Distribution and biliary excretion of polychlorinated biphenyls in rats

Abstract

Absorption, distribution, and excretion of two 3H-labeled polychlorinated biphenyls (PCB), 2,4,5,2′,4′,5′,-hexachlorobiphenyl (HCB) and 2,5,2′,5′-tetrachlorobiphenyl (TCB), were studied in surgically prepared male and female rats. Approximately 3–5 hr after surgery, HCB or TCB (50 mg/kg) was administered into the stomach. Bile, urine, and feces were collected for 24 hr after which the animals were sacrificed and tissues taken for determination of 3H content. The distribution of 3H remaining in the rats, expressed as percentage of dose, was highest in skeletal muscle, skin, liver, and small intestine for both isomers. The major difference observed between the PCBs was in biliary excretion. For HCB, 0.5 ± 0.2% (males, mean ± SE) and 1.1 ± 0.3% (females) of the dose were excreted in bile in 24 hr; for TCB, 42.2 ± 8.5% (males) and 25.7 ± 7.8% (females) were excreted by the same route. The lower biliary excretion of HCB than of TCB cannot be accounted for by a difference in absorption from the gastrointestinal tract and is thought to be due to a slower rate of HCB metabolism. More explicitly, the chlorines in the 4,4′ positions of HCB appear to prevent rapid biliary excretion of the compound by eliminating adjacent unsubstituted carbons which are necessary for rapid metabolism to occur. Urinary excretion of HCB and TCB was of minor importance compared to biliary excretion. Generally, absorption, distribution, and excretion of the PCBs were similar in males and females.