ESTROGEN FORMATION FROM ANDROSTENEDIONE IN HUMAN BONE

BACKGROUND AND OBJECTIVE Peripheral aromatization of testosterone and androstenedione is the principal source for circulating oestrogens in men and in castrated and post-menopausal women. Since human bone is a target organ for androgens and oestrogens, aromatase activity was assessed in human sponglosa obtained from patients who were undergoing orthopaedic surgery. DESIGN AND PATIENTS In initial experiments for assessing aromatization, oestrogen formation from 1,2,6,7-(3)Handrostenedione was compared with the release of tritiated water from 1 beta-H-3-androstenedione. Since the rates of enzyme activity were similar with the two methods, rates of oestrogen formation were determined under standardized conditions with the tritiated water generation technique in bone specimens obtained from 4 men and 11 post-menopausal women. RESULTS The apparent K-m of the aromatase ranged between 6 and 50 nM (20.4 +/- 3.9; mean +/- SEM), values in the range of those reported for human placental microsomes. The maximum velocity (V-max) of the aromatase activity ranged between 0.14 and 1.23 nmol/g DNA/h. CONCLUSIONS Oestrogens formed in human bone may play a physicological role in steroid hormone action in this tissue.