Negative relationship between PCBs and plasma retinol in low-contaminated free-ranging gray seal pups (Halichoerus grypus)

Polychlorinated biphenyls (PCBs) have been shown to affect retinol (vitamin A) homeostasis in adult as well as neonatal seals. The aim of the present study was to examine the relationships between plasma (PL)-retinol status and PCB concentrations in different blood compartments (blood cells (BCs), PL, and whole blood (WB)) of free-ranging neonatal gray seals (Halichoerus grypus) and to identify which PCB congeners may be responsible for the PL-retinol-depressing effects of PCBs. PL-retinol concentrations correlated positively with body mass and negatively with ΣPCB (lipid-weight basis, lw) in WB and ΣPCBlw in BCs. ΣPCBlw in WB was the parameter that best described the variation in PL-retinol concentration (r2=0.455, n=20, P=0.0007). Furthermore, PL-retinol concentrations correlated with nine of the 15 detected PCB congeners. It is possible that there is an equilibration between the concentrations of metabolizable congeners and their metabolites and that the retinol-depressing effect of PCBs in neonatal gray seals is caused by PCB-OH metabolites that interfere with the formation of PL transport complexes that transport retinol in PL and increase renal excretion of retinol. This suggestion is in accordance with previous mechanistic explanations of the retinol-depressing effect of PCB in rodents.