Inhibition Of Glycogen Synthesis Research Articles

Specific defects in insulin-mediated muscle metabolism in acute uremia

The mechanisms underlying the abnormal insulin-mediated muscle glucose metabolism occurring in acute uremia (ARF) have not been identified. To characterize the defects, insulin dose-response curves for glucose uptake, glycogen synthesis, glucose oxidation, glycolysis, and lactate release were measured in incubated rat epitrochlearis muscles. ARF did not affect insulin sensitivity, but decreased the responsiveness to insulin of glucose uptake, glycogen synthesis, and glucose oxidation. Glycogen synthesis was subnormal at all levels of insulin and at the maximal insulin concentration; it was 54% lower in muscles of ARF compared to control rats. This inhibition of glycogen synthesis in ARF could be caused by a 23% decrease in the total activity of muscle glycogen synthase and the percentage of enzyme in the activated form. Glycogen phosphorylase activity was unchanged by ARF. ARF also increased the ratio of muscle lactate release to glucose uptake at concentrations of insulin from 10 to 10(4) microU/ml. In the absence and presence of insulin, muscle protein degradation was increased by ARF. In individual muscles incubated with insulin, the rate of proteolysis was correlated with the ratio of lactate release to glucose uptake (r = + 0.82; P less than 0.01). From the insulin dose-response relationships and changes in enzyme activities, we conclude that ARF increases protein degradation in muscle and causes abnormal insulin-mediated glucose metabolism. The abnormalities in glucose metabolism are caused by changes in post-receptor events.

The hyperglycemic factor of the CNS of the freshwater snail Lymnaea stagnalis: Interaction with glucose stimulation of glycogen synthesis and evidence for its release during anaerobiosis

In the freshwater pulmonate snail Lymnaea stagnalis glycogen synthesis in the glycogen storage cells (GC) is stimulated by increasing external glucose concentrations. On the other hand, a hyperglycemic factor from the CNS inhibits glycogen synthesis and stimulates glycogen breakdown in these cells. This CNS factor may be involved in the physiological control of glycogen mobilization. In the present study the interaction between the inhibiting effect of the CNS factor and the stimulating effect of increasing glucose concentrations on glycogen synthesis in isolated GC was investigated. The results, analyzed by determination of the Michaelis-Menten parameters for saturation kinetics, suggest that the CNS factor increases the glucose concentration required for half-maximal stimulation of glycogen synthesis, but does not influence the maximum rate of synthesis (competitive type of inhibition). The role of the hyperglycemic factor during conditions of glycogen breakdown was investigated by extirpation of the cerebral ganglia (-CG), which contain the main release sites of the factor. Extirpation did not affect the hemolymph glucose concentration or the glycogen levels in the GC during starvation. However, -CG animals showed reduced levels of the hyperglycemia normally associated with exposure to anaerobic conditions.

Direct effects of the hyperglycemic factor of the freshwater snail Lymnaea stagnalis on isolated glycogen cells

In the freshwater pulmonate snail Lymnaea stagnalis special cells, the glycogen cells (GC) are present for the storage of glycogen reserves. These cells occur in large numbers in the anterior mantle region. In a previous paper in vitro experiments with intact anterior mantle tissue indicated that a hyperglycemic factor is released from the central nervous system (CNS) which stimulates glycogen mobilization in mantle tissue ( M. A. Hemminga, J. J. Maaskant, W. Koomen, and J. Joosse (1985). Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis. Gen. Comp. Endocrinol. 57, 117–123). In the present study the question of whether this factor affects glycogen metabolism of GC isolated from mantle tissue was investigated. It is reported that in high-K + Ringers the CNS is stimulated to release a factor which, in a dose-dependent way, inhibits glycogen synthesis in isolated GC (measured as a decreased incorporation of [ 14C]glucose into glycogen). Simultaneous with this glycogen synthesis-inhibiting effect, stimulation of glycogen degradation is found (measured as a decreased retention of prelabeled glycogen). It is concluded that (1) the factor released by the CNS having these effects on isolated GC is the same as the hyperglycemic factor which was reported to stimulate glycogen mobilization in intact mantle tissue, and (2) GC after isolation from mantle tissue have retained their ability to respond to this factor. High-K + bathing Ringers of the cerebral/buccal ganglia have a stronger inhibiting effect on glycogen synthesis in isolated GC than bathing Ringers of the remainder part of the CNS, indicating that in this part of the brain the major release sites of the hyperglycemic factor are located. Dorsal body hormone, ovulation hormone, or growth hormone of L. stagnalis probably are not identical with the hyperglycemic factor, as homogenates of parts of the cerebral ganglia which are known to contain these respective hormones do not influence glycogen synthesis in isolated GC.

