Effect Of ?7nAChR Mediated Cholinergic Anti-inflammatory Pathway On Inhibition Of Atrial Fibrillation By Low-level Vagus Nerve Stimulation

Objective To investigate the effect of a7nAChR mediated cholinergic anti-inflammatory pathway on inhibition of atrial fibrillation by low-level vagus nerve stimulation(LL-VNS).Methods Eighteen beagles were randomized into control group(n=6),LL-VNS group(n=6)and MLA+LL-VNS group(n=6).All the beagles were subjected to rapid atrial pacing at 800 beats/min for 6 hours.And the effective refractory period(ERP)of atriums and pulmonary veins and induced AF were measured hourly during non-pacing.After cessation of pacing for 3 hours,the beagles in control group were injected with saline into four GPs,the beagles in LL-VNS group were given LL-VNS and saline injected into four GPs,and the beagles in MLA+LL-VNS group were injected with methyllycaconitine(an a7nAChR inhibitor)into four GPs combined with LL-VNS.Then,the levels of tumor necrosis factor-alpha(TNF-a),interleukin-6(IL-6),and acetylcholine(ACh)in the plasma at baseline condition,3 h and 6 h were measured.At the end of this experiment,atrial tissues were collected to examine the levels of TNF-a,IL-6,ACh,NF-?B and STAT3 proteins.Results During the right atrium pacing for the first 3 hours,the ERPs were gradually decreased while AF inducibility were gradually increased in all groups,In control group,during the last 3 hours,in addition to decresed ERP of atriums and PVs,the induced times and duration of AF were significantly increased(P<0.05).At the end of this experiment,compared with the control group and MLA+LL-VNS group,the ERPs in LL-VNS group were increased,and the induced times and duration of AF were significantly decreased.The levels of TNF-a and IL-6 in plasma were all significantly decreased in LL-VNS group and MLA+LL-VNS group when compared with the control group(pg/ml)[IL-6:(100.96±5.65)vs(119.33±6.60),P<0.05;(102.35±5.34)vs(119.33±6.60),P<0.05;TNF-a:(17.75±1.66)vs(22.12±1.95),P<0.05;(17.91±2.15)vs(22.12±1.95),P<0.05].and the levels of ACh in plasma in the LL-VNS group and MLA group were higher than in the control group(?g/ml)[(150.79±12.77)vs(122.39±3.73),P<0.05;(145.09±4.93)vs(122.39±3.73),P<0.05].After cessation of pacing for 6 hours,compared with the control group and MLA+LL-VNS group,the tissue levels of TNF-a and IL-6 were significantly decreased in LL-VNS group(pg/ml)[IL-6:(192.38±7.10)vs(212.16±10.21),P<0.05;(192.38±7.10)vs(215.87±11.70),P<0.05;TNF-?:(26.03±3.56)vs(3 4.53±3.18),P<0.05;(26.03±3.56)vs(33.87±2.86),P<0.05].the levels of ACh in the LL-VNS group and MLA group were higher than in the control group(?g/ml)[RA:(55.91±4.16)vs(30.69±3.18),P<0.05;(46.43±3.85)vs(30.69±3.18),P<0.05;LA:(49.22±3.69)vs(35.38±3.16),P<0.05;(40.42±2.42)vs(35.38±3.16),P<0.05].The concentrations of NF-?B proteins in RA and LA were lower in the LL-VNS group than in the control group and MLA+LL-VNS group(P<0.01),and the levels of STAT3 proteins in those tissues were higher in the LL-VNS group than in the control group and MLA+LL-VNS group(P<0.05).Conclusion LL-VNS could inhibit the atrial electrical remodeling and atrial fibrillation induction,Cholinergic anti-inflammatory pathway mediated by a7nAChR may be the important mechanism in vagal nerve regulated AF.