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A Suppression of Gonadotropin Secretion by Cortisol in Castrated Male Rhesus Monkeys (Macaca Mulatta) Mediated by the Interruption of Hypothalamic Gonadotropin-Releasing Hormone Release1

1985; Oxford University Press; Volume: 33; Issue: 2 Linguagem: Inglês

10.1095/biolreprod33.2.423

1529-7268

A. K. Dubey, Tony M. Plant,

Sperm and Testicular Function

Four orchidectomized rhesus monkeys (3–3.5 yr of age) were treated for 62 days with daily i.m. injections of hydrocortisone acetate (HCA) at a dose of 10–20 mg/(kg BW•day), and blood samples were obtained daily or every other day before, during, and after treatment. Hydrocorti-sone acetate injections resulted in a progressive rise in mean plasma cortisol from basal concentrations of 17–35 μg/100 ml prior to initiation of steroid treatment to approximately 150 μg/100 ml 5 wk later. When serum cortisol concentrations reached 100 μg/100 ml, 3–4 wk after the initiation of HCA treatment, circulating luteinizing hormone (LH) and follicle-stimulating hormone (FSH) began to decline, reaching nondetectable concentrations 35 days later. Withdrawal of HCA resulted in a return in plasma cortisol concentrations to pretreatment control levels, which was associated with a complete restoration of gonadotropin secretion. In 2 animals, administration of an intermittent i.v. infusion of gonadotropin-releasing hormone (GnRH) (0.1 μg/min for 3 min once every hour), which appears to stimulate the gonadotropes in a physiologic manner, reversed the cortisolinduced inhibition of gonadotropin secretion, restoring circulating LH and FSH concentrations to within 80–100% of control. These results suggest that, in the rhesus monkey, the major site of the inhibitory action of cortisol on gonadotropin release resides at a suprapituitary level and is mediated by interruption of hypothalamic GnRH release.