Neuroendocrine control of glycogen mobilization in the freshwater snail Lymnaea stagnalis

In the freshwater snail Lymnaea stagnalis the anterior mantle region, which mainly consists of large numbers of special glycogen-storing cells, is an important depot for the energy reserves of this snail. In organ culture experiments the central nervous system (CNS), in contrast to other tissues, both inhibits glycogen synthesis (measured as incorporation of [ 14C]glucose into glycogen) and stimulates glycogen breakdown in anterior mantle tissue (measured as a decreased retention of prelabeled glycogen). These effects are dose dependent, with saturation at the highest doses tested. High-potassium Ringer solution stimulates the secretion of a CNS factor which induces glucose release by anterior mantle tissue. This glucose-release-stimulating effect of the CNS is also dose dependent, but saturation of the response was not achieved. It is concluded that inhibition of glycogen synthesis and stimulation of glycogen breakdown and glucose release are probably effects of a single neurohormone which controls glycogen mobilization from the storage cells in the mantle. Like similar factors in other animal phyla, this putative neurohormone is referred to as a hyperglycemic factor.

Effects of VIP and forskolin on alanine metabolism in isolated hepatocytes

The effects of vasoactive intestinal polypeptide (VIP) and of forskolin on alanine metabolism in hepatocytes isolated from fed and fasted rats were examined. VIP and 17 μM forskolin stimulated glucose production, gluconeogenesis from alanine, and ureagenesis, and inhibited glyconeogenesis to comparable degrees. However, combination of 17 μM forskolin with a maximal dose of VIP significantly augmented only the inhibition of glyconeogenesis. At 100 μM, forskolin induced metabolic responses comparable to those induced by glucagon, but similarly, in combination with maximal doses of VIP or glucagon, augmented only inhibition of glycogen synthesis. In addition to demonstrating modulation of alanine metabolism by VIP and forskolin, these results raise questions about the nature of the coupling between VIP receptor occupancy and metabolic response. Vasoactive intestinal polypeptide Forskolin Gluconeogenesis Alanine Glycogen metabolism

Inhibition of glycogen synthesis in rat hepatocytes by medium Zn 2+

In hepatocytes from fasted rats, Zn2+ in the range from 0 to 500 microM has relatively minor effects on gluconeogenesis from most substrates, or on ureagenesis from NH3. In hepatocytes from fed rats, Zn2+ does not affect glycogenolysis. In hepatocytes from fasted rats, in which glycogen is being actively synthesized using the substrate combination (Katz et al. (1976) Proc. Natl.Acad.Sci.USA 73,3433-3437) of glucose, lactate and glutamine (all 10mM), Zn2+ markedly inhibits glycogen synthesis, with total inhibition at 500 microM, and a half maximal effect in the range from 50 to 100 microM. Dipicolinate (pyridine 2,6-dicarboxylate), a zinc chelator, is about as effective as L-glutamine in activating glycogen synthesis with the substrate combination of dihydroxyacetone, lactate and glucose (all 10mM). This suggests the possible hypothesis that endogenous Zn2+ might control the rate of glycogen synthesis in vivo. However, alternate explanations such as metabolite accumulation are also possible, since dipicolinate causes inhibition of gluconeogenesis from L-lactate.

Glycogenolytic effects of the calcium ionophore A23187, but not of vasopressin or angiotensin, in foetal-rat hepatocytes.

