Synthetic pyrethroids account for more than 30% of insecticides used worldwide in agricultural, domestic and veterinary applications. Although mainly used as insecticides, these compounds have a wider spectrum of action including mammalian toxicity. We conducted experiments to determine physiological and biochemical responses of Wistar rats orally exposed for 30 days, to sublethal doses of lambda-cyhalothrin (1/100th and 1/10th of the LD50). We also investigated the protective role of the antioxidant, L-carnitine. We observed that body weight was adversely affected by exposure to lambda-cyhalothrin, as was the relative weight of testes; weights of liver and spleen, however, were significantly increased. Several haematological variables (total erythrocyte count, haemoglobin, serum protein) were negatively affected while total leukocyte count was increased. Plasma concentrations of glucose and urea were also elevated. Activities of metabolic enzymes (aspartate aminotransferase, alanine aminotransferase, acid phosphatase, alkaline phosphatase), were significantly enhanced in serum but suppressed in liver. Activity of lactate dehydrogenase was also increased in serum, and greatly increased in liver. Acetylcholinesterase activity in serum was not affected but activity of this enzyme in the brain was markedly suppressed. A significant increase was seen for several biochemical indicators of oxidative stress, such as thiobarbiturate-reactive substances in blood and liver and the concentrations of reduced glutathione in liver, testis, brain and kidney. The measurements taken together indicate that lambda-cyhalothrin causes a sublethal, dose-dependent syndrome of oxidative stress, with additional effects on haematopoiesis and carbohydrate metabolism. Most strikingly, simultaneous dosing of the anti-oxidant L-carnitine removed the oxidative stress status and eliminated the harmful effects in almost all cases. Our data confirm that sublethal mammalian toxicity of lambda-cyhalothrin is dominated by oxidative stress, despite the fact that its use as a pesticide relies on neurotoxicity. The anti-oxidant L-carnitine has a strong protective effect against lambda-cyhalothrin toxicity.

Keywords: Lambda-cyhalothrin, L-carnitine, oxidative stress, anti-oxidant, oral exposure, Wistar rat