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PubMed1981

Histochemistry of glycogen deposition in perinatal rat brain: importance of radial glial cells.

Changes in the glycogen content and patterns of deposition in the developing rat brain were studied using a light microscopic periodic acid-Schiff method on embryonic days (ED) 14, 16, 18, 20 and postnatal days (PD) 1, 3, 7, 12, 16 and 21. Regional and temporal differences were quantified with an automatic image analyser by estimation of stained material in subpial regions of cerebral cortex, thalamus, superior colliculus and medulla. The cellular localization of glycogen particles was investigated by electron microscopy on ED 18, ED 20 and PD 2. On ED 14 the first signs of glycogen storage were found in parts of the immature choroid plexus and in radial glial cells in the midbrain and medullary raphé. With advancing foetal age these structures retained their high capacity for glycogen storage but, in addition, an increasing number of radial fibres in most of the brain stem regions and in the cerebral cortex of older foetuses (ED 18-20) showed significant amounts of glycogen. The storage of glycogen in cerebral cortex was relatively low at all foetal age intervals studied. In new born animals the distribution of glycogen particles was similar to that found in the late foetal brain. A decrease of glycogen content commenced from PD 1 to 3 and reached the pattern of the adult brain between PD 7 and 21. Glycogen storage by radial glial cells in the developing rat brain might indicate their possible role as an energy source in perinatal carbohydrate metabolism.

Animals↗

PubMedDate not supplied

Skeletal muscle glycogen depletion during submaximal exercise in rats with chronic heart failure.

The purpose of the present study was to determine whether or not abnormalities in glycogen utilization occur in the working skeletal muscles of rats with a myocardial infarction (MI) and chronic heart failure (CHF). Accordingly, glycogen concentrations were measured at rest and following 45 min of submaximal swimming in noninfarcted (SHAM) and MI rats. The tissues examined included the liver and the vastus intermedius, plantaris, soleus and the white portions of the gastrocnemius and tibialis anterior muscles of the rat's hindlimb. Results were analyzed by a two-way analysis of variance and demonstrated that the exercise protocol produced a significant amount of glycogen depletion in the liver and the vastus intermedius and plantaris muscles of the SHAM and MI groups of rats. Although the amount of glycogen utilized in the liver was similar between the SHAM and MI groups of rats, the amount of glycogen utilized in the vastus intermedius and plantaris muscle was significantly greater for the MI group of rats when compared to their SHAM counterparts. The results suggest that the glycogen depletion abnormalities found in the working muscles of the MI rat with CHF are related to accelerated rates of glycogen breakdown and utilization. Furthermore, the results also support the contention that these glycogen depletion abnormalities are primarily located in muscles that are primarily oxidative in nature. The mechanisms responsible for these abnormalities in skeletal muscle glycogen utilization during exercise in the MI rat with CHF have yet to be determined.

Animals↗

PubMed2004

Further glycogen decrease during early recovery after eccentric exercise despite a high carbohydrate intake.

BACKGROUND: Delayed onset muscle soreness (DOMS) is a well-known phenomenon of athletes. It has been reported from muscle biopsies that the rate of muscle glycogen resynthesis is reduced after eccentric compared to concentric exercise. AIM OF THE STUDY: Try to compensate by a carbohydrate (CHO)-rich diet the decelerated glycogen resynthesis after eccentric exercise, measured by magnetic resonance spectroscopy. METHODS: Glycogen, phosphocreatine, ATP, and Pi were measured in the human calf muscle. Twenty athletes divided into two groups (DOMS and CONTROL), reduced glycogen in M. gastrocnemius during two different running protocols. Additionally, 12 DOMS subjects performed an eccentric exercise while the CONTROL group rested. Subsequently, subjects consumed a CHO-rich diet (> 10 g/kg body mass/24 h). RESULTS: In both groups, glycogen has been reduced by about 50%. The first 2 h after exercise, glycogen dropped further (-15.6 +/- 15.7 mmol/ kg ww) in the DOMS but rose by +18.4 +/- 20.8 mmol/kg ww in the CONTROL group (P < 0.001). CONTROL subjects reached resting glycogen within 24 h (137 +/- 47 mmol/kg ww), while DOMS subjects needed more than one day (91 +/- 23 mmol/kg ww; P < 0.001). Pi and Pi/PCr, indicators of muscle injury, rose significantly in the DOMS but not in the CONTROL group. CONCLUSION: The diet rich in CHO's was not able to refill glycogen stores after eccentric exercise. Glycogen decreased even further during the beginning of recovery. This loss, which to our knowledge has not been measured before is probably the consequence of muscle cell damage and their reparation.

