SPHINGOMYELIN METABOLISM IN RAT-LIVER AFTER CHRONIC DIETARY REPLACEMENT OF CHOLINE BY N-AMINODEANOL

Sphingomyelin (SM) is a structural element of cell membranes and lipop roteins, and participates in signal transduction. To determine whether a choline analog (N-amino-N,N-dimethylaminoethanol, N-aminodeanol, NA De) can be substituted for choline in the SM of liver, rats (male, Spr ague-Dawley-derived) were fed a diet that was low in choline and methi onine, and contained 35.5 mmol of NADe/kg. After 18 months, liver plas ma membranes and microsomes contained 48.9 +/- 3.6 and 93.6 +/- 6.9 nm ol/mg protein of phosphatidyl-NADe, respectively, and 3.2 +/- 0.2 and 3.5 +/- 0.1 nmol/mg protein of ceramide phospho-NADe. The SM content o f microsomes from NADe-fed rats was about one-third lower than for the control, and phosphatidylcholine (PC) was reduced by <10%; there was also a small decrease in PC, but not SM, in plasma membranes. In vitro assays of enzymes involved in SM metabolism found no change in PC:cer amide cholinephosphotransferase, but the NADe-fed animals had higher p hosphatidylethanolamine:ceramide ethanolaminephosphotransferase activi ty, greater incorporation of methyl groups from [methyl-H-3]-S-adenosy l methionine into SM, and a lower neutral sphingomyelinase activity. T hese results show that NADe-fed rats form considerable amounts of cera mide phospho-and phosphatidyl-NADe; however, liver plasma membranes re tain relatively normal levels of PC and SM, perhaps due to increases i n the de novo pathway for SM synthesis and decreases in SM turnover.