Differential nuclear binding of [3H]testosterone and its metabolites to androgen and estrogen receptors in brain, pituitary, heart, kidney and accessory sex glands of the mouse: an autoradiographic study.

Nuclear binding of [3H]testosterone ([3H]T) was studied by autoradiography in brain and peripheral tissues of normal male mice and androgen receptor (AR) deficient Tfm (testicular feminized) mice at various time points after injection. All tissues examined contain AR and estrogen receptors (ER). Nuclear binding (accumulation of radioactive hormone) was characterized by competition with excess of dihydrotestosterone (DHT) or estradiol (E2) and by inhibition of aromatization (AI). 2 h after injection of [3H]T, nuclear binding is found in certain regions of the forebrain of male and Tfm mice, but only in area postrema of hindbrain and in accessory sex glands of males. In pituitary, heart and kidney no nuclear binding is observed. In brain, except for area postrema, binding is inhibited by competition with E2 or by AI. DHT has no effect. This indicates predominant binding to ER. In the area postrema and in accessory sex glands binding is inhibited by DHT but not by E2, indicating binding only to AR. After [3H]T together with E2 or AI, additional nuclear binding is found in certain regions of the brain and in pituitary, unlabeled after [3H]T alone and after [3H]T with DHT. It suggests binding to AR which becomes detectable by an increased amount of androgen available for AR. Up to 1 h after [3H]T in the brain, binding is detectable at more sites than after 2 h. This additional binding is not suppressible by E2, indicating binding to AR. Since this additional binding is found only within the first hour after injection, a difference in binding to AR between brain and accessory sex glands after [3H]T is suggested.