Relaxin stimulates interstitial collagenase activity in cultured uterine cervical cells from nonpregnant and pregnant but not immature guinea pigs; estradiol-17 beta restores relaxin's effect in immature cervical cells.

Relaxin has been implicated in dilatation of the cervix at parturition. Dilatation of the guinea pig cervix at parturition is mediated by an estrogen-induced degradation of type I collagen by interstitial collagenase (matrix metalloproteinase I, MMPI). This study was designed to test the hypothesis that human recombinant relaxin (hrR) stimulates MMPI activity in cultured guinea pig cervical cells. Primary cervical monolayer cultures from immature, adult nonpregnant, and 50-day-pregnant Hartley guinea pigs were exposed to hrR (1-1000 ng/ml) daily for 3 days in serum-free Dulbecco's Modified Eagle's Medium (DMEM). The effect of priming immature cells with estradiol-1713 (E 2, 10 ' 6 M) daily for 3 days prior to treatment with hrR was also determined. Tissue inhibitors of metalloproteinases were inactivated by reduction, alkylation, and dialysis. MMPI activity at 96 h was assayed via a highly sensitive and specific assay that utilizes 1 3 H]telopeptidefree type I collagen as a substrate. Aminophenylmercuric acetate (0.5 mM) was used to activate latent MMPI. Phenanthroline-1,10 (1 mM), a known inhibitor of metalloproteinases, was used as a blank control. Phorbol-12-myristate-13-acetate (PMA, 103 M), a known stimulator of MMPI biosynthesis, was used as a positive control. The hrR in serum-free DMEM had no significant effect on cell number in nonpregnant, 50-day-pregnant, E 2-primed, or nonprimed immature animals. It stimulated MMPI activity in a dose-dependent manner with a maximum response at 10 ng/ml in nonpregnant (2-fold), 50-day-pregnant (3-fold), and E2-primed immature (3-fold) animals. PMA stimulated MMPI activity in nonpregnant (2-fold), 50-day-pregnant (3-fold), and E2-primed immature (3-fold) guinea pigs. Neither hrR nor PMA had any significant effect on MMPI in immature animals without E 2priming. These findings provide the first direct biochemical evidence that relaxin is involved in cervical dilatation by stimulating interstitial collagenase, a key enzyme involved in this process.