Specific binding of 5 alpha-androstan-3 beta, 17 beta-diol to protein fraction pituitary cytosol of female rats.

In cytosol fraction obtained from the pituitaries of adolescent female rats a protein was found which showed a specific binding of [3H]5 alpha-androstan-3 beta, 17 beta-diol [( 3H]3 beta-diol). With the aid of Scatchard plot two binding sites were detected showing K'D = 0.21 +/- 0.02 mmol 1(-1) and K"D = 17 +/- 2 nmol 1(-1) with a number of binding sites N' = 3.5 +/- 1 and N" = 28 +/- 4 fmol per mg of total protein, respectively. The data are presented showing the effects of various natural or synthetic estrogens and androgens on such a binding of [3H]3 beta-diol. With the aid of linear sucrose gradient a specific binding of [3H]3 beta-diol was found at 4.0-4.5 S and an unspecific binding at 8.0-8.5 S. Similarly, two fractions were detected with the aid of Sephadex G-200 gel filtration: 1. specific binding fraction approximately in a zone of bovine serum albumin; 2. unspecific binding in a zone of high molecular weight fraction. Specific binding of 3[H]3 beta-diol was decreased to about a half at 3 h after the administration of unlabelled 3 beta-diol in a dose of 100 micrograms kg-1; while it was increased after a daily administration of such a dose for 3 days. However, a dose of 1000 micrograms kg-1 suppressed the specific binding either after a single administration or after daily injections for 3 days.