angiotensinogen and Hypertension--Renovascular

Recent advances in molecular biological techniques provide us with genetic approaches for studying the renin-angiotensin system. Renin and angiotensinogen cDNAs have been cloned in several species, and the sequences are highly conserved between the species. The 5'-flanking region of the human renin gene indicated putative regulatory sequences of glucocorticoid, estrogen, progesterone, and cAMP. The 5'-flanking region of the human angiotensinogen gene also had putative regulatory sequences of glucocorticoid, estrogen, acute phase protein, and cAMP. These structures may be related to the tissue specific expression of the renin and angiotensinogen genes. In this review, expression of rat renin and angiotensinogen genes in various tissues in the following conditions are described: a) different sodium intake in the liver, kidney, and brain; b) angiotensin II and converting enzyme inhibition in the liver, kidney and brain; c) renovascular hypertension in the kidney and liver; d) aging in the liver and kidney; e) adrenal steroids in the liver, kidney and brain; f) gonadotropin and testosterone in the testes, liver and kidney; g) triiodothyronine in the liver, kidney and brain; h) nephrectomy in the liver and brain; i) high potassium, angiotensin II, sodium intake and nephrectomy in the adrenal gland; j) transgenic animal. Our results suggest that the expression of the renin and angiotensinogen genes are regulated in a tissue-specific manner.

Topics: Aging; Angiotensin II; Angiotensin-Converting Enzyme Inhibitors; Angiotensinogen; Animals; Dexamethasone; Gene Expression Regulation; Humans; Hypertension, Renovascular; Mice; Mice, Transgenic; Organ Specificity; Renin; Renin-Angiotensin System; RNA, Messenger

Topics: Adrenergic beta-Antagonists; Adult; Aldosterone; Angiotensinogen; Angiotensins; Animals; Blood Pressure; Female; Humans; Hyperaldosteronism; Hypertension; Hypertension, Malignant; Hypertension, Renovascular; Kidney Failure, Chronic; Male; Molecular Weight; Peptidyl-Dipeptidase A; Radioimmunoassay; Renin

In angiotensin II (ANG II)-dependent hypertension, there is an angiotensin type 1 receptor-dependent amplification mechanism enhancing intrarenal angiotensinogen (AGT) formation and secretion in the tubular fluid. To evaluate the role of increased arterial pressure, AGT mRNA, protein expression, and urinary AGT (uAGT) excretion and tissue injury were assessed in both kidneys of two-kidney, one-clip Sprague-Dawley hypertensive rats subjected to left renal arterial clipping (0.25-mm gap). By 18-21 days, systolic arterial pressure increased to 180 ± 3 mmHg, and uAGT increased. Water intake, body weights, 24-h urine volumes, and sodium excretion were similar. In separate measurements of renal function in anesthetized rats, renal plasma flow and glomerular filtration rate were similar in clipped and nonclipped kidneys and not different from those in sham rats, indicating that the perfusion pressure to the clipped kidneys remained within the autoregulatory range. The nonclipped kidneys exhibited increased urine flow and sodium excretion. The uAGT excretion was significantly greater in nonclipped kidneys compared with clipped and sham kidneys. AGT mRNA was 2.15-fold greater in the nonclipped kidneys compared with sham (1.0 ± 0.1) or clipped (0.98 ± 0.15) kidneys. AGT protein levels were also greater in the nonclipped kidneys. The nonclipped kidneys exhibited greater glomerular expansion and immune cell infiltration, medullary fibrosis, and cellular proliferation than the clipped kidneys. Because both kidneys have elevated ANG II levels, the greater tissue injury in the nonclipped kidneys indicates that an increased arterial pressure synergizes with increased intrarenal ANG II to stimulate AGT production and exert greater renal injury.

Topics: Angiotensinogen; Animals; Arterial Pressure; Body Weight; Drinking; Fibrosis; Hypertension, Renovascular; Immunity, Cellular; Kidney; Kidney Glomerulus; Kidney Medulla; Male; Rats; Rats, Sprague-Dawley; RNA, Messenger; Sodium

