<Originals>Effects of continuous exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from the cleavage to the larval stage on the development of the Xenopus laevis
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概要
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The developmental toxicity of 2,3,7,8-TCDD was evaluated in embryos and larvae of Xenopus laevis. Little effect was observed during the exposure period of 5 days after fertilization, but edema and death occurred at 9-10 days after fertilization. Significant increases in death rate, edema and growth retardation of larvae were noted at 100ppb or above. Most of the larvae with edema died, and hence the death of the larvae was considered to be closely related to edema, as in mammals. Edema was more severe, and the death rate was higher in larvae that developed edema in the early stage. In contrast, the recovery rate was higher, and the period until recovery was shorter in those that developed edema in the late stage. The incidence of edema and the death rate in the different exposure periods were higher on days 4-6 and 6-8 after fertilization than those on days 0-2 and 2-4. Histological examination of larvae exposed to 2,3,7,8-TCDD showed marked edema of loose tissues such as the eyes, the subcutaneous tissue of the thoracic and abdominal wall, and submucosal tissue of the digestive tract. Marked distention of the abdominal cavity (ascites), shortening of the digestive tract, marked dilation of submucosal vessels of the digestive tract, thoracic and abdominal subcutaneous hemorrhage were also noted. These findings suggest that edema is a characteristic manifestation of the delayed toxicity of 2,3,7,8-TCDD in Xenopus larvae, and that Xenopus laevis is useful as an alternative to mammals in developmental toxicity studies. In addition, the edema by vascular damages associated with vascular dilation and impairment of the digestive tract were strongly suggested to be causes of death.
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