Transport and cellular uptake of polychlorinated biphenyls (PCBs)--II. Changes in vivo in plasma lipoproteins and proteins of pigeons in response to PCBs, and a proposed model for the transport and cellular uptake of PCBs.

The complex distribution of polychlorinated biphenyl (PCB) isomers and congeners amongst plasma fractions of the pigeon suggests that the lipid and apolipoprotein components of lipoproteins, as well as plasma proteins, may be important in transporting PCBs to tissues (Borlakoglu et al., Biochem. Pharmac. 40, 265 (1990]. Pigeons were injected with the commercial PCB mixture Aroclor 1254 (1.5 mmol/kg body weight). After 120 hr triacylglycerol-like droplets accumulated in hepatocytes ('fatty liver syndrome'), there was proliferation of the hepatic smooth endoplasmic reticulum, and plasma concentrations of triacylglycerol and total cholesterol increased. This was accompanied by significant decreases in plasma concentrations of total protein, total apolipoproteins of the low density lipoprotein (LDL) and the high density lipoprotein (HDL) fractions, and albumin and by a significant increase in that of urea, indicating increased protein breakdown. These results suggest that Aroclor 1254 increased hepatic lipid synthesis, but decreased hepatic production of albumin and apolipoproteins. This would explain the accumulation of triacylglycerol in the liver and the increase in the proportion of triacylglycerol to apolipoprotein in the total lipoproteins. From the evidence presented, a model is proposed based on the association of PCBs with hydrophobic domains of lipids and proteins for the transport of PCBs by plasma fractions, their uptake into cells and intracellular metabolism, and their accumulation in adipose tissue.