Localization and steroid regulation of prostaglandin E2 receptor protein expression in ovine cervix

Although prostaglandin E2 (PGE2) has been identified as a central mediator of the cervical ripening process, the mechanisms responsible for PGE2 ripening are still poorly understood, partly because of the lack of information concerning the precise cellular localization and regulation of PGE2 (EP) receptors in the cervix. To provide new insights into the mechanisms of cervical ripening, we used indirect immunofluorescence to localize cervical EP receptor protein expression in ovariectomized ewes and examined the effect of administration of progesterone or estradiol. EP receptors were widely distributed in cervical blood vessels, epithelium of the cervical canal, circular and longitudinal muscles, and stroma. Estradiol replacement decreased EP1 and EP3 receptor protein in blood vessel media (by 23 and 31% respectively, P < 0.05) and decreased EP1 receptor protein expression in the longitudinal muscle layer (by 27%, P < 0.05). Stromal EP1 and EP3 receptor protein expression was also reduced by estradiol (by 29 and 20% respectively, P < 0.05). Progesterone replacement had no significant effect on EP receptor protein expression. The arterial changes would favor PGE2-induced vasodilatation, subsequent edema and leukocyte infiltration during the cervical ripening process whereas the muscular alterations would facilitate smooth muscle relaxation and cervical dilatation. Furthermore, estradiol provoked perinuclear localization of EP3 receptor protein in the longitudinal muscle layer. This latter result suggests that cellular EP receptor localization is regulated by estradiol and that PGE2 may also control smooth muscle contraction and regulate ovine cervical dilatation in an intracrine manner via EP3 receptors.