Cholinergic stimulation with pyridostigmine protects against exercise induced myocardial ischaemia

Targeting Parasympathetic Activity to Improve Autonomic Tone and Clinical Outcomes

In this review we will briefly summarize the evidence that autonomic imbalance, more specifically reduced parasympathetic activity to the heart, generates and/or maintains many cardiorespiratory diseases and will discuss mechanisms and sites, from myocytes to the brain, that are potential translational targets for restoring parasympathetic activity and improving cardiorespiratory health.

Benefits of pharmacological and electrical cholinergic stimulation in hypertension and heart failure

Systemic arterial hypertension and heart failure are cardiovascular diseases that affect millions of individuals worldwide. They are characterized by a change in the autonomic nervous system balance, highlighted by an increase in sympathetic activity associated with a decrease in parasympathetic activity. Most therapeutic approaches seek to treat these diseases by medications that attenuate sympathetic activity. However, there is a growing number of studies demonstrating that the improvement of parasympathetic function, by means of pharmacological or electrical stimulation, can be an effective tool for the treatment of these cardiovascular diseases. Therefore, this review aims to describe the advances reported by experimental and clinical studies that addressed the potential of cholinergic stimulation to prevent autonomic and cardiovascular imbalance in hypertension and heart failure. Overall, the published data reviewed demonstrate that the use of central or peripheral acetylcholinesterase inhibitors is efficient to improve the autonomic imbalance and hemodynamic changes observed in heart failure and hypertension. Of note, the baroreflex and the vagus nerve activation have been shown to be safe and effective approaches to be used as an alternative treatment for these cardiovascular diseases. In conclusion, pharmacological and electrical stimulation of the parasympathetic nervous system has the potential to be used as a therapeutic tool for the treatment of hypertension and heart failure, deserving to be more explored in the clinical setting.

Impact of Peripheral α7-Nicotinic Acetylcholine Receptors on Cardioprotective Effects of Donepezil in Chronic Heart Failure Rats

PURPOSE

Pharmacological modulation of parasympathetic activity with donepezil, an acetylcholinesterase inhibitor, improves the long-term survival of rats with chronic heart failure (CHF) after myocardial infarction (MI). However, its mechanism is not well understood. The α7-nicotinic acetylcholine receptor (α7-nAChR) reportedly plays an important role in the cholinergic anti-inflammatory pathway. The purpose of this study was to examine whether blockade of α7-nAChR, either centrally or peripherally, affects cardioprotection by donepezil during CHF.

METHODS

One-week post-MI, the surviving rats were implanted with an electrocardiogram or blood pressure transmitter to monitor hemodynamics continuously. Seven days after implantation, the MI rats (n = 74) were administered donepezil in drinking water or were untreated (UT). Donepezil-treated MI rats were randomly assigned to the following four groups: peripheral infusion of saline (SPDT) or an α7-nAChR antagonist methyllycaconitine (α7PDT), and brain infusion of saline (SBDT) or the α7-nAChR antagonist (α7BDT).

RESULTS

After the 4-week treatment, the role of α7-nAChR was evaluated using hemodynamic parameters, neurohumoral states, and histological and morphological assessment. Between the peripheral infusion groups, α7PDT (vs. SPDT) showed significantly increased heart weight and cardiac fibrosis, deteriorated hemodynamics, increased plasma neurohumoral and cytokine levels, and significantly decreased microvessel density (as assessed by anti-von Willebrand factor-positive cells). In contrast, between the brain infusion groups, α7BDT (vs. SBDT) showed no changes in either cardiac remodeling or hemodynamics.

CONCLUSION

Peripheral blockade of α7-nAChR significantly attenuated the cardioprotective effects of donepezil in CHF rats, whereas central blockade did not. This suggests that peripheral activation of α7-nAChR plays an important role in cholinergic pharmacotherapy for CHF.

