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PubMed1981

Decrease of blood glucose, liver glycogen, and insulin and changes in glucose tolerance in suckling rats treated neonatally with high L-thyroxine doses.

The neo-T4 syndrome was induced by sc administration of high doses (30 microgram) of L-T4 (T4) during 5 consecutive days in the early postnatal period. Rats were injected starting on the 3rd or 6th day of life. Blood glucose and insulin levels as well as liver glycogen levels were determined between the 5th and 20th days of life. This covers the critical period for brain development (the 7th to 12th day) during which most myelination takes place. Blood glucose and insulin and liver glycogen started to decrease after the second injection of T4 and remained quite low until 2 days after the last injection. Glucose tolerance testing was performed on 8- and 12-day-old neo-T4 rats; treatment was started at 3 days of age. After 70 min of fasting, 200 mg glucose/100 g BW were injected ip. Low plasma insulin levels were found after a glucose load. Plasma ketone bodies were higher in neo-T4 rats than in controls after 4 or 5 days of treatment. The rats appeared to be in a severe catabolic state and were using up their reserves. These alterations in carbohydrate metabolism in suckling rats should be considered when interpreting the brain damage produced by large doses of T4 during the early neonatal period.

Animals↗
PubMed1990

Long-term anoxia in crucian carp: changes in the levels of amino acid and monoamine neurotransmitters in the brain, catecholamines in chromaffin tissue, and liver glycogen.

Crucian carp (Carassius carassius L.), which are extremely anoxia-tolerant, were exposed to 17 days of anoxia at 8 degrees C. One group of fish was transferred to normoxic water for 1-8 h immediately after the anoxic period. All the eight amino acids measured in brain (including four putative neurotransmitters) were more or less strongly affected by anoxia. Gamma-aminobutyric acid (GABA) displayed a nearly fivefold increase during anoxia. It is hypothesized that the increased level of this inhibitory transmitter, maybe in combination with the decrease seen in excitatory amino acids (glutamate and aspartate), causes a lowered brain activity and, hence, is a key factor behind the decrease in physical activity and systemic energy metabolism seen in anoxic Carassius. The brain levels of serotonin, dopamine and norepinephrine were remarkably well preserved after anoxia (although their synthesis is oxygen-dependent), suggesting adaptive mechanisms. However, anoxia reduced the norepinephrine level in kidney (chromaffin tissue) by 92% and, in contrast to previous results on shorter anoxic periods (3-7 days), the peripheral catecholamine store showed little sign of recovery during the subsequent normoxia. Anoxia was found to deplete the liver glycogen store severely, and the few fish that died after 15-17 days of anoxia contained no detectable liver glycogen.

Amines↗
PubMed1976

Response of mouse liver glycogen cycle enzymes to endotoxin treatment.

The present study was undertaken to characterize endotoxin-induced changes in carbohydrate metabolism and more specifically, to determine the contribution of glycogenolysis to the loss of liver glycogen. Female ICR mice, fasted overnight, were injected with a median lethal dose (LD50, 9 mg/kg) of endotoxin extracted from Salmonella typhimurium strain SR-11. Glycogen synthase and glycogen phosphorylase activities were measured at 0.5 and 6 h after treatment. Endotoxin treatment did not alter total glycogen synthase activity, but the amount of enzyme present in the active form was significantly lower in endotoxic mice. There was no significant increase in glycogen phosphorylase activity in endotoxin-treated mice. Glycogen phosphorylase was activated to the same extent in control and endotoxic mice by decapitation or intravenous epinephrine (25 or 1 mug/kg). The results of this study indicate no significant increase in glycogen phosphorylase activity in endotoxic mice, contraindicating enhanced glycogenolysis as a mechanism for depletion of carbohydrate following endotoxin injection. Altered activation of glycogen synthase, however, may contribute to the loss of glycogen during endotoxemia.

Animals↗
PubMed1981

Effect of maternal dietary energy source on glucose homeostasis, liver glycogen and carcass lipid in the neonatal pig.

