Effect of cyclic guanosine monophosphate on certain indices of muscle tissue carbohydrate metabolism during the wound process

The effect of intraperitoneal administration of cGMP (0.5 mg per animal) on carbohydrate metabolism of wound area muscle tissue was studied in experiments on rats with linear skin wounds. The content of glycogen, gluconeogenesis, activity of glycogen phosphorylase, lactate dehydrogenase and malate dehydrogenase were studied. Cyclic GMP induced a substantial activation of glycogen metabolism (elevation of gluconeogenesis, increase in the activity of glycogen phosphorylase) even the third day after the operation. The animals not given cGMP demonstrated such an activation only the fifth day following the operation. Under the effect of cGMP the activity of lactate dehydrogenase rose the third day after the operation. Thus cGMP administration to the animals with wounds leads to an earlier mobilization of energy resources thereby promoting the acceleration of wound healing.     

Aberrant nutritional regulation of carbohydrate synthesis by parasitized Manduca sexta L

The present studies confirm that storage carbohydrate synthesis from [1-(13)C]glucose is elevated in Manduca sexta parasitized by Cotesia congregata, despite a decrease in the rate of metabolism of the labeled substrate. Further, the results demonstrate that a similar pattern of carbohydrate synthesis and glucose metabolism was induced in normal larvae by administration of the glycolytic inhibitor, iodoacetate. (13)C enrichment of C6 of trehalose and glycogen demonstrated randomization of the C1 label at the triose phosphate step of the glycolytic/gluconeogenic pathway and suggested that gluconeogenesis, that is, de novo carbohydrate formation, contributed to the synthesis of carbohydrate in both normal and parasitized insects. Accounting for differences in the (13)C enrichment in C1 of trehalose and glycogen due to direct labeling from [1-(13)C]glucose, the mean C6/C1 labeling ratios in trehalose and glycogen of parasitized larvae and insects treated with iodoacetate were greater than the mean ratio observed in normal larvae, suggesting a greater contribution of gluconeogenesis to trehalose labeling in parasitized insects. This conclusion was confirmed by additional investigations on the metabolism of [3-(13)C]alanine by normal and parasitized insects. The pattern of (13)C enrichment in hemolymph trehalose observed in normal larvae maintained on a low carbohydrate diet indicated a large contribution of gluconeogenesis, while gluconeogenesis contributed very little to trehalose labeling in normal insects maintained on a high carbohydrate diet. Parasitized insects maintained on a high or a low carbohydrate diet displayed a significantly greater contribution of gluconeogenesis to trehalose labeling than was observed in normal larvae maintained on the same diets. In conclusion, these investigations indicate that regulation over the utilization of dietary glucose for trehalose and glycogen synthesis as well as the dietary regulation of de novo carbohydrate synthesis were altered by parasitism.     

Gradual transfer to sea water of rainbow trout: effects on liver carbohydrate metabolism

The levels of glycogen and glucose, as well as of the activities of several key enzymes of glycogenolysis, glycolysis, gluconeogenesis and the pentose phosphate shunt were assessed in livers of small (97 g) and large (166 g) rainbow trout Oncorhynchus mykiss during gradual transfer to sea water (salinities of 0, 9, 18 and 28%). Plasma glucose and protein levels were also evaluated. Liver carbohydrate metabolism changed during gradual adaptation of rainbow trout to sea water. Glucose increased with salinity in livers of both sizes of animals, as did glycogenolysis and gluconeogenesis, but this latter only in large animals, and glycolytic rates in small animals. The different responses in metabolic parameters between sizes of animals may reflect a higher stress of the small animals and/or a better adaptation of large animals to increased salinities, in a way similar to that previously suggested by other authors after evaluation of non-metabolic parameters. The changes observed at 28% can also be the result of reduced food consumption.     

Diurnal rhythms in liver carbohydrate metabolism. Comparative aspects and critical review

Literature data on the diurnal rhythms of blood glucose, liver glycogen levels and key hepatic enzyme activities of glycolysis, gluconeogenesis, glycogen metabolism and lipogenesis in animals are reviewed. Materials on the diurnal rhythms of the activities of other enzymes involved in carbohydrate metabolism and related pathways such as the equilibrium glycolytic enzymes are also given. Interspecies comparison and analysis of the results and their interpretation are given.     

