Increase In Glycogenolysis Research Articles

Hiperglikemia pada Pasien Diabetes Melitus Tipe 1 dan 2 yang Menjalani Puasa Ramadan : Laporan Kasus

Background: Ramadan fasting is an obligation for every Muslim, including Muslim patients who suffer from diabetes mellitus. The most common complication in diabetic patients when fasting is hypoglycemia, but in special conditions, hyperglycemia can also occur, and even emergency occurs in both type 1 and type 2 diabetes patients. Purpose: To know the hyperglycemia complications in type 1 and 2 diabetes mellitus in Ramadhan fasting Methods: Reported a case of inpatient diabetes mellitus 1 and 2 who underwent fasting during Ramadan and complications of hyperglycemia occurred in dr. Saiful Anwar Hospital (RSSA) Malang during the month of Ramadan Results: Both patients experienced hyperglycemia which was a response to an increase in response to hypoinsulinemia in type 1 diabetes and an increase in glycogenolysis in DM type 2. Conclusion: Hyperglycemia can occur in patients with type 1 and 2 DM who fast during the month of Ramadan

Combination of Metformin and Exercise in Management of Metabolic Abnormalities Observed in Type 2 Diabetes Mellitus.

Excess nutrient intake and lack of exercise characterize the problem of obesity and are common factors in insulin resistance (IR). With an increasing number of prediabetic, and type 2 diabetic populations, metformin is still the most prescribed glucose-lowering drug and is often accompanied by recommendations for regular physical exercise. Metformin, by the inhibition of complex 1 of the electron transport chain, and exercise, by increasing energy expenditure, both elicit a low cellular energy state that leads to improvements in glucose control via activation of adenosine 5ʹ monophosphate-activated protein kinase (AMPK). An augmented stimulation of the energy-sensing enzyme AMPK by either of the two modalities leads to an increase in glycogenolysis, glucose uptake, fat oxidation, a decrease in glycogen and protein synthesis, and gluconeogenesis in muscle and the liver, which are remarked as having positive effects on metabolic pathophysiology observed in IR and type 2 diabetes mellitus (T2DM). While both modalities exploit the energy-sensing enzyme AMPK to attain glucose homeostasis, the synergistic effect of these two treatments is not distinctly supported by the literature. Further, an antagonistic dynamic has been observed in cases where metformin and exercise were combined. Reduction of insulin-sensitizing effects of exercise and an overall hindrance of exercise performance and adaptations have been reported and could suggest the possible incongruity of these two modalities. The aim of this review is to elucidate the effect that metformin and exercise have on the management of the metabolic abnormalities observed in T2DM and to provide an insight into the interaction of these two modalities.

Epinephrine Responsiveness is Reduced in Livers from Trained Mice

Catecholamines increase liver glucose production at least in part through increases in glycogenolysis and gluconeogenesis. To date, the effects of prior exercise training on the liver’s response to epinephrine, in vivo, have not been fully elucidated. To examine the role of epinephrine signaling on indices of liver glucose production in trained mice, male C57BL/6 mice were subject to either 12 days of voluntary wheel running (TR) or remained sedentary (SED). Epinephrine (0.5 mg/kg body weight), or vehicle were injected intraperitoneally following 12 days of training and tissues harvested 15 minutes post‐injection. The rise in blood glucose following epinephrine injection was significantly blunted in trained compared to sedentary mice and this was paralleled by a blunted reduction in liver glycogen in trained mice. There was a main effect of epinephrine to increase the phosphorylation of protein kinase‐A substrates (pPKAs), which was driven by increases in the sedentary, but not trained, mice. Similarly, epinephrine‐induced increases in the mRNA expression of α‐ and β‐adrenergic receptor 1 and 2 and glucose‐6‐phosphatase were greater in SED compared to TR mice. Exercise and epinephrine decreased serum insulin levels and increased glucagon levels, however, there were no differences within epinephrine treated groups. Changes in phosphorylated AKT, AMPK, and phosphodiesterase 4B protein content, negative regulators of PKA signaling, do not explain the protective effects of exercise training against epinephrine induced increases in blood glucose and liver glycogen breakdown. Taken together our data suggest that prior exercise training reduces the liver’s response to epinephrine. This could be beneficial in the context of training‐induced sparing of glycogen during exercise.Support or Funding InformationThis work was funded, in part, through a National Sciences and Engineering Research Council of Canada (NSERC) grant to D.C.W., who is a Tier II Canada Research Chair in Lipids, Metabolism, and Health. H.A.D was supported by an Ontario Graduate Scholarship. G.L.M. was supported by an Ontario Graduate Scholarship and subsequently an NSERC Canada Graduate Scholarship. L.K.T. was supported by a Dairy Farmers of Ontario Doctoral Research Assistantship and an NSERC Postgraduate Scholarship.