Two experiments were conducted to determine the effects of supplementary dietary energy (carbohydrate versus fat) fed to sows during late gestation on energy storage and glucose homeostasis in neonatal pigs. In the first experiment, 28 crossbred sows received one of two dietary treatments that were initiated on day 100 of gestation. The control group was fed daily 1.82 kg of a corn-soybean meal-based diet plus an additional .18 kg of cornstarch. Their counterparts were fed 1.82 kg of a corn-soybean meal diet containing 8% bleachable fancy tallow. The effect of maternal dietary energy source during late gestation on glucose homeostasis was evaluated by fasting pigs from birth (t0), whereas the gestation-lactation effect was evaluated by fasting pigs after they had nursed the sow for 24 hr (t24). Pigs on the tallow treatment responded differently to the t0 fast, as determined by the patterns of plasma glucose (treatment x time, P less than .05) and free fatty acids (treatment x time, P less than .10). The tallow group maintained a slightly higher glucose concentration during the initial 24 hr, after which no difference was observed. Control pigs reached a peak free fatty acid (FFA) concentration by 12 hr, whereas the tallow group reached a maximum by 24 hr, which corresponded with declining glucose concentration. Pigs on the t24 tallow treatment maintained a slightly higher plasma glucose concentration during the initial 24 hr of fasting (12 hr - 68.3 vs 63.2 mg/100 ml; 24 hr - 67.1 vs 56.3 mg/100 ml); however, no significant treatment effect or treatment x time interaction was observed. Pigs on the tallow treatment maintained a higher, although not significantly different, plasma FFA concentration during the fast (144 mueq/liter) than pigs in the control group (126 mueq/liter). In the second experiment, progeny of 12 sows were sacrificed immediately after birth. The respective carcass lipid (percentage) and liver glycogen (milligrams/gram) concentrations for pigs from sows fed the control and tallow diets were 1.48, 229.1 vs 1.50, 234.9. The liver glycogen to body weight ratio (milligrams:gram) was 7.1 and 7.8 for the control and tallow groups, respectively.

Animal Feed↗
PubMed1996

A calorimetric study of the binding of AMP to liver glycogen phosphorylase b.

The energetics of the interaction between liver glycogen phosphorylase b and the adenosine 5'-monophosphate (AMP) have been studied by equilibrium dialysis and isothermal titration calorimetry (ITC) at 25 degrees C. A concomitant net release of protons with AMP to phosphorylase binding was detected carrying out calorimetric experiments in three buffers having different heats of ionization at 25 degrees C. Four binding sites were found for AMP in the dimeric enzyme, which would correspond to the activator and the inhibitor sites identified in the muscle isozyme. The affinity of AMP for these four sites is similar. Thus, the binding of AMP to the activator sites seems to be non-cooperative and it does not perform the conformational change necessary to activate the enzyme. Moreover, the inhibitor sites are occupied almost in the same extension that the activator sites, which would impair any activation of the enzyme.

Adenosine Monophosphate↗
PubMed2005

Endogenous effectors of human liver glycogen phosphorylase modulate effects of indole-site inhibitors.

Phosphorylase is regulated by a number of small-molecular-weight effectors that bind to three sites on the enzyme. Recently, a fourth site referred to as the indole-inhibitor site has been identified. Synthetic compounds bind to the site and inhibit activity. However, the effects of these compounds in the presence of other endogenous effectors are unknown. We have determined the effects of four indole derivative glycogen phosphorylase inhibitors (GPI) on recombinant human liver glycogen phosphorylase a activity. The GPIs tested were all potent inhibitors. However, the endogenous inhibitors (glucose, ADP, ATP, fructose 1-phosphate, glucose 6-phosphate, UDP-glucose) and the activator (AMP) markedly reduced the inhibitory effect of GPIs. Consistent with these in vitro findings, the IC50 for the inhibition of glycogenolysis in cells and the liver drug concentration associated with glucose-lowering activity in diabetic ob/ob mice in vivo were also significantly higher than those determined in in vitro enzyme assays. The inhibitory effect of indole-site effectors is modulated by endogenous small-molecular-weight effectors of phosphorylase a activity. However, at higher concentrations (10-30 microM), the GPI effect was dominant and resulted in inhibition of phosphorylase a activity irrespective of the presence or absence of the other modulators of the enzyme.

Adenosine Diphosphate↗
PubMed1990

Influence of long-term diabetes on liver glycogen metabolism in the rat.

Diabetes acutely impairs the ability of the liver to synthesize glycogen. However, the effect of chronic diabetes on the glycogenic function of the liver is not known. We measured hepatic glycogen contents in streptozotocin (STZ)-diabetic rats 3 weeks or 9 months after the induction of diabetes, in the fed state and following a 24-hour fast. In the fed state, liver glycogen levels were markedly decreased in short-term diabetic animals (5.8 +/- 2.0 v 33.9 +/- 2.3 mg/g, P less than .001), but not in long-term diabetic rats (18.3 +/- 4.4 v 20.7 +/- 1.3 mg/g, P = NS) as compared with age-matched nondiabetic animals, despite comparable hyperglycemia (portal plasma glucose levels of 424 +/- 21 and 449 +/- 24 mg/100 mL, short- and long-term diabetics, respectively). In the fasted state, on the other hand, liver glycogen was depleted in acute diabetes (4.5 +/- 2.2 mg/g v 1.9 +/- 0.5 of control rats), but significantly increased in chronic diabetes (10.1 +/- 3.1 v 0.2 +/- 0.03 mg/g, P less than .001). The latter finding was confirmed by electron-microscopical examination of liver cells. Furthermore, the percentage of hepatic glycogen synthase in the active form (synthase a) was lower than normal in short-term diabetic rats and in old nondiabetic rats. In long-term diabetic animals, on the other hand, synthase a was significantly higher than in old controls (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed2000

Activation of human liver glycogen phosphorylase by alteration of the secondary structure and packing of the catalytic core.

