Prostaglandin E1 hyperthermia: effects on ability to work in the heat.

To assess the effects of preinduced hyperthermia on the ability to exercise in the heat, prostaglandin E1 (PGE1) was administered intracerebroventricularly to male rats weighing 275-350 g. Following injection of PGE1, a fever of 2 degrees developed within 20-30 min, at which time a 1-ml blood sample was taken. When these animals exercised in the heat (37 degrees C) to hyperthermic exhaustion (42.5-43 degrees C), their endurance capacity was significantly reduced (P less than 0.001) when compared with controls. Exercise to hyperthermic exhaustion resulted in significantly (P less than 0.05, minimal) increased plasma levels of lactate, potassium, and urea nitrogen in both control animals and those receiving PGE1. However, PGE1 pretreatment did not exacerbate these increments. Plasma glucose and sodium levels were significantly (P less than 0.05) increased in PGE1-treated animals, whereas glucose levels were reduced significantly (P less than 0.05) in both groups postrun. We concluded that preinduced hyperthermia severely reduces the ability to work in the heat. Although the clinical chemical indices of heat injury are unaffected by PGE1 pretreatment, the effects of PGE1 administration on circulating levels of glucose and sodium require further study.