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PubMed1976

Effect of orotic acid on liver glycogen of different animal species.

The effect of orotic acid on the liver glycogen content in the mice, frogs and catfish was studied. It was observed that the orotic acid significantly increases the glycogen content in the liver of mice and catfish as it does in rats. On the other hand it causes a fall of the glycogen level in frogs in experiments made both in autumn and spring. This effect was modified by amino acids administered together with orotic acid.

Animals↗

PubMed1981

Effects of maternal starvation on some blood metabolites, liver glycogen, birth weight and survival of piglets.

Pregnant crossbred sows were assigned to three treatments during the third trimester of gestation for an evaluation of the effects of maternal starvation on fetal development and piglet survival. Two groups of sows were taken off feed (water and trace mineralized salt only) on days 93 and 107 of gestation, respectively; the third group was fed 1.82 kg of complete sow diet/day and served as the control. Litter size, gestation length and pig birth weight in the 7-day and 21-day starvation groups were not different from those in the control group (P less than .05). Liver weight was depressed (P greater than .05) among the 7-day and 21-day progeny. However, liver glycogen concentrations and total liver glycogen were unaffected. Maternal blood glucose decreased to a fasting but steady level, while free fatty acid (FFA) increased in the two starved groups. Blood glucose and FFA at birth were similar for all treatment groups; however, FFA increased in the progeny of sows in the 7-day (P greater than .05) and 21-day (P greater than .01) starvation groups at 48 hr of age. Blood glucose at 48 hr did not vary (P less than .05), but the control progeny showed a faster glucose utilization, suggesting a greater dependence on carbohydrate metabolism than in the progeny of starved dams. Survival rate at 72 hr of age was higher among 21-day (43.8%) and 7-day (37.5%) progeny than among control progeny (8.5%). The increased plasma FFA level observed with fasting in the progeny of starved dams might indicate a shift toward lipid metabolism, which would account for the improved survival observed among the progeny of treated dams.

Animals↗

PubMed1981

Liver glycogen synthase in the developing foetal rat.

Kinetic constants for liver glycogen synthase (UDPglucose: glycogen 4-alpha-D-glucosyltransferase, EC 2.4.1.11) with respect to UDPglucose have been measured in foetal liver homogenates from samples taken during late gestation (days 17-22) and the first hours after birth. The V of the inactive form of glycogen synthase increased markedly in this period and there was a significant increase in V of the active enzyme to a maximum at day 20 of gestation. The Km for UDPglucose measured in the presence of glucose-6-P (total activity) did not vary greatly, mean values of 0.51 +/- 0.04 mM. Values derived for the inactive enzyme were almost identical. In contrast, Km values for active glycogen synthase in foetal livers during gestation were significantly higher than those for adult liver. Highest values were seen at day 19 of gestation (1.84 +/- 0.08 mM) followed by a steady fall to 0.55 +/- 0.05 mM in the newborn compared with a mean value of 0.48 +/- 0.04 mM for adult liver. Existence of a reduced affinity of active glycogen synthase for UDPglucose must be recognized when assaying the enzyme in foetal liver, particularly when extrapolating values to rates of glycogen synthesis in vivo. Data were obtained only after removal of an amylase-like contaminant from foetal liver samples which invalidated the radioassay of glycogen synthase. This work illustrates the care needed in the analysis of foetal tissue and the interpretation of resulting data when utilizing methods developed for adult tissue.

Amylases↗

PubMed1983

Ordered synthesis and degradation of liver glycogen involving 2-amino-2-deoxy-D-glucose.

The incorporation of 2-amino-2-deoxy-D-glucose from precursor 2-amino-2-deoxy-D-galactose into liver glycogen has been shown to be a metabolically inhomogeneous process after starvation. The protein-to-polysaccharide ratio is also heterogeneous with respect to molecular size, and enhanced overall as compared to normal glycogen. The results are discussed from the viewpoint of a molecular order in the synthesis and degradation of liver glycogen.

Animals↗

PubMed1982

[Daily variations of plasma enzymes, plasma albumin and liver glycogen in 8- and 28-month-old rats].