Frontline Science: Monocytes sequentially rewire metabolism and bioenergetics during an acute inflammatory response.

Metabolism directs the severe acute inflammatory reaction of monocytes to guard homeostasis. This occurs by sequentially activating anabolic immune effector mechanisms, switching to immune deactivation mechanisms and then restoring immunometabolic homeostasis. Nuclear sirtuin 1 and mitochondrial pyruvate dehydrogenase kinase metabolically drive this dynamic and are druggable targets that promote immunometabolic resolution in septic mice and increase survival. We used unbiased metabolomics and a validated monocyte culture model of activation, deactivation, and partial resolution of acute inflammation to sequentially track metabolic rewiring. Increases in glycogenolysis, hexosamine, glycolysis, and pentose phosphate pathways were aligned with anabolic activation. Activation transitioned to combined lipid, protein, amino acid, and nucleotide catabolism during deactivation, and partially subsided during early resolution. Lipid metabolic rewiring signatures aligned with deactivation included elevated n-3 and n-6 polyunsaturated fatty acids and increased levels of fatty acid acylcarnitines. Increased methionine to homocysteine cycling increased levels of s-adenosylmethionine rate-limiting transmethylation mediator, and homocysteine and cysteine transsulfuration preceded increases in glutathione. Increased tryptophan catabolism led to elevated kynurenine and de novo biosynthesis of nicotinamide adenine dinucleotide from quinolinic acid. Increased branched-chain amino acid catabolism paralleled increases in succinyl-CoA. A rise in the Krebs cycle cis-aconitate-derived itaconate and succinate with decreased fumarate and acetyl-CoA levels occurred concomitant with deactivation and subsided during early resolution. The data suggest that rewiring of metabolic and mitochondrial bioenergetics by monocytes sequentially activates, deactivates, and resolves acute inflammation.

Hepatic ketogenic insufficiency reprograms hepatic glycogen metabolism and the lipidome.

While several molecular targets are under consideration, mechanistic underpinnings of the transition from uncomplicated nonalcoholic fatty liver disease (NAFLD) to nonalcoholic steatohepatitis (NASH) remain unresolved. Here we apply multiscale chemical profiling technologies to mouse models of deranged hepatic ketogenesis to uncover potential NAFLD driver signatures. Use of stable-isotope tracers, quantitatively tracked by nuclear magnetic resonance (NMR) spectroscopy, supported previous observations that livers of wild-type mice maintained long term on a high-fat diet (HFD) exhibit a marked increase in hepatic energy charge. Fed-state ketogenesis rates increased nearly 3-fold in livers of HFD-fed mice, a greater proportionate increase than that observed for tricarboxylic acid (TCA) cycle flux, but both of these contributors to overall hepatic energy homeostasis fueled markedly increased hepatic glucose production (HGP). Thus, to selectively determine the role of the ketogenic conduit on HGP and oxidative hepatic fluxes, we studied a ketogenesis-insufficient mouse model generated by knockdown of the mitochondrial isoform of 3-hydroxymethylglutaryl-CoA synthase (HMGCS2). In response to ketogenic insufficiency, TCA cycle flux in the fed state doubled and HGP increased more than 60%, sourced by a 3-fold increase in glycogenolysis. Finally, high-resolution untargeted metabolomics and shotgun lipidomics performed using ketogenesis-insufficient livers in the fed state revealed accumulation of bis(monoacylglycero)phosphates, which also accumulated in livers of other models commonly used to study NAFLD. In summary, natural and interventional variations in ketogenesis in the fed state strongly influence hepatic energy homeostasis, glucose metabolism, and the lipidome. Importantly, HGP remains tightly linked to overall hepatic energy charge, which includes both terminal fat oxidation through the TCA cycle and partial oxidation via ketogenesis.

