LIPID EXCHANGE BETWEEN PLASMA AND LYMPH IN EXPERIMENTAL LIPÆMIA

1. The exchange of lipids between plasma and lymph was studied in two groups of rabbits made hyperlipaemic with cholesterol-feeding and by the intravenous injection of Tween 80. 2. In rabbits fed cholesterol the plasma cholesterol rose elevenfold, whereas the plasma phospholipid and total esterified fatty acid showed only a twofold increase. The concentrations in the thoracic duct lymph also increased, but to a relatively less extent than in the plasma. The phospholipid/cholesterol ratio fell from 2·2 to 0·4 in the plasma and from 2·4 to 0·7 in the lymph. 3. Tween 80 injections caused proportionately large increases of all the plasma-lipid fractions to about 5 or 6 times the normal levels. There was an increase in the plasma-lymph lipid gradient, as the lymph lipids showed only a two- or threefold increase. No significant change occurred in either the plasma or lymph phoshpolipid/cholesterol ratio. 4. The physical state of the plasma and lymph lipids in both groups was altered. The cholesterol-fed rabbits showed high concentrations of large cholesterol-containing lipoprotein molecules which migrated on filter paper behind and with the beta globulin. These molecules were retained by the capillary membrane to a large extent, and appeared in the lymph in relatively low concentrations. The Tween 80 treated rabbits showed increases in the concentration of large molecular lipoprotein and particulate lipid which appeared in the lymph in even smaller amounts than the beta-type lipoprotein of the cholesterol-fed rabbits.