Long-term effects of a single oral dose of polybrominated biphenyls on serum and liver lipids in rats

Adult (5 months) male Sherman strain rats received a single dose of either 0 or 500 mg polybrominated biphenyls (PBB) in corn oil/kg body weight by stomach tube. After an 18-month recovery period, serum and liver samples were examined. The primary serum lipid response was an increase in cholesterol (both free and esterified) and in total phospholipids. The percentage of esterified cholesterol was not significantly different from that of the controls, and no significant differences in the cholesterol ester fatty acid composition were observed. Serum triglycerides were also unaffected. In the PBB-dosed animals, the total hepatic fatty acids contained significantly less palmitic acid and more stearic acid, consistent with an increase in palmitic acid chain elongation activity. No significant differences could be detected in the n-3 or n-6 acids except for a slight decline in the content of 22:6 (n-3). Hepatic microsomal phospholipids were slightly higher (per milligram protein) in the PBB-dosed animals, and the cholesterol content was lower. Consequently, the cholesterol-phospholipid ratio was reduced, and microsomes from the latter group appeared to have an altered lipid domain on the basis of steady-state fluorescence anisotrophy measurements. In addition, total hepatic thiobarbituric acid-reactive substances (assayed as malondialdehyde) were significantly increased in the PBB-dosed animals. This observation appeared to reflect an increased susceptibility to peroxidative stress in the latter group, probably resulting from reduced membrane antioxidant concentrations. The PBB-dosed rats had significantly lower serum retinol levels and a reduced content of this vitamin in liver microsomes. Microsomes were also deficient in alpha-tocopherol in the PBB-dosed animals, although serum levels were normal.