Studies on the Role of Plasminogen Activator in Ovulation

A quantitative method is described for measuring the amount of plasminogen activator produced by rat ovarian granulosa cells following exposure to hormones in uiuo or in uitro. The results confirm the previously reported observation (Beers, W. H., Strickland, S., and Reich, E. (1975) Cell 6, (387-394) that granulosa cells in uiuo produce increasing amounts of plasminogen activator as the time of ovulation approaches and that the enzyme is produced only by cells obtained from follicles destined to ovulate. Inactive cells can be stimulated in vitro by gonadotropins to produce plasminogen activator. This response is timeand dose-dependent, and results in an increase of intracellular and extracellular enzyme. Studies of the specificity of this response indicate that preparations of follicle-stimulating hormone are much more effective than corresponding preparations of luteinizing hormone. The effect of other pituitary hormones is also presented. Molecules other than gonadotropins are also capable of stimulating the cells to produce the enzyme. Prostaglandins E1 and Ez and analogues of CAMP effectively stimulated the cells to produce plasminogen activator. cGMP and its analogues and prostaglandins F,,, and F,, were without effect as were the six steroids studied. The inactive compounds also did not inhibit the response of the cells to gonadotropins. The granulosa cell plasminogen activator has been analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and has an apparent molecular weight of 75,000. By this and other criteria, the granulosa cell enzyme is similar to one of the species of plasminogen activators obtained from cultures of simian virus 40-transformed rat embryo fibroblasts.