Methomyl (MET) is a broad-spectrum carbamate insecticide, classified by the World Health Organization as a highly hazardous compound (class 1B). It is one of the most used insecticides for controlling pests in agriculture and households. The present study was conducted to test the effect of three different doses of MET (e.g., 1-LD50, 1/10 LD50 and 1/100 LD50) on some hepato-renal functions and oxidative stress biomarkers, as well as the histopathological changes in selected organs induced by the three doses of MET. The possible protective role of zinc was also investigated. Sixty-four rats were segregated into 8 groups and the experimental period was extended up to 28 days for all groups except that of MET at 1-LD50. The rat group that received MET at 1-LD50 was sacrificed after 96 h due to severe toxicity symptoms. Compared with the control group, both the 1/10 and 1/100 LD50 of MET treatments caused significant decreases in body and relative organ weights and liver hepatomegaly. Liver and kidney functions increased significantly following MET administration, while butyryl cholinesterase activities were significantly declined. Oxidative stress was detected in terms of significant decreases in the levels of total antioxidant capacity (TAC) and superoxide dismutase (SOD) accompanied with high elevation in malondialdehyde (MDA) and some histological alterations in liver and kidney. Administration of Zn in conjunction with MET enhanced the liver and kidney functions, as well as the antioxidative status. The optimum improvement was reached with MET at 1/100 LD50 based on the estimated “amelioration index; AI”. It was concluded that Zn, when co-administered, has the ability to protect the liver and kidney from the damaging effects of MET and was able to overcome the lethal dose of MET (1-LD50), keeping rats alive up to the end of experimentation period.
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