Autocrine/paracrine action of oxytocin in pig endometrium

Luminal epithelial cells of porcine endometrium are unresponsive to oxytocin (OT) in vitro although they express the greatest quantity of OT and receptors for OT in vivo. Therefore, the objective of this study was to determine if oxytocin acted in an autocrine manner on luminal epithelial cells to stimulate prostaglandin (PC)F-2 alpha secretion. Treatment of endometrial explants or enriched luminal epithelial cells with OT antagonist L-366,948 decreased (P < 0.05) basal secretion of PGF(2 alpha). Oxytocin increased (P < 0.01) PGF(2 alpha) secretion from luminal epithelial cells that were pretreated with 1:5000 or 1:500 OT antiserum for 3 h to immunoneutralize endogenously secreted OT. However, OT only increased (P < 0.05) PGF(2 alpha) secretion from glandular epithelial cells when pretreated with 1:500 OT antiserum. Pretreatment with OT antiserum did not alter the ability of OT to induce PGF(2 alpha) secretion from stromal cells. Medium conditioned by culture of luminal epithelial cells stimulated (P < 0.05) phospholipase C activity in stromal cells, indicative of the presence of bioactive OT. Oxytocin was secreted by luminal epithelial cells and 33% was released from the apical surface, These results indicate that luminal epithelial cells secrete OT that acts in an autocrine and/or paracrine manner in pig endometrium to stimulate PCF2 alpha secretion.