[Effects of electroacupuncture pretreatment on GABAA receptor of fastigial nucleus and sympathetic nerve activity in rats with myocardial ischemia reperfusion injury].

Objective: To observe the effects of electroacupuncture (EA) pretreatment on cardiac function, sympathetic nerve activity, indexes of myocardial injury and GABA_A receptor in fastigial nucleus in rats with myocardial ischemia reperfusion injury (MIRI), and to explore the neuroregulatory mechanism of EA pretreatment in improving MIRI.

Methods: A total of 60 male SD rats were randomly divided into a sham operation group, a model group, an EA group, an agonist group and an agonist+EA group, 12 rats in each group. The MIRI model was established by ligation of the left anterior descending coronary artery. EA was applied at bilateral "Shenmen" (HT 7) and "Tongli" (HT 5) in the EA group and the agonist+EA group, with continuous wave, in frequency of 2 Hz and intensity of 1 mA, 30 min each time, once a day for 7 consecutive days. After intervention, the MIRI model was established. In the agonist group, the muscone (agonist of GABA_A receptor, 1 g/L) was injected in fastigial nucleus for 7 consecutive days before modeling, 150 μL each time, once a day. In the agonist+EA group, the muscone was injected in fastigial nucleus 30 min before EA intervention. The data of electrocardiogram was collected by PowerLab standard Ⅱ lead, and ST segment displacement and heart rate variability (HRV) were analyzed; the serum levels of norepinephrine (NE), creatine kinase isoenzyme MB (CK-MB) and cardiac troponin I (cTnI) were detected by ELISA; the myocardial infarction area was measured by TTC staining; the morphology of myocardial tissue was observed by HE staining; the positive expression and mRNA expression of GABA_A receptor in fastigial nucleus were detected by immunohistochemistry and real-time PCR.

Results: Compared with the sham operation group, in the model group, ST segment displacement and ratio of low frequency to high frequency (LF/HF) of HRV were increased (P<0.01), HRV frequency domain analysis showed enhanced sympathetic nerve excitability, the serum levels of NE, CK-MB and cTnI were increased (P<0.01), the percentage of myocardial infarction area was increased (P<0.01), myocardial fiber was broken and interstitial edema was serious, the positive expression and mRNA expression of GABA_A receptor in fastigial nucleus were increased (P<0.01). Compared with the model group, in the EA group, ST segment displacement and LF/HF ratio were decreased (P<0.01), HRV frequency domain analysis showed reduced sympathetic nerve excitability, the serum levels of NE, CK-MB and cTnI were decreased (P<0.01), the percentage of myocardial infarction area was decreased (P<0.01), myocardial fiber breakage and interstitial edema were lightened, the positive expression and mRNA expression of GABA_A receptor in fastigial nucleus were decreased (P<0.01). Compared with the EA group, in the agonist group and the agonist+EA group, ST segment displacement and LF/HF ratio were increased (P<0.01), HRV frequency domain analysis showed enhanced sympathetic nerve excitability, the serum levels of NE, CK-MB and cTnI were increased (P<0.01), the percentage of myocardial infarction area was increased (P<0.01), myocardial fiber breakage and interstitial edema were aggravated, the positive expression and mRNA expression of GABA_A receptor in fastigial nucleus were increased (P<0.01).

Conclusion: EA pretreatment can improve the myocardial injury in MIRI rats, and its mechanism may be related to the inhibition of GABA_A receptor expression in fastigial nucleus, thereby down-regulating the excitability of sympathetic nerve.