DISSOCIATION OF VASCULAR AND ADRENAL RESPONSIVENESS TO ANGIOTENSIN-IIFOLLOWING CALCIUM-CHANNEL BLOCKADE

Calcium channel blockers as a class reduce both vascular resistance an d systemic blood pressure. However, it is not known if different class es of calcium channel blockers have similar effects on the renin-angio tensin-aldosterone system. We investigated vascular and adrenal respon ses to endogenous and exogenous angiotensin II in normotensive subject s before and after receiving isradipine or diltiazem. Subjects achieve d low salt balance before study and underwent an angiotensin II infusi on and upright posture study. After re-achieving salt balance the subj ects received either isradipine (n=10), or diltiazem (n=7) for three d ays before repeating the study. Both agents lowered blood pressure and significantly shifted the dose response relationship of angiotensin I I and mean blood pressure (P<0.01). In contrast, aldosterone secretion in response to upright posture and angiotensin II infusion was signif icantly reduced (P<0.01) by isradipine but not by diltiazem. The in vi tro effects of both agents on aldosterone secretion from bovine adrena l glomerulosa cells paralleled the in vivo observations showing that a ngiotensin 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 b lockers. Dihydropyridine calcium channel blockers may exert their anti hypertensive effect by blocking both vascular and adrenal responses to angiotensin II.