Carbohydrate metabolism is perturbed in peroxisome-deficient hepatocytes due to mitochondrial dysfunction, AMP-activated protein kinase (AMPK) activation, and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) suppression

Hepatic peroxisomes are essential for lipid conversions that include the formation of mature conjugated bile acids, the degradation of branched chain fatty acids, and the synthesis of docosahexaenoic acid. Through unresolved mechanisms, deletion of functional peroxisomes from mouse hepatocytes (L-Pex5(-/-) mice) causes severe structural and functional abnormalities at the inner mitochondrial membrane. We now demonstrate that the peroxisomal and mitochondrial anomalies trigger energy deficits, as shown by increased AMP/ATP and decreased NAD(+)/NADH ratios. This causes suppression of gluconeogenesis and glycogen synthesis and up-regulation of glycolysis. As a consequence, L-Pex5(-/-) mice combust more carbohydrates resulting in lower body weights despite increased food intake. The perturbation of carbohydrate metabolism does not require a long term adaptation to the absence of functional peroxisomes as similar metabolic changes were also rapidly induced by acute elimination of Pex5 via adenoviral administration of Cre. Despite its marked activation, peroxisome proliferator-activated receptor α (PPARα) was not causally involved in these metabolic perturbations, because all abnormalities still manifested when peroxisomes were eliminated in a peroxisome proliferator-activated receptor α null background. Instead, AMP-activated kinase activation was responsible for the down-regulation of glycogen synthesis and induction of glycolysis. Remarkably, PGC-1α was suppressed despite AMP-activated kinase activation, a paradigm not previously reported, and they jointly contributed to impaired gluconeogenesis. In conclusion, lack of functional peroxisomes from hepatocytes results in marked disturbances of carbohydrate homeostasis, which are consistent with adaptations to an energy deficit. Because this is primarily due to impaired mitochondrial ATP production, these L-Pex5-deficient livers can also be considered as a model for secondary mitochondrial hepatopathies.     

Effect of diazepam treatment on metabolic indices in trained and untrained rats

Exercise training, like diazepam, is commonly employed as a means of reducing anxiety. Both diazepam and exercise training have been shown to modify carbohydrate and lipid metabolism as well as influence calcium metabolism in skeletal muscle. As receptor binding and thereby efficacy of diazepam has been demonstrated to be modulated by the lipid environment of the receptor, and changes in calcium levels can affect a number of intracellular signalling pathways, we sought to determine if the interaction of both chronic diazepam and exercise training would modify selected metabolic indices in an animal model. For this purpose, muscle and liver glycogen, blood glucose and plasma free fatty acids (FFA) were measured in sedentary, exercise trained and exercise trained, acutely exhausted animals. Alterations in lipid and carbohydrate metabolism were observed in all experimental groups. Diazepam treatment alone exerts metabolic consequences, such as elevated muscle glycogen and plasma FFA and depressed blood glucose levels, which are similar to those observed with exercise training. When animals are acutely exercised to exhaustion, however, differences appear, including a reduced rise in plasma FFA, which suggests that long-term diazepam treatment does influence exercise metabolism, possibly as a result of effects on the sympatho-adrenal system.     

Hepatic 11 beta-hydroxysteroid dehydrogenase 1 involvement in alterations of glucose metabolism produced by acidotic stress in rat

