The present study was designed to examine the vasorelaxant action of the herbal medicine Catuama and the hydroalcoholic extracts (HE) of each plant present in this product and to compare their effects with that caused by acetylcholine (ACh) in intact ((+)E) or in endothelium-rubbed ((-)E) rings of rat thoracic aorta (RA), guinea-pig pulmonary artery (GPPA), guinea-pig mesenteric artery (GPMA), rabbit pulmonary artery (RPA) and rabbit mesenteric artery (RMA) precontracted with noradrenaline (NA) or phenylephrine (PE). The extract of Catuama (1-3000 mu g/mL) produced graded relaxation of RA, (+)E or (-)E, with mean EC(50) of 430 mu g/mL and congruent to 3000 mu g/mL and E(max) of 81%+/-15% and 47%+/-4%, respectively. The nitric oxide (NO) synthase inhibitor, N-omega-nitro-L-arginine (L-NOARG, 100 mu M), inhibited its vasorelaxant action (p<0.05) in RA ((+)E), while indomethacin (3 mu M), propranolol (1 mu M), glibenclamide (1 mu M), methylene blue (10 mu M) and apamin (0.1 mu M) had no significant effect. ACh (1-1000 mu M) caused graded relaxation in RA with (+)E, these effects being markedly antagonized by L-NOARG (100 mu M), by methylene blue (10 mu M) and partially by apamin (0.1 mu M), but not by indomethacin (3 mu M), glibenclamide (1 mu M) or propranolol (1 mu M). The Catuama extract (1-3000 mu g/mL) produces partial relaxations in rings of RMA (mean EC(50) of 1073 mu g/mL and E(max) 56%+/-13%), an effect which was antagonized by L-NOARG (100 mu M). In RPA ((+)E) the extract produces partial relaxation followed by contraction (E(max) 28%+/-6% ), an effect which was abolished by L-NOARG (100 mu M) or methylene blue (10 mu M). The extract caused graded relaxation in rings of GPPA and GPMA with mean EC(50) values of 60 mu g/mL and 1148 mu g/mL and E(max) 96%+/-2% and 88%+/-12%, respectively, L-NOARG (100 mu M) blocked the Catuama extract vasorelaxation In GPPA and only partially in GPMA, but markedly antagonized the vasorelaxations caused by ACh in both GPPA and RMA. The HE Paullinea cupana, Zinziber officinalis and Trichilia catigua (1-3000 mu g/mL) caused a graded vasorelaxant effect (+)E of RA with a mean EC(50) of 22, 55 and 1793 mu g/mL and E(max) 100%, 86%+/-7%, 70%+/-2%, respectively. In addition, the HE of P. cupana also caused graded relaxation in (-)E of RA with EC(50) and E(max) of 233 mu g/mL and 100%, respectively, while T. catigua and Z. officinalis produced partial relaxation in RA (+)E. In contrast the HE of Ptychopetalum olacoides caused little contraction (46%+/-14%). These results demonstrate that the medicinal herb Catuama produces significant vasorelaxation responses in vessels from different animal species, and show that its effects are in great part dependent on the release of NO or NO-derived substances. Our results also demonstrate that the vasorelaxant action of the product Catuama seems to be due to the action of the active principles present mainly in P. capuna; T. catigua and, to a lesser extent, in Z. officinalis. Such results may contribute to the explanation of its beneficial effect of Catuama herbal medicine in the management of cardiovascular disturbances. (C) 1997 by John Wiley & Sons, Ltd.