Effects of a Polychlorinated Biphenyl Mixture (Aroclor 1254) and DDT on Biliary Thyroxine Excretion in Rats¹

Abstract

Treatment of rats with a polychlorinated biphenyl mixture (Aroclor 1254; PCB) causeda 4- to 5-fold increase in the 3-hr biliary excretion of 125I-thyroxine (T4). In treated rats bile flow was increased and the 125I-T4 bile:plasma ratios (B/Pratios) and biliary clearance rate of plasma 125I-T4 were greatly elevated. The proportion of biliary 125I present as T4-glucuronide was larger in PCB-treated rats. PCB also elevated thyroid 13II uptake andreduced serum PBI concentrations. DDT did not affect the biliary excretion of 125I-T4, but did increase bile flow and the biliary clearance rate of plasma 125I-T4. It also caused a marginal elevation of B/P ratios and increased the proportion of biliary 125I present as T4-glucuronide slightly but significantly. DDT did not affect thyroid 13II uptake or serum PBI concentrations. The effects of PCB were similar to those of the polycyclic hydrocarbon-type of enzyme inducers. The results of DDT-treatment were similar to those produced by the phenobarbital type of inducer. PCB treatment also reduced the binding of thyroid hormone to serum proteins as shown by enhanced resin uptake of 125I-triiodothyronine (T3) from the serum of PCB-treated rats; DDT administration did not influence resin T3 uptake. (Endocrinology95: 1150, 1974)