Examination of the role of calcium in ovulation in the in vitro perfused rabbit ovary with use of ethyleneglycol-bis(beta-aminoethyl ether)-n,n'-tetraacetic acid and verapamil.

The in vitro perfused rabbit ovary preparation was used to examine the role of calcium in the ovulatory process. Two groups of rabbits were studied. In the first group, verapamil hydrochloride (10(-4) mol/L), a calcium channel blocker, was used together with human chorionic gonadotropin (50 IU) in the perfusate. Verapamil had no apparent effect on human chorionic gonadotropin-induced ovulation. Verapamil treatment, however, significantly reduced the percentage of ovulated ova that were mature (68.8%) in comparison to ovulated ova from human chorionic gonadotropin-treated control ovaries (95.0%). In a second experimental group, ethyleneglycol-bis(beta-aminoethyl ether)-n,n'-tetraacetic acid (2.0 mmol/L), a calcium ion chelator, was included in the perfusate with gonadotropin. The ethyleneglycol-bis(beta-aminoethyl ether)-n,n'-tetraacetic acid significantly reduced ovulatory efficiency (16.7% +/- 9.43%) in comparison to that of controls exposed to human chorionic gonadotropin alone (79.5% +/- 11.1%). In addition, ovulation occurred at an earlier time in ovaries perfused with ethyleneglycol-bis(beta-aminoethyl ether)-n,n'-tetraacetic acid; however, only four ovulations occurred in these ovaries. These four ovulated ova were immature, probably reflecting the early time of ovulation. Furthermore, both verapamil and ethyleneglycol-bis(beta-aminoethyl ether)-n,n'-tetraacetic acid blocked ovarian smooth muscle contractions during ovarian perfusion. These data provide additional support for the concept that calcium dynamics influence the processes of ovulation and ovum maturation. Furthermore ovarian smooth muscle contractions do not appear to be essential for ovulation in this model.