Silencing of FGF‐21 expression promotes hepatic gluconeogenesis and glycogenolysis by regulation of the STAT3–SOCS3 signal

Insulin resistance is a metabolic disorder associated with type2 diabetes. Recent reports have shown that fibroblast growth factor-21 (FGF-21) plays an important role in the progression of insulin resistance. However, the biochemical and molecular mechanisms by which changes in FGF-21 activation result in changes in the rates of hepatic gluconeogenesis and glycogenolysis remain to be elucidated. In this study, we developed adenovirus-mediated shRNA against FGF-21 to inhibit FGF-21 expression in ApoE knockout mice. Using this mouse model, we determined the effects of FGF-21 knockdown invivo on hepatic glucose production, gluconeogenesis and glycogenolysis, and their relationship with the signal transducer and activator of transcription3 (STAT3)/suppressor of cytokine signaling3 (SOCS3) signal pathways. We show that liver-specific knockdown of FGF-21 in high-fat diet-fed ApoE knockout mice resulted in a 39% increase in glycogenolysis and a 75% increase in gluconeogenesis, accompanied by increased hepatic expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. Furthermore, FGF-21 knockdown decreased phosphorylation of STAT3 and SOCS3 expression in high-fat diet-fed mice. Our data suggest that hepatic FGF-21 knockdown increases gluconeogenesis and glycogenolysis by activation of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase via the STAT3/SOCS3 pathway, ultimately leading to exacerbation of hepatic insulin resistance.

Intestinal and liver changes after chronic ketamine and ketamine plus alcohol treatment

The effects of long-term chronic ketamine treatment on the intestine and the liver were studied in the ICR mice which had daily intraperitoneal injection of ketamine at 30 mg/kg per day for 7 months. The intestine showed no significant pathology after treatment but had a decrease of the positive sites of proliferative cell nuclear antigen in the mucosae of the intestines after ketamine and ketamine plus alcohol (added in the last month) treatment. No significant apoptosis (via TUNEL) nor necrosis (via lactic acid dehydrogenase) was detected in the intestines of all control and ketamine-treated groups, with the exception of an increase of lactic acid dehydrogenase in the mucosae of the intestines of the ketamine plus alcohol group. In the liver, loss of glycogen was observed in animals after ketamine and ketamine plus alcohol treatment, in addition to the pathology reported in a previous work. The decrease in quantity of glycogen in the liver reflected either a failure of glycogen synthesis from glucose or an increase of glycogenolysis in the liver.

Glucose production in response to glucagon is comparable in preterm AGA and SGA infants

Low plasma glucose concentrations are more often detected in small-for-gestational-age (SGA) than in appropriate-for-gestational-age (AGA) infants. This is ascribed to impaired glucose production due to presumed lower liver glycogen stores in SGA infants. The change in glucose production induced by glucagon is considered to be an indicator of liver glycogen content. We compared the effect of glucagon on glucose kinetics in preterm AGA and SGA infants. In 5 AGA and 5 SGA preterm infants (postnatal age: 3-6 days) glucose production and gluconeogenesis were measured using stable isotopes immediately before and for 1 h after a bolus of glucagon. After glucagon the plasma glucose concentration and glucose production increased significantly over time (P<0.05 and P<0.0001, respectively). The changes were comparable between AGA and SGA infants. Glycogenolysis contributed 75-80% to the increase in glucose production. The increase in glucose production after glucagon was similar in preterm AGA and SGA infants, and mainly due to an increase in glycogenolysis. Based on the assumption that glycogenolysis is an indicator of liver glycogen content, our data do not support the hypothesis that liver glycogen content is lower in preterm SGA compared to AGA infants after the first postnatal day.

