Depletion of glycogen synthetase and increase of glucose 6-phosphate dehydrogenase in livers of ethionine-treated mice

1. Ethionine-treated mice showed a marked depletion in liver glycogen, a decrease of glycogen-synthetase activity, an increase in activity of glucose 6-phosphate dehydrogenase and the solubilization of phosphorylase. 2. The administration of cortisol or glucose did not alleviate these changes but the effect of ethionine was completely prevented in animals given methionine as well as ethionine. 3. The activities of the following enzymes were unchanged: hexokinase, glucokinase, glucose 6-phosphatase, phosphoglucomutase, 6-phosphogluconate dehydrogenase, UDP-glucose pyrophosphorylase, UDP-glucose dehydrogenase and pyruvate kinase.     

Stimulation of pentose phosphate pathway dehydrogenase enzyme activities in ethionine-treated mice

1. Mice treated with ethionine (intraperitoneally, 5mg./day for 4 days or 10mg./day for 3 days) showed a profound loss of hepatic glycogen, a decrease of glycogen synthetase activity, a development of hypoglycaemia, a two- to five-fold increase in the activity of glucose 6-phosphate dehydrogenase but no change in 6-phosphogluconate dehydrogenase and an earlier manifestation of the solubilization of phosphorylase as compared with glycogen synthetase. The administration of ATP did not prevent these effects. 2. During the early post-injection period (2-3 days) there was a further enhancement of the activity of glucose 6-phosphate dehydrogenase (tenfold) in the liver and a clear elevation of 6-phosphogluconate dehydrogenase activity (twofold). Subsequently, the glycogen concentration was restored, followed by an earlier reassociation of glycogen particle with phosphorylase than with glycogen synthetase, along with a disappearance of ethionine effect at about the eighteenth day. 3. Glucose 6-phosphate dehydrogenase from both control and ethionine-treated animals showed a marked preference for glucose 6-phosphate as substrate rather than for galactose 6-phosphate, whose rate of oxidation was only 10% of that of the glucose 6-phosphate. 4. Since actinomycin D, puromycin, 5-fluorouracil and dl-p-fluorophenylalanine failed to block the ethionine-enhanced glucose 6-phosphate dehydrogenase activity, the possibility that new enzyme protein synthesis is responsible for the effect is doubtful.     

Effect of hydrocortisone and glucagon on glycogen metabolism in the fetal rat liver.

1. Hydrocortisone increases in vivo incorporation of [14C] glucose into fetal liver glycogen in the last days of gestation, whereas in glucagon-treated fetuses, a slight decrease in the incorporation rate was found. 2. Hydrocortisone increases total synthetase activity as that of synthetase a but was without effect on fetal liver glycogen phosphorylase. 3. Glucagon causes a slight increase in phosphorylase a activity on days 19-21, and was without effect on the activities of synthetase a and total synthetase. 4. Dibutyryl cyclic AMP had no effect on the key enzymes of glycogen metabolism 1 h after injection in utero, whereas after 6 h an increase in phosphorylase a activity was found without any change in synthetase a activity.     

Early effects of excessive retinol intake on hepatic glycogen metabolism

Oral adminstration of 30,000 IU of retinol once daily for 2-days caused deposition of glycogen in the liver with a concurrent stimulation of hepatic glycogen synthesis, as evidenced by increased in vivo incorporation of d-[U-¹⁴C]glucose into glycogen and increased net synthesis of the polysaccharide in response to feeding of glucose to 20-h fasted rats. Excessive intake of the vitamin increased markedly the activity of glycogen synthetase a and decreased that of phosphorylase. However, feeding of similar doses of retinol to bilaterally adrenalectomized rats failed to cause appreciable deposition of glycogen in the liver and the usual increase in the activity of glycogen synthetase a. Likewise, treatment of rats with actinomycin D blocked the deposition of glycogen in the liver and the increase in the activity of glycogen synthetase a. Adrenalectomy and actinomycin D, however, did not affect the accumulation of retinol in the liver. The adrenals appear to be, directly or indirectly, required for the manifestations of the effects of retinol on the hepatic glycogen metabolism.     

