Comparison of Specific 17²-Estradiol—Receptor Interactions in the Anterior Pituitary of Male and Female Rats1

Male and female rats, both intact and castrate, were decapitated and fractions of anterior pituitary homogenates were prepared by centrifugation. Sephadex G–200 gel nitration of incubated 105,000 g cytosol samples showed specific binding of 11.4 and 12.8% of added 3H—estradiol to a similar frontally—eluted macromolecular component in male and female samples, respectively, but no 3H—testosterone binding. Sucrose gradient centrifugation patterns showed specific estradiol binding to form an 8S complex; concentration of 8S—bound estradiol, in pmoles/mg cytosol protein, was 0.37 for male cytosol and 0.36 for female cytosol. 3H—Testosterone did not form a detectable 8S complex. Equilibrium dialysis of cytosol samples showed consistently high and constant uptake of estradiol. Extent of high—affinity interaction was calculated after redialysis and gel nitration as 0.12 pmoles/mg cytosol protein. (Endocrinology 92: 322, 1973)