Male Sprague-Dawley rats aged 8 and 28 months (each group 36 animals) were used in our study of the variations during the day in plasma glucose, total protein and albumin, the activities of plasma ALD, LDH, GOT, GPT and the glycogen content of the liver. The variations in these enzymes shown in rats of different ages and at different times of the day were interpreted as expressions of different metabolic conditions of the liver because when changes in the membrane permeability occur or liver cells die changes in plasma enzyme activity can be expected to follow the same direction. Lowered GOT and GPT levels in the old rats and the same glycogen content of the liver as that of the young rats indicated a decreased glucose metabolism in the old animals. The LDH activity did not follow any time pattern. Daily variations in GPT and liver glycogen (the maximum of both parameters was between 4.00 and 8.00) were shown more distinctly in the old rats, whereas the daily variations in the plasma total protein and albumin showed minima between 8.00 and 12.00 in the young animals. The authors concluded that daily rhythms, essential for the function of the organism as a whole, are accentuated with ageing. On the other hand, rhythms of minor importance are desynchronized.

Aging↗

PubMed1979

Effects of storage conditions in vitro on the assay of chick liver glycogen.

1. The reproducibility of an enzymic method for assaying chick liver glycogen was found to be +/- 1.6%. 2. Storage of liver at either -21 or -70 degrees C for up to 4 weeks, after freezing in liquid nitrogen, had no significant effect on glycogen concentration. However, the concentration of free glucose increased by about 50% during this time. 3. Storage of liver in ice-cold saline for up to 3 h proved unsatisfactory because of a significant loss of glycogen. 4. There was no significant difference in immediate glycogen concentration in liver tissue that was freeze-clamped, frozen in liquid nitrogen or collected into ice-cold saline. The free glucose concentration was higher, when estimated immediately after, with the latter two methods of collection of liver tissue.

Animals↗

PubMedDate not supplied

Effect of catecholamines and adrenergic antagonists on blood glucose, free fatty acids and liver glycogen levels in fed rats.

In fed rats the effects of catechloamines and adrenergic antagonists on blood glucose, free fatty acids (FFA), and liver glycogen levels were investigated in order to determine the role of alpha- and beta-adrenergic receptors in metabolic responses to catechloamines. Hyperglycemic responses to dopamine (DA), noradrenaline (NA), adrenaline (A) and isoprenaline (ISP) were dose-related and accompained by a depletion of liver glycogen. The relative potencies in producing hyperglycemia and in causing liver glycogenolysis were in descending order of potency, A, NA, DA and ISP. Hyperlipemic response was most potent to NA and DA, weaker to ISP, and least potent to A. Phentolamine antagonized completely both hyperglycemia and hepatic glycogen depletion induced by all catecholamines. Propranolol impaired only hyperglycemic responses to A and ISP. Phentolamine antagonized hyperlipemia induced by DA and NA but only partially impaired hyperlipemia after A. Propranolol only partially antagonized hyperlipemic responses to NA and ISP without influencing DA--and A-induced hyperlipemia. The results indicate that in fed rats hyperglycemic responses to catecholamines are mediated mainly by an alpha-adrenergic receptor, and hyperlipemic responses do not fit inton the alpha-receptor or beta-receptor classification.

Animals↗

PubMed1994

Elevated serum cortisol and glucose and liver glycogen in juvenile fish Clarias lazera after exposure to acid stress.

The exposure of juvenile Clarias lazera to acute (pH 3.1 for 96 h) and chronic (pH 5.4 or 4.7 for 12 weeks) acid stress (H2SO4) resulted in a number of physiological responses which could be considered as adaptive to the effects of stress. These responses were evident in the rapid rise of serum cortisol level from 43.0 +/- 0.76 microgram/dl in the control to 71.0 +/- 1.06 micrograms/dl (P < 0.001) 24 h after acute exposure. Also serum glucose level was increased from 123.66 +/- 1.85 mg/dl in the control and reached 295.0 +/- 2.89 mg/dl (P < 0.001) by the end of the experimental period (96 h). Chronic exposure of the fish to the two levels of pH (5.4 and 4.7) caused significant increase in serum cortisol and serum glucose level starting from the first week of exposure and lasted throughout the study period (12 weeks). As to the liver glycogen content, a slight but significant drop was found from 11.06 +/- 0.03 mg/100 mg tissue dry weight in the control to 10.80 +/- 0.06 mg/100 mg tissue dry weight (P < 0.025) 24 h after acute acid exposure. However, the values at 72 and 96 h were significantly higher than those in the control. In the chronic exposure study, the fish maintained at pH 5.4 showed a marked increase in liver glycogen content starting from week 2 and lasted till the end of experimental period (12 weeks). As early as after one week of treatment, in fish maintained in pH 4.7, liver glycogen content surged and remained significantly high till the twelfth week.

