Hypothalamic Growth Hormone-releasing Factor Research Articles

Pituitary GH and hypothalamic GHRF after median eminence implantation of ovine or human GH.

The effects of implanting human or ovine GH in the median eminence were measured on pituitary GH concentration, hypothalamic content of growth hormone releasing factor (GHRF) and serum prolactin activity. Adult female rats implanted with human or ovine GH showed a significant decrease in pituitary GH concentration and in hypothalamic GHRF content when compared with controls 7 days after implantation. Pituitary weights were also decreased in GH implanted rats. There were no significant changes in body weight or ovarian or uterine weights. Rats implanted with human GH showed decreased serum prolactin and atrophy of the mammary glands when compared with pre-implantation levels or controls implanted with cocoa butter. These results suggest that human and ovine GH act via the hypothalamus to decrease pituitary GH concentration. They also indicate that human GH, like prolactin from other species, can decrease serum prolactin levels and induce mammary gland regression when implanted in the median eminence of rat...

Effects of starvation on plasma GH activity, pituitary GH and GH-RF levels in the rat.

The effects of complete food removal for 7 days were measured on plasma GH activity, hypothalamic content of growth hormone releasing factor (GH-RF) and pituitary concentration of growth hormone (GH) in male rats. Control male rats were fed ad lib. for 7 days. In another experiment, the starved rats received replacement doses of L-Na-thyroxine (2.5 μg/ 100 g body weight/day) beginning on day 2 starvation. On day 8 all rats were weighed, anesthetized with ether and bled from the abdominal aorta. The pituitaries were removed and individually weighed; the hypothalami were placed in ice cold O.lN HC1 (0.1 ml/hypothalamus). Hypothalamic GH-RF was assayed by an in vitro incubation method. Lyophilized plasma, anterior pituitaries and incubation medium were assayed for GH by the standard tibia test, using a 4-point assay procedure. Statistical analysis of the data showed a significantly lower plasma GH content in starved or thyroxine-treated starved rats (p<0.01). Pituitary GH content and hypothalamic content of ...

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

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)

Growth Hormone-Releasing Activity in the Hypothalamus and Plasma of Rats Subjected to Stress.

SummaryExperiments were performed in the rat to determine whether the increased secretion of growth hormone (GH) during stress involves augmentation of synthesis and/or release of hypothalamlc GH-releasing factor (GRF). Two different stimuli were used as stress: injection of formalin, which was previously shown to be ineffective in inducing GH release; and cold exposure, which evoked depletion of pituitary GH. Exposure of rats to cold (4°C) for 1 hr resulted in a significant depletion of pituitary GH, which was accompanied by disappearance of hypothalamic GRF and appearance of GRF activity in plasma. Cold exposure for 5 minutes was ineffective. Injection of 10% formalin did not induce pituitary GH depletion, or affect hypothalamic and plasma GRF activity. These results indicate that some stressful stimuli, such as cold exposure, capable of releasing GH, induce this effect via the hypothalamus; other stresses, like formalin injection, which do not release GH, exert little effect on the GH-release mechanism...