Hormonal regulation of glycogen metabolism in neonatal rat liver

1. The development of active and inactive phosphorylase was determined in rat liver during the perinatal period. No inactive form could be found in tissues from animals less than 19 days gestation or older than the fifth postnatal day. 2. The regulation of phosphorylase in organ cultures of foetal rat liver was examined. None of the agents examined [glucagon, insulin or dibutyryl cyclic AMP (6-N,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate)] changed the amount of phosphorylase activity. 3. Glycogen concentration in these explants were nevertheless decreased more than twofold by 4h of incubation with glucagon or dibutyryl cyclic AMP. Incubation with insulin for 4h increased the glycogen content twofold. 4. Glycogen synthetase activity was examined in these explants. I-form activity (without glucose 6-phosphate) was found to decrease by a factor of two after 4h of incubation with dibutyryl cyclic AMP, whereas I+D activity (with glucose 6-phosphate) remained nearly constant. Incubation for 4h with insulin increased I-form activity threefold, with only a slight increase in I+D activity. 5. When explants were incubated with insulin followed by addition of dibutyryl cyclic AMP, the effects of insulin on glycogen concentration and glycogen synthetase activity were reversed. 6. These results indicate that the regulation of glycogen synthesis may be the major factor in the hormonal control of glycogen metabolism in neonatal rat liver.     

Lithium's effects on rat liver glucose metabolism in vivo

Oral administration of lithium carbonate to fed-healthy rats strongly decreased liver glycogen content, despite the simultaneous activation of glycogen synthase and the inactivation of glycogen phosphorylase. The effect seemed to be related to a decrease in glucose 6-phosphate concentration and to a decrease in glucokinase activity. Moreover, in these animals lithium markedly decreased liver fructose 2,6-bisphosphate, which could be a consequence of the fall in glucose 6-phosphate and of the inactivation of 6-phosphofructo-2-kinase. Liver pyruvate kinase activity and blood insulin also decreased after lithium administration. Lower doses of lithium carbonate had less intense effects. Lithium administration to starved-healthy and fed-streptozotocin-diabetic rats caused a slight increase in blood insulin, which was simultaneous with increases in liver glycogen, glucose 6-phosphate, and fructose 2, 6-phosphate. Glucokinase, 6-phosphofructo-2-kinase, and pyruvate kinase activities also increased after lithium administration in starved-healthy and fed-diabetic rats. Lithium treatment activated glycogen synthase and inactivated glycogen phosphorylase in a manner similar to that observed in fed-healthy rats. Glycemia was not modified in any group of animals. These results indicate that lithium acts on liver glycogen metabolism in vivo in at least two different ways: one related to changes in insulinemia, and the other related to the direct action of lithium on the activity of some key enzymes of liver glucose metabolism.     

Effect of fructose 1-phosphate on the activation of liver glycogen synthase.

The activation (dephosphorylation) of glycogen synthase and the inactivation (dephosphorylation) of phosphorylase in rat liver extracts on the administration of fructose were examined. The lag in the conversion of synthase b into a was cancelled, owing to the accumulation of fructose 1-phosphate. A decrease in the rate of dephosphorylation of phosphorylase a was also observed. The latency re-appeared in gel-filtered liver extracts. Similar latency was demonstrated in extracts from glucagon-treated rats. Addition of fructose 1-phosphate to the extract was able to abolish the latency, and the activation of glycogen synthase and the inactivation of phosphorylase occurred simultaneously. Fructose 1-phosphate increased the activity of glycogen synthase b measured in the presence of 0.2-0.4 mM-glucose 6-phosphate. According to kinetic investigations, fructose 1-phosphate increased the affinity of synthase b for its substrate, UDP-glucose. The accumulation of fructose 1-phosphate resulted in glycogen synthesis in the liver by inducing the enzymic activity of glycogen synthase b in the presence of glucose 6-phosphate in vivo and by promoting the activation of glycogen synthase.     

