The Reproductive Toxicity And Effect Of Testosterone After Mice Exposure To Melamine And Mixture Of Melamine And Cyanuric Acid

Numerous dogs,cats and even infants died after consumption of commercial pet foods or milk contaminated with which had been illegally added from 2007 to 2008.These occurrences had generated interest in the toxicity of melamine.Previous studies on toxicity of melamine in the absence and presence of cyanuric acid has mainly focused on lesions to kidney,but recently studies has shown that melamine or mixture of melamine and cyanuric acid could cause toxicity to digestive system,nervous system and reproductive system.However,the studies on male reproductive system mainly concentrated on the morphological damage to testis.Morever,there were only a few reports about it and most of them were fragmented and lack of the investigation on regulatory mechanisms.In this study,we mainly investigated the effects of melamine and mixture of melamine and cyanuric acid on morphology of testis,the number and morphology of sperm in epididymis and level of testosterone in serum.Meanwhile,we also investigated the relulatory mechanism on testosterone production,hoping to provide more information for the reproductive toxicity of melamine and mixture of melamine and cyanuric acid on male mice.Seventy ICR male mice were divided into seven groups randomly.The melamine groups were administered with melamine alone at different dose of 2mg/kg/d(low group),10mg/kg/d(middle group)and 50mg/kg/d(high group),respectively.The mixture groups of mice were administered with melamine and cyanuric acid(ratio of 1:1 in quality)at dose of 1mg/kg/d(low group),5mg/kg/d(middle group),25mg/kg/d(high group),respectively.The control group was administered with equal volume of corn oil.All of mice were orally administrated once a day and lasted for 28 days.At the end of the experiment,the weight of body,epididymis and testis,sperm number in epididymis,testosterone in serum and pathological changes to testes were evaluated.Reduction of food and water intake,lethargy,rough hair,and back ached were found after mice exposure to high dose of mixture.The similar results were also found in high dose group of melamine and midlle dose of mixture,but the dgree was relatively slight.No abnormal circumstances happened in other experimental groups.The body weight in high dose group of mixture were significantly decreased(p<0.05),the relative weights of testes in high dose group of melamine and high dose of mixture were obviously increased(p<0.05).The total sperm number dramatically decreased and the abnormal sperm number significantly increased after mice exposed to melamine and mixture of melamine and cyanuric acid(p<0.01).Pathological changes were found in the morphology of the testes,such as disruption of the seminiferous tubule structure,decrease of the spermatogenic cell series and coagulation necrosis,and the reduction or even disappearance of sperm.The decreased level of testosterone in serum was also found after mice administrated with melamine or mixture.Both melamine and mixture of melamine and cyanuric acid significantly inhibit the gene expression of steroidogenic acute regulatory protein(StAR),cytochrome P450 side chain cleavage(P450scc),and 17p-Hydroxysteroid dehydrogenase(17?-HSD)compared with the control group(p<0.05),and the inhibitory effect of each group was in a dose manner.Movever,the inhibitory effect of mixture of melamine and cyanuric acid was stronger than that of melamine alone.In addition,the reduction of the number of Leydig cells was obviously after mice exposure to melamine and mixture.These results demonstrated that melamine and mixture of melamine and cyanuric acid could inhibit the growth of male mice and development of testes,induce the reduction of sperm number while increasing the rate of abnormal sperm,cause damage to germ cells,reduce production of testosterone,and the reduction of testosterone caused by melamine in absence and presence of cyanuric acid was related with the inhibition of the activity of testosterone synthesis enzymes and the reduction of number of Leydig cells.