Nitric oxide-dependent vasorelaxation induced by extractive solutions and fractions of Maytenus ilicifolia Mart ex Reissek (Celastraceae) leaves

This study reveals that an ethanolic supernatant obtained from an aqueous extractive solution prepared from residues of methanolic extracts of ground leaves of Maytenus ilicifolia is able to cause a concentration- and endothelium-dependent relaxation in pre-contract rat aorta rings, with EC50 of 199.7 (190–210) μg/ml. The non-selective nitric oxide synthase inhibitors l-NAME and l-NMMA abolished this effect, while superoxide dismutase and MnTBAP (a non-enzymatic superoxide dismutase mimetic) enhanced it. Further, relaxation induced by this ethanolic supernatant have been strongly inhibited by the guanylate cyclase inhibitors methylene blue and ODQ, as well as by the potassium channel blockers 4-aminopyridine and tetraethylammonium, but was unchanged by the cyclooxigenase inhibitor indomethacin and the membrane receptor antagonists atropine, HOE-140 and pirilamine. Partition of the ethanolic supernatant between H2O and EtOAc generated a fraction several times more potent, able to fully relax endothelium-intact aorta rings with an EC50 of 4.3 (3.9–4.8) μg/ml. 13C NMR spectrum of this fraction showed signals typical of catechin. This study reveals that the leaves of M. ilicifolia possess one or more potent substances able to relax endothelium-intact rat aorta rings, an event that appears to involve nitric oxide production, guanylate cyclase activation and potassium channel opening.