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Background: In vitro studies suggest that angiotensin II type 1 and type 2 (AT1 and AT2) receptors exert opposite effects in terms of vasoconstriction, natriuresis, and cell growth, but the role of these receptors in cardiovascular remodeling in vivo is still an enigma. In this study, we tested the hypothesis that AT2 exerts an antiproliferative effect by inducing apoptosis, thereby antagonizing AT1a in vascular remodeling., Methods and Results: Vascular injury was induced by polyethylene cuff placement around the left femoral artery of AT1a-null (AT1aKO), AT2-null (AT2KO), and wild-type mice. Neointimal formation as well as DNA synthesis in vascular smooth muscle cells (VSMC) after vascular injury was exaggerated in AT2KO mice, but they were both suppressed in AT1aKO mice compared with those in wild-type mice. In contrast, the number of apoptotic cells in the injured artery in VSMC was significantly increased in AT1aKO mice but decreased in AT2KO mice. Reverse transcriptase-polymerase chain reaction analysis revealed that the expression of bax mRNA was attenuated in AT2KO mice. On the other hand, the expression of bcl-2 and bcl-x(L) mRNA was enhanced in AT2KO mice but attenuated in AT1aKO mice. Immunohistochemical staining with antibody to the bcl-2 protein family supported these results., Conclusions: Our results suggest that AT2 exerts antiproliferative effects and proapoptotic changes in VSMC by counteracting AT1a in the process of neointimal formation after vascular injury.

Objective: Angiotensin-converting enzyme (ACE) inhibitors and beta-blockers improve prognosis inpatients with chronic heart failure. Some patients, however, show little response to combined treatment with an ACE inhibitor and a beta-blocker. In addition, the ACE inhibitor cannot completely suppress angiotensin II production. Our objective was to examine whether replacing the ACE inhibitor with an angiotensin II antagonist can improve the condition of patients with chronic heart failure., Methods: In 11 patients with chronic heart failure treated with an ACE inhibitor and a beta-blocker, who have had severe left ventricular dysfunction or high plasma level of natriuretic peptides, left ventricular dimension, and fractional shortening, plasma atrial and brain natriuretic peptide (ANP and BNP) levels were determined before and 3 months after the change of treatment., Results: After substituting the ACE inhibitor with an angiotensin II antagonist, patients showed New York Heart Association functional class improvement, and significant decrease in left ventricular dimension and BNP., Conclusion: In patients with severe chronic heart failure treated with an ACE inhibitor and a beta-blocker, replacing the ACE inhibitor with an angiotensin II antagonist may be effective. However, this has to be confirmed by an adequately powered randomized controlled study.

This study was designed to clarify whether gene expression in the cardiac sarcoplasmic reticulum [sarcoplasmic reticulum Ca2+-ATPase (SERCA), phospholamban, ryanodine receptor and calsequestrin] changes in accordance with left ventricular functional alterations in the volume-overloaded heart. Further, the effect of the angiotensin II type 1 receptor antagonist, TCV-116, on the expression of these genes was also evaluated. Left ventricular fractional shortening was significantly increased at 7 days, had returned to control levels at 21 days, and had significantly decreased at 35 days after the shunt operation, compared with sham-operated rats. The level of SERCA mRNA was significantly decreased at both 21 days and 35 days after the shunt operation. The levels of ryanodine receptor and phospholamban mRNAs were significantly decreased at 35 days in shunt-operated rats. The decrease in the SERCA mRNA level preceded the development of cardiac dysfunction. The levels of SERCA and ryanodine receptor mRNAs were correlated positively with left ventricular fractional shortening (r=0.73, P<0.0001 and r=0.61, P<0.01 respectively). Attenuation of the decrease in left ventricular fractional shortening occurred on treatment with TCV-116. After the treatment with TCV-116, the levels of SERCA and phospholamban mRNAs were restored to the respective values in sham-operated rats. Ryanodine receptor mRNA levels remained unchanged after treatment with TCV-116. These results indicate that the down-regulation of SERCA and ryanodine receptor mRNA levels may be related to cardiac dysfunction in the volume-overloaded heart. In addition, treatment with an angiotensin II receptor antagonist may restore the altered sarcoplasmic reticulum mRNA levels to control levels, and this may result in attenuation of the functional impairment in the volume-overloaded heart.

