Regulation of plasma lipid levels by plasma viscosity in nephrotic rats

The viscosity of the extracellular medium of cultured hepatocytes has been shown to be a regulator of the secretion and synthesis of very low-density lipoproteins. At present, the role of plasma viscosity in regulation of plasma lipoprotein levels was examined in vivo using nephrotic hyperlipidemic rats. Plasma viscosity was increased by injection of macromolecules: 1) simultaneously with induction of nephrosis by aminonucleoside; and 2) after the lipid level had reached its maximum. In experiment 1 the elevation of plasma viscosity (which persisted for at least 2 days) delayed the development of the hyperlipidemia by at least 2 days. In experiment 2 increasing the plasma viscosity reduced plasma triglyceride and cholesterol levels by 70 and 40%, respectively, within 2 days. The hyperlipidemia was accompanied by increased plasma viscosity. The contribution of lipoproteins to plasma viscosity was 27% in the nephrotic-hyperlipidemic rats, compared with 4% in normal rats. It is suggested that plasma viscosity regulates lipoprotein levels in vivo, concordant with the observation in cultured hepatocytes.