Effect of prostaglandin E 1 administration on the liver glycogen synthetase and phosphorylase systems.
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Adrenal Glands↗
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[The effect of rostromedial coagulation of the hypothalamus on oxygen uptake, rectal temperature, heat transfer, blood sugar, muscle and liver glycogen as well as on chemical thermogenesis in young albino rats].
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Animals↗
The influence of sialoadenectomy, thymectomy and starvation on liver glycogen in the rat.
Hepatic glycogen was assayed in young and adult rats subjected to sialoadenectomy and/or thymectomy and starvation. Sialoadenectomy in young, but not in adult rats caused the rats to stop feeding. In young, but not in adult sialoadenectomized and starved rats the glycogen level was notably higher than in unoperated and starved rats, indicating active participation of salivary glucagon in immature animals in hepatic glycogenolysis under conditions of starvation. Simultaneous sialoadenectomy and thymectomy caused glycogen depletion in the liver of young rats in spite of the absence of the salivary glands. Acceleration of glycogenolysis in these rats was not due to thymectomy, being probably a result of excessive secretion of adrenal catecholamines.
Animals↗
Properties and regulation of liver glycogen phosphorylase phosphatase.
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Adenosine Triphosphate↗
Changes in the blood glucose and liver glycogen contents of healthy and trypanosome infected fish, Clarias batrachus, following intramuscular injection of glucose solution.
Changes in the blood glucose and liver glycogen contents in healthy and trypanosome infected fish Clarias following the intramuscular injection of glucose solution showed a rise in both the parameters within an hour. Peak levels were obtained almost simultaneously by the 2 groups in both the tissues. However, there was a rapid rise and an equally rapid decline of increased carbohydrate contents in the trypanosome infected fishes. This is attributed to the rapid consumption of sugars by the trypanosomes in diseased fish, besides replenishment of sugar reserves of various body tissues from the liver via blood.
Animals↗
Biochemical effects of diquat and paraquat. Disturbance of the control of corticosteroid synthesis in rat adrenal and subsequent effects on the control of liver glycogen utilization.
1. Administration of diquat (NN'-ethylene-2,2'-bipyridilium) or paraquat (NN'-dimethyl-4,4'-bipyridilium) prevents the normal depletion of liver glycogen in starved rats. 2. There is an increase in blood glucose, which returns to normal values after approx. 7h. 3. After administration of diquat or paraquat, plasma corticosteroids increase to very high concentrations and remain high for at least 24h, but plasma ACTH (adrenocorticotrophin) is only increased for 4h. 4. Adrenal cyclic AMP is considerably increased after administration of diquat and remains significantly higher than control values for at least 24h. 5. It is suggested that diquat and paraquat increase the response of the adrenal cortex to ACTH.
Adrenal Cortex Hormones↗
Glucose and caffeine regulation of liver glycogen phosphorylase activity in the freeze-tolerant wood frog Rana sylvatica.
We have examined the effect of glucose and caffeine inhibition on the activity of liver glycogen phosphorylase a from the freeze-tolerant frog Rana sylvatica. Kinetic studies indicate that this enzyme exhibits similar sensitivity to glucose inhibition (glucose dissociation constant = 12.5 mM) as the mammalian enzyme. Little inhibition (less than 25%) was observed at normal glucose concentrations (1-5 mM), while significant inhibition (60-95%) occurred at glucose concentrations (50-500 mM) present in freezing-exposed animals. These results favour the hypothesis that in the normal state glucose regulates phosphorylase activity primarily through the promotion of dephosphorylation of phosphorylase a, whereas during freezing regulation is achieved through phosphorylase a inactivation. The caffeine dissociation constant (0.93 mM) and the degree of synergism between caffeine and glucose (interaction factor, alpha = 0.14) were also similar to that observed for the mammalian enzyme. Hence, if a caffeine-like ligand exists in vivo, it must be in low enough amounts during freezing to allow sufficient phosphorylase a activity for high glucose production.
Animals↗
Sulphate-stimulate liver glycogen phosphorylase b: new evidence of changes in the conformation of the enzyme.
It has been known for same time that sulphate ions stimulate liver glycogen phosphorylase b, both in the presence and in the absence of AMP. In the present paper we describe some observations (like a modified method of purification of the enzyme after sulphate treatment of the animals) suggesting that actual changes of the physical properties of the enzyme occur after intravenous injection of sodium sulphate. In order to avoid formation of phosphorylase a these studies were performed on enzyme from phosphorylase-b-kinase deficient (gsd/gsd) rats.
Animals↗
Uridine 5'-(5-thio-alpha-D-glucopyranosyl pyrophosphate): chemical synthesis and activation of rat liver glycogen synthetase.
