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Objective: Paraquat （PQ） has been widely used as a general herbicide throughout the world. As is widely used on agricultural land in China, PQ poisoning is also gradually increasing. Although PQ is very effective as a herbicide, it is highly toxic to humans and animals. PQ is readily absorbed through skin , pneogaster or enteron. But the poisoning mechanism has not been fully elucidated, and there is lack of antidote heretofore. The mortality rate in clinical practice is very high. So PQ-induced changes of pathophysiology are becoming a hotspot in toxic therapeutics. After entering body, PQ impairs the lung firstly, the renal secondly and is excreted as the original form from the renal. So soundness of renal function is indispensable in terms of PQ elimination. The exact mechanism of renal injury of PQ has not been fully enunciated. Through determining content of malonyldialdehyde（MDA）, activity of superoxide dismutase （SOD） and glutathione peroxidase （GSH-Px） in renal tissue, observing the ultrastructure variation by HE staining and the expressions of apoptotic regulatory proteins― mutant P53 and Fas/Fas-L in renal of the acute paraquat-induced rats by the method of immunohistochemistry, and certifying the effect of melatonin（MT）, we try to elucidate possible mechanism and the rapeutical effect of melatonin（MT） on renal injury induced by PQ poisoning.Methods: one hundred and eight adult healthy Sprague-Dawley （SD） rats （54 female, 54 male） were randomly divided into three groups:⑴Control group （group A）: 36 rats,⑵Poisoned group （group B）: 36 rats,⑶MT group （group C）: 36 rats. The rats in group B and C were treated intraperitoneally with 1ml of PQ （25mg/kg） diluted with normal saline. Group A rats were treated with the same way of normal saline as group B and C. Group C rats were given 1 ml of MT intraperitoneally at a dose of 10mg/kg diluted with normal saline once a day immediately after the administration of the PQ. Group A and B rats were treated intraperitoneally with the same way of normal saline once a day like group C. After abdominal dissection with ether anaesthesia, six rats respectively from each of group B and C were taken tissue samples from kidney on day 1st, 3rd, 5th, 7th, 10thday and 14th day respectively. Tissue SOD, GSH-Px activity and MDA concentration were measured, and renal tissue was quickly remained to observe the expression of mutant P53 and Fas/Fas-L by the method of immunohistochemistry. Part of the renal tissue was stained with hematoxylin-eosin for pathological observation, and so did group A.Results: 1 Clinical signs and appearances after PQ poisoning: In group B and C, all of the rats began to demonstrate the changes to different extent in their clinical signs in 30mins2hrs, and were especially severe on 1st day 3rd day, including the respiratory system, urinary system , neural system and digestive system, etc. However, all the rats of group C demonstrated slighter clinical changes than those of group B.2 Renal tissue measurement:⑴The levels of MDA in group B were significantly higher than that in group A on the 1st, 3rd, 5th day （P<0.01）, on the 7th , 10th day （P<0.05）;Whereas the increases of renal tissue MDA were markedly intibited in group C, in which, the levels of renal tissue MDA on the 1st, 3rd, 5th day were significantly lower than group B （P<0.05）. Compared with that of group A, the statistically significantly higher levels of it in group C only kept on the 1st, 3rd day （P<0.05）.⑵The activity of renal tissue SOD in group B were significantly lower than that in group A on the 1st, 3rd day （P<0.01）, on the 5th, 7th day （P<0.05） and in group C on the 1st, 3rd, 5th , 7th day （P<0.05）; Compared with that of group A, the statistically lower levels of it in group C only kept on the 1st, 3rd day （P<0.01）.⑶The activity of GSH-Px in group B were significantly lower than that in group A on the 1st, 3rd day （P<0.05）; the activity of GSH-Px in group C remarkably increased, and was higher than that in group B on the 1st, 3rd day （P<0.01）, but there were no statistical differences all the time points between group A and group C （P>0.05）.3 HE staining: Group A:The structure of renal glomerulus and renal tubule was normal. Group B: Renal glomerulus had mild hyperaemia and distension. Renal tubule epithelial cell had edema and vacuolar degeneration and renal tubule lumina were narrowing on 1st day. There were edema exudation and necrosis on 3rd day. There were serious edema exudation and necrosis on 7thday, which gradually lessened. Inflammatory cell infiltration,edema and hyperaemia appear in renal interstitial. Group C: MT treatment weakened the pathological changes of renal tissue.4. Immunohistochemistry （IH） staining:⑴In group A, there was only very weak expressions of mutant P53 and Fas/Fas-L in the normal renal tissue. Mutant P53 can be observed in the nucleus of renal tubular epithelial cells, Fas/Fas-L in the cytoplasm.⑵In group B, the expressions of mutant P53 and Fas/Fas-L were significantly higher than that in group A on the 1st day which could be observed in renal tubule epithelial cells mainly. The expressions of mutant P53 and Fas/Fas-L could be observed in the nucleus and cytoplasm respectively. Both of them kept at the high levels till the 14th day, which was higher than Group A （P<0.01）.Conclusions:⑴PQ intraperitoneally poisoning can induce acute renal injury.⑵PQ intraperitoneally poisoning can elevate the levels of MDA and lower the activities of SOD and GSH-Px in renal tissue of rats , indicating disequilibrium between oxidation and anti-oxidation in body,which may be a cause of renal injury induced by PQ.⑶After PQ intraperitoneally poisoning, the changed expressions of mutant P53 and Fas/Fas-L in renal tissue may be a cause of renal injury induced by PQ.⑷MT decreased significantly the content of tissue MDA in PQ poisoning rats , increased significantly the activity of SOD and GSH-Px, weakened markedly the expressions of mutant P53 and Fas/Fas-L in renal tissue,which may due to the powerful antioxidant property of MT.
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