inosinic-acid and Hypoxia

A mathematical model of anaerobic muscle energy-metabolism was developed to predict pH and the concentrations of nine muscle metabolites over time. Phosphorous-31 Nuclear Magnetic Resonance was used to measure time-course data for some phosphate metabolites and pH in anoxic M. semitendinosus taken from three slaughtered sheep. Muscles were held at 35 degrees C during the experiment. Measurement commenced 25 min post mortem and concluded before rigor mortis. The model was fitted to these data within experimental error, by simultaneously varying model parameter values and initial substrate concentrations. The model was used to simulate the period from death until metabolic activity ceased, in order to predict the different stages of metabolic response to anoxia. The model suggested that alkalinisation would occur in all three muscles in the first few minutes after the onset of anoxia, followed by a steady decline in pH. For two of the muscles this decline continued until rigor, with final pH values of 5.60 and 6.07. For the other muscle, pH reached a low of 5.60 near rigor but then increased to a final value of 5.73. A rise in pH after rigor has been observed but not previously explained in the literature. The modelling results suggest it was caused by the alkalising effect of adenosine monophosphate deamination being greater at low pH than the acidifying effect of inosine monophosphate dephosphorylation.

Topics: Adenosine Monophosphate; Anaerobiosis; Animals; Deamination; Death; Energy Metabolism; Hydrogen-Ion Concentration; Hypoxia; Inosine Monophosphate; Magnetic Resonance Spectroscopy; Meat; Models, Biological; Muscle, Skeletal; Phosphorylation; Postmortem Changes; Rigor Mortis; Sheep

This study investigated the effects of hypoxia (experiment 1) and the effects of hypoxia following short-term training (experiment 2) on metabolism in working muscle. In experiment 1, eight males with a peak aerobic power (VO2peak) of 45 +/- 1.7 ml x kg(-1) x min(-1) (x +/- SE) cycled for 15 min at 66.1 +/- 2.1% VO2peak while breathing room air [normoxia (N)] or 14% O(2) [hypoxia (H)]. In experiment 2, nine males with a VO2peak of 43.3 +/- 1.6 ml x kg(-1) x min(-1) performed a similar protocol at 60.7 +/- 1.4% VO2peak during N and during H following 5 days of submaximal exercise training (H + T). Tissue samples extracted from the vastus lateralis before exercise and at 1, 3, and 15 min of exercise indicated that compared with N, H resulted in lower (P < 0.05) concentrations (mmol/kg dry wt) of creatine phosphate and higher (P < 0.05) concentrations of creatine, inorganic phosphate, and lactate, regardless of exercise time. When the exercise was performed at H + T and compared with N, no differences were observed in creatine phosphate, creatine, inorganic phosphate, and lactate, regardless of duration. Given the well-documented effects of the short-term training model on elevating VO2 kinetics and attenuating the alterations in high-energy phosphate metabolism and lactate accumulation, it would appear that the mechanism underlying the reversal of these adaptations during H is linked to a more rapid increase in oxidative phosphorylation, mediated by increased oxygen delivery and/or mitochondrial activation.

Topics: Adaptation, Physiological; Adenine Nucleotides; Bicycling; Exercise; Glucose; Glycolysis; Heart Rate; Humans; Hypoxia; Inosine Monophosphate; Lactic Acid; Male; Mitochondria, Muscle; Muscle Contraction; Oxidative Phosphorylation; Oxygen Consumption; Phosphocreatine; Pulmonary Gas Exchange; Quadriceps Muscle; Stress, Physiological; Time Factors; Young Adult

In this study, we compared survivorship, heat dissipation and biochemical features of anaerobiosis of two tiger beetle species (Coleoptera: Cicindelidae) exposed to anoxia. One species commonly experiences environmental immersion from rainfall and snowmelt (Cicindela togata), and the habitat of the other (Amblycheila cylindriformis) is not prone to flooding. The ancestral genus, A. cylindriformis, survives anoxia for only 2 days at 25 degrees C. In response to anoxia, these larvae immediately lose locomotory abilities, tissue concentrations of ATP fall precipitously within 12 h, and significant amounts of lactate are quickly produced. In contrast, C. togata larvae tolerate anoxia for 5 days. Heat dissipation is downregulated to a greater degree than that seen in A. cylindriformis (3.4% versus 14% of standard normoxic rate, respectively), the ability for locomotion is maintained and normoxic levels of ATP are defended for at least 24 h. Lactate is not accumulated until well into anoxic bout, and significant amounts of alanine are also produced. This study provides evidence that tiger beetles differ in physiological responses to anoxia, and that these differences are correlated with flooding risk and with species distribution.

