Studies on the Hormonal Regulation of Plasminogen Activator Production in the Rat Ovary

When granulosa cells are prepared from rats primed with PMSG, it is possible to induce plasminogen activator (PA) production in vitro with a variety of hormones. We have compared the effects of the gonadotropins FSH and LH on granulosa cells in culture. Although both hormones can induce enzyme secretion, the time courses of their effects are different. Whereas FSH yields a linear increase in PA production starting 2 h after the time of hormone addition, the effect of LH shows a longer lag phase, but it eventually reaches the same degree of stimulation as FSH. Experiments with an inhibitor of prostaglandin (PG) synthesis, indomethacin, and with PGs suggest the following interpretation. Granulosa cells that can produce PA can be directly stimulated by FSH, but only a small fraction of these cells can be induced by LH. However, the population that is responsive to LH begins to produce PGs after hormone treatment, and the PGs can then stimulate the entire population. Cumulus cells, which have few LH receptors, can be induced by FSH and PGs, but not LH. Experiments involving treatment of rats with indomethacin in vivo or treatment of follicles in vitro demonstrate that this compound can suppress PA secretion in the ovary, which may partially explain its ability to inhibit ovulation.