Expression, localization and function of prostaglandin receptors in myometrium.

Prostaglandins (PGs) play a role in the initiation and maintenance of labor, acting via specific relaxatory or contractile receptors on myometrium. Myometrial response to addition of PGs may be determined by the type and concentration of receptor expressed. Autoradiographic and ligand binding studies suggest a topographic distribution of receptors between fundus, lower segment, and cervix, and that hormonally regulated changes in expression occur with advancing gestation and labor. These receptors have now been cloned and sequenced allowing molecular studies. Current dogma suggests functional regionalization of the pregnant human uterus occurs with the lower segment displaying a contractile phenotype throughout gestation changing to a relaxatory phenotype at labor to allow passage of the fetal head whereas the upper segment has a relaxatory phenotype throughout most of gestation to accommodate the growing fetus and adopts a contractile phenotype for expulsion at labor. Studies to determine the role of PG receptors in this phenomenon are currently underway.