Thresholds for Na+ and Ca++ effects on thermoregulation

The evidence for threshold concentrations of Na+ and Ca++ that alter body temperature when introduced into (a) the hypothalamus and cerebral ventricles, and (b) intravenously and by oral ingestion is examined. For hypothamic and ventricular perfusion the threshold for any increase in core temperature (Tc) at rest with excess Na+ is about 10 mM, while there is a linear relationship between the level of excess Ca++ and the decrease in Tc, with a correlation co-efficient of 0.85. With intravenous and oral ingestion the resting threshold plasma concentration for an excess Na+ effect is about 5 mEq/1 per 0.1 degrees C rise in Tc, and the excess Ca++ level is about 1 mEq/1 per 0.1 degrees C decrease in Tc. With exercise, there is a dose-dependent attenuation of the rise in core temperature that is also about 0.1 degrees C per mM excess Ca++.