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 1,2,6,7-3H-androstenedlone was compared with the release of trltlated water from 1β-3H-androstenedlone. Since the rates of enzyme activity were similar with the two methods, rates of oestrogen formation were determined under standardized conditions with the trltlated water generation technique In bone specimens obtained from 4 men and 11 post-menopausal women.
RESULTS The apparent Km 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 mlcrosomes. The maximum velocity (Vmax) of the aromatase activity ranged between 0-14 and 1.23 nmol/g DNA/h.
CONCLUSIONS Oestrogens formed in human bone may play a physiological role In steroid hormone action in this tissue.