Abstract

Preganglionic sympathetic blockade in dogs has been used to distinguish between heart force increments arising from the reflex responses of acute hypotension and similar increments which may arise from a more direct mechanism of action. A series of drugs, which characteristically produce acute diastolic hypotension, was tested before and after sympathetic blockade. Quinidine and nitroglycerin produced moderate positive inotropic effects before blockade, whereas, these effects were abolished after blockade. Isoproterenol, aminophylline and papaverine produced relatively marked, positive inotropic effects in the control tests and the responses were approximately the same after sympathetic blockade. In fully conscious animals, all 5 drugs produced typical positive inotropic effects along with hypotension and tachycardia; the intensity and duration of these effects, however, was less than in anesthetized animals. Similarly, vagosympathectomy had the effect of reducing the typical responses when measured under morphine-pentobarbital anesthesia.

With papaverine, and to a lesser degree with the other drugs, a transitory decrease in heart force characteristically followed a stage in which tachycardia and hypotension coincided with sharply increased mechanical activity of the myocardium. Some possible interpretations are suggested for this pattern of response.