Autocrine/paracrine action of oxytocin in pig endometrium

Luminal epithelial cells of porcine endometrium are unresponsive to oxytoci n (OT) in vitro although they express the greatest quantity of OT and recep tors for OT in vivo. Therefore, the objective of this study was to determin e if oxytocin acted in an autocrine manner on luminal epithelial cells to s timulate prostaglandin (PC)F-2 alpha secretion. Treatment of endometrial ex plants or enriched luminal epithelial cells with OT antagonist L-366,948 de creased (P < 0.05) basal secretion of PGF(2 alpha). Oxytocin increased (P < 0.01) PGF(2 alpha) secretion from luminal epithelial cells that were pretr eated with 1:5000 or 1:500 OT antiserum for 3 h to immunoneutralize endogen ously secreted OT. However, OT only increased (P < 0.05) PGF(2 alpha) secre tion from glandular epithelial cells when pretreated with 1:500 OT antiseru m. Pretreatment with OT antiserum did not alter the ability of OT to induce PGF(2 alpha) secretion from stromal cells. Medium conditioned by culture o f luminal epithelial cells stimulated (P < 0.05) phospholipase C activity i n stromal cells, indicative of the presence of bioactive OT. Oxytocin was s ecreted by luminal epithelial cells and 33% was released from the apical su rface, These results indicate that luminal epithelial cells secrete OT that acts in an autocrine and/or paracrine manner in pig endometrium to stimula te PCF2 alpha secretion.