The distribution of cholesterol and apoprotein A-I between the lipoproteins in plasma and peripheral lymph from normal human subjects

The lipoproteins of peripheral lymph and plasma from normal human subjects were separated according to their density by sequential ultracentrifugation and according to their size by gradient gel electrophoresis and gel exclusion chromatography. High density lipoproteins (HDL) carried a higher proportion of the total cholesterol in lymph than in plasma. Within the HDL fraction, the less dense and more lipid-rich component (HDL2) carried a higher proportion of the total HDL cholesterol in lymph than in plasma. Gradient gel electrophoresis showed (1) a higher proportion of large to small HDL particles in lymph than in plasma and (2) the presence of at least three populations of apo A-I-containing lipoproteins with Stokes diameters larger than the Stokes diameter of HDL2. Separation by gel exclusion chromatography showed that the proportion of large HDL particles with a high cholester: apo A-I ratio was greater in lymph than in plasma. In view of the sieving effect of the blood capillaries, which favours the passage across the capillary walls of smaller vs larger particles, we suggest that the higher ratio of large to small HDL particles in lymph than in plasma is due to the conversion of small to large HDL in the interstitial fluid by incorporation of cholesterol and other lipids from extravascular cells into the smaller particles.