The Influence of Arterial Hypoxemia upon Labile Phosphates and upon Extracellular and Intracellular Lactate and Pyruvate Concentrations in the Rat Brain

Abstract

The influence of hypoxemia upon the energy metabolism of the brain was studied by measuring the tissue concentrations of phosphocreatine, ATP, ADP, AMP, inorganic P, lactate, pyruvate, α-ketoglutarate, glutamate, and ammonia in the brains of rats after a 30 min reduction in the paO₂ to minimally 15 mm Hg. Intracellular lactate and pyruvate concentrations were derived after correction for the lactate and pyruvate contained in the blood and extracellular fluid volumes of the tissue. When the pO₂ was reduced below about 50 mm Hg, there were progressive increases in the intracellular lactate concentrations, and in the lactate/pyruvate ratios. At pO₂'s of about 35 mm Hg, the phosphocreatine content was reduced, but there were no significant changes in ATP, ADP, or AMP until the pO₂ was reduced below 25 mm Hg. At these low pO₂'s the metabolic changes were exaggerated by even small decreases in the blood pressure.

Key Words:

• Acidosis
• brain
• cerebrospinal fluid
• energy metabolism
• hypoxemia
• intracellular pH
• labile tissue phosphates