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

L. A. C. Sesti, J. H. Britt
1993 Reproduction  
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 \m=+-\ 1.2 versus 0.2 \ m=+-\ 0.1 and 1.5 \m=+-\ 0.8, respectively). Concentrations of LH, FSH and oestradiol in serum during 90 h before slaughter were
more » ... reater (P < 0.05) in weaned sows and lactating sows killed on day 28 than in lactating sows killed on day 14 (LH: 0.72 \ m=+-\ 0.3 and 0.68 \ m=+-\ 0.3 versus 0.45 \ m=+-\ 0.2 ng ml-1; FSH: 39.3 \ m=+-\ 2.7 and 57.3 \ m=+-\ 4.0 versus 28.8 \ m=+-\ 1.6 ng ml-1; oestradiol: 10.9 \m=+-\ 1.6 and 5.6 \ m=+-\ 0.7 versus 2.7 \ m=+-\ 0.2 pg ml-1, respectively). Weights of anterior pituitaries did not differ among groups, but concentrations of LH in anterior pituitaries increased (P < 0.05) and concentrations of FSH in pituitaries tended to increase although the increase was not significant (P < 0.10) from day 14 to day 28 of lactation, whereas pituitary concentrations of gonadotrophins in weaned sows were intermediate (LH: 0.45 \ m=+-\ 0.2, 0.94 \ m=+-\ 0.2 and 0.65 \ m=+-\ 0.1 mg g-1; FSH: 8.7 \ m=+-\1.2, 13.8 \ m=+-\ 2.6 and 10.9 \m=+-\1.2 mg g-1 for day 14 lactating, day 28 lactating and weaned groups, respectively). Content of GnRH in the preoptic area, and medial basal hypothalamus did not differ among groups. Content of GnRH in stalk median eminence was lower (P < 0.05) in weaned sows, but was similar among sows killed on day 14 or day 28; however, the proportion of residual GnRH released by the stalk median eminence in response to a challenge with K+ in vitro was greater (P < 0.05) for sows at day 14 than for weaned sows and sows at day 28 (21.5 \m=+-\4.5 versus 13.7 \m=+-\2.8 and 7.0 \m=+-\ 1.6%, respectively), indicating an increase in rate of release of GnRH in vivo and a consequent stimulation of synthesis and release of LH and FSH. These results are consistent with the hypothesis that suckling/lactation alters endogenous rate of GnRH secretion, thereby influencing secretion of gonadotrophins and follicular development.
doi:10.1530/jrf.0.0980393 pmid:8410803 fatcat:j44exftoingcfalbdkhpx3qtdi