OBJECTIVE: To observe the effect of electroacupuncture (EA) stimulation of "Neiguan" (PC 6)-"Jianshi" (PC 7) on ischemic myocardial injury in myocardial ischemic (MI) rats, so as to explore its mechanism underlying improvement of MI. METHODS: A total of 48 male Wistar rats were randomly divided into normal, MI model, PC 6-PC 7, Sanyinjiao-Diji (SP 6-SP 8) groups (n=8 in each group for physiological experiments, n=4 in each group for immunoflorescence stain). The MI model was established by occlusion of the anterior descending branch of the left coronary artery. Electrocardiogram (ECG) of the neck-thoracic lead was recorded and the heart rate variability (HRV) analyzed by using a physiological signal collecting system (MP 150) and PowerLab software. EA (2 Hz/15 Hz, 0.5 mA) was applied to bilateral PC 6-PC 7 or SP 6-SP 8 for 30 min every time, on the 1,2,3 day after modeling. Serum creatine kinase-MB isoenzyme (CK-MB) and lactate dehydrogenase-1 (LDH 1) and endothelin (ET) contents were assayed by ELISA. The expression of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) and c-fos proteins in the nucleus ambiguus (NA) region of the medulla oblongata was detected by immunofluo-rescence stain. RESULTS: Compared with the normal group, the ECG J-point height (1 h), serum CK-MB, LDH 1 and ET contents (1 d and 3 d), HR (1 h and 1 d) and LF/HF levels of HRV (1 h, 1 d and 3 d) and the number of c-fos positive neurons (3 d) in the NA region were significantly increased in the model group (P<0.01, P<0.05), while HF levels (1 h, 1 d and 3 d) and ECG J-point height (1 d and 3 d) were considerably decreased after MI. After EA intervention, the ECG J-point height 3 d after MI was close to zero in both PC 6-PC 7 and SP 6-SP 8 groups, being better than that (negative value) of the model group, and serum CK-MB, LDH 1 and ET contents (1 d, 3 d) of both EA groups, and HR (1 d) and LF/HF (3 d) of the PC 6-PC 7 group were obviously down-regulated (P<0.01, P<0.05), and the decreased HF 3 d post-MI and the increased number of c-fos positive neurons were significantly up-regulated in the PC 6-PC 7 group (P<0.01). No significant differences were found between the two EA groups in raising J-point height and in down-regulating serum CK-MB, LDH 1 and ET contents (P>0.05). Compared with the model group, no significant changes were found in HR 1 d post-MI of the SP 6-SP 8 group, 3 d post-MI of both EA groups, in HF 3 d post-MI of the SP 6-SP 8 group, in LF/HF 1 d post-MI of both EA groups and 3 d post-MI of the SP 6-SP 8 group, in the number of c-fos positive neurons of the SP 6-SP 8 group, and ChAT and VAChT positive neurons of both EA groups (P>0.05). CONCLUSIONS: EA intervention may improve ischemic myocardial injury in MI rats, probably by activating neurons in the NA region, and enhancing the cardiac parasympathetic tension, and balancing cardiac sympathetic/parasympathetic nerve activities, but the effect of cholinergic neurons of NA needs being studied further.