RESUMO
Backgroand: In our previous study, it was demonstrated that estradiol-dependent prostaglandin synthesis may be mediated by cAMP elevation during the process of iplantation in rats. The present study was undertaken to investigate if estradio1, a hydrophobic molecule could interact with uterine plasma membrane, thereby influencing adenylate cyclase and cAMP. Methods: The specific binding of [3H]estradiol to plasma membrane prepared from rat uterus has been identified and characterized. Results: The association of [3H]estradiol to plasma membrane preparations reached equilibrium at 24 hrs. [3H]estradiol binding was directly proportional to the concentration of plasma membrane preparations and its binding was temperature-sensitive. This binding was saturable, reversible and binding site was one type with high affinity(Kd=0.16+0.03 nM) and high binding capacity(Bmax= 2.03 + 0.38pmol/mg protein). The dissociation constant was estimated as 1.6*10(-10)M. In a competition assay, binding was specific for estrogenic compounds. When 100% specific binding was detennined in the presence of 3*10(-6) M diethylstilbestrol, 17B-estradiol and tamoxifen displaced specific binding by 115% and 23%, respectively. Neither progesterone nor cortisol at 500-fold excess displaced the specific binding. Conclusion: These data suggest the presence of specific binding sites on the plasma membrane for estradiol in the rat uterus.