Enhanced muscle glucose uptake facilitates nitrogen efflux from exercised muscle

The hypothesis that glucose ingestion inthe postexercise state enhances the synthesis of glutamine and alaninein the skeletal muscle was tested. Glucose was infused intraduodenallyfor 150 min (44.5 µmol · kg¹ · min¹)beginning 30 min after a 150-min period of exercise(n = 7) or an equivalent durationsedentary period (n = 10) in18-h-fasted dogs. Prior exercise caused a twofold greater increase inlimb glucose uptake during the intraduodenal glucose infusion compared with uptake in sedentary dogs. Arterial glutamine levels fell graduallywith the glucose load in both groups. Net hindlimb glutamine effluxincreased in response to intraduodenal glucose in exercised but notsedentary dogs (P < 0.05-0.01).Arterial alanine levels, depleted by 50% with exercise, rose withintraduodenal 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 forthe first 90 min of glucose infusion. Beyond this point,it, too, rose significantly. We conclude that oral glucosemay facilitate recovery of muscle from prolonged exercise by enhancingthe removal of nitrogen in the form of glutamine andalanine.