[Changes in % free testosterone and sex-hormone binding globulin during danazol administration]

To clarify the androgen balance on the administration of danazol a study was conducted on the levels of % free testosterone (% free T) and sex-hormone-binding globulin (SHBG) during the therapy and the binding properties of danazol to SHBG and androgen receptor. It was found that danazol displaced testosterone (T) from SHBG and R1881 from androgen receptor, in vitro. During treatment with danazol, levels of % free T were increased about three fold, but in contrast the SHBG concentration were significantly decreased. Similar changes in % free T were observed by computer simulation. These data suggest that the androgenic effects of danazol were the results of increased free T levels by the T-displacing ability of danazol from SHBG. The concentration of SHBG might be reduced as a consequence of increased levels of free T. On the other hand, danazol binding to androgen receptor might partially inhibit the action of excess amounts of free T, because the androgenization during therapy was too weak to compare the levels of free T.