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

TLDR

The study measured brain tissue concentrations of phosphocreatine, ATP, ADP, AMP, inorganic phosphate, lactate, pyruvate, α‑ketoglutarate, glutamate, and ammonia in rats after a 30‑minute paO2 reduction to ~15 mm Hg, correcting intracellular lactate and pyruvate for blood and extracellular fluid content. When paO2 fell below ~50 mm Hg, intracellular lactate and lactate/pyruvate ratios rose, phosphocreatine dropped at ~35 mm Hg, while ATP, ADP, and AMP remained stable until paO2 dropped below 25 mm Hg, and these metabolic shifts were amplified by modest blood‑pressure reductions.

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.