Effect of high vs. low arterial blood oxygen content on cerebral energy metabolite levels during hypoxia with normothermia and hypothermia in the rat.
The effects of different levels of arterial blood oxygen content (CaO2) on brain tissue adenosine triphosphate (ATP), phosphocreatine (PCr), lactate, and reduced nicotinamide adenine dinucleotide (NADH) were studied during cerebral hypoxia in normothermic and hypothermic male Wistar rats with unilateral carotid ligation. Animals were exposed to hypoxia (PaO2 19--26 torr) for 25 min, and brain tissue metabolite values measured microfluorometrically were compared with those of normothermic normoxic controls. CaO2 was 4.0 +/- 0.2 ml/dl (mean +/- SEM) at PaO2 26 torr in normothermic animals. CaO2 was increased to 8.2 +/- 0.3 ml/dl at PaO2 26 torr by means of bicarbonate infusion producing a leftward shift of the oxyhemoglobin-dissociation curve in one normothermic hypoxic group. In all normothermic hypoxic groups ATP and PCr decreased and lactate and NADH increased significantly compared with control values. There was no significant difference in brain tissue metabolite values among these groups despite an increase in CaO2 by twofold in one group. Hypothermia (32 C) resulted in CaO2 8.4 +/- 0.2 ml/dl at PaO2 26 torr. This was decreased to 4.0 +/- 0.2 ml/dl by decreasing PaO2 to 19 torr in another group at the same temperature. ATP and PCr were well preserved in both groups despite the difference in CaO2s. Although the lactate and NADH levels were increased in the hypothermic group with CaO2 4.0 +/- 0.2 ml/dl, they were significantly lower than those values in normothermic hypoxic groups. These results indicate that the increase in CaO2 produced by hypothermia is not a major determinant in hypothermic protection during cerebral hypoxia.
D000255:Adenosine Triphosphate; D000818:Animals; D001794:Blood Pressure; D001921:Brain / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D004734:Energy Metabolism; D006863:Hydrogen-Ion Concentration; D007035:Hypothermia / Q000378:metabolism; D000860:Hypoxia / Q000378:metabolism*; D007773:Lactates; D008297:Male; D009243:NAD; D010100:Oxygen / Q000097:blood*; D010725:Phosphocreatine; D051381:Rats
D007773:Lactates; D010725:Phosphocreatine; D009243:NAD; D002245:Carbon Dioxide; D000255:Adenosine Triphosphate; D010100:Oxygen