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Biomedical subjects

J P Colombo

Publications and source records attributed to J P Colombo.

At least 91 records · Page 5Linked to original sources
PubMed1983

Increased tryptophan uptake into the brain in hyperammonemia.

Hyperammonemia was provoked in rats by urease injection over three days. Tryptophan transport into the forebrain measured by the bolus injection technique was increased in hyperammonemic rats in comparison with pairfed controls. The concentration of the large neutral aminoacids, of tryptophan and of 5-hydroxyindole acetic acid were increased in the forebrain and brainstem. Probenecid administration led to a significantly higher accumulation of 5-hydroxyindole acetic acid in the forebrain of hyperammonemic rats. Since liver function was not impaired the data indicate that hyperammonemia in absence of hepatic insufficiency alters the carrier function for large neutral aminoacids at the blood brain barrier.

Amino Acids↗
PubMed1983

Isoenzyme pattern and immunological properties of arginase in normal and hyperargininemia fibroblasts.

Arginase deficiency is an inborn error of the last step in the urea cycle and leads to profound hyperargininemia. The enzyme deficiency has been demonstrated in the liver and red blood cells. In cultured patient fibroblasts, the activity is normal. Arginase exists in multiple molecular forms only one of which is missing in hyperargininemic patients. In fibroblasts, three arginase isoenzymes can be demonstrated by DEAE-cellulose column chromatography, two by electrophoresis and by immunoprecipitation methods. From the present data, it is improbable that part of the A1 isoenzyme in fibroblasts originates from fetal calf serum arginase which supplements the culture media. None of the techniques for the separation and analyses of arginase isoenzyme allows to differentiate between the normal and the arginase-deficient phenotype. A possible explanation would be that the defect in A1 arginase observed in the liver is the result of a regulatory defect.

Amino Acid Metabolism, Inborn Errors↗
PubMed1982

Purification and properties of acetyl-CoA:L-glutamate N-acetyltransferase from human liver.

Acetyl-CoA:L-glutamate N-acetyltransferase (amino acid acetyltransferase, EC 2.3.1.1) was isolated from human liver mitochondria by precipitation with (NH4)2SO4 and chromatography on hydroxyapatite, DEAE-cellulose and Sephacryl 300. This gave a 360-fold purification. The molecular weight was estimated to be approx. 190 000. The kinetic properties in the absence of arginine are compatible with a rapid-equilibrium random Bi Bi mechanism. The estimated constants are: for the substrates Km,acetyl-CoA 4.4 mM, Ki,acetyl-CoA 4.7 mM, Km,glutamate 8.1 mM, Ki,glutamate 8.8 mM; for the products, Ki,acetylglutamate 0.28 mM, Ki,CoA 5.6 mM. The rate constant for the forward direction is 1.24s-1. If in vivo the constants are of the same order of magnitude as in vitro, the synthesis of N-acetylglutamate, an obligate activator of the first step of urea synthesis, can be expected to occur in the mitochondrion under conditions where the amino acid acetyltransferase is not saturated by its substrates. The regulation of the first step of urea synthesis could thus depend mainly on the intramitochondrial substrate and perhaps product concentrations of amino acid acetyltransferase.

Acetyl Coenzyme A↗
PubMed1982

Comparative evaluation of the new vasodilator carprazidil and minoxidil in the treatment of moderate to severe hypertension.

The efficacy and side effects of the new vasodilator carprazidil and the established vasodilator minoxidil were compared in 18 hypertensive patients inadequately controlled by 2 to 4 conventional drugs; the latter included diuretics, beta-blockers and/or sympatholytics and, in half the cases, vasodilators, such as hydralazine, diazoxide or the postsynaptic alpha-blocker prazosin. The vasodilators were withdrawn and, using a crossover design all patients received carprazidil (mean final dose 88 mg) and minoxidil (20 mg) for an average period of 5 to 6 months. The effects of the 2 agents appeared to be qualitatively and quantitatively similar. Both tended to cause sodium retention and an increase in heart rate, which required an increased dose of diuretic in one third of the cases or of a beta-blocker in a quarter. With this approach mean body weight and blood volume were not altered in the established phase of carprazidil or minoxidil treatment; heart rate and plasma norepinephrine tended to be only minimally increased, plasma renin was slightly increased, and plasma aldosterone and epinephrine were largely unchanged. Supine and upright blood pressure were reduced from initial values of 189/113 and 167/ 113 mm Hg, to 149/95 and 138/95 mm Hg (-18 and - 17%), respectively, during carprazidil, and to 154/95 and 141/96 mm Hg (-17 and - 15%) during minoxidil therapy. Hypertrichosis occurred with both agents in almost all patients, and limits their more prolonged use in females. No adverse side effects on haematological parameters, liver or renal function were observed, nor was antinuclear antibody detected. It is concluded that carprazidil and minoxidil are equivalent vasodilator agents in the treatment of severe hypertension, particularly in males.

Adult↗
PubMed1982

Incidence of disorders tested by systematic screening: confidence limits and comparison of programmes.