11 beta-hydroxysteroid dehydrogenase (HSDs) enzymes regulate the activity of glucocorticoids in target organs. HSD1, one of the two existing isoforms, locates mainly in CNS, liver and adipose tissue. HSD1 is involved in the pathogenesis of diseases such as obesity, insulin resistance, arterial hypertension and the Metabolic Syndrome. The stress produced by HCl overload triggers metabolic acidosis and increases liver HSD1 activity associated with increased phosphoenolpyruvate carboxykinase, a regulatory enzyme of gluconeogenesis that is activated by glucocorticoids, with increased glycaemia and glycogen breakdown. The aim of this study was to analyze whether the metabolic modifications triggered by HCl stress are due to increased liver HSD1 activity. Glycyrrhetinic acid, a potent HDS inhibitor, was administered subcutaneously (20 mg/ml) to stressed and unstressed four months old maleSprague Dawley rats to investigate changes in liver HSD1, phosphoenolpyruvate carboxykinase (PECPK) and glycogen phosphorylase activities and plasma glucose levels. It was observed that all these parameters increased in stressed animals, but that treatment with glycyrrhetinic acid significantly reduced their levels. In conclusion, our results demonstrate the involvement of HSD1 in stress induced carbohydrate disturbances and could contribute to the impact of HSD1 inhibitors on carbohydrate metabolism and its relevance in the study of Metabolic Syndrome Disorder and non insulin-dependent diabetes mellitus.     

Gluconeogenesis in the amphibian retina. Lactate is preferred to glutamate as the gluconeogenic precursor.

The capacity for gluconeogenesis in the isolated amphibian retina was found to be approx. 70-fold greater with lactate than with glutamate as the gluconeogenic precursor, 1426 versus 21 pmol of glucose incorporated into glycogen/h per mg of protein. It was also found that 11-15% of the glucosyl units in glycogen are derived from C3 metabolites of the glycolytic pathway, suggesting that lactate is recycled within the retina. In concert with these metabolic observations, a full complement of the gluconeogenic enzymes was detected in retinal homogenates. These included: glucose-6-phosphatase, fructose-1,6-bisphosphatase, acetyl-CoA-dependent pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Agents that regulate the rate of gluconeogenesis in hepatic tissue were tested on the retina. At concentrations of glutamate and lactate that are presumed to be relevant physiologically, it was found that vasoactive intestinal peptide, ionophore A23187 and elevated [K+] each enhanced the rate of gluconeogenesis in Ringer containing 50 microM-glutamate, whereas in Ringer containing 8.5 mM-lactate these agents inhibited the rate of gluconeogenesis. Further, it was found that the classic gluconeogenic hormone glucagon inhibited gluconeogenesis in both glutamate- and lactate-containing Ringer. Retinal energy metabolism was found to be altered in lactate-containing Ringer, in that lactate production was suppressed completely. In addition, glycogen metabolism appeared to be dependent on increased cytosolic Ca2+ and was insensitive to increased retinal cyclic AMP.     

Dietary carbohydrate effects on some plasma organic acids and aspects of glucose metabolism in turkey poults

The effects on newly-hatched turkey poults of feeding diets with varying levels of carbohydrate and of oral gavage with suspensions of corn starch were studied. Feeding lowered hepatic glucose-6-phosphatase activity and raised blood glucose and hepatic glycogen concentrations. In Nicholas strain turkeys, increases of dietary levels of carbohydrate enhanced hepatic glycogen stores without affecting blood glucose concentration or glucose-6-phosphatase activity. Oral gavage of poults with suspensions of corn starch in water raised blood glucose and hepatic glycogen concentrations and lowered glucose-6-phosphatase activity in dose- and time-dependent manners. Changes were noted at 1 hr post-gavage. Oral gavage with starch lowered lactate concentrations in muscle and plasma and lowered plasma concentrations of β-hydroxybutyrate and urate. Plasma concentrations of pyruvate appeared to decline with post-hatch holding without feed. Thus, the apparent effect of starch gavage on plasma pyruvate (high concentration) is dependent upon the length of the holding period for the controls. The data show that poults can alter their metabolism (decrease lipid oxidation and gluconeogenesis and increase carbohydrate stores) almost immediately (1 hr) after oral administration of carbohydrate.     

