Effects of acute and short-term repeated application of fullerene C-60 on agonist-induced responses in various tissues of guinea pig and rat

1. Effects of fullerene C-60 in trachea, right atria, ileum and stomach (fundus) of guinea pig and vas deferens and uterus of rat were studied pharmacologically. 2. C-60 (4 mu M) 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 C-60 30 mg/kg i.p. for 4 wk. 3. The pD(2) values (potencies) of acetylcholine in ileum and its longitudinal muscle from guinea pig after the short-term repeated application of C-60 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 C-60-treated and non-treated guinea pigs, and the pA(2) values for atropine were not significantly different with each other. 5. These results suggest that C-60 has no direct effects or antagonistic properties toward drug receptors, but sub-chronic exposure of C-60 decreased responsiveness. This may be due to a change in post-receptor processes.