INTRAUTERINE INJECTION OF OVINE INTERFERON-TAU ALTERS ESTROGEN-RECEPTOR AND OXYTOCIN RECEPTOR EXPRESSION IN THE ENDOMETRIUM OF CYCLIC EWES

This study determined the effects of intrauterine injections of recomb inant ovine interferon-tau (roIFN-tau; 2 x 10(7) antiviral units/day) or control proteins (6 mg/day) from day 11 to day 14 post-oestrus (oes trus=day 0) on endometrial expression of receptors for oestrogen, prog esterone and oxytocin in cyclic ewes. Plasma concentrations of progest erone were greater on day 15 in ewes receiving roIFN-tau compared with control proteins (P<0.02, treatment x day). Ewes injected with roIFN- tau had lower endometrial levels of oestrogen receptor mRNA (P<0.10) a nd protein (P<0.01) on day 15 compared with ewes receiving control pro teins. In situ hybridization analysis indicated that oestrogen recepto r mRNA was more abundant in the luminal and glandular epithelium of co ntrol ewes compared with roIFN-tau-treated ewes. Immunoreactive oestro gen receptor was also present in the luminal and glandular epithelium of control, but not roIFN-tau-treated ewes. Endometrial levels of prog esterone receptor mRNA and protein were not different (P>0.10) between control and roIFN-tau-treated ewes. In situ hybridization analyses in dicated that progesterone receptor mRNA abundance was low in endometri al epithelium and stroma of both control and roIFN-tau-injected ewes. Immunoreactive progesterone receptors were present in the endometrial stroma and epithelium of control ewes, but confined to the stroma of r oIFN-tau-treated ewes. Oxytocin receptor density was lower (P<0.10) in the endometrium of ewes injected with roIFN-tau than control proteins ; however, oxytocin receptor affinity was not affected (P>0.10) by tre atment. Concentrations of 13,14-dihydro-15-ketoprostaglandin F-2 alpha (PGFM) were not increased by exogenous oxytocin administration in con trol and roIFN-tau-treated ewes on days 10 or 12 post-oestrus. However , on day 14, control ewes responded to oxytocin with increased plasma concentrations of PGFM, whereas ewes receiving roIFN-tau remained unre sponsive to oxytocin. These results indicate that the antiluteolytic e ffects of IFN-tau are to prevent increases in endometrial oestrogen re ceptor mRNA and protein and oxytocin receptor density which abrogates uterine release of prostaglandin F-2 alpha during maternal recognition of pregnancy. IFN-tau may inhibit the synthesis of oestrogen receptor mRNA by a transcriptional or post-transcriptional regulatory mechanis m to suppress oxytocin receptor formation during early pregnancy in ew es.