IN-VITRO SUBSTRATE UTILIZATION FOR LIPID-SYNTHESIS IN LIVER EXPLANTS FROM HYPERTHYROID CHICKENS

1. Indian River male broiler chickens growing from 7 to 28 days of age were fed diets containing 12, 18, 24 and 30% protein + 0 or 1 mg trii odothyronine (T-3)/kg of diet to study energetic costs of lipogenesis and the use of various substrates for in vitro lipogenesis. 2. De novo lipid and CO2 production were determined in the presence of [1-C-14]p yruvate, [2(14)C]pyruvate, [3-C-14]pyruvate, [2-C-14]acetate and [U-C- 14]alanine. 3. Oxygen consumption was determined in mitochondrial prep arations to estimate the energetic costs in explants synthesizing lipi d. 4. Radiolabeled CO2 derived from [1-C-14]pyruvate was used as an es timate of coenzyme A availability in liver explants. Lipids derived fr om [2-C-14]pyruvate, [2-C-14]acetate and [U-C-14]alanine estimate rela tive substrate efficiency. 5. Labeled CO2 production from [1-C-14]pyru vate was greatest in that group fed a 12% protein diet and least in th e group fed a 30% protein diet. 6. In addition, T-3 increased CO2 prod uction from [1-C-14]pyruvate. 7. The production of (CO2)-C-14, from th e second carbon of pyruvate or acetate was increased by T-3. 8. The lo w-protein diet (12% protein) increased (P < 0.05) lipogenesis. 9. Addi ng T-3 to the diets decreased carbon flux into lipid from ail substrat es, but increased CO2 production from all substrates without changing stage 3 and 4 respiration rates in mitochondrial preparations. 10. The se observations imply that coenzyme A availability may have regulated de novo lipogenesis in the present study. 11. It was also concluded th at previously noted effects of T-3 on intermediary metabolism may invo lve metabolic pathways that do not involve changes in mitochondrial fu nction.