Vasopressin, angiotensin and phenylephrine stimulate glycogenolysis in postnatal rat liver by a Ca2+-mediated mechanism not involving cyclic AMP. To determine whether these hormones promote glycogenolysis in foetal liver, we have examined their effects, and those of the Ca2+ ionophore A23187, on glycogen metabolism in cultured foetal-rat hepatocytes. Vasopressin and angiotensin (0.1 nM-0.1 microM) had no effects on either glycogen synthesis (as assessed by [14C]glucose incorporation into glycogen) or phosphorylase a activity. However, A23187 at 1 and 10 microM inhibited glycogen synthesis by 31.3 and 89.1% respectively (both P less than 0.001) and stimulated phosphorylase a activity by 66.9 and 184.1% respectively (both P less than 0.01). Incubation of cells in Ca2+-deficient medium attenuated the effects of 10 microM-A23187 on glycogen synthesis and abolished the effects of 1 microM-A23187. As in postnatal liver, glucagon (1 and 20 nM) and isoprenaline (1 and 10 microM), which activate adenylate cyclase, inhibited glycogen synthesis and stimulated phosphorylase a activity in foetal hepatocytes. The minimal effective concentration of phenylephrine was 10 times that of isoprenaline. These results indicate striking differences in the ontogeny of cyclic AMP-mediated and Ca2+-mediated processes which regulate hepatic glycogenolysis. Since increases in cytosolic Ca2+ induce glycogenolysis in foetal-rat liver, the weak or absent responses to vasopressin, angiotensin and the alpha-adrenergic agonists may result from defects in hormone-receptor binding or in post-receptor events leading to the mobilization of intracellular Ca2+ stores.

GLYCOGENOLYTIC EFFECTS OF THE CALCIUM IONOPHORE A23187, BUT NOT VASOPRESSIN OR ANGIOTENSIN, IN FERTALRAT HEPATOCYTES

Vasopressin, angiotensin II and phenylephrine stimulate glycogenolysis in postnatal rat liver by a non-cAMP, calcium-mediated mechanism. To determine whether these hormones also promote glycogenolysis in fetal liver, we have examined their effects, and those of the calcium ionophore A23187 (A), on glycogen metabolism in cultured fetal rat hepatocytes. Vasopressin and angiotensin (10−10-10−7M) had no effects on either 14C-glucose incorporation into glycogen or phosphorylase a activity. However, A at concentrations of 1 and 10 uM inhibited glycogen synthesis by 31.3 and 89.1 percent, respectively (p< 0.001) and stimulated phosphorylase a activity by 66.9 and 184.1 percent respectively (p < 0.01). Incubation of cells in calcium-deficient medium markedly attenuated the effects of A on glycogen synthesis. As in postnatal liver, glucagon (1 and 20 nM) and isoproterenol (1 and 10 uM), which activate adenylate cyclase, inhibited glycogen synthesis and stimulated phosphorylase a activity in fetal hepatocytes. The minimal effective concentration of phenylephrine was 10 times that of isoproterenol. These results indicate striking differences in the ontogeny of cAMP-mediated and non-cAMP, calcium-mediated processes which regulate hepatic glycogenolysis. Since increases in cytosolic calcium induce glycogenolysis in fetal rat liver, the weak or absent responses to vasopressin, angiotensin and α - adrenergic agonists may result from defects in hormone-receptor binding or in postreceptor events leading to the mobilization of intracellular calcium stores. NIH grants HD07447 and HDO6301.

Influence of Nitrogen Sources on Glycogen Metabolism in Saccharomyces carlsbergensis

Summary: Storage of glycogen in yeast (Saccharomyces carlsbergensis) cells was strongly suppressed by the presence of nitrogen sources. Peptone initiated glycogen breakdown within minutes. This effect could not be duplicated with ammonium ions alone nor with single amino acids or mixtures of a few amino acids, but it could be duplicated by the addition of all the amino acids in the molar ratios found in casein. If fewer amino acids were supplied, glycogen was initially synthesized but then depleted after 30–60 min at 28 °C, the time being shorter for more easily utilized amino acids. In the presence of glucose, dinitrophenol (10-4 m) slowed down or inhibited glycogen synthesis, but it did not initiate glycogen breakdown in the absence of glucose. Energy charge and the concentrations of adenylates and UDP-glucose were not significantly different in the presence and absence of peptone; pyruvate accumulated under the former condition. No turnover of glycogen was observed during glycogen synthesis, pointing to an effective regulation of glycogen metabolism via an unknown mechanism.

