Comparative effects of nifedipine and diltiazem on vascular responses to norepinephrine and angiotensin II.

The effects of nifedipine and diltiazem on renal vascular responses to norepinephrine and angiotensin II were investigated in the isolated blood-free perfused rat kidney. The vasoconstrictor response induced by bolus injections of angiotensin II (5 and 10 ng) and norepinephrine (60, 80 and 100 ng) were assessed before and during perfusion of nifedipine (10(-9) mol l-1 to 10(-6) mol l-1) or diltiazem (3 X 10(-7) mol l-1 to 10(-4) mol l-1). At a concentration higher than 10(-9) mol l-1, nifedipine blunted to a similar extent the responses to both angiotensin II and norepinephrine. At concentrations of 3 X 10(-7) mol l-1 and 10(-6) mol l-1, diltiazem inhibited only the response to angiotensin II without affecting the vasoconstrictor effect of norepinephrine. Increase in diltiazem concentration to 10(-5) mol l-1 and 10(-4) mol l-1 was associated with a similar inhibition of the response to angiotensin II and norepinephrine. These results demonstrate that at concentration less than 10(-5) mol l-1, diltiazem acts as a selective antagonist of the effect of angiotensin II whilst no such selectivity of action was observed with all concentrations of nifedipine used in the present studies.