Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.3.4.6 (urease)
 7,490 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Children with inborn errors of urea synthesis who survive neonatal hyperammonemic coma commonly exhibit cognitive deficits and neurologic abnormalities. Yet, there is evidence that ammonia is not the only neurotoxin. Hyperammonemia appears to induce a number of neurochemical alterations. In rodent models of hyperammonemia, uptake of L-tryptophan into brain is increased. It has been reported that in an experimental rat model of hepatic encephalopathy, in the ammonium acetate-injected rat, and in patients with hepatic failure and inborn errors of ammonia metabolism, quinolinate, a tryptophan metabolite, is increased. Elevations in quinolinate are of particular concern, as quinolinate could excessively activate the N-methyl-D-aspartate subclass of excitatory amino acid receptors, thereby causing selective neuronal necrosis. We sought to identify an animal model that would replicate the increases in quinolinate that have been associated with hyperammonemia in humans. Levels of quinolinate were measured in hyperammonemic urease-infused rats and ammonium acetate-injected rats. In the urease-infused rat, brain tryptophan was doubled, and serotonin and its metabolite 5-hydroxyindoleacetic acid were significantly increased. Yet, despite the increase in tryptophan and evidence for increased metabolism of tryptophan to serotonin, there were no observed increases of quinolinate in brain, cerebrospinal fluid, or plasma. In the ammonium acetate-injected rat, significant increases of 5-hydroxyindoleacetic acid in cerebral cortex were also observed, but quinolinate did not change in cerebrospinal fluid or cerebral cortex. In summary, we were unable to demonstrate an increase of quinolinate in brain or cerebrospinal fluid in these rat models of hyperammonemia.
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PMID:Quinolinate in brain and cerebrospinal fluid in rat models of congenital hyperammonemia. 127 10

1. Portacaval shunting in rats results in several metabolic alterations similar to those seen in patients with hepatic encephalopathy. The characteristic changes include: (a) diminution of cerebral function; (b) raised plasma ammonia and brain glutamine levels; (c) increased neutral amino acid transport across the blood-brain barrier; (d) altered brain and plasma amino acid levels; and (e) changes in brain neurotransmitter content. The aetiology of these abnormalities remains unknown. 2. To study the degree to which ammonia could be responsible, rats were made hyperammonaemic by administering 40 units of urease/kg body weight every 12 h and killing the rats 48 h after the first injection. 3. The changes observed in the urease-treated rats were: (a) whole-brain glucose use was significantly depressed, whereas the levels of high-energy phosphates remained unchanged; (b) the permeability of the blood-brain to barrier to two large neutral amino acids, tryptophan and leucine, was increased; (c) blood-brain barrier integrity was maintained, as indicated by the unchanged permeability-to-surface-area product for acetate; (d) plasma and brain amino acid concentrations were altered; and (e) dopamine, 5-hydroxytryptamine (serotonin) and noradrenaline levels in brain were unchanged, but 5-hydroxyindoleacetic acid (5-HIAA), a metabolite of 5-hydroxytryptamine, was elevated. 4. The depressed brain glucose use, increased tryptophan permeability-to-surface-area product, elevated brain tryptophan content and rise in the level of cerebral 5-HIAA were closely correlated with the observed rise in brain glutamine content. 5. These results suggest that many of the metabolic alterations seen in rats with portacaval shunts could be due to elevated ammonia levels. Furthermore, the synthesis or accumulation of glutamine may be closely linked to cerebral dysfunction in hyperammonaemia.
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PMID:Hyperammonaemia causes many of the changes found after portacaval shunting. 170 23

Rats implanted with subcutaneous or intraperitoneal osmotic minipumps infusing 0.8-1.25 IU urease/kg/h develop sustained hyperammonemia (range 137-497 microM, controls 88 +/- 51 microM +/- SD) for 5-7 days. Glutamine levels are also significantly elevated in plasma (677 +/- 166 versus 428 +/- 122 microM) and cerebral cortex (13.2 +/- 9.8 versus 4.7 +/- 2.8 nmol/mg tissue). Neurobehavioral abnormalities include decreased food intake and increased stereotypic activity. Increased serotonin turnover was suggested by elevated levels of tryptophan and 5-hydroxyindoleacetic acid in cerebral cortex, brain stem, and cerebellum of urease-infused compared to sham-operated animals. There were no changes in norepinephrine or gamma aminobutyric acid, and there was no correlation between the degree of hyperammonemia or glutaminemia and brain levels of tryptophan or biogenic amines. Animals receiving a tryptophan-deficient diet had significantly lower levels of tryptophan and 5-hydroxyindoleacetic acid in brain regions compared to animals receiving a normal tryptophan intake, under both control and hyperammonemic conditions. Despite the prevention of increased serotonin flux in hyperammonemic animals receiving a tryptophan-deficient diet, food intake and weight declined and there was increased stereotypic behavior.
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PMID:Behavioral and neurotransmitter changes in the urease-infused rat: a model of congenital hyperammonemia. 379 24