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Biomedical subjects

N Seiler

Publications and source records attributed to N Seiler.

At least 145 records · Page 8Linked to original sources
PubMed1979

Metabolic inhibitors and subcellular distribution of GABA.

Experimental procedures are described which are believed to yield results that reflect, within certain limits, the in vivo changes of the size of the GABA pool in nerve endings in comparison with those of all other GABA pools. Two irreversible GABA-T inhibitors, vinyl GABA and acetylenic GABA, two GAD inhibitors, 3-mercaptopropionic acid and pyridoxal phosphate glutamyl-gamma-hydrazone, and di-n propylacetate, a clinically useful anticonvulsant, have been studied to determine their effects on GABA compartmentalization in mouse brain cortex. The changes elicited by these drugs in subcellular fractions of brain cortex homogenates support the notion that measurement of amino acid concentrations in crude synaptosomal fractions and in supernatant fractions under controlled conditions allow one to draw conclusions about relative changes of pool sizes in vivo. In particular this work showed that a specific increase in the concentration of GABA within the nerve endings is more important than a large increase of total brain GABA as a means of decreasing susceptibility to a variety of chemically or physically induced seizures.

3-Mercaptopropionic Acid↗
PubMed1979

Regulatory interrelations between GABA and polyamines. I. Brain GABA levels and polyamine metabolism.

Elevation of brain GABA levels by GABA-T inhibition is accompanied by a decrease of S-adenosylmethionine decarboxylase activity. This is followed by an increase of ornithine decarboxylase activity and a severalfold increase of brain putrescine levels. Spermidine and spermine levels are not significantly affected under these conditions. These unexpected findings support a regulatory interaction between GABA and polyamine metabolism.

4-Aminobutyrate Transaminase↗
PubMed1979

Regulatory interrelations between GABA and polyamines. II. Effect of GABA on ornithine decarboxylase and putrescine levels in cell culture.

GABA added to rat hepatoma (HTC) cells in spinner culture at the time of induction of cell proliferation increased levels of ornithine decarboxylase (ODC) up to two- to threefold above that of control cells. The increases in ODC were also reflected by concomitant increases of intracellular putrescine levels, while spermidine and spermine were unchanged. GABA seems to have a direct stabilizing effect on ODC, since the turnover of the enzyme was slowed almost twofold when measured in cells treated with 10(-2) M GABA. The stabilizing effect is most pronounced for GABA, although some amino acids such as asparagine, glutamine, and lysine as well as some GABA analogues and homologues also tend to increase ODC but to a significantly lesser extent than GABA itself. GABA metabolites had no effect on ODC. S-Adenosylmethionine decarboxylase and tyrosine aminotransferase were not affected by the presence of GABA. The GABA effect on ODC may be important in certain types of cells for the regulation of polyamine biosynthesis.

Aminocaproates↗
PubMed1979

Factors altering platelet monoamine oxidase. The influence of oral glucose intake.

The specific activity of human platelet monoamine oxidase from control subjects undergoing glucose tolerance tests is reduced drastically. Three hours after intake of 100 g of glucose only 25%-30% of the MAO-baseline activity was measured with tryptamine. beta-phenylethylamine and p-tyramine as substrates. At about 5 hr, platelet MAO activity has increased again. Inhibition was not due to small molecular weight inhibitors or other diffusible factors. Studies of other platelet enzymes, including succinate dehydrogenase and isocitrate dehydrogenase (NADP+ dependent) showed no parallel reductions; hGH, insulin, blood glucose and platelet glycogen concentrations did not correlate with platelet MAO activity. The changes of MAO activity in respect with p-tyramine and tryptamine as substrates 24 hr after glucose ingestion suggest changes of the lipid microenvironment of this enzyme of the outer mitochondrial membrane.

Adult↗
PubMed1979

On the formation of gamma-aminobutyric acid from putrescine in brain.

Gamma-aminobutyric acid is not formed in significant amounts from putrescine by incubation with rat brain homogenates. However, it is formed if acetyl-CoA is added to the incubation medium. This is taken as further evidence for the existence of a metabolic pathway in mammalian brain which comprises acetylation of putrescine to monoacetyl putrescine and oxidative deamination of monoacetyl putrescine by MAO. Nerve cells and glia cells have comparable capacities for putrescine degradation along this pathway.

Acetyl Coenzyme A↗
PubMed1978

Enzyme-activated irreversible inhibitors of L-ornithine:2-oxoacid aminotransferase. Demonstration of mechanistic features of the inhibition of ornithine aminotransferase by 4-aminohex-5-ynoic acid and gabaculine and correlation with in vivo activity.

L-Ornithine:2-oxoacid aminotransferase is a specific enzyme with respect to the amino group donor. Nevertheless it was found that this enzyme is inhibited by some 4-aminobutyrate analogs, 4-aminohex-5-ynoic acid and 5-amino-1,3-cyclohexadienyl-carboxylic acid (gabaculine), which are currently considered to be enzyme-activated irreversible inhibitors of 4-aminobutyrate:2-oxoglutarate aminotransferase. The inhibitory mechanisms for the two omega-aminotransferases are identical. A close structural analog of these inhibitors, 4-aminohex-5-enoic acid, is not inhibitory for ornithine aminotransferase, whereas it effectively inhibits 4-aminobutyrate aminotransferase. The reasons for this difference are discussed. The in vitro findings are entirely transferable to the in vivo situation: 4-aminohex-5-ynoic acid and gabaculine cause a long-lasting inhibition of ornithine aminotransferase in brain and liver, and reduce significantly in vivo ornithine degradation, whereas 4-aminohex-5-enoic acid is inactive both in vivo and in vitro toward this enzyme. The enzyme-activated irreversible inhibitors allow one for the first time to study the physiological consequences of irreversible ornithine aminotransferase inhibition.

