Acute, subacute, and residual effects of polychlorinated biphenyl (pcb) in rats. II. Pathology and electron microscopy of liver and serum enzyme study.

This study was undertaken to determine the residual effects of a polychlorinated biphenyl (Aroclor 1254) fed to male rats at dietary concentrations of 0, 5, 50, and 500 ppm in diet. The animals were treated for 4 wk (acute and subacute phase), then observed for periods of up to 50 wk following termination of exposure (residual phase). The most significant histopathologic alteration was fatty degenerative change in the liver, which was most marked at 9 wk. Forty-six weeks postexposure, more than 50% of the rats fed 500 ppm still demonstrated fatty degenerative changes. On electron microscopic examination, marked increases in lipid vacuoles and smooth endoplasmic reticulum (SER) occurred with a concomitant decrease in rough endoplasmic reticulum (RER) profiles in the animals receiving 50-500ppm for 4 wk. Thirty-seven weeks following the exposure period, rats dosed with 50 ppm showed partial recovery toward control morphology (less lipid, less SER, more RER), while those receiving 500 ppm did not. Persistent morphologic alterations included an increase in SER and medium-density lipid material within cisternae of Ser, Golgi and Golgi-condensing vesicles, as well as a decrease in parallel arrays of RER. The persistence of ultrastructural alteration throughout the 46-wk residual phase emphasizes the long-lasting effects of 4-wk exposure to polychlorinated biphenyl.