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At least 343 records · Page 19Linked to original sources
PubMed1983

Fasting reduces the response of liver glycogen phosphorylase to physiological levels of epinephrine in rats.

The effect of 24 h fasting on the response of rat liver glycogen phosphorylase activity to an i.v. bolus of 2.75, 5.50 or 22.00 nmol kg-1 of epinephrine was studied. Even the lowest dose increased activity of the a form of the enzyme in the liver of anesthetized, fed rats to approximately 70 - 80% of total enzyme activity two minutes after administration. Further increased epinephrine doses failed to potentiate the enzyme response significantly, but shortened the time necessary for attaining the response, and delayed the return of enzyme activity to control values. No activation of phosphorylase was demonstrable after 2.75 nmol kg-1 of the hormone injected to fasted rats, but after increasing the hormone dose to 5.50 nmol kg-1 the enzyme response was the same as in the corresponding fed group at 2 min, and after administering the highest dose both at 1 and 2 min. According to these results, an increased threshold to epinephrine should be added to the already described effects of fasting, i.e. decreased phosphorylase a and total enzyme activity and shortened response to catecholamines. The efficacy of the i.v. bolus of 5.50 nmol kg-1 of epinephrine in increasing plasma epinephrine level to the theoretical value of 27.5 pmol ml-1 was proven by measuring plasma epinephrine which increased during the first minute after hormone administration to 24.5 + 5.9 pmol ml-1, to decrease during an additional minute with a half life of cca 22.2 seconds.

Animals↗
PubMed2006

Activation of 4-alpha-glucanotransferase activity of porcine liver glycogen debranching enzyme with cyclodextrins.

Glycogen debranching enzyme (GDE) is a single polypeptide chain containing distinct active sites for 4-alpha-glucanotransferase and amylo-alpha-1,6-glucosidase activities. Debranching of phosphorylase limit dextrin from glycogen is carried out by cooperation of the two activities. We examined the effects of cyclodextrins (CDs) on debranching activity of porcine liver GDE using a fluorogenic branched dextrin, Glcalpha1-4Glcalpha1-4Glcalpha1-4(Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-6)Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4GlcPA (B5/84), as a substrate. B5/84 was hydrolyzed by the hydrolytic action of 4-alpha-glucanotransferase to B5/81 and maltotriose. The fluorogenic product was further hydrolyzed by the amylo-alpha-1,6-glucosidase activity to the debranched product, Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4Glcalpha1-4GlcPA (G8PA), and glucose. alpha-, beta- and gamma-CDs accelerated the liberation of B5/81 from B5/84, indicating that the 4-alpha-glucanotransferase activity was activated by CDs to remove the maltotriosyl residue from the maltotetraosyl branch. This led to acceleration of B5/84 debranching. The extent of 4-alpha-glucanotransferase activation increased with CD concentration before reaching a constant value. This suggests that there is an activator binding site and that the binding of CDs stimulates 4-alpha-glucanotransferase activity. In the porcine liver, glycogen degradation may be partially stimulated by the binding of a glycogen branch to this activator binding site.

Animals↗
PubMed1991

An engineered liver glycogen phosphorylase with AMP allosteric activation.

Liver and muscle glycogen phosphorylases, which are products of distinct genes, are both activated by covalent phosphorylation, but in the unphosphorylated (b) state, only the muscle isozyme is efficiently activated by the allosteric activator AMP. The different responsiveness of the phosphorylase isozymes to allosteric ligands is important for the maintenance of tissue and whole body glucose homeostasis. In an attempt to understand the structural determinants of differential sensitivity of the muscle and liver isozymes to AMP, we have developed a bacterial expression system for the liver enzyme, allowing native and engineered proteins to be expressed and characterized. Engineering of the single amino acid substitutions Thr48Pro, Met197Thr and the double mutant Thr48Pro, Met197Thr in liver phosphorylase, and Pro48Thr in muscle phosphorylase, did not qualitatively change the response of the two isozymes to AMP. These sites had previously been implicated in the configuration of the AMP binding site. However, when nine amino acids among the first 48 in liver phosphorylase were replaced with the corresponding muscle phosphorylase residues (L1M2-48L49-846), the engineered liver enzyme was activated by AMP to a higher maximal activity than native liver phosphorylase. Interestingly, the homotropic cooperativity of AMP binding was unchanged in the engineered phosphorylase b protein, and heterotropic cooperativity between the glucose-1-phosphate and AMP sites was only slightly enhanced. The native liver, native muscle and L1M2-48L49-846 phosphorylases were converted to the a form by treatment with purified phosphorylase kinase; the maximal activity of the chimeric a enzyme was greater than the native liver a enzyme and approached that of muscle phosphorylase a. From these results we suggest that tissue-specific phosphorylase isozymes have evolved a complex mechanism in which the N-terminal 48 amino acids modulate intrinsic activity (Vmax), probably by affecting subunit interactions, and other, as yet undefined regions specify the allosteric interactions with ligands and substrates.

