Abstract: AIM: To observe the influence of soy isoflavones preconditioning on ischemia/reperfusion injury(IRI) in isolated hearts in rats. METHODS: The ischemia/reperfusion(I/R) model of isolated perfused hearts was established by stopping and reperfusing Krebs-Henseleit (KH) fluid to the hearts of the rats. Forty SD rats were randomly divided into five groups: control group,ischemia/reperfusion group (I/R),three SI treatment groups(L-SI,M-SI,H-SI).0.5%CMC-Na were given in I/R group,SI 30,60,120 mg·kg^-1·d^-1 were given in L-SI,M-SI,H-SI groups.After 15 days, the changes of maximal rate of the pressure(+LVdp/dt_max) increase,maximal rate of the pressure(-LVdp/dt_max) decrease, left ventricular developed pressure(LVDP), left ventricular end-diastolic pressure (LVEDP)of heart, and rate-pressure product (RPP) were observed and analysis. The ultrastructure of heart cells were oberserved by electron micronscopy. RESULTS: Compared with control group,the level of LVEDP was increased obviously in I/R group(P＜0.01), the levels of LVDP,+dp/dt_max, -dp/dt_max,RPP were decreased (P＜0.05,P＜0.01). Compared with I/R group, the level of LVEDP was decreased obviously in M-SI group(P＜0.01), the level of RPP was increased(P＜0.05). Compared with I/R group, the levels of LVDP,+dp/dt_max, -dp/dt_max were increased in H-SI group(P＜0.05,P＜0.01). In I/R group,the mitochondria was swelling, myocardium muscle fibers was breaked and the iliac crest destruction was disappeared,the above changes were reduced obviously in M-SI,H-SI groups. CONCLUSION: M-SI,H-SI behave a protective effect on ischemia/reperfusion inisolated rat hearts.

Key words: Myocardial reperfusion injury, Soy isoflavones, Rat