Bioscientifica Proceedings

Transport of post-partum cows or sheep before an oestradiol-induced LH surge delayed gonadotrophin secretion possibly by affecting hypothalamic activity but not via an opioid mediated mechanism as the effect could not be reversed by naloxone. In addition, reduced LH responses to GnRH were observed in cattle during transport. In sheep, adrenocorticotrophic hormone (ACTH) also diminished the LH response to GnRH, but only when GnRH was administered 3 h after ACTH, not after 0.5 h...

Stress influences the activity of the reproductive system at several sites. One of the most significant effects is at level of the GnRH secretory system to reduce GnRH pulsatility and thus LH pulsatility. This in turn reduces the oestradiol signal that stimulates the GnRH–LH surge in the follicular phase. Three sequential phases have been identified in the induction of the GnRH–LH surge by oestradiol: (i) activation, (ii) transmission and (iii) surge secretion. There...