Dynamics of SHBG response to testosterone. Implications upon the immediate biological effect of sex hormones.
The dynamics of the changes in serum concentrations of SHBG to variations in serum testosterone was studied in rabbits. Castration of male rabbits failed to produce changes in SHBG within 2 days but induced a significant increment 2 months later. Administration of 15 mg of testosterone to 5 male castrates produced a rapid decrease in SHBG concentrations from 215 +/- 121 nmol/l before, to 114 +/- 15, 6 h after (mean +/- SD), while 25 mg of the androgen barely changed SHBG levels in 5 females (from 81 +/- 26 to 72 +/- 22). Three of the males and the 5 females showed a tendency to recover basal levels at 24 and 48 h. Since SHBG is a major regulator of the availability of sex hormones to be transported into tissue cells for both biological action and degradation, the rapid changes in serum SHBG induced by testosterone might play a role in controlling its own biological effect. A decrease in SHBG will result in a more effective stimulation in androgen-responsive tissues, but it will also favor a faster interruption of the effect by increasing the rate of degradation. These androgen induced changes in SHBG are apparently different in male and females.
D000818:Animals; D002369:Castration; D013196:Dihydrotestosterone / Q000378:metabolism; D005260:Female; D007700:Kinetics; D008297:Male; D011817:Rabbits; D012737:Sex Factors; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000494:pharmacology*
D012738:Sex Hormone-Binding Globulin; D013196:Dihydrotestosterone; D013739:Testosterone