THE INFLUENCE OF PITUITARY GROWTH HORMONE ON PLASMA INSULIN ACTIVITY

Abstract

SUMMARY The insulin activity of blood plasma has been studied by the application of a method of assay based upon the stimulation of the in vitro uptake of glucose by the isolated rat diaphragm. Treatment of the intact rat with growth hormone did not significantly alter the insulin activity of the blood plasma. Hypophysectomy of the rat greatly reduced the insulin activity of the plasma, though this fall could be prevented by treatment with growth hormone begun immediately after hypophysectomy. Treatment with growth hormone of the intact cat, but not of the depancreatized cat receiving a constant dose of insulin, greatly increased the insulin activity of the plasma. The in vitro addition of growth hormone to human or rat plasma did not alter its insulin activity. The plasma from cats rendered permanently diabetic by a short period of treatment with growth hormone possessed no significant insulin activity. After the plasma had been repeatedly frozen and thawed, insulin activity was found to be present. No appearance of insulin activity on freezing and thawing was observed with plasma from normal or depancreatized cats. The significance of the influence of growth hormone upon the secretion of insulin by the pancreas is discussed.