We investigated the effects of acute
pyridostigmine (PYR) treatment, an
acetylcholinesterase inhibitor, on arterial pressure (AP), heart rate (HR), cardiac sympathovagal balance, and the incidence of arrhythmias during the first 4 h after
myocardial infarction (MI) in anesthetized rats. Male Wistar rats were implanted with
catheters into the femoral artery and vein for AP recordings and
drug administration. Rats received the autonomic receptor blockers
methyl-atropine (1 mg/kg iv) and
propranolol (2 mg/kg iv) at intervals of 15 min, 1 h after saline (n=16) or PYR (0.25 mg/kg iv, n=18), to indirectly assess sympathovagal balance. Acute treatment with PYR increased cardiac vagal (86±7 vs. 44±5 beats/min) and decreased sympathetic tone (-31±8 vs. -69±7 beats/min). Different animals were implanted with ECG
electrodes and
catheters. A large MI was induced via left coronary artery
ligation after basal recordings. Rats received PYR (n=14) or saline (n=14) 10-15 min after MI, and the recordings lasted up to 4 h. In part of the animals, hearts were removed for
connexin43 quantification after all procedures. MI elicited a fall in AP (-45±5 mmHg), a progressive rise in HR (26±14 beats/min), and an increase in corrected QT interval (33±13 ms). PYR elicited a prompt
bradycardia (-50±14 beats/min) that returned to basal levels over time, and it prevented the lengthening of the corrected QT interval. Treatment with PYR increased by ∼20% the occurrence of rats free of arrhythmias after MI. MI markedly decreased
connexin43 in left ventricles, and PYR treatment partially prevented this decrease.