The steroid hormone dydrogesterone inhibits myometrial contraction independently of the progesterone/progesterone receptor pathway.

Aims: In this study, we aimed to investigate the direct effects of steroid hormones on pregnant myometrial contraction.

Main Methods: The effect of steroids on oxytocin-induced contraction was examined in vitro using pregnant rat or human myometrium. Subsequently, we evaluated whether RU486, a potent progesterone antagonist, influenced the effects of progestin on myometrial contraction.