Insulin inhibits glucagon-induced glycogenolysis normally in perivenous hepatocytes of Wistar fatty rats

Wistar fatty (WF) rats are obese, hyperinsulinemic and hyperglycemic, and thus a model of type 2 diabetes mellitus. Since we have found that insulin specifically inhibits glucagon-induced glycogenolysis in perivenous hepatocytes (PVH) from normal rats, we examined the inhibitory effect of insulin on glucagon-induced glycogenolysis in PVH of hyperinsulinemic WF rats. Basal glucose release was 64.0 ± 4.1 nmol/mg protein/30 min from PVH of lean littermates (WL rats) and 137.0 ± 19.3 nmol/mg protein/30 min from that of WF rats ( p < 0.01). These were proportional to the glycogen content in PVH of WL and WF rats (56.7 ± 7.2 and 131.0 ± 20.3 μg/mgprotein, p < 0.01), and increased to 109.0 ± 8.8 and 225.8 ± 17.9 nmol/mg protein/30 min, respectively, with 0.1 nmol/l glucagon. When 10 nmol/l insulin was coincubated, 0.1 nmol/l glucagon-induced increase in glucose release decreased to 93.3 ± 10.9 nmol/mg protein/30 min in PVH of WL rats ( p < 0.01) and to 181 ± 20.7 nmol/mg protein/30 min in PVH of WF rats ( p < 0.01). Thus, insulin antagonized glucagon-induced glycogenolysis in PVH similarly between WL and WF rats, to 56.7 ± 13.3% and to 46.1 ± 7.5%, respectively. Thus, the antagonizing effect of insulin on glucagon-induced increase in glycogenolysis was preserved in PVH of hyperinsulinemic and hyperglycemic WF rats.

Effects of acute insulin excess and deficiency on gluconeogenesis and glycogenolysis in type 1 diabetes.

To determine whether insulin induces acute changes in endogenous glucose production (EGP) via changes in gluconeogenesis (GNG), glycogenolysis (GL), or both, we measured GNG (with (2)H(2)O) and GL (EGP-GNG) in nine patients with type 1 diabetes during acute insulin excess produced by subcutaneous injection of insulin and during insulin deficiency which developed between 5 and 8 h after insulin injection. During insulin excess, free insulin concentration rose fivefold (from 36 to 180 pmol/l). Plasma glucose was maintained between 6.2 and 6.7 mmol/l for approximately 4 h with IV glucose. EGP (with 6,6-(2)H glucose) decreased from 17.1 to 9.8 micro mol. kg(-1). min(-1) after 1 h. This decrease was almost completely accounted for by a decrease in GL (from 10.7 to 4.6 micro mol. kg(-1). min(-1)). During insulin deficiency, plasma glucose rose from 6.2 to 10.5 mmol/l and EGP from 9.5 to 14.3 micro mol/kg min. The increase in EGP again was accounted for by an increase in GL. We conclude that in type 1 diabetes acute regulation of EGP by insulin is mainly via changes in GL while GNG changes little during the early hours of acute insulin excess or deficiency.

Thyroid hormone excess and glucose intolerance.

