Bioscientifica Proceedings

Summary. In the adult non pregnant ewe the secretion of FSH is sufficient to ensure a continuous growth and development of antral follicles to 3–5 mm size at all times. Further development and increased secretion of oestradiol through the final 72 h to ovulation depends on adequate stimulation by LH. During anoestrus and the luteal phase of the cycle LH pulses occur too infrequently to stimulate sufficient oestradiol to evoke an LH surge. Moreover, during...

Adult reproductive ability is to a large extent determined by the appropriate development of the reproductive axis during fetal life. Studies have investigated the role of the fetal hypothalamus in the ontogeny and regulation of pituitary gonadal function during fetal development in sheep. Using immunocytochemistry, we examined the ontogeny of gonadotroph development in the pituitary of female sheep fetuses. At day 70 of gestation (term = 145 days), only immunopositive LH&...

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

While the role of oestradiol and progesterone in the control of GnRH pulsatile secretion and generation of the preovulatory GnRH surge to induce release of the LH surge has been fully investigated, less attention has been given to changes in the pituitary gland that may sensitize gonadotrophs to switch from pulsatile release to surge release of LH, in particular. Furthermore, in the follicular phase while pulsatile secretion of LH is maximal, FSH secretion is reduced, yet both...

Summary. In the sheep both FSH and LH are necessary for development of large antral follicles. The secretion of FSH is controlled by the negative feedback effect of two ovarian hormones, oestradiol and inhibin, acting at the level of the anterior pituitary. Both are derived from the granulosa cells of large antral follicles which are present in sheep ovaries throughout the oestrous cycle. FSH stimulates growth and mitosis and so the fully differentiated granul...

Summary. Preovulatory follicle growth in the ewe is dependent on FSH although no precise relationship appears to exist between plasma concentrations of FSH and the number of preovulatory follicles which develop or ovulation rate. This may be related to a hitherto unrecognized influence of pulsatile LH on the growth of large follicles. Preovulatory follicle growth is dependent on the presence of basal amounts of LH, but pulsatile LH, while being essential to su...

The Booroola phenotype is associated with a point mutation in the kinase domain of the bone morphogenetic protein receptor 1B (BMPR1B), and is characterized by 'precocious' differentiation of ovarian follicles, leading to the production of large numbers of ovulatory follicles that are smaller in diameter than wild-type follicles. These smaller follicles attain differentiation markers, such as expression of mRNA for P450aromatase and inhibin-ßA subunit, granulosa c...

Abstract. The purpose of this review is to illustrate the critical value of integration of both in vitro and whole animal approaches in order to make real progress in terms of understanding the underlying mechanisms controlling ovarian follicle development and also in utilising domestic ruminants as models for the human in the translational development of interventions to address infertility. In terms of mechanistic aspects, this review concentrates o...