Myasthenia Gravis and Physical Exercise: A Novel Paradigm

The benefits of physical exercise for healthy individuals are well-established, particularly in relation to reducing the risks of chronic lifestyle related diseases. Furthermore, physical exercise has been seen to provide beneficial effects in many chronic diseases such as multiple sclerosis, rheumatoid arthritis, and chronic obstructive pulmonary disease and is therefore recommended as part of the treatment regimen. Myasthenia Gravis (MG) is a chronic autoimmune disease that causes neuromuscular transmission failure resulting in abnormal fatigable skeletal muscle weakness. In spite of this fluctuating skeletal muscle weakness, it is reasonable to assume that MG patients, like healthy individuals, could benefit from some of the positive effects of physical exercise. Yet exercise-related research in the field of MG is sparse and does not provide any guidelines on how MG patients should perform physical training in order to obtain exercise's favorable effects without risking disease deterioration or more pronounced muscle fatigue. A handful of recent studies report that MG patients with mild disease activity can adhere safely to general exercise recommendations, including resistance training and aerobic training regimens, without subjective or objective disease deterioration. These findings indicate that MG patients can indeed improve their functional muscle status as a result of aerobic and high-resistance strength training. This knowledge is important in order to establish collective as well as personalized guidelines on physical exercise for MG patients. This review discusses the present knowledge on physical exercise in MG.

Effects of Anticholinesterase Reversal Under General Anesthesia on Postoperative Cardiovascular Complications: A Retrospective Cohort Study

BACKGROUND

The anticholinesterase neostigmine and the muscarinic inhibitor glycopyrrolate are frequently coadministered for the reversal of neuromuscular blockade. This practice can precipitate severe bradycardia or tachycardia, but whether it affects the incidence of cardiovascular complications remains unclear. We hypothesized that anticholinesterase reversal with neostigmine and glycopyrrolate versus no anticholinesterase reversal increases the risk of postoperative cardiovascular complications among adult patients undergoing noncardiac surgery with general anesthesia.

METHODS

We conducted a prespecified retrospective analysis of hospital registry data from a major health care network for patients undergoing surgery with general anesthesia from January 2007 to December 2015. The primary outcome was a composite of cardiac dysrhythmia, acute heart failure, transient ischemic attack, ischemic stroke, and acute myocardial infarction within 30 days after surgery. We performed sensitivity analyses in subgroups and propensity score adjustment and explored the association between exposure and outcome in subgroups of patients with high risk of cardiovascular complications.

RESULTS

Of the 98,147 cases receiving neuromuscular blockade, 73,181 (74.6%) received neostigmine and glycopyrrolate, while 24,966 (25.4%) did not. A total of 5612 patients (7.7%) in the anticholinesterase reversal group and 1651 (6.6%) in the control group (P < .001) experienced the primary outcome. After adjustment for clinical covariates, neostigmine and glycopyrrolate exposure was significantly associated in a dose-dependent fashion (P for trend <.001, respectively) with tachycardia (adjusted odds ratio = 2.1 [95% CI, 1.97-2.23]; P < .001) and bradycardia (adjusted odds ratio = 2.84 [95% CI, 2.49-3.24]; P < .001) but not with postoperative cardiovascular complications (adjusted odds ratio = 1.03 [95% CI, 0.97-1.1]; P = .33). We identified a significant effect modification of anticholinesterase reversal by high age, high-risk surgery, and history of atrial fibrillation (P for interaction = .002, .001, and .02, respectively). By using linear combinations of main effect and exposure-risk interaction terms, we detected significant associations between anticholinesterase reversal and cardiovascular complications toward a higher vulnerability in these patient subgroups.

CONCLUSIONS

Neuromuscular blockade reversal with neostigmine and glycopyrrolate was associated with an increased incidence of intraoperative tachycardia and bradycardia but not with 30-day postoperative cardiovascular complications. Exploratory analyses suggest that a high postoperative cardiovascular complication risk profile may modify the effects of anticholinesterase reversal toward clinical relevance.

