Effects of continuous administration of angiotensin II on ventricular performance.

The effects of angiotensin II on circulatory dynamics and coronary blood flow were studied in the cat. With equal single doses of angiotensin II and norepinephrine a greater blood pressure response occurred with angiotensin. With continuous administration of angiotensin II a large initial blood pressure response occurred, but rapidly returned to an intermediate value. During this time the animal was refractory to further single doses. A sustained large increase of ventricular contractility was readily demonstrated with the continuous administration of norepinephrine, but could not be demonstrated with equal amounts of angiotensin II. Acute transient changes of ventricular contractility were observed. Frequently an acute increase of both stroke work at a given filling pressure, and mean rate of ejection occurred. Occasionally, however, marked acute myocardial depression, which rapidly returned to control values, was observed. In about one-third of the preparations prolonged myocardial depression was observed following a period of continuous angiotensin II infusion. This was in sharp contrast to continuous norepinephrine infusion following which myocardial depression was never observed. Measurements of coronary blood flow indicated that when ventricular work was maintained constant, continuous angiotensin II infusion was frequently associated with a transient reduction of coronary flow. This was usually small, but occasionally marked. During this phase concomitant myocardial depression was evident. Continuous norepinephrine infusion produced only an increase of coronary blood flow with an associated increase of myocardial contractility.