RESUMEN
<p><b>OBJECTIVE</b>To observe the effect of the estrogen on the mRNA expression of osteoprotegerin (OPG), osteoclast differentiation factor (ODF) and macrophage colony stimulating factor (M-CSF) in bone tissue of ovariectomized rats, and investigate the possible pathway of estrogen in preventing and treating postmenopausal osteoporosis. METHODS; Thirty healthy adult SD rats were randomly divided into sham operation group, ovariectomized group and estrogen-treated group. All rats were ovariectomized except those in the sham operation group. Bone density of the L3-L6 vertebra was detected 12 weeks after the operation. The total RNA were extracted from the femur to examine mRNA expression of OPG, ODF and M-CSF by real-time PCR.</p><p><b>RESULTS</b>Estrogen increased the bone density of the ovariectomized rat lumbar vertebra and up-regulated the expression of OPG, whereas down-regulated the expression of M-CSF and lowered ODF:OPG ratio.</p><p><b>CONCLUSION</b>The effect of estrogen in treating postmenopausal osteoporosis is closely correlated with the regulation of OPG and M-CSF expressions and ODF:OPG ratio.</p>