Ovulation and Ovum Maturation in the Rabbit Ovary Perfused in vitro

Publisher Website
Google Scholar
Abstract
The in vitro-perfused rabbit ovary serves as a useful tool for investigating ovulation. The present study was designed to evaluate the effects of 0, 5, 50, and 100 IU of hCG on ovulatory efficiency, the time interval between hCG administration and follicle rupture, the stage of maturity of ovulated and unovulated ova, the relationship between ovum maturity and time of ovulation, and ovarian edema in both in situ- and in vitro-perfused ovaries. Ovulation did not occur in ovaries without gonadotropin stimulation. Ovulatory efficiency, the percentage of mature follicles that proceed to rupture by 12 h after hCG treatment, was similar after either 50 or 100 IU of hCG (78.7% and 77.9%, respectively) and did not differ in right and left ovaries of the same animal. A dose level of 5 lU of hCG resulted in a significant reduction (P<0.005) in ovulatory efficiency. Ovulation occurred at 6.34 ± 0.14 h after 50 IU of hCG, and 5.90 ± 0.12 h after 100 IU of hCG (P<0.02). Microscopic examination of ova released from unruptured follicles revealed ova at all stages of maturity; however, the shorter the time interval between administration of hCG and follicle rupture, the less mature the ovum. Only those ova released 8 h or more after hCG administration had attained metaphase II. A greater percentage of ova aspirated from unruptured mature follicles were degenerated when compared with ovulated ova (P<0.0001). Comparisons of dry weight and wet weight suggest that ovarian edema observed in the in vitro system is associated with gonadotropin stimulation although perfused ovaries are more edematous than in situ ovaries. These observations suggest that follicle rupture and ovum maturation can proceed independently of one another and further indicate that the in vitro-perfused rabbit ovary preparation can be successfully used to study the mechanism of ovulation.