Fructose utilization by lung.

We have examined the role of fructose as a substrate for the mammalian lung. Isolated and ventilated rat lungs were perfused for 2 h in the presence of either [U-14C]- or [5-3H]fructose. Fructose utilization, 3H2O production, and lactate and pyruvate production were measured. Insulin had no effect on the production of radiolabeled lactate. The 14C label from [U-14C]fructose was incorporated into the neutral lipids, phospholipids, fatty acid moiety, and deacylated fraction of lung. The apparent Km and maximum velocity of enzyme reaction for fructose utilization were 0.5 mM and 75 nmol X h-1 X g dry wt-1, respectively. Recovery of fructose 1-phosphate and fructose 1,6-diphosphate after perfusion with fructose, as well as detection of fructokinase, aldolase, and triokinase activities in the lung homogenates, suggested that fructose had been metabolized via phosphorylation through fructose 1-phosphate. Activities of fructose-metabolizing enzymes were not altered by the induction of diabetes, hypophysectomy, or starvation. These results suggest that mammalian lungs may utilize fructose to synthesize fatty acids, which in turn are used for phospholipid biosynthesis. The utilization of fructose by lung does not seem to be affected by nutritional or hormonal conditions.