The effects of olive leaf extract and 28 days forced treadmill exercise on electrocardiographic parameters in rats

Background:

There is evidence that regular activity can prevent of cardiovascular diseases. There are many reports that exercise and the consumption of olive leaf extract (OLE) have a positive effect on cardiovascular parameters. This study was conducted to compare the effects of exercise and OLE alone and together on electrocardiographic parameters in rats.

Materials and Methods:

Male Sprague–Dawley rats were randomly divided into six groups (n = 8 rats in each): Control, exercise, OLE (100, 200, and 400 mg/kg, orally for 14 days), and exercise + OLE (200 mg/kg of extract, orally for 14 days). Exercise training in rats was performed using treadmill for 28 days (1 h/day). Electrophysiological parameters including heart rate, PR interval, QT interval, QT corrected (QTc), RR interval, QRS voltage, and duration were obtained from lead II electrocardiogram (ECG) recorded by a PowerLab system. Statistical evaluation was done by one-way analysis of variance followed by Fisher's least significant difference test and P < 0.05 was considered statistically significant.

Results:

The amounts of QT (P = 0.0009) and QTc interval (P = 0.0004), RR interval (P < 0.0001), QRS duration (P = 0.004), and QRS voltage (P = 0.003) in the exercise group were significantly higher than those of the control group. However, there were no significant differences in PR interval in comparison with the control group. Exercise (P < 0.0001) and OLE (400 mg/kg, P = 0.043) alone and both in combination (P = 0.007) reduced heart rate and increased the amount of QRS voltage (P = 0.003, P = 0.047, and P = 0.046, respectively) and RR interval (P < 0.0001, P = 0.046, and P = 0.0009, respectively).

Conclusion:

Results of this study indicated that administration of OLE alone and in combination with exercise has negative chronotropic and positive inotropic effects and also it can prevent of prolongation of QT and QTc interval induced by severe exercise.

The inhibitory effect of rosmarinic acid on overexpression of NCX1 and stretch- induced arrhythmias after acute myocardial infarction in rats

The incidence of arrhythmias is the main cause of high mortality after myocardial infarction (AMI). The aim of the present study was to determine whether the rosmarinic acid (RA) could reduce the stretch-induced arrhythmias (SIAs) related to overexpression of NCX1 after AMI. Adult male Sprague-Dawley rats were randomly allocated into six groups: Sham, MI (100 mg/kg of isoproterenol (Iso), subcutaneously, on two consecutive days), RA (30 mg/kg, orally, 14 days), and RA (10, 15 and 30 mg/kg, 14 days) + I. MI induction was performed on the 13th and 14th days of the study period. Forty-eight hours after the first injection of Iso, the parameters of hypertrophy, plasma levels of malondialdehyde (MDA) and lipid profile were evaluated. Using Langendorff apparatus, the isolated hearts were transiently stretched for 5 s with three different end-diastolic volumes (ΔV1to3 = 0.05, 0.1 and 0.2 mL). Cardiac function parameters were measured for 30 s, and ventricular arrhythmias were recorded for 3 min after each stretch. Finally, the levels of cardiac troponin-I and NCX1 mRNA expression were examined. The rats of MI group showed a significant increase in hypertrophy index, MDA, triglyceride and cholesterol (P < 0.001). Additionally, a marked impairment in cardiac parameters, an increase in the rates of SIAs and NCX1 expression, and a decrease in troponin-I (P < 0.001) were observed. RA at three doses especially 15 mg/kg strongly improved almost all the mentioned factors (P < 0.001). Our results confirm that RA pretreatment could prevent hypertrophia, arrhythmia and cardiac dysfunction following AMI which is associated with inhibition of lipid peroxidation and overexpression of NCX1.

The cardioprotective effect of rosmarinic acid on acute myocardial infarction and genes involved in Ca2+ homeostasis

Acute myocardial infarction (AMI) is a common cause of hospitalisation and high mortality due to lethal arrhythmias. Sarcoplasmic reticulum Ca2+ ATPase (SERCA2) and ryanodine receptor (RyR2) regulate the cytosolic Ca2+ ion concentration. Rosmarinic acid (RA) is one of the most common caffeic esters in Rosmarinus officinalis. The present study was conducted to test the hypothesis whether RA can protect cardiac function against AMI and arrhythmias induced by isoproterenol through the regulatory effect of SERCA2 and RyR2 gene expression. To this aim, male Sprague-Dawley rats were allocated into in vivo and ex vivo studies and received RA (10, 15, and 30 mg/kg; 14 days). AMI was induced by two consecutive subcutaneous injections of 100 mg/kg isoproterenol. Blood pressure (BP), heart rate, electrocardiography (ECG) parameters, plasma levels of cardiac biomarkers, and antioxidative enzymes were evaluated (in vivo study). Cardiac functions were measured in isolated hearts using Langendorff set up. Gene expressions of SERCA2 and RyR2 were measured in left ventricular heart. Isoproterenol administration showed a significant decline in BP, QRS voltage, activities of antioxidant enzymes, cardiac function, and gene expressions of SERCA2 and RyR2. The results also indicated a significant increase in heart rate, ST-elevation, cardiac biomarkers, and antioxidant enzymes. RA at 30 mg/kg dosage showed the best effect on the improvement of the mentioned factors. This study suggests that RA has potent cardioprotective effects against AMI and arrhythmia, which may be due to its ability to enhance expression of plasma antioxidant enzymes and genes involved in Ca2+ homeostasis SERCA2 and RyR2. The protective role of RA is also possibly related to its antiadrenergic effects.