The elevated plasma glucose levels in hyperthyroidism may be explained by increased rates of endogenous glucose production, due mainly to increased gluconeogenesis. The rates of insulin-stimulated glucose disposal in peripheral tissues in hyperthyroidism have been found, in general, either normal or increased. Skeletal muscle is the most important tissue for the disposal of glucose in response to insulin. In this tissue, insulin increases glucose disposal by stimulating glucose transport, glucose phosphorylation/glycolysis, glycogen synthesis and glucose oxidation. Studies examining insulin-stimulated glucose metabolism in skeletal muscle have suggested that, in the hyperthyroid state, it may be of primary importance to increase the rates of glycolysis and lactate formation relative to glucose oxidation in this tissue in order to provide substrate for gluconeogenesis (increase Cori cycle activity). This effect will be achieved primarily by a decrease in glycogen synthesis and an increase in glycogenolysis. When hyperthyroidism becomes more severe, an increased rate of glucose uptake into muscle may then be necessary since the increased conversion of glycogen to lactate could not be sustained for prolonged periods and might lead to a depletion in glycogen stores. This mechanism would ensure that the level of glucose in plasma is kept normal or slightly increased. Thus, an increased Cori cycle activity may be a necessary mechanism to provide optimal conditions in hyperthyroidism for the control of glucose utilization without increasing the risk of hypoglycemia. In addition to lactate, increased rates of gluconeogenesis in hyperthyroidism can also be sustained by increased plasma concentrations of amino acids (mostly glutamine and alanine) and glycerol, as well as by increased plasma concentrations of free fatty acids.

Effect of a selective rise in sinusoidal norepinephrine on HGP is due to an increase in glycogenolysis.

To determine the effect of a selective rise in liver sinusoidal norepinephrine (NE) on hepatic glucose production (HGP), norepinephrine (50 ng.kg-1.min-1) was infused intraportally (Po-NE) for 3 h into five 18-h-fasted conscious dogs with a pancreatic clamp. In the control protocol, NE (0.2 ng.kg-1.min-1) and glucose were infused peripherally to match the arterial NE and blood glucose levels in the Po-NE group. Hepatic sinusoidal NE levels rose approximately 30-fold in the Po-NE group but did not change in the control group. The arterial NE levels did not change significantly in either group. During the portal NE infusion, HGP increased from 1.9 +/- 0.2 to 3.5 +/- 0.4 mg.kg-1.min-1 (15 min; P < 0.05) and then gradually fell to 2.4 +/- 0.4 mg.kg-1.min-1 by 3 h. HGP in the control group did not change (2.0 +/- 0.2 to 2.0 +/- 0.2 mg.kg-1.min-1) for 15 min but then gradually fell to 1.1 +/- 0.2 mg.kg-1.min-1 by the end of the study. Because the fall in HGP from 15 min on was parallel in the two groups, the effect of NE on HGP (the difference between HGP in the two groups) did not decline over time. Gluconeogenesis did not change significantly in either group. In conclusion, elevation in hepatic sinusoidal NE significantly increases HGP by selectively stimulating glycogenolysis. Compared with the previously determined effects of epinephrine or glucagon on HGP, the effect of NE is, on a molar basis, less potent but more sustained over time.

ACTIVATION RATE OF GLYCOGEN PHOSPHORYLASE AND PYRUVATE DEHYDROGENASE IN HUMAN SKELETAL MUSCLE DURING INTENSE EXERCISE 588

The purpose of this study was to determine the time course for the transformation of glycogen phosphorylase and pyruvate dehydrogenase (PDH) during the first and third bouts of maximal intermittent exercise. Six subjects completed three 30-s bouts of maximal isokinetic cycling at 100 rpm, each separated by 4 min of rest. Biopsies of the vastus lateralis were taken before, and at 6s, 15s and 30s of bouts 1 and 3. Total work in bout 1 was 18.4±0.5 kJ, and decreased to 13.7±1.0 kJ in bout 3. Prior to bout 1, PDH was 14.2±0.1% activated, increased to 48.4±0.1% at 6s, and was totally activated by 15s. The mole fraction of active phosphorylase (PHOS a) was 9.9±2.2% at rest, increased to 46.8±5.3% and 47.4±6.4% at 6s and 15s, respectively, and by 30s, decreased to 21.8±4.2%. Prior to bout 3, PDH was 41.7±0.1% activated; by 6s it was 100% activated. PHOS a fraction increased from 10.5±2.7% to 14.7±2.7% and 20.5±1.6% at 6s and 15s, respectively, and was partially inactivated to 16.2±5.7% at 30s. Glycogen utilization was 127.0±35.1 and 15.1±10.2 mmol/kg dw in bouts 1 and 3, respectively. Lactate increased from 2.7±0.4 to 76.1±7.4 mmol/kg dw in bout 1 and from 97.7±16.7 to 107.1±15.3 mmol/kg dw in bout 3. In bout 1, the rapid transformation to PHOS a was associated with rapid increases in glycogenolysis and a large accumulation of lactate due to the delayed activation of PDH. However, in bout 3 the small change in PHOS a resulted in a lower rate of glycogenolysis and the rapid activation of PDH resulted in a greater oxidation of pyruvate and hence less lactate accumulation.

