Abstract
To understand the nature of the chemical substances responsible for the disease"Yusho, "a mixture of polychlorinated biphenyls (PCBs), polychlorinated dibenzofurans (PCQs) and polychlorinated dibenzofurans (PCDFs) having a composition similar to that found in the rice oil causing"Yusho"was prepared in our laboratory. Male Sprague-Dawley rats were daily given orally for 22 d a regimen consisting of PCBs, 1 mg/rat/d ; PCQs, 1 mg/rat/d ; PCDFs, 10 μg/rat/d ; or a mixture of PCBs, PCQs and PCDFs (Mixture, (1 mg+1mg+10 μg)/rat/d). Rats treated with PCBs, PCDFs and Mixture showed hepatic enlargement, reduction of serum corticoid level, increase of serum cholesterol level and increase in the hepatic microsomal drug-metabolizing enzyme activity, and the effect was larger in the order of Mixture > PCDFs > PCBs. In addition, when PCDFs or Mixture were administered to rats, atrophy of the thymus and suppression of body weight gain were observed. When Mixture was administered to rats, a significant decrease in serum glutamic pyruvic transaminase (GPT) level and a significant increase in serum triglyceride level were observed. In the PCQs-treated rats, increase in the hepatic microsomal drug-metabolizing enzyme activity and decrease in the adrenal corticoid levels were observed, but the degree of change was far less than that in the PCBs- or PCDFs-treated rats. PCDFs or Mixture showed induction of hepatic microsomal drug-metabolizing enzyme activity of the 3-methylcholanthrene (MC) type in the rat. On the other hand, PCBs and PCQs showed intermediary-type induction of the phenobarbital (PB) and MC types. Therefore, the predominant etiology of"Yusho"may involve PCDFs contained in the toxic rice oil.
