The expression of prostaglandin-E2 and its receptor in the oviduct of Chinese brown frog (Rana dybowskii)

• PGE2, COX-1, COX-2 and EP4 were expressed in oviducts of Rana dybowskii.
• Oviductal PGE2 concentration of Rana dybowskii was correlated with the changes of oviductal mass and histological appearance.
• PGE2 may play an autocrine or paracrine regulatory role in oviductal hypertrophy of Rana dybowskii during pre-hibernation.

The Chinese brown frog (Rana dybowskii) has one special physiological phenomenon, which is that its oviduct expands prior to hibernation rather than in the breeding period. In this study, we investigated the immunolocalization and expression levels of prostaglandin-E2 (PGE2), cyclooxygenase (COX)-1 and COX-2, as well as one of its receptor subtypes 4 (EP4) in the oviduct of Rana dybowskii during the pre-hibernation and breeding period. PGE2, COX-1, COX-2 and EP4 have been observed in glandular and epithelial cells in the breeding period, whereas only in the epithelial cells during the pre-hibernation. Consistently, the protein levels of COX-2 and EP4 were higher in the pre-hibernation as compared to the breeding period, but the diversity of COX-1 was not obvious. In addition, oviductal PGE2 concentration was also significantly higher in the pre-hibernation. These results suggested that prostaglandin-E2 may play an important autocrine or paracrine role in oviductal cell proliferation and differentiation of Rana dybowskii during pre-hibernation.