Osmotic interaction of plasma proteins with interstitial macromolecules.

The osmotic interaction of plasma proteins with collagen and hyaluronate has been evaluated by measuring the oncotic pressure of mixed solutions of varying composition. Collagen, despite its insolubility, exhibits a pronounced volume exclusion effect on plasma proteins, and the oncotic pressure of mixed solutions is considerably higher than that of the plasma protein stock solution. The volume exclusion of collagen on small molecules such as sucrose is negligible. A solution composed of 1.6% plasma proteins, 20% collagen, and .4% hyaluronate in Ringer solution, approximating the composition of the interstitium, was found to yield higher oncotic pressures than those previously reported from the interstitium. The probable role of impurities and degradation in the isolation process is discussed. Results reported earlier from in vitro and in vivo studies indicated that tissue oncotic pressures are considerably higher than generally recognized and that tissue fluid is in probable osmotic equilibrium with lymph in skin and muscle.