The involvement of cytokines derived from ovarian and hematopoietic cells have been suggested in the cyclic events of the ovary. In the present study the effects of two cytokines, interleukin-1 beta (IL-1 beta) and IL-2, on ovulation, steroidogenesis, and prostaglandin (PG) production were explored in rat ovaries perfused in vitro. Ovaries of equine CG (20 IU)-primed immature rats were perfused in a recirculating system for 20 h, and samples were taken for analysis of progesterone, estradiol, prostaglandin E (PGE), and PGF2 alpha. The number of ovulations was estimated by counting the number of oocytes released into the ovarian bursae. Unstimulated ovaries did not ovulate, whereas the addition of LH (100 ng/ml) resulted in 3.4 +/- 0.6 ovulations/treated ovary. The addition of human recombinant IL-1 beta (4 ng/ml) induced ovulation (1.6 +/- 0.4) and increased the LH-induced ovulation rate 3-fold (9.8 +/- 0.5). The addition of human recombinant IL-2 (40 ng/ml) did not induce ovulation and did not affect the LH-induced ovulation rate. Ovarian release of progesterone and PGF2 alpha was increased by IL-1 beta, but estradiol and PGE release was not affected. IL-2 did not affect steroidogenesis or PG release. To elucidate whether the IL-1 beta-stimulated ovarian synthesis of PGF2 alpha was crucial for the ovulatory effect of IL-1 beta, experiments were performed in the presence of indomethacin (5 micrograms/ml), an inhibitor of PG synthesis. Indomethacin (5 micrograms/ml) inhibited LH-induced ovulation almost completely (one ovulation in one of the five treated ovaries), but did not affect the IL-1 beta-induced ovulation rate (1.4 +/- 0.2). The number of ovulations in the group treated with LH and IL-1 beta was significantly reduced (3.2 +/- 0.6) in the presence of indomethacin. These data demonstrate that IL-1 beta induces ovulation in the rat ovary, and this effect may be partly mediated by the increased production of the ovulatory mediator progesterone.