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Metabolic Brain Disease
Published in: Metabolic Brain Disease 1/2009

01-03-2009 | Original Paper

Backflux of ammonia from brain to blood in human subjects with and without hepatic encephalopathy

Authors: Michael Sørensen, Ole Lajord Munk, Susanne Keiding

Published in: Metabolic Brain Disease | Issue 1/2009

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Abstract

In patients with hepatic encephalopathy (HE) the blood concentration of ammonia is usually highly elevated. Ammonia readily enters brain cells from the blood, and toxic effects of ammonia on brain metabolism and neurotransmission are believed to play a key role in the pathogenesis of HE. It has, however, been a matter of great controversy whether backflux of unmetabolized ammonia (NH3 + NH4 +) from brain cells to the blood occurs in man. In the present analysis of data from a dynamic PET study of brain 13N–ammonia metabolism in healthy subjects and cirrhotic patients with and without HE, we provide the first unambiguous evidence for backflux of ammonia from brain cells to the blood in man. The high temporal and spatial resolution of modern PET technology was employed to distinguish between unidirectional blood-brain transport of ammonia and subsequent metabolism of the ammonia in the brain. In all 16 subjects, clearance of the unidirectional transport of 13N–ammonia from the blood to brain cells (K1) was higher than the metabolic clearance of 13N–ammonia from the blood (Kmet=K1 k3/(k2+k3). This can only be explained by backflux (k2) of ammonia from brain cells to the blood. In conclusion, backflux of ammonia from the brain to the blood does indeed occur in both healthy subjects and cirrhotic patients with and without hepatic encephalopathy.
Footnotes
1
In this paper, the term ammonia refers to the sum of the unionized NH3 and the ionized NH4 +.
 
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Metadata
Title
Backflux of ammonia from brain to blood in human subjects with and without hepatic encephalopathy
Authors
Michael Sørensen
Ole Lajord Munk
Susanne Keiding
Publication date
01-03-2009
Publisher
Springer US
Published in
Metabolic Brain Disease / Issue 1/2009
Print ISSN: 0885-7490
Electronic ISSN: 1573-7365
DOI
https://doi.org/10.1007/s11011-008-9126-1

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