Endocrinology, Vol 124, 1310-1318, Copyright © 1989 by Endocrine Society

ARTICLES

Institution of combined treatment with testosterone and charcoal- extracted porcine follicular fluid immediately after orchidectomy prevents the postcastration hypersecretion of follicle-stimulating hormone in the hypothalamus-lesioned rhesus monkey (Macaca mulatta) receiving an invariant intravenous gonadotropin-releasing hormone infusion

SA Abeyawardene and TM Plant
Department of Physiology, University of Pittsburgh School of Medicine, Pennsylvania 15261.

In the male rhesus monkey, the negative feedback regulation of gonadotropin secretion by the gonad involves a specific inhibitory action of a testicular hormone on FSH release at the level of the anterior pituitary gland. Neither circulating testosterone (T) nor estradiol appears to be able to account for the testicular inhibition of FSH in this species. The purpose of the present study was to begin to examine the role of gonadal peptides in this regard. To this end, an episodic pattern of activity in the pituitary-Leydig cell axis was restored in seven hypothalamus-lesioned male rhesus monkeys with a chronic and unchanging intermittent iv infusion of GnRH (0.1 microgram/min for 3 min every 3 h). This preparation, known as the hypophysiotropic clamp, has been described in detail previously. Charcoal-extracted porcine follicular fluid (pFF) was used as the source of gonadal peptides. In five animals, initiation of combined T replacement and pFF treatment (10-15 ml, sc, every 12 h for 8 days) maintained circulating FSH at concentrations similar to those observed before gonadectomy. Withdrawal of pFF treatment for 8 days while maintaining T replacement resulted in a progressive and dramatic rise in plasma FSH concentrations. Reinitiation of pFF treatment resulted in a return of circulating FSH concentrations toward precastration control values. Changes in LH secretion throughout the experiment were unremarkable. In an attempt to assess any nonspecific effects of porcine protein on gonadotropin secretion, the remaining two animals received charcoal-extracted pig serum instead of pFF. In these animals circulating FSH concentrations rose 7- to 8-fold during the 8 days of combined T replacement and pig serum treatment. These findings provide evidence to support the view that a testicular peptide, most probably inhibin, plays a major role in the negative feedback regulation of gonadotropin secretion in the monkey by exerting an inhibitory action on FSH secretion directly at the level of the anterior pituitary gland.

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