EFFECTS OF GROWTH HORMONE AND OF HYPOPHYSECTOMY ON THE RELEASE OF INSULIN FROM RAT PANCREAS IN VITRO

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Abstract
The release of insulin from ligated rat pancreas in vitro was measured after pre-incubation of the tissue at either high or low glucose concentrations. Insulin release was estimated by determining the glucose uptake of rat hemidiaphragms after joint incubation with the pancreatic tissue. Addition of bovine growth hormone (GH) to the pre-incubation medium in a concentration of 0.1 mg/ml significantly increased the response to glucose stimulation. Pancreatic tissue of hypophysectomized rats failed to respond to GH in vitro, although previous hypophysectomy was shown to reduce the response to glucose stimulation. Pretreatment of hypophysectomized rats with GH in doses which restored the growth rate to normal, caused the reappearance of the effect of GH in vitro. The glucose sensitivity of pancreatic tissue was also increased by pretreatment with GH in vivo alone. It is concluded from these findings that GH may increase the sensitivity of the [beta]-cells to glucose by direct action. Since hypophysectomy exerts an opposite effect, it is suggested that physiological levels of endogenous GH may be involved in the regulation of insulin release.