Hospital Practice

ISSN: 2154-8331 (Print) 2377-1003 (Online) Journal homepage: https://www.tandfonline.com/loi/ihop20

Blood Glucose: How Reliable an Indicator of Brain Glucose? Jean Holowach Thurston To cite this article: Jean Holowach Thurston (1976) Blood Glucose: How Reliable an Indicator of Brain Glucose?, Hospital Practice, 11:9, 123-130, DOI: 10.1080/21548331.1976.11707002 To link to this article: https://doi.org/10.1080/21548331.1976.11707002

Published online: 06 Jul 2016.

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Blood Glucose: How Reliable an Indicator of Brain Glucose? I EA N Ho Low A c H THu R s ToN Washington University, St. Louis

It is usually assumed that the concentration of glucose in the brain reflects that in the blood, so that measuring the latter provides an accurate index of the former. However, in two experimental situations analogous to anoxia an9 salicylate poisoning, brain glucose Was found to be dangerously low in the presence of normal or even elevated blood glucose levels, and in these experiments administering glucose prolonged survival.

Since the brain cannot effectively store the energy it needs in order to function, it is believed to rely almost exclusively on circulating glucose as its energy source. Accordingly, blood glucose levels are usually regarded as a reliable index of the brain's status. For example, findings of normal blood glucose levels are often used to exclude hypoglycemia as a cause of abnormal neurologic signs and symptoms. ConVersely, when blood glucose levels are acutely and significantly reduced, the assumption is that there exists a proportionate reduction in brain glucose, too, and that Prompt glucose administration will help avoid brain damage and maintain normal brain function. All of this is well known. What may not be so well known is that in experimental equivalents of two very common clinical situations - anoxia and salicylate poisoning- blood and brain glucose levels are independent of each other, implying that clinical assumptions about bram glucose that are based on blood glucose findings can be seriously Wrong. In both experimental situations there is, in fact, a serious reduction in brain glucose levels despite normal or even elevated blood glucose. More important, in both situations the evidence suggests that the administration of glu~ose can be Jifesaving. In the discussion that follows, studIes that support these conclusions and possible mechanisms of action will be reviewed. We first became aware of the lack of proportionality between blood and brain glucose levels during a study of the effects of hydrocortisone administration in the brains of Young mice. For reasons that are still largely unknown, ACTH and the adrenocortical steroids have long been recognized to benefit the central nervous system in a variety of diseases. One example is the use of ACfH and corticosteroids in infantile myoclonic seizures. Intractable to ~ost forms of therapy, this disease entity, characterized by Isolated jackknife jerks of the body, carries a gloo~y prog-

nosis, with almost all affected infants ultimately deteriorating into mental retardation. ACTH or corticosteroid treatment of the disease does not alter the long-term prognosis, but there have been many instances - about a third of all patients so treated and reported in the literature -of shortterm favorable response, as measured by a decreased frequency of seizures and improvement in EEG findings. The explanation for these favorable responses is unknown, but clinical experience like this has a number of experimental analogues that suggest some form of enhanced carbo.hydrate metabolism in the brain. As early as the 195os, for example, F. Vaccari and M. Rossanda, University of Milan, and P.S. Timiras, D.M. Woodbury, and D. H. Baker, University of Utah, showed that adrenalectomized and intact animals responded to cortisone administration with increases in total brain carbohydrates or glycogen or both. It was not until the 1

Blood glucose: how reliable an indicator of brain glucose?

It is usually assumed that the concentration of glucose in the brain reflects that in the blood, so that measuring the latter provides an accurate ind...
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