A new exchange procedure for the quantitation of prostatic androgen receptor complexes formed in vivo

A procedure is described for the measurement of rat prostatic androgen receptor saturated in vivo with non-radioactive androgen. While NaSCN alone induces irreversible dissociation (denaturation) of androgen from the receptor, the combination of this chaotropic salt (0.15 M) with sucrose (15%) and sodium molybdate (10 mM) allows the exchange of R DHT with [3H]DHT at 0 degrees C with only minimal receptor denaturation. The validity of the present exchange assay is based on the following: a similar quantity of androgen receptor was detected when binding was measured directly after in vivo treatment with radioactive androgen or indirectly by [3H]DHT exchange after treatment with non-radioactive androgen. Steroid specificity, sedimentation analysis and equilibrium association constants indicated that this exchange assay labels the androgen receptor without interference from other prostatic steroid binding proteins. With this method it is now possible to quantitate not only prostatic androgen receptors bound to androgens in vitro but also hormone-receptor complexes formed in intact animals under the influence of endogenous androgen.