Intracerebroventricular infusion of donepezil prevents cardiac remodeling and improves the prognosis of chronic heart failure rats

Oral administration of donepezil, a centrally acting acetylcholinesterase inhibitor, improves the survival of rats with chronic heart failure (CHF). The mechanisms of cardioprotective effects of donepezil, however, remain totally unknown. To elucidate potential mechanisms, we examined whether central microinfusion of donepezil would exert cardioprotection. Intracerebroventricular microinfusion pumps with cerebroventricular cannula were implanted in rats with myocardial infarction. The rats were randomly divided into central saline treatment (CST) and central donepezil treatment (CDT) groups. We evaluated cardiac remodeling and function after a 6-week treatment and examined the 160-day survival rate. Compared to the CST, the CDT markedly improved the 160-day survival rate (68% vs. 32%, P = 0.002) through the prevention of cardiac remodeling and the lowering of plasma catecholamine, brain natriuretic peptide, and angiotensin II. These results suggest that the central mechanism plays an important role in the cardioprotective effects of donepezil.

The effects of acetylcholinesterase inhibitors on the heart in acute myocardial infarction and heart failure: From cells to patient reports

Cardiovascular diseases remain a major cause of morbidity and mortality worldwide. Cardiovascular diseases such as acute myocardial infarction, ischaemia/reperfusion injury and heart failure are associated with cardiac autonomic imbalance characterized by sympathetic overactivity and parasympathetic withdrawal from the heart. Increased parasympathetic activity by electrical vagal nerve stimulation has been shown to provide beneficial effects in the case of cardiovascular diseases in both animals and patients by improving autonomic function, cardiac remodelling and mitochondrial function. However, clinical limitations for electrical vagal nerve stimulation exist because of its invasive nature, costly equipment and limited clinical validation. Therefore, novel therapeutic approaches which moderate parasympathetic activities could be beneficial for in the case of cardiovascular disease. Acetylcholinesterase inhibitors inhibit acetylcholinesterase and hence increase cholinergic transmission. Recent studies have reported that acetylcholinesterase inhibitors improve autonomic function and cardiac function in cardiovascular disease models. Despite its potential clinical benefits for cardiovascular disease patients, the role of acetylcholinesterase inhibitors in acute myocardial infarction and heart failure remediation remains unclear. This article comprehensively reviews the effects of acetylcholinesterase inhibitors on the heart in acute myocardial infarction and heart failure scenarios from in vitro and in vivo studies to clinical reports. The mechanisms involved are also discussed in this review.

The non-neuronal cholinergic system in the heart: A comprehensive review

The autonomic influences on the heart have a ying-yang nature, albeit oversimplified, the interplay between the sympathetic and parasympathetic system (known as the cholinergic system) is often complex and remain poorly understood. Recently, the heart has been recognized to consist of neuronal and non-neuronal cholinergic system (NNCS). The existence of cardiac NNCS has been confirmed by the presence of cholinergic markers in the cardiomyocytes, which are crucial for synthesis (choline acetyltransferase, ChAT), storage (vesicular acetylcholine transporter, VAChT), reuptake of choline for synthesis (high-affinity choline transporter, CHT1) and degradation (acetylcholinesterase, AChE) of acetylcholine (ACh). The non-neuronal ACh released from cardiomyocytes is believed to locally regulate some of the key physiological functions of the heart, such as regulation of heart rate, offsetting hypertrophic signals, maintenance of action potential propagation as well as modulation of cardiac energy metabolism via the muscarinic ACh receptor in an auto/paracrine manner. Apart from this, several studies have also provided evidence for the beneficial role of ACh released from cardiomyocytes against cardiovascular diseases such as sympathetic hyperactivity-induced cardiac remodeling and dysfunction as well as myocardial infarction, confirming the important role of NNCS in disease prevention. In this review, we aim to provide a fundamental overview of cardiac NNCS, and information about its physiological role, regulatory factors as well as its cardioprotective effects. Finally, we propose the different approaches to target cardiac NNCS as an adjunctive treatment to specifically address the withdrawal of neuronal cholinergic system in cardiovascular disease such as heart failure.

Cholinesterase inhibition reduces arrhythmias in asymptomatic Chagas disease

INTRODUCTION

Parasympathetic dysfunction may play a role in the genesis of arrhythmias in Chagas disease.

