UP-REGULATION OF OXYTOCIN RECEPTOR MESSENGER-RIBONUCLEIC-ACID AND PROTEIN BY ESTRADIOL IN THE CERVIX OF OVARIECTOMIZED RAT

Oxytocin receptor (OTR) regulation has been extensively studied in ute rine myometrium and endometrium. However, studies in the cervix are li mited. The present studies utilized in situ hybridization and immunocy tochemistry to localize OTR mRNA and protein distribution in cervices of nonpregnant ovariectomized (OVX) rats and examined the effect of co mbined and independent treatments with estradiol and progesterone on c ervical OTR. Thirteen nonpregnant rats were bilaterally OVX under gene ral anesthesia. At least 7 days later, the rats were exposed to one of four different treatments 24 h prior to necropsy: 1) estradiol (50 mu g, n = 4); 2) progesterone (10 mg, n = 3); 3) both estradiol (50 mu g ) and progesterone (10 mg) (n = 3); 4) corn oil vehicle (n = 3). After 24-h estradiol treatment, OTR mRNA increased significantly (p < 0.05) in smooth muscle cells of the rat cervix as a result of increased cop y numbers of OTR mRNA per cell as well as an increased population of O TR mRNA-positive cells. Progesterone alone had no effect on OTR mRNA e xpression; however, progesterone combined with estradiol significantly inhibited the up-regulation of OTR mRNA by estradiol alone. The incre ase of OTR mRNA in cervical epithelial cells was minimal in all situat ions. Intensity of cervical OTR immunostaining in both the epithelial cells and cervical smooth muscle cells was also elevated after estradi ol treatment. The anti-rat OTR antiserum used for immunocytochemistry was validated by Western blot analysis. In conclusion, OTR and OTR mRN A were localized in smooth muscle cells and in epithelial cells of rat cervix. Estradiol-dependent activation of OTR gene expression and act ive OTR synthesis in smooth muscle cells account for the increased OTR level in rat cervix in vivo, in which progesterone acted as an antago nist of estradiol on OTR gene expression.