Responses of rats exposed to polychlorinated biphenyls for fifty-two weeks. II. Compositional and enzymatic changes in the liver.

Male Sprague-Dawley rats consumed a diet to which 100 ppm of various polychlorinated biphenyl (PCB) mixtures (Aroclors 1248, 1254, and 1262) were added for one year. Rats were hepatectomized at 13, 26, and 52 weeks during feeding and at 13 weeks following the discontinuation of the PCB diets. The liver homogenates of these rats had an increase in protein and RNA on a DNA basis and an increase in lipid and a decrease in DNA on the liver weight basis. The hepatic microsomes from these livers also had an increase in protein and cytochrome P-450. The RNA/microsomal protein levels were decreased, and no marked alterations were recorded for the phospholipids and cholesterol on a microsomal protein basis. Increased enzymatic activity was recorded for N-demethylase and nitroreductase. However, the specific activity of glucose-6-phosphatase was decreased throughout the treatment period.