Objective To investigate the effects of "Neiguan" (PC 6)-electroacupunture (EA) preconditioning on the myocardium and its mast cells in myocardial ischemia /reperfusion (MI/R) rats. Methods Eighteen male SD rats were randomly assigned to sham group

model (IR) group and EA group (n=6/group). MI/R model was established by occlusion of the descending anterior branch of the coronary artery. Blood samples were taken from the femoral vein before MI (T0)

EA for 30 min (T1)

30 min after MI (T2)

30 min after MI/R (T3) and 120 min after MI/R (T4) for assaying serum tumor necrosis factor (TNF)-α and histamine contents by using ELISA.Serum lactate dehydrogenase (LDH) and creatinkinase isoenzyme (CK-MB) le-vels were measured at T0

T3 and T4 by using an automatic biochemistry analyzer. The infarct size was detected by Evan's blue and tetrazolium chloride (TTC) staining. Myocardial TNF-α and histamine contents were detected by ELISA. The percentage of mast cell degranulation was determined by toluidine blue staining. Results Following MI/R

serum LDH and CK-MB levels at phase T3 and T4

serum TNF-α and histamine contents at phase T2 and T3

and myocardial mast cell degranulation rate increased significantly

and myocardial TNF-α and histamine contents decreased in model group in comparison with pre-MI/R (P<0.05). Compared with IR model group

serum LDH and CK-MB levels at phase T3 and T4

myocardial TNF-α and histamine contents all decreased significantly (P<0.05)

but serum TNF-α and histamine contents increased significantly in EA group(P<0.05). The infarct size was remarkably smaller in EA group than that in IR model group(P<0.05). Conclusion "Neiguan" (PC 6)-EA preconditioning has a cardioprotective effect on the ischemia-reperfusion myocardium by promoting mast cell degranulation.