GROWTH-HORMONE INDUCTION OF RAT GRANULOSA-CELL TISSUE-PLASMINOGEN ACTIVATOR EXPRESSION AND PROGESTERONE SYNTHESIS

The plasminogen activator (PA) system is present in the ovary and appe ars to be involved both in follicular growth and ovulation. Similarly, the growth hormone (GH) has been demonstrated to positively affect so me ovarian activities. Interestingly, GH appears not only as a mediato r of gonadotropin effects, but also as having an independent action of its own on the ovary. In the present study we wanted to investigate i f GH could affect ovarian plasminogen activator (PA) activity and ster oidogenesis. Granulosa cells from immature rats, injected with pregnan t mare serum gonadotropin (PMSG) for inducing follicular growth, were cultured for 24 h with increasing concentrations of GH. A significant dose-dependent increase in tPA activity was observed in the GH-treated cells. This effect was exerted at the mRNA level and the use of cyclo heximide, a protein synthesis inhibitor, suggested that GH did not req uire any other intermediary protein for inducing tPA-mRNA. Furthermore , cAMP levels were not affected by GH treatment. Finally, GH was found to increase progesterone (P) synthesis by granulosa cells. The correl ation between the PA system and ovulation and the importance of a norm al steroidogenesis for the ovarian physiology claim for a key role of GH in the ovarian activities.