Fetal-to-maternal progression of prostaglandin H2 synthase-2 expression in ovine intrauterine tissues during the course of labor

We examined whether spontaneous parturition in sheep was associated with tissue-specific changes in prostaglandin H-2 synthase-2 (PGHS-2) expression and/or with altered expression of myometrial EP and FP receptors, Placental and uterine tissues were collected from three groups of chronically catheterized sheep in relation to term spontaneous labor: late pregnancy, not in labor; early labor; and active labor. Expression of PGHS-2 mRNA and protein was determined by in situ hybridization, Western blotting, and immunohistochemistry. Semiquantitative reverse transcription-polymerase chain reaction was used to assess the presence of and changes in prostaglandin (PG) receptor subtypes. In placenta, PGHS-2 mRNA and protein localized to trophoblast uninucleate cells and tended to increase with early labor. PGHS-2 mRNA and protein localized to endometrial epithelium and to myometrium, where PGHS-2 protein levels rose in active labor tissues, Concentrations of PGE(2) in fetal plasma rose progressively with labor, whereas 13,14-dihydro-15-keto-PGF(2 alpha) in maternal plasma increased significantly only in active labor. Messenger RNA encoding four EP receptor subtypes and FP receptor were present: in myometrium, but levels did not change with labor, We suggest that spontaneous labor in sheep is associated with a progressive increase in PGHS-2 expression in a temporal and tissue-specific manner from trophoblast to maternal tissues, rather than alteration in PG receptor gene expression.