Vasorelaxant effect of the Lippia alba essential oil and its major constituent, citral, on the contractility of isolated rat aorta

The Lippia alba (Mill.) N.E. Brown (Verbenaceae) species popularly known as lemon balm has sedative, analgesic and spasmolytic properties. This study aimed to evaluate the vasorelaxant effect of the L. alba essential oil (EOLa) and its major constituent, citral, rat on aorta. Isometric muscle contraction were induced by potassium (K 60 mM) or phenylephrine (PHE, 0.1 mu M) in isolated aortic rings. EOLa and citral promoted a smooth muscle relaxant action, which was potentiated by the presence of the endothelium; PHE-induced contractions (0.1 mu M) in aorta with endothelium, had EC50 values of 352.73 +/- 19.39 mu g/mL and 99.34 +/- 7.2 mu g/mL for EOLa and citral, respectively. In the presence of a nitric oxide synthase inhibitor, L-NAME, the EC50 values were 654.19 +/- 10.46 mu g/mL and 601.66 +/- 10.922 mu g/mL for EOLa and citral, respectively. EOLa and citral dose-dependently relaxed contractions induced by BAY-K 8644, a calcium channel agonist, and by Phorbol 12,13-dibutyrate an activator of protein kinase C. EOLa and citral produced a vasorelaxant effect in isolated aorta which was potentiated by the presence of endothelium. In summary, EOLa and citral, probably using several mechanisms of action, relaxed aortic smooth muscle with maximal pharmacologic efficacy.