Relaxin increases the release of plasminogen activator, collagenase, and proteoglycanase from rat granulosa cells in vitro.

Relaxin (Rlx) is shown in vitro to increase the release of plasminogen activator (PA) activity from granulosa cells obtained from 28-day-old rats after priming 48 h before with PMSG. Priming with PMSG was essential for the subsequent marked increase in PA by the addition of Rlx to these cells in vitro. Under the same conditions Rlx also increased the release of both total collagenase and total proteoglycanase activities but not of beta-glucuronidase activity. The total collagenase and proteoglycanase activities of control cells are made up of essentially equal amounts of their respective active and latent enzymes. Rlx stimulation increases the amounts of the respective active enzymes while the latent collagenase and proteoglycanase activities are unchanged or decreased, respectively. The enzyme beta-glucuronidase was not stimulated by Rlx and appears not to be involved in follicular proteoglycan degradation. Granulosa cells harvested from preantral follicles responded most to FSH by PA production whereas cells from antral follicles responded more to LH, reflecting the known changes in concentration of FSH and LH receptors on these cells. The release of PA is maximal by all four hormones studied (FSH, LH, prostaglandin E1, and Rlx) on granulosa cells harvested from rats 48 h after PMSG treatment and this suggests that the follicles at this time are a mixture of both preantral and antral stages. The PA response to FSH is lost by 60 h after PMSG at the same time that the response to prostaglandin E1 is maintained at the same level, whereas that to Rlx and LH, although still significantly higher than controls, were decreased. By 70 h after PMSG, postovulatory, the responses to all hormones studied were lost. Thus, the involvement of PA in ovarian connective tissue alterations appears to be greatest in the period of follicular antrum formation rather than just before ovulation. Rlx is one of a number of hormones involved in the sequence of events culminating in follicle connective tissue remodeling as shown by its action on the release of three intrafollicular enzymes.