The goal of this program is to evaluate control of lung and surfactant phosphatidylcholine synthesis with special emphasis on the role of choline as a rate-limiting substrate. Using nutritional choline deficiency as a probe, we have shown that, in contrast to a large decrease in liver phosphatidyl choline, there is only a slight decrease in the pool of lung phosphatidylcholine. The capacity of the CDP-choline pathway of phosphatidylcholine synthesis in lung was not altered. The pathway for synthesis by N-methylation of phosphatidylethanolamine was stimulated 3-fold in the lung but nevertheless could not contribute significantly to the maintenance of lung phosphatidylcholine pools. Increased palmitate and glucose incorporation indicated increased rates of PC synthesis in the lung suggesting increased rates of PC turnover. These observations indicate compensatory changes in lung phosphatidyl choline metabolism as a consequence of choline deficiency in order to maintain the lung PC pool. We, therfore, propose to investigate possible compensatory mechanisms by the study of changes in choline transport, phosphatidylcholine turnover, and kinetics for the enzymes of CDP-choline pathway in lung in response to dietary choline deficiency using in vivo models, isolated perfused lung, and granular pneumocytes in primary culture. Choline transport mechanisms will be evaluated from measurement of tissue accumulation, metabolic fate, effect of metabolic substrates and inhibitors, and effect of specific inhibitors of choline uptake. Turnover of different moieties of lung phosphatidylcholine will be compared and the contribution of reuptake of surfactant phosphatidylcholine will be evaluated. Kinetics of the enzymes involved in the synthesis of phosphatidyl choline by the CDP-choline pathway will be evaluated from changes in specific activities and pool sizes of intermediates of this pathway. These studies will provide new information about the mechanisms through which choline can control the turnover of lung phosphatidyl choline.
