Ascites fluid lipoproteins in experimental nephrotic syndrome

Lipoprotein content and composition were studied in ascites fluid of puromycin aminonucleoside-nephrotic rats. All of the lipoprotein density classes were found in ascites fluid. Protein levels compared to plasma were: very low density lipoprotein (VLDL, d less than 1.006), 1.2%; intermediate density lipoprotein (IDL, 1.006 less than d less than 1.02), 2.6%; low density lipoprotein (LDL, 1.02 less than d less than 1.063), 1.0%; and high density lipoprotein (HDL, 1.063 less than d less than 1.21), 1.1%. The predominant protein in ascites fluid was albumin, present at 1.9% of the plasma level. Radioiodinated VLDL and HDL injected intravenously into nephrotic rats appeared in lipoprotein fractions of the ascites fluid. VLDL and IDL triacylglycerol content and particle diameter were low compared with plasma particles, suggesting peritoneal triacylglycerol lipase activity; such lipase activity could account for the increased proportion of LDL in the ascites fluid. Ascites fluid LDL and HDL phospholipid and free cholesterol were high and cholesteryl ester was low. Ascites lipoproteins contained the same apolipoproteins as plasma, but in different proportions. Ascites VLDL had higher apolipoprotein B and lower apolipoprotein E, while LDL and HDL had higher apolipoprotein E. Ascites HDL could be separated by heparin-Sepharose affinity column chromatography into a retained and a non-retained fraction, while nearly all nephrotic plasma HDL was non-retained. These data suggest that modification of ascites fluid lipoproteins occurs prior to their entry into the lymph and return to the blood, perhaps mediated by peritoneal macrophages.