ANALYSIS OF THE ROLE OF NITRIC-OXIDE IN THE RELAXANT EFFECT OF THE CRUDE EXTRACT AND FRACTIONS FROM EUGENIA-UNIFLORA IN THE RAT THORACIC AORTA

This study has evaluated the possible role played by the L-arginine-ni tric oxide pathway in the vasorelaxant action of the hydroalcoholic ex tract from Eugenia uniflora, and fractions from the extract, in rings of rat thoracic aorta. The addition of an increasing cumulative concen tration of hydroalcoholic extract from E. uniflora (1-300 mu g mL(-1)) caused a concentration-dependent relaxation response in intact endoth elium-thoracic aorta rings pre-contracted with noradrenaline (30-100 n M). The IC50 value, with its respective confidence limit, and the maxi mum relaxation (R-max) were 7.02 (4.77-10.00) mu g mL(-1) and 83.94+/- 3.04%, respectively. The removal of the endothelium completely abolish ed these responses. The nitric oxide synthase inhibitors N-omega-nitro -L-arginine (L-NOARG, 30 mu M) and N-omega-nitro-L-arginine methyl est er (L-NAME, 30 mu M), inhibited the relaxation (R-max) to -10.43+/-7.8 1% and -3.69+/-2.62%, respectively. In addition, L-arginine (1 mM), bu t not D-arginine (1 mM), completely reversed inhibition by L-NOARG. Me thylene blue (30 mu M), a soluble guanylate cyclase inhibitor, reduced the relaxation induced by the extract to 14.60+/-7.40%. These data in dicate that in the rat thoracic aorta the hydroalcoholic extract, and its fractions, from the leaves of E. uniflora have graded and endothel ium-dependent vasorelaxant effects.