Abstract: Objective:To investigate the mRNA, protein expression levels and the phosphorylation levels of key factors in rapidly accelerated fibrosarcoma/mitogen-activated protein kinase kinase/extracellular regulated protein kinases (Raf/MEK/ERK) pathway, and to clarify the regulatory function of Raf/MEK/ERK pathway in myocardial hypertrophy. Methods: Twenty SD rats were divided into sham-operated group and model group. The myocardial hypertrophy model was established by transverse aortic constriction (TAC). At 12 weeks after TAC, blood samples were collected from the submandibular vein, and the serum was separated to detect the content of N terminal pro B type natriuretic peptide (NT-proBNP). After that, the rats were subjected to echocardiography and hemodynamic measurement. Then the pathological changes of myocardial tissue were observed. And the levels of mRNA, protein expression and the phosphorylation of key factors in Raf/MEK/ERK pathway were detected in myocardial tissue.Results: Compared with sham-operated group, left ventricular end-diastolic interventricular septal thickness (IVSd), left ventricular end-systolic interventricular septal thickness (IVSs), left ventricular end-diastolic posterior wall thickness (LVPWd) and left vebtricular end-systolic posterior wall thickness (LVPWs) in TAC model group were increased significantly (P＜0.05,P＜0.01), left ventricular end-systolic diameter (LVIDs) was decreased significantly (P＜0.01), LV Mass and LW(LV Mass/Weight)were increased significantly (P＜0.05, P＜0.01). The levels of heart rate (HR), left ventricular pressure maximal rate of rise (+dp/dtmax), left ventricular pressure maximal rate of fall (-dp/dtmax) were decreased significantly (P＜0.01). The serum level of NT-proBNP in TAC rat was increased significantly (P＜0.01). The myocardial cells in TAC model group were arranged disorderly, myocardial cell hypertrophy, cytoplasm were increased significantly, and inflammatory cells infiltrated. A large amount of collagen fibers were deposited and large area of myocardial cells were stained blue in TAC rat. The expression levels of phospho-c-Raf (Ser259) and phospho-c-Raf (Ser338) in myocardial tissue were significantly increased (P＜0.01), meanwhile the expression levels of phospho- MEK1/2(Ser217/Ser221) and phospho-ERK1/2 (Thr202/Tyr204) were also significantly increased (P＜0.01).Conclusion: The regulatory role of Raf / MEK / ERK pathway in cardiac hypertrophy may be through the activation of phosphorylation of c-raf, MEK1, Mek2, ERK1 and ERK2 at specific sites.

Key words: rat, Raf/MEK/ERK pathway, cardiac hypertrophy, transverse aortic constriction, regulatory mechanism