AJP - Heart and Circulatory Physiology, Vol 248, Issue 6 890-H893, Copyright © 1985 by American Physiological Society
Physiological effects of pH changes on colloid osmotic pressures
B. R. Will and R. A. Brace
Our purpose was to explore the effects of variations in pH, particularly in
the physiological range, on the colloid osmotic pressure (COP) of the
body's fluids. Theoretically, changing pH would alter the electrical charge
density on plasma proteins and the interstitial ground substance, thereby
altering plasma and interstitial protein osmotic pressure as well as
interstitial fluid pressure. We found that the COP of human plasma, human
albumin, bovine albumin, and Wharton's jelly from human umbilical cords
increased linearly as pH increased over the range of 6.0-8.0. COP of plasma
and the albumins all displayed essentially the same sensitivity to pH. At
equal concentrations, hyaluronate in umbilical cords was approximately 16
times more sensitive to pH than was plasma. Dextran 70 displayed no COP
dependency on pH. For plasma, the albumins, and hyaluronate the pH
dependence of COP on pH also decreased linearly with concentration (C in
g/dl). For plasma and the albumins over the physiological range of pH, COP
= COPpH 7.4 [1.00 + 0.01C (pH -7.40)] at 37 degrees C. The data suggest
that, relative to the normal net transcapillary pressure gradient,
physiological variations in pH affect plasma COP as well as interstitial
fluid pressure and thus may play a significant role in regulating the
body's fluid distribution.
