Relationship of secretion of GnRH in vitro to changes in pituitary concentrations of LH and FSH and serum concentrations of LH during lactation in sows

Abstract

The objectives of this study were (1) to determine whether release of GnRH in vitro was related to concentrations of LH and FSH in serum and pituitaries and to oestradiol in serum of sows at mid- or late lactation, and (2) to determine whether weaning at mid-lactation changes concentrations of these hormones from values expected at mid-lactation to values expected at late lactation. Multiparous crossbred sows were killed on day 14 (n = 5) or day 28 (n = 5) of lactation or on day 14 post partum after litters had been weaned on day 10 (n = 5). Blood samples were taken every 6 h for 4 days before sows were killed, and the preoptic suprachiasmatic area, medial basal hypothalamus, stalk median eminence, anterior pituitary and ovaries were collected at slaughter. Sows killed on day 14 after having their litters weaned on day 10 had more (P < 0.01) preovulatory follicles (> 6 mm in diameter) than lactating sows killed on day 14 or 28 (7.0 +/- 1.2 versus 0.2 +/- 0.1 and 1.5 +/- 0.8, respectively). Concentrations of LH, FSH and oestradiol in serum during 90 h before slaughter were greater (P < 0.05) in weaned sows and lactating sows killed on day 28 than in lactating sows killed on day 14 (LH: 0.72 +/- 0.3 and 0.68 +/- 0.3 versus 0.45 +/- 0.2 ng ml-1; FSH: 39.3 +/- 2.7 and 57.3 +/- 4.0 versus 28.8 +/- 1.6 ng ml-1; oestradiol: 10.9 +/- 1.6 and 5.6 +/- 0.7 versus 2.7 +/- 0.2 pg ml-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Fatores ambientais e estimativa de herdabilidade para o intervalo desmame-cio de fêmeas suínas

“…Com o desmame e a ausência de estímulo por parte dos leitões, o mecanismo de retroalimentação, que inibia a liberação de gonadotrofinas durante a lactação, é removido. Desta forma, o crescimento de folículos ovarianos se acelera e os níveis sangüíneos de estrogênio aumentam, estimulando a ocorrência do cio e a descarga de LH, que desencadeia a ovulação (Sesti & Britt, 1993).…”

“…De acordo com Koketsu et al (1996), a diminuição da quantidade ingerida de nutrientes influencia potencialmente o estado metabólico e, portanto, a eficiência reprodutiva da fêmea durante a lactação e após o desmame. Kunavongkrit et al (1983) afirmam que o período para que a involução uterina ocorra é de duas semanas e, segundo Sesti & Britt (1993), nas duas primeiras semanas de lactação, os níveis de LH hipofisário são baixos e insuficientes para estimular a ovulação e a luteinização dos folículos. Assim, um período mínimo de dias em lactação é requerido após o parto para a estabilização do sistema hipotálamo-hipófise-ovário.…”

Agonist-Induced Release of Gonadotropin-Releasing Hormone, Luteinizing Hormone, and Follicle-Stimulating Hormone and their Associations with Basal Secretion of Luteinizing Hormone and Follicle-Stimulating Hormone throughout Lactation in Sows

“…Indeed, in a previous study [1] we reported that GnRH turnover rate, as estimated indirectly by proportion of residual GnRH released in vitro, increased from mid-(Day 14) to late (Day 28) lactation in multiparous sows.…”

“…Tissue concentrations of GnRH, as measured at a single point in time in the hypothalamus (preoptic area, medial basal hypothalamus, and stalk median eminence), do not change during lactation in the pig [1]. LH and FSH in blood are relatively low through the first 3-4 wk of lactation in sows and increase thereafter.…”

“…LH and FSH in blood are relatively low through the first 3-4 wk of lactation in sows and increase thereafter. Pituitary concentrations of LH and FSH have been reported to be lower in early than in late lactation [1][2][3][4][5]. The greater secretion of gonadotropins in late lactation is accompanied by an increase in number of larger follicles (> 6 mm) and greater serum concentrations of estrogens [1,6,7].…”