Effects of Growth Hormone and of Hypophysectomy on the Release of Insulin From Rat Pancreas in Vitro

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 β-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.

Direct effects of rat growth hormone on rat islets of Langerhans in tissue culture

“…This confirms studies using pancreatic pieces or whole pancreatic peffusion [4,9,12,27], although here the acute stimulation of insulin release by GH has also been reported [13,28,29].…”

Insulin secretion from pancreatic islets: Effect of growth hormone and related proteins

“…Previous reports have reached differing conclusions regarding the acute in vitro effects of growth hormone on insulin secretion [1][2][3][4][5]. With recent advances in protein isolation and purification, it has become possible to define more clearly the structural and functional properties of human growth hormone.…”

Insulin Sensitivity in Vitamin B₆-Deficient Rats

“…Depressed insulin levels may be the direct result of the deficiency of vitamin B6, which is known to func tion in amino acid and protein metabolism, or an adaptive mechanism to the deficiency. Adaptive mechanisms could include the eflfect(s) of inanition or hormonal systems such as GH which is reported to modulate insulin secretion [4,6,21,22], Since it has been shown that serum and pituitary GH levels are decreased in vitamin B6-deficient rats [23] and the data presented here and in previous studies [19,24] indicate altered effects of GH in vitamin B8-deficient rats, the modifying influences of altered GH secretion on insulin metabolism in the pancreas and/or adipose and muscle tissue must be considered. The rats studied here exhibited the reported biphasic effect of GH in adipose tissue, its early insulin-like and late insulin-antagonistic characteristics.…”