Are ovarian steroids required for ovum maturation and fertilization? effects of cyanoketone on the in vitro perfused rabbit ovary

An isolated perfused rabbit ovary preparation was used to determine the effects of cyanoketone, a potent inhibitor of 3β-hydroxysteroid dehydrogenase, on ovulation, ovum maturation and fertilizability, and steroid production. In the first experiment, cyanoketone (10^-4 M) was added to the perfusate of one ovary. The contralateral control ovary was perfused with medium alone. Thirty minutes after the onset of perfusion, hCG (50 IU) was added to the perfusate of both ovaries. The ovulatory efficiency of ovaries treated with cyanoketone plus hCG (82.3 ± 4.6%) was similar to that of ovaries treated with hCG alone (84.8 ± 4.4%). No difference was observed in the degree of ovum maturity or degeneration between control and cyanoketone-treated ovaries. Progesterone and estradiol production were significantly reduced by cyanoketone treatment; concentrations in the perfusate of ovaries treated with cyanoketone were 9.7% and 8.0% of the control values, respectively, 2 h after exposure to hCG. The concentration of 17-hydroxypregnenolone was not affected by cyanoketone treatment. Exposure to cyanoketone resulted in a significant (P < 0.005) reduction in the fertilizability of ova ovulated and fertilized in vitro. In the second experiment, the percentage of ova that showed evidence of normal fertilization was significantly (P < 0.025) increased in ovaries perfused with cyanoketone plus estradiol (64.5%) compared to that in ovaries perfused with cyanoketone alone (32.4%). In the third experiment, the addition of progesterone to the perfusate did not affect fertilizability of ovulated ova in ovaries perfused with cyanoketone plus estradiol. These results suggest that the presence of estradiol in the ovarian steroid environment may be essential for fertilizability of ova, but not for the processes of ovulation or meiotic maturation.