Animals↗

PubMed2005

Quantification of the glycogen cascade system: the ultrasensitive responses of liver glycogen synthase and muscle phosphorylase are due to distinctive regulatory designs.

BACKGROUND: Signaling pathways include intricate networks of reversible covalent modification cycles. Such multicyclic enzyme cascades amplify the input stimulus, cause integration of multiple signals and exhibit sensitive output responses. Regulation of glycogen synthase and phosphorylase by reversible covalent modification cycles exemplifies signal transduction by enzyme cascades. Although this system for regulating glycogen synthesis and breakdown appears similar in all tissues, subtle differences have been identified. For example, phosphatase-1, a dephosphorylating enzyme of the system, is regulated quite differently in muscle and liver. Do these small differences in regulatory architecture affect the overall performance of the glycogen cascade in a specific tissue? We address this question by analyzing the regulatory structure of the glycogen cascade system in liver and muscle cells at steady state. RESULTS: The glycogen cascade system in liver and muscle cells was analyzed at steady state and the results were compared with literature data. We found that the cascade system exhibits highly sensitive switch-like responses to changes in cyclic AMP concentration and the outputs are surprisingly different in the two tissues. In muscle, glycogen phosphorylase is more sensitive than glycogen synthase to cyclic AMP, while the opposite is observed in liver. Furthermore, when the liver undergoes a transition from starved to fed-state, the futile cycle of simultaneous glycogen synthesis and degradation switches to reciprocal regulation. Under such a transition, different proportions of active glycogen synthase and phosphorylase can coexist due to the varying inhibition of glycogen-synthase phosphatase by active phosphorylase. CONCLUSION: The highly sensitive responses of glycogen synthase in liver and phosphorylase in muscle to primary stimuli can be attributed to distinctive regulatory designs in the glycogen cascade system. The different sensitivities of these two enzymes may exemplify the adaptive strategies employed by liver and muscle cells to meet specific cellular demands.

Animals↗

PubMed1976

Regulation of rat liver glycogen synthesis and activities of glycogen cycle enzymes by glucose and galactose.

Direct regulation of rat liver glycogen metabolism by glucose and galactose was studied using an isolated liver perfusion system. Activation of glycogen synthase and net glycogen synthesis increased linearly when perfusate glucose concentration was increased from 125 to 500 mg/100 ml. Galactose, rapidly taken up by isolated rat liver regardless of circulating glucose concentration, increased these responses to glucose. In the presence of galactose (greater than or equal to 5 mg/100 ml), activation of synthase and glycogen synthesis were 1.5-fold higher at any given glucose concentration. The addition of insulin did not appreciably after synthase activation by glucose and galactose. Phosphorylase activity, low at circulating glucose levels above 125 mg/100 ml, was further decreased as glucose was increased or when galactose was added to the perfusate. Release of glucose into the perfusate in response to aglycemia was increased in the presence of galactose.

Animals↗

PubMed1992

Mechanism of activation of liver glycogen synthase by swelling.

The mechanism linking the stimulation of liver glycogen synthesis to swelling induced either by amino acids or hypotonicity was studied in hepatocytes, in gel-filtered liver extracts, and in purified preparations of particulate glycogen to which glycogen-metabolizing enzymes are bound. High concentrations of KCl, but not of potassium glutamate, were found to inhibit glycogen synthesis in permeabilized hepatocytes. Similarly, physiological concentrations (30-50 mM) of Cl- ions were also found to inhibit synthase phosphatase in vitro, whereas 10-20 mM Cl- ions, a concentration found in swollen hepatocytes, did not inhibit synthase phosphatase. Synthase phosphatase activity was more sensitive to inhibition by Cl- ions at low (0.1%) than at high (1%) concentrations of glycogen. By contrast, 10 mM glutamate and aspartate, a concentration observed in hepatocytes incubated with glutamine or proline, stimulated synthase phosphatase in vitro. Therefore, it is proposed that the fall in intracellular Cl- concentration as well as the increase in intracellular glutamate and aspartate concentrations, that are observed in swollen hepatocytes in the presence of amino acids, are responsible, at least in part, for the stimulation of synthase phosphatase and, hence, of glycogen synthesis.

Animals↗

PubMed2002

A correlative study on liver glycogen and endosulfan toxicity in Heteropneustes fossilis (Bloch.).

