Bicarbonate and chloride shifts in rat brain during acute and prolonged respiratory acid-base changes.

Abstract

(4 figures) In recent years the bicarbonate concentration ([HCO,]) in cerebrospinal fluid and in brain has attracted much interest. Several authors studied the buffering systems of the central nervous system in conditions of experimental acidosis and alkalosis and discussed the mechanisms of the observed changes. During metabolic acid-base changes in blood it appeared that pH and [HCOJ in cerebrospinal fluid (CSF) are only very slightly influenced in acute conditions (cfr DE BERSAQUES, 1955, for the literature; DE BERSAQUES and LEUSEN, 1954; ROBIN ef al., 1958; LEUSEN, 1965). More prolonged changes in plasma [HCOJ however are eventually reflected to a certain degree in CSF (for literature see MITCHELL et al., 1965, FENCL ef al., 1966 and MITCHELL, 1966) and variations in [HCOJ in CSF are compensated by changes in the chloride concentration ([Cl-I). Total brain tissue also showed only very small changes in [HCOJ after 6 hours non-respiratory changes in the bicarbonate concentration of blood plasma in the rat (SIESJO, 1964, 1965; SIESJO and PONTBN, 1966a and b). These authors conclude that the chloride ion equilibrated between plasma and brain tissue under the conditions of the experiment. More rapid changes are observed on the other hand in the bicarbonate concentration of CSF during respiratory changes in the acid-base equilibrium. These changes which are rather moderate in acute conditions, become progressively more pronounced with time.