Hyperthermia, lactic acid infusion, and the composition of arterial blood and cerebrospinal fluid

Abstract

The effect of an approximately 2 C rise in body temperature on arterial and cerebrospinal fluid (CSF) lactate concentration, pH, Pco2, and [HCO3–] was studied in eight artificially ventilated dogs maintained at constant end-tidal Pco2. The combined effect of hyperthermia and intravenous lactic acid infusion on CSF lactate concentration was also studied in three additional dogs. In normothermia the lactate concentration, Pco2, and [HCO3–] in the CSF were significantly higher than in arterial blood, whereas CSF pH was significantly lower than arterial pH. Rise in body temperature at constant end-tidal (and arterial) Pco2 resulted in no significant change in lactate concentration of blood or CSF, a parallel fall in arterial and CSF pH, a decrease in both arterial and CSF [HCO3–], and a rise in CSF PCO2. An intravenous lactic acid infusion had no measurable effect on CSF lactate concentration. A general entrance of lactate ion into the CSF from blood or brain does not appear to play a role in respiratory control during hyperthermia. The possibility remains that lactate enters CSF during exercise but from the brain rather than from the circulating blood. Limitations of the conventional pH scale preclude assessment of changes in hydrogen ion activity during hyperthermia.

Lactate Uptake and Metabolism by Brain During Hyperlactatemia and Hypoglycemia

“…Both barriers are sufficiently impermeable that the CSF La rose too slowly to be observed before one hour, as had been noted by both Alexander et al 4 and Leusen et al e Klein and Olsen 5 found no elevation of brain La 40 minutes after loading blood with La. This does not imply low permeability unless it is established that entering La is not metabolized.…”

“…This, however, does not establish either penetration into brain cells or net uptake and metabolism. Several reports 4 "* cast doubt on the quantitative transport of La into brain by showing that neither brain nor CSF La levels were increased 15 to 40 minutes after intravenous injection of large amounts of sodium lactate. Furthermore, Crone and S^rensen 7 were unable to detect brain uptake of labeled La during passage of blood through the brain.…”

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“…It is unlikely that the increase in CSF lactate in ALF is the result of increased blood levels of the metabolite since Alexander et al (1962) were unable to observe any significant increase in CSF lactate following its intravenous administration. Furthermore, Posner and Plum (1961) reported an independence of blood and CSF lactate in a range of neurological disorders.…”

Increase brain lactate in hepatic encephalopathy: Cause or consequence?

“…It has previously been demonstrated lactate cannot easily cross the bloodbrain barrier (Hertz andDienel, 2002 andAuer, 1986), infusing lactate intravenously does not increase CSF lactate (Alexander et al, 1962) and levels of blood and CSF lactate are regulated independently (Posner and Plum, 1967). However, others have documented that the blood-brain barrier is permeable to lactate (Dalsgaard et al, 2004, Smith et al, 2003and Oldendorf, 1973 and the lactate transporter MCT1 is expressed on endothelial cells (Gerhart et al, 1997).…”