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1.
Pathol Res Pract ; 202(9): 631-8, 2006.
Article in English | MEDLINE | ID: mdl-16781826

ABSTRACT

Glycogen autophagy, the sequestration and degradation of cell glycogen in the autophagic vacuoles, is a selective, hormonally controlled and highly regulated process, representing a mechanism of glucose homeostasis under conditions of demand for the production of this sugar. In the newborn animals, this process is induced by glucagon secreted during the postnatal hypoglycemia and inhibited by insulin and parenteral glucose, which abolishes glucagon secretion. Hormonal action is mediated by the cAMP/protein kinase A (induction) and phosphoinositides/mTOR (inhibition) pathways that converge on common targets, such as the protein phosphatase 2A to regulate autophgosomal glycogen-hydrolyzing acid glucosidase and glycogen autophagy. Intralysosomal phosphate exchange reactions, which are affected by changes in the calcium levels and acid mannose 6- and acid glucose 6-phosphatase activities, can modify the intralysosomal composition in phosphorylated and nonphosphorylated glucose and promote the exit of free glucose through the lysosomal membrane. Glycogen autophagy-derived nonphosphorylated glucose assists the hyaloplasmic glycogen degradation-derived glucose 6-phosphate to combat postnatal hypoglycemia and participates in other metabolic pathways to secure the fine tuning of glucose homeostasis during the neonatal period.


Subject(s)
Autophagy/physiology , Glucose/metabolism , Glycogen/metabolism , Growth and Development/physiology , Homeostasis/physiology , Animals , Animals, Newborn , Humans , Infant, Newborn
2.
Histol Histopathol ; 20(3): 689-96, 2005 07.
Article in English | MEDLINE | ID: mdl-15944916

ABSTRACT

The effects of glucagon, adrenalin or rapamycin on glycogen autophagy in the liver and heart of newborn rats were studied using biochemical determinations and electron microscopy. Glucagon or adrenalin increased autophagic activity in the hepatocytes and myocardiocytes, glycogen-hydrolyzing acid glucosidase activity in the liver and heart and degradation of glycogen inside the autophagic vacuoles. Glucagon or adrenalin also increased the maltose-hydrolyzing acid glucosidase activity in the liver, but not in the heart. Similar effects were produced in the newborn heart by rapamycin. These observations support previous studies suggesting that the cellular machinery which controls glycogen autophagy in the liver and heart of newborn animals, is regulated by the cyclic AMP and the mTOR pathways.


Subject(s)
Autophagy/drug effects , Glycogen/metabolism , Liver/metabolism , Myocardium/metabolism , Animals , Animals, Newborn , Epinephrine/pharmacology , Female , Glucagon/pharmacology , Heart/drug effects , Hepatocytes/drug effects , Hepatocytes/metabolism , Hepatocytes/ultrastructure , Liver/drug effects , Liver Glycogen/metabolism , Microscopy, Electron , Myocytes, Cardiac/drug effects , Myocytes, Cardiac/metabolism , Myocytes, Cardiac/ultrastructure , Pregnancy , Rats , Rats, Wistar , Sirolimus/pharmacology
3.
Microsc Res Tech ; 63(4): 215-9, 2004 Mar 01.
Article in English | MEDLINE | ID: mdl-14988919

ABSTRACT

The effects of rapamycin on glycogen autophagy in the newborn rat liver were studied using biochemical determinations, electron microscopy, and morphometric analysis. Rapamycin increased the fractional volume of hepatocytic autophagic vacuoles, the liver lysosomal glycogen-hydrolyzing activity of acid glucosidase, the degradation of glycogen inside the autophagic vacuoles, and decreased the activity of acid mannose 6-phosphatase. These findings suggest that rapamycin, a known inhibitor of the mammalian target of rapamycin (mTOR) signaling, induces glycogen autophagy in the newborn rat hepatocytes. mTOR may participate in the regulation of this process.


Subject(s)
Autophagy/drug effects , Immunosuppressive Agents/pharmacology , Liver Glycogen/metabolism , Liver/drug effects , Sirolimus/pharmacology , Animals , Animals, Newborn , Liver/metabolism , Liver/ultrastructure , Microscopy, Electron , Rats
4.
Microsc Res Tech ; 63(2): 87-93, 2004 Feb 01.
Article in English | MEDLINE | ID: mdl-14722905

ABSTRACT

The effects of glucagon on the ultrastructural appearance and acid glucosidase activities in the liver and heart of newborn rats were studied. Liver or heart glycogen-hydrolyzing activity of acid glucosidase increased 3 hours after birth and gradually decreased from 3 to 9 hours. Maltose-hydrolyzing activity of acid glucosidase also rose 3 hours after birth, maintained a plateau between 3 and 6 hours, and fell at 9 hours. The administration of glucagon increased autophagic activity in the hepatocytes at the age of 6 hours. Glycogen inside the autophagic vacuoles was decreased, apparently due to the increased glycogen degradation. Glycogen-hydrolyzing activity was elevated in both the liver and the heart. Maltose-hydrolyzing activity was elevated in the liver, but not in the heart. The results of this study suggest that the glycogen-hydrolyzing and maltose-hydrolyzing activities of acid glucosidase are due to different enzymes. Glucagon's effect on the glycogen-hydrolyzing acid glucosidase activity and autophagosomal morphology is similar in both the liver and the heart.


