Testosterone modulates growth hormone secretion at the hypothalamic but not at the hypophyseal level in the adult male rhesus monkey

Abstract

We investigated a possible modulation of growth hormone (GH) secretion by testosterone by measuring the growth hormone releasing hormone (GHRH)-stimulated and N-methyl-,-aspartic acid (NMA)-induced GH secretion in adult rhesus monkeys. Intact, orchidectomized and testosterone-substituted (testosterone enanthate 125 mg/ week, i.m. for 5 weeks) orchidectomized monkeys (n=5) were used in the study. GHRH (25 µg/kg body weight) or NMA (15 mg/kg body weight) was infused through a Teflon cannula implanted in the saphenous vein. Sequential blood samples were collected 30-60 min before and 60 min after the injection of the neurohormone or the drug at 10-20-min intervals. All bleedings were carried out under ketamine hydrochloride anaesthesia (initial dose 5 mg/kg body weight i.m., followed by 2·5 mg/kg at 30-min intervals). The plasma concentrations of GH, testosterone and oestradiol (E 2 ) were determined by using specific assay systems. Administration of GHRH elicited a significant increase in GH secretion in all three groups of animals. There was no significant difference in the responsiveness of pituitary somatotrophs to exogenous GHRH challenges between intact and orchidectomized monkeys and testosterone replacement in orchidectomized animals did not significantly alter the GHRH-induced GH response. The responsiveness of hypothalamic GHRH neurones apparently did undergo a qualitative change after orchidectomy, as GH response to NMA was less in orchidectomized animals than in intact monkeys. The responsiveness of GHRH neurones to exogenous NMA was restored and even potentiated when orchidectomized monkeys were treated with testosterone. Taken together, these findings suggest that testosterone does not affect the sensitivity of the pituitary somatotrophs to GHRH but stimulates the secretion of GH by modulation of the NMDA drive to GHRH neurones.

Long-term testosterone supplementation augments overnight growth hormone secretion in healthy older men

“…Similar results were observed in hypogonadal men after 24 wk of T replacement therapy (250 mg im every 3 wk) (5). As a consequence, other studies (5,34) have suggested that the stimulatory action of T may involve promoting GHRH release from the hypothalamus rather than potentiating its action at the level of the pituitary. In addition, T therapy in healthy older men is known to attenuate feedback inhibition by GH and IGF-I (42).…”

Short‐term testosterone supplementation does not activate GH and IGF‐I production in postmenopausal women

“…1,[43][44][45] The effect of Te in the human is not sex-limited, because masculinizing doses of Te stimulate the somatotropic axis in the genetically female premenopausal patient undergoing medical-surgical gender reassignment. Te also drives GH and IGF-I secretion in the monkey, cow, sheep and rat.…”

“…Te also drives GH and IGF-I secretion in the monkey, cow, sheep and rat. 1,[43][44][45] The effect of Te in the human is not sex-limited, because masculinizing doses of Te stimulate the somatotropic axis in the genetically female premenopausal patient undergoing medical-surgical gender reassignment. 9 In contrast, elevating Te concentrations by up to 8-fold for 1 week did not detectably increase GH secretion and IGF-I concentrations in healthy postmenopausal women.…”

The Effect of High Quality Feed Supplement on Growth Performance Post-Weaning Calves

“…A cattle reaches its sexual maturity at the age of 12 months old (Djarijah, 2012;Wejdmark, 2014). The androgen on male calves that spur body growth cause bone growth has not increased (Rizvi et al, 2000), so that there is no difference in body length and chest girth. This shows that sex does not affect the body length and chest girth.…”