The Effect of Hypovolemic Hypotension on Extra‐ and Intracellular Acid‐Base Parameters and Energy Metabolites in the Rat Brain

Abstract

Abstract S iesjö , B. K. and N. N. Z wetnow . The effect of hypovolemic hypotension on extra‐and intracellular acid‐base parameters and energy metabolites in the rat brain . Acta physiol. scand. 1970. 79 . 114–124. The influence of hypovolemic decreases in the mean arterial pressure upon intra‐ and extracellular acid‐base parameters in the brain, and upon tissue concentrations of ATP, ADP, AMP and phosphocreatine, was studied in immobilized and artificially ventilated rats. Hypotensive periods of 20 or 60 min duration did not lead to any significant changes in ATP, ADP, AMP or phosphocreatine concentrations until the mean arterial pressure was below 40 mm Hg, but there was a small gradual increase in tissue lactate concentration, and in the lactate/pyruvate ratio, even at a moderate decrease in blood pressure. The lactate and pyruvate changes were significant even after corrections for blood and CSF lactate and pyruvate contents, and similar changes were seen in the CSF. The moderate changes in extra‐ and intracellular lactate concentrations did not lead to any noticeable decreases in calculated extra‐ and intracellular pH values since even moderate reductions in blood pressure usually led to small concomitant falls in the tissue CO 2 tension. Thus, if it can be assumed that the cerebral blood flow was upheld at the moderately reduced perfusion pressures, the results strongly speak against the possibility that the decrease in cerebrovascular resistance, which occurs during autoregulation of flow in hypovolemic hypotension, is related to extracellular pH changes.