Adult↗

PubMed1998

Differential responses of brain, liver, and muscle glycogen to opiates and surgical stress.

We examined the effects of intracerebroventricular (ICV) cannula implantation followed by the administration of morphine sulfate (MOR) and its metabolite, morphine-6-glucuronide (M6G), on the glycogen content of the brain, liver, and muscle. ICV cannulation resulted in nearly a 30% reduction in brain glycogen, and ICV MOR resulted in a 36% reduction in liver glycogen content compared to time-matched controls, but it had no additional effect on either the brain or muscle glycogen content. ICV M6G showed a more significant reduction, to 50% of liver glycogen, but it had no effect on either brain or muscle glycogen. Neither IV MOR nor M6G produced any significant alteration in tissue glycogen content. These results indicate that the stress response associated with neurosurgery, especially the placement of the ICV cannula, is associated with a decrement in brain glycogen. The activation of opioid receptors in the brain results in enhanced hepatic glycogenolysis but has no additional effect on the brain glycogen content.

Analgesics, Opioid↗

PubMed1988

Glycogen synthase activation by sugars in isolated hepatocytes.

We have investigated the activation by sugars of glycogen synthase in relation to (i) phosphorylase a activity and (ii) changes in the intracellular concentration of glucose 6-phosphate and adenine nucleotides. All the sugars tested in this work present the common denominator of activating glycogen synthase. On the other hand, phosphorylase a activity is decreased by mannose and glucose, unchanged by galactose and xylitol, and increased by tagatose, glyceraldehyde, and fructose. Dihydroxyacetone exerts a biphasic effect on phosphorylase. These findings provide additional evidence proving that glycogen synthase can be activated regardless of the levels of phosphorylase a, clearly establishing that a nonsequential mechanism for the activation of glycogen synthase occurs in liver cells. The glycogen synthase activation state is related to the concentrations of glucose 6-phosphate and adenine nucleotides. In this respect, tagatose, glyceraldehyde, and fructose deplete ATP and increase AMP contents, whereas glucose, mannose, galactose, xylitol, and dihydroxyacetone do not alter the concentration of these nucleotides. In addition, all these sugars, except glyceraldehyde, increase the intracellular content of glucose 6-phosphate. The activation of glycogen synthase by sugars is reflected in decreases on both kinetic constants of the enzyme, M0.5 (for glucose 6-phosphate) and S0.5 (for UDP-glucose). We propose that hepatocyte glycogen synthase is activated by monosaccharides by a mechanism triggered by changes in glucose 6-phosphate and adenine nucleotide concentrations which have been described to modify glycogen synthase phosphatase activity. This mechanism represents a metabolite control of the sugar-induced activation of hepatocyte glycogen synthase.

Adenine Nucleotides↗

PubMed1990

Appearance of a nonfunctional isozyme of hepatic glycogen synthase in late gestation.

Glycogen levels, glycogen synthase activities, and glycogen synthase protein levels were determined in liver tissues obtained from 14- to 19-day-old fetal mice, newborn mice, and adult mice. The results of these experiments demonstrate a significant increase in the quantity of hepatic glycogen synthase beginning at Day 17 of gestation and reaching adult levels at birth. However, during the same time period, there is a dramatic decrease in total glycogen synthase activity suggesting that the accumulating glycogen synthase molecules are unable to transfer UDP-glucose to glycogen. These inversely coordinated changes in the quantity and activity of glycogen synthase are consistent with the suggestion that glycogen synthesis in the near-term fetal mouse is being maintained by preexisting enzyme, while accumulating enzyme molecules may represent a quiescent isozyme.

Aging↗

PubMed1992

Insulin alters the sensitivity of glycogen synthesis to inhibition by okadaic acid, a protein phosphatase inhibitor.

