To investigate the chronic toxicity of cyadox, a growth promoting agent, five groups of Wistar rats (30 rats/group/sex) were fed with the diets containing cyadox (0, 100, 400 and 2000 mg/kg) or olaquindox (400 mg/kg) for 78weeks. There were significant decreases in body weights in both genders during most of the study period in 2000 mg/kg cyadox and 400 mg/kg olaquindox rats. Significant decreases in serum alkaline aminotransferase in the 2000 mg/kg cyadox rats at weeks 26, 52 and 78 were observed. Relative weights of liver and kidney were significantly increased in 2000 mg/kg cyadox and 400 mg/kg olaquindox rats at weeks 26, 52 and 78. A significant increase in relative brain and heart weights in 2000 mg/kg cyadox males was observed. The histopathological examinations revealed that 2000 mg/kg cyadox diet or 400 mg/kg olaquindox diet could induce proliferation of bile canaliculi in the portal area of liver and swelling and fatty degeneration of the proximal renal tubular epithelial cells in kidneys. In conclusion, the target organs of cyadox for rats were liver and kidney. The no-observed-adverse-effect level of cyadox in this study was estimated to be 400 mg/kg diet.
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