Abstract: AimTo explore the effects of M₃ receptor on myocyte apoptosis induced by acute myocardial infarction in rats. MethodsRat model was induced by ligation of the anterior branch of the left coronary artery. All animals were divided into four groups: sham-operated group, occlusion group, choline group (10 mg·kg^-1, iv), and 4DAMP (4-diphenylacetoxy-N-methylpiperidine-methiodide) group (0.12 mg·kg^-1, iv). The serum malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were determined. The infarct size areas on the myocardium were identified by TTC staining. The apoptosis in cardiomyocyte was detected by TUNEL assay and apoptosis-related proteins in Bcl-2 and Fas expression were measured by immunohistochemistry assay. ResultsM₃ receptor agonist choline reduced serum MDA content and increased SOD activity. The myocardial expression of Bcl-2 was increased, whereas the expression of Fas was decreased by choline. However, blockade of M₃ receptor by 4DAMP completely inhibited these effects of choline on cardiac myocytes. ConclusionActivation of M₃ receptor has protective effect on myocyte apoptosis induced by acute myocardial infarction in rat, and this effect might be related to modulating the expression of some immediate-early genes including Bcl-2 and Fas.