Passage of postovulatory follicular fluid into the peritoneal cavity and the effect on concentrations of circulating hormones in mares

Reported data were reviewed and reexamined to evaluate the concept that most of the follicular fluid enters the peritoneal cavity at ovulation in mares and transiently alters the circulating concentrations of LH, FSH, estradiol, and inhibin. A transrectal ultrasonographic study supported the hypothesis that the large volume (40–50 ml) of evacuated follicular fluid passes through the infundibular fimbriae into the peritoneal cavity. A spike in circulating inhibin and a decrease in the rate of reduction in circulatory estradiol occurs at ovulation. Simultaneously, a disruption occurs in the increasing concentrations of the ovulatory LH surge and in the FSH surge that begins before ovulation. The concept was further supported by the present finding that the estradiol content of follicular fluid within a few hours before ovulation is equivalent to the amount reported to be needed for a negative effect on LH and for a synergistic negative effect of estradiol and inhibin on FSH.