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Hyperammonaemia depresses glucose consumption throughout the brain.
J Jessy1, M R DeJoseph, R A Hawkins
1Department of Physiology and Biophysics, Chicago Medical School, North Chicago, IL 60064.
The Biochemical Journal
|August 1, 1991
Summary
Hyperammonaemia, or high ammonia levels, significantly reduces cerebral metabolic rate of glucose (CMRGlc) across the entire brain in rats. This widespread decrease in brain function is linked to elevated brain glutamine, not just plasma ammonia levels.
Area of Science:
- Neuroscience
- Metabolic Research
- Toxicology
Background:
- Hyperammonaemia is implicated in metabolic alterations observed in portacaval-shunted rats, a model for hepatic encephalopathy.
- These alterations include a depressed cerebral metabolic rate of glucose (CMRGlc), indicating reduced brain function.
Purpose of the Study:
- To investigate if ammonia-induced CMRGlc depression is localized to specific brain regions or affects the entire brain.
- To compare the pattern of CMRGlc depression in hyperammonaemic rats to that observed in portacaval-shunted rats.
Main Methods:
- Rats were induced into a hyperammonaemic state using urease injections.
- Cerebral metabolic rate of glucose (CMRGlc) was measured using quantitative autoradiography with [6-14C]glucose.
- Plasma ammonia and brain glutamine levels were quantified.
Main Results:
- Hyperammonaemic rats exhibited significantly elevated plasma ammonia (610 nmol/ml vs. 70 nmol/ml) and brain glutamine levels.
- A 19% average decrease in CMRGlc was observed throughout the brain in hyperammonaemic rats.
- CMRGlc depression showed a stronger inverse correlation with brain glutamine content than with plasma ammonia levels.
Conclusions:
- Ammonia-induced CMRGlc reduction is a global phenomenon across the brain, mirroring patterns seen in portacaval-shunted rats.
- These findings support the hypothesis that hyperammonaemia is a primary cause of cerebral dysfunction in hepatic encephalopathy models.
- The stronger correlation between CMRGlc and brain glutamine suggests ammonia metabolism is a critical factor in the observed neuropathology.