The purpose of this study was to assess, in the murine kidney, the mechanisms underlying the endothelium-dependent control of vascular tone and whether or not, in a severe model of hypertension and renal failure, KCa channels contribute to its regulation. Wild-type (BL) and double-transgenic female mice expressing human angiotensinogen and renin (AR) genes received either control or a high-salt diet associated to a nitric oxide (NO) synthase inhibitor treatment (BLSL and ARSL). Changes in renal perfusion pressure (RPP) were measured in isolated perfused kidneys. BLSL and AR were moderately hypertensive without kidney disease while ARSL developed severe hypertension and renal failure. In the four groups, methacholine induced biphasic endothelium-dependent responses, a transient decrease in RPP followed by a cyclooxygenase-dependent increase in RPP. In the presence or not of indomethacin, the vasodilatations were poorly sensitive to NO synthase inhibition. However, in the presence of cyclooxygenase and NO synthase inhibitors, apamin, and/or TRAM-34, blockers of KCa2.3 and KCa3.1, respectively, abolished the decrease in RPP in response to either methacholine or the two activators of KCa2.3/KCa3.1, NS309, and SKA-31. Thus, KCa2/3 channels play a major role in the regulation of murine kidney perfusion and this mechanism is maintained in hypertension, even when severe and associated with kidney damage.

Topics: Angiotensinogen; Animals; Endothelium, Vascular; Female; Humans; Hypertension, Renovascular; Indomethacin; Intermediate-Conductance Calcium-Activated Potassium Channels; Methacholine Chloride; Mice; Mice, Inbred C57BL; Nitric Oxide Synthase; Potassium Channel Blockers; Renal Insufficiency; Renin; Small-Conductance Calcium-Activated Potassium Channels; Sodium, Dietary; Vasodilation

It is largely unknown to what extent genetic abnormalities contribute to the development of atherosclerotic renal artery disease. Among the potential candidate genes, those of the renin-angiotensin system and the endothelial nitric oxide synthase (eNOS) rank high because of their importance in the atherosclerotic process. We investigated the association of polymorphisms in these genes (the angiotensinogen Met235Thr, the angiotensin-converting enzyme insertion/deletion, the angiotensin II type-1 receptor A1166C, and the eNOS Glu298Asp) with the presence or absence of atherosclerotic renovascular disease in 456 consecutive hypertensive patients referred for renal angiography on the suspicion of renovascular hypertension. Nondiseased normotensive (n=200) and hypertensive (n=154) patients from a family practice served as external controls. Renal artery disease was present in 30% of our angiography group. The Asp allele of the eNOS Glu298Asp polymorphism was associated with atherosclerotic renal artery stenosis with an odds ratio of 1.44 (95% confidence interval 1.00 to 2.09) versus hypertensives with angiographically proven patent arteries, of 1.89 (1.24 to 2.87) versus hypertensive family practice controls, and of 2.09 (1.29 to 3.38) versus normotensive family practice controls. However, this allele also differed significantly between patients with patent renal arteries and normotensive and hypertensive controls. No differences were found with respect to the other genetic polymorphisms. We hypothesize that the Asp allele of the Glu298Asp polymorphism may predispose to the development of atherosclerotic lesions but that renal artery involvement depends on other factors, also.

Topics: Aged; Angiotensinogen; Arteriosclerosis; Female; Genotype; Humans; Hypertension, Renovascular; Logistic Models; Male; Middle Aged; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Peptidyl-Dipeptidase A; Polymorphism, Genetic; Radiography; Receptors, Angiotensin; Retinal Artery Occlusion; Risk Factors

The systemic renin-angiotensin system (RAS) plays an important role in blood pressure (BP) regulation during the development of 2-kidney, 1 clip (2K1C) hypertension. Its contributions decrease with time after constriction of the renal artery. During the chronic phase, the peripheral RAS returns to normal, but the hypertension is sustained for months. We hypothesized that in this phase the brain RAS contributes to the maintenance of high BP. To test the hypothesis, we studied the role of brain RAS by decreasing the synthesis of angiotensinogen (AGT) and the angiotensin II (Ang II) type 1a receptor (AT(1)R) with intracerebroventricular injections of antisense oligonucleotides (AS-ODNs). The response of systolic BP (SBP) to AS-ODNs to AGT mRNA was studied in 2K1C rats at 6 months after clipping, and the response to AS-ODNs to AT(1)R mRNA was studied at 10 months after clipping. Intracerebroventricular injection of AS-ODN-AGT (200 microgram/kg, n=5) significantly decreased SBP (-22+/-6 mm Hg, P<0.05) compared with the sense ODN (n=5) and saline (n=3) groups. Intracerebroventricular injection of AS-ODN-AGT reduced the elevated hypothalamic Ang II level. The hypothalamic Ang II content in sense ODN and saline groups was significantly (P<0.05) higher than in the nonclipped group. Compared with inverted ODN, intracerebroventricular injection of AS-ODN-AT(1)R (250 microgram/kg, n=6) significantly decreased SBP (-26+/-8 mm Hg, P<0.05) for 3 days after injection. This was a brain effect because intravenous AS-ODN-AT(1)R at a dose of 250 to 500 microgram/kg did not affect SBP. These results suggest that the brain RAS plays an important role in maintaining the elevated SBP in chronic 2K1C hypertension.

