Neuronal cholinergic signaling constrains norepinephrine activity in the heart.

It is well known that cholinergic hypofunction contributes to cardiac pathology, yet, the mechanisms involved remain unclear. Our previous study has shown that genetically engineered model of cholinergic deficit, the vesicular acetylcholine transporter knockdown homozygous (VAChT KDHOM) mice, exhibit pathological cardiac remodeling and a gradual increase in cardiac mass with aging. Given that an increase in cardiac mass is often caused by adrenergic hyperactivity, we hypothesized that VAChT KDHOM mice might have an increase in cardiac norepinephrine (NE) levels. We thus investigated the temporal changes in NE content in the heart from 3-, 6-, and 12-mo-old VAChT mutants. Interestingly, mice with cholinergic hypofunction showed a gradual elevation in cardiac NE content, which was already increased at 6 mo of age. Consistent with this finding, 6-mo-old VAChT KDHOM mice showed enhanced sympathetic activity and a greater abundance of tyrosine hydroxylase positive sympathetic nerves in the heart. VAChT mutants exhibited an increase in peak calcium transient, and mitochondrial oxidative stress in cardiomyocytes along with enhanced G protein-coupled receptor kinase 5 (GRK5) and nuclear factor of activated T-cells (NFAT) staining in the heart. These are known targets of adrenergic signaling in the cell. Moreover, vagotomized-mice displayed an increase in cardiac NE content confirming the data obtained in VAChT KDHOM mice. Establishing a causal relationship between acetylcholine and NE, VAChT KDHOM mice treated with pyridostigmine, a cholinesterase inhibitor, showed reduced cardiac NE content, rescuing the phenotype. Our findings unveil a yet unrecognized role of cholinergic signaling as a modulator of cardiac NE, providing novel insights into the mechanisms that drive autonomic imbalance.

Electrical stimulation of the aortic depressor nerve in conscious rats overcomes the attenuation of the baroreflex in chronic heart failure.

Chronic heart failure (CHF) is characterized by autonomic dysfunction combined with baroreflex attenuation. The hypotensive and bradycardic responses produced by electrical stimulation of the aortic depressor nerve (ADN) were examined in conscious CHF and control male Wistar rats (12-13 wk old). Furthermore, the role of parasympathetic and sympathetic nervous system in mediating the cardiovascular responses to baroreflex activation was evaluated by selective ß1-adrenergic and muscarinic receptor antagonists. CHF was induced by myocardial infarction. After 6 wk, the subjects were implanted with electrodes for ADN stimulation. Twenty-four hours later, electrical stimulation of the ADN was applied for 20 s using five different frequencies (5, 15, 30, 60, and 90 Hz), while the arterial pressure was recorded by a catheter implanted into the femoral artery. Electrical stimulation of the ADN elicited progressive and similar hypotensive and bradycardic responses in control (n = 12) and CHF (n = 11) rats, while the hypotensive response was not affected by methylatropine. Nevertheless, the reflex bradycardia was attenuated by methylatropine in control, but not in CHF rats. Atenolol did not affect the hypotensive or bradycardic response in either group. The ADN function was examined under anesthesia through electroneurographic recordings. The arterial pressure-ADN activity relationship was attenuated in CHF rats. In conclusion, despite the attenuation of baroreceptor function in CHF rats, the electrical stimulation of the ADN elicited a stimulus-dependent hypotension and bradycardia of similar magnitude as observed in control rats. Therefore, electrical activation of the aortic baroreflex overcomes both the attenuation of parasympathetic function and the sympathetic overdrive.

Autonomic cardiocirculatory control in mice with reduced expression of the vesicular acetylcholine transporter.

