Metabolism of phosphorylcholine and lecithin in normal and choline-deficient rats

Abstract

1. 1. The metabolism of phosphorylcholine and lecithin in liver and plasma of normal rats and rats in the early stages of choline-deficiency has been studied. 2. 2. A striking reduction (over 70%) of phosphorylcholine levels in choline-deficient livers and a greatly decreased labelling from 32P i and [1,2- 14C 2]choline was found. 3. 3. Levels of lecithin were slightly depressed in choline-deficient livers but there was increased incorporation of 32P i, [1,2- 14C 2]-choline and [ Me- 14C]methionine into liver lecithin. Increased radioactivity from the three precursors was found also in plasma phospholipids. 4. 4. The labelling of phosphorylcholine and lecithin from 32P i at different time intervals suggested that, in choline-deficient livers, although phosphorylcholine synthesis was depressed, it was not rate-limiting for lecithin formation and that there was, in fact, an increased conversion of 32P-labelled phosphorylcholine into lecithin. 5. 5. The labelling of liver phosphorylcholine and lecithin from [1,2- 14C 2]choline in the control animals was also consistent with a precursor-product relationship. However in the choline-deficient animals the specific activity of lecithin was almost equal to that of phosphorylcholine in the early intervals after injection of the tracer and it is suggested that [1,2- 14C 2]choline may, in part, be incorporated into liver lecithin by a pathway independent of phosphorylcholine. 6. 6. The possible relationship between these findings and the accumulation of liver fat in the choline-deficient animals is discussed.