RESUMO
We examined the effects of intravenous administration of purified arc-discharge single-walled carbon nanotubes (SWCNTs) on rabbit ileum to establish the possibility of using these SWCNTs as cell markers or drug carriers for the treatment of intestinal diseases. The SWCNT purification process eliminated carbonaceous impurities and decreased the amount of metals. SWCNTs increased the contractile responses induced by KCl, acetylcholine (ACh), and serotonin (5-HT) in rabbit ileum. Verapamil, apamin, glibenclamide, quinine and charybdotoxin reduced the contractile responses induced by ACh and 5-HT in ileum from rabbits treated with SWCNTs, indicating that voltage-dependent Ca2+ channels and small, intermediate, and large-conductance Ca(2+)-activated, ATP-sensitive, and voltage-dependent K+ channels are involved in these effects. Atropine and hexamethonium reduced the ACh response, indicating that muscarinic and nicotinic receptors are involved in this effect. Ondansetron and GR 113808 reduced the 5-HT response, indicating that serotonin 5-HT3 and 5-HT4 receptors are involved in this effect. SWCNTs increased the malondialdehyde plus 4-hydroxyalkenals and carbonyl levels in rabbit plasma and ileum, indicating that SWCNTs produce oxidative stress. SWCNTs did not produce relevant histological changes or modify the levels of the inflammatory mediators iNOS and COX-2 in the ileum. In conclusion, this study demonstrates that the intravenous administration of SWCNTs can evoke oxidative stress and affect contractility in rabbit ileum. These effects could reduce the possibility of using the arc-discharge SWCNTs as cell markers or drug carriers to treat intestinal diseases.