In cardiovascular diseases, sympathetic tone has been comprehensively studied, whereas parasympathetic tone has received minor attention. The vesicular ACh transporter (VAChT) knockdown homozygous (VAChT KD(HOM)) mouse is a useful model for examining the cardiocirculatory sympathovagal balance. Therefore, we investigated whether cholinergic dysfunction caused by reduced VAChT expression could adversely impact hemodynamic parameter [arterial pressure (AP) and heart rate (HR)] daily oscillation, baroreflex sensitivity, hemodynamic variability, sympathovagal balance, and cardiovascular reactivity to restraint stress. Wild-type and VAChT KD(HOM) mice were anesthetized for telemetry transmitter implantation, and APs and HRs were recorded 10 days after surgical recovery. Changes in HR elicited by methylatropine and propranolol provided the indexes of sympathovagal tone. Cardiovascular reactivity in response to a restraint test was examined 24 h after continuous recordings of AP and HR. VAChT KD(HOM) mice exhibited reduced parasympathetic and elevated sympathetic tone. Daily oscillations of AP and HR as well as AP variability were similar between groups. Nevertheless, HR variability, patterns with two dissimilar variations from symbolic analysis, and baroreflex sensitivity were reduced in VAChT KD(HOM) mice. The change in mean AP due to restraint stress was greater in VAChT KD(HOM) mice, whereas the tachycardic response was not. These findings demonstrate that the cholinergic dysfunction present in the VAChT KD(HOM) mouse did not adversely impact basal hemodynamic parameters but promoted autonomic imbalance, an attenuation of baroreflex sensitivity, and a greater pressure response to restraint stress. These results provide a framework for understanding how autonomic imbalance impacts cardiovascular function.

Formative assessment scores in tutorial sessions correlates with OSCE and progress testing scores in a PBL medical curriculum.

BACKGROUND: Effective assessments programs are a challenge in problem-based learning (PBL). One of the main principles of this educational setting is the Formative Assessment (FA). We hypothesized that students' performance assessed by FA in tutorial sessions in a PBL curriculum is related to other summative assessments. OBJECTIVE: To investigate the correlation among FA in tutorial sessions with grades obtained in Objective Structured Clinical Evaluation (OSCE) and Progress Testing (PT) to better understand the assessment process in PBL medical teaching approach and to predict student's future performance. DESIGN: An observational cross-sectional study was conducted comparing FA, OSCE and PT scores from 4th to 8th semester medical students. Correlation analyses were performed using pooled and separate data from the 4th and 8th semesters. RESULTS: From the 5th to 8th semester, OSCE scores were smaller compared to the FA, while PT scores were lower in all stages. In the pooled data, the correlation analysis showed a significant positive relationship between grades on FA and OSCE, FA and PT and OSCE and PT. A significant correlation among the three assessments strategies was also detected in the 8th semester, but not in the 4th semester. CONCLUSIONS: Assessment strategies in PBL approach, including FA, OSCE and PT, have positive correlations, which increases as the medical course becomes more complex.

Elastase-2, an angiotensin II-generating enzyme, contributes to increased angiotensin II in resistance arteries of mice with myocardial infarction.

BACKGROUND AND PURPOSE: Angiotensin II (Ang II), whose generation largely depends on angiotensin-converting enzyme (ACE) activity, mediates most of the renin-angiotensin-system (RAS) effects. Elastase-2 (ELA-2), a chymotrypsin-serine protease elastase family member 2A, alternatively generates Ang II in rat arteries. Myocardial infarction (MI) leads to intense RAS activation, but mechanisms involved in Ang II-generation in resistance arteries are unknown. We hypothesized that ELA-2 contributes to vascular Ang II generation and cardiac damage in mice subjected to MI. EXPERIMENTAL APPROACH: Concentration-effect curves to Ang I and Ang II were performed in mesenteric resistance arteries from male wild type (WT) and ELA-2 knockout (ELA-2KO) mice subjected to left anterior descending coronary artery ligation (MI). KEY RESULTS: MI size was similar in WT and ELA-2KO mice. Ejection fraction and fractional shortening after MI similarly decreased in both strains. However, MI decreased stroke volume and cardiac output in WT, but not in ELA-2KO mice. Ang I-induced contractions increased in WT mice subjected to MI (MI-WT) compared with sham-WT mice. No differences were observed in Ang I reactivity between arteries from ELA-2KO and ELA-2KO subjected to MI (MI-ELA-2KO). Ang I contractions increased in arteries from MI-WT versus MI-ELA-2KO mice. Chymostatin attenuated Ang I-induced vascular contractions in WT mice, but did not affect Ang I responses in ELA-2KO arteries. CONCLUSIONS AND IMPLICATIONS: These results provide the first evidence that ELA-2 contributes to increased Ang II formation in resistance arteries and modulates cardiac function after MI, implicating ELA-2 as a key player in ACE-independent dysregulation of the RAS.

