Effects of acute and short-term repeated application of fullerene C60 on agonist-induced responses in various tissues of guinea pig and rat.

1. Effects of fullerene C60 in trachea, right atria, ileum and stomach (fundus) of guinea pig and vas deferens and uterus of rat were studied pharmacologically. 2. C60 (4 microM) had no direct effect in all tissues. In guinea pig trachea and heart, relaxation and positive inotropic and chronotropic actions of isoprenaline and in isolated rat vas deferens and uterus the responses on norepinephrine and oxytocin were not affected by the short-term repeated application of C60 30 mg/kg i.p. for 4 wk. 3. The pD2 values (potencies) of acetylcholine in ileum and its longitudinal muscle from guinea pig after the short-term repeated application of C60 were significantly smaller than those obtained without the application. The value of 5-hydroxytryptamine in rat stomach (fundus) also tended to be smaller than obtained without the application. 4. Atropine inhibited competitively the contractions for acetylcholine in the longitudinal muscles prepared from C60-treated and non-treated guinea pigs, and the pA2 values for atropine were not significantly different with each other. 5. These results suggest that C60 has no direct effects or antagonistic properties toward drug receptors, but sub-chronic exposure of C60 decreased responsiveness. This may be due to a change in post-receptor processes.