Ovarian follicular fluid concentrations of prostaglandins E2, F2 alpha and I2 during the pre-ovulatory period in pigs.

The concentrations of prostaglandin (PG) E2, PGF2 alpha and PGI2 (measured as 6-oxo-PGF1 alpha) in follicular fluid collected from the ovaries of mature, cycling pigs during the immediate pre-ovulatory period have been estimated by radioimmunoassay. The concentrations of all three prostaglandins were low 24-32 hrs before the expected time of ovulation, with the ratio of the mean concentrations of PGE2, PGF2 alpha and 6-oxo-PGF1 alpha being 0.7:1.1:1.0. The concentration of PGE2 showed a small increase during the next 22 hrs but, in the 2 hr period before the expected time of ovulation, the mean concentrations of PGE2, PGF2 alpha and 6-oxo-PGF1 alpha increased 119-, 11- and 5-fold, respectively, which produced a ratio of these mean concentrations of 14.8:2.2:1.0. One sample of follicular fluid contained the highest concentration of 6-oxo-PGF1 alpha (54.4 ng/ml) yet reported for any tissue from any species, but this concentration was still lower than those of PGE2 (529 ng/ml) and PGF2 alpha (94.6 ng/ml). These results show that prostaglandin concentrations increase in the follicular fluid of mature, cycling pigs in the immediate preovulatory period, with PGE2 being the predominant prostaglandin produced. In "preovulatory" follicles which failed to ovulate, prostaglandin concentrations were at baseline values. The findings in this study are consistent with follicular prostaglandins being essential for ovulation in the pig.