EFFECT OF GROWTH-HORMONE ON THE RESPONSE TO INSULIN AND GLUCOSE-TURNOVER IN SHEEP

The hyperinsulinaemic euglycaemic clamp technique was used to determin e the effect of recombinant bovine growth hormone on the response to i nsulin in castrate male Corriedale sheep. Saline or growth hormone (6. 3 mu g/min/animal) was infused into four sheep from the beginning of e ach experiment for 9 h, such that eight clamp experiments were perform ed, four with growth hormone and four controls. After a basal period o f 3 h, insulin was sequentially infused at 1, 3 and then 6 mU/kg/min f or 2 h each and the plasma glucose concentration was maintained at the value noted during the basal period by a variable rate of glucose inf usion. Short-term growth hormone infusion decreased the glucose infusi on rate (CIR) required to maintain eugylcaemia as well as the rates of glucose appearance and disappearance. The glucose metabolic clearance rate (MCR) was also decreased by the growth hormone treatment at all rates of insulin infusion, the average decrease ranging between 20 and 30%. The insulin concentration causing half maximal stimulation of gl ucose MCR and GIR was unchanged by growth hormone treatment. Endogenou s glucose production was not consistently affected by either the growt h hormone or insulin treatments. The results of this experiment demons trate that growth hormone decreases the responsiveness of peripheral t issues to insulin, possibly at a site beyond the receptor.