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Acceleration of Oviductal Transport of Oocytes Induced by Estradiol in Cycling Rats Is Mediated by Nongenomic Stimulation of Protein Phosphorylation in the Oviduct¹

^a Unidad de Reproducción y Desarrollo, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile

ABSTRACT

In order to explore nongenomic actions of estradiol (E₂) and progesterone (P₄) in the oviduct, we determined the effect of E₂ and P₄ on oviductal protein phosphorylation. Rats on Day 1 of the cycle (C1) or pregnancy (P1) were treated with E₂, P₄, or E₂ + P₄, and 0.5 h or 2.5 h later their oviducts were incubated in medium with ³²P-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 E₂ effect by mRNA synthesis or protein kinases A (PK-A) or C (PK-C) was then examined. Rats on C1 treated with E₂ also received an intrabursal (i.b.) injection of -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 ³²P into total oviductal protein induced by E₂ was unchanged by Am, whereas it was completely suppressed by PK inhibitors. Local administration of H-89 was utilized to determine whether or not E₂-induced egg transport acceleration requires protein phosphorylation. Rats on C1 or P1 were treated with E₂ s.c. and H-89 i.b. The number and distribution of eggs in the genital tract assessed 24 h later showed that H-89 blocked the E₂-induced oviductal egg loss in cyclic rats and had no effect in mated rats. It is concluded that E₂ and P₄ 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 E₂ in the oviduct by waiving this nongenomic action as a requirement for E₂-induced embryo transport acceleration.

FOOTNOTES

First decision: 10 January 2001.

¹ This work received financial support from grants of FONDECYT nos. 2990007 and 8980008, the Rockefeller Foundation (RF 98024 no. 98), Cátedra Presidencial en Ciencias H. Croxatto, Laboratorios Silesia S.A., and MIFAB (Millennium Institute for Fundamental and Applied Biology).

² Correspondence: H.B. Croxatto, Unidad de Reproducción y Desarrollo, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Casilla 114-D, Santiago, Chile. FAX: 56 2 222 5515; hbcroxat{at}genes.bio.puc.cl

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