Dietary manipulation and exercise in the heat: thermoregulatory and metabolic effects in rats.

To determine the effects of dietary manipulation on the metabolic, physical, and physiological responses to exercise in the heat, adult male rats (n 5 16/group) were food deprived for 72 h followed by ad lib consumption of a high protein (HIPROT) or high carbohydrate (HICARB) diet for 96 h. Each dietary regimen was followed immediately by exercise (9.14 m . min-1) in the heat (35.58C) to hyperthermic exhaustion (TCO approximately 43 8C). Animals consuming the HICARB or HIPROT diet had an increased mean TCO prior to the acute heat/exercise protocol when compared with a control (CONT) group with uninterrupted access to a normal rodent diet; the HICARB rats also manifested a decreased endurance when compared with the CONT group. Plasma levels of urea nitrogen, lactate, and potassium were increased following exercise in the heat in all groups, but greatly exacerbated increments in urea nitrogen occurred in the HIPROT group. Following exercise, significant increments occurred in circulating levels of glucose and insulin in the HIPROT and HICARB groups. Plasma triglycerides were decreased by the exercise/heat regimen but increased by both diets. Thus, these dietary manipulations elicited a variety of metabolic responses which did not markedly alter the physiological and physical effects of work in the heat.