|
Registro Completo |
|
Biblioteca(s): |
Embrapa Caprinos e Ovinos. |
|
Data corrente: |
06/10/2008 |
|
Data da última atualização: |
03/01/2024 |
|
Autoria: |
FOSTER, D. L.; RYAN, K. D. |
|
Título: |
Endocrine mechanisms governing transition into adulthood in famale sheep. |
|
Ano de publicação: |
1981 |
|
Fonte/Imprenta: |
Journal Reproduction Fertility, v. 30, p. 75-90, 1981. |
|
Idioma: |
Inglês |
|
Conteúdo: |
It is proposed that the first follicular phase in the lamb is initiated when responsiveness to oestradiol inhibition of LH secretion decreases sufficiently to permit the expression of an inherent hourly LH pulse rhythm. The hourly LH pulse rhythm is believed to drive oestradiol production to levels that induce the first LH surge. This hypothesis is based upon several considerations. First, pulsatile LH secretion invariably occurs at low frequencies in immature lambs whereas hourly pulses are manifest in postpubertal lambs and mature ewes during the follicular phase of the oestrous cycle. Second, intravenous administration of LH at hourly intervals to immature lambs results in an increase in follicular size, induction of an LH surge, ovulation and corpus luteum formation. Third, hourly LH pulses will occur in the immature female if the ovaries are removed; the hourly frequency in the immature ovariectomized lamb can be reduced by exogenous oestradiol. Fourth, in the chronically oestradiol-treated ovariectomized lamb, responsiveness to oestradiol inhibition of LH secretion becomes markedly decreased during the pubertal period, and the hourly LH pulse rhythm is expressed. It is further proposed that a minimum body weight and short daylengths are necessary for the reduction in oestradiol negative feedback. With regard to photoperiod, the delay in onset of cyclicity in lambs born in the wrong season (autumn) may be due to retarded maturation or post-maturational seasonal anoestrus. MenosIt is proposed that the first follicular phase in the lamb is initiated when responsiveness to oestradiol inhibition of LH secretion decreases sufficiently to permit the expression of an inherent hourly LH pulse rhythm. The hourly LH pulse rhythm is believed to drive oestradiol production to levels that induce the first LH surge. This hypothesis is based upon several considerations. First, pulsatile LH secretion invariably occurs at low frequencies in immature lambs whereas hourly pulses are manifest in postpubertal lambs and mature ewes during the follicular phase of the oestrous cycle. Second, intravenous administration of LH at hourly intervals to immature lambs results in an increase in follicular size, induction of an LH surge, ovulation and corpus luteum formation. Third, hourly LH pulses will occur in the immature female if the ovaries are removed; the hourly frequency in the immature ovariectomized lamb can be reduced by exogenous oestradiol. Fourth, in the chronically oestradiol-treated ovariectomized lamb, responsiveness to oestradiol inhibition of LH secretion becomes markedly decreased during the pubertal period, and the hourly LH pulse rhythm is expressed. It is further proposed that a minimum body weight and short daylengths are necessary for the reduction in oestradiol negative feedback. With regard to photoperiod, the delay in onset of cyclicity in lambs born in the wrong season (autumn) may be due to retarded maturation or post-maturational seasonal anoestru... Mostrar Tudo |
|
Palavras-Chave: |
Puberdade. |
|
Thesagro: |
Endocrinologia; Estradiol; Oestrus Ovis; Ovino; Reprodução Animal. |
|
Thesaurus Nal: |
Body weight; Endocrinology; Estrus; Follicle-stimulating hormone; Gonadotropin-releasing hormone; Luteinizing hormone; Ovulation; Pharmacology; Pregnancy; Reproduction; Sheep. |
|
Categoria do assunto: |
-- |
|
Marc: |
LEADER 02414naa a2200337 a 4500
001 1533521
005 2024-01-03
008 1981 bl uuuu u00u1 u #d
100 1 $aFOSTER, D. L.
245 $aEndocrine mechanisms governing transition into adulthood in famale sheep.$h[electronic resource]
260 $c1981
520 $aIt is proposed that the first follicular phase in the lamb is initiated when responsiveness to oestradiol inhibition of LH secretion decreases sufficiently to permit the expression of an inherent hourly LH pulse rhythm. The hourly LH pulse rhythm is believed to drive oestradiol production to levels that induce the first LH surge. This hypothesis is based upon several considerations. First, pulsatile LH secretion invariably occurs at low frequencies in immature lambs whereas hourly pulses are manifest in postpubertal lambs and mature ewes during the follicular phase of the oestrous cycle. Second, intravenous administration of LH at hourly intervals to immature lambs results in an increase in follicular size, induction of an LH surge, ovulation and corpus luteum formation. Third, hourly LH pulses will occur in the immature female if the ovaries are removed; the hourly frequency in the immature ovariectomized lamb can be reduced by exogenous oestradiol. Fourth, in the chronically oestradiol-treated ovariectomized lamb, responsiveness to oestradiol inhibition of LH secretion becomes markedly decreased during the pubertal period, and the hourly LH pulse rhythm is expressed. It is further proposed that a minimum body weight and short daylengths are necessary for the reduction in oestradiol negative feedback. With regard to photoperiod, the delay in onset of cyclicity in lambs born in the wrong season (autumn) may be due to retarded maturation or post-maturational seasonal anoestrus.
650 $aBody weight
650 $aEndocrinology
650 $aEstrus
650 $aFollicle-stimulating hormone
650 $aGonadotropin-releasing hormone
650 $aLuteinizing hormone
650 $aOvulation
650 $aPharmacology
650 $aPregnancy
650 $aReproduction
650 $aSheep
650 $aEndocrinologia
650 $aEstradiol
650 $aOestrus Ovis
650 $aOvino
650 $aReprodução Animal
653 $aPuberdade
700 1 $aRYAN, K. D.
773 $tJournal Reproduction Fertility$gv. 30, p. 75-90, 1981.
Download
Esconder MarcMostrar Marc Completo |
|
Registro original: |
Embrapa Caprinos e Ovinos (CNPC) |
|
