Abstract

Purpose
This study was designed to determine if methylene blue inhibited the lipid peroxida-tion, the production of NO, and the gene expression of iNOS in acute lung injury induced by paraquat and if the inhibitory effect was dose dependent. Methods: Female Sprague-Dawley rats were divided into four groups: the control group, the group treated with paraquat only, the group treated with paraquat and a low dose of methylene blue (2 mg/kg), and the group treated with paraquat and a high dose of methylene blue (20 mg/kg). Methylene blue was administered via the jugular vein 1 h after paraquat administration, and animals were sacrificed 6 and 24 h after paraquat administration. Malondialdehyde (MDA) as lipid peroxidation, reduced glutathione (GSH) as an antioxidant defense, the plasma NO concentration, and the expression of iNOS mRNA in the lung tissue were measured Results: Lung MDA contents decreased, with no significant difference between the methylene-blue groups and the paraquat-only group. Lung GSH contents were significantly elevated at 24h in the methylene-blue groups compared with the paraquat-only group. Plasma NO concen-trations were significantly reduced at 6 and 24 h in the methylene-blue groups compared with the paraquat-only group. There was also a significant decrease in the plasma NO concentration at 6 h in the high-dose methylene-blue group compared with the low-dose methylene-blue group. The expression of iNOS mRNA in the lung tissue was slightly decreased in the methylene-blue groups. It was also markedly increased at 24 h in the paraquat-only group compared with the methylene-blue groups. The gene expression was relatively decreased in the high-dose methylene-blue group compared with the low-dose methylene-blue group. Conclusion: This study suggests that methylene blue has an inhibitory effect on the plasma NO concentration and the expression of iNOS mRNA in lung injury induced by paraquat. No inhibitory effect of methylene blue on lipid peroxidation or dose-dependent inhibitory effects were clearly shown.

• Keywords: Paraquat, Methylene blue, Malondialdehyde, Nitric oxide, Nitric oxide synthase