Topics: Angiotensin II; Angiotensin Receptor Antagonists; Angiotensinogen; Animals; Blood Pressure; Brain; Chronic Disease; Hypertension; Hypertension, Renovascular; Hypothalamus; Injections, Intraventricular; Male; Oligonucleotides, Antisense; Rats; Rats, Sprague-Dawley; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin; Renin-Angiotensin System; RNA, Messenger; Time Factors

The effect of acutely increasing renal perfusion pressure or extracellular fluid volume on renal medullary and cortical blood flow was examined in the low-renin deoxycorticosterone acetate (DOCA)-salt hypertension model in mice. A 50-mg DOCA tablet was implanted, and 1% saline was given as drinking water for 3 wk. Medullary and cortical blood flow were determined with laser-Doppler flowmetry, and whole-kidney blood flow was measured with a transit-time ultrasound flowprobe around the renal artery. In control mice, total renal blood flow ranged from 6.3 and 7.6 ml/min per g kidney weight and in DOCA-salt mice from 4.3 and 4.7 ml/min per g kidney weight, respectively, and was minimally affected as renal perfusion pressure was increased. Renal vascular resistance increased correspondingly. During stepwise increases in renal artery pressure from 90 to 140 mmHg, medullary blood flow progressively increased in control mice to 125% of baseline values, whereas cortical blood flow did not change. In DOCA-salt mice, increasing BP from 100 to 154 mmHg had no effect on either cortical or medullary blood flow. Urine flow and sodium excretion were lower in DOCA-salt mice than in controls and increased nearly to the same extent in both groups after volume expansion with isotonic saline. Total renal blood flow increased after saline loading, more in controls than in DOCA-salt mice. Increases in medullary blood flow after saline loading were up to 122% of baseline values in controls and demonstrated a significantly steeper slope than the 110% of baseline increases in DOCA-salt mice. Cortical blood flow, however, was not different between the groups. Thus, medullary blood flow is not as tightly autoregulated as cortical blood flow in normal mice. Natriuresis with acute volume loading is facilitated by increased medullary blood flow. In DOCA-salt mice, the medullary blood flow reaction to renal perfusion pressure increases is abolished, whereas flow increases with extracellular volume expansion are diminished. These results suggest that diminished pressure-natriuresis responses in DOCA-salt mice are related to perturbed medullary blood flow.

Topics: Angiotensinogen; Animals; Blood Flow Velocity; Blood Pressure; Blood Volume; Desoxycorticosterone; Diuresis; Gene Expression; Genes; Hematocrit; Hemodynamics; Hypertension, Renovascular; Kidney; Kidney Cortex; Kidney Medulla; Mice; Natriuresis; Peptidyl-Dipeptidase A; Perfusion; Potassium; Pressure; Receptor, Angiotensin, Type 1; Receptor, Angiotensin, Type 2; Receptors, Angiotensin; Regional Blood Flow; Renal Circulation; Renin; Renin-Angiotensin System; RNA, Messenger; Sodium; Sodium Chloride; Urination; Vascular Resistance

The behavior of the circulating renin-angiotensin system is well known; however, the actions of renin and the generation of angiotensin (ANG) II at the tissue level are less appreciated. We have used rat models to study this issue. We examined the cleavage of human angiotensinogen to ANG I by human renin and its inhibition by a human renin inhibitor in an isolated perfused hindlimb preparation from rats which express the human angiotensinogen gene. With this model, we were able to show that renin acts at the site of the vascular wall, rather than in the lumen, to generate ANG I, which is subsequently converted to ANG II. Furthermore, the cleavage is specifically dependent on renin and not on other lysosomal proteases. The renin gene is present in the vascular wall; however, whether or not renin is generated locally to act locally, or whether renin is taken up from the circulation to act locally was not clear. We used the same strain of transgenic rats to test this issue and showed that renin can be taken up by cardiac or coronary vasculature tissue and induces long-lasting local ANG II generation. Locally formed ANG I was converted to ANG II more effectively than infused ANG I. We did additional studies to examine the conversion step from ANG I to ANG II in the vessel wall. We perfused hindlimbs from Sprague-Dawley rats with ANG I and observed ANG II production, which was linear over a 10,000-fold concentration range of ANG I. However, when we increased angiotensin converting enzyme (ACE) gene expression in the vascular bed, which also increased ACE tissue concentrations, we were nevertheless able to demonstrate increased ANG II production with ACE upregulation. Taken together, these results demonstrate (1) the cleavage of local angiotensinogen to ANG I within the vascular wall by renin, (2) renin uptake from the circulation to evoke that local effect, and (3) a potential regulatory effect by vascular tissue ACE on ANG II production in the vessel wall. The findings support the notion of localized renin-angiotensin system-related effects on vascular function and structure.

