Androgen binding proteins in the anterior pituitary, hypothalamus, preoptic area and brain cortex of the rat

Abstract

The cytosol fractions of the anterior pituitary, hypothalamus, preoptic area and brain cortex of castrated male rats have been found to possess specific androgen binding proteins. The physicochemical characteristics of these binding proteins appear to be very similar. Thus, they were excluded by Sephadex G-100 gel and had a sedimentation coefficient of 6-7S by sucrose gradient centrifugation. The protein nature of the androgen binding components was supported by the fact that protease, but not DNase and RNase eliminated the binding of androgens. In addition, the elimination of the binding by 1 mM p-chloro-mereuriphenylsulfonate (PCMPS) and by heat treatment at 45 C for 30 min indicate that free sulfhydryl groups are necessary for androgen binding and that the proteins are thermolabile. Testosterone, 5alpha-dihydrotestosterone and the antiandrogen Cyproterone acetate were found to possess a much higher affinity than 17beta-estradiol and cortisol for the binding components. Dissociation studies revealed that [3H]testosterone is not easily displaced by unlabeled androgens. In the anterior pituitary, hypothalamus and preoptic area testosterone accounted for the major part of the radioactive material in the total tissue homogenates and also for the greater part of the bound radioactivity 15 min after in vivo administration of [3H]testosterone. [3H]17beta-estradiol accounted for less than 3% of the bound radioactivity under these conditions. If binding of a steroid sex hormone by specific proteins is a prerequisite for the hormonal action, the present study indicates the potential for a direct effect of androgens on the target cells of the anterior pituitary and of the central nervous system