Uridine 5'-(5-thio-alpha-D-glucopyranosyl pyrophosphate), UDPTG, appears to be a potent activator of rat liver glycogen synthetase a even though it is not a substrate. At 1.0 mM, UDPTG causes over 400% activation of glycogen synthetase a activity. Activation by UDPTG is accompanied by normalization of the otherwise sigmoidal kinetics for UDPG with glycogen synthetase a and a decrease in the apparent Km for UDPG from approximately 2.0 to 0.62 mM. UDPTG inhibits catalytic activity at higher concentrations. At the concentrations examined, UDPTG has no effect on glycogen synthetase b activity. The use of glycogen synthetase free from glycogen synthetase b phosphatase and the selective inhibition of glycogen synthetase b phosphatase by 100 mM NaF-indicate that conversion of synthetase b to a is not responsible for the activation. Moreover, the use of the colorimetric assay for glycogen synthetase activity precludes effects of UDPTG on glycogen phosphorylase activity. UDPTG, chemically synthesized in 60% yield, is characterized by chromatographic and electrophoretic procedures, by its uv spectra, and by analysis of products after chemical and enzymatic hydrolysis.
Animals↗
A sparing effect of increased plasma fatty acids on muscle and liver glycogen content in the exercising rat.
Increasing plasma free fatty acids decreased the degree of glycogen depletion, and increased the citrate concentration, in slow-red (soleus) and fast-red (deep portion of vastus lateralis) muscle during exercise (approx. 50% depletion of glycogen, as against 75% in control animals). There was no effect in fast-white muscle (superficial portion of vastus lateralis). Glycogen concentration in the liver decreased by 83% in controls, but only by 23% in animals with increased free fatty acids during exercise. The decreased glycogen depletion may be partly explained by the findings that (a) plasma-insulin concentration was two- to three-fold higher in animals with increased plasma free fatty acids and (b) the exercise-induced increase in plasma glucagon was lessened by increased free fatty acids. Blood glucose was higher in the animals with increased free fatty acids after the exercise. The rats with increased plasma free fatty acids utilized approx. 50% as much carbohydrate as did the controls during the exercise.
Animals↗
In vivo phosphorylation of liver glycogen synthase. Effect of glucose and glucagon treatment of liver cells on the distribution of the [32P]phosphate.
Glycogen synthase was phosphorylated in vivo by perfusing rat liver or incubating liver cells with [32P]phosphate. It was then isolated by immunoprecipitation and subjected to exhaustive tryptic proteolysis. The trypsin-derived [32P]phosphopeptides were separated by high pressure liquid chromatography (HPLC). Incubation of in vivo phosphorylated synthase with endogenous synthase phosphatase to convert synthase D to synthase R resulted in removal of phosphate from all of the labeled phosphopeptides. In prelabeled liver cells treated with glucagon or glucose, the activities of synthase and phosphorylase changed in the direction expected. The total labeling in the immunoprecipitated synthase was found to be increased to 126% and decreased to 67% of the control with glucagon and glucose treatment, respectively. When the HPLC [32P]phosphopeptide profile of synthase from glucagon-treated animals was compared with that of controls, there were only minor differences in the two profiles. All the peaks were present and the proportion of labeling in each remained similar. There also was only a modest change in the [32P]phosphopeptide profile with glucose treatment when compared with that of controls. These results indicate that regulation of synthase activity in the hepatocyte involves changes in phosphorylation at multiple sites. Indeed, in 32P-labeled liver cells, all of the labeled sites appeared to be involved.
Animals↗
Epidermal growth factor administration decreases liver glycogen and causes mild hyperglycaemia in mice.
Several laboratories report different effects of epidermal growth factor (EGF) on glycogen metabolism in hepatocytes. The discrepancies may be attributed to differences in the experimental conditions. It is therefore important to establish the actual effect of EGF in vivo. Because large physiological variations of EGF concentration in plasma occur in mice, we used this species to address this question. In freshly isolated mouse hepatocytes, EGF increased glycogen degradation in a dose-dependent manner. The maximal effect (36% increase over basal glycogenolysis) was smaller than maximal effects of classical glycogenolytic hormones like adrenaline or glucagon (more than 150% increase over basal). This is in keeping with the smaller effect of EGF on phosphorylase a activity. In contrast with these hormones, EGF did not inhibit glycolysis. Thus these effects of EGF in mouse hepatocytes are similar to those recently described by us in rat hepatocytes [Quintana, Grau, Moreno, Soler, Ramirez and Soley (1995) Biochem J 308, 889-894]. When administered to whole animals, EGF increased phosphorylase a activity, decreased the glycogen content in the liver and caused mild hyperglycaemia. Taking together the results obtained for isolated cells and for whole animals, we suggest that the glucosyl residues released from glycogen are used mostly by the liver rather than released to the circulation. This would be different from the action of the classical glycogenolytic hormones, adrenaline and glucagon.
