ALPHA-ADRENOCEPTORS IN ISCHEMIC CANINE HEART BLOCKED BY PHENTOLAMINE

Publisher Summary In the mammalian heart, both alpha and beta adrenoceptors exist; both of these adrenoceptors elicit an increase of ventricular contractility, whereas beta adrenoceptors dilate and alpha constrict the coronary blood vessels. Under ordinary circumstances, the prevalent effect of adrenoceptor stimulation reflects beta stimulation. The experimental demonstration of the existence of alpha adrenoceptors in the mammalian myocardium and coronary bed has been made chiefly on animal preparations that had their beta receptors blocked with propranolol or other similar drugs. This chapter is a report of another way of demonstrating alpha adrenoceptor activity without employing beta blocking agents. The authors of the chapter have used myocardial ischemia for altering the adrenoceptor quality in a circumscribed venticular region of the in situ canine heart. The nature of the effects has been shown to be altered by changes in myocardial metabolism. An increase in metabolism caused a predominance of beta receptors and a decrease in predominance of alpha receptors in the myocardium and in the coronary blood vessels.