Glycogen phosphorylases catalyze the breakdown of glycogen to glucose-1-phosphate, which enters glycolysis to fulfill the energetic requirements of the organism. Maintaining control of blood glucose levels is critical in minimizing the debilitating effects of diabetes, making liver glycogen phosphorylase a potential therapeutic target. To support inhibitor design, we determined the crystal structures of the active and inactive forms of human liver glycogen phosphorylase a. During activation, forty residues of the catalytic site undergo order/disorder transitions, changes in secondary structure, or packing to reorganize the catalytic site for substrate binding and catalysis. Knowing the inactive and active conformations of the liver enzyme and how each differs from its counterpart in muscle phosphorylase provides the basis for designing inhibitors that bind preferentially to the inactive conformation of the liver isozyme.

Adenosine Monophosphate↗
PubMed1990

ADP and glucose as possible synergistic partners in the stimulation of liver glycogen synthase activation.

Glucose administered either intravenously or orally causes liver glycogen synthase activation independent of a rise in circulating insulin. In vitro, physiological concentrations of glucose stimulate synthase phosphatase activity but only in the presence of a second effector which reduced the A0.5 for glucose. Caffeine and certain methylxanthines have been in vitro models for a putative natural effector. The present study demonstrates that, in vitro, ADP also reduced the A0.5 for glucose comparable to the effect of caffeine. The maximum stimulation by glucose in the presence of caffeine or ADP was comparable. The effect of ADP was specific among the major nucleoside diphosphates. However, the A0.5 for ADP was greater than the normal liver concentration which does not change in response to either glucose or insulin administration. The effect of ADP appeared distinct from that of the methylxanthines since it was observed that at near saturating concentrations of ADP and of glucose, stimulation was increased by addition of theophylline. Similarly, addition of adenosine, a natural cell constituent, caused increased stimulation. Subsequently, it was shown that adenosine reduced the A0.5 for ADP to a nearly physiological concentration. Thus, while ADP is not the inducible putative effector which has been predicted it may be part of an intracellular amplification system for glycogen synthase activation which increases the sensitivity to an induced effector. The present work suggests that the effective concentration of the natural ligand may be less than originally anticipated. This work also suggests that the putative effector could be structurally related to adenosine. Phosphorylase phosphatase activity known to be stimulated by ADP and glucose is further stimulated by the combination which may be acting in synergy.

Adenosine↗
PubMed1997

Glycogenin-2, a novel self-glucosylating protein involved in liver glycogen biosynthesis.

Glycogenin is a self-glucosylating protein involved in the initiation phase of glycogen biosynthesis. A single mammalian gene had been reported to account for glycogen biogenesis in liver and muscle, the two major repositories of glycogen. We describe the characterization of novel forms of glycogenin, designated glycogenin-2 (GN-2), encoded by a second gene that is expressed preferentially in certain tissues, including liver, heart, and pancreas. Cloning of cDNAs encoding glycogenin-2 indicated the existence of multiple species, including three liver forms (GN-2alpha, GN-2beta, and GN-2gamma) generated in part by alternative splicing. Overall, GN-2 has 40-45% identity to muscle glycogenin but is 72% identical over a 200-residue segment thought to contain the catalytic domain. GN-2 expressed in Escherichia coli or COS cells is active in self-glucosylation assays, and self-glucosylated GN-2 can be elongated by skeletal muscle glycogen synthase. Antibodies raised against GN-2 produced in E. coli recognized proteins of Mr approximately 66,000 present in extracts of rat liver and in cultured H4IIEC3 hepatoma cells. In H4IIEC3 cells, most of the GN-2 was present as a free protein but some was covalently associated with glycogen fractions and was only released by treatment with alpha-amylase. H4IIEC3 cells also expressed the muscle form of glycogenin (glycogenin-1), which was attached to a chromatographically separable glycogen fraction.

Amino Acid Sequence↗
PubMed1966

The structure and deposition of human-liver glycogens.

1. Glycogen was extracted from and the amount determined in human foetal livers ranging in age from 13(1/2) to 26 weeks. 2. The detailed structures of human foetal- and child-liver glycogens were examined and shown to be essentially the same. 3. The deposition of glycogen in different mammalian species is discussed.

Amylases↗
PubMed1979

Effect of the combination of voluntary exercise and dietary protein levels on the deposition of glycogen, liver and serum lipids in mice.

