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At least 505 records · Page 28Linked to original sources
PubMed1998

Hypoglycemia-associated hyperammonemia caused by impaired expression of ornithine cycle enzyme genes in C/EBPalpha knockout mice.

Ammonia produced by amino acid metabolism is detoxified through conversion into urea by the ornithine cycle in the liver, whereas carbon skeletons of amino acids are converted to glucose by gluconeogenic enzymes. Promoter and enhancer sequences of several genes for ornithine cycle enzymes interact with members of the CCAAT/enhancer-binding protein (C/EBP) transcription factor family. Disruption of the C/EBPalpha gene in mice causes hypoglycemia associated with the impaired expression of gluconeogenic enzymes. Here we examined the expression of ornithine cycle enzyme genes in the livers of C/EBPalpha-deficient mice. mRNA levels for the first, third, fourth, and fifth enzymes of five enzymes in the cycle were decreased in C/EBPalpha-deficient mice. Protein levels for the first, second, fourth, and fifth enzymes were also decreased. In situ hybridization analysis revealed that the enzyme mRNAs were distributed normally in the periportal region but were disordered in C/EBPalpha-deficient mice with relatively higher mRNA levels in the midlobular region. Blood ammonia concentrations in the mutant mice were severalfold higher than in wild-type mice. Thus, C/EBPalpha is crucial for ammonia detoxification by ornithine cycle enzymes and for coordination of gluconeogenesis and urea synthesis.

Ammonia↗
PubMed1987

An arginine-deficient diet in humans does not evoke hyperammonemia or orotic aciduria.

The essentiality of dietary arginine was examined in adult humans with three biochemical indices: plasma levels of ammonium and amino acids and urinary orotic acid excretion. Three male and two female subjects participated in the 10-d study. Subjects consumed an L-amino acid diet containing 0.74 g protein equivalent/kg body weight on d 1-5; these amino acid concentrations were doubled on d 6-10. The diet was devoid of arginine on d 3-8. Daily urine was collected and blood samples were drawn on 6 of the 10 d at 0, 0.5, 1, 2, 3 and 4 h after the breakfast meal. When arginine was removed from the diet, urinary orotic acid did not increase, in contrast to what has been reported in most other animal species tested. Plasma ammonium concentrations remained within normal limits throughout the study. A small postprandial decrease in plasma arginine concentration was observed when the arginine-deficient diet was consumed; this decline disappeared when the diet was resupplied with arginine. The results of this study suggest that over the short term the adult human's capacity for de novo arginine synthesis when fed a dietary deficiency of arginine is sufficient for the maintenance of normal cellular metabolism.

Adult↗
PubMed1985

Effect of associated antiepileptic treatment on valproate-induced hyperammonemia.

It has recently been shown that acute changes of venous blood ammonia (NH3) may predict short-term adverse effects of valproic acid (VPA). In the present study, the time course of NH3 concentration after a single oral dose of VPA (800 mg) was monitored in 68 epileptic patients. Patients were classified into four groups: previously untreated patients (group A, n = 21), patients under treatment with either phenobarbital (group B, n = 14) or phenytoin (group C, n = 13) or both (group D, n = 20). In each patient, venous blood for the NH3 assay was taken before the VPA dose (predose level) and at 1, 2, 3, and 4 h after the dose (postdose levels). While in patients receiving only VPA the postdose NH3 concentrations did not differ from the predose level, in each of groups B, C, and D the postdose concentrations appeared to be significantly higher than the predose concentration. The greatest increase was observed in group D. In the light of the data reported in the literature, those patients whose NH3 concentration after the VPA dose exceeds 100 micrograms/dl should be considered at higher risk for short-term, VPA-induced adverse effects during long-term therapy. Thus, our data suggest that caution should be exercised in adding VPA to anticonvulsant treatments including phenobarbital or phenytoin or both.

