Myocardial alterations following hypothalamic stimulation in the intact conscious dog

Abstract

We sought to determine if electrical stimulation of the posterior hypothalamus at physiologic levels could induce myocardial injury in the unanesthetized dog. Biphasic pulses of 1.0 msec. duration, 100 Hz., and 0.2 to 0.8 ma. intensity for 15 sec. via stereotaxically implanted electrodes in six unanesthetized dogs immediately increased heart rate (95 per cent) and mean aortic blood pressure (73 per cent). In two dogs instrumented for aortic and coronary blood flow measurements, stimulation immediately raised cardiac output (21 per cent) and coronary blood flow (185 per cent). All parameters returned to control within 8 to 10 minutes after stimulation. In two dogs killed four hours after stimulation, electron microscopy revealed foci of discrete single-cell degeneration. In two dogs killed 72 and 168 hours after stimulation, light microscopy showed multiple foci of myocytolysis and fibrosis located perivascularly and subendocardially. These lesions resembled catecholamine-induced injury or myocardial lesions secondary to hypoxia. The electron microscopy findings suggest that the lesions are catecholamine-induced. These results suggest that physiologic stimulation of the hypothalamus plays a role in some types of myocardial injury.