The effects of voluntary exercise on the growth, glycogen of muscle and lipid contents of the liver and serum of mice fed different levels of dietary protein were investigated. In both the exercise and non-exercise groups, body weight gains were significantly greater in the 20% and 30% protein diet groups than in the 6% and 4% protein diet groups. After 6 weeks of age, it was shown that the amount of voluntary exercise by the 6% and 4% protein diet groups was greater than that by the 20% and 30% protein diet groups. As for hematological status, the raising of hemoglobin levels due to increasing dietary protein levels was further exaggerated by voluntary exercise. Hematocrit values rose with the increase in dietary protein levels. However the effect of exercise on hematocrit values was not clear. Liver glycogen levels, which were elevated with the increase in dietary protein levels, rose further due to exercise, though no changes were observed in muscle glycogen due to dietary protein levels and exercise. The lipid contents of the liver in all groups tended to be lower in exercise groups compared with non-exercise groups and it was observed that the high levels of dietary protein depressed the increase in liver lipids. Liver triglyceride levels of all groups fed the dietary protein levels except for the 20% casein diet group decreased due to voluntary exercise, and liver triglyceride levels were also lowered as dietary protein levels increased. The levels of serum triglyceride of all groups decreased due to voluntary exercise. This phenomenon was most remarkable in rats fed a 6% casein diet. The tendency for serum cholesterol levels to decrease due to exercise. However it was not further influenced by voluntary exercise in the 4% casein diet group.

Animals↗
PubMed1982

Ultrastructural and physicochemical studies on glycogen macromolecules from ascites hepatoma AH 13 cells. A comparison with normal adult rat muscle, liver and fetal liver glycogen.

Glycogen extracted from rat ascites hepatoma AH 13 cells was compared with that from adult rat liver, adult rat muscle, and fetal rat liver 3 days before delivery, by electron microscopic, biochemical and physicochemical techniques. The ascites hepatoma AH 13 glycogen revealed two major different types of glycogen macromolecules by sucrose discontinuous density gradient centrifugation. The glycogen of the light fraction was very similar to rat muscle glycogen macromolecules in its size and shape except that it exhibited a stronger Cotton effect on measurement of the optical rotatory dispersion and circular dichroism than the muscle glycogen. Furthermore, this light material different from normal muscle glycogen. The other glycogen which also included very small amounts of irregular particles of glycogen macromolecules was contained in the heavy fraction was very similar to the adult rat liver glycogen macromolecules which did not display the Cotton effect. Electron micrographs showing the ultrastructure of the glycogen particles extracted from the AH 13 cells by negative staining revealed a variety of size and shape, and they contained two types of glycogen macromolecules with the smaller muscle types and larger adult type of liver glycogen macromolecules. The glycogen macromolecules also formed varied irregular structures in conformation.

Animals↗
PubMed1987

Transferrin, haematological indices and liver glycogen in field mice collected from a coal mining area and a control site in Poland.

A polymorphism for serum transferrin in field mice from polluted and control sites was compared with body-morphological and haematological parameters, and with liver glycogen concentration. The distribution of genotypes in the polluted area was not panmictic, due to higher frequencies of the rare allele Trf(c) occurring mainly in males. In the polluted area, transferrin-c was accompanied by slowly migrating, Fe-binding protein fractions. Since the Trf(c)/Trf(c) homozygote possessed higher red blood cell parameters, it is suggested that these extra proteins have an Fe-transport function. The morpho-physiology of heterozygotes from the polluted area did not differ significantly from those from the control site. The animals from the polluted area possessed a high concentration of liver glycogen, indicative of poor environmental conditions. Also, a generally lower level of red blood cell parameters suggests that non-oxygenic processes dominate over oxygenic ones in the polluted area.

Journal Article↗
PubMed1989

The rate of degradation of liver glycogen phosphorylase is specifically decreased in the C57BL/KsJ-db/db mouse.

We have recently demonstrated that the activity of liver glycogen phosphorylase, the rate-limiting enzyme of glycogenolysis, is elevated in genetically diabetic (db/db) mouse and that it is primarily due to the presence of increased amounts of this enzyme. In the present study, we examined the turnover of glycogen phosphorylase in vivo in order to elucidate the mechanism for this specific increase. The rate of phosphorylase synthesis was slightly decreased in the diabetic mouse compared to controls. However, the relative rates of synthesis were similar in these two groups. The rate of degradation of this enzyme was decreased 20% (p less than 0.05) in the diabetic mouse compared to controls. More importantly, the relative rate of degradation of phosphorylase was found to be lower in the diabetic animals. This indicates that the elevated concentration of phosphorylase in the liver of the db/db mouse is likely due to a specific decrease in its rate of degradation.

Amino Acids, Branched-Chain↗