The effects of hypercapnia and hypocapnia upon the cerebrospinal fluid lactate and pyruvate concentrations and upon the lactate, pyruvate, ATP, ADP, phosphocreatine and creatine concentrations of cat brain tissue.

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AbstractThe lactate and pyruvate concentrations in cisternal cerebrospinal fluid (CSF), and the lactate, pyruvate, ATP, ADP, phosphocreatine, and creatine concentrations in brain tissue were measured in cats during hyper‐ and hypocapnia. (PaCO2 10–100 mm Hg). Both the CSF and the tissue concentrations of lactate and pyruvate varied inversely with the arterial CO2 tension. In hypercapnia the tissue lactate/pyruvate ratio increased in accordance with a theoretical curve, calculated for a pH dependent equilibrium between the lactate/pyruvate and the NADH/NAD+ systems. In hypocapnia, however, there was no corresponding decrease in the CSF and tissue lactate/pyruvate ratios but a progressive increase at arterial CO2 tensions below 25–20 mm Hg. The inter‐pretation of these results, which indicate the presence of tissue hypoxia at such low CO2 tensions, were complicated by the presence of unchanged tissue levels of ATP and phosphocreatine. The results also showed that in hypocapnia, pyruvate, but not lactate, was distributed between the extra‐ and intracellular spaces according to the pH gradient, while in hypercapnia, lactate, but not pyruvate, had this distribution. The similarity of the changes in CSF and tissue lactate and pyruvate concentrations lend further support to the assumption that the CSF lactate/pyruvate system reflects cellular redox states.