Adenosine Monophosphate↗
PubMed1983

[Hormonal activity control of liver glycogen phosphorylases with special reference to their significance within the scope of a stress reaction].

For the mechanism of glycogen metabolism in the liver hormonal action of epinephrine, norepinephrine, glucagon, vasopressin and angiotensin II is of importance. The potential importance of hormonal regulation for interpreting the changes in glycogen metabolism under conditions of stress is underlined. Own results show an acute increase of glycogen phosphorylase activity in stress within 1-2 minutes. 24 hours fasting decreases the sensibility of this enzyme towards the hormonal influence.

Angiotensin II↗
PubMed1983

The actions of dichloroacetic acid on blood glucose, liver glycogen and fatty acid synthesis in obese-hyperglycaemic (ob/ob) and lean mice.

Obese-hyperglycaemic mice and lean mice were injected with dichloroacetate to determine the significance of gluconeogenesis in maintaining the hyperglycaemia of obese mice and to investigate the effects of a fall in blood glucose on fatty acid synthesis. One hour after the second of two, hourly, injections of dichloroacetate the blood glucose concentrations in fed and starved lean mice were decreased, whereas in obese mice they were sharply increased. In obese and lean mice, both fed and starved, dichloroacetate decreased plasma lactate but insulin was unchanged. The quantity of liver glycogen was decreased in all dichloroacetate treated mice, with the largest falls in fed and starved obese mice, which had much larger glycogen stores than lean mice. Dichloroacetate treatment decreased the concentration of plasma non-esterified fatty acids in fed and starved obese mice and fed lean mice but not in starved lean mice. Fatty acid synthesis in white (inguinal, subcutaneous) adipose tissue was stimulated by dichloroacetate in fed obese mice and inhibited in fed lean mice. Fatty acid synthesis in brown adipose tissue (scapular) was faster than in white adipose tissue and was less affected by dichloroacetate although the changes were in the same direction as in white adipose tissue. We attribute the increased hyperglycaemia of obese mice treated with dichloroacetate to increased glycogenolysis coupled with a failure to secrete additional insulin in response to the raised blood glucose. This high blood glucose concentration in dichloroacetate treated obese mice may in turn explain the increased fatty acid synthesis in their white adipose tissue.

Acetates↗
PubMed1977

Hormone control in regeneration: effects of somatostatin on appendage regeneration, blood glucose and liver glycogen in Diemictylus viridescens.

In the present communication, synthetic somatostatin, a hypothalamic factor which has a known inhibitory effect on the release of growth hormone, thyroid-stimulating hormone, prolactin, insulin and glucagon in man and other mammals, was found to have an inhibitory effect on limb and tail regeneration in adult Diemictylus viridescens, when the newts were treated with a daily dose of 3-5 or 15 microgram/animal for a period of 34 days post-amputation. At the higher dose, the animals exhibited total inhibition of appendage regeneration in a few cases and the remainder showed a considerable delay compared to the controls; none of the experimental animals reached the advanced four-digit stage achieved by the controls. Furthermore, the blood glucose and liver glycogen values in the somatostatin-treated animals were significantly lower than the control values. Mechanisms in the storage, mobilization and utilization of glucose (involving hormones) are discussed in relation to appendage regeneration in the newt and possible controls of regeneration at the level of the hypothalamus are suggested.

Animals↗
PubMed1988

A viscous fibre (methylcellulose) lowers blood glucose and plasma triacylglycerols and increases liver glycogen independently of volatile fatty acid production in the rat.

1. Adult male rats were maintained on diets containing 80 g methylcellulose/kg of low (25 cP), medium (400 cP) and high (1500 cP) viscosity. 2. After 10 d, the viscosity of stomach and caecal contents was found to have increased in proportion to that of the dietary fibre. Concentrations of volatile fatty acids in caecal digesta were lowest with the high-viscosity fibre but acetate was the major acid present with all three diets. Acetate was the only acid found in significant quantities in hepatic portal venous plasma and concentrations of this acid were unaffected by diet. 3. Concentrations of glucose in arterial blood were low with the medium- and high-viscosity diets while the content of liver glycogen was high. These effects of fibre were not directly on glucose absorption as the intestines were net removers of the hexose at the time of sampling. 4. Hepatic lipogenesis and plasma triacylglycerol concentrations were both higher in rats fed on the low-viscosity fibre. Plasma cholesterol concentrations, hepatic cholesterol synthesis and faecal bile acid excretion were not altered by dietary fibre viscosity. 5. We conclude that the effects of dietary fibre on carbohydrate absorption and storage and fatty acid synthesis are a function of the viscosity of the fibre in solution, high viscosity slowing the digestion and absorption of nutrients in the small intestine. Large-bowel microbial fermentation is not of direct significance to these events. In contrast, effects of fibre polysaccharides on sterol metabolism seem not to be related to their rheological properties.

