Angiotensin II (Ang II) is a potent vasopressor peptide that interacts with 2 major receptor isoforms -AT1 and AT2. Although blood pressure is increased in AT2 knockout mice, the underlying mechanisms remain undefined because of the low levels of expression of AT2 in the vasculature. Here we overexpressed AT2 in vascular smooth muscle (VSM) cells in transgenic (TG) mice. Aortic AT1 was not affected by overexpression of AT2. Chronic infusion of Ang II into AT2-TG mice completely abolished the AT1-mediated pressor effect, which was blocked by inhibitors of bradykinin type 2 receptor (icatibant) and nitric oxide (NO) synthase (L-NAME). Aortic explants from TG mice showed greatly increased cGMP production and diminished Ang II-induced vascular constriction. Removal of endothelium or treatment with icatibant and L-NAME abolished these AT2-mediated effects. AT2 blocked the amiloride-sensitive Na + /H + exchanger, promoting intracellular acidosis in VSM cells and activating kininogenases. The resulting enhancement of aortic kinin formation in TG mice was not affected by removal of endothelium. Our results suggest that AT2 in aortic VSM cells stimulates the production of bradykinin, which stimulates the NO/cGMP system in a paracrine manner to promote vasodilation. Selective stimulation of AT2 in the presence of AT1 antagonists is predicted to have a beneficial clinical effect in controlling blood pressure.

In situ hybridization studies have suggested that the subtype 2 angiotensin (AT2) receptor gene is expressed in fetal and newborn rat kidney but is undetectable in the adult animals. In the present study, we investigated the expression of AT2 receptor protein in the fetal (days 14 and 19 of fetal life), newborn (day 1 postpartum), and adult (4-week-old and 3-month-old) rat kidney. Polyclonal anti-peptide antiserum was raised against the amino terminus of the native AT2 receptor. The selectivity of the antiserum was validated by recognition of the AT2 receptor in a stably transfected COS-7 cell line by Western blot and immunocytochemical analysis. As a positive control, the AT2 receptor signal was detected strongly in the adrenal gland. Positive immunohistochemical staining was observed in the mesenchymal cells and ureteric buds of the 14-day fetal kidney and in the glomeruli, tubules, and vessels in the 19-day fetal and newborn kidney. Glomeruli expressing the AT2 receptor were localized mainly in the outer layer of the renal cortex. In the young (4-week-old) and mature (3-month-old) adult rat on normal sodium intake, renal AT2 receptor immunoreactivity was present in glomeruli but substantially diminished compared with that of newborn rats. In both young and mature adult rats, dietary sodium depletion increased the renal AT2 receptor signal, mainly in the glomeruli and interstitial cells. Preimmune and preadsorption controls were negative. Western blot analysis detected a single 44-kD band in the fetal and newborn rat kidney and in the young and mature adult rat kidney. Dietary sodium depletion increased the density of the AT2 receptor band in mature adult rat kidneys. These data provide evidence that the AT2 receptor protein is expressed in the fetal and newborn rat kidney, diminishes in adult life, and is reexpressed in the adult in response to sodium depletion.

Abstract-We have previously demonstrated that stimulation of the angiotensin (Ang) II type 2 receptor in vascular smooth muscle cells caused bradykinin production by activating kininogenase in transgenic mice. The aim of this study was to determine whether overexpression of AT 2 receptors in cardiomyocytes attenuates Ang II-induced cardiomyocyte hypertrophy or interstitial fibrosis through a kinin/nitric oxide (NO)-dependent mechanism in mice. Ang II (1.4 mg/kg per day) or vehicle was subcutaneously infused into transgenic mice and wild-type mice for 14 days. The amount of cardiac AT 2 receptor relative to AT 1 receptor in transgenic mice was 22% to 37%. Ang II caused similar elevations in systolic blood pressure (by Ϸ45 mm Hg) in transgenic mice and wild-type mice. Myocyte hypertrophy assessed by an increase in myocyte cross-sectional area, left ventricular mass, and atrial natriuretic peptide mRNA levels were similar in transgenic and wild-type mice. Ang II induced prominent perivascular fibrosis of the intramuscular coronary arteries, the extent of which was significantly less in transgenic mice than in wild-type mice. Inhibition of perivascular fibrosis in transgenic mice was abolished by cotreatment with HOE140, a bradykinin B 2 receptor antagonist, or L-NAME, an inhibitor of NO synthase. Cardiac kininogenase activity was markedly increased (Ϸ2.6-fold, PϽ0.001) after Ang II infusion in transgenic mice but not in wild-type mice. Immunohistochemistry indicated that both bradykinin B 2 receptors and endothelial NO synthase were expressed in the vascular endothelium, whereas only B 2 receptors were present in fibroblasts. These results suggest that stimulation of AT 2 receptors present in cardiomyocytes attenuates perivascular fibrosis by a kinin/NO-dependent mechanism. However, the effect on the development of cardiomyocyte hypertrophy was not detected in this experimental setting. Key Words: receptors, angiotensin II Ⅲ kinins Ⅲ mice Ⅲ fibrosis Ⅲ hypertrophy A ngiotensin (Ang) II is an important humoral factor responsible for cardiomyocyte hypertrophy as well as interstitial hyperplasia. 1 Both of the major Ang II receptor subtypes, AT 1 and AT 2 , are expressed in the heart. 2 The AT 2 receptor (AT 2 R) has been implicated in suppression of myocardial hypertrophy, 3-5 fibroblast proliferation, 6,7 and vascular cell hyperplasia. 8,9 However, little is known about the mechanisms by which this receptor subtype exerts such antigrowth effects and the role of the cardiac AT 2 R in cardiac diseases in vivo. Previous studies have suggested possible involvement of the bradykinin/nitric oxide (NO)/cGMP system in AT 2 R-mediated physiological functions in the rat aorta, 10 canine coronary artery, 11 a rat model of heart failure caused by myocardial infarction, 12,13 hypertrophied rat heart caused by aortic coarctation, 4 and in the kidney. 14 We have recently demonstrated that AT 2 R overexpression in vascular smooth muscle cells activates the vascular kinin system and causes vasodilation in transgenic mice. 15 However,...

Chronic infection with HP may be involved in the development of the atherosclerosis via endothelial dysfunction and systemic and vascular inflammation.