Subject(s)
Autophagy/drug effects , Glucagon/pharmacology , Glycogen/metabolism , Liver/metabolism , Myocardium/metabolism , Protein Synthesis Inhibitors/pharmacology , Animals , Animals, Newborn , Glucosidases/metabolism , Heart/drug effects , Heart/physiology , Hepatocytes/drug effects , Hepatocytes/metabolism , Hepatocytes/ultrastructure , Liver/drug effects , Liver/ultrastructure , Maltose/metabolism , Microscopy, Electron , Myocardium/ultrastructure , Rats , Time Factors
5.
Morphologie ; 88(283): 176-8, 2004 Dec.
Article in English | MEDLINE | ID: mdl-15693419

ABSTRACT

The localization of acid mannose 6-phosphatase activity in newborn rat hepatocytes was demonstrated at the electron microscopic level by using a histochemical method based on the work of Robinson and Karnovsky. Reaction product was virtually restricted to the lysosomes. Most of them exhibited various grades of reactivity. Some were devoid of activity. Our observations suggested that this histochemical method could be used to differentiate distinct subpopulations of lysosomes on the basis of their acid mannose 6-phosphatase activity.


Subject(s)
Hepatocytes/enzymology , Lysosomes/enzymology , Phosphoric Monoester Hydrolases/metabolism , Animals , Animals, Newborn , Histocytochemistry , Kinetics , Rats , Rats, Wistar
6.
Histol Histopathol ; 18(4): 1103-13, 2003 10.
Article in English | MEDLINE | ID: mdl-12973679

ABSTRACT

Peritoneal and bronchoalveolar macrophages activated in vitro by endotoxin, exhibit alterations in the acid phosphatase activity of cell lysates when certain hormones or autacoids are present in the culture medium. They also show morphological changes concerning general appearance and acid phosphatase cytochemistry. Certain agents known to increase the intracellular levels of cyclic AMP, such as dopamine and prostaglandin E2, decreased this enzyme activity in the lysates of peritoneal macrophages. Adrenalin had no effect on this activity at 14 hours, but was found to increase the activity in the culture medium at the initial hours of incubation. Glucagon decreased whereas insulin increased acid phosphatase activity in bronchoalveolar macrophages. Serotonin or histamine, known to activate phospholipase C, increased this activity in peritoneal or bronchoalveolar macrophages. The results of this study, taken together with previously published data (Kondomerkos et al., 2003), suggest that hormones and autacoids may control certain parameters of macrophage activation including acid phosphatase activity.


Subject(s)
Acid Phosphatase/metabolism , Autacoids/pharmacology , Endotoxins/pharmacology , Hormones/pharmacology , Macrophages, Alveolar/enzymology , Macrophages, Peritoneal/enzymology , Acid Phosphatase/antagonists & inhibitors , Animals , Cells, Cultured , Coloring Agents , Culture Media , Cyclic AMP/physiology , Enzyme Inhibitors/pharmacology , Female , Hematoxylin , Hydrogen Peroxide/metabolism , In Vitro Techniques , Lipopolysaccharides/pharmacology , Macrophage Activation/drug effects , Macrophages, Alveolar/drug effects , Macrophages, Alveolar/ultrastructure , Macrophages, Peritoneal/drug effects , Macrophages, Peritoneal/ultrastructure , Male , Rats , Rats, Wistar , Type C Phospholipases/physiology
7.
Histol Histopathol ; 18(3): 811-8, 2003 07.
Article in English | MEDLINE | ID: mdl-12792893

ABSTRACT

The effects of propranolol on the glycogen autophagy in newborn rat hepatocytes were studied by using biochemical determinations, electron microscopy and morphometric analysis. Propranolol lowered the liver cyclic AMP and cyclic AMP-dependent protein kinase activity. It also decreased the formyl-methionyl-leucyl-phenylalanine (FMLP)-inhibitable Ca2+-ATPase activity including lysosomal calcium uptake pump. The normal postnatal increase in the volume of autophagic vacuoles and the activity of acid glycogen-hydrolyzing alpha glucosidase were inhibited. Also, the degradation of glycogen inside the autophagic vacuoles was apparently inhibited. The activity of acid mannose 6-phosphatase was increased. These findings indicate that propranolol influences several steps in the sequence of events leading to the breakdown of glycogen in the autophagic vacuoles of newborn rat hepatocytes. This supports our previous studies suggesting that cyclic AMP regulates glycogen autophagy.