Animals↗
Circadian pattern of blood pressure, heart rate, and double product in liver glycogen storage disease.
The objective of this study was to determine systolic, diastolic, and mean arterial blood pressure (SBP, DBP, and MAP), heart rate (HR), double-product (DP: SBP x HR), and activity levels and their 24h pattern in liver glycogen storage disease (LGSD) patients. A case series of 12 (11 pediatric and one adult) diurnally active LGSD (seven type I, three type III, and two type IX) subjects were simultaneously assessed by 24h ambulatory blood pressure monitoring and wrist actigraphy. Nine subjects were judged to be hypertensive based on the criterion of an elevated 24h mean SBP and/or DBP being elevated beyond reference standards or the SBP and/or DBP load (percentage of time BP exceeds normal values) being greater than 25%. Two of the three other subjects, not viewed as hypertensive based on their 24h average SBP or DBP, exhibited daytime or nighttime SBP and/or DBP load hypertension. Each study variables displayed statistically significant (p < 0.001) group circadian rhythmicity. The SBP, DBP, and MAP displayed comparable 24h patterns of appreciable amplitude (total peak-trough variation equal to 17.7, 23.6, and 19.6%, respectively, of the 24h mean) with highest values (orthophase) occurring approximately 11 h after the commencement of daytime activity. The sleep-time trough (bathyphase) occurred approximately 4.5 h before morning awakening. The statistically significant (p < 0.006) circadian rhythms of HR (amplitude equal to 33.2% of the 24h mean) and DP (amplitude equal to 49.4% of the 24h mean) peaked earlier, approximately 7.4 h into the daytime activity span. The sleep-time trough occurred approximately 3 h before morning awakening. The 24h pattern in the cardiovascular variables was correlated with the 24h pattern of activity, with r ranging from 0.50 for DBP to 0.39 for HR.
Adolescent↗
Postexercise muscle and liver glycogen metabolism in male and female rats.
Male and female Wistar rats were run for 5 min at 1.7 mph at a 17% grade to determine whether a sex difference exists in the rate of glycogen resynthesis during recovery in fast-twitch red muscle, fast-twitch white muscle, and liver. Rats were killed at one of three time points: immediately after the exercise bout, and at 1 or 4 h later. Males had significantly higher resting muscle glycogen levels (P less than 0.05). Exercise resulted in significant glycogen depletion in both sexes (P less than 0.01). Males utilized approximately 50% more glycogen during the exercise bout than females (P less than 0.05). During the food-restricted 4-h recovery period, muscle glycogen was repleted significantly during the 1st h (P less than 0.05). Liver glycogen was not depleted as a result of the exercise bout, but fell during the first h of recovery (P less than 0.05) and remained low during the subsequent 3 h. The greater glycogen utilization in red and white fast-twitch muscle during exercise by males could represent a true sex difference but could also be attributable in part to the males having performed more work as a result of 20% greater body mass. We conclude that no sex difference was observed in the rates of muscle glycogen repletion after exercise or in liver glycogen metabolism during and after exercise, and rapid postexercise muscle glycogen repletion occurred at a time of accelerated liver glycogen depletion.
Animals↗
In vivo portal-hepatic venous gradients of glycogenic precursors and incorporation of D-[3-3H]glucose into liver glycogen in the awake rat.
Male Wistar fed rats were chronically cannulated and fed ground chow for 2 h for 6 days. On the 7th post-operative day, blood was simultaneously drawn from the portal and hepatic veins over a 2-h feeding period. The position of the hepatic vein cannula was verified using a tritiated water washout technique. In separate experiments, 200 microCi of [3-3H]glucose was added to the food in order to determine the relative contribution of D-glucose and 3-C precursors to newly synthesized glycogen. The 22-h fasting plasma portal vein concentrations of D-glucose, L-lactate, and L-alanine were 4.8 +/- 0.03, 0.81 +/- 0.06, and 0.20 +/- 0.03 mM, respectively (n = 5). The fasting hepatic vein plasma concentrations were 5.1 +/- 0.2, 0.70 +/- 0.15 and 0.19 +/- 0.03 mM, respectively. The portal-hepatic vein gradients after 22 h were -0.24, +0.16, and +0.01 mM for D-glucose, L-lactate, and L-alanine, respectively. At 20 min after beginning the meal, the respective gradients were +2.2, +0.53, and +0.44 mM, indicating hepatic uptake of all glycogen precursors. Of the total carbon from the three major precursors entering the liver as C-6, D-glucose contributed 82%, while alanine and lactate contributed 18% at 20 min. As portal vein D-glucose and L-alanine levels exceeded 6.65 +/- 0.69 and 0.32 +/- 0.07 mM, respectively, the portal-hepatic venous gradient became positive and increased linearly with portal concentrations. The glycogen concentration in the liver increased from a 22-h fast value of 5 mumol of glucosyl units/g wet weight to 101 +/- 7 mumol/g 2 h after the meal. The mean specific activity of portal vein plasma of [3-3H]glucose was 11,490 +/- 1,180 dpm/mumol (+/- S.E.) and that in the glycogen isolated from liver was 8,175 +/- 785 dpm/mumol of glycosyl units 2 h after the meal. The specific activity of liver [3H]glycogen relative to glucose after the meal was 0.73 +/- 0.08. It was concluded that a minimum of 73% of the newly synthesized glycogen was formed from the uptake and direct phosphorylation of portal blood D-glucose by the liver without prior conversion of glucose to 3-C units.
