Hypo- and hyperglycemia in rats: effects on endurance and heat/exercise injury

To investigate the hypothesis that circulating glucose levels may affect exercise performance and the severity of hyperthermic injury, rats were made hypoglycemic (n = 12, IV insulin, 4 U) or hyperglycemic (n = 12, IP glucose, 750mg) before exercise in the heat to hyperthermic exhaustion (Tco = 42.5-43 degrees C). The endurance of rats administered glucose was significantly greater than insulin-treated controls (n = 12). Hematocrit levels were unaffected by exercise in control and insulin-treated rats, but were significantly (p less than 0.01) increased in those glucose-treated. Lactate levels were increased (p less than 0.001) post-run in all groups, and these increments were exacerebated in glucose-treated rats. Glucose levels pre-run were decreased by insulin and increased by glucose, and remained depressed (p less than 0.01) post-run in the insulin-treated group. Potassium concentrations were reduced (p less than 0.05) by insulin administration. Urea nitrogen and creatinine were increased (p less than 0.001) post-run in all groups. We concluded that, while hyperglycemic rats had increased endurance compared to hypoglycemic animals, mortality of at least 50% in all groups was unaffected by circulating glucose levels.