Glucose uptake and glucose transporter proteins in skeletal muscle from undernourished rats

Undernutrition in rats impairs secretion of insulin but maintains glucose n ormotolerance, because muscle tissue presents an increased insulin-induced glucose uptake. We studied glucose transporters in gastrocnemius muscles fr om food-restricted and control anesthetized rats under basal and euglycemic hyperinsulinemic conditions. Muscle membranes were prepared by subcellular fractionation in sucrose gradients. Insulin-induced glucose uptake, estima ted by a 2-deoxyglucose technique, was increased 4- and 12- fold in control and food-restricted rats, respectively. Muscle insulin receptor was increa sed, but phosphotyrosine-associated phosphatidylinositol 3-kinase activity stimulated by insulin was lower in undernourished rats, whereas insulin rec eptor substrate-1 content remained unaltered. The main glucose transporter in the muscle, GLUT-4, was severely reduced albeit more efficiently translo cated in response to insulin in food-deprived rats. GLUT-1, GLUT-3, and GLU T-5, minor isoforms in skeletal muscle, were found increased in food-depriv ed rats. The rise in these minor glucose carriers, as well as the improveme nt in GLUT-4 recruitment, is probably insufficient to account for the insul in-induced increase in the uptake of glucose in undernourished rats, thereb y suggesting possible changes in other steps required for glucose metabolis m.