Acute myocardial infarction (AMI) is the main cause of morbidity and mortality worldwide and is characterized by severe and fatal arrhythmias induced by cardiac ischemia/reperfusion (CIR). However, the molecular mechanisms involved in these arrhythmias are still little understood. To investigate the cardioprotective role of the cardiac Ca²⁺/cAMP/adenosine signaling pathway in AMI, L-type Ca²⁺ channels (LTCC) were blocked with either nifedipine (NIF) or verapamil (VER), with or without A₁-adenosine (ADO), receptors (A₁R), antagonist (DPCPX), or cAMP efflux blocker probenecid (PROB), and the incidence of ventricular arrhythmias (VA), atrioventricular block (AVB), and lethality (LET) induced by CIR in rats was evaluated. VA, AVB and LET incidences were evaluated by ECG analysis and compared between control (CIR group) and intravenously treated 5 min before CIR with NIF 1, 10, and 30 mg/kg and VER 1 mg/kg in the presence or absence of PROB 100 mg/kg or DPCPX 100 µg/kg. The serum levels of cardiac injury biomarkers total creatine kinase (CK) and CK-MB were quantified. Both NIF and VER treatment were able to attenuate cardiac arrhythmias caused by CIR; however, these antiarrhythmic effects were abolished by pretreatment with PROB and DPCPX. The total serum CK and CK-MB were similar in all groups. These results indicate that the pharmacological modulation of Ca²⁺/cAMP/ADO in cardiac cells by means of attenuation of Ca²⁺ influx via LTCC and the activation of A₁R by endogenous ADO could be a promising therapeutic strategy to reduce the incidence of severe and fatal arrhythmias caused by AMI in humans.

Background: Although several studies suggest that heparins prevent arrhythmias caused by acute myocardial infarction (AMI), the molecular mechanisms involved remain unclear. To investigate the involvement of pharmacological modulation of adenosine (ADO) signaling in cardiac cells by a low-molecular weight heparin (enoxaparin; ENOX) used in AMI therapy, the effects of ENOX on the incidences of ventricular arrhythmias (VA), atrioventricular block (AVB), and lethality (LET) induced by cardiac ischemia and reperfusion (CIR) were evaluated, with or without ADO signaling blockers. Methods: To induce CIR, adult male Wistar rats were anesthetized and subjected to CIR. Electrocardiogram (ECG) analysis was used to evaluate CIR-induced VA, AVB, and LET incidence, after treatment with ENOX. ENOX effects were evaluated in the absence or presence of an ADO A1-receptor antagonist (DPCPX) and/or an inhibitor of ABC transporter-mediated cAMP efflux (probenecid, PROB). Results: VA incidence was similar between ENOX-treated (66%) and control rats (83%), but AVB (from 83% to 33%) and LET (from 75% to 25%) incidences were significantly lower in rats treated with ENOX. These cardioprotective effects were blocked by either PROB or DPCPX. Conclusion: These results indicate that ENOX was effective in preventing severe and lethal arrhythmias induced by CIR due to pharmacological modulation of ADO signaling in cardiac cells, suggesting that this cardioprotective strategy could be promising in AMI therapy.

Defined as systemic hypotension caused by intense vasodilation due to the loss of systemic vascular resistance, vasoplegic syndrome (VS) is associated with elevated morbidity and mortality in humans. Although vasopressors such as norepinephrine and vasopressin are the first-choice drugs for VS treatment, several other drugs such as methylene blue (MB) can be used as adjuvant therapy including rescue therapy. To develop new pharmacological strategies to reduce the risk of VS, we investigated the effects of treatments with MB (2 mg/kg/IV), omeprazole (OME, 10 mg/kg/IV), and their combination in an animal model of cardiac ischemia–reperfusion (CIR). The ventricular arrhythmia (VA), atrioventricular block (AVB), and lethality (LET) incidence rates caused by CIR (evaluated via ECG) and serum levels of the cardiac lesion biomarkers creatine kinase–MB (CK-MB) and troponin I (TnI) in adult rats pretreated with saline solution 0.9% and submitted to CIR (SS + CIR group) were compared to those pretreated with MB (MB + CIR group), OME (OME + CIR group), or the MB + OME combination (MB + OME + CIR group). The AVB and LET incidence rates in the MB + CIR (100%), OME + CIR (100%), and MB + OME + CIR (100%) groups were significantly higher compared to the SS + CIR group (60%). The serum level of CK-MB in these groups were also significantly higher compared to the SS + CIR group, demonstrating that the treatments before CIR with MB, OME, and MB + OME produced similar effects in relation to cardiac function and the occurrence of lesions. These results demonstrate that the treatment of animals subjected to the CIR protocol with OME produced the same effects promoted by the treatment with MB, which may suggest the possibility of using OME alone or in combination with MB in medical clinics in treatment of VS.