Topics: Angiotensin I; Angiotensin II; Angiotensinogen; Animals; Animals, Genetically Modified; Aorta; Blood Vessels; Coronary Vessels; Hindlimb; Humans; Hypertension, Renovascular; In Vitro Techniques; Peptidyl-Dipeptidase A; Rats; Rats, Sprague-Dawley; Renin; Renin-Angiotensin System; Swine

The aim of the present study was to provide an overview of the role of circulating gonadal steroids on the adaptive changes of the renin-angiotensin system to chronic hypobaric hypoxia (CHH: 4400 m simulated altitude in an hypobaric chamber) and the development of experimental hypertension by bilateral renal ischemia. In order to fulfill this goal, blood pressure (BP), plasma renin activity (PRA) and plasma angiotensinogen concentration (PAoC) as well as haematocrit (Htc) and body weight (BW) of intact and post-puberal castrated normotensive (Nt) and hypertensive (Ht) rats of both sexes were studied following an experimental design similar to that of previous works. Post-puberal castration decreased BP of Nt and Ht rats subjected to CHH. Sexual dimorphism in BP, PRA and PAoC was maintained while that in haematocrit disappeared after castration. Results suggest that circulating sexual steroid hormones are involved in the response of the renin-angiotensin system to the experimental conditions of environmental reduced O2 partial pressure.

Topics: Adaptation, Physiological; Altitude; Angiotensinogen; Animals; Blood Pressure; Body Weight; Female; Gonadal Steroid Hormones; Hematocrit; Hypertension, Renovascular; Hypoxia; Male; Orchiectomy; Ovariectomy; Rats; Rats, Wistar; Renin; Renin-Angiotensin System

The effective development of human renin inhibitors meets its major obstacle in the absence of a suitable experimental rodent model and the species-specificity of human renin, exclusively cleaving its natural substrate human angiotensinogen. We have reconstructed the human renin-angiotensin system in transgenic rats over expressing the human angiotensinogen gene TGR (hAOGEN) 1623 by chronically injecting i.v. human recombinant renin. We have first established new in vitro enzyme kinetic techniques to measure the various components of the chimeric renin-angiotensin system and distinguished the two human and rat-specific pathways of generating angiotensin I by the human specific renin inhibitor Ro 42-5892 (Hoffmann-La Roche). Male heterozygous TGR had plasma levels of rat angiotensinogen of 1.2 +/- 0.2 mg Ang l/ml while the plasma levels of the transgene were 141 +/- 98 mg Ang l/ml (n = 41; not normally distributed). Transgene expression was found in the liver kidney, aorta, heart and adrenals. Four rats were infused i.v. with human recombinant renin at 50 ng/h over 9 days which chronically increased their blood pressure to > 200 mmHg while total plasma renin activity increased by a factor of 300. Rat renin disappeared form the plasma. This new model of experimental human renin-induced hypertension in rats will facilitate the screening and characterization of human renin inhibitors.

Topics: Angiotensinogen; Animals; Animals, Genetically Modified; Disease Models, Animal; Gene Transfer Techniques; Humans; Hypertension, Renovascular; In Vitro Techniques; Male; Rats; Renin; Renin-Angiotensin System

