Aroclor 1242 and Aroclor 1016 are polychlorinated biphenyl (PCB) mixtures with similar chlorine content (42 vs 41%), but Aroclor 1242 contains 9% biphenyl homologs with five or more chlorines while Aroclor 1016 contains only 1%. The effects of Aroclor 1242 and Aroclor 1016 on induction of hepatic porphyria and drug-metabolizing enzymes were compared in female rats fed 100 ppm or 500 ppm of each. At 1 wk, Aroclor 1242 markedly increased liver weight and all drug-metabolizing pathways tested including cytochrome P-450, liver weight, N-demethylase, nitroreductase, aniline hydroxylase, and glucuronyl transferase, while Aroclor 1016 had produced only very minimal effects. At 6 mo, however, 500 ppm of either Aroclor markedly increased drug-metabolism, while at the lower dose, Aroclor 1016 was much less effective than Aroclor 1242. Both doses of Aroclor 1242 produced prophyria, but only the higher dose of Aroclor 1016 was prophyrogenic. The porphyria occurred after a lag of 1-6 mo and was characterized by excretion and hepatic storage or uroporphyrins. Aroclor tissue concentrations were similar in rats fed equal doses of the two mixtures. Therefore, the marked differences in the biological effects of Aroclor 1016 and Aroclor 1242 cannot be explained by differences in absorption, metabolism, or excretion.

contained in PB 280 889 titled Journal articles on Toxicology. Group 14.