Mucopolysaccharide osmotic pressure in the measurement of interstitial pressure

Subatmospheric pressures were recorded from cotton wicks inserted into Wharton's jelly of human umbilical cords (mean=-7.6+/-5.0 (SD) cmH2O; n=10). Hyaluronate concentrations (mean=0.69+/-0.30 g/100 g) and wick pressures correlated negatively (r=-0.825; P less than 0.01) but calculated hyaluronate osmotic pressures (mean=4.0+/-2.7 cmH2O) were insufficient to explain the full wick pressure. In model systems composed of asbestos fibers (mean radius=0.5 micron) and 0.9% saline, subatmospheric pressures were recorded which varied with the volume of saline added. When hyaluronate (1 g/100 g) was substituted for saline, lower wick pressures were recorded at each volume. The pressure lowering effect of hyaluronate was not seen in a matrix of glass fibers (mean radius=1.0 micron). It is suggested that the effect of hyaluronate in asbestos fibers is due to its immobilization by the matrix and the consequent development of osmotic pressure recorded via the wick. In the coarser glass-fiber matrix, hyaluronate was not immobilized and therefore had no osmotic effect. These experiments support the hypothesis that subatmospheric interstitial pressures result from osmotic pressure of immobilized mucopolysaccharide macromolecules.