The role of vasopressin and oxytocin in the regulation of glycemia levels and carbohydrate metabolism in the liver

Vasopressin and oxytocin administered subcutaneously and intravenously in a dose of 0.5 IU/kg were studied in experiments on albino male rats for their effect on the glycogen content and gluconeogenesis enzymes activity in the liver as well as on the glycemia level. Neurohormones injected subcutaneously have no effect on the values of the measured indices. Vasopressin already the first 15-60 min after its intravenous injection in the mentioned dose leads to an essential decrease of the glucose content in blood, glycogen amount, glucose-6-phosphatase and fructose-1.6-diphosphatase (EC 3.1.3.9 and 3.1.3.11) activity in the liver of test animals. The intravenous injection of oxytocin in the same dose induces changes in the carbohydrate metabolism indices similar in their direction and magnitude to the effects of intravenous injection of vasopressin.     

Mechanisms of Pathogenesis in Listeria monocytogenes Infection III. Carbohydrate Metabolism

Several enzymes and metabolites concerned with carbohydrate metabolism were examined in mice infected with Listeria monocytogenes. Liver glycogen and glucose decreased parallel to severity of infection. The concentration of glucose in the blood fell to abnormally low levels with a hypoglycemia being most evident at 72 hr. There was a significant decrease in the activity of hepatic uridine diphosphate glucose-glycogen transglucosylase. This decrease in enzymatic activity correlated with the rate of glycogen depletion. Phosphorylase activity declined in a similar fashion, contraindicating enhanced glycogenolysis as the mechanism responsible for glycogen depletion. Although glucose-6-phosphatase decreased throughout the infection period, it did not appear to be the major metabolic defect causing hypoglycemia in Listeria-infected mice. Further distortion of carbohydrate metabolism was indicated by findings of increased levels of pyruvate and lactate in the blood of infected animals.     

Hepatocyte heterogeneity in the metabolism of carbohydrates.

Periportal and perivenous hepatocytes possess different amounts and activities of the rate-generating enzymes of carbohydrate and oxidative energy metabolism and thus different metabolic capacities. This is the basis of the model of metabolic zonation, according to which periportal cells catalyze predominantly the oxidative catabolism of fatty and amino acids as well as glucose release and glycogen formation via gluconeogenesis, and perivenous cells carry out preferentially glucose uptake for glycogen synthesis and glycolysis coupled to liponeogenesis. The input of humoral and nervous signals into the periportal and perivenous zones is different; gradients of oxygen, substrates and products, hormones and mediators and nerve densities exist which are important not only for the short-term regulation of carbohydrate metabolism but also for the long-term regulation of zonal gene expression. The specialization of periportal and perivenous hepatocytes in carbohydrate metabolism has been well characterized. In vivo evidence is provided by the complex metabolic situation termed the 'glucose paradox' and by zonal flux differences calculated on the basis of the distribution of enzymes and metabolites. In vitro evidence is given by the different flux rates determined with classical invasive techniques, e.g. in periportal-like and perivenous-like hepatocytes in cell culture, in periportal- and perivenous-enriched hepatocyte populations and in perfused livers during orthograde and retrograde flow, as well as with noninvasive techniques using miniature oxygen electrodes, e.g. in livers perfused in either direction. Differences of opinion in the interpretation of studies with invasive and noninvasive techniques by the authors are discussed. The declining gradient in oxygen concentrations, the decreasing glucagon/insulin ratio and the different innervation could be important factors in the zonal expression of the genes of carbohydrate-metabolizing enzymes. While it is clear that the hepatocytes sense the glucagon/insulin gradients via the respective hormone receptors, it is not known how they sense different oxygen tensions; the O2 sensor may be an oxygen-binding heme protein. The zonal separation of glucose release and uptake appears to be important for the liver to operate as a 'glucostat'. Thus, zonation of carbohydrate metabolism develops gradually during the first weeks of life, in part before and in part with weaning, when (in rat and mouse) the fat- and protein-rich but carbohydrate-poor nutrition via milk is replaced by carbohydrate-rich food. Similarly, zonation of carbohydrate metabolism adapts to longer lasting alterations in the need of a 'glucostat', such as starvation, diabetes, portocaval anastomoses or partial hepatectomy.     

