Abstract: Objective To explore protective effect and mechanism of secoisolariciresinol diglycoside (SDG)on myocardial ischemic-reperfusion injury in ovariectomized rats.Methods Fifty 10-week-old female healthy specific-pathogen-free (SPF) Sprague-Dawley (SD)rats were randomly divided into 2 groups:control and ovariectomized (OVX) according to their weight.The OVX group was then divided into four groups:sham operation (SHAM),myocardial ischemic-reperfusion injury (MIRI),estradiol treated (EST),and SDG treated.The rats of SDG group were gavaged with SDG dissolved in distillation water at the dose of 50 mg/kg,while those of EST group were gavaged with estradiol at the dose of 0.8 mg/kg;the rats in other two groups were treated the same but with only distillation water.Results Compared to the SHAM rats,the MIRI rats showed an increased body weight (275.42±3.40 g),decreased uterus index (0.69±0.36 mg/g),increased serum inflammatory factor levels including tumor necrosis factor α (TNF-α:149.52±17.12 ng/L),interleukin 1β (IL-1β:174.74±15.72 ng/L),and interleukin 6(IL-6:79.53±7.07ng/L),decreased serum nitric oxide(NO:15.67±0.68μmol/L)and myocardial constitutive nitric oxide synthase (cNOS:0.255±0.0690 mgprot).Compared to the MIRI rats,the SDG rats had a decreased body weight (275.42±3.40 g),increased uterus index (1.53±0.31 mg/g),significantly decreased serum inflammatory factor levels including TNF-α (86.10±2.91 ng/L),IL-1β (127.66±8.86 ng/L)and IL-6 (46.63±4.13 ng/L),increased serum NO (46.49±1.32μmol/L)and myocardial cNOS (0.496±0.052 U/mgprot).Conclusion SDG has some protective effect on myocardial ischemic-reperfusion injury in ovariectomized rats and the mechanism of the effect may be related with the decrease of TNF-α,IL-1β,IL-6 and the increase of serum NO and myocardial cNOS.