Rhesus Monkey Oocyte Maturation and Fertilization in Vitro: Roles of the Menstrual Cycle Phase and of Exogenous Gonadotropins1

Our objectives were to improve the efficiency of rhesus monkey oocyte maturation and fertilization in vitro and to determine the influence of menstrual cycle phase and exogenous gonadotropins on these processes. Immature oocytes were recovered from antral follicles of ovaries excised from unstimulated animals (n = 14). The highest yield and quality was associated with oocytes obtained from early follicular phase ovaries, and more of these oocytes underwent germinal vesicle breakdown (GVBD; 55%) and matured to metaphase II (MII; 40%) than did oocytes from late follicular (GVBD, 28%; MII, 9%) or luteal (GVBD, 13%; MII, 10%) phase ovaries. Exogenous human (h) FSH and hLH improved GVBD and MII levels for oocytes recovered from late follicular phase ovaries and increased GVBD, but not MII, for oocytes from luteal phase ovaries. MII levels for oocytes from early follicular phase ovaries were adversely affected. Early follicular phase oocytes underwent GVBD faster and attained MII sooner than did those from either late follicular or luteal phase ovaries. Whereas exogenous gonadotropins did not significantly affect oocyte fertilization, follicular phase oocytes tended to be fertilized at a higher rate (p = 0.07). These results demonstrate that higher maturation levels are obtained with oocytes from early follicular phase ovaries and that gonadotropins influence oocyte performance in a cycle phase-dependent manner.