CARBOHYDRATE HANDLING IN THE HIND LEG MUSCLE OF EXERCISING RATS

The arterio-venous concentrations of oxygen, glucose and lactate, as w ell as blood flow and muscle levels of lactate, glucose, hexose-phosph ates and glycogen of rat hind leg muscle were determined under basal c onditions and under mild and intense exercise, as well as during post- exercice recovery. During intense exercise and fatigue glycogen is pra ctically exhausted, providing glycosyl residues to the hexose-phosphat es pool in addition to increased glucose uptake from the blood. The re sult is the production of huge amounts of lactate, which accumulates i n muscle and the skin, and buildup the arterial concentrations. During recovery lactate is slowly disposed of, and the muscle takes up large amounts of glucose which is stored into glycogen, with fully reinstat ed glucose oxidation. The data shown suggest that the shift from oxida tive to mainly anaerobic utilization of glucose is not as streamlined as is usually assumed, since the results found here hint at the wastef ul utilization of glycogen-derived hexose skeletons for other syntheti c pathways. Glucose, nevertheless, is of paramount importance as energ y staple to sustain untrained intense exercise in the rat.