Partial food restriction increases hepatic inner ring deiodinating activity in the chicken and the rat

The effects of a long term partial food restriction were studied in chickens and rats. In chickens the treatment resulted in increased plasma T-4 levels while T-4 levels in rats remained unchanged. Plasma T-3 decreased in both species. In vitro hepatic outer ring deiodinating type I (ORD-I) activity was not influenced by the food restriction, suggesting that the amount of ORD-I enzyme present in the liver remained unchanged. In vitro hepatic inner ring deiodinating type III activity, on the contrary, was greatly increased in both species. This increase may contribute to the decreased circulating T-3 levels by increasing the degradation of T-3 and diverting the deiodination of T-4 to rT(3) instead of to T-3. (C) 1995 Academic Press, Inc.