AIM

This study evaluates the acute effects of pyridostigmine (PYR), a reversible cholinesterase inhibitor, on the occurrence of arrhythmias in patients with Chagas cardiac disease.

METHOD

Following a double-blind, randomized, placebo-controlled, cross-over protocol, 17 patients (age 50±2 years) with Chagas cardiac disease type B underwent 24-hour Holter recordings after oral administration of either pyridostigmine bromide (45 mg, 3 times/day) or placebo (PLA).

RESULTS

Pyridostigmine reduced the 24-hours incidence (median [25%-75%]) of premature ventricular beats-PLA: 2998 (1920-4870), PYR: 2359 (940-3253), P=.044; ventricular couplets-PLA: 84 (15-159), PYR: 33 (6-94), P=.046. Although the total number of nonsustained ventricular tachycardia in the entire group was not different (P=.19) between PLA (1 [0-8]) and PYR (0 [0-4]), there were fewer episodes under PYR in 72% of the patients presenting this type of arrhythmia (P=.033).

CONCLUSION

Acute administration of pyridostigmine reduced the incidence of nonsustained ventricular arrhythmias in patients with Chagas cardiac disease. Further studies that address the use of pyridostigmine by patients with Chagas cardiac disease under a more prolonged follow-up are warranted.

Effects of cholinergic stimulation with pyridostigmine bromide on chronic chagasic cardiomyopathic mice

The aim of the present study was to assess the effects of an anticholinesterase agent, pyridostigmine bromide (Pyrido), on experimental chronic Chagas heart disease in mice. To this end, male C57BL/6J mice noninfected (control:Con) or chronically infected (5 months) with Trypanosoma cruzi (chagasic:Chg) were treated or not (NT) with Pyrido for one month. At the end of this period, electrocardiogram (ECG); cardiac autonomic function; heart histopathology; serum cytokines; and the presence of blood and tissue parasites by means of immunohistochemistry and PCR were assessed. In NT-Chg mice, significant changes in the electrocardiographic, autonomic, and cardiac histopathological profiles were observed confirming a chronic inflammatory response. Treatment with Pyrido in Chagasic mice caused a significant reduction of myocardial inflammatory infiltration, fibrosis, and hypertrophy, which was accompanied by a decrease in serum levels of IFNγ with no change in IL-10 levels, suggesting a shift of immune response toward an anti-inflammatory profile. Lower nondifferent numbers of parasite DNA copies were observed in both treated and nontreated chagasic mice. In conclusion, our findings confirm the marked neuroimmunomodulatory role played by the parasympathetic autonomic nervous system in the evolution of the inflammatory-immune response to T. cruzi during experimental chronic Chagas heart disease in mice.

Pyridostigmine restores cardiac autonomic balance after small myocardial infarction in mice

The effect of pyridostigmine (PYR) - an acetylcholinesterase inhibitor - on hemodynamics and cardiac autonomic control, was never studied in conscious myocardial infarcted mice. Telemetry transmitters were implanted into the carotid artery under isoflurane anesthesia. Seven to ten days after recovery from the surgery, basal arterial pressure and heart rate were recorded, while parasympathetic and sympathetic tone (ΔHR) was evaluated by means of methyl atropine and propranolol. After the basal hemodynamic recording the mice were subjected to left coronary artery ligation for producing myocardial infarction (MI), or sham operation, and implantation of minipumps filled with PYR or saline. Separate groups of anesthetized (isoflurane) mice previously (4 weeks) subjected to MI, or sham coronary artery ligation, were submitted to cardiac function examination. The mice exhibited an infarct length of approximately 12%, no change in arterial pressure and increased heart rate only in the 1st week after MI. Vagal tone decreased in the 1^st week, while the sympathetic tone was increased in the 1^st and 4^th week after MI. PYR prevented the increase in heart rate but did not affect the arterial pressure. Moreover, PYR prevented the increase in sympathetic tone throughout the 4 weeks. Concerning the parasympathetic tone, PYR not only impaired its attenuation in the 1^st week, but enhanced it in the 4^th week. MI decreased ejection fraction and increased diastolic and systolic volume. Therefore, the pharmacological increase of peripheral acetylcholine availability by means of PYR prevented tachycardia, increased parasympathetic and decreased sympathetic tone after MI in mice.

