Early Events in the Steroidal Regulation of α2u Globulin in Rat Liver

Abstract

1 A double-antibody radioimmunoassay for α_2u globulin has been developed. With the help of this highly sensitive radioimmunoassay the early effects of both androgen and estrogen treatments on the hepatic synthesis of α_2u globulin in the rat have been investigated. 2 Results show that the earlier observation of the long lag period in the androgenic induction of α_2u globulin is more apparent than real. 3 Single injections of either 5α-dihydrotestosterone (5α-dihydro-17β-hydroxy-4-androsten-3-one) or its physiological antagonist estradiol-17β (1,3,5(10)-estratriene-3,17β-diol) to castrated female rats resulted in the induction of α_2u globulin reaching maximum hepatic level of the protein between 6 – 9 h after the hormone administration. Administration of cycloheximide 15 min prior to hormone treatment blocked both androgenic and estrogenic induction of α_2u globulin. 4 Daily pretreatments with 5α-dihydrotestosterone increased the sensitivity of subsequent androgenic response to α_2u globulin synthesis. On the other hand, daily pretreatments with estradiol-17β decreased and ultimately abolished the estrogenic induction of α_2u globulin. 5 The possible mechanism of both androgenic and estrogenic induction of α_2u globulin in rat liver mediated through a sex-hormone-binding protein with dual affinity for both dihydrotestosterone and estradiol has been suggested.