Loss of hepatic autoregulation after carbohydrate overfeeding in normal man.

To determine the effect of increased glycogen stores on hepatic carbohydrate metabolism, 15 nondiabetic volunteers were studied before and after 4 d of progressive overfeeding. Glucose production and gluconeogenesis were assessed with [2-3H] glucose and [6-14C] glucose (Study I, n = 6) or [3-3H] glucose and [U-14C]-alanine (Study II, n = 9) and substrate oxidation was determined by indirect calorimetry. Overfeeding was associated with significant (P < 0.01) increases in plasma glucose (4.97 +/- 0.10 to 5.09 +/- 0.11 mmol/liter), insulin (18.8 +/- 1.5 to 46.6 +/- 10.0 pmol/liter) and carbohydrate oxidation (4.7 +/- 1.4 to 18.0 +/- 1.5 mumol.kg-1.min-1) and a decrease in lipid oxidation (1.2 +/- 0.2 to 0.3 +/- 0.1 mumol.kg-1.min-1). Hepatic glucose output (HGO) increased in Study I (10.2 +/- 0.5 to 13.1 +/- 0.9 mumol.kg-1.min-1, P < 0.01) and Study II (11.17 +/- 0.67 to 13.33 +/- 0.83 mumol.kg-1.min-1, P < 0.01), and gluconeogenesis decreased (57.6 +/- 6.4 to 33.4 +/- 4.9 mumol/min, P < 0.01), indicating an increase in glycogenolysis. The increase in glycogenolysis was only partly compensated by an increase in glucose cycle activity (2.2 +/- 0.2 to 3.4 +/- 0.4 mumol.kg-1.min-1, P < 0.01) and the fall in gluconeogenesis, thus resulting in increased HGO. The suppression of gluconeogenesis despite increased lactate and alanine (glycerol was decreased) was associated with decreased free fatty acid (FFA) oxidation and negligible FFA enhanced gluconeogenesis. These studies suggest that increased liver glycogen stores alone can overwhelm normal intrahepatic mechanisms regulating carbohydrate metabolism resulting in increased HGO in nondiabetic man.

In vivo nuclear magnetic resonance studies on the lugworm Arenicola marina. I. Free inorganic phosphate and free adenylmonophosphate concentrations in the body wall and their dependence on hypoxia

The cytoplasmic concentrations of free inorganic phosphate and free AMP in the body wall of the lugworm Arenicola marina were estimated in order to verify their proposed regulatory role in glycogenolysis during anaerobiosis (Kamp 1993). Using in vivo 31P nuclear magnetic resonance spectroscopy the concentration of free inorganic phosphate was determined to be 4.7±0.7 mmol·1-1 (±standard deviation, n=3) varying with season (Juretschke and Kamp 1995). These values were two to three times lower than those measured in perchloric acid extracts. In contrast, values for the phosphagen phosphotaurocyamine assessed biochemically in the extracts and by in vivo nuclear magnetic resonance were very similar. During the transition from normoxia to hypoxia the concentration of free inorganic phosphate increased to the same extent and at the same rate as the concentration of phosphotaurocyamine decreased. A discrepancy was also found for the biochemically determined AMP and ADP concentrations in the extract and those derived from the equilibrium constants of the taurocyamine kinase (ADPfree) and adenylate kinase (AMPfree) reactions. Calculated concentrations of ADPfree and AMPfree in normoxic specimens were about two or even four orders of magnitude lower than the values determined in extracts. During hypoxia the concentrations of AMP and ADP increase moderately when measured biochemically in extracts, while the values for ADPfree and AMPfree rise three- and nine-fold during the first 3 h of hypoxia. Thereafter, the levels stay constant due to a progressive acidosis. If during hypoxia pHi is stabilized by addition of buffering substances to the incubation medium, both ADPfree and AMPfree rise continuously. The significant changes found for the concentrations of free inorganic phosphate and AMPfree support their assumed regulatory role in glycogenolysis during anaerobiosis, though these AMPfree values seem too low to actually activate glycogen phosphorylase. The strong effect of pHi on the levels of ADPfree and AMPfree suggest a mechanism by which acidosis prevents a continuing increase of glycogenolysis (ATP-producing pathway) during prolonged anaerobiosis (protective effect of acidosis).

