AimTo investigate the protective effects and mechanism of N-acetylcysteine (NAC) on myocardial injury in diabetic rats.MethodsThe diabetic model was established with streptozotocin (STZ).The fifty male SD rats were randomly divided into five groups: the normal group, the diabetic group, the low, middle and high dose N-acetylcysteine treatment group.N-acetylcysteine of 50, 100 and 200 mg/kg was respectively given to the low, middle and high dose drug treatment groups by gavage 12 weeks.Rats’ heart function, body weight (BW), heart weight (HW) and left heart weight (LHW) were tested, HW/BW and LHW/BW were calculated, the activities of SOD and GSH-PX in serum and myocardial tissue were measured.Morphological change was observed and myocardial collagen volume fraction was measured by Masson staining.The protein expression levels of TGF-β1, SMAD3 and SMAD7 were determined by immunohistochemistry.ResultsCompared with the control group, LVEDP of the diabetic group was significantly increased (P<0.01) and LVSP, ±dp/dtmax were significantly reduced (P<0.01).All the cardiac mass index and left ventricular mass index were higher (P<0.01).The activities of SOD and GSH-PX were significantly reduced (P<0.01).The levels of TGF-β1 and SMAD3 were significantly up-regulated (P<0.01), the level of SMAD7 was declined significantly (P<0.01).Compared with the diabetic group, all above indexes of NAC treatment groups had been improved by gavage 12 weeks, high dose group had been improved obviously (P<0.01).ConclusionsNAC has a protective effect on myocardial in diabetic rats, the mechanism may be related to the inhibition of oxidative stress, reducing the expression of TGF-β1, SMAD3 and increasing the expression of SMAD7.