TRAINING ENHANCED HEPATIC GLUCONEOGENESIS - THE IMPORTANCE FOR GLUCOSE-HOMEOSTASIS DURING EXERCISE

Endurance training has long been known to improve the individual's res istance to exercise-induced hypoglycemia. Traditionally attributed to a reduction in glucose uptake subsequent to enhanced fat oxidation, th is issue has only recently been directly addressed. This paper briefly reviews the evidence for reduced glucose uptake versus enhanced gluco se production in the improved hypoglycemic resistance following traini ng. While whole body glucose removal and production may be reduced fol lowing training, this has only been demonstrated under exercising cond itions in which glycemia demonstrates little deviation from rest. Unde r exercise conditions where untrained animals demonstrate substantial reductions in blood glucose, training enhanced hypoglycemic resistance has been shown to result entirely from enhanced glucose production vi a gluconeogenesis. Using the in situ perfused liver preparation, the a uthors have provided direct evidence for a training enhanced hepatic g luconeogenic capacity. The site of adaptation within the gluconeogenic pathway has now been constrained to below the level of the triose pho sphates. Lack of evidence for suppressed skeletal muscle glucose uptak e following training, a uniform observation for humans and rats, is al so discussed. It is concluded that the improved hepatic gluconeogenic capacity of endurance trained individuals, at least in rats, is critic al to their demonstrated resistance to exercise-induced hypoglycemia.