Topics: Adaptation, Physiological; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Anaerobiosis; Animals; Coleoptera; Disasters; Energy Metabolism; Environment; Glycogen; Hot Temperature; Hypoxia; Inosine Monophosphate; Lactic Acid; Oxygen; Phylogeny

Using the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), we determine the contribution of the adenosine pathway to the abundant purine release of two Langendroff-perfused rat heart models which differ particularly in inorganic phosphate (Pi) content: the 2-deoxy-D-glucose (2DG) perfused heart and the anoxic heart. We measure the release of coronary purines by high performance liquid chromatography, and the content of myocardial metabolites by 31P nuclear magnetic resonance spectroscopy. In the 2DG-perfused heart (2 mM for 45 min), the release of inosine [130 nmol/(min.gww)] is much larger than that of adenosine, and EHNA (50 microM) has little effect, showing that the pathway of inosine monophosphate (IMP) accounts for 97% of purine catabolism. In the anoxic heart (100% N2 for 45 min), where inosine and adenosine release are comparable in the absence of EHNA, the inhibitor reduces the release of inosine and catabolites from 50 to 20 nmol/(min.gww) and increases that of adenosine [from 30 to 55 nmol/(min.gww)], showing that the contributions of the IMP and adenosine pathways are 23 and 77%. The difference between the two models has been ascribed to the inhibition of AMP deaminase by Pi in the anoxic heart (Chen W, et al., 1996). We discuss the physiological significance of this heart-specific duality of degradation pathways.

Topics: Adenine; Adenosine Deaminase; Adenosine Deaminase Inhibitors; Adenosine Monophosphate; Animals; Antimetabolites; Deoxyglucose; Enzyme Inhibitors; Heart; Hemodynamics; Hypoxia; In Vitro Techniques; Inosine Monophosphate; Myocardium; Perfusion; Phosphates; Purine Nucleosides; Rats; Rats, Sprague-Dawley

We tested the hypothesis that residual oxygen supply during acute low-flow ischaemia or hypoxemia is a major regulator of myocardial performance, metabolism and recovery. Rat hearts were exposed for 20 min to either ischemia (coronary flow reduced to 10% of baseline), hypoxemia (oxygen content reduced to 10% baseline) or a "mixed" condition (combined ischaemia and hypoxemia). The oxygen supply (coronary flow x oxygen content) was matched in all groups (n = 16 per group). Hypoxemic hearts had the highest performance (systolic and developed pressures, +/- dP/dtmax and oxygen uptake) and content of IMP and AMP. Ischaemic hearts had the highest content of ATP, phosphocreatine, adenine nucleotides and purines. As flow and/or oxygenation were restored, post-ischemic hearts showed better functional and metabolic recovery than post-hypoxemic ones. "Mixed" hearts were more similar to hypoxemic ones during oxygen shortage but to ischemic ones during recovery. We conclude that as oxygenation is critically limiting, coronary flow is relatively more important than oxygen supply in determining myocardial function, metabolism and recovery, most likely secondary to changes in the metabolism of diffusible substances.

Topics: Adenine Nucleotides; Adenosine Triphosphate; Animals; Coronary Circulation; Diastole; Hypoxia; In Vitro Techniques; Inosine Monophosphate; Male; Myocardial Contraction; Myocardial Ischemia; Myocardial Reperfusion; Myocardium; Oxygen Consumption; Phosphocreatine; Purines; Rats; Rats, Sprague-Dawley

The level of systemic hypoxia required to alter neonatal myocardial metabolism and its resultant effect on tolerance to global ischemia is unknown. This study examines myocardial purine nucleotides, glycogen (MG), lactate, creatine phosphate (CP) and the subsequent tolerance to ischemia in hearts exposed to varying levels of hypoxia (2 h). Three-day-old swine were randomly allocated into five study groups. Animals were anaesthetized and ventilated (2 h) with varying mixtures of medical air and nitrogen to achieve their target PaO2 (mmHg): normoxia (PaO2 = 80, n = 18), mild (PaO2 = 60, n = 10), moderate (PaO2 = 40, n = 12), moderately-severe (PaO2 = 30, n = 7) and severe (PaO2 = 20, n = 9). Arterial blood gases verified PaO2 and normal PaCO2 (39.5 +/- 0.5 mmHg). Subsequently, the heart was exposed and the metabolic profile determined from a freeze-clamp LV biopsy. The heart was excised and tolerance to ischemia determined by time (min) to ischemic contracture onset (TICo) and peak (TICp). The results demonstrated a tendency to decreased MG with progressive hypoxia which reached significance in severe hypoxia (6.6 +/- 2.7 mumol/g, P < 0.05). Despite a doubling of myocardial lactate with moderately-severe hypoxia, increases only reached significance with severe hypoxia (27.8 +/- 6.3 mumol/g, P < 0.0001). Despite the reduction in LV adenosine triphosphate (ATP) with severe hypoxia (2.16 +/- 0.68 mumol/g, P < 0.05), CP was unaltered.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Animals, Newborn; Blood Gas Analysis; Glycogen; Hypoxia; Inosine Monophosphate; Lactates; Male; Myocardial Ischemia; Myocardium; Phosphocreatine; Severity of Illness Index; Swine; Time Factors

