Uterine stretch and progesterone action

Progesterone administration reduces the risk of preterm labor in high-risk women with singleton pregnancies but has no effect in women with a multiple pregnancy.

We investigated whether progesterone is able to inhibit stretch-induced gene expression and/or whether stretch in turn inhibits progesterone action, perhaps providing an explanation for the functional progesterone withdrawal associated with human labor.

In a series of in vitro studies using primary cultures of human myometrial cells, we found that preincubation with progesterone did not block stretch-induced ERK1/2 activation and cyclooxygenase-2 mRNA expression. Furthermore, we found that stretch did not alter the ability of progesterone to: 1) modulate progesterone-responsive gene expression; 2) activate a luciferase-linked progesterone response element; or 3) repress IL-1β-driven cyclooxygenase-2 mRNA expression. We did find that stretch reduced the expression of progesterone receptor mRNA via nuclear factor κB activation but that this did not alter myometrial progesterone response.

These data show that progesterone does not inhibit stretch-induced MAPK activation or gene expression, possibly explaining why progesterone is ineffective in the prevention of preterm labor in multiple pregnancy. Although stretch did reduce progesterone receptor expression in a nuclear factor κB-dependent manner, this was not sufficient to inhibit progesterone action, suggesting that it is not responsible for the functional progesterone withdrawal observed with the onset of human labor.