Using the data from screening done in Switzerland since 1965, we showed that the probability of finding cases with increased phenylalanine or leucine concentrations is compatible with a Poisson distribution. If there are no trends present from year to year and if the Poisson distribution is an accurate fit further statistical treatment is possible. The advantage of using the Poisson distribution is exemplified by the calculation of confidence limits for the incidence of hyperphenylalaninaemia, maple syrup urine disease and hypothyroidism. Furthermore, statistical comparisons between different screening programs are easily done.

Epidemiologic Methods↗
PubMed1982

N-Acetylglutamate synthetase: enzyme assay in human liver.

In the context of diagnostic procedures for congenital hyperammonaemias a methods is described for the determination of N-acetylglutamate synthetase in human liver tissue homogenates. The method uses [14C-U] glutamate and acetyl CoA as substrates. The reaction product, N-acetylglutamate is separated from the substrate L-glutamate by chromatography on Extrelut. In a subsequent step on ITLC-SG ready plates N-acetylglutamate is separated from other labeled metabolites such as Krebs cycle intermediates. The recovery of N-acetylglutamate was 97.8%. The precision within run and between days was 8.5% (CV) and 9.6% (CV) respectively. Reference values were established for adult human liver.

Acetyltransferases↗
PubMed1982

[Hyperammonemia: a suggestion for diagnostic and therapeutic procedures].

Hyperammonemia in pediatrics leads to emergency situations. Adequate decisions for treatment have to be taken rapidly. These depend on the underlying disorder. While the patient's history and symptoms should lead to a search for hyperammonemia, the further steps will depend on biochemical results of aminoacid determinations in plasma and urine, and orotic acid excretion. In some cases where this latter metabolite is not increased, the determination of organic acids in urine and enzyme assays in liver are needed. A scheme for the diagnostic and therapeutic measures is proposed.

Amino Acids↗
PubMed1982

[Lethal neonatal deficiency of carbamyl phosphate synthetase (author's transl)].

This is a report of a male neonate with hyperammonemia who showed progressive neurologic symptoms and pulmonary bleeding due to carbamyl phosphate synthetase deficiency. This newborn male died in coma after only 119 hours. His elder brothers died under similar circumstances in the first days of life, and a CPS-deficiency is not to be excluded. The pulmonary bleeding in the patient and in one brother caused by hyperammonemia is emphasized. In the pedigree repeated consanguinity could be detected.

Amino Acid Metabolism, Inborn Errors↗
PubMed1981

Arginase activity in human fibroblast cultures.

Controversial results have been published as to the presence of arginase activity in human skin fibroblasts in normal cells and in argininemia. Experiments were undertaken to see if arginase is intrinsic to the fibroblasts or may be there as the result of exogenous contamination inherent to the mode of cell culturing. The mode of harvesting by scraping or trypsin treatment demonstrated similar arginase activity. No significant differences of arginase activity were found between the fibroblasts grown on fetal calf or human serum. In the conditioned serum-free medium arginase separated on DEAE-cellulose into an A1 and A4 form. These fractions are identical with those found in the cells. Arginase activity varies, however, with age of the fibroblasts. These observations are also valid for fibroblasts from a case of argininemia. Arginase activity is therefore intrinsic to diploid human fibroblasts.

Amino Acid Metabolism, Inborn Errors↗
PubMed1981

Computer simulation of the urea cycle: trials for an appropriate model.

Several models of the urea cycle with normal and deficient enzymes were simulated on a desk-top computer in order to test if a model fitting data of patients suffering from deficiencies of urea cycle enzymes could be obtained. Discrepancies were notable if only the four enzymes of the urea cycle were used. The effect of adding either n-acetylglutamate synthetase and CPS or the mitochondrial transport system of ornithine and its catabolism to the model were tested singly or combined. The use of the combined model with the rate constants adjusted to recent data of the human enzymes together with a transport system for N-acetylglutamate out of the mitochondrium improved the results. Computer simulations are thus a useful tool for testing concepts of the functioning of the urea cycle.

Acetyltransferases↗
PubMed1981

Metabolic effects of fasting in steers.

The effect of starvation for five days on blood levels of various hormones and metabolites was studied in seven steers. There was a significant decrease (P less than 0.05) in thyroxine (free and total), 3,5,3'-triiodothyronine (free and total), immunoreactive insulin, propionic acid, butyric acid and glucose, 3,3',5'-triiodothyronine and alpha-aminoacid-N levels did not change. Free fatty acids, beta-hydroxybutyrate, acetoacetate, urea, isobutyrate, alpha-methylbutyrate and isovalerate, total protein and albumin significantly (P less than 0.05) increased.

Animals↗
PubMed1980

Diagnostic value of orotic acid excretion in heritable disorders of the urea cycle and in hyperammonemia due to organic acidurias.

Orotic acid excretion in urine in increased in ornithine transcarbamylase deficiency, citrullinemia and argininemia; it is barely increased in argininosuccinic aciduria and normal in carbamylphosphate synthetase deficiency and in hyperammonemia due to organic aciduria. The determination of orotic acid excretion is useful in differentiating the cases of hyperammonemia and reduces the need for enzymatic assays on tissue biopsies for decisions on therapy. The data indicate that orotic acid does not merely reflect ammonia concentration in plasma, but depends on carbamylphosphate concentration. Arginine could play a key role in the regulation of ammonia detoxication.

Amino Acid Metabolism, Inborn Errors↗