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)