Oxytocin and estrogen receptor expression in the myometrium of pregnant relaxin-deficient (Rlx-/-) mice.

Relaxin decreases oxytocin-stimulated rat myometrial contractions in vitro. This study used pregnant relaxin-deficient (Rlx-/-) mice to investigate the interaction between relaxin, oxytocin receptor (OTR), and estrogen receptor (ER) expression in the myometrium. Myometrial OTRs were significantly decreased on gestation day 18.5 in Rlx-/- mice than in Rlx+/+ mice. An increase in ERalpha in Rlx+/+ mice at term was correlated with a decrease in ERbeta, which was not observed in Rlx-/- mice. Treatment of Rlx-/- mice with relaxin had no effect on OTR, LGR7, or ERalpha expression, but it caused a significant decrease in ERbetas.