The N-metabolism of 6 male and 6 female runners are characterized with the help of the N-15 tracer technique using [N-15]glycine as a tracer substance. The tracer kinetic data coming from the excretion of the isotope in the urine were determined using the priming technique. The parameters of the protein metabolism were calculated on the basis of a 3-pool model. The experimental results are discussed.

Mil Hilfe der 15N-Tracertechnik wurde der N-Stoffwechsel von je 6 Läufern und Läuferinnen charakterisiert. Als Tracersubstanz wurde [15N]Glycin eingesetzt. Die tracerkinetischen Daten, die sich aus der Ausscheidung des lsotops im Urin ergeben, wurden unter Verwendung der Priming-Technik vermittelt. Die Parameter dcs Proteinstoffwechscls wurden auf der Grundlage eines 3-Pool-Stoffwechselmodells herechnet. Die experimentellen Ergebnisse werden diskutiert. The N-metabolism of 6 male and 6 female runners are characterized with the help of the 15N tracer technique using [15N]glycine as a tracer substance. The tracer kinetic data coming from the excretion of the isotope in the urine were determined using the priming technique. The parameters of the protein metabolism were calculated on the basis of a 3-pool model. The experimental results are discussed.

(1992). Messung des Energieumsatzes in biologischen Systemen mit stabilen Isotopen. Isotopenpraxis Isotopes in Environmental and Health Studies: Vol. 28, No. 1, pp. 43-44.

The functional state of the liver can be assessed by oral administration of 15N labelled ammonium chloride (tracer) and subsequent isotope analysis of [15N]urea and [15N]ammonia in urine. Clinical tests based on the ratio of the excess abundances of [15N]ammonia to [15N]urea excreted in urine 3 hours after oral administration of the tracer gave values for patients with liver diseases which differed significantly from these of healthy subjects.

The application of stable isotopes creates further possibilities for our understanding of the metabolism. New concepts especially for non-invasive diagnostic procedures could be developed. An important step in our research program was the performing of a 1-year experiment on a volunteer. On the basis of a 10-pool model we received a lot of informations. Based on this knowledge we developed 2 simplified methods for calculating whole body protein turnover. Knowing the problems with whole body protein calculations we intensified our intentions for determining the protein enrichment in organs and isolated cells (hepatocytes), estimating at the same time the precursor pool in the cells. Of special importance was an extensive study, wherein all those 15N-estimations were performed we are able to do up to now. We calculated whole body protein, but especially we studied the enrichment of the cellular protein fractions in hepatocytes, of plasmaproteins, and of the intracellular precursor pool. This study is the base for further tracer investigations.

Click to increase image sizeClick to decrease image sizeKeywords: amino acidsisotope rationitrogen 15thin-layer chromatography

The 15N tracer technique teas used to investigate liver specific reactions (urea and hippurate synthesis) for studying the metabolism in the healthy and damaged pig liver. After [15N]ammonium chloride administration the tracer distribution on non-protein compounds of serum and urine was followed. Blood sampling before and after the liver passage made possible a direct analysis of the [15N]ammonium metabolism. The thioacctamide induced liver damage was used as a model for an acute liver intoxication. In our studies the capacity for urea synthesis was not influenced by means of this noxious substance, but the metabolism of amino acids and the hippuric acid. The considerable depressed excretion of [15N] hippurate might be a suitable indicator of a liver disfunction.

It is possible to investigate the influence of parenteral applicated L-amino acids on protein metabolism of whole organism by the help of 15N-tracer technique in this paper described. We can determine the utilization of nitrogen parenteral applicated quantitatively. On the basis of graphical methods the protein synthesis rate can be calculated. We get this from mathematical models, based on 3-pool-model. The calculation bases on 15N-elimination in urine after intravenous infusion of 15N labeled amino acids solution during the time of 24 h (endproduct method). We describe 3 graphical methods, using the so-called values of plateau of cumulative 15N-excess amount (96 h) (plateau method A) or 15N abundance after 24 h (plateau method B) and the slope of the curve of 15N excess, amount at 24 h ('slope' method). By the help of these methods the therapeutical nutritive conceptions can be evaluated.

