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Titolo:
THYROXINE IS PERMISSIVE TO SEASONAL TRANSITIONS IN REPRODUCTIVE NEUROENDOCRINE ACTIVITY IN THE EWE
Autore:
DAHL GE; EVANS NP; THRUN LA; KARSCH FJ;
Indirizzi:
UNIV MICHIGAN,REPROD SCI PROGRAM,300 N INGALLS BLDG,RM 1101 SW ANN ARBOR MI 48109 UNIV MICHIGAN,REPROD SCI PROGRAM ANN ARBOR MI 48109 UNIV MICHIGAN,DEPT BIOL ANN ARBOR MI 48109 UNIV MICHIGAN,DEPT PHYSIOL ANN ARBOR MI 48109
Titolo Testata:
Biology of reproduction
fascicolo: 3, volume: 52, anno: 1995,
pagine: 690 - 696
SICI:
0006-3363(1995)52:3<690:TIPTST>2.0.ZU;2-6
Fonte:
ISI
Lingua:
ENG
Soggetto:
GONADOTROPIN-RELEASING-HORMONE; NEGATIVE FEEDBACK ACTION; LUTEINIZING-HORMONE; THYROID-GLAND; ESTROUS-CYCLE; LH-SECRETION; SUFFOLK EWE; ESTRADIOL; SUPPRESSION; SHEEP;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
33
Recensione:
Indirizzi per estratti:
Citazione:
G.E. Dahl et al., "THYROXINE IS PERMISSIVE TO SEASONAL TRANSITIONS IN REPRODUCTIVE NEUROENDOCRINE ACTIVITY IN THE EWE", Biology of reproduction, 52(3), 1995, pp. 690-696

Abstract

The observation that circulating thyroxine concentration increases during the breeding season of the ewe, coupled with the finding that thyroid hormones are required for the transition from the breeding seasonto anestrus in this species, led us to test the hypothesis that the transition to anestrus is driven by a rise in circulating thyroxine. Suffolk ewes were thyroidectomized (THX) late in the anestrous season. Thyroxine was then either not replaced or provided at doses that produced nadir, incremental (simulating the seasonal rise), or mildly hyperthyroid concentrations in serum. Additional ewes remained thyroid-intact. To monitor seasonal changes in reproductive neuroendocrine activity, the ewes were ovariectomized and received implants of constant-release silastic capsules containing estradiol. Serum concentrations of LH and thyroxine were determined in samples collected twice weekly. In all groups, LH increased in mid-September, signifying that manipulation of thyroid status did not influence onset of the neuroendocrine breeding season. In thyroid-intact controls, LH decreased to low concentrations in mid-January, marking the neuroendocrine transition to anestrus. As expected, LH remained elevated through the end of the study (April) in THX controls not receiving thyroxine, confirming that the neuroendocrine transition to anestrus is dependent on thyroid hormones. The seasonal decrease in LH was seen in all ewes treated with thyroxine. This decrease in LH was neither advanced in mildly hyperthyroid ewes nordelayed in ewes exposed to low serum concentrations of thyroxine. These results lead to the conclusion that the seasonal increase in circulating thyroid hormone in the ewe does not drive the transition from the breeding season to anestrus. This supports the view that thyroid hormones act permissively to allow the neuroendocrine changes that lead to the seasonal cessation of reproductive activity.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 02/12/20 alle ore 07:18:34