We investigated the interactions of insulin and okadaic acid, an inhibitor of protein phosphatases type-2A and type-1, on glycogen synthesis in rat, guinea pig and rabbit hepatocytes. Insulin stimulated glycogen synthesis in rat and guinea pig but not in rabbit hepatocytes. In rat and guinea pig hepatocytes, the stimulation of glycogen synthesis by insulin was inhibited by low concentrations of okadaic acid (2.5-5 nM), which did not inhibit glycogen synthesis in the absence of insulin. In rabbit hepatocytes, insulin increased the sensitivity of glycogen synthesis to inhibition by low concentrations of okadaic acid even though it did not stimulate glycogen synthesis, and in the presence of insulin and okadaic acid (5 nM) glycogen synthesis was significantly lower than in the presence of okadaic acid alone. An increase in extracellular pH from 7.4 to 7.8 in a bicarbonate-free buffer, decreased the concentration of okadaic acid causing half-maximal inhibition of glycogen synthesis. It is suggested that an increase in cytosolic pH may be one mechanism by which insulin alters the sensitivity of glycogen synthesis to phosphatase inhibition.

Animals↗

PubMed1988

Respiratory muscle response to load and glycogen content in type I and II fibers.

To study the relation between the response of respiratory muscle to inspiratory loads and glycogen content, we subjected unanesthetized sheep to moderate and severe inspiratory flow resistive (IFR) loads. Only severe IFR loads eventually led to a decrease in transdiaphragmatic pressure (Pdi) and a concomitant rise in PaCO2. Respiratory and nonrespiratory skeletal muscle samples were obtained at necropsy. Glycogen content was determined biochemically in muscle homogenates. Frozen sections were stained with periodic acid-Schiff (PAS) for glycogen and fibers were typed using myosin ATPase stain. Fibers were categorized as full, intermediate, or devoid of glycogen by a subjective scoring system of PAS staining intensity. We found that glycogen content decreased in the costal and crural diaphragm and in the intercostal muscles as the duration of moderate IFR loaded breathing was increased. With severe loads glycogen content decreased significantly, reaching about 40 and 22% of control levels in the costal and crural diaphragm, respectively (P less than 0.01). In addition, with severe IFR loads, a statistically significant proportion of both type I and type II muscle fibers was depleted of glycogen when compared with that of controls (P less than 0.05), but more type II fibers were depleted than type I fibers (50 vs 23%). These data indicate that in sheep subjected to IFR loads: (1) glycogen content in the respiratory muscles decreases as the severity and duration of loaded breathing increases and (2) respiratory muscle fatigue occurs at a time when considerable glycogen is still present in type I fibers in the diaphragm.

Airway Resistance↗

PubMed1985

The hyperglycemic factor of the CNS of the freshwater snail Lymnaea stagnalis: interaction with glucose stimulation of glycogen synthesis and evidence for its release during anaerobiosis.

In the freshwater pulmonate snail Lymnaea stagnalis glycogen synthesis in the glycogen storage cells (GC) is stimulated by increasing external glucose concentrations. On the other hand, a hyperglycemic factor from the CNS inhibits glycogen synthesis and stimulates glycogen breakdown in these cells. This CNS factor may be involved in the physiological control of glycogen mobilization. In the present study the interaction between the inhibiting effect of the CNS factor and the stimulating effect of increasing glucose concentrations on glycogen synthesis in isolated GC was investigated. The results, analyzed by determination of the Michaelis-Menten parameters for saturation kinetics, suggest that the CNS factor increases the glucose concentration required for half-maximal stimulation of glycogen synthesis, but does not influence the maximum rate of synthesis (competitive type of inhibition). The role of the hyperglycemic factor during conditions of glycogen breakdown was investigated by extirpation of the cerebral ganglia (-CG), which contain the main release sites of the factor. Extirpation did not affect the hemolymph glucose concentration or the glycogen levels in the GC during starvation. However, -CG animals showed reduced levels of the hyperglycemia normally associated with exposure to anaerobic conditions.

Anaerobiosis↗

PubMed1992

The metabolic zonation of glycogen synthesis in rat liver after fasting and refeeding.