Time course for cryoprotectant synthesis in the freeze-tolerant chorus frog, Pseudacris triseriata

Increases in liver glycogen phosphorylase activity, along with inhibition of glycogen synthetase and phosphofructokinase-1, are associated with elevated cryoprotectant (glucose) levels during freezing in some freeze-tolerant anurans. In contrast, freeze-tolerant chorus frogs, Pseudacris triseriata, accumulate glucose during freezing but exhibit no increase in phosphorylase activity following 24-h freezing bouts. In the present study, chorus frogs were frozen for 5- and 30-min and 2- and 24-h durations. After freezing, glucose, glycogen, and glycogen phosphorylase and synthetase activities were measured in leg muscle and liver to determine if enzyme activities varied over shorter freezing durations, along with glucose accumulation. Liver and muscle glucose levels rose significantly (5-12-fold) during freezing. Glycogen showed no significant temporal variation in liver, but in muscle, glycogen was significantly elevated after 24 h of freezing relative to 5 and 30 min-frozen treatments. Hepatic phosphorylase a and total phosphorylase activities, as well as the percent of the enzyme in the active form, showed no significant temporal variation following freezing. Muscle phosphorylase a activity and percent active form increased significantly after 24 h of freezing, suggesting some enhancement of enzyme function following freezing in muscle. However, the significance of this enhanced activity is uncertain because of the concurrent increase in muscle glycogen with freezing. Neither glucose 6-phosphate independent (I) nor total glycogen synthetase activities were reduced in liver or muscle during freezing. Thus, chorus frogs displayed typical cryoprotectant accumulation compared with other freeze-tolerant anurans, but freezing did not significantly alter activities of hepatic enzymes associated with glycogen metabolism.     

Glycogen and glycogen enzymes in the liver and striated muscle of rats under altered thyroid states

Changes induced in liver and striated muscle glycogen and glycogen enzymes (glycogen synthetase, glycogen phosphorylase and alpha-amylase) by hypothyroidism and hyperthyroidism in rats have been determined. There were no changes in liver glycogen synthetase, phosphorylase and amylase activities in the hypothyroid group. Hyperthyroid rats showed lower liver glycogen synthetase, phosphorylase a and amylase activities. In muscle, hypothyroid rats had lower phosphorylase activity. In the hyperthyroid group glycogen synthetase was increased.--The results presented do not completely agree with the glycogen levels found in both tissues studied, and they are obviously more related to other factors such as glucose availability. It can be concluded that under the conditions studied, the glycogen enzyme levels could not alone explain the variations of glycogen levels.     

Glycogen synthetase and the control of glycogen synthesis in the cellular slime mould Dictyostelium discoideum during the growth (myxamoebal) phase

1. Myxamoebae of the cellular slime mould Dictyostelium discoideum Ax-2 that are grown in axenic medium containing 86mm-glucose have seven times the glycogen content of the same myxamoebae grown in the same medium but lacking added carbohydrate. 2. During the transition from the exponential to the stationary phase of growth in axenic medium containing glucose myxamoebae preferentially synthesize glycogen and can have as much as three times the glycogen content during the stationary phase as they have during the exponential phase of growth. 3. The rate of glycogen degradation by myxamoebae is, under all conditions of growth, small compared with the rate of glycogen accumulation and the changes in glycogen content thus reflect altered rates of glycogen synthesis. 4. There is no correlation between the rate of glycogen synthesis by myxamoebae and the glycogen synthetase content of the myxamoebae. 5. The activity of glycogen synthetase of D. discoideum is inhibited by a physiological concentration of ATP and this inhibition is overcome by glucose 6-phosphate. Both effects are especially marked at physiological concentrations of UDP-glucose. 6. The rate of glycogen accumulation by myxamoebae growing exponentially in axenic media can be satisfactorily accounted for in terms of the known intracellular concentrations of glucose 6-phosphate, UDP-glucose and glycogen synthetase. The rate-limiting factors controlling glycogen synthesis by the myxamoebae are apparently the substrate (UDP-glucose) and effector (glucose 6-phosphate and ATP) concentrations rather than the amount of the enzyme.     

