Autoradiographic localization of steroid binding in human tissue labeled in vitro

A procedure for the rapid preparation of autoradiograms from tissues incubated in vitro with 3H-estradiol is described. Slices of tissue were incubated in culture medium containing 17 nM 3H-estradiol, washed to remove unbound steroid, then processed for thaw-mount autoradiography. Exposure times were generally 3 to 4 weeks. Simultaneous in vitro competition with unlabeled progesterone, dihydrotestosterone, or hydrocortisone had no effect on the distribution or intensity of exposed silver grains, while competition with unlabeled estradiol or moxestrol abolished nuclear localization of silver grains. The exchange of labeled estradiol for bound endogenous estradiol during in vitro incubation of the tissues was demonstrated by a comparison of the pattern of incorporation of 3H-estradiol in tissues previously treated in vivo with unlabeled estradiol versus those not primed. A similar distribution and intensity of silver grains was observed in both the treated and untreated tissue groups. The rationale for the advantages of in vitro steroid autoradiography versus the in vivo technique is discussed.