In this work, we studied the effect of the norlignan 2-(2'-hydroxy-4',6'-dimethoxyphenyl)-5-[( E)-propenyl]benzofuran (DMPP) in the rat aorta. In aortic rings with intact endothelium, DMPP inhibited in a concentration-dependent manner the vasodilator effect produced by acetylcholine with an IC50 value of 31.2+/-6.3 microM. DMPP also inhibited basal nitric oxide production. In endothelium-denuded vessels DMPP was without effect whereas superoxide dismutase (SOD) was effective in potentiating responses to the NO donor SIN-1. Contractile effects of carbachol in guinea-pig ileum and trachea were unaffected by DMPP. It is concluded that DMPP inhibits the endothelium-dependent relaxation induced by acetylcholine in the rat aorta without affecting receptor or smooth muscle cells function. Decreased nitric oxide production by endothelial cells seems to be the mechanism involved in the inhibitory effect of DMPP.