Human peripheral lymph lipoproteins are enriched in sphingomyelin

The concentrations of total choline-containing phospholipids and of sphingomyelin have been determined in peripheral lymph from six volunteers. The concentration in lymph of total phospholipids was 14.6 +/- 6.0 mg/dl and of sphingomyelin 6.1 +/- 2.7 mg/dl; the estimated concentration of phosphatidylcholine (by subtracting the concentration of sphingomyelin from that of total choline-containing lipoproteins) was 8.5 +/- 5.1 mg/dl. The concentration of free choline in lymph was less than 1 mg/dl. The ratio of the concentration in lymph to that in the subject's own plasma of sphingomyelin was 0.18 +/- 0.07 and that of (estimated) phosphatidylcholine 0.05 + 0.04; the difference between these two ratios was significant at P less than 0.002. The present data are compatible with the hypothesis that some of lipoprotein phosphatidylcholine is lost while crossing from plasma to lymph.