Intracellular alkalosis during hypoxia in newborn mouse brain in the presence of systemic acidosis: a phosphorus magnetic resonance spectroscopic study

We investigated the in vivo changes in cerebral energy metabolism and pHi in newborn mice noninvasively during 8 h of hypoxia with FiO2 = 5%, using phosphorus magnetic resonance spectroscopy continuously. The intracellular brain pH (pHi) increased from 7.20 ± 0.03 to 7.36 ± 0.03 (P< 0.05) at 1 h of hypoxia and then decreased gradually. On the other hand, the mixed arterial and venous blood pH decreased gradually during hypoxia, reaching a minimum value of 7.16 ± 0.01 at the end of the hypoxia. There was no significant difference in PCO2 between control (47.4 ± 0.8 mm Hg) and 1-h hypoxic (49.0 ± 1.1 mm Hg) mice. The blood glucose concentration was significantly increased at 1 h of hypoxia. These results indicate that the alkaline shift in pHi during hypoxia was caused neither by systemic alkalosis due to hypocapnia nor hypoglycemia.