We hypothesized that the gene expression of angiotensinogen, angiotensin-converting enzyme, and angiotensin II type 1 receptor, in addition to renin, is increased in kidneys after renal artery stenosis. Two-kidney, one clip renovascular hypertension was initiated in Sprague-Dawley rats by clipping of the left renal artery; control rats were sham operated. Blood pressure was not changed for the first 2 days after clipping but was elevated on day 4 (mean arterial pressure, 104 +/- 4 versus 87 +/- 2 mm Hg in sham-operated control rats, P < .002) and increased further during the next 24 days. Rats were killed 2, 4, 7, 14, and 28 days after clipping or sham operation, and poly(A)(+)-purified renal cortical RNA was analyzed by Northern blotting. Autoradiographs were quantitated by densitometry and normalized for the expression of a housekeeping gene. Renin expression was increased in the clipped kidney (by 149% on day 2) and decreased in the nonclipped kidney (by 82% on day 2), compared with kidneys of control rats. Expression of the angiotensin-converting enzyme was increased in clipped kidneys from the first day after clipping (158%) and throughout the experiment (66% on day 28), but was unchanged or slightly decreased in nonclipped kidneys. Angiotensinogen mRNA showed little change. Angiotensin II type 1 receptor expression was decreased in nonclipped kidneys but unchanged during the first 7 days in clipped kidneys. Our results show that components of the renin-angiotensin system other than renin are also differentially expressed in clipped kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensin II; Angiotensinogen; Animals; Hypertension, Renovascular; Kidney; Male; Peptidyl-Dipeptidase A; Rats; Rats, Sprague-Dawley; Receptors, Angiotensin; Renin; RNA, Messenger

Previous studies have shown that chronic low-dose administration of 40 ng/min angiotensin II by osmotic minipump to uninephrectomized rats mimics the temporal hypertensive response and the circulating angiotensin II levels observed in two-kidney, one clip Goldblatt rats. Furthermore, renal tissue angiotensin II contents were higher than the circulating angiotensin II levels, suggesting that circulating angiotensin II induces endogenous intrarenal angiotensin II production. The present study examined the molecular mechanisms by which intrarenal angiotensin II production is modulated in angiotensin II-induced and two-kidney Goldblatt hypertension. Two weeks after clipping, intrarenal renin mRNA levels were elevated threefold in the clipped kidney of Goldblatt rats but were markedly suppressed in the nonclipped kidneys of Goldblatt rats (28% of control values) and in the remaining kidney of uninephrectomized angiotensin II-infused rats (7% of control values). In contrast, there were sustained levels of angiotensinogen mRNA in the kidneys and livers of Goldblatt and angiotensin II-infused rats, indicating differential regulation of the genes of the renin-angiotensin system. Renal kallikrein gene expression was not altered in either of the hypertensive groups 14 days after the induction of hypertension, suggesting the absence of an enhanced counteracting kinin influence.

Topics: Angiotensin II; Angiotensinogen; Animals; Blood Pressure; Blotting, Northern; Gene Expression Regulation; Hypertension, Renovascular; Kallikreins; Kidney; Male; Rats; Rats, Sprague-Dawley; Renin; Renin-Angiotensin System; RNA; RNA, Messenger

An imbalance in the activity of the vasopressor renin-angiotensin and vasodepressor kallikrein-kinin systems may play an important role in the pathogenesis of hypertension after unilateral renal artery constriction. To test this hypothesis, we examined the expression of the renin, angiotensinogen (Ao), and tissue kallikrein genes 7 and 25 days after placement of a 0.25-mm clip on the left renal artery of rats. One week after clipping, renin mRNA levels were 4.6-fold higher in the clipped and 50% lower in the nonclipped kidneys compared with kidneys from sham-operated rats. At 25 days, renin mRNA levels in the clipped kidneys were not different from sham kidneys, but were suppressed to almost undetectable levels in the nonclipped kidneys. Steady-state Ao mRNA levels in the clipped kidneys were not different from those of nonclipped or sham kidneys at either 7 or 25 days. However, at 25 days, Ao mRNA levels were lower in the liver (70%), left ventricle (55%), and aorta (45%) of clipped than sham-operated rats. The expression of the renal kallikrein gene was unchanged at 7 days and was suppressed by 50% at 25 days. These results are consistent with the notion that activation of the intrarenal renin-angiotensin system occurs during the initial phase of the two-kidney, one-clip hypertension model. The renal kallikrein gene, in marked contrast to renin, becomes downregulated in the chronic phase. The differential regulation of renin-angiotensin and kallikrein genes may be an important pathogenetic factor in renovascular hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensinogen; Animals; Blotting, Northern; DNA; Down-Regulation; Gene Expression; Hypertension, Renovascular; Kallikreins; Kidney; Male; Rats; Rats, Sprague-Dawley; Renin; RNA, Messenger; Time Factors

