histological and biochemical study of the protective effect of melatonin on acute paraquat toxicity in albino rats

ABSTRACT

The acute toxic effect of the herbicide paraquat [PQ] and the protective effect of the antioxidant melatonin against its toxicity were experimentally investigated both biochemically and histologically. Sixty rats were divided into six equal groups. Melatonin [Mgroup] and saline [Control group] were given once i.p. [10 mg /kg] to rats of both groups. PQ in high dose [50 mg /kg] and low dose [15mg /kg] was given i.p. to rats of high and low PQ groups i.p. [HPQ and LPQ]. A single dose of melatonin was injected i.p. 30 minutes prior to high and low PQ doses in rats of MHPQ and MLPQ groups. All rats were sacrificed after 24 hours and blood samples were collected for the biochemical analysis. Lung, liver and kidney specimens were processed for staining with haematoxylin and eosin, and P.A.S. reaction for light microscopic examination. Liver frozen sections were prepared and stained by Sudan black for lipid demonstration. The results revealed that both doses of PQ significantly increased serum malondialdehyde level and decreased serum concentration of glutathione and glutathione reductase activity compared to control values. These changes improved significantly in groups received melatonin prior to PQ i.e. MHPQ and MLPQ groups. Histologically, extensive damage to lung, liver and kidney was observed in rats of HPQ group. In the lung, marked congestion and bleeding were observed and the alveoli appeared filled with coagulated material, collapsed or manifested a compensatory emphysema. The bronchiolar wall showed sloughing of the epithelial lining and peribronchiolar lymphocytic infiltration. In the liver, blood sinusoids were markedly congested, the normal lobular pattern was lost and the hepatocytes exhibited vacoulation, fatty degeneration and necrosis. In the kidney, glomerular alterations and renal tubular necrosis were observed. Melatonin did not improve the toxic effect of PQ on the three organs in rats of MHPQ group. The low dose of PQ induced minimal tissue damage compared to HPQ group and the kidney was the most affected organ. Melatonin prior to low PQ dose improved the histological picture of the three organs which appeared almost similar to the controls, except the kidney which showed some degenerative changes. In conclusion, melatonin affords protection for the biochemical parameters affected by both doses of PQ while histologically, the single dose of melatonin can protect the organs only in animals exposed to low dose of PQ