A double-antibody radioimmunoassay for alpha2mu globulin has been developed. With the help of this highly sensitive radoimmunoassay the early effects of both androgen and estrogen treatments on the hepatic synthesis of alpha2mu globulin in the rat have been investigated. 2. Results show that the earlier observation of the long lag period in the androgenic induction of alpha2mu globulin is more apparent than real. 3. Single injections of either 5alpha-dihydrotestosterone(5alpha-dihydro-17beta-hydroxy-4-androsten-3-one) or its physiological antagonist estradiol-17beta (1,3,5(10)-estratriene-3,17beta-idol) to castrated female rats resulted in the induction of alphamu globulin reaching maximum hepatic level of the protein between 6--9 h after the hormone administration. Administration of cycloheximide 15 prior to hormone treatment blocked both androgenic andestrogenic induction of alpha2mu globulin. 4. Daily pretreatments with 5alphamu-dihydrotestosterone increased the sensitivity of subsequent androgenic response to alpha2muglobulin synthesis. On the other hand, daily pretreatments with estradiol 17beta decreased and ultimately abolished the estrogenic induction of alpha2mu globulin. 5. The possible mechanism of both androgenic and estrogenic induction of alpha2mu globulin in rat liver mediated through a sex-hormone-binding protein with dual affinity for both dihydrotestosterone and estradiol has been suggested.
