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Hypertension and Atherosclerosis Section, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118
Bradykinin has vasodilatory and tissue-protective effects exerted via its B2 type receptor, whereas the B1 receptor is constitutively absent but inducible by inflammation and toxins. In previous studies, we found that B2 receptor gene knockout mice exhibit overexpression of the B1 receptor, which assumes a vasodilatory function and is further upgraded in renovascular hypertension. The present study was designed to explore the effects of excess angiotensin II (ANG II) on B1 receptor and B2 receptor gene expression in mouse cardiomyocytes and rat vascular smooth muscle cells (VSMC) in vivo (after a 3-day infusion of 30 ng/min ANG II in 11 wild-type and in 13 genetically engineered mice with deleted B2 receptor gene) and in vitro (ANG II added in rat VSMC culture in the presence or absence of AT1 or AT2 receptor antagonist). Expression of B1 and B2 receptor mRNA was assessed by reverse transcriptase-polymerase chain reaction. ANG II infusion caused upregulation by 30% of the already significantly overexpressed B1 receptors in cardiomyocytes of the B2 receptor gene knockout mice, but in the wild-type mice it upregulated only the B2 receptor mRNA by 47%. The addition of ANG II in VSMC culture produced a time-dependent induction of B1 and upregulation of B2 receptor gene expression, maximal at 3 h (by fivefold), declining almost to baseline by 24 h. The addition of losartan completely blocked this effect, whereas the AT2 blocker PD-123319 made no difference, indicating that this is an AT1-mediated effect of ANG II. The data indicate that excess ANG II in subpressor doses in vivo upregulates expression of the B2 receptor, but in its absence, the already overexpressed B1 receptor is further upregulated, evidently assuming a counterregulatory response; in vitro, it transiently upregulates both bradykinin receptors.
angiotensin infusion; B2 gene knockout mice; cell culture
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