Effect of fasting on carbohydrate metabolism in frugivorous bats (Artibeus lituratus and Artibeus jamaicensis)

The compensatory changes of carbohydrate metabolism induced by fasting were investigated in frugivorous bats, Artibeus lituratus and Artibeus jamaicensis. For this purpose, plasma levels of glucose and lactate, liver and muscle glycogen content, rates of liver gluconeogenesis and the activity of related enzymes were determined in male bats. After a decrease during the first 48 h of fasting, plasma glucose levels remained constant until the end of the experimental period. Plasma lactate levels, extremely high in fed bats, decreased after 48 h of fasting. Similarly, liver glycogen content, markedly high in fed animals, was reduced to low levels after 24 h without food. Muscle glycogen was also reduced in fasted bats. The expected increase in liver gluconeogenesis during fasting was observed after 48 h of fasting. The activities of liver glucose-6-phosphatase and fructose-1,6-bisphosphatase were not affected by food withdrawn. On the other hand, fasting for 24 h induced an increase in the activity of liver cytosolic phosphoenolpyruvate carboxykinase. The data indicate that liver gluconeogenesis has an important role in the glucose homeostasis in frugivorous bats during prolonged periods of food deprivation. During short periods of fasting liver glycogenolysis seems to be the main responsible for the maintenance of glycemia.     

Metabolical changes induced by chronic phenol exposure in matrinxã Brycon cephalus (teleostei: characidae) juveniles

Phenol and its derivatives are xenobiotics present in many industrial wastewaters and in non-specific pesticides. It is a lipophilic compound and, therefore, accumulates along the trophic chain. Phenol is often found in marine and fresh water environments. The aim of this work was to detect metabolic changes induced by phenol in Brycon cephalus juveniles. Several enzymes activities and metabolites were quantified in the liver, white muscle and plasma. Among the enzymes assayed are alanine and aspartate amino transferases (ALAT and ASAT), lactate dehydrogenase (LDH) and malate dehydrogenase (MDH). Glucose, glycogen, lactate, ammonia and pyruvate were also quantified in tissues and plasma (glycogen in tissues only). The liver was the most responsive organ. The activities of the transaminases increased in muscle and liver, followed by an increase in hepatic ammonia. Correlation between ammonia and transaminases points towards phenol-induced consumption of protein. Hepatic glycogen and glucose contents were lower followed exposure to phenol. The same was observed for muscle glucose, suggesting considerable use of carbohydrate stores. The activity of hepatic lactate dehydrogenase increased with negative correlation with muscle lactate. This suggests that hepatic gluconeogenesis supplies tissues like muscle and brain with glucose. These results indicate that phenol intoxication demands metabolic energy and leads to significant changes of the metabolic profile of the fish, inducing to a certain extent a shift from carbohydrate catabolism to protein catabolism and the activation of gluconeogenesis.     

Effects of altered thyroid status on beta-adrenergic actions on skeletal muscle glycogen metabolism

The effects of hypothyroidism on glycogen metabolism in rat skeletal muscle were studied using the perfused rat hindlimb preparation. Three weeks after propylthiouracil treatment, serum thyroxine was undetectable and muscle glycogen and Glc-6-P were decreased. Basal and epinephrine-stimulated phosphorylase a and phosphorylase b kinase activities were also significantly reduced, as were epinephrine-stimulated cAMP accumulation and cAMP-dependent protein kinase activity. Conversely, basal and epinephrine-stimulated glycogen synthase I activities were significantly higher while the Ka of the enzyme for Glc-6-P was lower in hypothyroid animals. Propylthiouracil-treated rats also had increased phosphoprotein phosphatase activities towards phosphorylase and glycogen synthase and decreased activity of phosphatase inhibitor 1. beta-Adrenergic receptor binding and basal and epinephrine-stimulated adenylate cyclase activities were reduced in muscle particulate fractions from hypothyroid rats. Administration of triiodothyronine to rats for 3 days after 3 weeks of propylthiouracil treatment restored the altered metabolic parameters to normal. It is proposed that the decreased beta-adrenergic responsiveness of the enzymes of glycogen metabolism in hypothyroid rat skeletal muscle is due to increased activity of phosphoprotein phosphatases and to reduced beta-adrenergic receptors and adenylate cyclase activity.     

