Effect of local pH on interstitial fluid pressure.

It has been suggested that electrostatic interactions between the electric charges on the interstitial gel matrix play a significant role in determining tissue elasticity and interstitial fluid pressure (IFP). The relationship between the net charge and IFP, however, has not been adequately established. Our purpose was to explore the net electric charge-IFP relationship, and in vivo experiments were performed to test its validity. IFP was measured in the subcutaneous tissue of anesthetized rats with the chronically implanted capsule method, and the acid-base status in blood and interstitial fluid was monitored. The net charge, which can be varied by pH, was altered by electrolysis procedure. H+ and OH- generated inside the capsule caused transient and dose-dependent IFP responses. The curve, describing the relationship between capsular pressure changes and amount of generated H+ and OH-, has a maximum at zero net charge, and the excess electric charge, either positive or negative, results in a significant decrease in capsular pressure in accordance with the hypothesis. The time course, as well as the dose dependency, of IFP suggests that the subcutaneous tissue gel in control condition has slightly positive net charge.