Possible involvement of oxytocin and its receptor in the local regulation of prostaglandin secretion in the cat endometrium

Ovarian originated oxytocin (OT) is involved in several reproductive process, amongst them its role in the regulation/modulation of the estrous cycle in several species has been demonstrated. Although the systemic role of endometrial originated prostaglandins (PGs), especially prostaglandin F2α (PGF2α), is equivocal in cats, their possible involvement in the local regulation of uterine events during the estrous cycle is uncertain. We examined the spontaneous and LH-stimulated OT production in cultured luteal cells, the spatial and temporal arrangement of OT receptors (OTR) in a cat endometrium and, finally the effects of OT on PG secretion and prostaglandin-endoperoxide synthase (PTGS2) expression in the feline cultured endometrial cells. Uteri together with ovaries were collected from adult domestic cats (n = 27) at different stages of the estrous cycle, after routine ovariohisterectomy procedures. The endometrial and luteal cells were separated enzymatically. Luteinizing hormone (LH) augmented OT secretion in cultured luteal cells 2-fold compared with control (P < 0.05). Oxytocin receptor was abundantly expressed in different ovarian structure, as well as in uterine tissues collected at early/developing and mid-luteal phase. The secretion of PGF2α by endometrial epithelial cells was increased by OT at a dose 10−7 M (P < 0.001). Atosiban (specific OTR blocker) alone did not affect PG secretion but atosiban in combination with OT abolished the stimulating effect of OT on PGF2α secretion. Oxytocin augmented PGE2 secretion at a dose 10−7 M and 10−6 M in the endometrial stromal cells (P < 0.001). The treatment with atosiban did not abrogated positive effect of OT on PGE2 production in the stromal cells. Effect of OT on PTGS2 mRNA expression, the rate-limiting enzyme in PG production, was examined by Real Time-PCR and PTGS2 mRNA expression was significantly affected by OT in both epithelial and stromal cell cultures (P < 0.01). The present observations have shown that OT is locally produced by the early/developing corpora lutea and that corpora lutea delivered OT may regulate PG secretion in a cat endometrium especially at early- and mid-diestrus, by affecting PTGS2 mRNA expression.