Hypothalamus, sino-aortic reflexes and activity of the gut.

Abstract

1. The effect of stimulation of the sympathetic division of the hypothalamus on gut and cardiovascular system shows two phases: 1. the sympathetic phase which appears mainly during stimulation and is characterized by inhibition of the gut and rise in blood pressure and heart rate; 2. a phase of delayed excitation of the gut appearing either immediately after cessation of stimulation or after an interval of up to two minutes. No signs of sympathetic excitation appear in the cardiovascular system during this phase. 2. The delayed excitation of the gut which persists after vagotomy increases with increasing hypothalamic sympathetic excitation and is interpreted as a “rebound” phenomenon serving homeostatic purposes. 3. Although hypothalamic stimulation (directly with square ware currents or indirectly via stimulation of somatic nerves) results frequently in generalized sympathetic effects (inhibition of the gut, rise of blood pressure and heart rate and contraction of the nictitating membrane) and, dependant on the site and the parameters of stimulation, also in generalized parasympathetic effects (increase in tone and activity of the gut and fall in blood pressure and heart rate) attention is called to certain deviations from this scheme. A sympathetic effect leading to a rapid or marked rise in blood pressure is often associated with an increased activity of the gut. Evidence is presented for the assumption that the latter results from increased baroreceptor reflexes.