The metabolism of estradiol was investigated in postmenopausal women after 4 weeks'
treatment with oral or transdermal unopposed estradiol. The urinary excretion of the
metabolites was examined. With both administration routes, 2-hydroxyestrone, the main
A-ring metabolite, and 16α-hydroxyestrone, the main D-ring metabolite, were excreted
in higher amounts than estradiol and estrone. The ratio of 2-hydroxyestrone to 16α-hydroxyestrone
remained the same for both administration routes. It has been suggested that dominance
of D-ring metabolism, i.e. increase of 16α-hydroxyestrone production, is associated
with an increased risk of breast cancer. The present study indicates that neither
oral nor transdermal estradiol substitution shift this ratio to a higher level of
possible risk. Oral estradiol substitution, however, in our study leads to higher
metabolite concentrations which may be regarded as hazardous for women with diseases
favoring D-ring metabolism.
Key words
Estradiol metabolism - Transdermal and oral estradiol replacement therapy - Postmenopausal
women
