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  • 1
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The inhibition of rat small intestinal cytochrome c oxydase by in vivo administration of chloramphenicol and oxytetracycline has been demonstrated histochemically. Since the dwelling time of newly formed epithelial cells in the crypts of jejunum is 10–14 h, it was surprising to find inhibition of cytochrome c oxydase after 12 h treatment not only in the crypts but also in the villus. These experiments led to the conclusion that cytochrome c oxidase is continuously synthesized, and probably also degraded in the villous cells. Coupling of oxidative phosphorylation is still present after 48 h antibiotic treatment, when the effect on cytochrome c oxydase appeared to be maximal, as judged by the persistance of 2,4-dinitro-phenol-stimulated adenosinetriphosphatase. Finally, prolonged (⩾48 h) antibiotic treatment often led to retraction of connective tissue (which supports the villous epithelial cells), resulting in loosening and loss of cells from the tops of the villi.
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  • 2
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the presence of excess β-glycerophosphate or p-nitrophenylphosphate NADPH diaphorase of the epithelial cell in rat small intestine has its highest activity in the villi at the basis of the microvilli, where smooth endoplasmic reticulum of the cells is present. In the absence of β-glycerophosphate or p-nitrophenylphosphate the diaphorase activity is much higher and broader localized in crypts and villi. The increased activity is due to the conversion of NADPH to NADH by non-specific (mostly alkaline-) phosphatase activity, so that both NADPH and NADH diaphorase activities are measured. When NADPH is generated by a specific NADP+-linked dehydrogenase, such as glucose-6-phosphate dehydrogenase, and nitroblue tetrazolium is present to trap the reducing equivalents formed, the histochemical localization of the dehydrogenase is identical to that of NADPH diaphorase, although the dehydrogenase may be present in another cell compartment (glucose-6-phosphate dehydrogenase for instance has a cytosolic distribution). Therefore the localization of a dehydrogenase may be falsely interpreted histochemically, according to the diaphorase reaction involved. A different localization may be obtained when the diaphorase reaction is circumvented by the addition of an alternative hydrogen carrier, such as phenazine methosulphate. Also in coupled dehydrogenase assays this may be observed. The hexokinase reaction, coupled to the glucose-6-phosphate dehydrogenase reaction in the presence of nitroblue tetrazolium and the absence of phenazine methosulphate, has a distribution identical to NADPH diaphorase. In the presence of phenazine methosulphate the enzyme has an almost ubiquitous distribution in the small intestinal epithelial cell. When a substrate may react both with NADP+- and NAD+-linked dehydrogenases, such as L-malate: NADP oxido-reductase (decarboxylating) and L-malate: NAD oxidoreductase respectively, the high activity of intestinal alkaline phosphatase may influence the histochemical distribution by converting part of NADP+ to NAD+. The addition of another phosphate ester, such a β-glycerophosphate or p-nitrophenylphosphate, may therefore influence the observed distribution.
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  • 3
    ISSN: 1573-7276
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Synvinolin (MK-733), a potent inhibitor of 3-hydroxy-3-methylglutaryl coenzyme-A reductase (HMG-CoA reductase) depressingde novo synthesis of cholesterol, was given to BN472 tumor cells in culture medium, 2 days prior to i.v. injection of the cells into syngeneic rats. Another group of rats received cells cultured under the same conditions but without synvinolin. Two different types of culture medium were used, a ‘complete’ medium (Hybridoma) and a medium (RPMI 1640) to which 1 per cent of fetal calf serum (FCS) was added. Tumor cells cultured in the presence of synvinolin showed significantly lower cholesterol values than untreated cells. Tumor cells treated with synvinolin had a decreased ability to form metastatic nodules when compared with control cells. The results supply further evidence for the suggestion that cholesterol modulates the ability of mononuclear cells to eliminate tumor cells, although it cannot be excluded that alteration of cell growth plays an important role as well.
