Hypothermia induced by 5-thio-D-glucose: Effects on treadmill performance in the heat.

In continuing our studies on the effects of preinduced hypothermia on the endurance capacities, thermoregulatory responses, and clinical chemical indices of heat injury, 10 mg of 5-thio-D-glucose (5-TG) were administered intravenously to restrained rats kept at 4 degrees C. When rectal temperatures (Tre) fell to 29-30 degrees C, the rats were removed to a hot environment (35 degrees C), where they exercised on a level treadmill (9.14 m/min) to hyperthermic exhaustion (Tre = 41.5-43 degrees C). Preinduced hypothermia was effective in significantly (p < 0.001) prolonging the time to hyperthermic exhaustion. In these hypothermic rats, increments in Tre (degree C/min) while on the treadmill were significantly (p < 0.001) increased while rates of skin temperature (Tsk) heating were significantly (p < 0.001) reduced when compared to normothermic controls. Administration of 5-TG effected significant (p < 0.001) hyperglycemia, which returned to control levels following the exhaustive run in the heat. Prolonged endurance times among the hypothermic rats caused slight increases in the levels of circulating plasma indices of heat/exercise injury. We concluded from these studies that hypothermia induced by 5-TG administration and cold exposure is effective in increasing the endurance capacity of rats exercising in the heat. However, homeostatic mechanisms supercede to increase the heating rate, and thus return Tre to equilibrium levels.