Some reports have stated that central norepinephrine (NE) depletion inhibited the development of hypertension in the rat. On the other hand, this pharmacological treatment induces changes on the central renin-angiotensin system. The present study was designed to follow the development of 2 kidney-2 clip (2k-2c) renovascular hypertension in rats depleted of central NE and to analyze the central and peripheral renin-angiotensin system. Male Wistar rats (n = 40) were used. Half of the animals was injected, intracisternally, with 6-hydroxydopamine (6-OHDA), the remaining rats only received the vehicle. One week later a silver clip was placed on each renal artery on half of the 6-OHDA treated rats and on half of the vehicle treated animals. A sham operation was performed on the remaining rats. Blood pressure was measured weekly during 7 weeks. Then, blood and cerebrospinal fluid (CSF) samples were obtained. The brain was dissected in several areas. NE and angiotensinogen concentration (AoC) were determined in tissue samples. AoC was evaluated in plasma and CSF; plasma renin activity was also measured. Hypertension development was not prevented by central NE depletion, which was significant in all central areas (p < 0.001). Other significant results showed that renal ischemia and/or NE depletion induced a significant increase in angiotensinogen concentration in the hypothalamus (p < 0.01) and in CSF (p < 0.05). In summary: central NE depletion was not able to modify the development of 2 k - 2 c hypertension. Treatment and renal ischemia induced an increase of central AoC.

Topics: Angiotensinogen; Animals; Blood Pressure; Brain; Hypertension, Renovascular; Male; Norepinephrine; Oxidopamine; Rats; Rats, Wistar; Renin; Renin-Angiotensin System; Sympathectomy, Chemical; Sympathetic Nervous System

To investigate the molecular pathology of two-kidney, one-clip (2K-1C) rats, we examined the gene expressions of the renin-angiotensin system (RAS) and angiotensin II (ANG II) concentration in various tissues in the early (4 wk) and chronic (16 wk) phases of hypertension. Four weeks after clipping, the brain renin mRNA level was lower in 2K-1C rats than in control rats (P < 0.05). On the other hand, the levels of brain and renal angiotensinogen mRNA were not significantly different in the two groups. The brain and adrenal ANG II concentrations were significantly higher in 2K-1C rats than in control rats. Sixteen weeks after clipping, there was no significant difference in the brain renin mRNA levels in the two groups, and renal and brain angiotensinogen mRNA levels were normal. Moreover, the ANG II concentrations in the adrenals and brain (except the cortex) of 2K-1C rats were not significantly higher than those in control rats. These results show a differential pattern of tissue RAS gene expression in rats during the development of 2K-1C hypertension, which is regulated in a tissue-specific manner. Furthermore, the data suggest that brain ANG II may be affected by circulating ANG II, but not by the brain renin angiotensin system, and may regulate brain renin, probably by negative feedback through its own receptor.

Topics: Actins; Angiotensin II; Angiotensinogen; Animals; Blotting, Northern; Brain; Cerebellum; Gene Expression; Hypertension, Renovascular; Hypothalamus; Kidney; Male; Medulla Oblongata; Rats; Rats, Wistar; Renin; Renin-Angiotensin System; RNA, Messenger

To assess the role of the vascular angiotensin II-generating system in one-kidney, one clip hypertension, we determined the angiotensin converting enzyme activity in plasma and vascular tissues and examined the pressor response to angiotensin II, angiotensin I, and tetradecapeptide renin substrate in isolated mesenteric arteries from one-kidney, one clip hypertensive rats 7 and 30 days after clipping the renal artery and in mesenteric arteries from age-matched normotensive rats. Angiotensin converting enzyme activity, determined in aortic and mesenteric tissues, was significantly augmented in the hypertensive (30 days after clipping) group, whereas plasma activity was normal. The vasoconstrictor responses elicited by angiotensin I and tetradecapeptide in arteries from hypertensive rats were found to be significantly potentiated 30 days after clipping, whereas the angiotensin II responses were basically unchanged. Saralasin completely blocked the vasoconstrictor responses, whereas captopril blocked only the responses to angiotensin I without affecting the responses elicited by angiotensin II and tetradecapeptide. Enalapril, an angiotensin converting enzyme inhibitor given intravenously to unanesthetized rats, significantly lowered the blood pressure of hypertensive rats. The pressor responses elicited by angiotensin II, angiotensin I, and tetradecapeptide were completely inhibited by saralasin, whereas enalapril blocked only the responses of angiotensin I but not those elicited by angiotensin II and tetradecapeptide. These results indicate that local formation of angiotensin II is increased in arteries of one-kidney, one clip hypertensive rats. The data obtained with tetradecapeptide renin substrate suggest an important role for nonrenin proteases in vascular angiotensin II formation.

