Turnover and Metabolism of Polychlorinated Biphenyls in Relation to their Chemical Structure and the Movement of Lipids in the Pigeon

Experiments with White Carneau pigeons have established that the ease of metabolism of polychlorinated biphenyls (PCBs) composing Aroclor 1254® is determined principally by chlorine substitution patterns rather than degree of chlorination. Rapidly metabolized PCBs have 2,3, 3,4, or 2,3,6 chlorine substitution on at least one phenyl ring. Those PCBs which are not metabolized have a combination of 2,4,5, 2,3,4, and 2,3,4,5 chlorine substitutions on both rings. PCBs containing 2,5 substitutions were metabolized over a 31 day period, but much more slowly than PCBs with 2,3 or 3,4 chlorine substitutions.Chemical structure of PCBs does not affect their rate of mobilization from adipose tissue and subsequent movement through the circulation. The fractional turnover of all PCBs is approximately equivalent to the fractional turnover of the lipid pool under fully fed conditions as well as during periods of starvation induced depletion of lipid reserves. A net movement of PCBs from adipocytes to other lipid pools, principally muscle cells, occurred during starvation. On subsequent refeeding, the net movement of PCBs from muscle back into adipose tissue was similar to the net movement out of adipose tissue. PCB metabolites tend to be rapidly excreted and do not accumulate in adipose tissue, muscle, or liver. Brain and, to a lesser extent, kidney tissue appear to accumulate PCB metabolites, particularly during the refeeding stage in a starvation/refeeding cycle.