PCB-associated alteration of hepatic steroid metabolism in harbor seals ('Phoca vitulina')

Hepatic cytochrome P-450 (CYP450) isozymes are involved in xenobiotic detoxification and steroid metabolism. Seals are highly exposed to polychlorinated biphenyls (PCBs) in the environment, resulting in CYP450 induction, which may have concomitant effects on CYP450 steroid metabolism. Experiments were conducted to determine rates of steroid metabolism in harbor seal (Phoca vitulina) liver. CYP450 was induced with increasing liver PCB concentrations between 0.2 and 5.73 microg/g (wet weight). Progesterone metabolism was significantly decreased with increasing liver PCB concentration. Testosterone metabolism was also increased with increasing liver PCB concentration. The results indicate a change in steroid metabolism associated with increasing PCB burden, suggesting that PCBs may have a modulating effect on hepatic steroid biotransformation in environmentally exposed seals. The possible implications of this for endocrine homeostasis in seals are discussed.