The positive inotropic effect of the ethyl acetate fraction from Erythrina velutina leaves on the mammalian myocardium: the role of adrenergic receptors

Objectives We studied the effects of ethyl acetate fraction (EAcF) obtained from Erythrina velutina leaves on mammalian myocardium. Methods The effect of EAcF on the contractility was studied using guinea‐pig left atria mounted in a tissue bath (Tyrode's solution, 29°C, 95% CO2, 5% O2) and electrically stimulated (1 Hz). Concentration‐response curves of EAcF were obtained in the presence of propranolol (1 μm), nifedipine (1 μm) and in reserpinized animals (5 mg/kg). The involvement of l‐type calcium current (ICa,L) on the EAcF effect was observed in cardiomyocytes of mice assessed using patch‐clamp technique. Key findings EAcF (550 μg/ml) had a positive inotropic effect, increasing the atrial force by 164% (EC50 = 157 ± 44 μg/ml, n = 6), but it was less potent than isoproterenol (EC50 = 0.0036 ± 0.0019 μg/ml, n = 8). The response evoked by EAcF was abolished by propranolol or nifedipine. Reserpine did not alter the inotropic response of EAcF. Furthermore, an enhancement of the ICa,L peak (31.2%) with EAcF was observed. Chemical analysis of EAcF revealed the presence of at least 10 different flavonoid glycoside derivatives. Two were identified as vicenin II and isorhoifolin. Conclusions We conclude that EAcF increases the cardiac contractile force by increasing the l‐type calcium current and activating the adrenergic receptor pathway.