Acceleration of oviductal transport of oocytes induced by estradiol in cycling rats is mediated by nongenomic stimulation of protein phosphorylation in the oviduct
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2001
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Abstract
In order to explore nongenomic actions of estradiol (E,) and progesterone (P-4) in the oviduct, we determined the effect of E-2 and P-4 on oviductal protein phosphorylation. Rats on Day 1 of the cycle (C1) or pregnancy (P1) were treated with E-2, P-4, or E-2 + P-4, and 0.5 h or 2.5 h later their oviducts were incubated in medium with P-32-orthophosphate for 2 h. Oviducts were homogenized and proteins were separated by SDS-PAGE. Following autoradiography, protein bands were quantitated by densitometry. The phosphorylation of some proteins was increased by hormonal treatments, exhibiting steroid specificity and different individual time courses. Possible mediation of the E-2 effect by mRNA synthesis or protein kinases A (PK-A) or C (PK-C) was then examined. Rats on C1 treated with E-2 also received an intrabursal (i.b.) injection of alpha -amanitin (Am), or the PK inhibitors H-89 or GF 109203X, and 0.5 h later their oviducts were incubated as above plus the corresponding inhibitors in the medium. increased incorporation of P-32 into total oviductal protein induced by E-2 was unchanged by Am, whereas it was completely suppressed by PK inhibitors. Local administration of H-89 was utilized to determine whether or not E-2-induced egg transport acceleration requires protein phosphorylation. Rats on C1 or P1 were treated with E-2 s.c. and H-89 Lb. The number and distribution of eggs in the genital tract assessed 24 h later showed that H-89 blocked the E-2-induced oviductal egg loss in cyclic rats and had no effect in mated rats. It is concluded that E-2 and P-4 change the pattern of oviductal protein phosphorylation. Estradiol increases oviductal protein phosphorylation in cyclic rats due to a nongenomic action mediated by PK-A and PK-C. In the abscence of mating, this action is essential for its oviductal transport accelerating effect. Mating changes the mechanism of action of E-2 in the oviduct by waiving this nongenomic action as a requirement for E-2-induced embryo transport acceleration.
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estradiol, kinases, mechanisms of hormone action, oviduct, ovum, progesterone, steroid hormones