Uterine and placental expression of canine oxytocin receptor during pregnancy and normal and induced parturition.

Oxytocin (OT) plays an important role as an inducer of uterine contractility, acting together with its receptor (OTR) to increase synthesis of prostaglandins. Although OT is commonly used in the treatment for dystocia and uterine inertia in the bitch, little attention has been paid to the role of OT in mechanisms regulating parturition in the dog, so that knowledge about the expression of OTR in the canine uterus and placenta is sparse. Consequently, the expression and cellular localization of OTR were investigated in canine utero/placental compartments and interplacental sites throughout pregnancy and at normal and antigestagen-induced parturition, by real-time PCR, immunohistochemistry, western blot and in situ hybridization. The utero/placental and interplacental expression of OTR was constant from pre-implantation until mid-gestation, with a significant increase observed at prepartum luteolysis. In antigestagen-treated mid-pregnant dogs, OTR was upregulated in both interplacental and utero/placental samples. Besides clear myometrial signals, cellular localization of OTR was evident in the endometrial surface epithelial, stromal and vascular endothelial cells. Weaker signals were observed in superficial and deep uterine glandular epithelial cells. Placental OTR was localized in maternal decidual cells and capillary pericytes. Finally, OTR was colocalized with the progesterone receptor (PGR) in maternal decidual cells, coinciding with previously reported increased availability of prostaglandins in the foetal part of the placenta during normal and induced parturition. These findings suggest involvement of OTR in the signalling cascade leading to the prepartum release of prostaglandins from the pregnant canine uterus.