UPTAKE OF RADIOLABELED TESTOSTERONE, 5- a -D I H V D ROTESTOSTE RO N E, EST RA D I0 L, A N D PREGNENOLONE BY CANINE PROSTATE

Twenty-five male dogs received injections into the common sacral artery of labeled testoster one, 5-a-dihydrotestosterone, estradiol, or preg nenolone. No advantage in prostatic percent uptake was achieved by injecting radiolabeled 5-cr-dihydrotestosterone as compared with its “prohormone,â€(cid:157) testosterone. An increase in the specific activity of 5-a-dihydrotestosterone by an order of magnitude was accompanied by a simi br increase in percent uptake. Attempts to in crease the binding capacity or binding affinity by pretreatment with testosterone had no effect. Attempts to desaturate the binding sites of en dogenous androgens by pretreatment with cas tration was without effect. Although the same percent uptake was achieved with labeled es tradiol, the uptake of the common precursor pregnenolone with the same specific activity re sulted in an order of magnitude less uptake in percent dose/gm of prostate. These uptakes were not achieved using the intravenous route of administration.