Effect of thyroid hormone on peroxisomal flavin enzymes in rat liver and kidney

The effect of thyroid hormone on peroxisomal enzyme activity was studied in thyroidectomized- and T4-administered-thyroidectomized rats. In liver, the activities of isozyme A of L-alpha-hydroxyacid oxidase, D-amino acid oxidase, urate oxidase and catalase were decreased by thyroidectomy, and the diminished enzyme activities were restored by T4 administration to rats. These modifications induced by thyroidectomy or by T4 administration, however, were prominent only in immature animals (20-day-old rats). Although the changes in-alpha-hydroxyacid oxidase and D-amino acid oxidase activities, induced by thyroidectomy or by T4 administration, were also observed in 40-day-old rats, those in urate oxidase and catalase activities were not significant in 40-day-old rats. Acyl CoA oxidase activity was not affected by thyroidectomy or by T4 administration in either 20- or 40-day-old rats. In the kidney, isozyme B of L-alpha-hydroxyacid oxidase activity was reduced by thyroidectomy and the diminished enzyme activity was restored by T4 administration in both 20- and 40-day-old rats. D-Amino acid oxidase and catalase activities in kidney, however, were not significantly modified by thyroidectomy or by T4 administration in either 20- or 40-day-old rats. The results suggest that thyroid hormone can modify the peroxisomal enzyme activity, which is prominent in immature animals.