Estrogen receptor, cyclic adenosine monophosphate, and protein kinase A are involved in the nongenomic pathway by which estradiol accelerates oviductal oocyte transport in cyclic rats

This investigation examined the role of estrogen receptor (ER) on the stimulatory effect of estradiol (E₂) on protein phosphorylation in the oviduct as well as on E₂-induced acceleration of oviductal oocyte transport in cyclic rats. Estrous rats were injected with E₂ s.c. and with the ER antagonist ICI 182 780 intrabursally (i.b.), and 6 h later, oviducts were excised and protein phosphorylation was determined by Western blot analysis. ICI 182 780 inhibited the E₂-induced phosphorylation of some oviductal proteins. Other estrous rats were treated with E₂ s.c. and ICI 182 780 i.b. The number of eggs in the oviduct, assessed 24 h later, showed that ICI 182 780 blocked the E₂-induced egg transport acceleration. The possible involvement of adenylyl cyclase, protein kinase A (PK-A), protein kinase C (PK-C), or tyrosine kinases on egg transport acceleration induced by E₂ was then examined. Selective inhibitors of adenylyl cyclase or PK-A inhibited the E₂-induced egg transport acceleration, whereas PK-C or tyrosine kinase inhibitors had no effect. Furthermore, forskolin, an adenylyl cyclase activator, mimicked the effect of E₂ on ovum transport and E₂ increased the level of cAMP in the oviduct of cycling rats. Finally, we measured PK-A activity in vitro in the presence of E₂ or E₂-ER complex. Activity of PK-A in the presence of E₂ or E₂-ER was similar to PK-A alone, showing that E₂ or E₂-ER did not directly activate PK-A. We conclude that the nongenomic pathway by which E₂ accelerates oviductal egg transport in the rat requires absolute participation of ER and cAMP and partial participation of PK-A signaling pathways in the oviduct.