Topics: Angiotensin I; Angiotensin II; Angiotensinogen; Animals; Blood Pressure; Blood Vessels; Captopril; Enalapril; Hypertension, Renovascular; In Vitro Techniques; Male; Mesenteric Arteries; Peptidyl-Dipeptidase A; Rats; Rats, Inbred Strains; Reference Values; Saralasin

To investigate the vascular renin-angiotensin system in two-kidney, one clip (2K1C) hypertension, we measured angiotensinogen messenger RNA (mRNA) in the aorta and aortic and plasma angiotensin II (Ang II) concentration in 2K1C rats during early (4 weeks) and chronic (16 weeks) phases. Four weeks after clipping, there was no significant change in aortic angiotensinogen mRNA in both groups. However, the levels of plasma and aortic Ang II in 2K1C rats were significantly elevated compared with levels in control rats (p less than 0.05). Sixteen weeks after clipping, aortic angiotensinogen mRNA in 2K1C rats did not differ compared with the level in control rats. The aortic Ang II level in 2K1C rats was significantly increased compared with that in control rats (p less than 0.05), whereas there was no significant difference in the plasma Ang II level between the groups during this chronic phase. During both phases, morphological studies in 2K1C rats showed arteriosclerotic changes, with a significant increase in the wall-to-lumen ratio (p less than 0.01). The present study is the first to demonstrate an increase in vascular Ang II levels and concomitant morphological arteriosclerotic changes during both the early and chronic phases in 2K1C rats. Together with the results of our previous study that demonstrated an elevation of vascular renin activity during the early phase and increased vascular angiotensin converting enzyme activity during the chronic phase, we conclude that the elevated vascular renin activity and vascular angiotensin converting enzyme activity during each phase may play a dominant role in the increase in vascular Ang II observed during both phases.

Topics: Angiotensin I; Angiotensin II; Angiotensinogen; Animals; Aorta, Abdominal; Hypertension, Renovascular; Hypertrophy; Male; Rats; Rats, Inbred Strains; Renin-Angiotensin System; RNA, Messenger; Veins

To examine and characterize the vascular renin--angiotensin system in low-renin models of renal hypertension with and without the presence of overt renal insufficiency, we studied the formation and metabolism of angiotensin in isolated perfused rat hindquarter preparations. Rats with 5/6 nephrectomy (5/6NX) and rats with one-kidney, one clip (1K1C) hypertension were compared to sham operated (sham) animals. Angiotensin peptides in plasma or perfusate were characterized by high-performance liquid chromatography and radioimmunoassay (RIA). Plasma angiotensin II was lower, and blood pressure was higher in both experimental groups, compared to sham animals. Plasma angiotensinogen, measured by both direct and indirect RIA, was increased in both experimental groups. The spontaneous release of angiotensin I and angiotensin II from perfused hindquarters did not differ between the groups. Angiotensin I conversion was not different in 5/6NX or 1K1C groups compared with controls. Furthermore, angiotensin conversion was completely inhibited by captopril (1 mumol/l) in all groups. Renin-induced angiotensin release was significantly increased in 5/6NX as compared with sham rats, whereas there was no difference in renin-induced angiotensin release between 1K1C and sham animals. Angiotensin II degradation was significantly attenuated in 5/6NX rats when compared with sham rats (27.6% versus 53.9%, respectively, P less than 0.05) but was unaltered in 1K1C rats. Thus, in chronic uremic hypertension, renin-induced angiotensin formation was increased in the face of decreased angiotensin II degradation. These data suggest that vascular angiotensin may contribute to the elevated blood pressure observed in chronic renal failure. In 1K1C rats, vascular angiotensin formation and metabolism was unchanged despite suppressed plasma angiotensin II.

Topics: Angiotensin II; Angiotensinogen; Animals; Blood Vessels; Chromatography, High Pressure Liquid; Hindlimb; Hypertension, Renal; Hypertension, Renovascular; Male; Radioimmunoassay; Rats; Rats, Inbred Strains; Renin; Renin-Angiotensin System; Uremia

