Effect of thyroid state on ketogenic capacity of the isolated perfused liver of starved rats.

The effect of different thyroid states on the oxidation of free fatty acids was investigated in the isolated perfused liver of 24-h-starved rats. 1. Compared with the euthyroid control the oxidation of oleate to ketone bodies as well as to CO2 was increased in hyper-, while it was unchanged in hypothyroid livers. 2. The addition of carnitine stimulated oleate oxidation in livers from eu- and hyperthyroid rats, but was without effect in hypothyroid livers. 3. Glucose did not affect the thyroid hormone-mediated effect of oleate conversion to ketone bodies. 4. Hepatic oxidation of octanoate was similar in all thyroid states. 5. Re-esterification of oleate was enhanced in hypo-, but reduced in hyperthyroidism. 6. The concentration of hepatic malonyl-CoA was decreased in hypo- and unchanged in hyperthyroid livers. 7. The concentration of cyclic AMP was elevated in the liver of hyperthyroid rats, no differences were observed between eu- and hypothyroid livers. However, increasing the hepatic cyclic AMP content by the addition of glucagon did not stimulate ketogenesis in eu- and hypothyroid livers. 8. The results indicate that thyroid hormones stimulate oleate oxidation by an accelerated transport of its CoA derivative into the mitochondrial compartment.