Thermoregulatory responses to central injections of excess calcium in monkeys

Abstract

In unanesthetized monkeys (4-8 kg), artificial cerebrospinal fluid (ACSF) containing excess (greater than 1.3 mM) amounts of Ca2+ was infused at 20 microliters/min for 5 min into the cerebral ventricles. Core and skin temperatures, respiratory gas exchange, heart rate, and sweat rate were monitored. At 22 degrees C, intracerebroventricular infusions of 13-39 mM Ca2+ produced a dose-related hypothermia associated with a dose-related fall in metabolic rate and heart rate and a rise in average skin temperature. General body sweating was not initiated, and respiratory water loss was unaffected; however, exercise activated sweating and elevated it from 0.05 to 0.22 mg X (cm2 X min)-1. At 35 or 40 degrees C, infusion of 26 mM Ca2+ failed to influence ongoing general body sweating; however, subsequent exercise increased sweat rate by 63%. Heart rate was unaffected. At 15 degrees C metabolic rate increased 50%. After infusing 26 mM Ca2+, metabolism decreased 6% and core temperature declined 0.8 +/- 0.24 degrees C. Skin temperatures continued to fall, heart rate fell, and sweating was not initiated. In contrast, infusing ACSF increased metabolism 11% and core temperature fell only 0.18 +/- 0.14 degrees C. The inability of exogenous Ca2+ to 1) initiate sweating at 22 degrees C, 2) elicit vasodilation at 15 degrees C, 3) initiate or stimulate sweating at 35 or 40 degrees C, or 4) lower core temperature at 35 or 40 degrees C argues against a set-point function for this cation.