Age dependency of triiodothyronine-induced thermogenesis in young chicks: inhibition by propylthiouracil

Age dependency of triiodothyronine (T3)-induced thermogenesis of young chicks at 1 and 2 wk of age was investigated by dietary administration of .5% propylthiouracil (PTU), an inhibitor of thyroid hormone synthesis. Heat production measured by indirect calorimetry was increased by an intraperitoneal injection of T3, but the thermogenic effect was larger at 2 wk than at 1 wk of age. Heat production at 2 wk of age was decreased by PTU when the T3 was not administered, whereas the inhibitory effect of PTU was not found at 1 wk of age. It would appear, therefore, that little or no thermogenesis is responsive to exogenous T3 in young chicks at 1 wk of age even though the suppression of endogenous T3 is likely to occur by the PTU treatment.