The inducing properties of polychlorinated biphenyls on hepatic monooxygenases

The polychlorinated biphenyls (PCBs) represent a newly recognized and widely distributed category of environmental pollutants whose biologic impact on animals and man may be both substantial and highly detrimental. The pharmacologic effects of these agents on enzymes in the liver which metabolize drugs and other foreign compounds, such as carcinogens, are powerful and long lasting. PCBs mimic the effects produced on these enzymes by drugs, such as phenobarbital, and carcinogens, such as 3-methylcholanthrene. They are potent inducers of cytochromes P-45O and P-448 and associated enzymic activities. Further, these chemicals can cross the placental barrier and be transmitted through maternal milk to the newborn infant causing marked increases in drug biotransformation enzymes in the fetus and the neonate. Studies with the use of microscope immersion oils containing PCBs show that application of minute amounts of these oils to the skin of experimental animals results in a marked induction of the drug-and carcinogen-metabolizing enzymes. These findings suggest that even trivial skin exposure to chemicals, such as PCBs, can have significant and perhaps harmful biologic effects in man.