Comparative toxicity in rats of polychlorinated biphenyls (PCBs), polychlorinated quaterphenyls (PCQs) and polychlorinated dibenzofurans (PCDFs) present in rice oil causing "yusho"

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.