To investigate the molecular mechanism of sustained hypertension in two-kidney, one clip (2K1C) hypertensive rats, possible changes in renin gene expression in the kidney and angiotensinogen in the liver were studied. In 2K1C rats 4 weeks after clipping, the plasma renin and angiotensin II levels were significantly higher than those in sham-operated rats, but the plasma angiotensinogen levels were similar in the two groups. At this time, expression of the renin gene in the ischaemic kidney of 2K1C rats was 2.6-times that in sham-operated rats (P less than 0.05), but expressions of the angiotensinogen gene were similar in the two groups. Sixteen weeks after clipping, the plasma renin and angiotensin II levels in 2K1C rats were not significantly higher than those in sham-operated controls, but expression of the renin gene in the kidney was still 2.2-times higher in 2K1C rats than in controls (P less than 0.05). The plasma angiotensinogen level was significantly higher in 2K1C rats than in controls (P less than 0.05), and expression of the angiotensinogen gene in the liver was 2.9-times higher in 2K1C rats than in controls (P less than 0.01). These results indicate that the roles of the renin-angiotensin system in maintenance of hypertension in 2K1C rats differ in the acute and chronic phases: in the acute phase, over-expression of the renal renin gene coupled to increased renin secretion plays the major role in elevating the blood pressure; in the chronic phase, a counter-regulatory mechanism may affect the post-transcriptional fate of renin.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensinogen; Animals; Blotting, Northern; Gene Expression; Hypertension, Renovascular; Kidney; Liver; Male; Rats; Rats, Inbred Strains; Renin; Renin-Angiotensin System; RNA, Messenger

The participation of the central serotonergic system in the development of two-kidney, two clip (2K2C) Goldblatt renovascular hypertension in the rat has been examined. Half of the rats were treated with desmethylimipramine intraperitoneally and 5,7-dihydroxytryptamine intracisternally; the other half received only desmethylimipramine and the 5,7-dihydroxytryptamine vehicle. Two days later, a silver clip was placed in both renal arteries in half of the rats of each group. A sham operation was performed in the remaining rats. Blood pressure was recorded during the 5 weeks after treatment. At the end of the experiment, blood and cerebrospinal fluid samples were obtained. The brain was dissected into several areas and kept frozen. Norepinephrine, serotonin, angiotensinogen, and renin-like concentration were evaluated in the brain areas. Plasma renin activity and angiotensinogen concentration in the plasma and cerebrospinal fluid were estimated. In the sham-operated groups, blood pressure was lower in the treated than in the control rats. The curve of blood pressure increase, as well as the final blood pressure, was similar in the treated and control 2K2C rats. Serotonin was significantly depleted by the 5,7-dihydroxytryptamine treatment in all brain areas. Treatment did not induce any changes in central norepinephrine concentration. Plasma renin activity was diminished in the treated sham-operated rats. These data indicate that the central serotonin depletion does not prevent the development of hypertension and confirm the role of the amine in normal blood pressure regulation. On the other hand, the peripheral renin-angiotensin system might participate in the development of high blood pressure in serotonin-depleted animals.

Topics: 5,7-Dihydroxytryptamine; Angiotensinogen; Animals; Blood Pressure; Brain; Desipramine; Hypertension, Renovascular; Male; Norepinephrine; Osmolar Concentration; Rats; Rats, Inbred Strains; Renin; Serotonin

The effect of ketanserin (Kt) has been analyzed during the development of two-kidney-two-clip (2k-2c) renovascular hypertension in the rat. Male Wistar rats were divided into four experimental groups: (1) clip Kt (ClKt) (n = 12)--A silver clip (0.25 mm width) was placed in each renal artery 3 days after beginning the administration of Kt (10 mg/kg/day) in the drinking water; (2) sham Kt (ShKt) (n = 13)--Similar to group 1, but the clips were placed in, and immediately removed from, the renal arteries; (3) untreated clip (UCl) (n = 10)--Similar to group 1, but the rats drank water; (4) untreated sham (USh) (n = 10)--Similar to group 2, but the rats drank water. Blood pressure (BP) was measured before surgery and was followed weekly for 7 weeks. At the end of this period, blood and cerebrospinal fluid (CSF) samples were obtained in all the animals. Plasma renin activity (PRA) and plasma and CSF angiotensinogen concentration (AoC) were evaluated. The results have shown that Kt partially inhibited the increase in BP induced by bilateral renal ischemia (BP: UCl rats 180.5 +/- 12.4 versus ClKt rats 149.8 +/- 5.1 mm Hg; p less than 0.01; USh rats 116.7 +/- 3.7; ShKt rats 114.4 +/- 5.0 mm Hg). PRA was similar in hypertensive and control rats whether or not they had received Kt. AoC in plasma was decreased in clipped treated and untreated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensinogen; Animals; Blood Pressure; Hypertension, Renovascular; Ketanserin; Male; Rats; Rats, Inbred Strains; Renin-Angiotensin System