Heterogeneity and distribution of estrogen binding sites in guinea pig seminal vesicle

Cytosol fractions from the separated epithelium and fibromuscular stroma of the guinea pig seminal vesicle exhibit two types of [3H] 17 beta-estradiol binding. High affinity, low capacity, estrogen-specific sites are observed in each component. In addition, secondary binding sites with moderate affinity (Kd = 35 nM) and high capacity (500 fmol/mg cytosolic protein) are also observed. In epithelial cytosol, 10 mM sodium molybdate or 1 mM dithiothreitol enhance [3H] 17 beta-estradiol binding to the secondary sites. In stromal cytosol, sodium molybdate is without effect while dithiothreitol completely abolishes binding of [3H] 17 beta-estradiol to the secondary sites. Specificity studies indicate that [3H] 17 beta-estradiol binding to the secondary sites in stromal cytosol is inhibited by estrogens, but not by androgens. In epithelial cytosol estrogenic specificity is not evident. These results demonstrate the existence of [3H] 17 beta-estradiol binding sites in the fibromuscular stroma which are similar to the Type II estrogen binding components present in rat uterus and prostate. The secondary sites in epithelium may in part, represent binding of [3H] 17 beta-estradiol to another steroid hormone receptor present in this tissue component. These results also suggest a possible mechanism which may account for the known sensitivity of the seminal vesicle fibromuscular stroma to estrogen stimulation.