Inhibition by bradykinin of the vascular action of angiotensin II in the dog kidney.

In the dog anesthetized with pentobarbital, the effect of bradykinin on the lowering of renal blood flow produced by bolus injections of angiotensin II was studied. Injection into the renal artery of angiotensin II (0.06--0.50 microgram) caused vasoconstriction and decreased blood flow to the kidney in a dose-related manner. Renal arterial infusion of bradykinin (10 ng kg-1 min-1), prostaglandin (PG) E2 (4 ng kg-1 min-1) or PGI2 (4 ng kg-1 min-1) produced renal vasodilation and inhibited the vasoconstrictor effect of angiotensin II. However, renal arterial infusion of another vasodilatory peptide, substance P (2 ng kg-1 min-1), did not alter the effect of angiotensin II on the renal vasculature. Pretreatment of dogs with an inhibitor of PG synthesis, sodium meclofenamate (5 mg/kg), abolished the inhibitory effect of bradykinin on angiotensin II-induced renal vasoconstriction. In contrast, renal arterial infusion of either PGE2 or PGI2 was equally effective in reducing the renal vascular effect of angiotensin II in animals with and without meclofenamate pretreatment. These results suggest that bradykinin reduces the reactivity of the renal vasculature to angiotensin II by a mechanism dependent upon PG synthesis.