Electrophysiological and pharmacological evaluation of the nicotinic cholinergic system in chagasic rats

Background

Two theories attempt to explain the changes observed in the nicotinic acetylcholine receptors (nAChRs) in chagasic cardiomyopathy. The neurogenic theory proposes that receptor changes are due to loss of intracardiac ganglia parasympathetic neurons. The immunogenic theory proposes that the nAChRs changes are the result of autoantibodies against these receptors. Both theories agreed that nAChRs functional expression could be impaired in Chagas disease.

Methods

We evaluated nAChRs functional integrity in 54 Sprague Dawley rats, divided in two groups: healthy and chronic chagasic rats. Rats were subjected to electrocardiographic studies in the whole animal under pentobarbital anesthesia, by isolation and stimulation of vagus nerves and in isolated beating hearts (Langendorff’s preparation).

Results

Nicotine, 10 μM, induced a significant bradycardia in both groups. However, rats that had previously received reserpine did not respond to nicotine stimulation. β-adrenergic stimulation, followed by nicotine treatment, induced tachycardia in chagasic rats; while inducing bradycardia in healthy rats. Bilateral vagus nerve stimulation induced a significantly higher level of bradycardia in healthy rats, compared to chagasic rats; physostigmine potentiated the bradycardic response to vagal stimulation in both experimental groups. Electric stimulation (e.g., ≥ 2 Hz), in the presence of physostigmine, produced a comparable vagal response in both groups. In isolated beating-heart preparations 1 μM nicotine induced sustained bradycardia in healthy hearts while inducing tachycardia in chagasic hearts. Higher nicotine doses (e.g.,10 – 100 uM) promoted the characteristic biphasic response (i.e., bradycardia followed by tachycardia) in both groups. 10 nM DHβE antagonized the effect of 10 μM nicotine, unmasking the cholinergic bradycardic effect in healthy rats only. 1 nM α-BGT alone induced bradycardia in healthy hearts but antagonized the 10 μM nicotine-induced tachycardia in chagasic rats. In healthy but not in chagasic hearts, 10 μM nicotine shortened PQ and PR interval, an effect counteracted by MA, DHβE and αBGT

Conclusion

Our results suggest that cholinergic function is impaired in chronic Chagas disease in rats, a phenomena that could be related to alteration on the nAChR expression.

The Clinical Utility of Cardiopulmonary Exercise Testing in Suspected or Confirmed Myocardial Ischemia

Heart disease is a major cause of morbidity and mortality in the United States, with coronary artery disease (CAD) representing more than half of all cardiovascular events. Stable patients presenting with symptoms suggestive of CAD are likely to undergo an exercise electrocardiogram (ECG) and/ or imaging study as a first-line diagnostic assessment. A cardiopulmonary exercise test (CPX) is an ECG stress test plus ventilatory gas analysis. Recently, CPX has been used to detect exercise-induced myocardial ischemia (EIMI) suggestive of underlying CAD. Two CPX variables, oxygen pulse (VO2/HR) and the slope of oxygen consumption versus work rate (Δ VO2/ Δ WR), have been identified to be especially indicative of EIMI. Currently, there are a number of diagnostic tests available for the identification of CAD, with the most widely used being stress ECG, stress myocardial perfusion imaging (MPI) and echocardiography, and cardiac catheterization. Exercise ECG, although inexpensive, has a number of well-recognized limitations, including low sensitivity resulting in false-negative results. Stress (exercise or pharmaceutically induced) MPI and catheterization are more accurate but also more invasive and expensive. It appears that CPX may improve the diagnostic accuracy of exercise ECG. This review will address the potential utility of CPX in patients with suspected or confirmed myocardial ischemia.