Alanine↗
Mutations in the liver glycogen phosphorylase gene (PYGL) underlying glycogenosis type VI.
Deficiency of glycogen phosphorylase in the liver gives rise to glycogen-storage disease type VI (Hers disease; MIM 232700). We report the identification of the first mutations in PYGL, the gene encoding the liver isoform of glycogen phosphorylase, in three patients with Hers disease. These are two splice-site mutations and two missense mutations. A mutation of the 5' splice-site consensus of intron 14 causes the retention of intron 14 and the utilization of two illegitimate 5' splice sites, whereas a mutation of the 3' splice-site consensus of intron 4 causes the skipping of exon 5. Two missense mutations, N338S and N376K, both cause nonconservative replacements of amino acids that are absolutely conserved even in yeast and bacterial phosphorylases. We also report corrections of the PYGL coding sequence, sequence polymorphisms, and a partial PYGL gene structure with introns in the same positions as in PYGM, the gene of the muscle isoform of phosphorylase. Our findings demonstrate that PYGL mutations cause Hers disease, and they may improve laboratory diagnosis of deficiencies of the liver phosphorylase system.
Amino Acid Sequence↗
Measurement of glucose recycling and liver glycogen synthesis in mice using doubly labeled substrates.
Tracer experiments have been carried out using gorging and nibbling mice to study several related aspects of carbohydrate metabolism: 1) inhibition of gluconeogenesis shortly after animals ingest a glucose-rich meal; 2) the extent to which dietary glucose carbon is recycled by way of 3C compounds after dietary glucose is absorbed; and 3) recycling of glucose by exchange between free and a hypothetical, "bound" glucose pool. Fasted, gorging mice were allowed to eat 120 mg [U-14C,6-T]glucose (58% glucose diet) in 4 min. Plasma glucose-C specific activity rapidly reached that of the dietary glucose-C. Superficially, this suggested nearly complete inhibition of hepatic gluconeogenesis. However, plasma [6-T]glucose, glycogen-[14C, 3H]glucose analyses, and [14C]-glycerol conversion to glucose showed that hepatic gluconeogenesis continued during alimentary hyperglycemia. Half of liver glycogen seemed to be formed from a hepatic G-6-P pool that was never labeled. Indirect kinetic evidence of a large, bound exchangeable glucose pool was presented. Since no direct evidence of such a pool has been obtained, the possibility is raised that a serious artifact of the tracer technique exists or else some unconventional model of carbohydrate metabolism is required to explain our data.
Animals↗
Rabbit liver glycogen synthase. Purification and comparison of the properties of glucose-6-P-dependent and glucose-6-P-independent forms of the enzyme.
Methods are described for the purification, close to homogeneity, of rabbit liver glycogen synthase in forms dependent on (D-form) or independent (I-form) of glucose-6-P for activity. In previous studies (Camici, M., DePaoli-Roach, A. A., and Roach, P. J. (1982) J. Biol. Chem. 257, 9898-9901), the D-form enzyme was shown to have apparent subunit molecular weight by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (Mapp) of 90,000 and to be susceptible to partial proteolytic degradation. We report here that the purified I-form consisted of a single polypeptide of Mapp = 85,000, even when protease inhibitors were present during the purification. However, appropriate phosphorylation of the I-form enzyme led to a decrease in the electrophoretic mobility of the subunit to generate a species of Mapp = 90,000, identical to that of the D-form. Exposure of the I-form enzyme (subunit Mapp = 85,000) to trypsin caused degradation in the sequence 85,000----82,000----79,000----72,000; concomitantly, the enzyme underwent partial inactivation whether assayed in the presence or absence of glucose-6-P. As purified, the I-form enzyme had a Vmax, determined from variation of UDP-glucose concentration, some 35 times greater than that of the D-form. The UDP-glucose concentration necessary for half-maximal activity was not greatly different, in the range 1-2 mM, for the two enzyme forms.
Animals↗