Bioscientifica Proceedings

Abstract unavailable© 1995 Journals of Reproduction and Fertility Ltd...

The physiological mechanisms controlling ovulation rate in mammals involve a complex exchange of endocrine signals between the pituitary gland and the ovary, and a localized exchange of intraovarian hormones between the oocyte and its adjacent somatic cells. The discoveries in sheep of mutations in bone morphogenetic protein 15 (BMP15) and bone morphogenetic protein receptor type IB (BMPR-IB) together with recent findings on the physiological effects of growth differentiation ...

Recent studies have demonstrated that an important component of the positive feedback response to oestradiol in mammals is an action within the central nervous system to induce a large surge in the secretion of gonadotrophin-releasing hormone (GnRH). This oestradiol-induced neuroendocrine signal for ovulation has been best characterized in ewes. The GnRH surge is high in amplitude; the amount secreted increases on average more than 40 times above the pre-surge baseline value. ...

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...

Early follicular growth refers to the development of an ovarian follicle from the primordial to early antral phase. In sheep and cows these phases of growth can be classified by the configuration of granulosal cells in the largest cross–section of the follicle as types 1 (primordial), la (transitory) 2 (primary), 3 and 4 (preantral) and 5 (early antral). Follicles classified as type 1 may be highly variable within each species with respect to number of granulosal cells an...