Roland Scholz

Influence of fatty acids on energy metabolism. 1. Stimulation of oxygen consumption, ketogenesis and CO2 production following addition of octanoate and oleate in perfused rat liver.

: Changes in metabolic rates (oxygen consumption, ketogenesis, 14CO2 production from labelled fatty acids, glycolysis) following the addition of octanoate or oleate were studied in isolated livers from fed and starved rats perfused with Krebs-Henseleit bicarbonate buffer in a non-recirculating system. The following results were obtained. The infusion of fatty acids caused a large increase in the rate of oxygen consumption. The effect was greater with octanoate than with oleate and was half-maximal with fatty acid concentrations (free plus albumin bound) around 0.1 mM. The effects of oleate were only partially suppressed when the perfusate contained albumin concentrations near the physiological range. When fatty acids were oxidized at high rates, the glycolytic rate was diminished by 50%. The increase in oxygen consumption could not be explained fully by the increased ATP demand for fatty acid metabolism or by a compensation for the diminished extramitochondrial ATP generation. In the presence of phenylalkyl oxirane carboxylic acid, an inhibitor of the transport of long-chain acyl-CoA derivates into the mitochondria, ketogenesis and 14CO2 production from labelled oleate were strongly inhibited, whereas the increase in oxygen consumption was only slightly affected. In the presence of antimycin A, the increase in oxygen consumption due to fatty acids was totally abolished. Following pretreatment of rats with ciprofibrate (induction of enzymes for peroxisomal beta-oxidation of long-chain fatty acids), ketogenesis (but not 14CO2 production) from oleate was enhanced threefold. The increase in oxygen consumption, however, was not affected. In conclusion, the increase in hepatic oxygen consumption due to addition of fatty acids reflects a mitochondrial process; it is, in part, independent of the ATP demand of the cell. An uncoupling-like effect of fatty acids on the respiratory chain and its possible physiological significance in ketogenesis are discussed.

Regulation of oxygen consumption in perfused rat liver: decrease by α-sympathetic nerve stimulation and increase by the α-agonist phenylephrine

In livers perfused with Krebs-Henseleit bicarbonate buffer containing bovine red cells, 5 mM glucose and 2 mM lactate, electrical stimulation round the hepatic artery and the portal vein caused via α-receptors a decrease in oxygen consumption and portal flow, an increase in glucose output and a switch from lactate uptake to output.In livers perfused with erythrocyte- and substrate-free buffer both in a volume- or pressure-constant system stimulation of the liver nerves resulted in similar changes. Infusion of the α-agonist phenylephrine mimicked the metabolic and hemodynamic nerve effects, but led to an increase in oxygen uptake. The converse effects of α-sympathetic nerve stimulation and α-agonist infusion on oxygen consumption indicate either a different mode of action or a complex mechanism with opposing metabolic and hemodynamic components.

Control of energy metabolism by glucagon and adrenaline in perfused rat liver

Changes in subcellular distribution of adenine nucleotides, mitochondrial/cytosolic proton gradients, rates of respiration, gluconeogenesis (fasted state) and glycogenolysis (fed state) were studied in isolated perfused rat livers following addition of glucagon (10−8 M) or adrenaline (10−7 M). Glucagon increased the gradient in all states. The cytosolic ATP/ADP ratio was increased in the fasted but decreased in the fed state which is consistent with a diminished futile cycling in gluconeogenesis (fasted state) or a decreased glycolytic rate (fed state). Adrenaline caused an increase in the proton gradient and the mitochondrial ATP/ADP ratio. The two effects are attributed to increased calcium entry into the matrix space.

Actions of glucagon on flux rates in perfused rat liver. 2. Relationship between inhibition of glycolysis and stimulation of respiration by glucagon.

