Direct effects of 3,5,3'-triiodothyronine and 3,5-diiodothyronine on mitochondrial metabolism in the goldfish Carassius auratus

Direct effects of 3,5,3'-triiodothyronine (T3) and 3,5-diiodothyronine (T2) on the metabolism of the goldfish (Carassius auratus) were assessed using mitochondria isolated from liver and red muscle. Following a 5-min incubation with either T3 or T2, the oxidation rates of substrates involved in amino acid and carbohydrate metabolism and lipid catabolism were measured. State 3 oxidation of pyruvate was significantly higher for liver mitochondria treated with T2 and for red muscle mitochondria incubated with T3 when compared to control mitochondria. Rapid elevation of state 3 rates of substrate oxidation by thyroid hormones may be important in mediating diurnal changes in mitochondrial metabolism. Significant increases in liver and red muscle mitochondrial state 4 rates were also observed for pyruvate in T2- and T3-treated mitochondria and for glutamate in T3-treated mitochondria.