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Titolo:
Seasonal changes in the negative feedback regulation of the secretion of the gonadotrophins by testosterone and inhibin in rams
Autore:
Tilbrook, AJ; de Kretser, DM; Clarke, IJ;
Indirizzi:
Monash Univ, Dept Physiol, Clayton, Vic 3168, Australia Monash Univ Clayton Vic Australia 3168 siol, Clayton, Vic 3168, Australia Monash Univ, Inst Reprod & Dev, Clayton, Vic 3168, Australia Monash Univ Clayton Vic Australia 3168 Dev, Clayton, Vic 3168, Australia Prince Henrys Inst Med Res, Clayton, Vic 3168, Australia Prince Henrys Inst Med Res Clayton Vic Australia 3168 Vic 3168, Australia
Titolo Testata:
JOURNAL OF ENDOCRINOLOGY
fascicolo: 1, volume: 160, anno: 1999,
pagine: 155 - 167
SICI:
0022-0795(199901)160:1<155:SCITNF>2.0.ZU;2-K
Fonte:
ISI
Lingua:
ENG
Soggetto:
FOLLICLE-STIMULATING-HORMONE; LUTEINIZING-HORMONE; PITUITARY-GLAND; MALE SHEEP; CASTRATED RAMS; PHOTOPERIODIC CONTROL; MELATONIN RECEPTORS; LH-RELEASE; RESPONSIVENESS; ESTRADIOL;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Citazioni:
42
Recensione:
Indirizzi per estratti:
Indirizzo: Tilbrook, AJ Monash Univ, Dept Physiol, Clayton, Vic 3168, Australia Monash Univ Clayton Vic Australia 3168 , Vic 3168, Australia
Citazione:
A.J. Tilbrook et al., "Seasonal changes in the negative feedback regulation of the secretion of the gonadotrophins by testosterone and inhibin in rams", J ENDOCR, 160(1), 1999, pp. 155-167

Abstract

Three experiments were conducted with castrated Romney Marsh rams (wethers) to investigate the ability of testosterone and inhibin to suppress the secretion of LH and FSH during the breeding and the non-breeding seasons. In Experiment 1, wethers (n=5/group) were treated every 12 h for 7 days with oil of 16 mg testosterone propionate (i.m.) and were then given two i.v. injections either of vehicle or of 0.64 mu g/kg human recombinant inhibin A (hr-inhibin) 6 h apart. Blood samples were collected for I h before inhibin or vehicle treatment and for 6 h afterwards for the assay of LH and FSH. In Experiments 2 and 3 wethers underwent hypothalamo-pituitary disconnection (HPD) and were given 125 ng GnRH i.v. every 2 h. In Experiment 2, HPD wethers (n=3/group) were injected (i.m.) every 12 h with oil or testosterone and blood samples were collected over 9 h before treatment and 7 days after treatment. In Experiment 3, HPD (n=5/group) wethers were treated with vehicle or hr-inhibin, as in Experiment 1, after treatment with oil, or 4, 8 or 16 mg testosterone twice daily for 7 days. Blood samples were collected over 4h before treatment with vehicle or hr-inhibin and for 6 h afterwards. Treatment of wethers with testosterone (Experiment 1) resulted in a significantdecrease in the plasma concentrations of LH and number of LH pulses per hour but the magnitude of these reductions did not differ between seasons. Testosterone treatment had no effect on LH secretion in GnRH-pulsed HPD wethers in either season and treatment with hr-inhibin did not affect LH secretion in wethers or HPD wethers in any instance. Plasma concentrations of FSH were significantly (P<0.05) reduced following treatment with testosterone alone during the breeding season but not during the non-breeding season. FSHlevels were reduced to a greater extent by treatment with hr-inhibin but this effect was not influenced by season. During the non-breeding season, the effect of hr-inhibin to suppress FSH secretion was enhanced in the presence of testosterone. These experiments demonstrate that the negative feedback actions of testosterone on the secretion of LH in this breed of rams occurs at the hypothalamic level and is not influenced by season. In contrast, both testosterone and inhibin act on the pituitary gland to suppress the secretion of FSH and these responses are affected by season. Testosterone andinhibin synergize at the pituitary to regulate FSH secretion during the non-breeding season but not during the breeding season.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 28/09/20 alle ore 22:01:49