Differential participation of endothelin receptors in estradiol-induced oviductal egg transport acceleration in unmated and mated rats

Objective: To determine the role of endothelin (EDN) signaling in the estradiol (E₂) nongenomic and genomic mechanism that regulates egg transport in the oviduct. Methods: The effect of the selective agonists of ET_A (BQ610) or ET_B (BQ788) on the E₂-induced egg transport acceleration in unmated and mated rats was compared. Then, the level and distribution of ET_A or ET_B in the oviduct of unmated and mated rats following E₂ treatment was analyzed. Finally, the effect of E₂ on the oviductal release of EDN1 in unmated and mated rats was determined. Results: The intraoviductal E₂ nongenomic pathway required participation of ET_A and ET_B while the E₂ genomic pathway required only ET_A. Furthermore, expression of ET_A and ET_B was present in the oviduct although their levels were similar between unmated and mated rats and following E₂ treatment. On other hand, both EDN receptors were differentially localized in the oviductal cells where ET_A was mainly localized in the apical zone of epithelial cells and in the stroma and muscle while ET_B was localized exclusively in the apical zone of the epithelium. However, mating and E₂ treatment did not affect the localization of these receptors in the oviductal cells. Conclusions: These results indicate that mating influences the role of EDN signaling in the effect of E₂ on egg transport in the rat oviduct. This effect of mating on EDN signaling is not explained by a change in the expression or localization of their receptors along the oviduct. These findings provides the first evidence of an association between mating and EDN in order to modulate a physiological process regulated by E₂ in the mammalian oviduct.