Chronotropic and Inotropic Effects of Bradykinin on Isolated, Blood-perfused Canine Atrium

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Abstract
Effects of bradykinin on SA [sinoatrial] node pacemaker activity and atrial contractility were studied using isolated, blood-perfused dog atrium preparations. Bradykinin (0.1-100 .mu.g) caused a slightly but consistently positive chronotropic action, but did not produce a consistent inotropic action. When successive doses of bradykinin were given in a short period, the preparations displayed tachyphylaxis. Bradykinin-induced action was not suppressed by a potent .beta.-adrenoceptor blocking agent, carteolol. Kallikrein (0.1-3 units), was administered into the sinus node artery to investigate the effect of endogenous kinins. Kallikrein had no effect on SA node pacemaker activity nor atrial contractility at any examined doses. A kallikrein inhibitor, aprotinin, induced dose-relatedly a negative inotropic and chronotropic effect at a dose range from 100-3000 units. The negative actions of aprotinin were not blocked by an adequate dose of atropine. Apparently, bradykinin has a slight direct positive chronotropic effect, and aprotinin has direct negative inotropic and chronotropic effects in the isolated, blood-perfused canine atrium in a wide dose range.