Decrease in brain glucose in anoxia in spite of elevated plasma glucose levels

Abstract

Anoxia was produced in 34 mice less than 12 hr of age by exposure to N2 at 37° (PO2, less than 5 mm Hg). Although brain glucose levels fell from the normal value of 0.60 ± 0.14 mmol/kg to 0.22 ± 0.04 mmol/kg after 6 min of anoxia, in the livers of the same animals there was a fourfold increase in glucose concentration from 2.61 ± 0.28 mmol/kg to 10.45 ± 0.45. In 22 other animals of the same age plasma glucose levels increased from 3.04 ± 0.03 mM to 5.56 ± 1.09 mM during this interval of anoxia. Further studies concerned the mechanism of this unexpected independence of blood and brain glucose values during anoxia. During the 6 min of anoxia brain lactate increased 7.49 mmol/kg. This increase is more than twice that accounted for by the total decrease in brain glucose and glycogen. One explanation for this finding is an increased uptake of glucose from the blood by the brain. If so, the rate of glucose influx is almost 5 times that reported for newborn mice with an adequate O2 supply. Another possibility is a transport or diffusion of lactate from the blood to the brain. However, a study of the effect of lactate administration on levels of lactate in plasma and brain of 17 newborn mice suggests that permeation of the blood-brain barrier to lactate is a less likely explanation. Inasmuch as glycolysis increases 10-fold in ischemic brain of the neonatal mouse, it appears that brain glucose decreases in these animals because the demand for glucose during anoxia exceeds the supply. In experimental animals levels of glucose in plasma are not always an accurate reflection of glucose levels in the brain. This is the case in anesthesia, after chronic administration of hydrocortisone, and in acute salicylate poisoning. The present study is another example of this paradox. During 6 min of anoxia, brain glucose in newborn mice fell 72% despite a doubling of the concentration of glucose in plasma. Because it is generally accepted that a decrease in the brain glucose reserve is potentially serious, it is important to recognize that a normal or even increased blood sugar need not signify adequate cerebral glucose levels. Furthermore, there is some evidence to suggest that, under these circumstances, the administration of glucose may be life saving. © 1973 International Pediatric Research Foundation, Inc.