The preovulatory decline in follicular oestradiol is not required for ovulation in the rabbit

Using a method of in vitro perfusion of the rabbit ovary with a chemically defined medium in a recirculation system, normal appearing follicular ruptures occurred following exposure of the ovaries to hCG in vivo (100 IU) or following addition of LH (0.25 microgram/ml of NIH B9) to the perfusate. The addition of oestradiol-17 beta (10 micrograms/ml) to the perfusate did not inhibit these follicular ruptures, although the follicular fluid oestradiol contents were increased more than 100-fold as compared to the control side not receiving the addition of oestradiol. These data suggest that the physiological decline of follicular oestrogen, normally observed in vivo prior to ovulation in the rabbit, is not required as part of the mechanism of ovulation and that normal appearing ovulations can occur even though follicular oestrogen levels are kept artificially elevated.