EXPERIMENTAL EXTENSION OF THE TIME-INTERVAL BETWEEN OOCYTE MATURATIONAND OVULATION - EFFECT ON FERTILIZATION AND FIRST CLEAVAGE

Objective: To test the hypothesis that impaired fertility in human pat ients with high LH concentrations throughout the follicular phase of t he menstrual cycle reflects premature maturation of their oocytes. Des ign: Previous information that resumption of meiosis is induced by low er hCG concentrations than that required for stimulation of follicular rupture was confirmed and used for establishment of a rat animal mode l in which oocyte maturation and ovulation can be separated experiment ally. In further experiments hypophysectomized, pregnant mare serum go nadotropin (PMSG)-primed, immature female rats injected with 1.1 IU of hCG, a dose found to induce maturation in 72.9% +/- 6% of the rats wi th no effect on ovulation, were administered with a second injection o f an ovulatory dose (4 IU) of hCG, 24 hours later. The ovulated eggs w ere subjected to IVF. Results: Fertilization and first cleavage in ooc ytes recovered from our experimental animal model were similar to that observed in control PMSG-primed, either hypophysectomized or intact r ats, treated by a single injection of 4 IU of hCG. Conclusions: The ex tension of the time interval between oocyte maturation and ovulation i n the rat does not result in a lower rate of fertilization or a reduce d incidence of cleavage. However, an inferior developmental capacity o f these embryos cannot be ruled out.