Dissociation of vascular and adrenal responsiveness to angiotensin ii following calcium channel blockade

Abstract

Calcium channel blockers as a class reduce both vascular resistance and systemic blood pressure. However, it is not known if different classes of calcium channel blockers have similar effects on the renin-angiotensin-aldosterone system. We investigated vascular and adrenal responses to endogenous and exogenous angiotensin II in normotensive subjects before and after receiving isradipine or diltiazem. Subjects achieved low salt balance before study and underwent an angiotensin II infusion and upright posture study. After re-achieving salt balance the subjects received either isradipine (n=10), or diltiazem (n=7) for three days before repeating the study. Both agents lowered blood pressure and significantly shifted the dose response relationship of angiotensin II and mean blood pressure (P<0.01). In contrast, aldosterone secretion in response to upright posture and angiotensin II infusion was significantly reduced (P<0.01) by isradipine but not by diltiazem. The in vitro effects of both agents on aldosterone secretion from bovine adrenal glomerulosa cells paralleled the in vivo observations showing that angiotensin II-stimulated aldosterone secretion was markedly blunted by isradipine and minimally by diltiazem. These results suggest a tissue specificity for the effects of different classes of calcium channel blockers. Dihydropyridine calcium channel blockers may exert their antihypertensive effect by blocking both vascular and adrenal responses to angiotensin.