Reflex responses of the vascular system and renal sympathetic efferents induced by potassium ions injected into the superior mesenteric artery and the effect of tonic baroreceptor inflow thereon

A sympathetic reflex elicited by distension of the mesenteric venous bed

1. The proximal ends of the distal portions of severed nerves coming from the small intestine were monitored for nerve impulses. When the mesenteric venous pressure was increased by mechanical obstruction of the portal vein there was a proportional increase in the frequency of afferent action potentials, the frequency falling immediately the venous pressure was reduced. The stimulus for the increased rate of nerve discharge appeared to be pressure within the mesenteric venous bed and not anoxia, for obstruction of the arterial supply to the gastrointestinal tract did not activate the same fibres.2. Obstruction of the portal vein led to an increased efferent nervous discharge to the intestines. The reflex increase persisted after bilateral vagotomy, after transection of the spinal cord at the level of C7 and after section of the hepatic nerves, but was abolished by section of the intestinal nerves.3. It is suggested that the spinal reflex is concerned with local distribution of blood and that the mesenteric venous ;volume' or ;stretch' receptors which initiate the reflex are similar to those described elsewhere in the body.