Abstract: Objective: To observe the delayed protection effects of monophosphoryl lipid A(MLA) on ischemia-reperfusion(I/R) injury in rabbits,and investigate the protect effects of inducible nitric oxide synthase(iNOS) combined with protein kinase C(PKC) on cardioprotection induced by MLA.Methods: Twenty four newsland rabbits were randomly divided into the control group(intravenous injection of 0.9 sodium chloride solution),MLA group(intravenous injection of MLA) and inhibition group(Polymyxins combined with intravenous injection of MLA).Three groups were treated with I/R( 30 min of ischemia and 60 min of reperfusion),the PKC inhibitor/Polymyxin B(PMB) was intravenously injected into the inhibition group before 30 min of I/R.The creatine kinase(CK) releasing,arrhythmia happening and expression of iNOS were measured in rabbits induced by MLA.Results: The level of CK in MLA group was significantly lower than that in control group and inhibition group(P < 0.01).The arrhythmia in MLA group was not found,and the expression integral of iNOS in MLA group was significantly more than that in control group and inhibition group(P < 0.01).The differences of the expression integral of iNOS in cardiac muscular tissue between ischemic region and non-ischemic region in 3 groups were not statistically significant(P > 0.05).Conclusions: The MLA pretreatment can effectively alleviate the I/R myocardium injury after 24 h,namely mediating the delayed protection.PKC maybe involve in the delayed protection by regulating iNOS expression.