Enhanced in vitro hepatic glucuronidation of thyroxine in rats following cutaneous application or ingestion of polychlorinated biphenyls

In rats four daily skin applications of a 30% solution of a polychlorinated biphenyl (PCB) mixture in mineral oil or of a microscope immersion oil, containing 34% PCB, led to increases in liver weight, protein concentration of the 10 000 × g supernatant fluid of liver homogenates and the in vitro glucuronidation of thyroxine (T4) by the supernatant fluid, whether related to liver weight or to protein concentration in the reaction mixture. Similar effects occurred after feeding 250 ppm (mg/kg) of PCB in either Purina chow or a low-iodine diet for 11 days. It is concluded that increased hepatic T4 glucuronidation contributes to the enhanced biliary excretion of T4 previously observed in PCB-treated rats.