Activity of glycogen metabolizing enzymes in glucose deprived HT 29 adenocarcinoma cell-line

When deprived of glucose, the cultured HT 29 adenocarcinoma cells are able to mobilize their glycogen within 4 hours. Glycogen phosphorylase is strongly activated during the first hour of glucose starvation. Then, while the a/a + b ratio for phosphorylase is declining, glycogen synthase is partially converted into the a form; this conversion does occur although glycogen phosphorylase is far from being totally inactivated. After 4 hours, activity of both a and total forms of glycogen synthase decrease. Cell UDP-glucose and glucose-6-P levels are declining during the 24 hours period of glucose starvation. Cell ATP content decreases by only 50 percent over the same period of time.     

Glycogen metabolism in novikoff ascites-hepatoma cells

A study of the enzymes of the glycogen pathway in Novikoff ascites hepatoma shows that glycogen synthetase has the lowest activity and that the tumour contains no high-K(m) soluble glucokinase. However, incubation of tumour cells with metabolizable sugars in vitro, or intraperitoneal administration of glucose into the tumour-bearing rat, results in glycogen accumulation by the tumour cells. Glycogen synthesis in the tumour is supported by aerobically produced ATP but is decreased anaerobically and by uncouplers of oxidative phosphorylation. Absence of P(i) from the incubation medium increases glycogen synthesis and decreases glycolysis. The optimum temperature for glycogen synthesis is 37 degrees . The capacity of the intact tumour cell to degrade deposited glycogen is low, but is accelerated by 2,4-dinitrophenol. Tumour homogenates prepared after osmotic shock do not incorporate [(14)C]glucose into glycogen. The glucose moiety of glucose 1-phosphate and of UDP-glucose is incorporated into glycogen by the homogenates and the incorporation of glucose 1-phosphate is greatly enhanced by AMP. Glucose 6-phosphate is a poor precursor of glycogen in the homogenate system, probably because it inhibits activation of phosphorylase b by AMP.     

Histochemical study of the enzymes of glycogen metabolism in the human endometrium during the normal menstrual cycle]

The content of glycogen in the human endometrium is dependet on the activity of enzymes involved in processes of synthesis and dissociation of glicogen: glycogen-synthetase, phosphorilase and glycogen-6-phosphatase. The activation of "D" form of glycogensynthetase dependent on glucose-6-phosphate and the increase of the glycoogen quantity in the endometrium glands epithelium is observed in the period of growing gestagenic function of the ovaries. At the end of the secretory phase there occurs activation of the glycogen dissociation enzme-phosphorilase which goes in parallel with abrupt inhibition of the glycogensynthetase activity and disappearance or glycogen from the gland epithelium. The inhibition of glycogen synthetase is conditioned by a decreased level of intracellular glucose-6-phosphate which appears due to activation of glucose-6-phosphate in this period.     

Pathway-specific response to cortisol in the metabolism of catfish

Cortisol produced biochemical pathway-specific effects on metabolic enzymes and other macromolecules in the freshwater catfish, Clarias batrachus. Injection of cortisol increased 1.6-fold activity of citrate synthase (CS) in brain, liver and skeletal muscle of the fish over vehicle-injected control, while administration of metyrapone (a cortisol synthesis inhibitor) reduced CS activity by 52%. Cortisol treatment of metyrapone-treated fish induced CS activity by approximately 2.5-fold, which was blocked after administration of actinomycin D or cycloheximide. This shows de novo synthesis of CS to enhance aerobic capacity of fish. In contrast the activities of glucose-6-phosphate dehydrogenase (G6-PDH) and lactate dehydrogenase (LDH) increased in response to metyrapone and decreased after administration of cortisol in all the three tissues. The cortisol-mediated decrease in G6-PDH and LDH activities reflects reduction in biosynthetic and anaerobic capacity of fish. Administration of metyrapone significantly increased RNA/DNA ratio and protein but cortisol decreased these macromolecular contents in brain, liver and skeletal muscle. It shows cortisol-induced decrease in protein synthesis capacity of fish. The present study suggests that cortisol-induces catabolic and aerobic but inhibits anabolic and anaerobic processes in freshwater catfish. The cortisol-dependent metabolic responses may also be associated with the permissive effect of cortisol on other hormone(s) in fish.     

