Ovarian changes during the first spontaneous ovulation in intact and indomethacin treated rats

Ovarian events during first spontaneous ovulation were studied and compared with those during later ovulations in adult rats. During the period of ovulation, from 24.000 hours to 04.00 hours, the pubertal ovaries showed, probably because of disappearance of marked interstitial oedema, a decrease in weight not observed in the adult animals. The preovulatory follicles showed prior to ovulation a similar increase in size in the pubertal and the adult animals. However, in the pubertal animals follicles were smaller and showed characteristic structural features. A group of pubertal rats received indomethacin (2.5 mg/rat) at prooestrus. This treatment reduced the increase in ovarian weight normally developing in the period before onset of ovulation, 17.00 hours at 24.00 hours. Indomethacin caused furthermore a greater increase in size of the preovulatory follicles during this same period and led to ovulatory processes at which only few eggs left the ovaries, the majority either remaining trapped in the follicles or being released into the ovarian stroma.