Oestrogen formation from androstenedione in human bone.
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 spongiosa obtained from patients who were undergoing orthopaedic surgery.


METHODS
In initial experiments for assessing aromatization, oestrogen formation from 1,2,6,7-3H-androstenedione was compared with the release of tritiated water from 1 beta-3H-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 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 microsomes. 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.
Schweikert
H U
HU
Department of Internal Medicine, University of Bonn, Germany.
Wolf
L
L
Romalo
G
G
D000368:Aged; D000369:Aged, 80 and over; D000735:Androstenedione / Q000378:metabolism*; D001141:Aromatase / Q000378:metabolism*; D001842:Bone and Bones / Q000201:enzymology*; D002855:Chromatography, Thin Layer; D046508:Culture Techniques; D004967:Estrogens / Q000096:biosynthesis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017698:Postmenopause / Q000378:metabolism; D014316:Tritium
D004967:Estrogens; D014316:Tritium; D000735:Androstenedione; D001141:Aromatase