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

Objective: To test the hypothesis that impaired fertility in human patients with high LH concentrations throughout the follicular phase of the menstrual cycle reflects premature maturation of their oocytes. Design: Previous information that resumption of meiosis is induced by lower hCG concentrations than that required for stimulation of follicular rupture was confirmed and used for establishment of a rat animal model in which oocyte maturation and ovulation can be separated experimentally. In further experiments hypophysectomized, pregnant mare serum gonadotropin (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 with no effect on ovulation, were administered with a second injection of an ovulatory dose (4 IU) of hCG, 24 hours later. The ovulated eggs were subjected to IVF. Results: Fertilization and first cleavage in oocytes recovered from our experimental animal model were similar to that observed in control PMSG-primed, either hypophysectomized or intact rats, treated by a single injection of 4 IU of hCG. Conclusions: The extension of the time interval between oocyte maturation and ovulation in the rat does not result in a lower rate of fertilization or a reduced incidence of cleavage. However, an inferior developmental capacity of these embryos cannot be ruled out.