The effects of blockade of the renin-angiotensin system at three different sites on regression of left ventricular hypertrophy (LVH) were investigated in spontaneously hypertensive rats (SHRs). Angiotensin-converting-enzyme (ACE) inhibitor, angiotensin II type 1 (AT1) receptor antagonist, renin inhibitor, or the combination of hydralazine and hydrochlorothiazide was administered for 7 days to SHRs to obtain the same decrease in blood pressure. Treatment with ACE inhibitor, AT1 receptor antagonist, or renin inhibitor significantly decreased left ventricular mass. On the other hand, hydralazine administration failed to diminish LVH in SHRs. These findings indicate that blockade of the renin-angiotensin system regressed LVH irrespective of the site of the blockade and independent of hemodynamic changes.

A simplified and sensitive method for measuring expression levels of type-1 angiotensin II (AT1) receptor subtypes, AT1A and AT1B, was established. The two receptor cDNAs were co-amplified and measured by polymerase chain reaction using primers based on the corresponding receptor subtype genes. Both AT1A and AT1B mRNAs were widely expressed in the rat tissues including adrenal gland, kidney, heart, aorta, lung, liver, testis, pituitary gland, cerebrum and cerebellum. AT1A mRNA was predominantly expressed in the rat tissues examined except adrenal gland and pituitary gland where AT1B mRNA was predominantly expressed. Sodium depletion did not change mRNA levels of AT1A and AT1B in the all tissues. However, both AT1A and AT1B mRNA levels in the heart and aorta were down-regulated by treatment with AT1 specific antagonist, TCV 116. In contrast, AT1B mRNA in the adrenal gland was mainly reduced by the treatment. These results suggest that the expression level of AT1B mRNA in the adrenal gland depends on the activity of the renin-angiotensin-aldosterone system (RAAS) and both receptor subtypes mediate contraction and hypertrophy of the smooth and cardiac muscles via the RAAS.

The effects of angiotensin II, thyroxine and 17 beta estradiol on plasma renin substrate concentration in rats and renin substrate production by perfused rat livers were investigated. The addition of angiotensin II (1-10 microgram) to the perfusion system did not affect the synthesis of renin substrate. After treatment with thyroxine (2.5 mg/kg/day), plasma renin substrate concentration, plasma renin activity, plasma aldosterone concentration and the rate of renin substrate synthesis were all significantly increased. 17 beta estradiol (2 mg) raised both plasma renin substrate concentration and the amount of renin substrate production by the liver. Isoelectric focusing profiles of renin substrate of liver perfusate and of plasma from estrogen-treated rats were different from that of liver perfusate from normal rats. But the profile of renin substrate in plasma was essentially similar to those to liver perfusates both in normal and estrogen-treated rats.

We studied the effects of intracerebroventricular administration of angiotensin II (ANG II), bradykinin (BK), leucine-enkephalin (Leu-ENK) and neurotensin (NT) on plasma renin activity (PRA), blood pressure and heart rate in conscious and unrestrained rats. Five microliters of each peptide solution was injected into the lateral cerebral ventricle. These four peptides all produced pressor effects after intracerebroventricular injection. ANG II and NT significantly suppressed PRA, BK did not affect PRA, and Leu-ENK significantly increased PRA. The central peptidergic stimulation caused by these four peptides increased blood pressures in conscious rats but showed different effects on PRA.

We studied the effects of intracerebroventricular (ICV) administration of angiotensin II (ANG II), bradykinin (BK), leucine-enkephalin (Leu-ENK) and neurotensin (NT) on plasma renin activity (PRA), blood pressure and heart rate in acute (less than 4 weeks) and chronic (more than 12 weeks) two-kidney, one clip (2K-1C) hypertensive rats. These four peptides all produced pressor responses. The pressor responses caused by ICV injection of ANG II, BK, Leu-ENK and NT in hypertensive rats did not differ significantly from the response in normal rats. In both acute and chronic 2K-1C hypertensive rats, ANG II and BK significantly suppressed PRA, NT did not affect PRA, and Leu-ENK produced a significant increase in PRA followed by a significant decrease in PRA. As compared to normal rats, suppression of PRA by ANG II and NT was attenuated or abolished but BK and Leu-ENK produced significant reductions in PRA in 2K-1C hypertensive rats. The results indicate that the effects of these four centrally administered peptides on blood pressure, heart rate and PRA in acute and chronic 2K-1C hypertensive rats were not essentially different from those in normal rats.

