Renal vascular response to heat stress in baboons--role of renin-angiotensin.

To determine if hyperthermia in the baboon caused a reduction of renal blood flow (RBF) similar to that reported in man, we repeatedly exposed six unanesthetized male baboons (Papio cynocephalus) to ambient temperatures of 42.5-49.0 degrees C for 55-175 min. Internal temperatures rose 1.0-2.0 degrees C. On the average, RBF fell 23.7% per degrees C, renal vascular resistance (RVR) rose 34.0% per degrees C, and mean arterial pressure (MAP) fell by only 2.9 Torr. Plasma renin activity (PRA), measured in four baboons, rose 97.5% per degrees C. To investigate the role of the renin-angiotensin system in this renal response, we infused propranolol or saralasin (1-sar-8-ala-angiotensin II), an angiotensin II antagonist, systemically in 14 experiments on three baboons. Both propranolol and saralasin infusions prevented most of the reduction in RBF during hyperthermia. Propranolol prevented the increase in PRA. We conclude that renal vasoconstriction accompanies moderate hyperthermia in the awake baboon, and much of this response is mediated by a beta-adrenergic release of renin.