Reference

Relative binding affinity of anabolic-androgenic steroids: comparison of the binding to the androgen receptors in skeletal muscle and in prostate, as well as to sex hormone-binding globulin

Relative binding affinity of anabolic-androgenic steroids: comparison of the binding to the androgen receptors in skeletal muscle and in prostate, as well as to sex hormone-binding globulin. Saartok, Tonu; Dahlberg, Erik; Gustafsson, Jan Aake (Karolinska Inst., Huddinge Univ. Hosp., Huddinge S-141 86, Swed.). Endocrinology (Baltimore), 114(6), 2100-6 (English) 1984. CODEN: ENDOAO. ISSN: 0013-7227. DOCUMENT TYPE: Journal CA Section: 2 (Mammalian Hormones) When several anabolic steroids were tested as competitors for the binding of 3H-labeled methyltrienolone (MT) [965-93-5] to the androgen receptor (AR) in rat and rabbit skeletal muscle and rat prostate, resp., MT itself was the most efficient competitor. 1a-Methyl-5a-dihydrotestosterone (1a-methyl-DHT) [1424-00-6] bound most avidly to sex hormone-binding globulin (SHBG) [relative binding affinity (RBA) about 4 times that of DHT]. Some anabolic-androgenic steroids bound strongly to the AR in skeletal muscle and prostate [RBAs relative to that of MT: MT >19-nortestosterone [434-22-0] > methenolone [153-00-4] > testosterone (T) [58-22-0] > 1a-methyl-DHT]. In other cases, AR binding was weak (RBA values < 0.05): stanozolol [10418-03-8], methanedienone [72-63-9], and fluoxymesterone [76-43-7]. Other compds. had RBAs too low to be detd.( e.g. oxymetholone [434-07-1] and ethylestrenol [965-90-2]). The competition pattern was similar in muscle and prostate, except for a higher RBA of dihydrotestosterone (DHT) [521-18-6] in the prostate. The low RBA of DHT in muscle was probably due to the previously reported rapid redn. of its 3-keto function to metabolites, which did not bind to the AR [5a-androstane-3a,17b-diol (32-diol) [1852-53-5] and its 3b-isomer (3b-diol) [571-20-0]]. Some anabolic-androgenic steroids (only a few synthetic) bound to SHBG (1a-methyl-DHT >> DHT > T > 3b-adiol > 3a-adiol = 17a-methylT [58-18-4] > methenolone > methanedienone > stanozolol). The ratio of the RBA in rat muscle to that in the prostate (an est. of the myotrophic potency of the compds.) was close to unity, varying only between about 0.4 and 1.7 in most cases. Results indicate that the existence of a putative anabolic receptor distinct from the AR must be questioned, that many anabolic steroids interact with the AR, and that some steroids with anabolic-androgenic activity in vivo do not bind to the AR, and must have an indirect mechanism of action (e.g. via biotransformation to active compds., by influencing the metab. of other steroids, or by displacing them from SHBG).