LOCALIZATION AND DEVELOPMENTAL-CHANGES IN PROSTAGLANDIN-H SYNTHASE (PGHS) AND PGHS MESSENGER-RIBONUCLEIC-ACID IN OVINE PLACENTA THROUGHOUT GESTATION

In numerous animal species, increased prostaglandin output by intraute rine tissues occurs in association with parturition, In the sheep, pro staglandin H synthase (PGHS) is particularly important in regulating t his process, and it has been shown recently that the placental content of the inducible form of the enzyme (PGHS-2) increases during the lat ter part of gestation whereas no change occurs in the constitutive for m (PGHS-1). The purpose of the present study was to examine the distri bution of cells containing immunoreactive PGHS-2 and PGHS-2 mRNA in th e ovine placenta throughout the second half of gestation (80-147 days) . Commercially available antisera to PGHS-2 were used for immunohistoc hemistry with paraffin-embedded tissues, and a S-35-labeled oligonucle otide probe specific for PGHS-2 mRNA was used for in situ hybridizatio n on frozen sections. Immunohistochemistry indicated that there was an increase in the placental content of immunoreactive PGHS-2 after 140 days gestation. At term, the PGHS-2 was located mainly in the uninucle ate trophoblast cells in the placentomes. In situ hybridization showed that the distribution of PGHS-2 mRNA was confined to the trophoblasts , with little or no hybridization signal in the maternal endometrium o r the maternal syncytium, Autoradiograms of the sections after in situ hybridization were quantified with a computerized image analysis syst em. There was an increase in the placental content of PGHS-2 mRNA from around 140 days gestation to term, but no change was found in the lev el of PGHS-1 mRNA. These studies indicate that an increase in the expr ession of PGHS-2 occurs in the placental trophoblast tissue near partu rition in the sheep. The increase in PGHS-2 mRNA is probably responsib le for the increase in PGHS-2 protein and PGHS activity that occurs at this time and may contribute to the large increase in prostaglandin p roduction by the ovine placenta at term.