Inhibition of agonist-induced vasocontraction and impairment of endothelium-dependent vasorelaxation by extract of motorcycle exhaust particles in vitro

The in vitro effects of motorcycle exhaust particulate extract (MEPE) on bl ood vessels were studied in thoracic aorta isolated from Wistar rat. The ME PE relaxed the phenylephrine-precontracted aorta with an EC50 value or 0.05 +/- 0.004 mg/ml. This relaxing effect of MEPE persisted in endothelium-den uded aorta, suggesting that the relaxation induced by MEPE is endothelium-i ndependent. The phenylephrine-induced vasocontraction and inositol 1,4,5-tr iphosphate formation were inhibited concentration dependently in aorta pret reated with MEPE. However, the high-K+-induced vasocontraction and the Ca2 sensitivity of the contractile proteins were not significantly affected by MEPE. In addition to the inhibitory effects on agonist-induced contraction , the vasorelaxing effects both of acetylcholine and of sodium nitroprussid e were impaired by MEPE. The inhibitory effects of MEPE on acetylcholine an d sodium nitroprusside, bur not phenylephrine, were reversed by cotreatment with superoxide dismutase. These results showed that the MEPE, added in vi tro, inhibited the phenylephrine-induced, but nor depolarization-induced, v asocontraction of aorta. The MEPE also impaired the vasorelaxation induced by acetylcholine in a superoxide anion-dependent manner.