Acute effects of exogenous growth hormone in man: time- and dose-bound modification of glucose tolerance and glucose-induced insulin release.

The time and dose dependency of the effects of a 30-min long iv infusion of human growth hormone (GH) on glucose tolerance and glucose-stimulated insulin release was investigated in 19 healthy subjects. Glucose tolerance deteriorated immediately following GH, and the k-value continued to decrease up to 300 min later. A small but significant reduction of glucose tolerance persisted 24 h after GH administration. Significant deterioration of glucose tolerance was observed with the smallest GH dose used (5 mug per kg body weight), increasing the amount of the hormone having no further major influence. Glucose-stimulated insulin release was significantly inhibited 1 h after administration of a relatively high GH dose (40 mug per kg), both if expressed as mean plasma insulin levels, or as insulin release per magnitude of glucose stimulation (insulinogenic index). In the majority of subjects, insulin release was inhibited also by lower GH doses (5-20 mug GH per kg). However, the mean change with these doses was not statistically significant. The inhibitory effect of GH on insulin secretion seemed to have a duration of several hours. Five hours, but not 24 h, after GH administration (10 mug GH per kg) insulin release was still significantly suppressed. It is suggested that the initial effect of GH on pancreatic beta cells may be inhibition of insulin release, in contrast with the enhancement of insulin secretion observed during chronic administration of GH.