Regulation of the basal and cyclic AMP-stimulated rates of glycogen synthesis in [formula omitted] by an intermediate of purine biosynthesis

In Escherichia coli an abrupt increase in the rate of glycogen synthesis occurs at the onset of total nitrogen starvation. We present here both in vivo and in vitro data indicating that this increase occurs because of the loss of a nitrogen-containing intermediate of purine biosynthesis (apparently 5-aminoimidazole-4-carboxamide ribonucleotide) that inhibits glycogen synthesis. We also show that this inhibitory intermediate antagonizes the stimulation of glycogen synthesis by 3′,5′-cyclic AMP. The uncovering of the regulation of glycogen synthesis by this inhibitor apparently provides the first link in understanding the 23-year-old observation of a reciprocal relationship between growth rate and glycogen accumulation in E. coli .

Cardiac calmodulin and its role in the regulation of metabolism and contraction

Calmodulin, the ubiquitous and multifunctional Ca 2+-dependent regulatory protein, is capable of activating a number of enzymes through the formation of active ternary complexes Ca 2+-calmodulin-enzyme, upon increase of the cytosolic Ca 2+ level from pCa 8 to pCa 5. In cardiac muscle, calmodulin is involved in the Ca 2+-dependent activation of cyclic nucleotide phosphodiesterase and, perhaps, inhibition of adenylate cyclase. Cardiac and vascular myosin light chain kinases are also Ca 2+-calmodulin-dependent. Whereas light chain phosphorylation is required for vascular smooth muscle contraction, the effect of cardiac myosin phosphorylation is as yet unknown. Calmodulin is involved in the control of the phosphorylation of the sarcoplasmic reticulum Ca 2+ pump activator, phospholamban, thereby modulating the rate of Ca 2+ uptake. Calmodulin is likely to be a subunit of cardiac glycogen phosphorylase b kinase, that triggers glycogen breakdown and presumably inhibits glycogen synthesis. Finally calmodulin binds to other calmodulin-binding proteins of hitherto unknown function.

Interference of chemicals with glycogen metabolism in isolated hepatocytes

Freshly isolated hepatocytes in suspension were used to evaluate the possible effects of certain chemicals. Conditions including the choice of the incubation medium have been defined for maintaining the cells competent for a sufficient length of time. Using paracetamol alone or in combination with diethylmaleate, we have been able to show that these chemicals markedly alter the metabolic state of the cells, as indicated by an inhibition of glycogen synthesis and even by an enhancement of glycogen degradation, without modifying membrane integrity. These effects are dose-dependent and probably mediated through modification of glycogen phosphorylase activity.

Effects of epinephrine and the cyclic AMP phosphodiesterase inhibitor SQ 20009 on glucose and glycogen metabolism in skeletal muscle

In rat diaphragm incubated in vitro, epinephrine and isoproterenol inhibited glucose uptake and the incorporation of radioactive glucose into glycogen. The metabolic effects of epinephrine were inhibited by the beta-adrenergic blocking agents, propranolol and sotalol, but not by the alpha-adrenergic blocking drug, phentolamine. The phosphodiesterase inhibitor, 1-ethyl-4-(isopropylidine-hydrazino)-1H-pyrazolo-(3,4-b)-pyridine-5-carboxylic acid, ethyl ester, hydrochloride (SQ 20009), also decreased glucose uptake and glycogen synthesis. In contrast to the action of epinephrine, exogenous calcium ions were required for the effects of SQ 20009 on phosphorylase activation, increased tissue glucose- 6-phosphate levels and lactate production. It was concluded that the inhibition of glucose uptake that occurred when tissue cyclic AMP levels were increased by beta-adrenergic drugs or phosphodiesterase inhibitors was not due directly to accumulation of glucose-6-phosphate from glycogenolysis but was a result of a cyclic AMP-mediated inhibition of glycogen synthesis.

