Studies On The Regular Pattern And Mechanism Of Cardiac Effect Rebound After Washout Of Acetylcholine

Object: To study the regular pattern and mechanism of positive inotropic effect after washout of ACh(rebound of myocardial contractile force)and investigate the influence of acetylcholine perfusion and washout on transmural dispersion of atrial repolarization in isolated rabbit heart.Methods: On the one hand, the changes of myocardial contractile force after perfusion and washout of ACh was observed in 28 isolated Langendorff perfused rabbit hearts. On the other hand, With the monophasic action potential (MAP) recording technique, MAPs of endocardial, midmyocardial, and epicardial cells were recorded at the atrial myocardium in isolated Langendorff perfused rabbit heart. Monophasic action potential duration at 50% and 90% repolarization (MAPD50 and MAPD90) and transmural dispersion of repolarization (TDR) among three atrial myocardial layers were compared after perfusion and washout of ACh(1×10-5 mol/L , 0.3 ml/kg).Results: Maximum rebound rate induced by ACh of 10-8~10-3 mol/L were 2.22%±1.702%,6.71%±3.40%,9.18%±3.54%,14.16%±3.27%,4.37%±5.86% and 1.03%±6.86%, respectively. Compared with the ACh of 1×10-5 mol/L in control group, adrenaline enhanced rebound of myocardial contractile force,maximum rebound rate in adrenaline group was 29.25%±5.83% (P<0.05, n=7), propranolol reduced rebound, and maximum rebound rate in propranolol group was 5.15%±4.45% (P<0.05, n=7), we had not detected rebound of myocardial contractile force in 800 s after addition ACh in verapamil group. During perfusion of ACh, MAPD50, MAPD90 and MAPD90-50were shorter (P<0.05, n=9) ,and TDR50, TDR90 TDR90-50 were longer (P<0.05, n=9) than before. Compared with the state before ACh perfusion, but MAPD50, MAPD90, MAPD90-50 and TDR did not alter significantly after washout of ACh (P>0.05, n=9).Conclusion: In isolated rabbit heart, positive inotropic effect after washout of ACh have relevance to the activities of calcium current channel andβ-adrenergic receptor. Perhaps there were some different aspects in the mechanism of positive inotropic effect between perfusion of high ACh concentration and after washout of ACh.