Enhanced muscle glucose uptake facilitates nitrogen efflux from exercised muscle

The hypothesis that glucose ingestion in the postexercise state enhances the synthesis of glutamine and alanine in the skeletal muscle was tested. Glucose was infused intraduodenally for 150 min (44.5 micromol . kg-1 . min-1) beginning 30 min after a 150-min period of exercise (n = 7) or an equivalent duration sedentary period (n = 10) in 18-h-fasted dogs. Prior exercise caused a twofold greater increase in limb glucose uptake during the intraduodenal glucose infusion compared with uptake in sedentary dogs. Arterial glutamine levels fell gradually with the glucose load in both groups. Net hindlimb glutamine efflux increased in response to intraduodenal glucose in exercised but not sedentary dogs (P < 0. 05-0.01). Arterial alanine levels, depleted by 50% with exercise, rose with intraduodenal glucose in exercised but not sedentary dogs (P < 0.05-0.01). Net hindlimb alanine efflux also rose in exercised dogs in response to intraduodenal glucose (P < 0.05-0.01), whereas it was not different from baseline in sedentary controls for the first 90 min of glucose infusion. Beyond this point, it, too, rose significantly. We conclude that oral glucose may facilitate recovery of muscle from prolonged exercise by enhancing the removal of nitrogen in the form of glutamine and alanine.