Effect of Time and Dose of Indomethacin on FoUicular Prostaglandins and Ovulation in the Rabbit*

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Abstract
This study determined specifically when ovarian prostaglandins (PGs) increase during ovulation and how effectively different doses of indomethacin inhibit PGs and ovulation. Rabbit ovarian follicles were removed at hourly intervals after stimulating the animals with hCG (50 IU/kg). The follicles were homogenized in 0.1 M acetate buffer (pH 4.5), and the PGE and PGF in the extracts were measured by RIA. Ovulation rates were determined by calculating the percentage of mature follicles that ruptured after stimulation by hCG. Before hCG, the normal levels of PGE and PGF were 111.1 .+-. 14.7 and 51.0 .+-. 6.6 pg/mg follicle, respectively. By 2 h after hCG treatment, PGE and PGF both increased to 162.6 .+-. 17.0 and 80.6 .+-. 13.3 pg/mg follicle, respectively. Approximately 5 h later, there was a second, sharper increase in both PGs which peaked at 652.6 .+-. 63.5 and 345.4 .+-. 32.3 pg/mg follicle, respectively, 10 h after hCG treatment, i.e. at the expected time of ovulation. We found that regardless of whether indomethacin was given early or late during the ovulation process, this agent significantly reduced follicular PG production within 5 min after its administration. For example, only 5 min after 10 mg/kg indomethacin were administered 8 h after hCG, PGE and PGF dropped from 317.7 .+-. 50.0 and 125.0 .+-. 10.5 pg/mg follicle to 93.3 .+-. 17.4 and 49.3 .+-. 10.5 pg/mg follicle, respectively. Unexpectedly, when graded doses of indomethacin were administered either 1 or 8 h after hCG, there was not a statistically significant correlation between follicular PG levels and ovulation rate. For example when doses of 1.25, 2.5, 5.0 and 10.0 mg/kg indomethacin were given 8 h after hCG, the PGE and PGF levels at the expected time of ovulation (i.e., 2 h later) were always equal to or less than the PG levels in follicles that had not been stimulated by hCG, yet ovulation proceeded at rates of 46.7 .+-. 12.3%, 30 .+-. 7.7%, 14.3 .+-. 9.3%, and 0%, respectively. Therefore, the results raise question about the specific role of PGS in the ovulation process.