Nutrient Uptake by the Hindlimb of Growing Pigs Treated with Porcine Somatotropin and Insulin

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The shift in nutrient partitioning induced by porcine somatotropin (pST) is accompanied by a decrease in insulin sensitivity for whole-body glucose uptake. The relative contribution of metabolic changes in the hindlimb was investigated in eight pigs (55 kg) that had received recombinant pST (120 μg/kg) or excipient (control) for 7 d. Uptake of metabolites by the hindlimb was measured under basal conditions and during hyperinsulinemic-euglycemic clamps at low [14 ng/(kg·min)] and high [360 ng/(kg·min)] insulin infusion rates. Dextrose infusion rate required to maintain euglycemia was used as an index of whole-body glucose uptake in response to exogenous insulin. Effects of pST on hindlimb and whole-body glucose uptake were evident only at physiological levels of insulin (basal and low insulin infusion rate). During the low rate of insulin infusion, dextrose infusion rate was 79% lower for pST-treated pigs and glucose uptake by the hindlimb was 59% lower compared with control pigs. The decrease in glucose uptake by the hindlimb was entirely accounted for by the estimated reduction in glucose utilization by adipose tissue of the hindlimb. Glucose:oxygen quotients were reduced during basal (57%) and low insulin infusion (63%) with pST treatment, indicating a change in the pattern of substrate utilization. This is consistent with the concept that pST directs nutrients away from adipose and towards muscle growth by altering the response of tissues to homeostatic signals such as insulin.