Aminocaproates↗
PubMed1978

Determination of di-and polyamines by high-performance liquid chromatographic separation of their 5-dimethylaminonaphthalene-1-sulfonyl derivatives.

Using a Lichrosorb RP-8 reversed-phase column and a methanol--water gradient elution program, it is possible to separate within 40 min and to determine routinely in picomole quantities the natural di- and polyamines. The precision of the method is comparable to the thin-layer chromatographic procedures, the separations are most efficient, and the method can be fully automated. A modified gradient enables the repeated assay of spermidine and spermine within 20 min. The method is suited for polyamine analyses in tissues and body fluids.

Animals↗
PubMed1978

Increase of ornithine decarboxylase activity elicited by reserpine in the peripheral and central monoaminergic systems of the rat.

Ornithine decarboxylase activity was increased about tenfold in adrenal glands and in brain regions preponderantly containing aminergic neurons, by a single dose of 16 mumol/kg of reserpine. Maximal enzyme activity in the adrenal glands was observed at about 8 hr after reserpine administration. The ornithine decarboxylase activity-time curves in the brain regions showed a concomitant polyphasic course, with the highest maximum at 12 hr postinjection. Ornithine decarboxylase induction is discussed as an early event in the cascade of molecular events preceding the induction of cell typic enzymes.

Adrenal Glands↗
PubMed1977

Substrate-typic changes of platelet monoamine oxidase activity in sub-types of schizophrenia.

Monoamine oxidase (MAO) activity has been measured in the platelets of controls (n = 42) and schizophrenic patients (n = 49) of three subtypes, using beta-phenylethylamine, p-tyramine, and tryptamine as substrates. Characteristic differences of MAO activity were observed between platelets of patients and controls; the differences were substrate-typic: decreased enzyme activity was found with all three substrates in platelets of the parnaoid subtype. With tryptamine, MAO activity was decreased in the platelets of all three sub-types of schizophrenia. With p-tyramine, MAO was low in patients with affective psychoses and paranoid schizophrenia. The value of MAO activity measurements as a means for distinguishing sub-types of schizophrenic disorders is improved by using two substrates; tryptamine and p-tyramine. Possible mechanisms of the substrate-typic changes of platelet MAO activity in schizophrenia are discussed.

Adult↗
PubMed1977

Chromatography of biogenic amines. I. Generally applicable separation and detection methods.

This first part of the review on "Chromatography of Biogenic Amines" is devoted to the description of generally applicable separation and detection methods. Gas chromatographic and gas chromatographic-mass spectrometric methods, and applications of chromatographic methods to specific amines or groups of related amines and their metabolites, will be covered in Part II. Trends in the development of separation methods (paper and thin-layer chromatography, paper and thin-layer electrophoresis and ion-exchange methods) are described, using mostly aliphatic amines as examples as they do not exhibit features that permit their specific determination. Reagents suggested for the formation of coloured and fluorescent derivatives of amines are reviewed and their applications are described. Within the limitation of the reviewed and their applications are described. Within the limitation of the mostly inadequate information that is available, the relative usefulness of the different derivative-forming reactions are compared.

Biogenic Amines↗
PubMed1977

Assay procedures for polyamines in urine, serum, and cerebrospinal fluid.

Putrescine (1,4-diaminobutane) and the polyamines spermidine and spermine have attracted interest as possible markers of malignancy and of response to chemotherapy. The assay methods currently in use for these amines are reviewed and compared in respect to sensitivity, reproducibility, and applicability to routine analysis for them in urine, blood, and cerebrospinal fluid.

Chromatography, Gas↗
PubMed1976

A routine assay procedure for monoamine oxidase and its application to human blood platelets.

In the radiometric assay procedure for monoamine oxidase separation of the reaction products by ion-exchange column chromatography was optimized. A device was constructed that allowed the separation of 48 samples at the same time. This device can be applied for a great variety of analytical methods. With a 0.1 mM substrate concentration in the incubation mixture, reaction products could be determined with a reproducibility of 2-5%, where the standard deviation depends on the substrate. Using beta-phenylethylamine as substrate 20 mug of platelet protein was sufficient for monoamine oxidase activity determinations. The dependence of human blood platelet monoamine oxidase on age and sex were studied using the method.

Adolescent↗
PubMed1976

Autoradiographic studies on the distribution of 3H-2,3,4-trimethoxy-beta-phenylethylamine in the mouse.

The regional distribution of radioactivity was studied in the brain and in other organs of the mouse by light microscopic autoradiography after injection of 3H-2,3,4-trimethoxy-beta-phenylethylamine (2,3,4,-TMPEA), a nonhallucinogenic isomer of mescaline. The distribution patterns were compared with biochemical and autoradiographic results obtained after 3H-mescaline. Although 2,3,4-TMPEA is rapidly deaminated compared to mescaline its distribution pattern in the brain is similar to that of mescaline at 1 h after injection. However, contrary to mescaline the radioactive labeling becomes more and more homogenously distributed in the brain with tiem. The distribution patterns in kidney, pancreas, adrenal, and spinal ganglia were also different from those observed after application of 3H-mescaline.

Animals↗