Effect of Changes in Plasma Na+ and Ca++ Ion Concentration on Body Temperature during Exercise

Plasma osmolarity and plasma Na+ and Ca++ ion concentrations were changed in human subjects by having them drink hypertonic solutions of NaCl or CaCl2. Plateau values of body temperature during work were raised by increase in [Na+] and lowered by increase in [Ca++] compared to values in normal conditions. The effect on body temperature could be ascribed to a faster onset of sweating in the Ca++ experiments and a slower onset in the Na+ experiments. The effect on body temperature of increased osmotic concentrations in plasma was due to action of the specific ions rather than a general effect of change in osmolarity. It was not possible to show whether the effects of Na+ and Ca++ were due to action on the central nervous system and thermoregulatory centers, or to peripheral interference with the function of the sweat glands.