Adolescent↗
PubMed1985

Effect of hyperammonemia and methionine sulfoximine on the kinetic parameters of blood-brain transport of leucine and phenylalanine.

The activity of the blood-brain neutral amino acid transport system is increased in rats infused with ammonium salts or rendered hyperammonemic by a portacaval anastomosis. This effect may be due to a direct action of ammonia or to some metabolic consequence of high ammonia levels, such as increased brain glutamine synthesis. To test these possibilities we evaluated the kinetic parameters of blood-brain transport of leucine and phenylalanine in control rats, in rats after continuous 24 h infusion of ammonium salts (NH4+ = 2.5 mmol X kg-1 X h-1), and in rats treated with methionine sulfoximine, an inhibitor of glutamine synthetase, before infusion of ammonium salts. In ammonia-infused rats without methionine sulfoximine treatment, the KD and Vmax of phenylalanine transport were increased, respectively, about 170% and 80% compared to controls, whereas the Km and Vmax of leucine transport were increased, respectively, about 100% and 200%. Electron microscopy demonstrated marked swelling of astrocytic processes around brain capillaries of ammonia-infused rats; however, capillary permeability to horseradish peroxidase apparently was not increased by ammonia infusion. Administration of methionine sulfoximine before ammonia infusion inhibited glutamine synthesis and prevented the changes in transport of leucine and phenylalanine, but apparently did not reverse the perivascular swelling. These results suggest that the ammonia-induced increase in the activity of transport of large neutral amino acids across the blood-brain barrier requires glutamine synthesis in brain, and is not a direct effect of ammonia.

Ammonia↗
PubMed1987

Endurance training reduces the magnitude of exercise-induced hyperammonemia in humans.

The purpose of this study was to determine the influence of endurance-type exercise training on alterations of the ammonia content of blood in exercising humans. Seven females and four males trained 6 days/wk for 7 wk alternating days of continuous cycling (40 min) and interval running (five 5-min bouts). The NH3 content of blood was determined before and during cycle ergometer (CE) exercise (4 min) at power outputs (PO) of 119, 172, and 241 W pretraining and of 163, 230, and 271 W posttraining. These PO for each occasion represent relative work loads of approximately 65, 90, and 115% of peak CE maximum O2 uptake (PCE VO2), respectively. Training increased (P less than 0.05) PCE VO2 approximately 32% (2.72 +/- 0.25 to 3.56 +/- 0.29 l/min or 38.5 +/- 1.9 to 51.2 +/- 2.3 ml X kg-1 X min-1). Both pre- and posttraining the NH3 content of blood increased (P less than 0.05) with increasing intensity of exercise. Training did not influence the measure of these responses during exercise at the same relative intensity. During exercise at the same absolute PO, approximately 168 or 235 W, however, increases in blood NH3 were less (P less than 0.05) after training. The results indicate that the magnitude of increase in blood NH3 during exercise is determined by the energy requirement of the absolute work load, relative to an individual's aerobic power.

Adult↗
PubMed1984

Hyperammonemia and valproate-induced alterations of the state of consciousness. A report of 8 cases.

Sodium valproate was administered to 38 patients, admitted to our unit in the last 18 months, and chosen because they had: (1) poor control of their seizures; (2) therapeutic concentrations in their plasma of at least two major antiepileptic drugs. In 8 of them, a therapeutic dosage of VPA caused modifications of the state of consciousness ranging from coma to drowsiness and stupor. These patients also showed gastrointestinal disturbances, asterixis, ataxia, tremor and a worsening of EEG abnormalities. The side effects of the drug were constantly associated with increased concentration of blood ammonia. Better penetration of ammonia into the CNS of patients undergoing frequent seizures and possibly having imperfectly functioning biological barriers, could explain our observations. In view of the unusually high percentage of patients suffering from serious VPA side effects, it is probably advisable to carefully monitor ammonemia in the first few days of VPA therapy in every patient treated with multiple anticonvulsants.

Adult↗