BLOCKADE OF THE POSITIVE INOTROPIC ACTIONS OF EPINEPHRINE AND THEOPHYLLINE BY ACETYLCHOLINE

¹ Department of Pharmacology, Marquette University, School of Medicine, Milwaukee, Wisconsin

Acetylcholine effectively blocked the positive inotropic action of epinephrine without altering the response to calcium in electrically stimulated isolated perfused turtle and rabbit ventricles. This blocking action of acetylcholine was readily antagonized by atropine. Acetylcholine also blocked the positive inotropic response to theophylline in the turtle ventricle. This action of acetylcholine was also inhibited by atropine. Our results indirectly support the hypothesis of Sutherland et at. (1965), that the positive inotropic response to epinephrine is triggered by an increase in the intracellular concentration of cyclic adenosine 3’ ,5’-phosphate, a substance whose concentration is known to be affected by acetylcholine, epinephrine and theophylline.