Responses of rats exposed to polychlorinated biphenyls for fifty-two weeks I. Comparison of tissue levels of PCB and biological changes.

Male Sprague-Dawley rats were fed a diet containing mixtures of polychlorinated biphenyls (PCB) isomers (Aroclor 1248, 1254 and 1262) at a concentration of 100 ppm in the diet for 52 weeks. During the subsequent 13 weeks the rats were placed on a control diet. Throughout the course of the experiment the animals ate well, were healthy in appearance and gained weight as rapidly as the control animals. Their hemograms were normal. In spite of the gross normalcy of these animals throughout the 52-week experimental period, clinical and morphologic examinations revealed distinct alterations. There was a decided increase in their total serum lipids and cholesterol and a transient increase in triglycerides accompanied by distinct morphological changes in the liver. Generalized liver hypertrophy and focal areas of hepatocellular degeneration were followed by a wide spectrum of repair processes. The tissue levels of PCB were greater in the animals receiving the higher chlorine mixtures. High levels persisted in these tissues even after the PCBs had been discontinued.