The biochemical tests were conducted to find out the relationship between liver glycogen and endosulfan toxicity on a catfish, Heteropneustes fossilis (Bloch.) using 0.00075, 0.00050 and 0.000375 ppm concentrations for 15, 30, 45 and 60 days of exposure periods. The quantity of liver glycogen showed decreasing trend as concentration of toxicant increased. The depletion in glycogen contents is greatly affiliated to cellular damage in hepatic cells.

Animals↗

PubMed1984

Phosphorylation of rat liver glycogen synthase by phosphorylase kinase.

Phosphorylation of rat liver glycogen synthase by rabbit skeletal muscle phosphorylase kinase results in the incorporation of approximately 0.8-1.2 mol of PO4/subunit. Analyses of the tryptic peptides by isoelectric focusing and thin layer chromatography reveal the presence of two major 32P-labeled peptides. Similar results were obtained when the synthase was phosphorylated by rat liver phosphorylase kinase. This extent of phosphorylation does not result in a significant change in the synthase activity ratio. In contrast, rabbit muscle glycogen synthase is readily inactivated by rabbit muscle phosphorylase kinase; this inactivation is further augmented by the addition of rabbit muscle cAMP-dependent protein kinase or cAMP-independent synthase (casein) kinase-1. Addition of cAMP-dependent protein kinase after initial phosphorylation of liver synthase with phosphorylase kinase, however, does not result in an inactivation or additional phosphorylation. The lack of additive phosphorylation under this condition appears to result from the phosphorylation of a common site by these two kinases. Partial inactivation of liver synthase can be achieved by sequential phosphorylation with phosphorylase kinase followed by synthase (casein) kinase-1. Under this assay condition, the phosphate incorporation into the synthase is additively increased and the synthase activity ratio (-glucose-6-P/+glucose-6-P) is reduced from 0.95 to 0.6. Nevertheless, if the order of the addition of these two kinases is reversed, neither additive phosphorylation nor inactivation of the synthase is observed. Prior phosphorylation of the synthase by phosphorylase kinase transforms the synthase such that it becomes a better substrate for synthase (casein) kinase-1 as evidenced by a 2- to 4-fold increase in the rate of phosphorylation. This increased rate of phosphorylation of the synthase appears to result from the rapid phosphorylation of a site neighboring that previously phosphorylated by phosphorylase kinase.

Animals↗

PubMed2005

Sources of plasma glucose and liver glycogen in fasted ob/ob mice.

Alterations in intrahepatic carbohydrate fluxes in ob/ob mice and the effects of acute leptin administration were studied in vivo by use of a dual-isotope tracer infusion. Metabolic sources of plasma glucose (gluconeogenesis (GNG) and glycogenolysis) and hepatic glycogen (GNG, direct synthesis and pre-existing) were determined in 20-h-fasted mice infused with [2-13C1]glycerol and [U13C6]glucose for 3 h. Total glucose output (TGO) and the rate of appearance (Ra) of plasma glycerol were measured by isotope dilution. GNG, the direct pathway of hepatic glycogen synthesis and hepatic triose-phosphate flux were determined by mass isotopomer distribution analysis (MIDA). Serum glucose, insulin, leptin and liver glycogen concentrations were also measured. After a 24-h fast, ob/ob mice had 2-fold higher TGO, 2.5-fold elevated liver glycogen content and markedly higher glycogenolytic flux to glucose, absolute GNG and direct glycogen synthesis rates (10-fold increased) compared to the control group. Ob/ob mice also had elevated triose-phosphate flux compared to controls (40 vs. 22 mg/kg lean body mass/min). A model of intrahepatic flux distributions in control and ob/ob mice is presented. In summary, elevated fasting plasma glucose concentrations are due to increased TGO in ob/ob mice, which is maintained by both increased GNG and increased glycogenolysis. Furthermore, the ob/ob mice have major alterations in fasting hepatic carbohydrate fluxes into triose-phosphate pools and glycogen. We support the model that actions of leptin on hepatic glucose metabolism require insulin or other factors.

Animals↗

PubMed1978

Liver glycogen synthesis and glucose tolerance in rats adapted to diets with a high proportion of fructose or glucose.

Glucose tolerance and in vivo incorporation of glucose into liver glycogen were investigated in rats fed high carbohydrate diets containing glucose or fructose as the sole carbohydrate source. As compared with control glucose-adapted rats, a slight deterioration of the glucose tolerance was observed in fructose-adapted rats. The possivle cause of the deteriorated glucose tolerance in fructose-adapted rats seems to be among others reduced glucose incorporation into liver glycogen and a smaller depression of endogenous glucose production by exogenous glucose.