The most common cause of morbidity and death worldwide is acute myocardial infarction (AMI), which is typified by severe and deadly arrhythmias resulting from cardiac ischemia and reperfusion (CIR). We chose to investigate the possible cardioprotective activity of epiisopiloturine (EPI), an imidazole alkaloid presents in the leaves of Pilocarpus microphyllus, in an animal model of CIR in rats. Control rats were treated with 0.9% saline solution and then subjected to CIR (SS + CIR); they were compared to rats pretreated with either 10 mg/kg (EPI10 + CIR group) or 15 mg/kg EPI (EPI15 + CIR) before CIR. ECG analysis was used to assess the incidence of ventricular arrhythmias (VAs), atrioventricular block (AVB), and lethality (LET) brought on by CIR in these rats. Serum creatine kinase-MB (CK-MB) was assessed using a colorimetric assay. In comparison to the SS + CIR group, animals treated with EPI15 + CIR had lower AVB incidence, which decreased from 85.7% to 21.4%, while LET incidence decreased from 71.4% to 21.4%. In both EPI10 + CIR and EPI15 + CIR groups, serum CK-MB was lower than in SS + CIR positive controls. These findings suggest that administration of EPI (15 mg/kg) before CIR could reduce the incidences of AVB and LET, as well as cardiac injury markers, which suggests that, likely due to its antioxidant effects, EPI may be a promising drug to reduce LET in patients with severe and fatal arrhythmia due to AMI.

Characterized by severe and fatal arrhythmias induced by cardiac ischemia/reperfusion (CIR), acute myocardial infarction (AMI) is the main cause of morbidity and mortality worldwide. To investigate the cardioprotective role of cardiac Ca2+/cAMP/adenosine signaling in AMI, the effects of L-type Ca2+ channels (LTCC) blocker Nifedipine (NIF) and Verapamil (VER), in the absence and presence of A1-adenosine receptors (A1R) blocker (DPCPX), on the incidence of ventricular arrhythmias (VA), atrioventricular block (AVB) and lethality (LET) induced by CIR in rats were evaluated. CIR was induced in adult male Wistar rats (290-320 g) by occlusion of the left anterior descendent coronary artery (10 min) followed by reperfusion (75 min). VA, AVB and LET incidences were evaluated by ECG analysis and compared between control (CIR group) and intravenously treated 5 min before CIR with NIF 1, 10, and 30 mg/kg (NIF+CIR groups) or DPCPX 100 µg/kg plus NIF 10 mg/kg (DPCPX+NIF+CIR group) and VER 1 mg/kg (VER+CIR group) or DPCPX 100 µg/kg plus VER 1 mg/kg (DPCPX+VER+CIR group). Serum levels of cardiac injury biomarkers (TCK and CK-MB) were quantified. In CIR group, VA, AVB and LET incidences were 90, 80 and 70%, respectively. In NIF+CIR group, incidence of VA was reduced to 50, 30 and 30%, AVB to 25, 10 and 20%, and LET to 25, 20 and 20%, and respectively. In DPCPX+NIF+CIR group, these incidences were not different from CIR group. TCK and CK-MB levels were similar in all groups. These results indicate that pharmacological modulation of the Ca2+/cAMP/adenosine signaling in cardiac cells by LTCC blockade and A1R stimulation could be a new strategy cardioprotective for human AMI therapy.

Acute myocardial infarction (AMI), which is characterized by severe and fatal arrhythmias resultant from cardiac ischemia/reperfusion (CIR), is the leading cause of morbidity and mortality in the world. Considering that epiisopiloturin (EPI), an imidazole alkaloid found in the leaves of Pilocarpus microphyllus produded anti-inflammatory and antioxidant effects in an animal model of peritonitis, paw edema and peritonitis in mice, we decided to investigate the potential cardioprotective activity of EPI in animal model of CIR. Then, adult rats submitted to CIR pretreated with EPI 10 mg/kg (EPI10+CIR group) or 15 mg/kg (EPI15+CIR group) were compared to control animals submitted to CIR treated with saline solution 0.9% (CIR group). To evaluate the incidence of ventricular arrhythmias (VA), atrioventricular block (AVB) and lethality (LET) induced by CIR in these rats, the ECG analysis was performed. Serum levels of cardiac damage markers, total creatine kinase (CK) and CK-MB, were measured. The results showed that the AVB incidence was reduced from 80% to 30%, and LET incidence was reduced from 70% to 20%, compared to CIR group. Serum levels of LDH, total CK and, CK-MB was similar in all groups studied. These results indicate that the treatment with EPI (15 mg/kg, IV) before CIR was effective to produce cardioprotective effects. Thus, the use of EPI could be a promisse strategy to reduce the incidence of severe and fatal arrhythmias associated with AMI.