Cholinergic stimulation improves autonomic and hemodynamic profile during dynamic exercise in patients with heart failure

BACKGROUND

Parasympathetic dysfunction is an independent risk factor for mortality in heart failure for which there is no specific pharmacologic treatment. This article aims to determine the effect of pyridostigmine, an anticholinesterase agent, on the integrated physiologic responses to dynamic exercise in heart failure.

METHODS AND RESULTS

Patients with chronic heart failure (n = 23; 9 female; age = 48 +/- 12 years) were submitted to 3 maximal cardiopulmonary exercise tests on treadmill in different days. The first test was used for adaptation and to determine exercise tolerance. The other tests were performed after oral administration of pyridostigmine (45 mg, 3 times/day, for 24 hours) or placebo, in random order. All patients were taking their usual medication. Pyridostigmine reduced cholinesterase activity by 30%, inhibited the chronotropic response throughout exercise, up to 60% of maximal effort (pyridostigmine = 108 +/- 3 beats/min vs. placebo = 113 +/- 3 beats/min; P = .040), and improved heart rate reserve (pyridostigmine = 73 +/- 5 beats/min vs. placebo = 69 +/- 5 beats/min; P = 0.035) and heart rate recovery in the first minute after exercise (pyridostigmine = 25 +/- 2 beats/min vs. placebo = 22 +/- 2 beats/min; P = .005), whereas peak heart rate was similar to placebo. Oxygen pulse, an indirect indicator of stroke volume, was higher under pyridostigmine during submaximal exercise.

CONCLUSIONS

Pyridostigmine was well tolerated by heart failure patients, leading to improved hemodynamic profile during dynamic exercise.

Cholinergic stimulation with pyridostigmine prevents the impairment in ventricular function during mental stress in coronary artery disease patients

Mental stress causes physiological autonomic adjustments that may trigger myocardial ischemia and ventricular dysfunction in patients with coronary artery disease. Thus, it was hypothetized that cholinergic stimulation may counteract the ventricular dysfunction provoked by mental stress in coronary disease. Six patients with coronary disease underwent a randomized, double-blind, cross-over, and placebo-controlled protocol in which they received placebo or a single dose of pyridostigmine bromide (45 mg p.o.), a reversible cholinesterase inhibitor, and thus, a cholinomimetic agent 2 h before a standard mental stress task (Stroop color-word test), while hemodynamic and echocardiographic variables were continuously monitored. There were no signs of myocardial ischemia on ECG during mental stress under PYR or placebo. Heart rate and blood pressure increased during mental stress (P<0.01) similarly with placebo and PYR (P>0.05). There were no ventricular wall motion abnormalities during mental stress with either placebo or PYR, but mental stress decreased ejection fraction (pre 63+/-2%, stress 57+/-2%; P=0.004) and impaired the indices of diastolic ventricular function. On the other hand, PYR prevented the fall in ejection fraction (pre 62+/-2%, stress 64+/-2%; P=0.13) and in the indices of diastolic function (P>0.05). In conclusion, cholinergic stimulation with pyridostigmine prevented the impairment in myocardial function during mental stress in patients with coronary artery disease.

Sarin produces delayed cardiac and central autonomic changes

The aim was to evaluate the acute and delayed effects of low dose sarin exposure on cardiac autonomic and brainstem catecholaminergic function in mice. The rationale was to expand our knowledge of the cardiovascular effects of this neurotoxic, acetylcholinesterase (AChE) inhibitor. C57BL/6 male mice with telemetric arterial catheters were injected with saline or sarin (8 microg/kg, 0.05x LD(50); sc, two injections) with blood pressure (BP) measurements made at 1 and 10 weeks after sarin exposure. BP and pulse interval variability (PI) and low and high frequency spectral oscillations were measured using autoregressive spectral analysis. In situ hybridization (ISH) was used to quantify tyrosine hydroxylase (TH) mRNA expression in brainstem cardiovascular centers. Sarin had no effect on blood AChE activity, heart rate (HR) or BP. There was a biphasic response in PI variance, an early increase (+140%) and a delayed decrease (-62%) at more than 2 months after sarin exposure. There were no changes in BP variance. Assuming that increased PI variance is a positive outcome, the short-term response to sarin should be protective. This is opposite for the delayed decrease in PI variance which is associated with adverse cardiovascular effects. There was an increase in TH mRNA in both locus coeruleus (0.18+/-0.05 vs. 1.4+/-0.2 microCi/g; control vs. sarin) and dorsal vagal complex (0.09+/-0.06 vs. 1.17+/-0.03 microCi/g; control vs. sarin). Results show that a dose of sarin which had no peripheral cholinergic effects caused changes in autonomic modulation, a short-term enhancement followed by a delayed impairment in heart rate variability. Sarin-induced cardiac effects suggest a controversial aspect to the use of pharmacological agents which target AChE for management of cardiovascular risk.

