Metabolic Studies in the African Pygmy

Abstract

Major metabolic effects of human growth hormone (HGH) were assessed in the African Babinga pygmy. Plasma free fatty acid (FFA) and glucose concentrations were measured in pygmies, HGH-deficient dwarfs, Bantu tribesmen, and Caucasian controls after each received 4 mg of HGH intravenously over a 20 min period. Pygmies had an early decrease of plasma FFA and glucose concentration, but did not exhibit a later lipolytic response. In neighboring Bantu tribesmen, American controls, and HGH-deficient dwarfs, both the early and late responses to intravenous HGH were present. The failure of plasma FFA concentration to increase in the pygmy after intravenous HGH was not due to a generalized defect in lipolysis since a normal lipolytic response was obtained with epinephrine (2 μg/min for 20 min). Pygmies, like HGH-deficient dwarfs, had significantly reduced insulin responses to both oral glucose and arginine. Insulin secretion was significantly reduced when compared with either Bantu tribesmen or American controls and was not altered by 2 wk of a high carbohydrate/high protein diet. HGH treatment in pygmies (5 mg b.i.d. for 5 days) failed to augment either glucose or arginine-induced insulin secretion. Glucagon consistently caused normal insulin secretion in HGH-deficient dwarfs and was, likewise, effective in each pygmy studied. In two offspring from different pygmy mothers and Bantu fathers, insulin responses to glucose were initially normal and increased in a normal manner after HGH treatment. In previous studies, HGH failed to reduce serum urea nitrogen concentration in pygmies. Sulfation factor was found to be normal. A consideration of the data in toto is consistent with a hypothesis that the metabolic findings in the pygmy may result from partial nonresponsiveness to either HGH or to a factor generated by HGH. This defect is not transmitted as either an autosomal or sex-linked dominant trait.