INTERACTION OF PCB CONGENERS AND 2,3,7,8-TCDD IN THE RAT-LIVER - AN ELECTRON-MICROSCOPE STUDY

Polyhalogenated aromatic compounds such as polychlorinated biphenyls ( PCBs) and polychlorinated dibenzo-p-dioxins continue to be environment al contaminants because of their bioaccumulation in the food chain and resistance to biodegradation. This study was undertaken to determine if WHO-IPCS PCB congeners or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD ) individually or their coadministration in rats produced morphologica l alterations in the liver. Groups (N = 5) of female Sprague Dawley ra ts received TCDD (0, 2.5, 25, 250, 1,000 ng/kg bw/day) or PCB (0, 2, 2 0 mu g/kg bw/day) either alone, or each dose of PCB coadministered wit h that of TCDD. The test substances were dissolved in corn oil and giv en by gavage at 0.2 ml/100 g bw/day for 28 days. At the end of the exp eriment the rats were killed and liver samples were prepared for trans mission electron microscopy. Electron micrographs of the liver from an imals of the control groups revealed characteristic normal hepatocyte architecture. An increase in smooth endoplasmic reticulum (SER) profil es and a corresponding decrease in the profiles of rough endoplasmic r eticulum (RER) proportional to the increased doses of the compounds wa s revealed in the micrographs. Coadministration of PCBs and TCDD induc ed greater SER proliferation and a greater decrease in the number of R ER profiles compared to either compound administered individually. The PCBs and TCDD at the doses used apparently interacted to induce hepat ic ultrastructural alterations. These changes may represent an attempt by the organism to metabolize and neutralize the effects of xenobioti cs.