The quantitative analysis of total glycogen and two fractions of the glycogen content was made by means of cytophotometry in hepatocytes with respect to the portal and central zones of the liver lobule after 48 hr starvation and 15, 30, 60, 120 min after refeeding using the Magiscan image analyzer. It was shown that glycogen content was minimal after 48 hr starvation, although a few cells of the central zone contained a noticeable glycogen quantity. Glycogen synthesis initiation was observed after 15 min refeeding. Glycogen synthesis has been characterized by an increasing glycogen content in the portal zone of the liver lobule compared to the pericentral zone, and this difference increased with time. The distinctive morphological changes were observed in the total glycogen content as well as fractions with different optical density in the process of glycogen synthesis after starvation of rats.

Animals↗

PubMed1994

Receiver operating characteristic analysis of glycogenated nuclei in liver biopsy specimens: quantitative evaluation of their relationship with diabetes and obesity.

Glycogenated hepatocyte nuclei are a common finding in liver biopsy specimens from patients presenting with a variety of clinical disorders. Most commonly, glycogenated nuclei from part of a spectrum of pathological changes in the diabetic or obese patient. However, no previous investigation has assessed glycogenated hepatocyte nuclei in a quantitative manner. In this study we used receiver operating characteristic (ROC) analysis to assess quantitatively the strength of glycogenated nuclei as a marker for diabetes and/or obesity. The study population consisted of 102 liver biopsy specimens from the adult population: 20 from diabetic patients, 41 from obese patients, 10 from both obese and diabetic patients, and 31 from neither diabetic nor obese patients. The mean age was 48.5 years with a range of 18 to 80 years. We evaluated the extent of glycogenated nuclei by averaging the number present per high power field over a minimum of 10 high power fields, representing all zones of the liver. The extent of steatosis was graded on a numerical scale from 1 to 10. In ROC analysis perfect tests are associated with an area of 1.0 and completely random tests with an area of 0.5. Receiver operating characteristic analysis showed that glycogenated nuclei are a relatively good test for distinguishing diabetic from nondiabetic patients (area, 0.75), a poor test for distinguishing obese from nonobese patients (area, 0.60), and a fair test for either condition (area, 0.67). In addition, we observed that glycogenated nuclei were preferentially distributed in the periportal "zone 1" of the liver, showed no correlation with steatosis, and had no relation to patient age. For our patient study population the prevalence of diabetes mellitus was 12%. At a cutoff level of four glycogenated nuclei per 400 x high power field, the specificity and sensitivity of glycogenated nuclei as a test for diabetes are 0.98 and 0.30, respectively, with a positive predictive value of 66%.

Adult↗

PubMedDate not supplied

The structure of placental glycogen.

Glycogen was purified from human term placenta and its structural features investigated. The beta-amylolysis limit and average chain lengths indicated that some degradation of the glycogen had occurred prior to its extraction. The sedimentation coefficient distribution of the purified glycogen showed that it contained a significant proportion of aggregated material. Diffusion coefficient measurements allowed calculation of the molecular weight distribution. The placental glycogen contained a significant proportion of high molecular weight material, although not as much as liver or skeletal muscle glycogens. Because the high molecular weight glycogen of liver and skeletal muscle is associated with the lysosome it is likely that this is also true of the large placental glycogen. Lysosomal glycogen is degraded hydrolytically to glucose and so placental glycogen may be involved in fetal glucose homeostasis.

Chemical Phenomena↗

PubMed1984

Glycogen, its transient occurrence in neurons of the rat CNS during normal postnatal development.

