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PubMedDate not supplied

[Dynamics of diurnal content of carbohydrate metabolism intermediates in the rat liver].

Diurnal variations of glycolytic intermediates and Pi concentrations are studied in the laboratory rat liver. It is shown that tissue concentrations of glucose, glucose-6-phosphate and Pi vary synchronously during the day exhibiting maxima in light period and minima at night. Circadian fructose 1,6-diphosphate rhythm is similar to the rhythms of the metabolites mentioned above. Diurnal variations of the phosphoenolpyruvate and pyruvate content in the tissue are shifted up to 3-6 h. The data indicate that circadian regulation of hepatic carbohydrate energy metabolism did not take place at control points of gluconeogenesis only.

Animals↗
PubMedDate not supplied

Studies on the interaction of fructose 1,6-P2 aldolase with methylglyoxal.

Reaction of rabbit muscle fructose 1,6-P2 aldolase with methylglyoxal results in a biphasic loss of activity. The kinetics of the initial rapid phase are first order with respect to the inhibitor. Dihydroxyacetone phosphate and fructose 1,6 bisphosphate afford complete protection whereas inorganic phosphate provides only a partial protection against inactivation. The treatment with methylglyoxal modifies the aldolase ability to bind D-Ga3P and DHAP. Loss of activity correlates with the modification of 1.7 arginine residues but data suggest that probably one of these arginine residues is essential. A likely role of this residue could be its interaction with the C1 negatively charged phosphate binding site of the enzyme.

Aldehydes↗
PubMed1981

Irreversible hemorrhagic shock: treatment and cardiac pathophysiology.

Anesthetized dogs were subjected to hypotension at 35 mm Hg mean arterial pressure for 3 hours according to Wiggers' modified technique. One group of dogs received IV fructose-1,6-diphosphate (FDP) while the other group received equimolar glucose throughout the oligemic period. At 3 hours of hypotension, five glucose-treated and six dogs that received FDP were sacrificed for determination of myocardial ATP, creatine phosphate, and lactic acid tissue content. The remaining 14 dogs (six glucose-treated and eight FDP-treated) were retransfused with the shed blood and allowed to recover. The mean arterial pressure measured at 1 1/2 hours posttransfusion in the FDP-treated group returned to control values while the glucose controls remained 34 mm Hg below control. All controls had EKG ischemic changes, whereas no such changes were observed in the FDP-treated group. Endocardial ATP and creatine phosphate content in the controls were depleted to the same degree as found in acute myocardial ischemia, whereas in the FDP-treated dogs they were nearly normal range. All six retransfused dogs treated with glucose died, whereas all eight dogs that received FDP survived and had normal bowel and renal function and no apparent neurological deficit. These data indicate that FDP appears to be a potential therapeutic agent in the treatment of irreversible hemorrhagic shock by intervening in the Embden-Meyerhof pathway both as a metabolic regulator and high energy substrate.

Adenosine Triphosphate↗
PubMedDate not supplied

[Effect of fructose derivatives on platelet aggregation].

Fructose diphosphate, fructose monophosphate and inorganic phosphate decrease platelet aggregation. Fructose does not affect the function under study. The most pronounced antiaggregation action is displayed by fructose diphosphate which enhances calcium binding with thrombocytic membranes. The action of fructose diphosphate depends on the time of its presence in the blood channel. Fifteen minutes after injection the substance inhibits the formation of experimental thrombocytic thromboses. After one hour such an effect does not manifest since fructose diphosphate is absent from the blood flow by that time.

Animals↗
PubMed1980

A time study of hepatic glycolytic intermediates in endotoxemic and septic rats and mice.

A time study was conducted on three key glycolytic intermediates in endotoxemic rat liver to determine which metabolite showed the earliest concentration changes. Glucose-6-phosphate (G6P) was found to be significantly decreased one hour after IV injection of endotoxin, whereas phosphoenolpyruvate (PEP) and fructose-1,6-diphosphate (FDP) were unaltered until three hours. In rat peritonitis produced by cecal incision, liver biopsy at five hours again revealed that only G6P levels were significantly influenced by the septic challenge. In a similar murine peritonitis model, which permitted longer survival times, analysis of liver samples at 12 and 18 hours supported the conclusion that G6P was the metabolite that responded first or most consistently to endotoxin and sepsis. Later changes in FDP and PEP appear to be secondary events. It is postulated that endotoxin may have a direct or indirect action on G6P regulating enzymes. Since rational therapy for septic shock must combat early changes, it would seem that measures that restore G6P levels might prevent the disturbed carbohydrate metabolism that characterizes late and severe sepsis.

