HOME HELP CONTACT US SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by D'Occhio, M. J. Articles by Setchell, B. P. Search for Related Content PubMed PubMed Citation Articles by D'Occhio, M. J. Articles by Setchell, B. P.

Castrated sheep were used to study the effects of gonadectomy on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. In the first experiment serum LH and FSH concentrations were determined in intact rams, recently castrated (2 days and 3 weeks) and long-term castrated animals (> 2 years, wethers) during intravenous testosterone infusion at physiological and supraphysiological levels. In intact rams, testosterone infusions effectively suppressed serum LH whilst FSH levels were suppressed only after prolonged infusion at the supraphysiological dose. Recently castrated sheep, which had higher gonadotrophin levels than intact rams, were less sensitive to testosterone feedback. Neither rate of testosterone infusion had any effect on the raised gonadotrophin levels in wethers. In a second experiment gonadotrophin concentrations and mating behaviour were determined in wethers bearing subdermal polydimethylsiloxane implants of testosterone, dihydrotestosterone and oestradiol. Testosterone implants stimulated mating behaviour in all wethers but suppressed gonadotrophins in only a proportion (three out of seven) of the animals. Both oestradiol and dihydrotestosterone suppressed LH and FSH in all wethers, whilst oestradiol, but not dihydrotestosterone, also stimulated mating behaviour. The present findings indicate that testosterone imposes continuing negative feedback on gonadotrophin secretion and that changes in the gonadotrophin regulatory system, which lead eventually to a loss in sensitivity to testosterone feedback, develop soon after gonadectomy. The results also provide the first direct evidence that long-term gonadectomy in male sheep has differential effects on sensitivity to testosterone of brain centres associated with gonadotrophin negative feedback and with mating behaviour. A loss in sensitivity to testosterone feedback in castrated animals may involve a lesion in 5-reductase, the enzyme required for conversion of testosterone to dihydrotestosterone.

J. Endocr. (1985) 104, 69–75

This article has been cited by other articles:

				C. J. Scott, D. E. Kuehl, S. A. Ferreira, and G. L. Jackson Hypothalamic Sites of Action for Testosterone, Dihydrotestosterone, and Estrogen in the Regulation of Luteinizing Hormone Secretion in Male Sheep Endocrinology, September 1, 1997; 138(9): 3686 - 3694. [Abstract] [Full Text] [PDF]