THE INFLUENCE OF POSTOVULATORY AGING ON THE RETARDATION OF MOUSE OOCYTE MATURATION AND CHROMOSOME SEGREGATION INDUCED BY VINBLASTINE

Certain compounds can induce ovulated metaphase I (MI) oocytes. To stu dy if these MI oocytes can overcome this blockage, ICR mice were given human chorionic gonadotrophin and 0.6 mg/kg vinblastine sulfate (VBS) . Their ovulated oocytes were collected at 17, 19, 21, 23 and 25 h lat er. The results showed that the frequencies of MI oocytes decreased, t he proportions of diploid metaphase II (MII) oocytes increased and the frequencies of hyperploid MII oocytes did not significantly differ (P > 0.05) among the five harvest or postovulatory times. We also found that the proportions of MII oocytes exhibiting premature anaphase II a nd premature centromere separation increased with postovulatory ageing , and that these frequencies were consistently higher in controls than in the VBS groups. These findings indicate that some of the oocytes b locked in MI can overcome this inhibition and produce primarily diploi d MII. oocytes. The ultimate fate of ovulated MI and diploid oocytes o n aneuploid production hinges upon the formation of a functioning meio tic spindle, which is affected by both dosage and the specific chemica l.