Naproxen inhibits hepatic glycogenolysis induced by Ca 2+-dependent agents

1. 1. The non-steroidal anti-inflammatory naproxen inhibited steady-state glycogenolysis stimulation caused by norepinephrine, phenylephrine ( α 1-agonists) and methotrexate (not receptor mediated) in the isolated perfused rat liver. Stimulation of glycogenolysis caused by these agents is Ca 2+-dependent. 2. 2. Naproxen did not inhibit glycogenolysis stimulation caused by glucagon. 3. 3. The action of naproxen depended on the extracellular Ca 2+ concentration. At 0.25 mM extracellular Ca 2+ the norepinephrine stimulated glycogenolysis was inhibited by 60% by 0.5 mM naproxen. At 3.5 mM Ca 2+ inhibition was reduced to 25%. The inhibition degree correlated linearly with the extracellular Ca 2+ concentration. 4. 4. 45Ca 2+ efflux stimulation caused by norepinephrine was not affected by naproxen, indicating that the mobilization of the intracellular Ca 2+ pools was not significantly affected by naproxen. The initial increases in glycogenolysis caused by norepinephrine in the absence of extracellular Ca 2+(pre steady-state) were not affected by naproxen. These increases depend on intracellular Ca 2+ mobilization. 5. 5. It can be concluded that the action of naproxen is most probably related to the cytosolic Ca 2+ concentration which, under steady-state conditions, depends on the extracellular one during the action of Ca 2+-dependent glycogenolytic agents.

Correlation between fructose 2,6-bisphosphate and lactate production in skeletal muscle

The epinephrine-induced production of lactate in nonexercising muscles may be due in part to allosteric activation of 6-phosphofructo-1-kinase by fructose 2,6-bisphosphate (F-2,6-P2). To determine if a correlation exists between F-2,6-P2 and lactate production in skeletal muscle, isolated rat hindlimbs were perfused for 30 min with a medium containing epinephrine at concentrations varying between 1.7 +/- 0.5 and 72.4 +/- 4.2 nM. In comparison to control values, hindlimbs perfused with 72.4 +/- 4.2 nM epinephrine had a two- to threefold increase in F-2,6-P2 and a fourfold increase in muscle lactate production. Hindlimb lactate production was highly correlated to gastrocnemius adenosine 3',5'-cyclic monophosphate (r = 0.80), fructose 6-phosphate (r = 0.87), and F-2,6-P2 (r = 0.81). The adenosine 3',5'-cyclic monophosphate-mediated increase in glycogenolysis with consequent increase in fructose 6-phosphate (substrate for 6-phosphofructo-1-kinase and 6-phosphofructo-2-kinase) is likely important for induction of lactate production by inactive muscle. The high correlation between muscle F-2,6-P2 and muscle lactate production at varying concentrations of epinephrine supports the hypothesis that the epinephrine-induced activation of glycolysis and lactate production in nonexercising muscle is mediated in part by increases in F-2,6-P2 levels.

Effects of somatostatin on glucagon-stimulated glycogenolysis and gluconeogenesis in hepatocytes cultured in vitro.