Mit Hilfe der in dieser Arbeit vorgestellten 15N-Tracermethodik kann der Einfluß parenteraler L-Aminosäurenzufuhr auf den Proteinstoff-wechsel des Gesamtorganismus untersucht werden. Gleichzeitig läßt sich die Verwertung des parenteral zugeführten Stickstoffs quantitativ bestimmen. Die Berechnung der Proteinsynthesegeschwindigkeit, unter der Voraussetzung, daß der NPN-Pool über den gesamten Versuchszeitraum weitestgehend konstant bleibt, erfolgt auf der Grundlage graphischer Verfahren. Diese Verfahren ergeben sich aus einem mathematischen Formalismus, der sich aus dem 3-Pool-Modell ableiten läßt. Die Ermittlung der Werte basiert auf der 15Elimination im Urin nach 24 h intravenöser Infusion 15N-markierter Aminosäurenlösungen (Endproduktmethode). Es werden 3 graphische Verfahren beschrieben, bei denen sogenannte Plateauwerte der kumulativen 15N-Exzeßmenge nach 96 h (Plateaumethode A) bzw. der 15N-Exzeßhäufigkeit nach 24 h (Plateaumethode B) sowie der Anstiegswinkel der kumulativen 15Exzeßmenge innerhalb 24 h (Anstiegsmethode) genutzt werden. Diese Verfahren ermöglichen die Bewertung u.a. ernährungstherapeutischer Konzepte.

Folgende Untersuchungen an Rattenorganen waren durch 15N-NMR-Messungen möglich: – Verteilung von in vivo applizierten 15N-markierten Verbindungen auf verschiedene Organe in Abhängigkeit voń der Einwirkungszeit; – Ermittlung der Biotransformationskinetik von [15N]Glycin als Maβ für die fortdauernde metabolische Aktivität der entnommenen Leber; – Nachweis intermediär auftretender Metabolite des Glycins. Es wurden [15N2]Harnstoff und [15N]Glycin injiziert. Aus den Ergebnissen folgt, daβ die 15N-NMR-Spektroskopie in Verbindung mit der traditionellen 15N-Analyse eine neue Möglichkeit zur Verfolgung des Stickstoffstoffwechscls von Pflanze, Tier und Mensch am intakten Organismus eröffnet. Using 15N NMR measurements functional studies in rat organs were possible and could be demonstrated with the following examples: – 15N distributions to various rat organs depending on the effective time of the injected compounds; – measurement of biotransformation kinetics of [15NJglycine showing the continued metabolic activity of the isolated rat liver; – occurrence of intermediary metabolites of glycine. Wistar rats had received an injection of [15N2] urea and [15N2] glycine. The results establish that 15NNMR spectroscopy in connection with traditional 15N analysis is able to open new possibilities to study nitrogen turnover of plants, animals, and humans also in the intact organism.

Malfunction of the liver involves disturbances of urea synthesis and ammonia detoxification. These phenomena became apparent, especially during ammonia loading of patients. The functional state of the liver can be assessed by oral administration of 15NH4Cl and subsequent analysis of 15N-urea and 15N-ammonia in urine by emission spectrometry. Clinical tests based on the ratio of the excess abundances (see Appendix) of 15N-ammonia to 15N-urea excreted in urine 3 h after oral administration gave values for patients with liver disease which differed significantly from those for healthy subjects. Absorption disturbances, which often accompany liver diseases, do not influence the effectiveness of the method.

A simple, non-invasive, non-radioactive liver-function test is proposed. After an oral dose of 3 mg 15N-methacetin per kilogram body mass, the kinetics of 15N excretion via urine were characterized by the quotient of the amounts of 15N excreted in two successive urine samples (Q value). The stable nitrogen isotope 15N was found to be an excellent and easily detectable indicator of the sum of all methacetin metabolites present in urine. Alterations in the nature or ratio of methacetin metabolites due to liver diseases could not be found. From the investigation of 11 men, 3 pregnant women and 15 children, a clear difference was observed in Q values of healthy persons and patients suffering from liver-cell-activity diseases. The discriminating power of our new liver-function test is shown to be equivalent to that of the 14CO2 breath test.