The Effects of Lipotropic Factors on Phospholipide Turnover in the Plasma of Normal Persons as Indicated by Radioactive Phosphorus 1

Abstract

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).

The Effects of Lipotropic Factors on Phospholipide Turnover in the Plasma of Patients With Cirrhosis of the Liver, as Indicated by Radioactive Phosphorus 1

“…The ratio between the urine phosphate and the plasma phosphate should vary proportionately to the slope of the descending curve of the inorganic phosphate, unless there is some impairment in the renal excretion of phosphate. The finding of a ratio less than 1 in three normal persons (10) and in two of the present series is more difficult to explain. Similar observations, however, have been made in animals during the first few hours after the introduction of radioactive phosphorus.…”

“…Because of the wide variations between individuals, both normal and cirrhotic, it was necessary to use each patient as his own control (9,10).2…”

“…The methods and plan of study were similar to those previously described for normal individuals (10). De-terminations have been made on the inorganic fraction of the plasma so that the isotopic concentration in the lipide fraction can be expressed as a function of the specific activity of the inorganic phosphorus ("relative specific activity").…”

“…In several of these patients, treated and untreated, the effect of a single large dose ("test dose") of lipotropic material was also studied, and the results were compared with those obtained in normal persons (10).…”

“…were studied, and an apparent deficiency of lipotropic substances was demonstrated in human beings for the first time. This study has been extended to include a larger series of patients (10).…”