Fat deficiency and the calorigenic action of L-thyroxine

¹ Department of Physiology and Division of Endocrine and Cancer Research, Jefferson Medical College, Philadelphia, Pennsylvania

The influence of a fat-deficient diet on the calorigenic action of l-thyroxine was investigated. The BMR, endogenous and substrate respiration (succinate) of liver slices and hemidiaphragms were determined. The increase of BMR in fat-deficient animals was confirmed. Furthermore, both endogenous and ‘substrate’ respiration of liver and diaphragm were higher than in controls. When thyroxine was administered, the fat-deficient animals demonstrated a greater BMR response than did controls. Substrate respiration of liver and diaphragm indicated that both fat deficiency and thyroxine treatment increase succinate utilization and that these effects are additive in these tissues.