Tissue-specific ontogenic expression of prostaglandin H synthase 2 in the ovine myometrium, endometrium, and placenta during late gestation and at spontaneous term labor

OBJECTIVE: The purposes of this study were to determine (1) whether uterine tissues as well as the fetal placenta are involved in the development of p rostaglandin-synthesizing capacity associated with impending labor in pregn ant sheep and (2) whether the key enzyme of prostaglandin synthesis, prosta glandin H synthase 2, is differentially expressed in the different intraute rine tissues during late gestation and in association with labor. STUDY DESIGN: Myometrium, endometrium, and fetal placenta were removed from ewes at 95 days' gestation, (n = 3), 101 to 110 days' gestation (n = 3), 1 11 to 120 days' gestation (n = 3), 121 to 130 days' gestation (n = 3), 131 to 140 days' gestation (n = 3), and 141 to 145 days' gestation (n = 4) and from ewes in spontaneous term labor at 143 to 147 days' gestation (n = 4). Expressions of prostaglandin H synthase 2 messenger ribonucleic acid and pr otein were determined by Northern blot and Western blot analyses. Prostagla ndin H synthase 2 was localized in the fetal placenta by immunohistochemica l means. RESULTS: Levels of both prostaglandin H synthase 2 messenger ribonucleic ac id and protein increased gradually from 115 days' gestation in the fetal pl acenta and from 131 days' gestation in the endometrium. A further and more significant increase in prostaglandin H synthase 2 concentration occurred i n the placenta and endometrium during spontaneous term labor. In contrast, myometrial concentrations of prostaglandin H synthase 2 messenger ribonucle ic acid and protein remained at steady basal levels during the course of pr egnancy and increased only during labor. Prostaglandin H synthase 2 was loc alized in the trophoblast cells of the fetal placenta. CONCLUSIONS: Tissue-specific ontogenic expression of prostaglandin H syntha se 2 was observed in myometrium, endometrium, and placenta during late ovin e gestation and spontaneous term labor. Fetal placenta and endometrium show ed increased expression of prostaglandin H synthase 2 messenger ribonucleic acid and protein during late ovine gestation, whereas myometrial prostagla ndin H synthase 2 concentration remained low throughout late gestation. Pro staglandin H synthase 2 concentrations in the myometrium, endometrium, and placenta are all upwardly regulated during labor.