THE INCORPORATION OF GLUCOSE INTO BRAIN GLYCOGEN AND THE ACTIVITIES OF CEREBRAL GLYCOGEN PHOSPHORYLASE AND SYNTHETASE: SOME EFFECTS OF AMPHETAMINE

Abstract— The effects of amphetamine sulphate (5 mg/kg intraperitoneally) on the incorporation of radioactive carbon from [U-¹⁴C]glucose into the glycogen of mouse cerebral cortex, midbrain and hind-brain have been investigated. In all brain regions studied amphetamine induced a rapid decrease in glycogen followed by a slower return to control values. No significant alterations were observed in the steady state concentration of cerebral glucose. The initial fall in glycogen was associated with a fall in its specific radioactivity relative to that of cerebral glucose, whereas the resynthesis of the polysaccharide was associated with a marked increase in the relative specific radioactivity of glycogen. Other experiments demonstrated that amphetamine initially stimulates the breakdown of prelabelled glycogen and that the resulting molecule has fewer 1,4 linked glucose side chains.
Studies of the relative forms of the enzymes glycogen phosphorylase and glycogen synthetase suggested that rapid post mortem changes were less likely to occur if cerebral tissue was fixed by means of a freeze-blowing technique. Amphetamine administration resulted in a rapid though transient elevation of phosphorylase a activity in mouse forebrain. The level of glycogen synthetase I activity was unchanged initially but was markedly elevated during the period when there was a large increase in the rate of incorporation of glucose into glycogen. It is suggested that cerebral glycogen metabolism is controlled, at least in part, by the interconversion of the 'active' and 'inactive' forms of glycogen phosphorylase and synthetase.     

Liver glycogen metabolism in endotoxin shock. I. Endotoxin administration decreases glycogen synthase activities in dog livers

The effects of E. coli endotoxin administration on hepatic glycogen content and glycogen synthase activities in dogs were studied. Liver glycogen content was decreased by 80% 2 hr after endotoxin injection. When enzyme preparations were preincubated at 25 degrees C for 3 hr prior to their assays, 75% of total glycogen synthase was in I form in control dogs. Under such conditions, endotoxin administration decreased the percentage I activity from 75 to 37%; decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 62.2 and 35.3%, respectively; decreased the Vmax and Km for UDP-glucose for glycogen synthase I by 75.6 and 15.6%, respectively; increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 126% at high (10 mM) and by 18-fold at low (1 mM) UDP-glucose concentration; increased the percentage D activity from 24 to 72%; decreased the I50 for ATP for the inhibition of total glycogen synthase by 49.7%; decreased the I50 for ATP for the inhibition of glycogen synthase I by 26.4%; and decreased the percentage I activity from 78 to 33% at ATP concentrations below 6 mM. When enzyme preparations were not preincubated prior to their assays, 90% of total glycogen synthase was in D form in control dogs. Under such conditions, endotoxin administration decreased the Vmax and Km for UDP-glucose for total glycogen synthase by 47.1 and 33.3%, respectively, and increased the A0.5 for glucose-6-P for the activation of glycogen synthase D by 24.2% at high (10 mM) and by 106% at low (1 mM) UDP-glucose concentration. From these results, it is clear that endotoxin administration greatly impaired hepatic glycogenesis by decreasing the activity of glycogen synthase; this impairment is at least in part responsible for the depletion of liver glycogen content in endotoxin shock. Kinetic analyses revealed that the decrease in the activity of glycogen synthase in endotoxic shock is a result of a decrease in the interconversion of this enzyme from inactive to active form and an increase in the interconversion from active to inactive form.     

