Cardiac alpha1-adrenoceptors mediate positive inotropy via myofibrillar sensitization

Alpha1-adrenoceptor agonists have advantages over standard cardiac inotropic agents because these sensitize myofibrils via a receptor-mediated mechanism. Alpha1-adrenoceptor stimulation enhances myocardial contraction without producing adverse rhythmic effects and calcium overload by increasing sensitiviity to calcium influx. This may be due to alkalinization of the intracellular pH and consequent increase in alkaline phosphatase-sensitive phosphorylation. The focus of cardiac pharmacology now centers on the phosphoinositol and adrenergic pathways in muscular contraction.