Alpha(1)-Adrenoceptors Activation Decreases Myocardial Contractility in Newborn Rats

Abstract

Alpha(1)-adrenergic receptors (α1-AR) are found in cardiomyocytes, endothelial cells, and smooth muscle cells of humans and animals. Despite the fact that α1-AR make up 10% of the total number of adrenergic receptors, these receptors also involved in the regulation of inotropic and chronotropic functions of the heart. According to some scientists, the effects of α1-AR activation are not required for the basal contractile function of the heart while other group of researchers believe that α1-AR can be considered as cardioprotective targets; in particular, it is postulated that the α1A-subtype of adrenergic receptors can provide significant inotropic support in cardiac pathologies. This study was carried out on 6-7-day-old outbred newborn rat pups to evaluate the effect of alpha(1)-adrenoceptors activation on the myocardial contractility in newborn rats. For this, Alpha1-adrenergic receptors were stimulated by the pharmacological drug methoxamine at concentrations of 10-9-10-6 mol and the reaction of the contractile force of the strips of myocardium ventricles and heart atria in response to the agonist was investigated. Results of study revealed that stimulation of alpha1-adrenergic receptors, regardless of the methoxamine concentration, led to a negative inotropic reaction of the myocardium of atria and ventricles of newborn rat pups. This study showed unidirectional inotropic responses on rat atrial and ventricular myocardium in response to α1-adrenergic receptors stimulation. Methoxamine smoothly reduces the contractile force of the strips of myocardium atria and ventricles. At the same time, the concentration dependence on the inotropic reaction of the myocardium was observed. Results of study suggested that probably α1-adrenergic receptors along with the main regulators β-adrenergic receptors carry out fine tuning of the heart activity.