The effects of somatostatin (SS-14) on glycogenolysis and gluconeogenesis in rat hepatocytes cultured in vitro in a serum-free medium were investigated. Somatostatin (122 nmol l-1) did not significantly change the basal glucose production with or without pyruvate (10 mmol l-1). Glucagon strongly (over 100%) increased the glucose production in hepatocytes incubated in a medium supplemented with 10 mmol l-1 pyruvate. This increase in glucose production is the result of increased rates of gluconeogenesis and glycogenolysis. Somatostatin partially inhibited the glucagon stimulated increase in glucose production. Glucagon also significantly increased the glucose production in a glucose-free medium without pyruvate, which resulted from an increase of glycogenolysis. Somatostatin did not inhibit the increase in glucose production in these conditions. After a 4 h 'fast', glycogen in hepatocytes fell to a very low level. Glucose production was minimal. After the addition of pyruvate, there was a increase in gluconeogenesis and glucose production. Glucagon stimulated the rate of gluconeogenesis. Somatostatin completely inhibited this glucagon-stimulated increase in gluconeogenesis.

Transient activation of hepatic glycogenolysis by thrombin in perfused rat livers.

Thrombin, a peptide with native protease activity, caused a rapid (less than 1 min) increase in glycogenolysis of about 30%, assessed from rates of production of glucose+lactate+pyruvate, and in oxygen uptake in perfused rat liver. These increases were followed by a rapid return to basal values within 5 min. The effect of thrombin on glycogenolysis was dose-dependent and was maximal at perfusate concentrations around 1 U/ml. Interestingly, the effect of thrombin on glycogenolysis could be elicited only once in any given liver. The activation of glycogenolysis by thrombin was diminished nearly 50% by prior infusion of the protease inhibitor, diisopropyl fluorophosphate (10 microM), and over 90% when thrombin was treated with diisopropyl fluorophosphate prior to infusion. The stimulation of glycogenolysis by thrombin could be detected in isolated hepatocytes or in livers stored for 24 h in cold Euro-Collins solution, a treatment which destroys endothelial cells. Further, thrombin stimulated production of prostaglandin D2 from arachidonic acid in cultured hepatic endothelial but not Kupffer cells. The effect of thrombin on carbohydrate output was also blocked by a phospholipase A2 inhibitor (quinacrine, 50 microM) and by an inhibitor of the cyclooxygenase (indomethacin, 20 microM), suggesting the involvement of cyclooxygenase in the mechanism of action of thrombin. In support of this idea, the transient kinetics of stimulation of glycogenolysis by thrombin and arachidonic acid was nearly identical to release of thromboxane B2 (80-420 pg/ml) and prostaglandin D2 (300-900 pg/ml) from the perfused liver. Further, a second addition of thrombin failed to increase thromboxane and prostaglandin D2 release as well as carbohydrate production, supporting a causal link between these phenomena. Taken together, these data support the hypothesis that thrombin interacts with receptors in the liver, possibly on endothelial cells, leading to activation of phospholipase A2 and subsequent transient production of prostaglandins and thromboxanes. These mediators subsequently interact with receptors on parenchymal cells, leading to a transient stimulation of glycogenolysis.

Activation of glycogenolysis by methotrexate: Influence of calcium and inhibitors of hormone action

The influence of Ca 2+ and the possible action of hormone blockers on the activation of glycogenolysis by methotrexate were investigated. Methotrexate was inactive on glycogenolysis and oxygen uptake when the liver, depleted of intracellular Ca 2+, was perfused with Ca 2+-free medium. The action of methotrexate in calcium-depleted hepatocytes could be restored by the addition of extracellular Ca 2+. When Ca 2+ was absent in the extracellular medium, but the intracellular stores were not depleted, methotrexate produced transient and progressively attenuated increases in glycogenolysis and oxygen uptake. Like many agonists, methotrexate produced transient increases in Ca 2+ efflux. The action of methotrexate was not blocked by the antagonists of norepinephrine, phenylephrine, isoproterenol, vasopressin and angiotensin II. It was concluded that methotrexate acts through a Ca 2+-dependent mechanism, which is similar to that of the Ca 2+-dependent agonists. This action, however, seems not to be receptor mediated.