Elastase-2, a Tissue Alternative Pathway for Angiotensin II Generation, Plays a Role in Circulatory Sympathovagal Balance in Mice.

In vitro and ex vivo experiments indicate that elastase-2 (ELA-2), a chymotrypsin-serine protease elastase family member 2A, is an alternative pathway for angiotensin II (Ang II) generation. However, the role played by ELA-2 in vivo is unclear. We examined ELA-2 knockout (ELA-2KO) mice compared to wild-type (WT) mice and determined whether ELA-2 played a role in hemodynamics [arterial pressure (AP) and heart rate (HR)], cardiocirculatory sympathovagal balance and baroreflex sensitivity. The variability of systolic arterial pressure (SAP) and pulse interval (PI) for evaluating autonomic modulation was examined for time and frequency domains (spectral analysis), whereas a symbolic analysis was also used to evaluate PI variability. In addition, baroreflex sensitivity was examined using the sequence method. Cardiac function was evaluated echocardiographically under anesthesia. The AP was normal whereas the HR was reduced in ELA-2KO mice (425 ± 17 vs. 512 ± 13 bpm from WT). SAP variability and baroreflex sensitivity were similar in both strains. The LF power from the PI spectrum (33.6 ± 5 vs. 51.8 ± 4.8 nu from WT) and the LF/HF ratio (0.60 ± 0.1 vs. 1.45 ± 0.3 from WT) were reduced, whereas the HF power was increased (66.4 ± 5 vs. 48.2 ± 4.8 nu from WT) in ELA-2KO mice, indicating a shift toward parasympathetic modulation of HR. Echocardiographic examination showed normal fractional shortening and an ejection fraction in ELA-2KO mice; however, the cardiac output, stroke volume, and ventricular size were reduced. These findings provide the first evidence that ELA-2 acts on the sympathovagal balance of the heart, as expressed by the reduced sympathetic modulation of HR in ELA-2KO mice.

Pyridostigmine prevents haemodynamic alterations but does not affect their nycthemeral oscillations in infarcted mice.

The increase in acetylcholine yielded by pyridostigmine (PYR), an acetylcholinesterase inhibitor, was evaluated for its effect on the haemodynamic responses-mean arterial pressure (MAP) and heart rate (HR)-and their nycthemeral oscillation in mice before and one week after myocardial infarction (MI). Mice were anesthetized (isoflurane), and a telemetry transmitter was implanted into the carotid artery. After 5 days of recovery, the MAP and HR were recorded for 48 h (10 s every 10 min). Following this procedure, mice were submitted to surgery for sham or coronary artery ligation and received drinking water (VEHICLE) with or without PYR. Five days after surgery, the haemodynamic recordings were recommenced. Sham surgery combined with VEHICLE did not affect basal MAP and HR; nevertheless, these haemodynamic parameters were higher during the night, before and after surgery. MI combined with VEHICLE displayed decreased MAP and increased HR; these haemodynamic parameters were also higher during the night, before and after surgery. Sham surgery combined with PYR displayed similar results for MAP as sham combined with VEHICLE; however, PYR produced bradycardia. Nevertheless, MI combined with PYR exhibited no change in MAP and HR, but these haemodynamic parameters were also higher during the night, before and after surgery. Therefore, MI decreased MAP and increased HR, while PYR prevented these alterations. Neither MI nor PYR affected nycthemeral oscillations of MAP and HR. These findings indicate that the increase in acetylcholine yielded by PYR protected the haemodynamic alterations caused by MI in mice, without affecting the nycthemeral haemodynamic oscillations.

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 1st week, while the sympathetic tone was increased in the 1st and 4th 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 1st week, but enhanced it in the 4th 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.

Analysis of cardiovascular system responses to forced vital capacity in COPD.

