[Effect of isoproterenol on regional myocardial oxygen balance in dog hearts with coronary stenosis].

Effects of intravenous and intracoronary isoproterenol on oxygen balance in the regional myocardium as well as on coronary hemodynamics were investigated in eight dogs with coronary stenosis under droperidol-fentanyl anesthesia. From these observations, the effect of an increase in myocardial contractility per se on regional myocardial oxygen balance was deduced. After intravenous isoproterenol of 0.5 microgram.kg-1, oxygen tension at the regional subendocardium decreased (23.7--15.4 mmHg) although transmural blood flow increased (26.0--41.4 ml.min-1). Function of the whole heart improved; heart rate increased (85--161 beats.min-1); and aortic blood pressure decreased (94--60 mmHg). After intracoronary isoproterenol of 0.005 microgram.kg-1, oxygen tension at the regional subendocardium slightly but significantly increased (22.8--25.4 mmHg). Although transmural blood flow (27.6--36.6 ml.min-1) and cardiac function improved, heart rate (83--93 beats.min-1) and aortic blood pressure (106--104 mmHg) remained at the pre-isoproterenol level. The results suggest that oxygen balance at the regional subendocardium is deteriorated through tachycardia and hypotension and a vasodilatory effect is seen largely at the subepicardium after isoproterenol to the heart with coronary stenosis, and that an increase in myocardial contractility per se does not deteriorate the oxygenation at the subendocardium.