Ground substance mucopolysaccharides and plasma proteins: their role in capillary water balance

The osmotic interaction of mucopolysaccharides and plasma proteins, normally present in the interstitium, has been investigated. It has been found that hyaluronate-plasma protein mixtures may be treated as a two-phase system and that the two phases are in osmotic equilibrium. The osmotic pressures exerted by these mixtures are higher than the algebraic sum of the two components. At concentrations normally present in the interstitium of skin and muscle (0.6% mucopolysaccharides and 2% protein), the osmotic pressure exerted by the mixture is on the order of 10 mmHg, which is in agreement with predictions from earlier computer-simulation studies. The partition of fluid between the gel-like mucopolysaccharide compartment and the free-fluid containing the protein is approximately 50% in the "gel" phase at concentrations found in the interstitium. The volume exclusion effects of the interstitial mucopolysaccharides are significant, both in terms of selection of tracer molecules for interstitial volume measurements and also as an osmotic buffering mechanism which aids in maintaining the partition of fluid between the circulation and the interstitial space.