Positive chronotropic and inotropic effects of angiotensin II in the dog heart.

The effects of angiotensin II on sinus rate and atrial contractility were investigated in 17 isolated canine atria and 5 isolated paced ventricular preparations perfused with arterial blood conducted from a heparinized donor dog. When angiotensin II was injected into the cannulated sinus node artery, positive chronotropic responses were dose-dependently produced starting from the 0.01 microgram dose although inotropic responses to angiotensin II were not consistently induced. Angiotensin II produced a similar inotropic response pattern in the paced ventricular preparation. Moreover, when angiotensin II was given into the jugular vein of the donor dog, similar positive chronotropic and inotropic responses were also shown in the isolated atrium. Angiotensin II-induced positive chronotropic and slight inotropic effects were not influenced by treatment with the beta-adrenoceptor blocking agents, propranolol and carteolol, but significantly suppressed by saralasin which has been reported to be a competitive antagonist of angiotensin II. From these results, it is suggested that angiotensin II induced a positive chronotropic and slight positive inotropic effect via angiotensin II receptors in the dog heart.