To examine a potential role for
phytoestrogens in
postmenopausal bone loss, the oophorectomized (OOX) rat model has been used in three studies to investigate the effects of the
phytoestrogens coumestrol,
zearalanol and a mixture of
isoflavones on
estrogen-dependent bone loss. In the studies of
coumestrol and
zearalanol, the rats were allocated to a control group, a
phytoestrogen-treated group (1.5 micromol
coumestrol or 3.1 mmol
zearalanol twice per week, intramuscular) or, in the
coumestrol study, an
estrogen-treated group (28.1 nmol, intramuscular). In the
isoflavone study, the rats were allocated to a control group, an
estrogen treated group or a treatment group that received 131.25 mg of
phytoestrogens per week incorporated into the nonpurified rat diet. Bone mineral density was measured globally and at the spine and femur at base line and 6 wk post-
oophorectomy. In the
coumestrol study, blood and urine samples were collected. Compared with the control group, rats receiving
coumestrol and
zearalanol had significantly reduced bone loss at all sites measured. The
estrogen-treated group had significantly greater bone density than the control and the
coumestrol-treated groups in the spine and global measurements.
Coumestrol reduced urine
calcium excretion and the
bone resorption markers
pyridinoline and
deoxypyridinoline after 1 wk of treatment. Oral
isoflavone phytoestrogens had no effect on oophorectomized rats including bone loss at the dose used. Thus, for the first time, the bioactivity of
coumestrol and
zearalanol in preventing bone loss has been demonstrated in a well-recognized model of
postmenopausal bone loss.