Hepatic Fatty Acid Synthesis and Plasma Free Fatty Acid Levels in Chicks Subjected to Short Periods of Food Restriction and Refeeding

Abstract

The effects of short-term fasting and refeeding on hepatic fatty acid synthesis, on the activities of related enzymes and on plasma levels of free fatty acids were studied in the chick. The results of these experiments demonstrate that fatty acid synthesis from acetate-1-14C or from glucose-U-14C, measured in vitro or in vivo, decreases within 30 minutes of food withdrawal and is depressed by about 90% after 2 hours of food deprivation. Fatty acid synthesis returned to normal after 30 to 60 minutes of refeeding following a 2-hour fast. An “overshoot” in hepatic lipogenesis appeared to be induced by longer periods of refeeding. The specific activities of malic enzyme and citrate cleavage enzyme were not altered by the short periods of fasting or refeeding studied. The marked depression in hepatic lipogenesis resulting from a short period of fast was closely related to increased levels of plasma free fatty acids. The level of circulating free fatty acids increased with time of fasting and returned to normal upon refeeding. It was noted that the free fatty acid level reached a maximum before the rate of lipogenesis was minimized and started to decline after the maximal depression of lipogenesis. Possible mechanisms responsible for these rapid alterations in hepatic lipogenic capacity are discussed.