Animals↗
PubMed1981

Development of gluconeogenic enzymes in the liver of fasting or suckling newborn pigs.

Gluconeogenic enzymes and substrates were measured in the livers of fasted and suckled newborn pigs in the first 48 h postpartum. The activities at birth of glucose-6-phosphatase, fructose-1,6-diphosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase were, respectively, 70%, 45%, 117% and 35% of adult values. At birth, cytosolic phosphoenolpyruvate carboxykinase represented 35% of total activity, a similar distribution to that in the adult. In suckled piglets, all activities were greater at 24 and 48 h that at birth. In starved piglets, the increases were greater in all cases; the increase in cytosolic phosphoenolpyruvate carboxykinase was much more pronounced than for that for the particulate enzyme, with the former representing more than 50% of total at 48 h. The levels of gluconeogenic enzymes in the piglets in the early neonatal period would appear to be adequate for their needs and do not provide an explanation for their fasting hypoglycaemia. Hepatic levels of lactate, pyruvate, phosphoenolpyruvate, ketone bodies, and amino acids were determined in these piglets. No significant differences were observed in these metabolites between fasted and suckled animals except that glutamine was doubled in fed piglets, Evidence for the metabolic block in the livers of fasted animals was lacking and ketone bodies did not accumulate. These observations suggest that the limitations to gluconeogenesis result from unavailability of energy substrates and/or carbon precursors to the liver or the deficiency in their uptake.

Animals↗
PubMed1978

[Creatine phosphate synthesis coupled to glycolytic reactions in heart cell cytosol].

It is shown that a cytosolic fraction of proteins from rat heart, containing all glycolytic enzymes and creatine phosphokinase (CPK) in natural proportions, catalyses in the presence of creatine (Cr) the intensive creatine phosphate (CP) synthesis coupled to glycolytic depletion of glucose, fructose-1,6-diphosphate (FDP) and phosphoenolpyruvate (PEP). The ratio of CP to lactate produced was 1.0 in the case of PEP as glycolytic substrates. In the CP production process the CPK reaction was not the rate limiting step: the mass action ratio for CPK was equal to the apparent equilibrium constant for this reaction, and the maximal rate of the CPK reaction exceeded the observed rate of glycolysis by a factor 6. It is concluded that in such a system the components of the CPK reaction are in quasiequilibrium and the mechanism of CP synthesis can be considered to be a continuous decrease in ADP concentration due to its phosphorylation in the glycolytic reactions, ATP concentration being constant due to its continuous utilization and resynthesis, this leading to an increase in CP concentration. The possible role of the CPK system in regulation of glycolysis in muscle cells is discussed.

Adenine Nucleotides↗
PubMed1980

[Variations of placental enzymes in hypoxia (author's transl)].

Tissue of normal-term placentas, after normal pregnancy and spontaneous delivery, was incubated under normoxic and hypoxic conditions. Placental tissue samples were taken under sterile conditions, immediately after delivery, and incubated six hours in a medium to which six per cent or 26 per cent oxygen were supplied. After incubation, the tissue was homogenised, and the following enzymes were determined in the supernatant: aldolase, lactate-dehydrogenase, alkaline phosphatase, acid phosphatase, and glucose-6-dehydrogenase. - The activities of aldolase, glucose-6-dehydrogenase, and acid phosphatase increased and those of lactate-dehydrogenase and acid phosphatase decreased under conditions of oxygen deficit. Such changes in enzyme activity seem to suggest that in hypoxia anaerobic glycolysis is likely to increase, while maternal-foetal exchange drops, all accompanied by beginning compensatory proliferation of the trophoblast.

Acid Phosphatase↗
PubMed1993

Effect of oestradiol on the carbohydrate metabolism of immature rat uterus: the role of fructose-2, 6-bis-phosphate and of phosphoribosyl pyrophosphate.

