Hypothalamic Control of the Distribution of Cardiac Output in the Unanesthetized Rhesus Monkey

Regional organ blood flow and resistance changes evoked after 10 minutes of electrical stimulation of pressor areas in the anterior hypothalamus were studied in six unanesthetized, restrained rhesus monkeys. Five other monkeys served as controls. The regional changes produced by stimulus intensities which did not affect systemic arterial pressure, central venous pressure, cardiac output, or pulse rate were similar to those produced by the stimulations at higher levels which significantly increased the levels of these variables. With both low and high levels of stimulation the fractions of cardiac output to skeletal muscle and chest wall were increased 51 and 146% at the expense of the output to the kidneys, skin, stomach, spleen, pancreas, mesentery, and thyroid which decreased 38 to 79%. In each of two monkeys tested, the marked rise in blood flow and vasodilatation of skeletal muscle was only slightly affected by atropine. Therefore, there is at least some hypothalamic control over skeletal muscular vasodilatation in the unanesthetized monkey that is not cholinergically mediated.