Extracellular Fluid Viscosity: Its Role in the Regulation of Membrane Lipid Metabolism and Cellular Secretion
Plasma viscosity, which is determined by the concentration of proteins and other macromolecules, is elevated in various pathological states associated with the excess production of plasma proteins (1). The concentration of albumin and other macromolecules in the plasma have been assumed to be involved in the control of the synthesis of proteins and lipids in the liver (2): Studies with nephrotic animals have demonstrated that the resultant hypoalbuminemia is followed by increased rates of synthesis of albumins and lipoproteins (3). In both nephrotic patients and experimental animals, infusions of macromolecules, such as dextrans or albumin, reduced plasma lipoprotein levels (4). These observations seem to support the hypothesis that colloid osmotic pressure, which is governed by the macromolecule concentration, plays a role in determining hepatic plasma protein production, although other studies have given inconclusive results (5). The colloid osmotic pressure hypothesis was further examined in hepatocyte cultures, a more well defined and controllable system (6,7). Increasing the concentrations of various macromolecules (dextrans, albumins and γ-globulins) in the culture medium had no effect on albumin synthesis, but markedly inhibited the synthesis of very low density lipoproteins (VLDL). However this effect did not correlate with either osmolarity, mass concentration or the chemical nature of the macromolecules present in the extracellular medium.
KeywordsMinimal Essential Medium Relative Viscosity Plasma Viscosity Viscous Medium Medium Viscosity
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