Maturation of ovarian follicles after inhibition of ovulation in rats

Abstract

The present investigation was performed to elucidate the mechanism of the initiation of follicular maturation after inhibition of ovulation in rats treated with pentobarbitone sodium at 13.30 h and progesterone at 14.00 h on the day of pro-oestrus (day 0 denotes the day of these treatments). Ovulation was completely inhibited and the next spontaneous ovulation occurred on day 5, the expected day of the next oestrus. Follicular responsiveness to injection of human chorionic gonadotrophin (hCG) indicated that preovulatory follicles at the time of treatment with pentobarbitone and progesterone regressed by 05.00 h on day 2. Maturation of a new set of follicles began from 17.00 h on day 2 and all rats were induced to ovulate by hCG injection by 17.00 h on day 3, the number of oocytes ovulated being comparable to normal ovulation. In the animals receiving pentobarbitone sodium and progesterone treatment, two selective rises in plasma FSH, which had peak levels at 05.00 h on day 1 and 11.00 h on day 2, were observed without a rise in LH. Preovulatory surges of FSH and LH occurred on the afternoon of day 4. These results suggest that the second rise in FSH was induced by regression of Graafian follicles present at the time of treatment with pentobarbitone sodium and progesterone and that this surge of FSH was responsible for initiation of maturation of a new set of follicles destined to ovulate in the subsequent cycle. The mechanism of induction and the role of the first rise of FSH from the night of day 0 to the morning of day 1 cannot be explained at present.

Initiation of ovarian follicular maturation without a surge of FSH in cyclic rats treated with antiserum to LH-releasing hormone

“…This observation is not consistent with previous reports in cyclic rats, in which it was suggested that the periovulatory FSH surge in 4-or 5-day cyclic rats is responsible for follicular re¬ cruitment for the next oestrous cycle (Schwartz, 1974;Welschen & Dullaart, 1976;Sasamoto et al 1977: Hirshfield & Midgley, 1978aHoak & Schwartz, 1980;Hirshfield & DePaolo, 1981;Sasamoto et al 1981;Mizuno et al 1983). However, the development and maturation of Graafian follicles were observed during late pregnancy and lactation without an FSH surge (Richards & Kersey, 1979;Richards, 1980;Taya & Sasamoto, 1981).…”

“…When ovulation is blocked by treatment with pentobarbitone and progesterone, the new wave of follicular maturation and the secretion of oestrogen, deduced from the pattern of changes in uterine weights (Mizuno et al 1983), appears to be similar to those observed in the present experiments. The presence of early atretic follicles on day 1 in rats treated with LHRH-AS or pentobarbi¬ tone and progesterone may exert an inhibitory effect on the initiation of new follicular maturation by inhi¬ biting FSH binding to granulosa cells through the local action of an FSH-binding inhibitor derived from the follicular fluid of large follicles (Darga & Reichert, 1978).…”

“…When ovulation is blocked in rats with a 4-day oestrous cycle by treatment with pentobarbitone and progesterone, a new wave of follicular maturation preceded by a small surge of FSH begins immediately after the regression of the Graafian follicles present at the time of the treatment (Mizuno, Otani, Shirota & Sasamoto, 1983). It has been assumed that this small surge of FSH is responsible for the initiation of matu¬ ration of the new set of follicles destined to ovulate in the subsequent cycle.…”

Pentobarbital and ketamine suppress serum concentrations of sex hormones in the female rat

“…In normal rats, the ovaries secrete predominantly E 2 before ovulation and produce mainly progesterone after ovulation [17]. Mizuno et al [18] reported that ovulation in rats was delayed by 24 h by the administration of pentobarbital early in the afternoon of proestrus. We administered the anesthetics twice at 1 and 2 days to block ovulation completely.…”