Effect of ethanol on the peripheral metabolism of thyroxine

To determine the effect of ethanol on peripheral metabolism of T4, deiodinative clearance of T4 and serum concentration of T4, T3 and rT3 were measured in rats isotopically equilibrated with T4. Ethanol 8 g/Kg weight/day was given for 3 days to fasted rats and the results were compared with those normally fed or totally fasted animals. In fasted rats, deiodinative clearance of T4 and serum T4 and T3 concentration, and T3/T4 ratio, were decreased significantly, while serum rT3 concentration and serum rT3/T4 ratio was increased significantly when compared to those in normal rats. When ethanol was administered to fasted rats, deiodinative clearance of T4, serum T4 and T3 concentration and serum T3/T4 returned to normal level while serum rT3 concentration and rT3/T4 ratio remained at higher levels than in normally fed animals. These results could not be interpreted on the basis of shift of 5 monodeiodinase to 5' form or vise versa, and imply that the two deionative process may be independent each other.