Follicular steroidogenesis and oocyte maturation after superovulation of goats (Capra hircus) with gonadotrophins

Abstract

Follicles were sampled at three different times after treatment with 1200 iu pregnant mares' serum gonadotrophin (PMSG) or 12 mg ovine follicle-stimulating hormone (FSH), and from untreated control animals. The meiotic status and protein synthesis of the oocyte from each follicle was determined and correlated with the intrafollicular concentration of oestradiol and progesterone. Significantly higher amounts of oestradiol were present in PMSG-treated animals at sponge withdrawal than in FSH-treated and control goats. Twenty hours later, both oestradiol and progesterone concentrations in the PMSG group were higher than those in the FSH group, and were equivalent to control animals at the onset of oestrus. At 18 h after the administration of human chorionic gonadotrophin (hCG), oestradiol decreased markedly in all three treatment groups, whereas progesterone remained significantly higher in PMSG-treated follicles. Although these high concentrations of intrafollicular steroids were associated with a higher incidence of premature condensation of chromatin in oocytes, the two events were not causally related. Moreover, cytoplasmic maturation was not prematurely activated in these oocytes and a changed pattern of protein synthesis was observed in oocytes from all three treatment groups after the hCG injection. Whereas disturbances in follicular steroidogenesis of oestradiol and progesterone occur in vivo in goats superovulated with PMSG, they do not underlie the premature activation of the initial stages of nuclear maturation in oocytes but are associated with normal cytoplasmic maturation.