Reduced Hemodynamic Responses to Physical and Mental Stress Under Low-Dose Rilmenidine in Healthy Subjects

Activation of the sympathetic nervous system plays a major role in the pathogenesis and prognosis of cardiovascular diseases. Rilmenidine is an I(1)-imidazoline receptor agonist that reduces blood pressure by modulation of central sympathetic activity, but the effects of low-dose rilmenidine on the hemodynamic responses to physiological maneuvers that increase adrenergic drive is not known. To assess the effects of low-dose rilmenidine on the hemodynamic responses to stress, 32 healthy subjects (20-56 years old) underwent acute physical exercise (n = 15, individualized ramp protocol on treadmill) and mental stress (n = 17, word color Stroop and mental arithmetics tests) two hours after the oral administration of 0.5 mg of rilmenidine (RIL) or placebo (PLA) following a randomized, double-blind, placebo controlled crossover study. No subject complained of any side effect. Rilmenidine reduced peak exercise heart rate (PLA: 187 +/- 7; RIL: 181 +/- 9 bpm; P = 0.003), but did not modify peak aerobic power (VO(2max) - PLA: 41.7 +/- 6.2; RIL: 42.3 +/- 6.7 ml/kg/min; P = 0.26). During mental stress, rilmenidine inhibited the peak systolic (PLA: 123 +/- 10; RIL: 114 +/- 8 mmHg; P = 0.02) and diastolic (PLA: 86 +/- 7; RIL: 81 +/- 7 mmHg; P <0.05) blood pressure responses. In conclusion, rilmenidine reduced the hemodynamic response to physical and mental stress stimuli without limiting exercise capacity. These results support the concept that rilmenidine, at a dose lower than the ones recommended to treat hypertension, reduced the myocardial oxygen demand to stress and may carry potential clinical impact.

Pyridostigmine reduces QTc interval during recovery from maximal exercise in ischemic heart disease

Following a randomized, cross-over, and double-blind design, 14 patients with coronary heart disease were submitted, to maximal cardiopulmonary exercise tests on a treadmill, 2 h after the oral administration of either placebo or pyridostigmine bromide (45 mg), a reversible cholinesterase inhibitor. One observer, who was blind to the experimental condition, measured RR and QT intervals over the 12 electrocardiographic leads in the first and third minute of active recovery from exercise. Paired t test was used to compare each variable measured in the same moment after placebo and pyridostigmine. Pyridostigmine reduced the QTc interval in the first minute of active recovery when compared to placebo (P=0.004). Two patients, whose heart rate recovery (1st minute) was below normal values (patient 1=4 bpm; patient 2=7 bpm; i.e. <12 bpm) presented with correction of this variable after pyridostigmine ingestion (patient 1=22 bpm; patient 2=36 bpm). Prospective trials should evaluate the impact of cholinergic stimulation with pyridostigmine on mortality.

The subacute effects of exercise: concept, characteristics, and clinical implications

Physical exercise represents a physiological stress to the organism producing acute integrative physiological adjustments, whereas repetitive and regular sessions of physical effort provoke chronic physiological adaptations that develop throughout the weeks of training and increase exercise capacity. The present work presents and discusses the concept of subacute effects of exercise, those physiological responses occurring between single bouts of exercise.