Divergent effects of two low-dose oral contraceptives on sex hormone-binding globulin and free testosterone.
The effect of a triphasic combination of ethinyl estradiol and levonorgestrel on the serum concentrations of total testosterone, free testosterone, and sex hormone-binding globulin as measured directly by radioimmunoassay and on the binding capacity of sex hormone-binding globulin was compared with that of a preparation containing ethinyl estradiol and desogestrel. Blood samples were taken on days 6, 11, 21, and 28 of a control cycle, the third cycle of treatment with either ethinyl estradiol-levonorgestrel or ethinyl estradiol-desogestrel (11 volunteers each), the third cycle of a 3-month washout period, and the third treatment cycle after crossover change of the preparations. There was a significant reduction in total testosterone by 16% during treatment with both preparations. Ethinyl estradiol-desogestrel increased the concentration (+175%) and binding capacity (+330%) of sex hormone-binding globulin to a much greater extent than with ethinyl estradiol-levonorgestrel (+92% and +160%). Contrary to this, a significant suppression of non-protein-bound testosterone by 35% was found during treatment with both oral contraceptives. The results demonstrate that an excessive elevation of the levels of sex hormone-binding globulin above the normal range does not cause a corresponding suppression of free testosterone. It is assumed that the decrease in the apparent binding affinity of high sex hormone-binding globulin concentrations to testosterone may be due to protein-protein interactions.
D000328:Adult; D003277:Contraceptives, Oral, Combined / Q000494:pharmacology*; D017135:Desogestrel; D004997:Ethinyl Estradiol / Q000494:pharmacology*; D019304:Ethinyl Estradiol-Norgestrel Combination; D005260:Female; D006801:Humans; D009644:Norgestrel / Q000494:pharmacology*; D009652:Norpregnenes / Q000494:pharmacology*; D011863:Radioimmunoassay; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism*; D013739:Testosterone / Q000097:blood*
D003277:Contraceptives, Oral, Combined; D009652:Norpregnenes; D012738:Sex Hormone-Binding Globulin; D009644:Norgestrel; D013739:Testosterone; D004997:Ethinyl Estradiol; D019304:Ethinyl Estradiol-Norgestrel Combination; D017135:Desogestrel