXB₂ by aortic vessels of GB rats, being without effect in normotensive animals. Increased plasma NO_x and TBARS, and decreased liver total glutathione (GSH) levels and glutathione peroxidase (GPX) activity were observed in GB hypertensive rats compared to the control animals. Normalisation of plasma NO_x and TBARS concentrations and improvement of the antioxidant defences system in liver accompanied the antihypertensive effect of quercetin. We conclude that chronic oral treatment with quercetin shows both antihypertensive and antioxidant effects in this model of renovascular hypertension. (Mol Cell Biochem 270: 147–155, 2005)M.F. García-Saura and M. Galisteo are equal contributors to this work