Prostaglandin's (PG's) produced by intrauterine tissues appear to have a major role in the initiation and/or maintenance of parturition. The response and sensitivity of myometrium to PG's may be governed by differential expression of various PG receptors which are part of the superfamily of G protein coupled receptors that have seven transmembrane spanning domains. The response to any particular prostaglandin (e.g. PGE2) may depend on the receptor isoforms and their subtypes expressed at any particular time. Currently there is no comprehensive data on expression of PG receptors in the pregnant myometrium or their hormonal regulation. It is also currently suggested that the pregnant human uterus may show a functional regionalization at term whereby the lower segment relaxes to allow passage of the fetal head, but the upper segment contracts to expel the fetus. This regionalization may be mediated via differential expression of PG receptor isoforms. The cloning and sequencing of these receptors offers the opportunity to study isoforms and subtypes present, their ontongeny throughout gestation and changes with parturition and hormonal manipulation. The overall hypothesis to be tested is that uterine responsivity to prostaglandins is in part regulated by differential expression of contractile and relaxatory PG receptor isoforms in myometrium and that this expression is hormonally regulated in part by estrogen/progesterone. The objectives of the study are (1) to study mRNA and protein expression and localization for contractile FPI, EP1, EP3, and TP and relaxatory IP, EP2, and EP4 receptors in pregnant rat myometrium (day 16 to one day postpartum) and in pregnant animals with hormonal manipulation to alter the endocrine (estrogen/progesterone) milieu at term (day 16 onwards) (2) to study expression and localization of contractile and relaxatory PG receptors in paired upper and lower segment pregnant human myometrial samples obtained either at term or preterm from patients who are or are not in labor (3) to study the cellular localization of PG receptors in myometrium using confocal microscopy on tissue sections and isolated myocytes (4) to determine the response elements in the 5' flanking region of the EP2 gene that determine alterations in expression at term. These studies will provide a comprehensive picture of which receptors are expressed in myometrium, how the expression changes with gestation and the onset of labor and the effect of estrogen/progesterone on this expression. The human studies will also reveal if there is a functional compartmentalization in human myometrium associated with differential expression of PG receptors. The confocal microscopy will provide information on cellular localization of receptors and the promoter analyses will reveal potential regulatory sites for control of expression of uterine receptors at parturition.