Subject(s)
Glycogen/metabolism , Hepatocytes/metabolism , Propranolol/pharmacology , Adenosine Triphosphatases/metabolism , Adrenergic beta-Antagonists/pharmacology , Animals , Animals, Newborn , Autophagy , Biochemical Phenomena , Biochemistry , Cells, Cultured , Cyclic AMP/metabolism , Cyclic AMP-Dependent Protein Kinases/metabolism , Immunohistochemistry , Liver/metabolism , Microscopy, Electron , Phosphoric Monoester Hydrolases/metabolism , Rats , Time Factors , alpha-Glucosidases/metabolism
8.
Histol Histopathol ; 18(1): 55-65, 2003 01.
Article in English | MEDLINE | ID: mdl-12507284

ABSTRACT

Peritoneal macrophages activated in vitro by endotoxin exhibit alterations of their capability to produce hydrogen peroxide after phorbol ester stimulation when certain hormones or autacoids are present in the culture medium. They also show morphological changes, mainly concerning cell size and nuclear appearance. Agents known to increase the intracellular levels of cyclic AMP, e.g. adrenalin and PGE2 reduce the hydrogen peroxide production. Insulin, which is known to decrease cyclic AMP levels, produces opposite results. Agents postulated to act via phospholipase C, e.g. serotonin, augment the production of hydrogen peroxide. We assume that this form of modulation may represent a regulatory mechanism of macrophage activation.


Subject(s)
Autacoids/pharmacology , Hormones/pharmacology , Hydrogen Peroxide/metabolism , Macrophage Activation/drug effects , Macrophages, Peritoneal/drug effects , Animals , Cells, Cultured , Dexamethasone/pharmacology , Dinoprostone/pharmacology , Dopamine/pharmacology , Epinephrine/pharmacology , Glucagon/pharmacology , Insulin/pharmacology , Lipopolysaccharides/pharmacology , Macrophages, Peritoneal/cytology , Macrophages, Peritoneal/metabolism , Rats
9.
Microsc Res Tech ; 57(6): 507-11, 2002 Jun 15.
Article in English | MEDLINE | ID: mdl-12112433

ABSTRACT

The effects of agents that could manipulate the lysosomal calcium such as phorbol myristate acetate, ionophore A23187, and phentolamine on the lysosomal glycogen degradation were studied by electron microscopy, morphometric analysis, and biochemical assays in newborn rat hepatocytes. Phorbol myristate acetate, which promotes the input of calcium to lysosomes, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid alpha 1,4 glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles and also decreased the activity of acid mannose 6-phosphatase. Ionophore A23187, which releases lysosomal calcium, produced opposite results in these enzyme activities. Phentolamine, an alpha-adrenergic blocking agent which interferes with the generation of phosphoinositides and may activate the lysosomal calcium uptake pump, increased the total volume of autophagic vacuoles and the activity of lysosomal glycogen-hydrolyzing acid glucosidase and decreased the fractional volume of undigested glycogen inside the autophagic vacuoles. The results of this study constitute evidence that changes in lysosomal calcium may influence certain aspects of autophagy, including the degradation of glycogen inside the autophagic vacuoles. They also support our previous postulate [Kalamidas and Kotoulas (2000a,b) Histol Histopathol 15:29-35, 1011-1018] that stimulation of autophagic mechanisms in newborn rat hepatocytes may be associated with acid mannose 6-phosphatase activity-deficient lysosomes.


Subject(s)
Autophagy/drug effects , Calcimycin/pharmacology , Glycogen/metabolism , Ionophores/pharmacology , Phentolamine/pharmacology , Tetradecanoylphorbol Acetate/pharmacology , Animals , Animals, Newborn , Calcimycin/administration & dosage , Cells, Cultured , Cyclic AMP/administration & dosage , Hepatocytes/drug effects , Hepatocytes/metabolism , Hepatocytes/ultrastructure , Ionophores/administration & dosage , Liver/cytology , Lysosomes/metabolism , Microscopy, Electron , Phentolamine/administration & dosage , Rats , Rats, Wistar
10.
Histol Histopathol ; 15(4): 1011-8, 2000 10.
Article in English | MEDLINE | ID: mdl-11005224

ABSTRACT

Glycogen autophagy in newborn rat hepatocytes was studied by using enzyme determinations and electron microscopy. Cyclic AMP induced glycogen autophagy in these cells. Glycogen-hydrolyzing acid glucosidase activity increased whereas acid mannose 6-phosphatase activity decreased in the liver of these animals. Parenteral glucose, which prevents postnatal glucagon secretion and tissue cyclic AMP elevation, and propranolol which antagonizes cyclic AMP, inhibited glycogen autophagy. Glucosidase activity decreased and phosphatase activity increased. These findings raise the possibility that cyclic AMP-induced autophagic mechanisms in newborn rat hepatocytes are associated with changes in the activity of acid mannose 6-phosphatase.


