The effects of lipotropic factors on phospholipide turnover in the plasma of normal persons as indicated by radioactive phosphorus.

The action of choline and methionine in preventing or curing the fatty infiltration of the liver which is produced experimentally in animals by low protein diets is believed to result from an increased turnover of phospholipides in the liver (1, 2). Since this organ is the main, if not the sole, source of phospholipides in plasma (3), it would seem that changes in the formation of phospholipides in the liver would be reflected by corresponding changes in the amounts of newly formed phospholipides in the plasma (4). No methods were available for the determination of newly formed plasma phospholipides until isotopic techniques were developed and radioactive tracers became available. It is now possible to study the formation of plasma phospholipides following the administration of radioactive phosphorus, and to obtain an indication of the turnover of these compounds in the liver. Few data of this sort are available for human subjects, however. Hence, it became necessary to estimate the turnover in normal persons, before the effects of lipotropic agents such as choline and methionine could be investigated and information could be obtained on the mode of action and possible therapeutic application of these substances. Preliminary experiments to determine the validity of the method for determining the radioactivity and phosphorus of the plasma lipides in persons with and without liver disease were done and the results obtained were used to calculate the turnover of phospholipides (specific activity) (5).