Localization of prostaglandin synthase type-1 (PGHS-1) mRNA and prostaglandin synthase type-2 (PGHS-2) mRNA in ovine myometrium and endometrium throughout gestation

Increased prostaglandin production by tissues in the sheep uterus and place nta are thought to be important for the onset of parturition. In the sheep placenta, this is most likely due to increased expression of prostaglandin synthase type-2 (PGHS-2) rather than prostaglandin synthase type-1 (PGHS-1) . However, there is no information concerning expression of PGHS isoenzymes in maternal uterine tissues during pregnancy. Therefore, the purpose of th e present study was to examine the expression of PGHS-1 and PGHS-2 in the s heep myometrium and endometrium during late gestation using in situ hybridi zation and immunohistochemistry. Using S-35-labelled oligonucleotide probes , which give specific hybridization signals in other tissues, we localized PGHS-2 mRNA to endometrial epithelium, and apparently to other cells in bot h endometrium and myometrium. This artefactual signal was still present wit h 100-fold excess unlabelled oligonucleotide probe and with sense probes, b ut was resolved with the use of P-33-oligonucleotides. Using P-33-labelled oligonucleotide probes we could not detect either PGHS-1 or PGHS-2 mRNA in myometrium, and found expression only of PGHS-2 mRNA in endometrium. PGHS-2 mRNA localized to the endometrial epithelium and was undetectable in gland ular epithelium. The level of PGHS-2 expression rose significantly between days 80 and 85 of pregnancy and term, and this corresponded to the appearan ce of immunoreactive PGHS-2 protein, measured by immunohistochemistry, in t he endometrial epithelium. Therefore we conclude that P-33-labelled probes are: preferred for detection of mRNAs encoding PGHS-2 in ovine uterine tiss ues. Expression of PGHS-2 mRNA is greater than that of PGHS-1, increases du ring gestation, and predominates in the endometrial epithelium, consistent with the site of PGHS-2 protein localization.