Chemico-biological interactions
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Chem. Biol. Interact. · Jan 1988
Study on the mechanism of interference of 3,4,3',4'-tetrachlorobiphenyl with the plasma retinol-binding proteins in rodents.
The mechanism of plasma retinol reduction in rodents by 3,4,3',4'-tetrachlorobiphenyl (TCB) was investigated by radioimmunochemical analysis of the amounts of circulating and hepatic retinol-binding protein (RBP) and transthyretin (TTR) in exposed and control animals. Plasma RBP concentrations were markedly reduced in C57BL/Rij mice (50%) at 4 days, in DBA/2 mice (37-41%) at 4 and 8 days, and in Sprague-Dawley rats (58%) at 2 days after exposure to TCB. These reductions paralleled the time course of reduction of plasma retinol after exposure to TCB. ⋯ The dissociation constants of the RBP-TTR complex as analysed by polarization of fluorescence appeared to be significantly increased (from 0.5 x 10(-7) M-1 to 2.4 x 10(-7) M-1) in the presence of a TCB metabolite, isolated from plasma of TCB-treated rats. In addition, the estimated number of binding sites for RBP on the TTR molecule was reduced (from 2.8 to 1.7 sites) upon treatment of TTR with the TCB metabolite. These data support the hypothesis that plasma retinol reduction by TCB might result from a weakening of the RBP-TTR complex, in the presence of the TCB metabolite bound to the TTR.