Turkey liver xanthine dehydrogenase. Reactivation of the cyanide-inactivated enzyme by sulphide and by selenide

1. The glycogen present in the liver of rat foetuses was labelled by injecting a trace amount of [6-(3)H]glucose into the mother at 19.5 days of gestation. The radioactivity incorporated in the glycogen 4h after the administration of the label was still present 38h later. A large proportion of this radioactivity was on the outer chains of the polysaccharide. These results indicate that there is normally almost no glycogen degradation in the foetal liver. In contrast, glycogen breakdown occurs very rapidly in the livers of foetuses whose mother is anaesthetized. 2. Glycogen synthetase is present in the liver at day 16 of gestation at a concentration as high as 30% of that in the adult, but essentially as an inactive (b) enzyme. The appearance of synthetase phosphatase between days 18 and 19 corresponds to that of synthetase a and to the beginning of glycogen synthesis. From day 19 to 21.5 the amount of synthetase a present in the foetal liver is just sufficient to account for the actual rate of glycogen deposition. 3. The content of total phosphorylase in the foetal liver increases continuously from day 16 to birth. However, a precise measurement of the a and b forms of the enzyme in the liver of non-anaesthetized foetuses is not possible. Taking the rate of glycogenolysis as an appropriate index of phosphorylase activity, we conclude that this enzyme is almost entirely in the inactive form in the foetal liver under normal conditions. 4. The accumulation of glycogen in the liver during late pregnancy may therefore be explained by a relatively slow rate of synthesis and a nearly total absence of degradation.     

Effect of tangeretin,a polymethoxylated flavone on glucose metabolism in streptozotocin-induced diabetic rats

The present study was designed to evaluate the antihyperglycemic potential of tangeretin on the activities of key enzymes of carbohydrate and glycogen metabolism in control and streptozotocin induced diabetic rats. The daily oral administration of tangeretin (100 mg/kg body weight) to diabetic rats for 30 days resulted in a significant reduction in the levels of plasma glucose, glycosylated hemoglobin (HbA1c) and increase in the levels of insulin and hemoglobin. The altered activities of the key enzymes of carbohydrate metabolism such as hexokinase, pyruvate kinase, lactate dehydrogenase, glucose-6-phosphatase, fructose-1,6-bisphosphatase, glucose-6-phosphate dehydrogenase, glycogen synthase and glycogen phosphorylase in liver of diabetic rats were significantly reverted to near normal levels by the administration of tangeretin. Further, tangeretin administration to diabetic rats improved hepatic glycogen content suggesting the antihyperglycemic potential of tangeretin in diabetic rats. The effect produced by tangeretin on various parameters was comparable to that of glibenclamide – a standard oral hypoglycemic drug. Thus, these results show that tangeretin modulates the activities of hepatic enzymes via enhanced secretion of insulin and decreases the blood glucose in streptozotocin induced diabetic rats by its antioxidant potential.     

Regulation of glycogen metabolism in the adrenal gland. IV. The effect of insulin on glycogen synthetase, phosphorylase, and related metabolites

Previous studies have indicated that the glycogen content of adrenal glands of fasted rats can be depleted by insulin per se (Bindstein, E., Piras, R., and Piras, M. M., Endocrinology88, 223, 1971). In order to establish the mechanism of action of this hormone in the adrenal gland, the effect of insulin has been now investigated on glycogen synthetase (UDP-glucose: α-1,4 glucan α-4-glueosyl-transferase, EC 2.4.1.11), glycogen phosphorylase (α-1,4 glucan: orthophosphate glucosyl-transferase, EC 2.4.1.1) and metabolites related to these enzymes.Approximately 40% of total adrenal glycogen phosphorylase of fasted rats is in the active form, which increases to 75% 1 hr after insulin treatment (75 mU/100 g body wt). This conversion occurs without apparent large changes of 3′-5′ cyclic AMP. Concomitantly with the enzymatic change, the levels of glucose-6-P, UDP-glucose and P_i suffer alterations which favor an increased phosphorolytic activity during the first hour of insulin treatment. Glycogen synthetase, which did not change during this period, is converted to the glucose-6-P independent form during the 2–3 hr of treatment. This conversion is preceded by an increased glycogen synthetase phosphatase activity, which seems to follow an inverse relationship with the glycogen level.The results obtained suggest that the effect of insulin on the adrenal gland of fasted rats is glycogenolytic, that is, opposite to that described for this hormone in other normal tissues. The glycogen depletion, on the other hand, seems to set in motion the mechanism for glycogen synthetase activation, with the subsequent glycogen resynthesis.