The purpose of this study was to adduce further evidence for a paracrine role for human decidual
relaxin (Rlx) in the remodelling of
collagen in the fetal membranes in the peripartal period. The binding of [125I]porcine Rlx to membrane-enriched fractions from fetal membranes as well as from dispersed cells from the fetal membranes was used to demonstrate the presence of specific Rlx receptors. Rlx added in vitro to cultured amnion/chorion cells increased the release of
plasminogen activator and
collagenase into the medium. Rlx had no effect on the release of
beta-glucuronidase. An in vivo correlate of these in vitro results was obtained, the detection of
plasminogen activator and
collagenase in amniotic fluids. The active fraction of
collagenase was increased in amniotic fluids collected after
spontaneous rupture of the membranes. PRL, hCG,
estrogen, and
progesterone added in equimolar amounts to cultured amnion/chorion cells from elective
cesarean sections and normal term deliveries also effected the release of
plasminogen activator and
collagenase. The greatest effects were found in cells from
cesarean section tissue, in terms of the stimulation of
plasminogen activator release by Rlx and PRL and of
collagenase release by
prostaglandin F2 alpha and, to a lesser extent, by Rlx, PRL, and hCG. We conclude that human fetal membranes are targets for a number of
hormones, including the decidual paracrine
hormones Rlx, PRL, and
prostaglandin F2 alpha as well as
estrogen,
progesterone, and hCG. These
hormones act to release or inhibit the
enzymes involved in
collagen breakdown before
rupture of the fetal membranes.