Serum sex hormone binding globulin and testosterone binding after estradiol administration, castration, and their combination in men with prostatic carcinoma.

We measured serum sex hormone binding globulin (SHBG) binding capacity, the index of testosterone binding to SHRG, and the serum concentrations of testosterone, 5 alpha-dihydrotestosterone, and estradiol in 16 patients treated for advanced prostatic carcinoma in order to evaluate the effectiveness of various therapeutic regimes in reducing total and biologically active androgen in blood. Polyestradiol phosphate (Estradurin, 80 mg im as a monthly injection) treatment alone is not as efficient as castration in reducing serum testosterone and 5 alpha-dihydrotestosterone. There was no clear difference between the castration and combination treatment (castration followed by polyestradiol phosphate administration) groups in this respect. It is apparent that Estradurin treatment alone and in combination with castration results in small but significant increases in SHBG binding capacity, whereas this parameter did not alter after castration alone. All three forms of treatment resulted in relatively similar significant increases in the index of testosterone binding to SHBG. The rather mild effect of Estradurin on the parameters measured may be attributable to the binding of the exogenous estradiol to SHBG, which thus greatly reduces its biologic activity. We concluded that castration is clearly more effective in reducing the amount of biologically active testosterone than Estradurin and the combination of these treatments has little influence on further reducing total or biologically active circulating testosterone.