Progressive changes in the postnatal incidence, distribution and duration of glycogen in neurons of the pons, medulla and spinal cord were studied by light and electron microscopy using cytochemical and quantitative methods. Albino rats of 11 ages ranging from newborn to adult were used for this investigation. Methacrylate sections, stained with periodic acid-Schiff-dimedone (PAS) were surveyed to identify nerve cell groups containing the polysaccharide, glycogen. The PAS reaction was positive in neuronal cell groups of the hypoglossal nucleus, the mesencephalic nucleus of V, nucleus ambiguus, the abducens nucleus, the facial motor nucleus and anterior horn cells of the spinal cord. The intensity and duration of the PAS reaction appeared greatest in the hypoglossal nucleus. Neurons of the mesencephalic nucleus of V demonstrated a reaction of moderate intensity and duration. The remaining nerve cell groups exhibited a weak, diffuse reaction of brief duration. Postnatal differences in the incidence and patterns of disposition of glycogen were quantified using ultrathin sections of the hypoglossal nucleus, the site richest in glycogen. The presence of glycogen was verified by the periodic acid-thiosemicarbizide-silver proteinate (PA-TSC-SP) ultracytochemical stain. The incidence of glycogen in neuronal perikarya of hypoglossal nuclei was related to age. All neurons contained some glycogen during the first postnatal week. By 24 days postnatal (dpn), the majority of hypoglossal neurons lacked glycogen and all neurons of adult rats were glycogen-free.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1983

Stereospecific effects of (+)- and (-)-catechin on glycogen metabolism in isolated rat hepatocytes.

(+)- and (-)-catechin showed opposite effects on glycogen metabolism in isolated rat hepatocytes. Addition of 0.5 mM catechin to hepatocytes from fasted rats resulted in the case of the (+)-isomer in a 90% stimulation and the case of the (-)-isomer in a 90% inhibition of net glycogen production. When 0.5 mM of the two isomers were added to hepatocytes from fed rats, (+)-catechin inhibited glycogenolysis by 33%, whereas the (-)-isomer stimulated the same process by 42%. At equal concentrations, the effects of (-)-catechin were stronger than those of the (+)-isomer. (-)-Epicatechin acted in a manner similar to (+)-catechin; however, the effect was less pronounced. (+)-Catechin antagonized the inhibitory action of suboptimal doses of glucagon on glycogen production whereby no change in basal or glucagon-elevated cyclic AMP level was observed. The activities of glycogen synthase a and glycogen phosphorylase a were changed by (+)- and (-)-catechin in a way corresponding to the changes in glycogen production and breakdown. (-)-Catechin, however, stimulated the activities of both glycogen synthase a and glycogen phosphorylase a in hepatocytes from fed rats. A possible interaction of the flavonoids or of their metabolites with glycogen phosphorylase is discussed.

Animals↗

PubMed1996

Incorporation of 2-deoxy-D-glucose into glycogen. Implications for measurement of tissue-specific glucose uptake and utilisation.

Estimation of glucose uptake in vivo using 2-deoxy-D-[2,6-3H]glucose (2DG) relies upon the assumption that the phosphorylated form, 2-deoxy-D-2,6-3H]glucose 6-phosphate (2DGP), cannot be further metabolised. We aimed to determine whether this assumption leads to underestimation of glucose uptake due to the incorporation of 2DGP into glycogen. Rats were infused with [U-14C]glucose and 2-[3H]DG, and the incorporation into glycogen was measured. These were compared to the accumulation of 2-[3H]DGP in heart, liver, muscle, white adipose tissue and brown adipose tissue. 2DG was incorporated into glycogen in an insulin-dependent manner (e.g. in soleus, at basal, physiological and supraphysiological insulin concentrations, glycogen synthesis rates from 2DG were 17.81 +/- 3.07, 64.47 +/- 7.47 and 203.23 +/- 44.52 nmol glycogen incorporated/g min-1, respectively). The rate of glycogen synthesis from 2-[3H]DG was identical to that for [U-14C]glucose in all tissues studied except for heart and brown adipose tissue (e.g. in soleus at physiological insulin concentration, 2-[3H]DG incorporation was 64.47 +/- 7.47 and [U-14C]glucose incorporation was 61.87 +/- 7.56 nmol glucose/g min-1). Furthermore, the proportion of 2DG incorporated into glycogen was significant with respect to total glucose uptake at all plasma insulin concentrations (10.7% +/- 0.9, 14.0 +/- 1.9 and 25.6% +/- 5.6 at basal, physiological and supraphysiological insulin concentrations, respectively). 2DG was metabolised to glycogen in all tissues studied causing an underestimation of the rate of glucose uptake by measurement of 2DGP accumulation alone. In addition, use of 2DG could provide a method for assessing the rate of direct glycogen synthesis in the rat.

