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The effects of hyperammonemia on brain function have been studied in three different experimental models in the rat: acute liver ischemia, urease-treated animals and methionine sulfoximine-treated animals. To quantify the development of encephalopathy, clinical grading and electroencephalographic spectral analysis were used as indicators. In all three experimental models brain ammonia concentrations increased remarkably associated with comparable increases in severity of encephalopathy. Furthermore, in vivo 1H-nuclear magnetic resonance spectroscopy of a localized cerebral cortex region showed a decrease in glutamate concentration in each of the aforementioned experimental models. This decreased cerebral cortex glutamate concentration was confirmed by biochemical analysis of cerebral cortex tissue post mortem. Furthermore, an increase in cerebral cortex glutamine and lactate concentration was observed in urease-treated rats and acute liver ischemia rats. As expected, no increase in cerebral cortex glutamine was observed in methionine sulfoximine-treated rats. These data support the hypothesis that ammonia is of key importance in the pathogenesis of acute hepatic encephalopathy. Decreased availability of cerebral cortex glutamate for neurotransmission might be a contributing factor to the pathogenesis of hyperammonemic encephalopathy. A surprising new finding revealed by 1H-nuclear magnetic resonance spectroscopy was a decrease of cerebral cortex phosphocholine compounds in all three experimental models. The significance of this finding, however, remains speculative.

ObjectiveThe preservation of nutritional status and growth is an important aim in critically ill infants, but difficult to achieve due to the metabolic stress response and inadequate nutritional intake, leading to negative protein balance. This study investigated whether increasing protein and energy intakes can promote anabolism. The primary outcome was whole body protein balance, and the secondary outcome was first pass splanchnic phenylalanine extraction (SPEPhe).DesignThis was a double-blind randomised controlled trial. Infants (n=18) admitted to the paediatric intensive care unit with respiratory failure due to viral bronchiolitis were randomised to continuous enteral feeding with protein and energy enriched formula (PE-formula) (n=8; 3.1±0.3 g protein/kg/24 h, 119±25 kcal/kg/24 h) or standard formula (S-formula) (n=10; 1.7±0.2 g protein/kg/24 h, 84±15 kcal/kg/24 h; equivalent to recommended intakes for healthy infants <6 months). A combined intravenous-enteral phenylalanine stable isotope protocol was used on day 5 after admission to determine whole body protein metabolism and SPEPhe.ResultsProtein balance was significantly higher with PE-formula than with S-formula (PE-formula: 0.73±0.5 vs S-formula: 0.02±0.6 g/kg/24 h) resulting from significantly increased protein synthesis (PE-formula: 9.6±4.4, S-formula: 5.2±2.3 g/kg/24 h), despite significantly increased protein breakdown (PE-formula: 8.9±4.3, S-formula: 5.2±2.6 g/kg/24 h). SPEPhe was not statistically different between the two groups (PE-formula: 39.8±18.3%, S-formula: 52.4±13.6%).ConclusionsIncreasing protein and energy intakes promotes protein anabolism in critically ill infants in the first days after admission. Since this is an important target of nutritional support, increased protein and energy intakes should be preferred above standard intakes in these infants.Dutch Trial Register number: NTR 515.