Enzymes and metabolic intermediates of glycolysis, pentose phosphate pathway and the tricarboxylic acid cycle were measured in immature rat uterus after treatment with oestradiol. The flux of glucose through alternative pathways was examined. Fructose-2,6-bis-phosphate, the well known regulator of glycolytic pathway, increased after the injection of oestradiol and remained elevated. This increase was accompanied by raised levels of most of glycolytic intermediates and by increase in glycolytic flux. The key enzymes of glycolysis and all the enzymes of pentose phosphate pathway showed a gradual increase in the activity with administration of oestradiol up to 48 hours. Phosphoribosyl pyrophosphate, the metabolite required in nucleotide synthesis, was also elevated. Marked changes in the levels of key metabolic intermediates and the enzyme activities are correlated with the increased nucleic acid, protein and lipid synthesis occurring following oestradiol treatment.

Animals↗
PubMed1995

Myocardial toxicity of cyclosporin A: inhibition of calcium ATPase and nitric oxide synthase activities and attenuation by fructose-1,6-diphosphate in vitro.

Use of cyclosporin A (CsA) in transplantation medicine has been shown to cause a number of toxic cellular side effects, which has prompted a search for formulations that afford protection from these undesirable sequelae. Previously we demonstrated that fructose-1,6-diphosphate (FDP) can reverse a variety of toxic cellular effects that arise upon use of various chemical agents. The present studies were undertaken to study the effects of CsA on rat myocardial Ca2+, calmodulin (Cam)-dependent enzymes such as Ca2+ ATPase and nitric oxide synthase (NOS) and the role of FDP in attenuating these changes in vitro. Rat ventricular sarcoplasmic Ca2+ ATPase was studied by measuring the inorganic phosphorous liberated on ATP hydrolysis and rat heart 100,000 g fraction NOS activity by monitoring the formation of [3H]-citrulline in the presence of 10-1000 microM CsA and 1000 microM CsA + 1000 microns FDP in vitro. CsA in all concentrations significantly (P < 0.001) inhibited both Ca2+ ATPase and NOS activities of rat myocardium and FDP at 1000 microM concentration completely reversed the 1000 microM CsA-inhibited Ca2+ ATPase and cNOS activities of rat myocardium. These data indicate that CsA may inhibit Ca2+ ATPase and NOS activities in the rat myocardium through interference with its Ca2+/Cam-mediated events and thus may cause myocardial toxicity. FDP may reverse these changes.

Animals↗
PubMed1995

[Fructose 1,6-diphosphate can be a substrate to accelerate glycolysis].

Fructose 1,6-diphosphate (F1, 6P) is a glycolytic intermediate which has already been used clinically to treat congestive heart failure. F1, 6P has been shown experimentally to improve glycolytic flux, although theoretical background is unclear. Since there is two possible mechanism of F1, 6P effect on acceleration of glycolysis, including pharmacological effect and substrate effect, we sought to determine the real mechanism of action of F1, 6P on glycolysis. Langendorff-perfused rabbit hearts were infused with F1, 6P (5 and 10 mM) in a first group, and in a second group, 30 minutes of perfusion with modified Krebs-Henselit (K-H) buffer with reduced glucose concentration (5 mM), plus 2-deoxy glucose (5 mM) and with or without 10 mM F1, 6P followed by 30 minutes of wash with normal K-H buffer. We measured contractile function, oxygen consumption, and high energy phosphate by 31p-NMR spectroscopy. In the first group of experiments, F1, 6P resulted in a dose dependent increase in high energy phosphate production and inorganic phosphate (Pi). There was also a marked decline in developed pressure (Dev P) due mostly to the ability of F1, 6P to chelate calcium. Intracellular Mg2+ which was also reduced during F1, 6P infusion might be related to intracellular Ca2+ and/or accelerated glycolysis. In the model of glycolysis inhibited by 2-DG, Dev P was consistently decreased during the infusion of 2-DG, and wash-out period along with the deterioration of high energy phosphate. However, F1, 6P could provide excellent recovery of contractile function after wash along with superior high energy potential during the 2-DG infusion and wash.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Fructose 2,6 bisphosphate promotes the monomer-tetramer conservation of Leishmania mexicana amazonensis pyruvate kinase type two.

The enzyme pyruvate kinase of Leishmania mexicana amazonensis presents two forms with different kinetic properties and behavior for the heterotrophic activator fructose 2,6 bisphosphate. Pyruvate kinase 1, which is isolated as a tetramer, is inhibited by this metabolite. The second activity, Pyruvate kinase 2, is activated by fructose 2,6 bisphosphate, which promotes the monomer-tetramer conversion of this enzyme.

Animals↗