Alteration by halothane of glucose and glycogen metabolism in rat skeletal muscle.

Exposure of resting rat diaphragm for one hour in vitro to halothane (1-1.5, 2-2.5 and 4-4.5 per cent in oxygen) produced significant alterations of intracellular glucose disposition. Glycolysis (as measured by lactate production) increased, while glycogen formation was inhibited in a dose-related fashion. Net glucose uptake was unaffected by the anesthetic except during exposure to 4-4.5 per cent halothane, when 14 per cent depression of uptake was found. Total glycogen content decreased, due mainly to the inhibition of glycogen synthesis and to some extent to a stimulation of glycogenolysis. The anesthetic did not interfere with the effect of insulin on glucose uptake or the intracellular disposition of glucose. Creatine phosphate concentrations decreased following exposure of diaphragm to 1-1.5, 2-2.5 and 4-4.5 per cent halothane, while the adenosine triphosphate concentration declined after exposure to 4-4.5 per cent only. Although the mechanism(s) whereby halothane alters glucose and glycogen metabolism are unknown, it is possible that the anesthetic acts primarily by affecting membranes containing enzymes involved in the metabolism of glycogen.

Involvement of polyamines in the progestin-induced stimulation of endometrial glycogen synthesis during organ culture

Addition of progesterone to an organ culture of endometrial fragments increased glycogen levels 2–3 fold. Concomitant with this increase in glycogen was an increase in S-adenosyl-L-methionine decarboxylase activity and the conversion of putrescine into spermidine. When an inhibitor of S-adenosyl-L-methionine decarboxylase, methylglyoxyl bis(guanylhydrazone), was added to the culture with progesterone, glycogen synthesis was blocked. Inhibition of glycogen synthesis was reversed by the addition of spermidine, suggesting that spermidine synthesis may be necessary for the progestin-induced accumulation of endometrial glycogen.

The interaction of chemical compounds with the functional state of the liver

Most of the enzymes which are involved in the biotransformation of chemical compounds are located in the liver. The activities of these enzymes can be altered by a great variety of foreign compounds. Especially lipophilic and relatively stable agents are capable of enhancing the activities of drug-metabolizing enzymes, after chronic exposure, by increasing the amount of these enzymes. Metabolism of foreign compounds generally results in the formation of much less toxic endproducts which can be excreted easily due to their more hydrophilic nature. However it is known that certain chemicals are converted to very toxic compounds which can produce various injuries. Enzyme inducers of course raise the possibility of impairments by accelerating the synthesis of these toxic metabolites. Numerous xenobiotic compounds are also capable of stimulating carbohydrate metabolism via the D-glucuronic acid pathway. In this pathway hexose is converted via UDPglucose, UDPglucuronic acid and D-glucuronic acid into D-glucaric acid, L-ascorbic acid and L-xylulose respectively. It has been demonstrated that at least in the case of short-term treatment a stimulation of the D-glucuronic acid pathway is based on an increased availability of UDPglucose in the liver cell which, in turn, is the result, of an inhibition of glycogen synthesis. Evaluation of the urinary excretion of D-glucaric acid as a reliable nonspecific test for diagnosing exposure to chemical compounds as well as the drug-metabolic capacity, will be the subject of the next article.

Effects of epinephrine and cyclic AMP phosphodiesterase inhibitors on the glycogen synthetic pathway and glucose content in skeletal muscle

