Relaxin stimulates plasminogen activator secretion by rat granulosa cells in vitro.

Granulosa cells isolated from the ovaries of pregnant mare serum gonadotropin (PMSG)-treated immature rats were cultured with relaxin or FSH. Both hormones increased the secretion of plasminogen activator into the culture medium. Relaxin caused a dose-related rise in plasminogen activator but did not increase cAMP or progesterone levels in the medium of freshly harvested granulosa cells, although they were responsive to FSH. This ability of relaxin to stimulate plasminogen activator synthesis without progesterone or cAMP rises indicates that the pathways of post-receptor events leading to stimulation of plasminogen activator differ markedly from those of the gonadotropins. Relaxin is thus a fully characterized peptide hormone produced by the ovary with a well-defined action upon the granulosa cell and may have an intraovarian role in the events leading to ovulation.