Animals↗
PubMed1986

Changes in blood glucose, liver glycogen, ketone bodies and plasma insulin in suckling rats treated with a single high cortisol dose one day after birth.

Rats treated with cortisol, 0.5 mg one day after birth, show a decrease in body and organ weight and a decrease in pituitary TSH and GH when compared to controls together with a lack of response of TSH to TRH. These alterations have been previously found in animals treated with large doses of thyroxine, neo-T4 syndrome, in both populations a brain underdevelopment has been observed. Plasma insulin in cortisol-treated animals was higher (P less than 0.01) than in the controls at 8 and 12 days of life and lower at 22 days (P less than 0.001). Plasma ketone bodies were increased significantly at 8 but not at 12 and 22 days of life in the cortisol treated animals. Liver glycogen was higher than in controls at 2, 4, 6 days of life and lower at 8, 12 and 22 days. Blood glucose was higher than in controls at 2, 4 days and lower at 6, 8, 12 and 22 days of life. The timing of metabolic events is important for the adaptation and development of the post-natal animal. The perturbances in carbohydrate metabolism in suckling rats were also previously found in neo-T4 rats during the period when the brain growth spurt and energy need are the greatest; but in the rats treated with cortisol the timing of the alterations was different. This different timing of the metabolic perturbances could correlate with a different maturation in cerebral tissue found in histological studies in the two populations.

Age Factors↗
PubMed2002

Liver glycogen synthase but not the muscle isoform differentiates between glucose 6-phosphate produced by glucokinase or hexokinase.

Using adenovirus-mediated gene transfer into FTO-2B cells, a rat hepatoma cell line, we have overexpressed hexokinase I (HK I), glucokinase (GK), liver glycogen synthase (LGS), muscle glycogen synthase (MGS), and combinations of each of the two glucose-phosphorylating enzymes with each one of the GS isoforms. FTO-2B cells do not synthesize glycogen even when incubated with high doses of glucose. Adenovirus-induced overexpression of HK I and/or LGS, two enzymes endogenously expressed by these cells, did not produce a significant increase in the levels of active GS and the total glycogen content. In contrast, GK overexpression led to the glucose-dependent activation of endogenous or overexpressed LGS and to the accumulation of glycogen. Similarly overexpressed MGS was efficiently activated by the glucose-6-phosphate (Glc-6-P) produced by either endogenous or overexpressed HK I and by overexpressed GK. These results indicate the existence of at least two pools of Glc-6-P in the cell, one of them is accessible to both isoforms of GS and is replenished by the action of GK, whereas LGS is excluded from the cellular compartment where the Glc-6-P produced by HK I is directed. These findings are interpreted in terms of the metabolic role that the two pairs of enzymes, HK I-MGS in the muscle and GK-LGS in the hepatocyte, perform in their respective tissues.

Adenoviridae↗
PubMed1993

Characterization of the 5' flanking region of the gene encoding rat liver glycogen phosphorylase.

A genomic region encompassing 800 bp of the promoter-regulatory region and exon 1 of the gene (LGP) encoding rat liver glycogen phosphorylase has been isolated and characterized. Transcripts of the LGP gene initiate predominantly within an 8-bp region 48-bp upstream from the start codon. Additional transcripts were detected that initiate as far as 95 bp upstream from the start codon. To identify cis-acting sequences involved in regulating transcription, HepG2 cells were transfected with vectors containing serial deletions of the promoter-regulatory region of LGP ligated to the cat reporter gene. Two upstream regions were found to enhance transcription. One of these regions contains an alternating purine-pyrimidine sequence. LGP, which lacks a consensus TATA sequence, is like TATA-less and CAAT-less housekeeping genes in that it contains G + C-rich domains upstream from multiple transcription start points. Nuclear proteins from adult rat tissues bound in a tissue-specific fashion to one of these G + C-rich regions.

Amino Acid Sequence↗
PubMed2006

Histological changes of liver glycogen storage in mice (Mus musculus) caused by high-protein diets.

