The expression of melatonin receptors MT1 and MT2 is regulated by E2 in sheep oviduct

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Some of the functions of melatonin in mammals are exerted through its membrane receptors (MRs) and studies have shown that estradiol (E2) might play an important role in regulating the expression of these proteins in female reproductive organs. However, no reports have reported the expression of MRs in the sheep oviduct or whether they are regulated by E2. Thus, herein, we detected the localization of MT1 and MT2 in the sheep oviduct. Moreover, we also investigated the expression pattern of these markers in the ovulating and non-ovulating side of the oviduct in the sheep ampulla and isthmus. Immunohistochemistry analyses revealed that both MT1 and MT2 are mainly expressed on oviduct epithelial cells. Both real-time polymerase chain reaction (qPCR) and western blot analyses showed that MT1 and MT2 genes and proteins are highly expressed on the non-ovulating side of the oviduct ampulla, but not the ovulating side. However, regarding the oviduct isthmus, there were no significant differences between the ovulating and non-ovulating sides. In vitro, 10 ng/ml and 1 µg/ml of E2, as well as 1 µg/ml of E2 combined with 0.1 µg/ml, 1 µg/ml, and 10 µg/ml of ICI182780 (a non-selective estrogenreceptor antagonist), were used to treat oviduct epithelial cells. We found that E2 inhibited the expression of MT1 and MT2 in cultured oviduct cells. Moreover, the inhibitory effect was suppressed by ICI182780. In conclusion, it was demonstrated that MRs are present in the sheep oviduct, and that E2, via the ER pathway, regulates their expression in the oviduct.