Inhibition of oxytocin receptor and estrogen receptor-α expression, but not relaxin receptors (LGR7), in the myometrium of late pregnant relaxin gene knockout mice

This study used relaxin (RLX) gene knockout mice (Rlx(-/-)) to investigate the effects of RLX on myometrial oxytocin receptor (OTR) and estrogen receptor (ER)-alpha gene expression in late gestation. We also characterized the temporal expression of the RLX receptor (LGR7) and demonstrated gene transcripts in the myometrium of Rlx(+/+) and Rlx(-/-) mice. There was a significant (P < 0.05) decrease in myometrial LGR7 gene expression on d 17.5 and 18.5 post coitum (pc) compared with earlier stages of gestation, but no differences between Rlx(+/+) and Rlx(-/-) mice. Myometrial OTR mRNA levels increased at the end of gestation in Rlx(+/+) but not Rlx(-/-) mice. ERα gene expression was up-regulated on d 14.5 pc in Rlx(+/+) mice, with mRNA levels remaining high throughout late gestation. In contrast, ERα mRNA levels were significantly lower in Rlx(-/-) mice on d 14.5 and 18.5 pc. These data show that the increases in myometrial OTR and ERα expression in late pregnant Rlx(+/+) mice were attenuated in Rlx(-/-) mice. The effects of RLX on OTRs are probably mediated via activation of ERα. Finally, RLX receptor expression in the myometrium of Rlx(-/-) mice did not differ from wild-type mice, implying that RLX does not influence expression of its receptor.