The relationship between inhibition of glycolysis and stimulation of oxygen consumption by glucagon was studied in perfused rat livers. The two effects exhibit similar kinetics and dose-response curves; they are slower and less sensitive to the glucagon concentration than the stimulatory effect on glycogenolysis. A stoichiometry of 1 mol extra oxygen consumed/1.8 mol of diminished lactate plus pyruvate production was found. Under conditions where glucagon did not cause a marked inhibition of glycolysis (i.e. low glycolytic flux rates in the fasted state or in the presence of ethanol), oxygen consumption was also not markedly increased. These findings provide evidence that the major portion of glucagon-induced stimulation of hepatic respiration in the fed state is due to an enhanced demand for mitochondrial oxidative phosphorylation to compensate for the diminished extramitochondrial ATP production following inhibition of glycolysis by glucagon.

Stimulation of Ethanol Metabolism by Catecholamines

The effects of catecholamines (epinephrine, phenylephrine, isoproterenol) on rates of ethanol utilization, oxygen uptake and glucose, lactate and pyruvate production from endogenous sources were studied in livers from fed rats perfused in a non-recirculating system.

Dependence of Mitochondrial and Cytosolic ATP Systems on the Metabolic State of Perfused Rat Liver

Adenine nucleotides are the link between energy generating and energy utilizing processes in the cell. ATP is generated mainly in the mitochondria and is utilized mainly in the cytosol. It is transported across the mitochondrial membrane by a specific carrier in exchange for ADP. Since ATP and ADP are substrates and products of many reactions, most metabolic processes depend upon the phosphorylation potentials of the subcellular adenine nucleotide system. Moreover, ATP and ADP also act as modulators of several regulatory enzymes. A knowledge of their subcellular concentrations or phosphorylation potentials as reflected largely by the ATP/ADP ratios, therefore, will certainly increase our understanding of how metabolism is regulated in the living cell.

Investigation of Rapid Metabolic Reactions in Whole Organs by Multiple Pulse Labelling

Flux rates of metabolic and transport processes in whole organs may be determined by conventional compartmental system analysis (1,2). However, this approach is not consistent with the events in real organs characterized by continuous variation of tracer concentrations with space. When the events under study are comparable in rate with transit times or recirculation, their adequate description is only possible by using distributed model systems.

Strahlensensibilität und DNA-Reparatur: Zum Mechanismus und Polymorphismus von Enzymsystemen zur Reparatur von DNA-Schäden

Lebewesen reagieren unterschiedlich auf chemische und physikalische Noxen. Hinsichtlich der akuten Strahlenwirkung variieren die letalen Dosen („LD50“, d.i. die Dosis, bei der 50% der Bestrahlten nicht uberleben) speziesabhangig uber drei Grosenordnungen; am empfindlichsten sind Saugetiere; unter denen gehort der Mensch zur besonders strahlensensiblen Gruppe [1]. Fur Radiologen ist es eine alltagliche Erfahrung, das Patienten nach therapeutischer Rontgenbestrahlung unterschiedlich heftig mit Nebenwirkungen reagieren. Auch die verschiedenen Zellarten eines Organismus unterscheiden sich in ihrer Strahlenempfindlichkeit. Ohne diese Tatsache ware eine Tumorbestrahlung nicht moglich. Allgemein gilt, je rascher ein Gewebe wachst, je haufiger sich darin die Zellen teilen, um so strahlenempfindlicher ist es.

HEMOGLOBIN-FREE PERFUSION OF RAT LIVER**Supported by grants of the Squibb Institute for Medical Research, New Brunswick, New Jersey.

Publisher Summary This chapter presents an experiment in which a rat liver was extracorporally perfused by a hemoglobin-free fluid of restricted complexity. Regulation of the lactate–pyruvate ratio is not only found to be a significant contribution of the liver to the homeostasis of plasma constituents in vivo but also a sensitive indicator of the metabolic fitness of the perfused organ. Higher sensitivity is gained by using a liver homogenate reduced by dithionite as a reference. An advantage of the hemoglobin-free perfusion is that the oxygen consumption of the organ can be easily recorded. Cell-specific sensibilities for barbiturates are probably responsible for the difference of concentrations for half-maximal effects on liver and ascites cells. In the experiment described in the chapter, surface fluorometry, reflection photometry, and measurements of surface oxygen tensions and of respiratory rates were coordinated with enzymatic and chromatographic analyses of metabolite contents.