Adaptation, Physiological↗

PubMed1977

Molecular and metabolic heterogeneity of liver glycogen.

On refeeding after starvation, the resynthesis of rabbit-liver glycogen proceeds inhomogeneously and over-produces material of low molecular weight. The fate of radioactivity incorporated into glycogen from D-glucose-14C can be explained if glycogen of high molecular weight is synthesised on a protein backbone. Confirmation of this view is given by the effect upon glycogen of reagents that break disulphide bonds; these cause loss of the polysaccharide of high molecular weight. Buoyant densities of glycogens are found to be independent of molecular weight and even of extensive degradation. It is concluded that glycogen synthesis proceeds by two routes; one results in the production of polysaccharide of high molecular weight which has a protein backbone capable of forming disulphide bonds, and another results in the production of polysaccharide of low molecular weight which has either no protein backbone or a protein backbone that is incapable of forming disulphide bridges. Apart from size, the two species are physicochemically indistinguishable.

Animals↗

PubMed2026

Application of 13C MRS demonstrates carbohydrate feeding spares muscle but not liver glycogen utilization during high-intensity interval exercise.

We examined liver and muscle glycogen utilization during high-intensity interval cycling, and the impact of carbohydrate (CHO) feeding, using noninvasive 13C magnetic resonance spectroscopy (MRS). Following 24 h of standardized dietary intake, nine male cyclists completed 8 × 5-min intervals (1-min recovery), ingesting either placebo (PLA), 60 g maltodextrin (CHO), or 60 g maltodextrin plus caffeine, taurine, l-theanine, l-citrulline, and citicoline (CHO+) in a randomized crossover design. 13C MRS and 1H imaging were performed pre- and postexercise to determine liver and muscle glycogen and liver volume, respectively. Liver glycogen utilization was not significantly different between trials (P = 0.101) despite lower postexercise plasma glucagon concentrations in CHO and CHO+ (P = 0.001). In contrast, muscle glycogen utilization was significantly lower (∼40%) with CHO feeding compared with PLA (P = 0.006), yet this sparing effect was not evident with CHO+ (P = 0.073) in accordance with a higher mean power output during the late intervals (+2.8%, P = 0.046). Plasma glucose was comparable between trials (P = 0.175), whereas plasma lactate was higher in CHO+ versus CHO (P = 0.003), alongside lower blood bicarbonate (P = 0.005), base excess (P < 0.001), and total CO2 (P = 0.004). These findings demonstrate preferential use of skeletal muscle glycogen during high-intensity interval training (HIIT), which is attenuated under conditions of CHO feeding. This sparing effect is, however, not evident with the coingestion of a caffeine-containing multi-ingredient blend, potentially due to an increased capacity to sustain higher power outputs resulting in greater glycogen utilization.NEW & NOTEWORTHY Using 13C MRS, we provide data demonstrating preferential use of skeletal muscle glycogen during HIIT. Furthermore, data show muscle glycogen utilization is attenuated with CHO feeding, yet sparing is not evident when coingesting a caffeine-containing formulation, potentially reflecting increased capacity to perform more total work rather than a direct metabolic effect of caffeine. In contrast, liver glycogen utilization was not significantly different with CHO feeding despite a modest reduction of ∼5 g versus placebo.

Male↗

PubMed1980

Circadian rhythm of liver glycogen metabolism in rats: effects of hypothalamic lesions.

The effects of electrolytic lesions of the suprachiasmatic nucleus (SCN) and ventromedial nucleus (VMH) of the hypothalamus on the circadian rhythm of liver glycogen metabolism were studied in rats fed during the dark period (2000-0800 h). Bilateral lesions of the SCN did not affect appreciably the circadian rhythmicity in three parameters of liver glycogen metabolism, i.e., glycogen content and glycogen synthetase I and phosphorylase a activities. In contrast, bilateral lesions of the VMH resulted in almost complete loss of circadian rhythmicity in phosphorylase a activity by lowering the high activity normally observed in late evening. VMH lesions also reduced the amplitudes of the rhythms of synthetase I activity and glycogen content, but did not abolish their rhythmicities. These results suggest that the integrity of the VMH, rather than the SCN, is important for regulation or expression of the food-triggered circadian rhythm of liver phosphorylase a activity. The implication of the lateral hypothalamic nucleus in regulation of the circadian rhythm of liver synthetase I is also discussed.

Animals↗