Abstract

A relationship between formation of methylsulfonyl (MeSO₂) metabolites of 2,2′,4,5,5′-pentachlorobiphenyl (PentaCB) and decrease in serum thyroxine (T₄) level was examined in the rats and mice after a single i.p. injection of PentaCB (342 μmol/kg body weight). In either rats or mice, levels of the 3- and 4-MeSO₂ metabolites of PentaCB in the liver and feces increased in a time-dependent fashion up to 8 days after PentaCB-treatment. However, there was a marked difference between rats and mice in the amount of the metabolites formed, and the cumulative amount of the either MeSO₂ metabolite for 8 days after PentaCB treatment in the liver was 4 to 15 times higher in mice than in rats. On the other hand, a 40 to 60% decrease in level of serum total T₄ occurred in both rats and mice at 1 day after PentaCB treatment, and the decrease was retained up to 8 days after PentaCB treatment. Thus, there was a marked difference between rats and mice in the formation of MeSO₂ metabolites from PentaCB but not a significant difference between rats and mice in PentaCB-induced decrease in the level of serum total T₄, indicating that PentaCB-induced decrease in the level of serum total T₄ is not necessarily dependent on the MeSO₂ metabolites formed.