Ovarian oestrogen-dependent maturation of the LH/FSH surge mechanism during prepubertal development in the gilt

Abstract

An involvement of ovarian secretions and in particular oestradiol-17 beta in the maturation of the positive feedback mechanism controlling gonadotrophin surge secretion was studied in prepubertal gilts. The LH/FSH responses to an intramuscular injection of age- and body weight-related doses of oestradiol benzoate (OB) were compared in intact gilts at 60 days of age with or without oestradiol-17 beta pretreatment from 30 to 52 days of age. Four further groups of gilts were challenged with OB at 160 days and were intact, ovariectomized at 60 days, ovariectomized at 60 days and given oestrogen therapy from days 60 to 130 or ovariectomized at 130 days. A significant increase in the magnitude of LH surge responses to OB and a decrease in the time to the first consistent period of surge secretion in intact gilts at 160 compared to 60 days of age confirmed earlier studies and is considered to represent a real maturational change in positive feedback activity. A longer response interval was also present in the majority of ovariectomized gilts. Furthermore a significant reduction in the magnitude of OB-induced LH responses at day 160 occurred in gilts ovariectomized at day 60 compared to those ovariectomized at day 130 and with intact control animals. Oestrogen therapy after ovariectomy at day 60 effectively restored the magnitude of the LH response however. It is concluded that maturation of the positive feedback mechanism is ovarian, and probably oestrogen, dependent.

Gonadotropin Secretion in Ovariectomized Chinese Meishan and Hybrid Large White Gilts; Responses to Challenges with Estradiol Benzoate, Gonadotropin-Releasing Hormone, or Porcine Follicular Fluid1

“…The response of the acutely ovariectomized hLW gilts to an EB challenge was typical in relation to that reported in previous studies with gilts ovariectomized after reaching puberty [18][19][20]. The basis for the acutely ovariectomized MS gilts exhibiting large LH episodes at random intervals before and after treatment with EB, and for generally failing to show unequivocal suppression of LH secretion immediately after EB injection, is uncertain.…”

Ontogeny of pituitary gonadotrophin secretion in the fetal and post-natal pig in response to LHRH in vitro

“…These maturational changes appear to reflect alterations in numbers of gonado¬ tropi« and/or pituitary gonadotrophin content. Evaluation of several publications on the ontogeny of basal plasma LH and FSH concentrations in male (Colenbrander et ai, 1977(Colenbrander et ai, ,1982aAllrich et al, 1982) and female (for review see Christenson et al, 1985) pigs suggests that there is no simple relationship between in-vitro release and in-vivo concentrations of gonadotrophins and that post¬ natal maturational changes in the hypothalamo-pituitary axis, such as the development of the positive oestrogen feedback on LH release in the gilt (see Foxcroft et al, 1984), mainly involve maturation of control mechanisms other than pituitary responsiveness to LHRH.…”

Response of sows to oestradiol benzoate treatment after weaning at two stages of lactation

“…Blood samples were analysed for LH (Foxcroft, Pomerantz & Nalbandov, 1975), FSH and oestradiol-17ß (Foxcroft, Elsaesser, Stickney, Back & Haynes, 1983) and progesterone (Haresign, Foster, Haynes, Crighton & Lamming, 1975) by previously validated radioimmunoassays. Interand intra-assay coefficients of variation (CV) were 12 and 6% and 15 and 4% for LH and FSH respectively.…”