Oestradiol regulation of oxytocin receptor expression in cyclic bovine endometrium

Oestradiol treatment can increase uterine oxytocin receptor expression in vivo. The actions of oestrogen are usually mediated via its receptor, but it also has direct nongenomic effects in some cells. This study investigated the effect of oestradiol and the role of the oestradiol receptor in regulating endometrial oxytocin receptor expression in the bovine uterus. Explant cultures (in triplicate) from late luteal phase non-pregnant endometrium received the following treatments: control (serum-free medium), oestradiol (0.1 and 0.01 mu mol l(-1)), oestradiol (0.1 mu mol l(-1)) with the oestradiol receptor antagonist ICI 182780 (0.5 mu mol l(-1)), and ICI 182780 (0.5 mu mol l(-1)) alone. Explants were collected 12, 24 and 48 h after the start of culture. Oxytocin receptor mRNA expression in the explants was measured by in situ hybridization and oxytocin protein concentrations were measured by autoradiography with the iodinated oxytocin receptor antagonist d(CH2)(5) [Tyr (Me)(2) Thr(4) Tyr NH29]-vasotocin (I-125-labelled oxytocin receptor antagonist). Oxytocin receptor mRNA and protein expression were initially low but spontaneous upregulation occurred in the luminal epithelium between 24 and 48 h (P < 0.01). Oestradiol increased oxytocin receptor mRNA upregulation in the first 24 h (P < 0.05) but the effect on 125I-labelled oxytocin receptor antagonist binding was not significant. ICI 182780 inhibited the oestrogenic effect but had no significant effect on oxytocin receptor mRNA expression when given alone. Ln conclusion, the results showed that oestradiol exerts its effect via the oestradiol receptor. Oestradiol facilitates oxytocin receptor gene transcription by increasing it more rapidly, but spontaneous upregulation of endometrial oxytocin receptor still occurs in the absence of oestradiol.