Effect of hypoglycemia on the content of pituitary growth hormone (GH) and hypothalamic growth hormone-releasing factor (GHRF) in the rat.

Abstract

The effect of insulin-induced hypoglycemia on the content of growth hormone (GH) in the pituitary and growth hormone-releasing factor (GHRF) in the hypothalamus of adult male rats was studied. GH was estimated by the tibial epiphyseal cartilage test and GHRF activity was determined by the depletion of pituitary GH evoked by intravenous (iv) administration of hypothalamic extracts into normal male rats. Initial studies revealed that a doseresponse relationship existed between the logdose of ovine hypothalamic extract administered and the degree of depletion of pituitary GH in recipient rats. Cerebral cortical extract was inactive. A dose of crystalline insulin (1 U/kg) was administered intraperitoneally, and blood sugar, pituitary GH and hypothalamic GHRF were estimated 1 hr later. Control rats received an equal volume of saline. The treatment with insulin induced a profound hypoglycemia which was accompanied by a significant depletion in pituitary GH and an even greater depletion in hypothalamic GHRF. It was concluded that the hypoglycemic stimulus to GH secretion acts via release of GHRF, which then triggers GH release from the pituitary gland. (Endocrinology81: 333, 1967)