Effects of unilateral nephrectomy on plasma renin concentration and renin substrate (angiotensinogen) concentration were studied over an experimental period of 10 days in rats. The maximum increase in plasma renin substrate concentration after bilateral nephrectomy was 9 times higher than the preoperative level. Very low but measureable plasma renin concentrations were found in rats nephrectomized bilaterally 24 hrs previously. In unilateral nephrectomized rats the concentration of renin substrate in plasma increased maximumly 3.5-fold within 24 hrs after the operation and on the third day it was decreased to half of the maximum level. Even 10 days after uninephrectomy the concentration of plasma renin substrate was significantly higher than that of normal rats. Twenty four hours after unilateral nephrectomy plasma renin concentration decreased to similar low levels as those found in bilateral nephrectomized rats. The decreased concentration of plasma renin, however, returned to normal 3 days after uninephrectomy. The inverse relationship was seen between the concentrations of plasma renin and plasma renin substrate. However, substrate concentration in plasma rised faster and longer than plasma renin decreased.

Human plasma renin substrate was purified and separated from renin by a concanavalin A-Sepharose affinity column. Human renin substrate as well as renin were bound to concanavalin A. Renin substrate was eluted with 0.1 M D-glucose in 20 mM Tris/HCl buffer, pH 8.0. The specific activity increased from 38.5 to 653 ng of angiotensin-I equivalents per mg of protein (17-fold) and the recovery was 85%. Renin was eluted completely with 0.2 M alpha-D-methylglucoside and 0.2 M alpha-D-methylmannoside.

The effects of three experimental conditions on the concentration of plasma renin substrate were studied with special reference to plasma renin concentration in unilaterally nephrectomized rats. After simultaneous bilateral nephrectomy the maximum increase in plasma renin substrate was 17 times higher than normal within 24 h, while in rats which were unilaterally nephrectomized 10 days previously, followed by the removal of the remaining kidney (two-step bilateral nephrectomy), the maximum increase in plasma renin substrate was markedly suppressed (6-fold of normal). The maximum increases in plasma renin substrate by estradiol treatment in normal and unilaterally nephrectomized rats were about the same, associated with similarly decreased plasma renin concentrations. The similar increase in plasma renin substrate was found after ureteral ligation in unilaterally nephrectomized rats and bilateral ligation of the ureters in normal rats. This was the case where the plasma renin concentrations changed differently after ureteral ligation. After two-step bilateral nephrectomy plus estradiol treatment the maximum increase in plasma renin substrate was found to be higher than that found after two-step bilateral nephrectomy, but was lower than that after simultaneous bilateral nephrectomy. It is suggested that under the pathological conditions that stimulate renin substrate production, the plasma rein substrate concentration is less affected by circulating renin.

Atrial fibrillation (AF) occurs in about 20% of patients with hypertrophic cardiomyopathy (HCM). HCM patients with AF have an increased risk for clinical decline and thromboembolism. In addition, AF is known to be associated with the atrial renin-angiotensin system (RAS). However, the relation between AF and the RAS in HCM has not been investigated. We genotyped the insertion/deletion (I/D) polymorphism of the angiotensin-converting enzyme (ACE) gene in 138 HCM patients (26 with AF, 112 with sinus rhythm). Distribution of the ACE genotypes (DD, ID, and II) among the total HCM patients was 15%, 46%, and 38%. AF was documented in 3 patients with the DD genotype, 7 with the ID genotype, and 16 with the II genotype (P < 0.03 vs. sinus rhythm group). The odds of AF were 3.2-fold greater in patients with the II genotype than in those with the other genotypes (P = 0.009, 95% confidence interval = 1.3–7.8). Kaplan-Meier curves examining the time to the first documented AF event showed a significant difference between genotypes during the follow-up period (mean 116 months, P < 0.05). These findings suggest that the II genotype of the ACE gene is a significant risk factor for AF in patients with HCM. [ABSTRACT FROM AUTHOR]