Regulation of the rat ovarian plasminogen activator system during follicular development.

Successful ovarian follicular growth and ovulation require controlled and directional proteolytic activity for cell migration and follicular wall rapture. Plasminogen activator (PA) system is known to be involved in tissue remodelling during various physiologic and pathologic processes. PA system comprises two activators (tissue-type, tPA and urokinase-type, uPA), three inhibitors (PAI-1, PAI-2 and protein nexin-I) and one receptor (uPAR). In vivo expression of the PA system during follicular development was studied in the immature female rat. Whereas tPA, PAI and uPAR mRNA expression and protein distribution increased in both granulosa and theca-interstitial layers during follicular maturation and reached maximum levels during the preovulatory period, the opposite was true for uPA. Urokinase PA was highly expressed at early stage of development and markedly decreased prior to the expected time of ovulation. Net secreted PA (PAs) and cell associated PA (PAc) activities were higher in differentiated cells and PAs accounted for 70-80% of the total PA activity in both cell stages of follicular development. Our results suggest that (1) a coordinated expression of ovarian PA system exists during follicular development when granulosa cells undergo transformation from undifferentiated and proliferatively active cells to highly differentiated but mitogenically relatively quiescent ones, and (2) in addition to gonadotropins, several intra-ovarian factors play an important role in the regulation of the ovarian PA system during follicular development. (Abstract shortened by UMI.