Characterization and Biological Activity of the Monocytosis-producing Agent of Listeria monocytogenes

Experiments directed toward determining the lipids in extracts of Listeria monocytogenes containing monocytosis-producing agent (MPA) and the effect of these extracts on several biochemical parameters previously shown to change during experimental Listeria infection were conducted. MPA-containing extracts were found to be a complex of lipids with glycerides, glycolipids, and phospholipid being present. No common cell wall carbohydrates were found. A glyceride, designated glyceride A, was determined to cause the characteristic mononuclear response observed in mice injected with MPA-containing extracts. Fasted MPA-treated animals showed less gluconeogenesis than did controls. Blood glucose levels declined in MPA-treated animals. Increases observed in both blood urea nitrogen and plasma glutamic-pyruvic transaminase were greater in the control groups. Incorporation of (14)C-alanine into liver glycogen was depressed in MPA-treated animals. Liver steroid levels in the control groups increased during fasting and remained elevated for the duration of the experiments, while levels in the MPA-treated groups declined initially and showed no increase until 72 hr after injection. MPA appears to affect steroid metabolism and consequently the animals' homeostatic mechanisms seem to be impaired. Possibly as a consequence, carbohydrate metabolism is altered. The apparent effect of MPA on steroid metabolism and on the gluconeogenic process may indicate participation in the carbohydrate derangement observed in experimental Listeria infection.     

Dietary fructose induces a wide range of genes with distinct shift in carbohydrate and lipid metabolism in fed and fasted rat liver

Dietary fructose has been suspected to contribute to development of metabolic syndrome. However, underlying mechanisms of fructose effects are not well characterized. We investigated metabolic outcomes and hepatic expression of key regulatory genes upon fructose feeding under well defined conditions. Rats were fed a 63% (w/w) glucose or fructose diet for 4 h/day for 2 weeks, and were killed after feeding or 24-hour fasting. Liver glycogen was higher in the fructose-fed rats, indicating robust conversion of fructose to glycogen through gluconeogenesis despite simultaneous induction of genes for de novo lipogenesis and increased liver triglycerides. Fructose feeding increased mRNA of previously unidentified genes involved in macronutrient metabolism including fructokinase, aldolase B, phosphofructokinase-1, fructose-1,6-bisphosphatase and carbohydrate response element binding protein (ChREBP). Activity of glucose-6-phosphate dehydrogenase, a key enzyme for ChREBP activation, remained elevated in both fed and fasted fructose groups. In the fasted liver, the fructose group showed lower non-esterified fatty acids, triglycerides and microsomal triglyceride transfer protein mRNA, suggesting low VLDL synthesis even though plasma VLDL triglycerides were higher. In conclusion, fructose feeding induced a broader range of genes than previously identified with simultaneous increase in glycogen and triglycerides in liver. The induction may be in part mediated by ChREBP.     

Post-exercise glycogen resynthesis in trained high-protein or high-fat-fed rats after glucose feeding

This study examined the effect on glycogen resynthesis during recovery from exercise of feeding glucose orally to physically trained rats which had been fed for 5 weeks on high-protein low fat (HP), high-protein/long-chain triglyceride (LCT) or high carbohydrate (CHO) diets. Muscle glycogen remained low and hepatic gluconeogenesis was stimulated by long-term fat or high-protein diets. The trained rats received, via a stomach tube, 3 ml of a 34% glucose solution immediately after exercise (2 h at 20 m.min-1), followed by 1-ml portions at hourly intervals until the end of the experiments. When fed glucose soleus muscle glycogen overcompensation occurred rapidly in the rats fed all three diets following prolonged exercise. In LCT- and CHO-fed rats, glucose feeding appeared more effective for soleus muscle repletion than in HP-fed rats. The liver demonstrated no appreciable glycogen overcompensation. A complete restoration of liver glycogen occurred within a 2- to 4-h recovery period in the rats fed HP-diet, while the liver glycogen store had been restored by only 67% in CHO-fed rats and 84% in LCT-fed rats within a 6-h recovery period. This coincides with low gluconeogenesis efficiency in these animals.