AROMATIZATION OF [4-C-14]TESTOSTERONE TO [C-14] ESTRADIOL-17-BETA BY TESTICULAR TISSUE FROM MALE-TO-FEMALE TRANSSEXUALS ON ESTROGEN THERAPY

Abnormality in testicular biosynthesis of sex hormones may accompany o r cause transsexualism. With a view to determine whether the cells of male transsexual testicular tissue possess aromatic cytochrome P-450 a ctivity, homogenates of the tissue from 4 phenotypic male-to-female tr anssexuals (2 Chinese and 2 Malays, aged 23-34 years) with XY karyotyp e who had been on estrogen therapy for 9-17 years until orchidectomy w ere incubated with [4-C-14]testosterone as substrate. Using reverse-is otope dilution analysis, identity was established for [C-14]estradiol- 17 beta. No such metabolite was found in parallel incubations of heat- denatured enzymes. The extent of enzyme-catalyzed conversion was 9.3 x 10(-3) to 3.4 x 10(-2)%. The specific biosynthetic aromatase cytochro me P-450 activity contained in the tissue system can synthesize [C-14] estradiol-17 beta from [4-C-14]testosterone. Elevated aromatic express ion in situ may have important effects on target tissues.