Metabolism and biochemical toxicity of PCBs and PBBs

One of the major biochemical effects of PCBs is the induction of microsomal enzymes in the liver. Risebrough et al. (1) suggested that PCBs have the capability to induce the activities of microsomal enzymes. Subsequently, Street et al. (2), demonstrated the induction of liver enzymes in rats by PCBs. Since then, a great number of articles have been published on this subject. The enzyme systems studied have included mainly hydroxylases, Nand O-demethylases and nitroreductases, and to a lesser extent nonspecific carboxylesterase, bromosulfophthalein-glutathione conjugating enzyme, p-nitrophenol UDP-glucuronyl transferase and EPN-detoxification systems. The induction of microsomal enzymes by commercial PCBs has been demonstrated perorally in rabbits (3) rats (4) and primates (5) and via intraperitoneal injection (6) and skin application in rats (7). Values reported for the threshold of enzyme induction by PCBs vary between 0.5 and 25 ppm (3, 8, 9) (et al., 1974). The time course of microsomal enzyme induction was studied by Litterst et al. in rats (10). They