INFLUENCE OF OUABAIN ON THE POSITIVE INOTROPIC RESPONSES TO NOREPINEPHRINE IN ISOLATED GUINEA-PIG AND DOG HEART PREPARATIONS AT 37° AND 27°

¹ Department of Pharmacology, University of Oklahoma School of Medicine, Oklahoma City, Oklahoma

Effects of ouabain on contractile force responses to norepinephrine at 37° and 27°C, and on responses to isoproterenol and aminophylline at 27°, were examined in isolated guinea-pig heart preparations. Norepinephrine only increased contractile force of isolated, perfused guinea-pig hearts both before and during administration of ouabain at 37°. At 27°, norepinephrine evoked a triphasic contractile force pattern characterized by an initial, brief increase, a transient decrease and subsequent prolonged increase in force. In the presence of ouabain at 27°, norepinephrine only decreased contractile force, but after ouabain was removed from the perfusion fluid norepinephrine again evoked the triphasic pattern. When isolated strips of right ventricle were employed, ouabain had no significant effect on the contractile response to norepinephrine at 37°. Norepinephrine did not cause a triphasic force pattern in the ventricle strip at 27°, but norepinephrine in the presence of ouabain at 27° only decreased force. Positive inotropic responses to isoproterenol and aminophylline were also blocked by ouabain at 27°. The positive inotropic responses to norepinephrine, isoproterenol and aminophylline were all restored after removing ouabain from the muscle bath. Ouabain blocked the positive inotropic response to norepinephrine in dog ventricle strips at 28°.