BACKGROUND: The forced vital capacity (FVC) test is routinely performed to evaluate pulmonary function in patients with chronic obstructive pulmonary disease (COPD). However, the influence of the FVC maneuver on the cardiovascular system of patients with COPD is poorly understood. OBJECTIVES: To analyze the behavior of heart rate (HR), blood pressure (BP) and heart rate variability (HRV) during the FVC test in COPD patients. METHODS: Nineteen men with COPD (72±7 years, GOLD stage I=3, II=5, III=7 and IV=4 patients) performed the FVC test while having their HR monitored. HRV was assessed in time (rMSSD) and frequency domains (LF, HF and LF/HF) at rest, before and after the best FVC maneuver. BP was measured at rest, immediately before and at the end of the test, as well as 10 minutes after the end of the test. RESULTS: At the beginning of the FVC maneuver, HR decreased (p<0.001) and then increased gradually until the end of the test (p<0.001). After the end of maneuver, HR continued to increase until it reached a peak (p<0.001), and then it fell quickly to below at-rest values (p<0.001) prior to returning to baseline. The BP and HRV indices did not change during the assessment. CONCLUSION: The FVC test influences the behavior of COPD patient HR without changing autonomic control or BP.

Analysis of cardiovascular system responses to forced vital capacity in COPD / Análise das respostas do sistema cardiovascular ao teste de capacidade vital forçada na DPOC

BACKGROUND: The forced vital capacity (FVC) test is routinely performed to evaluate pulmonary function in patients with chronic obstructive pulmonary disease (COPD). However, the influence of the FVC maneuver on the cardiovascular system of patients with COPD is poorly understood. OBJECTIVES: To analyze the behavior of heart rate (HR), blood pressure (BP) and heart rate variability (HRV) during the FVC test in COPD patients. METHODS: Nineteen men with COPD (72±7 years, GOLD stage I=3, II=5, III=7 and IV=4 patients) performed the FVC test while having their HR monitored. HRV was assessed in time (rMSSD) and frequency domains (LF, HF and LF/HF) at rest, before and after the best FVC maneuver. BP was measured at rest, immediately before and at the end of the test, as well as 10 minutes after the end of the test. RESULTS: At the beginning of the FVC maneuver, HR decreased (p<0.001) and then increased gradually until the end of the test (p<0.001). After the end of maneuver, HR continued to increase until it reached a peak (p<0.001), and then it fell quickly to below at-rest values (p<0.001) prior to returning to baseline. The BP and HRV indices did not change during the assessment. CONCLUSION: The FVC test influences the behavior of COPD patient HR without changing autonomic control or BP.

CONTEXTUALIZAÇÃO: O teste de capacidade vital forçada (CVF) é rotineiramente realizado na avaliação da função pulmonar de pacientes com doença pulmonar obstrutiva crônica (DPOC). Entretanto, permanece pouco compreendida a influência do teste de CVF sobre o sistema cardiovascular de pacientes com DPOC. OBJETIVOS: Analisar o comportamento da frequência cardíaca (FC), pressão arterial (PA) e variabilidade da frequência cardíaca (VFC) no teste de CVF na DPOC. MÉTODOS: Dezenove homens com DPOC (72 ± 7 anos, no estágio de gravidade GOLD I=3, II=5, III=7 e IV=4 pacientes) realizaram a manobra de CVF e tiveram sua FC monitorada durante todo o exame, e a VFC analisada nos domínios do tempo (rMSSD) e da frequência (BF, AF e BF/AF) durante o repouso, antes e após a melhor manobra de CVF. A PA foi analisada no repouso, imediatamente ao final da manobra de CVF e 10 minutos após o término de todos os testes. RESULTADOS: Ao início da manobra de CVF, a FC reduziu (p<0,001) e, em seguida, aumentou progressivamente até o final do teste (p<0,001). Após término da manobra, a FC continuou a aumentar até atingir um pico (p<0,001) e depois caiu rapidamente a valores inferiores aos de repouso (p<0,001) e retornou ao seu valor basal. A PA e os índices da VFC não sofreram alterações nos períodos analisados. CONCLUSÃO: O teste de CVF influencia o comportamento da FC, sem alterar o seu controle autonômico, bem como a PA em pacientes com DPOC nos períodos analisados.