Characteristics of the hypothalamic and hypophyseal cytoplasmic estradiol binding substances. Effects of neontaal castration and testosterone administration.

Some physicochemical characteristics and binding capacities of the cytoplasmic estradiol-receptor complexes of the rat hypophysis and hypothalamus, were determined in intact males and females, neonatal castrated males and neonatal and adult testosterone injected females. By gel filtration and density gradient centrifugation the hormone receptor complexes obtained in vitro, shared the same properties in both tissues. The hydrodynamic radius was estimated to be 60 A, The sedimentation coefficient 8.5 S, the frictional coefficient f/fo was 1.42 corresponding to axial ratio (prolate) of 7.85. The molecular weight was 263 000. The data suggest a highly asymmetric molecule similar to the uterine soluble estradiol-receptor complex. No differences were observed in the hypothalamic binding capacities of diestrous females and adult males. The results expressed as fmol of hormone bound/mg cytoplasmic protein were 2.40 +/- 0.32 and 2.54 +/- 0.26, respectively. For estrous females it was 3.72 +/- 0.44. Neonatal castration or testosterone administration increased significantly the binding activity in adulthood. Adult females treated with testosterone showed the lowest level of the hypothalamic estradiol receptors (1.41 +/- 0.56). No differences were observed in the in vitro titration of the pituitary cytoplasmic estrogen binding sites.