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  • 4
    ISSN: 1573-4919
    Keywords: lipoprotein lipase ; heart ; endotoxin ; lipopolysaccharide ; tumor necrosis factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Lipopolysaccharide (LPS), the active principle of certain endotoxins, protein-free perfused in rat hearts leads in 3 h to a considerable loss of lipoprotein lipase (LPL) activity. In the presence of albumin LPS has virtually no effect. Tumor necrosis factor (TNF) added instead of LPS had no effects on LPL activity during 3 hin vitro perfusion. LPS injected into rats intravenously leads within 3 h to severe toxic phenomena amongst which increased capillary permeability. This was visualized as increased rate of interstitial fluid formation in Langendorff hearts mounted 3 h after rats had been treated with LPS. LPL activity did not decline in 3 h lasting endotoxemia. Six hours after LPS injection, however, cardiac LPL activity was considerably lowered, although immunoblotting and immunohistochemistry still showed LPL protein to be present. These date indicate the presence of a considerable pool of inactive LPL protein in addition to active LPL, that can be released in the presence of heparin. The LPL activity is lowered by LPS injection after a lag phase of at least 3 h, while capillary endothelial cells are influenced more rapidly. The relatively late expression of TNF toxicity in cardiomyocytes of the intact heart is discussed.
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  • 5
    ISSN: 1573-4919
    Keywords: lipoprotein lipase ; heart ; glucocorticoids ; tumor necrosis factor ; endotoxin ; lipolysis ; glycolysis ; cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Tumor Necrosis Factor (TNF) inhibits lipoprotein lipase activity in cultured myocytes and in the Langendorff rat heart after 3 h perfusion with TNF of glucocorticoid-pretreated rats. TNF acutely stimulates glyc(ogen)olysis and concomitantly endogenous lipolysis. The latter was significantly increased only when rats had been pretreated with glucocorticoid or fed a trierucate-rich diet. Under these conditions, contractile activity of the Langendorff hearts was acutely increased by TNF The mechanism of the actue increase of contractile function and the accompanying increased glycolytic and lipolytic activities, by TNF, may be explained by increased cytosolic Ca2+ and cAMP levels.
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  • 6
    ISSN: 1573-4919
    Keywords: myocardial lipid metabolism ; normoxia ; ischemia ; regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Fatty acids, the preferred substrate in normoxic myocardium, are derived from either exogenous or endogenous triacylglycerols. The supply of exogenous fatty acids is dependent of the rate of lipolysis in adipose tissue and of the lipoprotein lipase activity at the coronary vascular endothelium. A large part of the liberated fatty acids is reesterified with glycerol-3-phosphate and converted to triacylglycerols. Endogenous lipolysis and lipogenesis are intracellular compartmentalized multienzyme processes of which individual hormone-sensitive steps have been demonstrated in adipose tissue. The triacylglycerol lipase is the rate-limiting enzyme of lipolysis and glycerol-3-phosphate acyltransferase and possibly phosphatidate phosphohydrolase are the rate-limiting enzymes of lipogenesis. The hormonal regulation of both processes in heart is still a matter of dispute. Triacylglycerol lipase activity in myocardial tissue has two intracellular sources: 1, the endoplasmic reticular and soluble neutral lipase, and 2. the lysosomal acid lipase. Studies in our laboratory have indicated that whereas lipolysis is enhanced during global ischemia and anoxia, overall lipolytic enzyme activities in heart homogenates were not altered. In addition we were unable to demonstrate alterations in tissue triacylglycerol content and glycerol-3-phosphate acyltransferase activity under these conditions. Lipolysis, is subject to feedback inhibition by product fatty acids. Therefore all processes leading to an increased removal of fatty acids from the catalytic site of the lipase will stimulate lipolysis. These studies will be reviewed. In addition, studies from our department have demonstrated the capacity of myocardial lysosomes to take up and degrade added triacylglycerol-particles in vitro. Such a process, stimulated by Ca2+ and stimulated by acidosis, offers another physiological target for hormone actions.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-7241
    Keywords: propionate ; propionyl-CoA ; propionyl-L-carnitine ; ischemia ; reperfusion ; plasmalemma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This article briefly discusses biochemical reactions involved in the metabolism of propionate, propionylCoA, and propionyl-L-carnitine in the heart. The aim is to understand the way in which propionyl-L-carnitine can exert a protective effect on the ischemic/reperfused heart. The protection of the plasmalemma by propionyl-L-carnitine during acidosis of the heart is also discussed. One protective mechanism is based on the ability of propionate to replenish mitochondria with dicarboxylic acid intermediates of the citric acid cycle and to increase the cellular content of carnitine, both of which may stimulate the generation of energy in the postischemic reperfusion phase. Another mechanism presumes a stabilizing action of acylcarnitines upon biomembranes.
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