Adipose Tissue↗

PubMed2006

Interaction between glycogenin and glycogen synthase.

Glycogen synthase plays a key role in regulating glycogen metabolism. In a search for regulators of glycogen synthase, a yeast two-hybrid study was performed. Two glycogen synthase-interacting proteins were identified in human skeletal muscle, glycogenin-1, and nebulin. The interaction with glycogenin was found to be mediated by the region of glycogenin which contains the 33 COOH-terminal amino acid residues. The regions in glycogen synthase containing both NH2- and COOH-terminal phosphorylation sites are not involved in the interaction. The core segment of glycogen synthase from Glu21 to Gly503 does not bind COOH-terminal fragment of glycogenin. However, this region of glycogen synthase binds full-length glycogenin indicating that glycogenin contains at least one additional interacting site for glycogen synthase besides the COOH-terminus. We demonstrate that the COOH-terminal fragment of glycogenin can be used as an effective high affinity reagent for the purification of glycogen synthase from skeletal muscle and liver.

Binding Sites↗

PubMed2005

Glycogen phosphorylase reactivity in the entorhinal complex in familiar and novel environments: evidence for labile glycogenolytic modules in the rat.

Active and total glycogen phosphorylase were measured histochemically in the entorhinal complex of male Sprague-Dawley rats. Rats were sacrificed from their home cage, or after 5 min in a novel holeboard. Hemispheres from each group were paired, sectioned and processed together. Glycogen phosphorylase reactivity highlighted entorhinal cortex in contrast to less densely stained perirhinal cortex or neocortex. The presubiculum, but not parasubiculum, was strongly reactive for glycogen phosphorylase. Within medial and lateral entorhinal cortex, modularity of active glycogen phosphorylase reactivity was apparent. In inner Layer I there were small ( approximately 50 microm) intense patches of active glycogen phosphorylase. In Layer III there were both small and larger ( approximately 200 microm), patches of active glycogen phosphorylase. Lamina dessicans was reactive. Layers V and VI were relatively unreactive. Exposure to a holeboard intensified the small patches of active glycogen phosphorylase in inner Layer I, while attenuating active glycogen phosphorylase reactivity in Layer III. Total glycogen phosphorylase was unaffected by exposure to the novel environment and exhibited a pattern of continuous dense reactivity suggesting enzyme reserves, particularly in superficial layers of entorhinal cortex. These patterns confirm earlier evidence that glycogenolytic demand in Layers I and III of rat entorhinal cortex is organized in a modular fashion and show that such demand can be modified by brief exposure to a novel holeboard.

Animals↗

PubMed2004

Energy transfer from astrocytes to axons: the role of CNS glycogen.

We tested the hypothesis that astrocytic glycogen supports axon function under both pathological and physiological conditions. Functional activity of the rat (RON) or mouse optic nerve (MON), representative central white matter tracts, was assessed electrophysiologically as the area under the supramaximal compound action potential (CAP). During aglycaemia the CAP area of rodent optic nerve persisted for up to 30 min, after which the CAP rapidly failed. Glycogen content measured biochemically during the aglycaemic insult fell with a time course compatible with its rapid degradation in the absence of glucose. Pharmacological up-regulation of glycogen content prior to the aglycaemic insult with incubation in hyperglycaemic ambient glucose delayed CAP failure, whereas down-regulation of glycogen content induced by nor-adrenaline accelerated CAP failure. Inhibiting lactate transfer between astrocytes and axons during aglycaemia, where glycogen is the only utilisable energy reserve, resulted in accelerated CAP failure, implying that glycogen-derived lactate supports function when exogenous energy metabolites are withdrawn. Under normoglycaemic conditions glycogen content decreased during high frequency axon discharge, although CAP function was fully maintained. Both prior depletion of glycogen content, or blocking axonal lactate uptake rendered nerves incapable of fully supporting CAP function during high frequency firing in the presence of normoglycaemic glucose. These results indicated that during aglycaemia and increased metabolic demand, astrocytic glycogen was degraded to form lactate, which was used as a supplemental energy source when ambient normoglycaemic glucose was incapable of meeting immediate tissue energy demands.

Action Potentials↗