Data/hora: 21/06/2024 23:27:44

Biblioteca(s): | Embrapa Caprinos e Ovinos.
Data corrente: | 01/08/1992
Data da última atualização: | 02/06/2023
Autoria: | MARTIN, G. B.
Título: | Factors affecting the secretion of luteinizing hormone in the ewe.
Ano de publicação: | 1984
Fonte/Imprenta: | Biology Review, v. 59, n. 1, p. 1-87, Feb. 1984.
DOI: | 10.1111/j.1469-185X.1984.tb00401.x
Idioma: | Inglês
Conteúdo: | Abstract: (1) Luteinizing hormone (LH) is secreted as discrete pulses throughout all stages of the reproductive cycle of the ewe, including pre-pubertal, seasonal and lactational anoestrus, and the luteal and follicular phases of the oestrous cycle. Secretion is probably also pulsatile during the preovulatory surge of LH. (2) The secretion of LH is affected by the ovarian steroids, oestradiol and progesterone, both of which act principally to reduce the frequency of the pulses. During the luteal phase the two steroids act synergistically to exert this effect, and during anoestrus oestradiol acts independently of progesterone. Androstenedione secreted by the ovary apparently has no role in the control of LH secretion. (3) The amplitude of the pulses may also be affected by the steroids but there are conflicting reports on these effects, some showing that amplitude is lowered by the presence of oestrogen and others showing increases in amplitude in the presence of oestrogen and progesterone. (4) The secretion of LH pulses is affected by photoperiod, social environment and nutrition. Under the influence of decreasing day-length, oestradiol alone cannot reduce the frequency of pulses and the ewe experiences oestrous cycles. When day-length is increasing, the hypothalamus becomes more responsive to oestradiol which reduces the frequency of the pulses. (5) A hypothetical pheromone secreted by rams can increase the frequency of the LH pulses in anoestrous ewes and thereby induce ovulation, possibly by inhibiting the negative feedback exerted by oestradiol. (6) The relationships between nutrition and reproduction are poorly understood, but it seems likely that the effects of nutrition are mediated partly through the hypothalamus and its control of the secretion of LH pulses. (7) The pulses of LH secreted by the anterior pituitary gland are evoked by pulses of GnRH secreted by the hypothalamus. The location of the centre controlling the GnRH pulses and the neurotransmitter involved are not known.
Palavras-Chave: | Chemical stimuli; Hormônio luteinizante; LH; Oestrous cycle.
Thesagro: | Endocrinologia; Ovino; Reprodução.
Thesaurus Nal: | Endocrinology; Estrous cycle; Ewes; Luteinizing hormone; Preovulatory period; Progesterone; Reproduction; Sheep; Steroid hormones; Steroids.
Categoria do assunto: | L Ciência Animal e Produtos de Origem Animal
Registro original: | Embrapa Caprinos e Ovinos (CNPC)
Exemplares: | CNPC - (7663-1) - ADD - AP - DD -  -  -  - DIS