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T Sugano

Publications and source records attributed to T Sugano.

At least 163 records · Page 9Linked to original sources
PubMed1980

Intracellular redox state and stimulation of gluconeogenesis by glucagon and norepinephrine in the perfused rat liver.

The role of the cellular redox state in the hormonal stimulation of gluconeogenesis was studied in hemoglobin-free perfused rat liver, by fluorimetric measurement of the redox states of intracellular pyridine nucleotides. The maximum rate of glucose production from lactate/pyruvate mixture was observed with a lactate/pyruvate ratio of 10/1, which corresponds to the ratio observed in vivo. Increased reduction of pyridine nucleotides on infusion of ethanol or octanoate was associated with an increased production of glucose from pyruvate, whereas glucose production from lactate decreased. Stimulation of gluconeogenesis from lactate by glucagon was affected by the lactate/pyruvate ratio; a decrease of the lactate/pyruvate ratio resulted in a decrease of the efficacy of glucagon. Stimulation by glucagon of glucose production from pyruvate was abolished during octanoate infusion, although it was still observable during ethanol infusion. In contrast to glucagon, the stimulatory effect of norepinephrine on gluconeogenesis was unaffected by the ratio of lactate to pyruvate. Norepinephrine in the presence of octanoate and ethanol still induced stimulation of glucose production from lactate and pyruvate, which was always accompanied by a transient reduction of pyridine nucleotides. The results demonstrate that the regeneration of NADH in the cytosol is one of the regulatory factors in gluconeogenesis, and that the effects of glucagon and norepinephrine on gluconeogenesis and on the redox state of pyridine nucleotides are not identical.

Animals↗
PubMed1980

Effects of calcium ions on the activation of gluconeogenesis by norepinephrine in perfused rat liver.

The effects of calcium ions on the activation of gluconeogenesis by norepinephrine were studied in the perfused rat liver. The norepinephrine-mediated enhancement of gluconeogenesis was accompanied by a transient increase in the reduction level of pyridine nucleotides. There was a positive correlation between the increases in the rate of glucose production and the reduction level of pyridine nucleotides induced by norepinephrine. These changes were "dose-dependent" with respect to the norepinephrine concentration from 5 nM to 1 muM and were mimicked by phenylephrine. The omission of calcium from the perfusate did not modify the basal rate of gluconeogenesis from lactate and pyruvate or the increased rate of glucose production induced by glucagon and isoproterenol. The extents of the responses to norepinephrine and phenylephrine, however, were decreased markedly in liver perfused with a calcium-free medium and/or with phentolamine. Infusion of calcium into the calcium-deficient liver caused an abrupt elevation of glucose production together with a transient reduction of pyridine nucleotides, and the original extent of the response to norepinephrine was recovered. The data presented provide evidence indicating that stimulation of gluconeogenesis by norepinephrine is mediated through an alpha-adrenergic and calcium-dependent mechanism in which redox changes of mitochondrial pyridine nucleotides are involved.

Animals↗
PubMed1978

Biochemical and ultrastructural evaluation of isolated rat liver systems perfused with a hemoglobin-free medium.

The viability of hemoglobin-free perfused rat liver was examined with respect to several liver functions and to the intactness of subcellular structures under electron microscopic observation. Provided that rat livers were perfused with the oxygenated buffer solution at a flow rate between 3 and 3.5 ml/min per g of liver, all the biochemical parameters measured in the perfused liver system, i.e. the rates of glucose, pyruvate, and lactate production, the rate of oxygen consumption and the tissue contents of adenine nucleotides, were similar to those observed with perfusion systems containing erythrocytes or albumin. The perfused liver showed a sensitive response to norepinephrine, involving a reduction of pyridine nucleotides and enhancements of glucose production and oxygen consumption. On electron microscopic examination, changes in hepatic-structure indicative of hypoxic injury particularly vacuolar degeneration and mitochondrial swelling, were not detected in the liver after 70 min of perfusion; the fact that the fine structure of the hepatocyte was preserved in all parts of the organ confirmed that the supply of oxygen to the perfused liver was sufficient under the conditions employed. From viewpoint of the generally accepted criteria for the viability of perfused liver, therefore, the results confirmed that the perfusion of liver with a hemoglobin- and albumin-free medium is a convenient and reliable tool for biochemical investigation of the reactions occurring in whole liver.

Adenine Nucleotides↗
PubMed1976

Oxidative phosphorylation in brown adipose tissue mitochondria from rats kept under normal environmental conditions.

Based on criteria such as the ADP/O ratio and respiratory control by ADP, the energy-coupling efficiency of brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions for a long time decreased remarkably. The presence of bovine serum albumin, GTP, or ATP plus carnitine in the reaction medium markedly increased the efficiency of oxidative phosphorylation of brown adipose tissue mitochondria. Pre-treatment of brown adipose tissue mitochondria with 2% bovine serum albumin, GTP, or ATP plus carnitine caused a decrease in the amount of free fatty acids bound to the mitochondria from 13.1 to 7.0, 9.0, or 8.2 mug per mg protein, respectively. Removal of the free fatty acids by means of these pre-treatments resulted in restoration of efficient oxidative phosphorylation; there was a correlation between the amount of free fatty acids removed and the degree of recovery in the respiratory control ratio. The elimination of only a fraction of the free fatty acids, as little as 4 mug per mg protein, was sufficient to ensure respiratory control by ADP. It appears that the free fatty acids which lie mainly outside the inner mitochondrial membrane are responsible for the decrease in the efficiency of oxidative phosphorylation in brown adipose tissue mitochondria isolated from rats kept under normal environmental conditions.

Adenosine Diphosphate↗
PubMed1975

Optical measurement of the catalase-hydrogen peroxide intermediate (Compound I) in the liver of anaesthetized rats and its implication to hydrogen peroxide production in situ.

The spectrophotometric determination of the catalase-H2O2 intermediate (Compound I) was extended to the liver in situ in anaesthetized rats. The rate of H2O2 production was determined for the liver in situ with endogenous substrates, and in the presence of excess of glycollate. Glycollate infusion doubled H2O2 production rate in the liver of air-breathing rats, and caused a fourfold increase when rats breathed O2 at 1 times 10(5) Pa. Hyperbaric O2 up to 6 times 10(5) Pa did not increase H2O2 generation supported by endogenous substrates, nor did it increase H2O2 production above that produced by 1 times 10(5) Pa O2 in glycollate-supplemented rats. The rates of ethanol oxidation via hepatic catalase and via alcohol dehydrogenase in the whole body were separately measured. The contribution of hepatic catalase to ethanol oxidation was found to be approx. 10 percent in endogenous conditions and increased to 30 percent or more of the total ethanol oxidation in rats supplemented with glycolate.

Alcohol Oxidoreductases↗