title: Effects of Acetaminophen on Left Atrial Contractility.
abstract: BACKGROUND
  It has been observed that acetaminophen shows cardioprotective efficacy in mammals. In this study, we investigated the electromechanical effects of acetaminophen on the left atrium (LA).
  
  
  METHODS
  Conventional microelectrodes were used to record the action potentials (AP) in rabbit LA preparations. The action potential duration (APD) at repolarization levels of 90%, 50% and 20% of the AP amplitude (APD90, APD50, and APD20, respectively), resting membrane potential, and contractile force were measured during 2 Hz electrical stimulation before and after sequential acetaminophen administration to the LA.
  
  
  RESULTS
  Acetaminophen (0.1, 0.3, 1, and 3 mM) reduced APD20 from 9.4 ± 1.2 to 8.0 ± 1.1 (p < 0.05), 7.1 ± 0.8 (p < 0.05), 7.8 ± 1.1, and 6.8 ± 1.2 ms (p < 0.05), respectively, and APD50 from 20.2 ± 1.9 to 17.4 ± 2.0, 15.6 ± 1.8 (p < 0.05), 15.8 ± 2.2 (p < 0.05), and 14.1 ± 2.4 ms (p < 0.05), respectively, in a concentration-dependent manner. APD90 was reduced from 72.0 ± 3.6 to 64.7 ± 4.2, 61.9 ± 4.3, 60.5 ± 3.7, and 53.4 ± 4.4 ms (p < 0.05), respectively. Acetaminophen increased LA contractility from 45 ± 9 to 52 ± 10 (p < 0.05), 55 ± 9 (p < 0.01), 58 ± 9 (p < 0.01), and 60 ± 9 mg (p < 0.01), respectively, in a concentration-dependent manner. In the presence of the NOS inhibitor L-NAME or PKG-I inhibitor DT-2, additional acetaminophen treatment did not significantly increase LA contractility.
  
  
  CONCLUSIONS
  Acetaminophen modulated the electromechanical characteristics of LA by inhibiting the NOS and PKG I pathway, and then contributed to the positive inotropic effect.
authors.affiliation: Biomedical Engineering Program, Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology;
authors.forename: Jun-Hei
authors.initials: JH
authors.lastname: Chang
authors.affiliation: Department of Physiology and Biophysics, National Defense Medical Center;
authors.forename: Pao-Yun
authors.initials: PY
authors.lastname: Cheng
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Tri-Service General Hospital, National Defense Medical Center;
authors.forename: Chih-Hsueng
authors.initials: CH
authors.lastname: Hsu
authors.affiliation: Department of Biomedical Engineering and Institute of Physiology, National Defense Medical Center, Taipei, Taiwan.
authors.forename: Yao-Chang
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Biomedical Engineering Program, Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology;
authors.forename: Po-Da
authors.initials: PD
authors.lastname: Hong
keywords: Acetaminophen; Contractility; Left atrium