Acid-base changes in the brain in nonrespiratory acidosis and alkalosis.

Abstract

Changes in the bicarbonate and the chloride concentrations in the brain, as well as in the bicarbonate concentration of the cisternal cerebrospinal fluid (CSF), were measured in rats made acidotic or alkalotic for a period of 6 hours by means of intraperitoneal injections of acid and basic solutions. The difference in the plasma chloride concentrations between the acidotic and the alkalotic groups was 8.6 mEq/l, while the corresponding difference in the tissue concentrations was 4.5 mEq/kg of wet tissue. These results demonstrate that the chloride ion equilibrated between the plasma and the “chloride space” of the brain tissue under the conditions of the experiments. However, although the marked difference in the plasma bicarbonate concentrations between the same groups (17.4 mEq/l) was accompanied by a difference in the CSF bicarbonate concentrations of 7.6 mEq/kg, there were no significant differences in the actual tissue bicarbonate concentrations, attributable to the extracellular bicarbonate changes. Provided that CSF is representative of the extracellular fluid (ECF), these results can either be interpreted to show that the bicarbonate of the ECF is distributed in a very small tissue compartment (probably less than 5 per cent of the tissue volume), or that nonrespiratory acid-base changes are not accompanied by net fluxes of bicarbonate ions between the plasma and the extracellular space of the brain tissue but rather by redistributions of bicarbonate ions between extra-and intracellular fluids.