Subject(s)
Hepatocytes/metabolism , Liver Glycogen/metabolism , Animals , Animals, Newborn , Cyclic AMP/metabolism , Glucosidases/metabolism , Hepatocytes/enzymology , Hepatocytes/ultrastructure , Microscopy, Electron , Phosphoric Monoester Hydrolases/metabolism , Rats , Rats, Wistar , Tissue Fixation
11.
Histol Histopathol ; 15(1): 29-35, 2000 01.
Article in English | MEDLINE | ID: mdl-10668192

ABSTRACT

The effects of hydrocortisone on newborn rat liver were studied by using biochemical assays, electron microscopy and quantitative morphometry. Hydrocortisone increased the number of lysosomes in the hepatocytes. Most of the lysosomes represented glycogen-containing autophagic vacuoles. The glucocorticoid also increased the activity of the liver glycogen-hydrolyzing acid glucosidase and the breakdown of glycogen inside lysosomes. The activity of the liver acid mannose 6-phosphatase was decreased. This may be related to the stimulation of autophagic mechanisms in the newborn rat hepatocytes.


Subject(s)
Hydrocortisone/pharmacology , Liver Glycogen/metabolism , Liver/metabolism , Lysosomes/metabolism , Animals , Animals, Newborn , Autophagy , Dactinomycin/pharmacology , Ethionine/pharmacology , Glucosidases/metabolism , Liver/drug effects , Liver/ultrastructure , Lysosomes/drug effects , Lysosomes/ultrastructure , Phosphoric Monoester Hydrolases/metabolism , Rats , Rats, Wistar , Vacuoles/metabolism , Vacuoles/ultrastructure
12.
Histol Histopathol ; 14(1): 23-30, 1999 01.
Article in English | MEDLINE | ID: mdl-9987646

ABSTRACT

The lysosomal glucosidase activities and glycogen degradation in newborn rat liver were studied by using biochemical assays, electron microscopy and quantitative morphometry. Glycogen-hydrolyzing, maltose-hydrolyzing and isomaltose-hydrolyzing activities were low at birth but increased afterwards. At the age of 6 hours they were markedly elevated. Actinomycin prevented the development of glucosidase activities indicating that these depend on protein synthesis. Parenteral glucose inhibited all three activities. This was apparently due to the abolition of normal postnatal hypoglycemia and the need for blood glucose. Cyclic AMP increased the glycogen-hydrolyzing but not the maltose-hydrolyzing activity. Propranolol inhibited the glycogen-hydrolyzing but not the maltose-hydrolyzing activity. The observations of this study provide further support for the hypothesis made by previous investigators that these activities are due to different enzymes.


Subject(s)
Glucan 1,4-alpha-Glucosidase/metabolism , Glycogen/metabolism , Liver/enzymology , Oligo-1,6-Glucosidase/metabolism , alpha-Glucosidases/metabolism , Animals , Animals, Newborn , Female , Hydrolysis , Isomaltose/metabolism , Liver/cytology , Lysosomes/metabolism , Maltose/metabolism , Rats , Rats, Wistar
13.
Histol Histopathol ; 9(4): 691-8, 1994 Oct.
Article in English | MEDLINE | ID: mdl-7894141

ABSTRACT

The effects of parenteral glucose, cyclic AMP and caffeine on the breakdown of glycogen in the lysosomes of newborn rat hepatocytes, were studied by using biochemical assays, electron microscopy and quantitative morphometry. Glucose prevented the normal postnatal increase in lysosomal volume, acid alpha 1,4 glucosidase activity and lysosomal glycogen breakdown. On the contrary, cyclic AMP and caffeine promoted this increase. There was a positive correlation between liver cyclic AMP concentration and acid glucosidase activity (R = 0.84, p < 0,001). Cyclic AMP also induced a change in the shape of lysosomes. The postulation that glucagon secreted after birth is the natural stimulus for the cyclic AMP-mediated postnatal increase in acid glucosidase activity and mobilization of the lysosomal glycogen in rat hepatocytes, is supported by these experimental findings.


Subject(s)
Liver Glycogen/metabolism , Liver/metabolism , Animals , Animals, Newborn , Blood Glucose/metabolism , Caffeine/pharmacology , Cyclic AMP/metabolism , Cyclic AMP/pharmacology , Glucose/pharmacology , In Vitro Techniques , Liver/drug effects , Liver/ultrastructure , Lysosomes/drug effects , Lysosomes/metabolism , Lysosomes/ultrastructure , Microscopy, Electron , Rats , Rats, Wistar , alpha-Glucosidases/metabolism
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