Improved method for the estimation of plasma ammonia by ion exchange

Some pitfalls and considerations of plasma ammonia estimation

Several approaches to the estimation of plasma ammonia have been tested and compared: indophenol, Nessler, iodometric techniques were studied as well as enzymatic spectrophotometric and radiometric methods. Their lower safe limits of estimation were determined and it was found that most of them were not viable for plasma estimations because of its very low ammonia levels. The need for a concentration/purification step and the lack of repetability in this phase at very low concentrations, made very unreliable the utilization of all methods studied except for the enzymatic radiometric method tested that was barely usable for plasma ammonia estimations.

Hyperammonemia in neonates receiving intravenous nutrition

Inadequate arginine intake has been suggested as an etiology for hyperammonemia in neonates on parenteral nutrition. We randomized 26 nonasphyxiated neonates to receive amino acid solutions containing either 3.6 or 10.4% of total nitrogen as arginine when intravenous nutrition (IVN) therapy was initiated. Neonates in both amino acid solution study groups were observed to have significantly elevated blood ammonia (BA) concentrations during IVN (p less than 0.01) as compared to pre-IVN levels. Blood ammonia concentrations tended to be higher in infants receiving the 3.6% arginine amino acid solution. Septic infants were at particular risk for hyperammonemia as compared to nonseptic patients (p less than 0.025). Other clinical parameters including birth weight, gestational age, oxygen requirements, enteral nutritional intake, congenital anomalies, and heart disease did not appear to be related to BA concentration.

Plasma ammonia levels in newborn infants admitted to an intensive care baby unit

A fatal case associated with severe hyperammonaemia is described in which no urea cycle enzyme deficiency could be found. This prompted further investigation of blood ammonia levels in neonates admitted to the premature baby unit at Hammersmith Hospital. 102 specimens were taken from 42 babies within the first 3 weeks of life; the babies had a variety of clinical conditions. The mean ammonia level was 94.5 mumol/l (132.3 micrograms/100 ml) (range 32-255 mumol/l) (44.8-357 micrograms/ml), SD +/- 41.0). These results, although higher than the range for older babies in hospital, were not as high as in the baby with severe hyperammonaemia. Serial levels in 10 babies suggested that the range of blood ammonia levels was greatest in the first 2 weeks of life and narrowed considerably after this period. Great care is needed in collecting blood samples and measuring them if accuate results are to be obtained.

Continuous-flow analysis of ammonia in perchloric acid supernate of blood or plasma using an ammonia-selective electrode

A simple automated method for the estimation of ammonia in perchloric acid supernate of blood or plasma using an ion-selective electrode (Orion Ammonia-selective electrode, Model 95-10) is described. The reliability of the proposed method has been checked against an ion-exchange resin procedure, which has been chosen as a standard procedure. Regression equation and correlation coefficient for the proposed method are y = 0.7 X + 10 and 0.945, respectively, as compared with the chosen standard method. Within-run and between-run precision are 2.1% and 3.5% respectively. The average percent recovery is 97.5% and a tentative range is 13-73 microgram/dl (9-52 micronmol/l) ammonia nitrogen.

Thiamine dependency in a patient with congenital lacticacidaemia due to pyruvate dehydrogenase deficiency

A patient with congenital lactic acidosis, muscular hypotonia and severe ataxia is reported. The aetiology of his disease was found to be a deficiency of pyruvate dehydrogenase (E.C. 4.1.1.1.). Thiamine treatment (1.8 g/day) was successful in correcting biochemical and clinical symptoms. The mechanism of its action is probably based on activation of pyruvate dehydrogenase through interference in the physiologic regulation.

Treatment of carbamyl phosphate synthetase deficiency with keto analogues of essential amino acids

Congenital carbamyl phosphate synthetase deficiency was diagnosed by liver biopsy in a 13-year-old girl, alpha-Keto analogues of essential amino acids have been shown to spare nitrogen by reducing urea formation; hence, they were given to this patient in the hope of reducing hyperammonemia and improving protein tolerance. After intravenous infusion of the keto analogues of valine, leucine, isoleucine, methionine and phenylalanine, the corresponding plasma amino acids, including alloisoleucine and tyrosine, rose sharply. Twenty-four hours later, fasting plasma ammonia had fallen from the preinfusion value of 0.050 to 0.028 mM. Protein intake was kept at 0.5 g per kilogram for two weeks. Addition of keto acids by mouth reduced plasma ammonia and alanine to normal or near normal levels. Seizures and episodes of vomiting and lethargy decreased in frequency. Urinary nitrogen decreased, suggesting that nitrogen balance improved. These data indicate that keto acids may be useful in the treatment of congenital hyperammonemia.

Ammonia production by intestinal bacteria

Bacterial growth and the production of ammonia from urea and by deamination of peptone has been examined at various pHs in both conventional static bacterial cultures and in a continuous cultivation system. Growth occurred on primary testing of 93 out of 100 strains of aerobic Gram-negative bacteria at pH 5, and 48 out of 50 strains of Esch. coli at pH 4.6. Hydrolysis of urea by Proteus mirabilis decreased steadily from pH 7.2 to pH 5.3; below pH 5.3 little hydrolysis occurred. Ammonia production from peptones by Esch. coli decreased from pH 7.2 to pH 4.6. Considerable variation was noted in the ability of different strains to produce ammonia. Experiments with cultures containing both Esch. coli and Pr. mirabilis showed that more ammonia was produced at low pH than was produced by cultures of single organisms. At low pH reduction in the count of organisms was not found to be an essential prerequisite for reduction of ammonia formation.