THE EFFECT OF INTRAVENOUS INSULIN INFUSION ON PREMEAL AND POSTMEAL PLASMA GROWTH-HORMONE CONCENTRATIONS IN CALVES

The effect of an intravenous infusion of insulin on the pre- and post- meal secretion of growth hormone (GH) was investigated in Japanese, bl ack female calves. During the period from 5 h before (pre-meal) to 5 h after (post-meal a meal, 10 mU bovine insulin per kg of body weight ( BW), or insulin (10 mU/kgBW/h) plus glucose (75 mg/kgBW/h) was infused intravenously. Saline was infused as the control. The plasma concentr ations of insulin, GH, glucose and free fatty acid (FFA) were measured at 30-min intervals during the period of 6 h before to 5 h after the meal. The insulin infusion raised (p < 0.05) the plasma-insulin level and lowered (p < 0.05) the glucose level. In the insulin plus-glucose- infused calves, the insulin level was also elevated (p < 0.05), howeve r, the glucose concentration was kept at a level that was the same as the control. In the insulin- and the insulin-plus-glucose-infused cave s, pre-meal insulin levels were less than 41.0 mU/ml, while post-meal levels were in the range 51.9-151.8 mU. No significant difference in p lasma FFA concentration was observed between the treatments. The area under the curve (AUC) of GH after the meal was smaller (p < 0.05) than the premeal AUC in the insulin- and the insulin-plus-glucose-infused calves, although no significant difference was observed between pre- a nd post-meal AUC of GH of the control. These results indicate that hig h plasma-insulin levels enhance the post-meal depression of GH secreti on in calves.