[Changes of prostaglandin receptors in myometrium--interaction between steroids and prostaglandins--(author's transl)].

One of the most important actions of prostaglandins (PGs) is contraction of myometrium. On the other hand, the inhibitory action of progesterone(P) on myometrial contraction is well known. The purpose of this study is to elucidate the mechanism of uterine contraction, analyzing the interaction between PGs and steroids on the receptor level. 1) PG receptor in myometrium was increased after the administration of estradiol (E) into castrated rabbits and addition of P and E enhanced the increases of PG receptor. On the contrary, PGF2 alpha in myometrium was decreased by E, but addition of P and E recovered the decrease. 2) P receptor was increased after the injection of PG in the castrated rabbits, but E receptor showed no significant changes in its level. These results suggest that PG acts on myometrium partly through the changes of steroid hormone receptor and vice versa. 3) PGE1 and PGF2 alpha receptor in pregnant rabbits were increased 4 hours after castration. From these results, it becomes clear that the increase of PG receptor and PG synthesis play an important role in the onset of uterine contraction.