Objective      To determine the effect of equol (Eq) on osteoporosis in ovarietomized rats.       Methods      Ovariectomized female SD rats were employed to establish a model of osteoporosis. Three-month-old healthy female SD rats were randomly divided into 5 groups

that is

sham-operation group (sham)

ovariectomized group (OVX)

OVX and high-dose of Eq [0.5 mg/(kg·d)] group

OVX and low-dose of Eq [0.25 mg/(kg·d)] group

OVX+estradiol (E2) positive control group. In 8 weeks after ovariectomization

all rats were treated as described above through intraperitoneal injection for another 8 weeks. The bone mineral density (BMD)

blood calcium

phosphorus and osteocalcin content were detected. Moreover

the levels of serum estrogen (ES)

osteoprotegerin (OPG)

and receptor activator of nuclear factor kappa B ligand (RANKL) were measured by ELISA. The expression of OPG and RANKL at mRNA level were determined by qRT-PCR.       Results      Compared with the sham group

the levels of ES

BMD and serum calcium were significantly decreased (P0.05) in the OVX group

respectively

which were 78.1%

84.4% and 83.2% of sham group

respectively. Meanwhile

the levels of serum phosphorus and bone gla protein (BGP) in OVX group were notably increased (P0.05) compared to the sham group

indicating the osteoporosis model was successful. Eq and E2 markedly induced the mRNA and protein expression of OPG and inhibited RANKL protein and mRNA expression

and thereby

enhanced the levels of BMD and serum calcium

and reduced the content of serum phosphorus and BGP in OVX rats (P0.05).       Conclusion      Eq could improve osteoporosis in ovariectomized rats possibly through enhancing OPG secretion and inhibiting RANKL secretion.