1) Estradiol showed the pregnancy period prolonging effect and the inhibitory effects on mechanic and electric activities of myometrium in vitro. Those inhibitory effects of estradiol could not be explained by the change of resting potentials of myometrial cells, but by the suppression of the ACh binding with depot protein and receptor.
2) Estradiol inhibited the accelerating effect of oxytocin on the binding of ACh with depot protein and receptor. These fact coincide with the inhibitory effect of estradiol on myometrial contractions induced by oxytocin.
3) Considered from the standpoint of ACh, the accelerating effect of estradiol on myometrial contractions may depend on the increase of myometrial ACh after administration of estradiol.
4) In conclusion, it is emphasized that estradiol has two functional faces to accelerate and inhibit myometrial contractions.
