Influence of temperature on the composition of fatty acids and on lipogenesis in frog tissues

Abstract

1. 1. Frogs ( Rana esculenta) were adapted to various temperatures and the fatty acid composition of tissues and lipogenesis from radioactive precursors were studied. The activities of NADPH-generating enzyme systems were also compared. 2. 2. Liver and adipose tissue from cold-adapted frogs contained more unsaturated fatty acids and less saturated, than the corresponding tissues from frogs kept at higher temperatures. However, differences were found mostly in the proportions of polyenoic acids and not in those of the monoenoic acids. The changes in fatty acid composition of phospholipids and of neutral lipids were similar. 3. 3. As a result of in vitro lipogenesis from 1-C 14-acetate mostly saturated and monoenoic fatty acids were formed and there was no indication of de novo formation of linoleic acid in tissues from either cold-adapted frogs or those kept at 20°C. 4. 4. The temperature of adaptation did not influence either the extent of hepatic lipogenesis from C 14-acetate or the distribution of radioactivity in lipid fractions. On the other hand, in adipose tissue of frogs kept at 20°C both lipogenesis and esterification of newly formed fatty acids were strongly inhibited as compared with the tissue from cold-adapted animals. 5. 5. No correlation between the rate of lipogenesis and the activities of NADPH-generating enzymes could be observed and under the conditions of depressed lipogenesis formation of NADPH did not seem to be rate limiting.