LIPID-SYNTHESIS - A THERMOGENIC MECHANISM IN COLD-EXPOSED ZUCKER FA FA RATS

1. The oxygen consumption and carbon dioxide production of Wistar and Zucker lean (Fa/?) and obese (fa/fa) rats was measured at 4, 10, 20 an d 30-degrees-C. 2. There was a net synthesis of lipid at the expense o f carbohydrate in Wistar rats at 20-degrees-C, with active lipid oxida tion at 4-degrees-C, and increasing heat production at lower temperatu re. Zucker lean rats also showed this trend. 3. Zucker fa/fa rats synt hesized lipid at 4, 10 and 20-degrees-C, showing a less marked increas e in heat production with lowering temperature. 4. It is postulated th at Zucker obese rats synthesize lipids as a way to obtain residual met abolic heat to maintain their body temperature. This is part of a proc ess-fully functional in Wistar and Zucker lean rats, and truncated in Zucker obese rats-in which liver lipogenesis can combine with brown ad ipose tissue lipolysis to generate enough heat to maintain body functi ons under a cold environment.