Reflex effects of thoracic sympathetic afferent nerve stimulation on the kidney.

Thoracic sympathetic afferents may play a role in the reflex control of renal vascular resistance during hypotension. Mongrel dogs were anesthetized with ketamine hydrochloride and maintained on a 50-50, O2-N2O mixture supplemented with 0.5%-1.0% halothane. Systemic arterial blood pressure was lowered to 50 mmHg with use of a constant pressure hemorrhage technique. The renal circulation was perfused with a constant-flow perfusion system. Low-frequency (3 Hz) stimulation of thoracic sympathetic afferents produced renal vasodilation. A reduction of renal vascular resistance was measured as a decrease in constant-flow perfusion pressure. Vagotomy accentuated the dilator response to stimulation. High-frequency (30 Hz) afferent stimulation produced renal vasoconstriction. Renal efferent nerve activity and renal blood flow responded to afferent stimulation (3 Hz) by transient inhibition of efferent activity and increases in renal blood flow. Afferent stimulation (30 Hz) caused increases in renal efferent nerve activity and decreases in renal blood flow. The thoracic sympathetic afferents carry information from cardiopulmonary structures that alter renal efferent nerve activity and renal hemodynamics during hypotension.