Lipid metabolism by rat lung in vitro. Utilization of citrate by normal and starved rats

Abstract

1. The utilization of [1,5-¹⁴C₂]citrate by lung slices and cell cytosol preparations, and the activities of liver and lung cytosol citrate-cleavage enzyme (EC 4.1.3.8), l-malate–NAD oxidoreductase (malate dehydrogenase, EC 1.1.1.37) and phosphoenolpyruvate carboxylase (EC 4.1.1.32) were examined in normal and starved rats. 2. Lipogenesis from citrate was decreased by approx. 70% in both the phospholipid and neutral lipid fractions of lung slices from starved rats as compared with fed controls. 3. Incorporation of citrate by lung cytosol preparations into fatty acids was decreased by approx. 35% in the starved rats. The apparent inhibition by avidin of fatty acid synthesis was overcome partially by preincubation of lung cytosol preparations with biotin. These results are consistent with the presence in lung tissue of the malonyl-CoA pathway for fatty acid synthesis. 4. Lung citrate-cleavage enzyme activity decreased in rats that had been starved for 72h whereas malate dehydrogenase and phosphoenolpyruvate carboxylase activities remained unchanged. The results suggest that the pattern of utilization of lipid precursors by rat lung may be altered during various nutritional states.