Lipid metabolism by rat lung in vitro. Effect of starvation and re-feeding on utilization of [U-14C]glucose by lung slices

Abstract

1. The incorporation of [U-(14)C]glucose into several lipid components of lung and liver slices, and the activities of glucose 6-phosphate dehydrogenase (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), ;malic' enzyme (EC 1.1.1.40) and NADP-isocitrate dehydrogenase (EC 1.1.1.42) of the cell cytosol were examined in normal, starved and re-fed rats. 2. Lipogenesis and the activities of these enzymes in liver were decreased markedly in rats starved for 72h. Re-feeding starved rats on a fat-free diet for 72h resulted in the well documented hyperlipogenic response in liver, particularly in its ability to convert glucose into neutral lipid, and increased activities of glucose 6-phosphate dehydrogenase, ;malic' enzyme and 6-phosphogluconate dehydrogenase to values approx. 700, 470 and 250% of controls respectively. 3. Approx. 70% of the total label in lung lipids was present in the phospholipid fraction. Hydrolysis of lung phospholipids revealed that lipogenesis from glucose was considerable, with approx. 40% of the total phospholipid radioactivity present in the fatty acid fraction. 4. Incorporation of glucose into total lung lipids was decreased by approx. 40% in lung slices of starved rats and was returned to control values on re-feeding. Although phospholipid synthesis from glucose was decreased in lung slices of starved rats, the decrease proportionally was greater for the fatty acid fraction (approx. 50%) as compared with the glycerol fraction (approx. 25%). 5. The activities of lung glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and NADP-isocitrate dehydrogenase were not affected by the dietary alterations. ;Malic' enzyme activity was not detected in lung cytosol preparations. 6. The results are discussed in relation to the surface-active lining layer (surfactant) of the lung.