Cholinergic stimulation with pyridostigmine improves autonomic function in infarcted rats Raquel N de La Fuente,* Bruno Rodrigues,* † Ivana C Moraes-Silva,* Leandro E Souza,* Raquel Sirvente,* Cristiano Mostarda,* K atia De Angelis, ‡ Pedro P Soares, § Silvia Lacchini, ¶ Fernanda Consolim-Colombo* and Maria-Cl audia Irigoyen* *Heart Institute (InCor), Medical School, University of Sao Paulo, † Human Movement Laboratory, Sao Judas Tadeu University, ‡ Translational Physiology Laboratory, Nove de Julho University, Sao Paulo, § Department of Physiology and Pharmacology, Fluminense Federal University, Niteroi, Rio de Janeiro and ¶ Biomedical Sciences Institute, University of Sao Paulo, Sao Paulo, Brazil SUMMARY 1. In the present study we evaluated the effects of short- term pyridostigmine bromide (0.14 mg/mL) treatment started early after myocardial infarction (MI) on left ventricular (LV) and autonomic functions in rats. 2. Male Wistar rats were divided into control, pyridostig- mine, infarcted and infarcted + pyridostigmine-treated groups. Pyridostigmine was administered in the drinking water, starting immediately after MI or sham operation, for 11 days. Left ventricular function was evaluated indirectly by echocardiography and directly by LV catheterization. Car- diovascular autonomic control was evaluated by baroreflex sensitivity (BRS), heart rate variability (HRV) and pharma- cological blockade. All evaluations started after 7 days pyridostigmine treatment and were finalized after 11 days treatment. 3. Pyridostigmine prevented the impairment of +dP/dT and reduced the MI area in infarcted + pyridostigmine compared with infarcted rats (7 ± 3% vs 17 ± 4%, respectively). Mean blood pressure was restored in infarcted + pyridostigmine compared with infarcted rats (103 ± 3 vs 94 ± 3 mmHg, respectively). In addition, compared with the infarcted group, pyridostigmine improved BRS, as evaluated by tachycardic (1.6 ± 0.2 vs 2.5 ± 0.2 b.p.m./mmHg, respectively) and brady- cardic (À0.42 ± 0.01 vs À1.9 ± 0.1 b.p.m./mmHg) responses, and reduced the low frequency/high frequency ratio of HRV (0.81 ± 0.11 vs 0.24 ± 0.14, respectively). These improvements are probably associated with increased vagal tone and reduced sympathetic tone in infarcted + pyridostigmine compared with infarcted rats. 4. In conclusion, the data suggest that short-term pyridostigmine treatment started early after MI can improve BRS, HRV and parasympathetic and sympathetic tone in experimental rats. These data may have potential clinical implications because autonomic markers have prognostic significance after MI. Key words: cardiac autonomic function, cardiovascular function, myocardial infarction, pyridostigmine bromide. INTRODUCTION Myocardial infarction (MI) afflicts nearly 1 million people in the US each year and accounts for tens of billions of dollars in hos- pital costs. 1 It is well known that MI induces autonomic, func- tional and structural changes in the heart. 2 Autonomic balance is shifted to sympathetic dominance and reduced parasympathetic modulation of the heart. This autonomic imbalance is frequently associated with ventricular arrhythmias and sudden cardiac death in patients with coronary disease. 3 Autonomic markers, such as heart rate variability (HRV) and baroreflex sensitivity (BRS), have been shown to carry prognostic value after MI, 4 as well as in patients with heart failure. 5,6 One successful way of decreasing cardiovascular mortality has been the use of beta-blockers, because their ability to alter cell signalling at the receptor level has been shown to mitigate the pathogenic effects of sympathetic nervous system hyperactiva- tion. 7,8 Conversely, some attempts to restore autonomic balance in cardiovascular diseases have focused on the concept that increasing parasympathetic modulation may be a therapeutic alternative. Scopolamine, low-dose pirenzepine, clonidine and experimental drugs, such as zatebradine, have been tested in experimental and clinical settings. 9–13 In addition, vagal stimula- tion has a powerful antifibrillatory effect and can prevent ventric- ular fibrillation induced by acute myocardial ischaemia, 14 with subsequent studies providing evidence of significant improve- ments in different animal models of heart failure. 15,16 Cholinergic stimulation has been shown to protect against ventricular arrhythmia in experimental models 17 and to interrupt ventricular tachycardia in humans. 18 Pyridostigmine bromide, a reversible anticholinesterase agent, has an important effect on the motor plate in skeletal muscle and has been used in the treatment of myasthenia gravis. Regarding cardiovascular autonomic func- tion, treatment with pyridostigmine increased HRV and BRS in Correspondence: Dr Maria-Cl  audia Irigoyen, Heart Institute (InCor), Medical School of University of Sao Paulo, Avenue Dr Eneas de Carvalho Aguiar, 44–Bloco 1, Subsolo, S~ ao Paulo, SP, Brazil. Email: hipirigoyen@incor.usp.br Received 22 January 2013; revision 15 May 2013; accepted 19 May 2013. © 2013 Wiley Publishing Asia Pty Ltd Clinical and Experimental Pharmacology and Physiology (2013) 40, 610–616 doi: 10.1111/1440-1681.12121