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The influence of the extracellular concentration of glucose on the respiratory quotient of isolated tissue
Der Einfluß der extrazellulären Konzentration von Glukose auf den Respiratorischen Quotienten isolierter Gewebe
Helgoländer wissenschaftliche Meeresuntersuchungen volume 14, pages 291–301 (1966)
Kurzfassung
Der Sauerstoffverbrauch von Gewebeschnitten der Ratte unterliegt Schwankungen bei einer Temperaturänderung. In gleicher Weise variieren die Werte des Respiratorischen Quotienten (R. Q.), insbesondere im Bereich der normalen Körpertemperatur. Bei Rattennierenschnitten, die 2 Stunden kalter Ringerlösung mit verschiedenen Glukosekonzentrationen ausgesetzt waren, treten im Temperaturbereich von 40,5° bis 37,5° C starke Oszillationen des R. Q. (von 0,65 bis 1,0) auf, jedoch nur, wenn die extrazelluläre Glukosekonzentration innerhalb der Grenzen des normalen Blutzuckergehalts liegt. Ähnliche Ergebnisse (mit grundsätzlich niedrigeren R. Q.-Werten) finden sich in der Niere alloxandiabetischer Ratten. Anhand statistischer Analysen läßt sich ein zweifacher Verlauf des R. Q. nachweisen: (1) bei niederen Werten besteht eine Kompetition zwischen Fettsäuren und Kohlenhydrat um den Sauerstoff; (2) bei einem R. Q. von 0,8 hört diese auf. Bis zu diesem Punkt findet die Oxydation innerhalb der Mitochondrien statt, deren Struktur auf einer amphiphilen kristallinen Verbindung von Fettsäuren und Lecithin beruht. Der teilweise Abbau dieser kristallinen Struktur unter dem Einfluß des Hydroxylgruppen enthaltenden Zuckermoleküls bringt den Zugang oxydierender Enzyme zu Glykolyseprodukten und damit das Auftreten hoher R. Q.-Werte mit sich.
Summary
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1.
Oxygen consumption of rat tissue slices has been followed in a respirometer as the temperature falls, while contact with warm Ringer's solution was avoided. Under these conditions rate of O2-consumption oscillates. Simultaneous observations on O2-consumption and CO2-production demonstrated that the respiratory quotient (R. Q.) also varies sharply within the range of temperatures prevailing within the body. All variations must be taken into account in studying the responses of the whole animal.
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2.
Experiments were made on slices of rat kidney, which had been exposed for two hours to a small volume of cold Ringer's solution, containing various concentrations of glucose. Wide oscillations in R. Q. were found only when the extracellular glucose concentration lay within the limits of the normal blood sugar level. Above and below this the R. Q.s are low.
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3.
In experiments with alloxan diabetics rats, this limitation of the range of R. Q. prevails at all extracellular glucose concentrations above a very low value.
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4.
Statistical analyses of experimental results show that the course of the R. Q.s is divisible in to two portions. In the lower portion there is a sharp competition between fatty acids and carbohydrates for oxidation; this breaks off at an R. Q. value of 0.8. Arguments are presented in support of the conception that up to this point, oxidation is carried on inside the mitochondria, the structure of which is based on an amphiphilic crystalline conjunction of fatty acid and lecithin. The partial breakdown of this crystalline structure — under the influence of the hydroxyl containing glucose molecules at a concentration associated with the normal extracellular glucose — allows access of the oxidizing enzymes to the products of glycolysis and, in consequence, the appearance of the upper zone of R. Q.s.
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O'Connor, J.M. The influence of the extracellular concentration of glucose on the respiratory quotient of isolated tissue. Helgolander Wiss. Meeresunters 14, 291–301 (1966). https://doi.org/10.1007/BF01611625
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DOI: https://doi.org/10.1007/BF01611625