High Protein diets (HP) have been popular for people who want to lose weight since the 1960s. Even though these diets do not harm healthy people in the short term, there is insufficient data to support their safe use and efficiency over a long period. Because of the fact that the proteins in these diets are mainly from animal sources, it induces a higher intake of total fat, saturated fat and cholesterol. It is proven that high protein diets cause both physical and pathological abnormalities in the body. However, there exist very few studies about the effects of high protein nutrition on liver glycogen storage. For this study 40 Swiss albino mice consisting of two groups were used. The first group was fed with 25% High Protein; the other was fed with standard meal. The two groups were fed with respect to their diets for 30 days. At the end of 15th, 20th, 25th and 30th days 5 from each group were killed with cervical dislocation. The livers were removed after perfusion then fixated. The routine paraffin pursuit was applied before cutting into 5 micrometer sections and staining with H-E, PAS and silver. There were major differences in weight loss between the first and the fifteenth days. Glycogen storage was significantly reduced in HP (15) stained with PAS. Hydropic degeneration and regenerative activity was observed in H-E and silver stained HP group. As a result for the high protein diet group, weight loss at the 15th day and a significant decrement in glycogen storage at the 30th day was observed.

Animal Feed↗
PubMed1999

Sparing effect of leptin on liver glycogen stores in rats during the fed-to-fasted transition.

The effect of moderate hyperleptinemia ( approximately 20 ng/ml) on liver and skeletal muscle glycogen metabolism was examined in Wistar rats. Animals were studied approximately 90 h after receiving recombinant adenoviruses encoding rat leptin (AdCMV-leptin) or beta-galactosidase (AdCMV-betaGal). Liver and skeletal muscle glycogen levels in the fed and fasted (18 h) states were similar in AdCMV-leptin- and AdCMV-betaGal-treated rats. However, after delivery of a glucose bolus, liver glycogen levels were significantly greater in AdCMV-leptin compared with AdCMV-betaGal rats (P < 0.05). To investigate the mechanism(s) of these differences, glycogen levels were measured immediately after the cessation of a 3- or 6-h glucose infusion or 3, 6, and 9 h after the cessation of a 6-h glucose infusion. Similar increases in liver and skeletal muscle glycogen occurred in hyperleptinemic and control rats in response to glucose infusions. However, 3 and 6 h after the cessation of a glucose infusion, liver glycogen levels were approximately twofold greater (P < 0.05) in AdCMV-leptin-treated compared with AdCMV-betaGal-treated animals. Skeletal muscle glycogen levels were similar in AdCMV-leptin-treated and AdCMV-betaGal-treated animals at the same time points. Glycogen phosphorylase, phosphodiesterase 3B, and glycogen synthase activities were unaltered by hyperleptinemia. We conclude that moderate increases in plasma leptin levels decrease liver glycogen degradation during the fed-to-fasted transition.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Multiple phosphorylation of rat-liver glycogen synthase by protein kinases.

The phosphorylation sites in liver synthase were studied using gel filtration and high performance liquid chromatography of 32P-labeled tryptic peptides. Phosphorylase b kinase, calmodulin-dependent glycogen synthase kinase and glycogen synthase kinase 4 from liver phosphorylated the same low Mr tryptic peptide. cAMP-dependent protein kinase mainly phosphorylated the low Mr tryptic peptide, but also incorporated phosphate into two other peptides. Glycogen synthase kinase 5 phosphorylated a single tryptic peptide, whereas glycogen synthase kinase 3 phosphorylated several tryptic peptides. Calcium-phospholipid-dependent protein kinase phosphorylated two tryptic peptides, the major one of which had the same chromatographic properties as the low Mr peptide described above. These findings confirm that liver glycogen synthase undergoes multi-site phosphorylation and suggest that the topography of the sites is generally similar to that in muscle glycogen synthase.

Animals↗
PubMed1982

The role played by hormonal factors in the rapid activation of liver glycogen phosphorylase in traumatized rats.

In adult male SPF rats anaesthetized with pentobarbital and subjected to traumatization in revolving Noble-Collip drums for 2 min (= 120 revolutions) maximal increases of liver glycogen phosphorylase activity were observed. In experiments on rats with permanent arterial catheters for blood sampling no posttraumatic increase of plasma norepinephrine and an only slight increase of plasma epinephrine was observed if the animals were traumatized under anaesthesia, in contrast to the considerable increases in the plasma level of both hormones in rats subjected to the injury without anaesthesia. Time and extent of the phosphorylase response of anaesthetized rats after trauma were compared with changes in enzyme activity after i.v. administration of exogenous epinephrine or glucagon. A nearly maximal response after 1 microgram kg-1 epinephrine was present within 1 min, whereas after 0.1 micrograms kg-1 of glucagon there was comparable phosphorylase activation 2 min after administration of the hormone. The plasma renin-angiotensin activity was not increased after injury for 2 min under anaesthesia so that only the increase in plasma vasopressin fitted in with the criteria for possible activators of phosphorylase. An additional role of glucagon also cannot be excluded on the basis of data obtained by the present authors. The increase of phosphorylase activity in this type of stress is ensured by several mechanisms. Moreover, the high effectivity of these hormonal factors in evoking the phosphorylase response even without major activation of the sympathicoadrenal system is underlined.

Anesthesia↗