Objective    To investigate the effect of a reconstructed isoflavone F11 on the breast in ovariectomized rats.     Methods    The ovariectomized rat model was established in female Wistar rats. F11 was injected intraperitoneally once daily for 12 weeks

while normal saline or estrogen (E

2

) were given in the controls. The serum level of E

2

was detected every 4 weeks. Twelve weeks later

all rats were sacrificed by blood letting from femoral artery. The breast tissues were collected and observed histomorphologically. PCNA

ERα and ERβ in rat breast tissues were examined by immunofluorescence and Western blot.     Results    In the ovariectomized rats

F11 increased the serum level of E2 in the early period (4 weeks after administration)

ameliorated breast atrophy

and up

regulated the expressions of ERβ and PCNA

but not the expression of ERα in the breast tissues.     Conclusion    The reconstructed isoflavone F11 presents estrogen activity and ameliorates effectively breast atrophy in ovariectomized rats

which may be related to the increased expression of ERβ.