The actions on carbohydrate metabolism of epinephrine and the cyclic AMP phosphodiesterase inhibitors, theophylline and SQ 20009, were studied using rat hemidiaphragms incubated in vitro. The inhibition of glucose uptake produced by epinephrine was almost equal to the decrease in the incorporation of [ 14C]glucosc into glycogen, while incorporation into lactate of 14C from labeled glucose was not influenced by the hormone. Although epinephrine decreased total tissue glycogen, it had relatively little effect on the removal of radioactive glucose incorporated into glycogen during a preincubation in the absence of hormone when the tissue was subsequently incubated with nonradioactive glucose. This indicates that the decrease in the net incorporation of [ 14C]glucose into glycogen produced by the hormone in vitro is caused predominantly by an inhibition of glycogen synthesis and cannot be accounted for by an increase in the turnover rate of glycogen. Theophylline and SQ 20009 produced a dose-dependent inhibition of glucose uptake and glycogen synthesis, similar to that of epinephrine. Incubation of hemidiaphragms with epinephrine or cyclic AMP phosphodiesterase inhibitors in the presence of glucose led to an increased intracellular accumulation of glucose. Possible explanations for this phenomenon are discussed. The uptake of the nonmetabolizable sugar. 3- O-methylgucose, by skeletal muscle was not affected by epinephrine, indicating that the hormone influences only the uptake of the natural substrate, glucose, which can be incorporated into glycogen. The alterations in muscle metabolism described here were associated with increases in the tissue content of cyclic AMP and it was concluded that an important action of epinephrine in resting muscle is a cyclic AMP-mediated inhibition of the glucose-to-glycogen synthetic pathway.

Stimulation of the glucuronic acid pathway in isolated rat liver cells by phenobarbital

1. 1. Administration of phenobarbital to suspensions of isolated rat hepatocytes resulted within 90 min in an enhanced synthesis of d-glucaric acid, l-ascorbic acid and uridine diphosphate glucuronic acid (UDPGA). 2. 2. No alterations in the in vitro activities of UDPGdehydrogenase and UDPglucuronyltransferase were found within 120 min after treatment of the cells with phenobarbital. 3. 3. At increasing phenobarbital concentrations the uridine diphosphate glucose (UDPG) level increased significantly whereas a decrease in the glycogen concentration occurred. 4. 4. C 14-labeling experiments showed a lower rate of d-glucose-1-C 14 incorporation in glycogen (expressed as per mg protein) of phenobarbital treated cells, whereas an equal increase in specific activities as a function of time was observed in both phenobarbital treated and control cells. This strongly suggests that the lowered glycogen concentration, after treatment with phenobarbital, is caused by a decreased synthesis of glycogen, resulting in an enhanced availability of UDPG. On account of these results it has been concluded that a stimulation of the D-glucuronic acid pathway most probably is based on an inhibition of glycogen synthesis.

ChemInform Abstract: SYNTHESIS AND ANTITUMOR ACTIVITY OF 5′‐PHOSPHATES AND CYCLIC 3′,5′‐PHOSPHATES DERIVED FROM BIOLOGICALLY ACTIVE NUCLEOSIDES

AbstractAus den entsprechenden Ribonucleosiden (I) entstehen mit Phosphoroxychlorid und Triäthylphosphat Phosphate wie (II), die zu (III) cyclisiert werden.

Evidence for the coordinate control of glycogen synthesis, glucose utilization, and glycolysis in Escherichia coli. II. Quantitative correlation of the inhibition of glycogen synthesis and the stimulation of glucose utilization by 2,4-dinitrophenol with the effects on the cellular levels of glucose 6-phosphate, fructose, 1,6-diphosphate, and total adenylates.

In cultures of Escherichia coli W4597(K) and G34 under various nutritional conditions the rates of glucose utilization and cellular levels of fructose-1,6-P2 are quantitatively related by the Hill equation where the value of the Hill coefficient is approximately equal to 2. This is the first evidence that fructose-P2, or any metabolite which covaries with fructose-P2, modulates glucose utilization in E. coli. In light of previous observations from our laboratory this new observation and those in the succeeding report provide the first evidence that in E. coli glycolsis, glycogen synthesis and glucose utilization are coordinately regulated, thus providing for the coupling of ATP utilization and production under various metabolic circumstances. Alterations in the level of ATP apparently affect the velocity of phosphofructokinase, the rate-limiting enzyme in glycolsis, altering the cellular levels of glucose-6-P or fructose-P2. Changes in the levels of these hexose phosphates are quantitatively related to alterations in the rates of glucose utilization and glycogen synthesis in the intact E. coli cell.