Relationship between liver microsomal function and serum thyroid hormones in rats treated with carbon tetrachloride

Liver cytochrome P-450, b5, and serum thyroid hormones were measured before and 2-6 h after intra-peritoneal injections of CCl4 (1 mg/kg) in rats, to elucidate the relationship between serum thyroid hormones and liver microsomal function. Serum total protein, thyroxine (T4), free T4, triiodothyronine (T3), and cytochrome P-450 and b5 were decreased significantly after CCl4 administration, whereas reverse T3 (rT3) was unchanged. In addition to decreased conversion of T4 to T3 in liver microsomes, decreased serum binding capacities appeared to contribute to the change in serum hormone levels, since serum T4 correlated significantly with serum total protein. Serum T3, the T3/T3 + rT3 ratio, and the rT3/T3 ratio correlated significantly with cytochrome P-450 or b5, whereas the T3/T4 and T3/free T4 ratios did not. These results suggest that serum T3, the T3/T3 + rT3 ratio, and the rT3/T3 ratio are closely correlated with microsomal dysfunction in the severe case of CCl4-induced liver injury where serum binding proteins of thyroid hormones are decreased.