Substrate utilization for phosphatidylcholine synthesis by type II pneumocytes of neonatal rats

Type II pneumocytes isolated from neonatal rat lungs, using an isolation procedure developed for adult rats, were found to be phenotypically stable and metabolically active in culture. The cells, purified by metrizamide gradient centrifugation and differential adherence, were capable of synthesizing phospholipids from 14C-labeled choline, palmitate, glucose, and acetoacetate. Regardless of the 14C-labeled substrates used, greater than two thirds of the radioactivity incorporated into phosphatidylcholine was recovered in disaturated phosphatidylcholine, the major component of surfactant phospholipids. The incorporation of palmitate into phosphatidylcholine and other phospholipids (i.e. phosphatidyl-ethanolamine, -glycerol, -serine, and -inositol) indicates that the neonatal type II cells have the capacity to produce surfactant lipids. The neonatal cells preferentially utilized acetoacetate over glucose as a precursor of phospholipids. In the adult type II cells, glucose was incorporated into phospholipids more rapidly than acetoacetate. The rate of glucose incorporation in the neonatal cells was enhanced by exogenous insulin. The preferential utilization of acetoacetate by the neonatal type II cells is consistent with the stimulated acetoacetyl CoA synthetase pathway in the lung. The depressed glucose incorporation into phospholipid, on the other hand, may be attributed to insulin insufficiency in the neonate.