Responses of Essential Fatty Acid-Deficient Rats to Fasting-Refeeding and Partial Hepatectomy

Abstract

The proportion of arachidonate in liver phospholipids in young rats decreases from about 30 to 10-12% after 4 weeks of feeding an essential fatty acid-deficient diet (1-3). Subsequently, arachidonate decreases only slowly (3)(4)(5), and turnover of liver phospholipids appears reduced ( 5 ) . It is generally assumed that a certain level of essential fatty acids (EFA) in phospholipids is required for membrane integrity, function, and formation (6). Reduced phospholipid turnover ( 5 ) might be one consequence of a decrease in EFA in membrane phospholipids.Information on the need for EFA-containing phospholipids in membrane structure, as well as on the ability of EFA-depleted liver to form phospholipids, could be obtained by subjecting EFA-deficient rats to stimuli which normally increase phospholipid formation. Little or no response would occur if a relatively high proportion of EFA were required. Considerable response would occur if nonessential unsaturated fatty acids could replace essential fatty acids to a large extent in these functions. Stimulation of liver phospholipid formation could also produce even greater depletion of liver EFA than is usually obtained in EFA-deficient rats.Two conditions which stimulate liver phospholipid formation are (a) partial hepatectomy (7, 8) and (b) refeeding of a high carbohydrate diet after fasting (9-1 1). Partial hepatectomy normally produces liver hyperplasia and hypertrophy which require formation of new phospholipid-containing membranes (8). Refeeding after fasting increases lipoprotein secretion (9). Park et al.(1 1 ) reported that fasting-refeeding also decreased the concentrations of arachidonate and linoleate in microsomal phospholipids, To whom all correspondence should be addressed.presumably as a result of increased lipoprotein secretion.Decreases in phospholipid EFA may underlie increased activities of liver glucose-6phosphate dehydrogenase (G6PD) and other lipogenic enzymes in rats refed high carbohydrate diets after fasting (10, 11). The activities of liver lipogenic enzymes are already elevated in EFA-deficient rats fed ad libitum ( 1 ) . Thus, these enzyme activities might become even higher if additional decreases in phospholipid EFA were produced by fasting-refeeding of EFA-deficient rats.In the present report, we have subjected EFA-deficient rats to fasting-refeeding or to partial hepatectomy and then have measured liver phospholipid fatty acid composition and recovery of liver and body weights. Activities of glucose-6-phosphate dehydrogenase (G6PD) and fatty acid synthetase (FAS) were also measured in the fastedrefed deficient rats.Materials and methods. Male weanling Long-Evans or Sprague-Dawley rats (Simonsen Farms, Gilroy, Calif.) were caged individually in galvanized screen wire-bottom cages and were fed ad libitum either a fat-free diet or the same diet supplemented with 5 % safflower oil (1). The oil replaced an equal weight of sucrose. In the fastingrefeeding study, rats were fed the fat-free diet ad libitum for 7 weeks after weaning, then fasted fo...