Accumulation, excretion and effects on hepatic enzymes of polychlorinated quaterphenyl congeners in rats

Six skeletal congeners of polychlorinated quaterphenyls (PCQs), namely polychlorinated o-quaterphenyl (2,2'-PCQ), 2,3'-diphenylbiphenyl (2,3'-PCQ), 2,4'-diphenylbiphenyl (2,4'-PCQ), m-quaterphenyl (3,3'-PCQ), 3,4'-diphenylbiphenyl (3,4'-PCQ) and p-quaterphenyl (4,4'-PCQ), were orally administered to Wistar rats at a dose of 10 mg/rat. On the 5th day after administration of PCQs, the rats were examined for accumulation of PCQ congeners, hepatic enzyme activities and organ weight changes. Accumulation of 3,3'-PCQ, 3,4'-PCQ and 4,4'-PCQ were 1.5-3.2% of dose in the liver, while those of 2,2'-PCQ, 2,3'-PCQ and 2,4'-PCQ were only 0.1 to 0.2%. The amount of 4,4'-PCQ accumulated in the mesenteric adipose tissue, 20 micrograms/rat, was much higher than those of other PCQ congeners. Large amounts of the PCQ congeners administered were excreted in the feces on the first day, accounting for 96 to 98% of dose for 2,2'-PCQ and 4,4'-PCQ, and 55 to 75% for the other PCQ congeners, and the daily excretions of PCQs after the second day were very small, less than 10% of the dose. Benzo [a] pyrene 3-hydroxylase activity was significantly depressed by the treatment with 3,3'-PCQ, 3,4'-PCQ and 4,4'-PCQ, contrasting to the toxic congeners of polychlorinated biphenyls and dibenzofurans which enhanced markedly this enzyme activity. DT-Diaphorase activity was also depressed by the treatment with 2,3'-PCQ, 2,4'-PCQ and 3,4'-PCQ. Significant atrophy of the thymus was observed by the treatment with 4,4'-PCQ.