In vivo Fatty Acid and Cholesterol Synthesis in Fasted and Fasted-refed Chicks

Abstract

The effects of fasting and refeeding following a fast on in vivo hepatic fatty acid and cholesterol synthesis were studied in growing chicks. Also investigated was the influence of these treatments on liver lipid and glycogen content and on the activities of hepatic glucose 6-phosphate and 6-phosphogluconate dehydrogenases and malic enzyme. Hepatic fatty acid and cholesterol synthesis were significantly depressed by a 24-hour fast and continued to decrease during the 3-day starvation period studied. Fatty acid synthesis increased to 275% and 364% of normal after 1 and 2 days of refeeding, respectively, following a 3-day fast. On day 3 of refeeding, fatty acid synthesis returned to normal and remained so throughout the remainder of the 5-day refeeding period. Cholesterol synthesis remained depressed until day 3 of refeeding, when a significant increase was observed, and reached near-normal values on day 4. The activity of the pentose pathway dehydrogenases was very low in chick liver and was not greatly influenced by fasting or refeeding. Malic enzyme activity was severely decreased by fasting and returned to control values after 2 days of refeeding. Liver weight and liver glycogen decreased markedly during the fasting period, increased to above normal values during the first 2 days of refeeding and returned to control levels after 3 days of refeeding. Liver total lipid was not significantly influenced by fasting but increased upon refeeding and began to decrease after 3 days of refeeding. Liver cholesterol content increased during fasting and decreased rapidly upon refeeding.