Abstract: Objective To explore the protective effect and mechanism of lutein on myocardial fibrosis induced by isopropyl adrenaline in rats.Methods Sixty Wistar rats (half male and half female) were divided into six groups randomly.All the rats were subcutaneously injected with isoproterenol (Iso) at the dose of 5 mg/kg/d for 7 consecutive days to establish myocardial fibrosis model,except for those of the normal control group.At the second day of Iso treatment,the rats of low-,moderate-,and high-lutein groups were gavaged with lutein at the dosages of 20,40,and 80 mg/kg/d and the rats of positive control group were gavaged with captopril (10 mg/kg/d);the rats of model and normal control group were given distilled water of same quantity for 28 consecutive days.By the end of last treatment,the heart weight index of the rats were calculated;Bl-420E+ biological function experiment system was adopted to detect the heart function,electrocardiogram,and exercise endurance of the rats;hydroxyproline (HYP),glutathione (GSH),and malondialdehyde (MDA) in myocardial tissues and serum superoxide dismutase (SOD) were measured;and myocardial pathological changes of the rats were observed with hematoxylin-eosin (HE) staining.Results Compared with the normal control rats,the model rats showed decreased exercise tolerance,significantly increased heart weight index (HWI) (3.73±0.58 mg/g) and left ventricular mass index (LVMI) (2.57±0.43 mg/g) (both P<0.01) and obviously increased heart rate.Significantly increased HYP (0.48±0.07 g/mg),MDA (2.37±0.84 nmol/mgpr),and GSH (55.19±2.08 U/mg)(P<0.05 for all) in myocardial tissues and significantly decreased serum SOD (512.17±26.48 U/ml) (P<0.01) were detected in the model rats.The increase of stroma components,distance enlargement between cell nucleus,large number of inflammatory cells,and fibrous hyperplasia complicated with myocardial hypotrophy were observed in myocardial tissues of the model rats.Compared with the model rats,the rats with high-dose lutein treatment exhibited increased exercise tolerance,significantly decreased HWI (3.02±0.28 mg/g)and LVMI (2.09±0.17 mg/g) (both P<0.01),remarkably decreased myocardial HYP (0.28±0.06 g/mg) and MDA (1.89±0.61 nmol/mgpr) (both P<0.05) and obviously increased myocardial GSH (72.70±0.05 U/mg) and serum SOD (571.19±15.58 U/ml) (both P<0.01).Minor increase of stroma components and fibrous hyperplasia but no inflammatory cell infiltration and hypotrophy were observed in myocardial tissues of the rats with high-dose lutein treatment.Conclusion Lutein presents certain protective effect on isopropyl adrenaline-induced myocardial fibrosis in rats and the mechanism of the effect may be related to the improvement of antioxidant ability.