African pygmies who appear to be insensitive to the metabolic effects of human growth hormone (HGH) are insulinopenic after administration of either glucose or arginine. Contrary to our expectation, insulin responses in this group were normal after tolbutamide and glucagon. To clarify this observation, insulin secretion was studied in twenty-nine normal controls and six dwarfs with growth hormone deficiency.
After arginine and glucose, peak insulin responses in controls were, respectively, 90.4 ± 8.6 μU./ml. and 108.0 ± 12.0 μU./ml. In HGH deficient dwarfs, responses were 38.6 ± 6.0 μU./ml. and 40.0 ± 6.4 μU./ml. (p < .01). In controls as well as HGH deficient dwarfs, the mean maximal insulin responses to arginine and glucose were increased two- to fourfold by HGH treatment (5 nig. twice a day for five days). Similar results occurred after ingestion of mixed meals.
Both tolbutamide and glucagon caused normal insulin responses in the HGH deficient group. Mean maximal responses to tolbutamide were 69.4 ± 15.0 μU./ml. in controls and 61.6 ± 7.7 μU./ml. in HGH deficient dwarfs. Mean maximal responses to glucagon were 101.6 ± 19.4 μU./ml. and 102.0 ± 9.4 μU./ml., respectively. Unlike arginine and glucose, HGH had no effect upon insulin responses to either agent in controls.
The data support the division of pancreatic pools of insulin into two major groups: those dependent and those not dependent upon pituitary secretion of HGH.
