Effects of growth hormone on glucose metabolism.

Growth hormone (GH) counteracts in general the effects of insulin on glucose and lipid metabolism, but shares protein anabolic properties with insulin. Under physiological circumstances GH does not affect total glucose turnover directly. There is however evidence that GH acutely decreases glucose oxidation (secondary to an increase in lipid oxidation) and suppresses muscle uptake of glucose, suggesting that GH redistributes glucose fluxes into a non-oxidative pathway, which could be a build up of glycogen depots through gluconeogenesis. Since GH secretion is inhibited in the fed state these actions are mainly important in the postprandial or fasting state. Under pathological conditions of GH excess (e.g. acromegaly, poorly controlled tp. 1 diabetes or high dose GH treatment) the diabetogenic actions of GH become apparent. In these patients increased endogenous glucose production, decreased muscle glucose uptake and rising blood glucose levels are observed. In patients with intact beta-cell function these changes are counterbalanced by hyperinsulinemia--such hyperinsulinemia may in the long term induce increased cardiovascular morbidity and mortality ('Reavens syndrome X'). When stimulated with insulin these patients exhibit insulin resistance at the liver, in adipose tissue and in muscle. Few elaborate studies on the effects of GH on glucose metabolism in GH deficient patients have been conducted. These patients are hypersensitive to the actions of insulin on glucose metabolism and there is some evidence that when GH initially is given to such patients in the GH deprived state, paradox insulin-like effects of GH may be observed. Whether this may relate to increased activity of insulin-like growth factors is unsettled.