Effects of treatments for induced ovulation with hCG during 96 hours after successive administrations of charcoal-treated porcine follicular fluid (CTPFF) on the ovulation rate and plasma concentration of progesterone (P) in rabbits were examined.
In experiment 1, four does or three does which were injected with 4 ml of CTPFF or saline (control), respectively, at 12-hour intervals for 5 days (10 times) showed no difference in the total number of follices. No large follicles (≥ 2.0 mm in diameter) appeared in ovaries of the treated group, in comparison with their presence in those of the control.
In experiment 2, forty-two does were injected with 4 ml of CTPFF in the same manner as in experiment 1. Thirty-six of them were divided into 6 groups according to the number of hours from the final administration of CTPFF to hCG injection-12, 24, 36, 48, 72 and 96 hours. The number of ovulations in six other does which were ovulated by injection of hCG simultaneously with the final administration of CTPFF (group 0F) were significantly lower than those of any other group, and the number increased with interval up to 36 hours from the end of CTPFF treatment to hCG injection. The number of follicles of large size (≥ 2.0 mm in diamter) in ovaries of does in group 12 (12-hour interval) at 4 days after hCG injection was larger than in any other treatment group.
In does of groups 24, 36, 48 and 72, plasma P levels 4 hours after hCG injection were higher than those of the other groups of does. In group 12, P levels at 4 days after hCG injection were higher than those of any other group.
Vulval swelling and coloration receded 1 day after the beginning of CTPFF treatment, and recovered slightly after the end of CTPFF treatment until hCG injection. These results indicate that successive treatments of CTPFF for 5 days during the follicular phase decrease ovulation rate, and the inhibitory effect on ovulation is lost within a short time. Follicle-stimulating hormone levels may rebound within 36 hours after the final administration of CTPFF treatment, because the ovulation rate in group 36 was the highest.