Glycogen phosphorylase (GPase) from the body wall of the lugworm Arenicola marina (Annelida, Polychaeta) probably exists as a phospho-dephospho hybrid (GPase ab). The hybrid was identified by phosphorylation of purified lugworm GPase b (unphosphorylated form) with rabbit muscle GPase kinase and [gamma-32P]ATP. The completeness of phosphorylation was checked on DEAE-Sephacel. Only one GPase form was eluted. Its 32P incorporation was determined to 0.52 +/- 0.08 mol 32P/100,000 x g protein (n = 4). This GPase ab produced by in vitro phosphorylation has shown similar dependences on AMP and caffeine as GPase extracted from the body wall of the lugworm. Its reversible conversion with endogenous phosphatase and kinase to GPase b has also been demonstrated while a completely phosphorylated form (GPase a) was not detected neither in vivo nor in vitro. Lugworm GPase ab has shown a 2.4-fold higher specific activity as GPase b. The Km for P(i) was 16 mmol/l in absence and 13 mmol/l in presence of AMP. Half maximum activation by AMP was reached at 9 mumol/l. IMP up to 10 mmol/l did not activate and ATP up to 4 mmol/l did not inhibit GPase ab in absence of AMP.

Topics: Adenosine Monophosphate; Animals; Buffers; Chromatography, Ion Exchange; DEAE-Cellulose; Enzyme Activation; Hypoxia; Inosine Monophosphate; Kinetics; Phosphorus Radioisotopes; Phosphorylases; Phosphorylation; Polychaeta; Sodium Fluoride

Stimulation of skeletal muscle to contract activates phosphorylase b-to-a conversion and glycogenolysis. Despite reversal of the increase in percentage of phosphorylase a after a few minutes, continued glycogen breakdown can occur during strenuous exercise. Hypoxia causes sustained glycogenolysis in skeletal muscle without an increase in percentage of phosphorylase a. We used this model to obtain insights regarding how glycogenolysis is mediated in the absence of an increase in percentage of phosphorylase a. Hypoxia caused a 70% decrease in glycogen in epitrochlearis muscles during an 80-min incubation despite no increase in percentage of phosphorylase a above the basal level of approximately 10%. Muscle Pi concentration increased from 3.8 to 8.6 mumol/g muscle after 5 min and 15.7 mumol/g after 20 min. AMP concentration doubled, attaining a steady state of 0.23 mumol/g in 5 min. Incubation of oxygenated muscles with 0.1 microM epinephrine induced an approximately sixfold increase in percentage of phosphorylase a but resulted in minimal glycogenolysis. Muscle Pi concentration was not altered by epinephrine. Despite no increase in percentage of phosphorylase a, hypoxia resulted in a fivefold greater depletion of glycogen over 20 min than did epinephrine. To evaluate the role of phosphorylase b, muscles were loaded with 2-deoxyglucose 6-phosphate, which inhibits phosphorylase b. The rate of glycogenolysis during 60 min of hypoxia was reduced by only approximately 14% in 2-deoxyglucose 6-phosphate-loaded muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Monophosphate; Animals; Epinephrine; Glucose-6-Phosphate; Glucosephosphates; Glycogen; Hypoxia; Inosine Monophosphate; Male; Muscles; Osmolar Concentration; Phosphorus; Phosphorylase a; Phosphorylase b; Rats; Rats, Wistar

Deamination of AMP to inosine monophosphate (IMP) and NH3 is thought to be regulated by the observed increases in ADP, AMP, and H+. We have examined this hypothesis by comparing the rate of IMP accumulation in contracting and noncontracting rat skeletal muscle. The rate of IMP formation was high during ischemic contraction, and consistent with previous studies, formation of IMP was associated with high levels of muscle lactate, depletion of phosphocreatine (PCr), and increased levels of ADP and AMP. When the contraction period was followed by 5-min anoxic recovery, the metabolic changes were maintained, but no further IMP or lactate was formed. During long-term (2-4 h) anoxia, the rate of IMP formation was less than 4% of that during contraction, despite similar changes in PCr, lactate, ADP, and AMP. It is concluded that the observed changes in the intracellular chemical environment are not sufficient to explain the high rate of IMP formation during contraction but that a combination of metabolic stress and a high ATP turnover rate is required. It is suggested that a high ATP turnover rate during conditions of metabolic stress results in transient increases in ADP and AMP at the site of ATP hydrolysis and that these activate AMP deaminase and glycolysis. An alternative hypothesis is that these processes are regulated by the increase in cytosolic Ca2+ in a contracting muscle.

Topics: Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Creatine; Energy Metabolism; Glycolysis; Hypoxia; In Vitro Techniques; Inosine Monophosphate; Inosine Nucleotides; Lactates; Male; Muscle Contraction; Muscles; Phosphocreatine; Rats; Rats, Inbred Strains

By means of in vivo 31P nuclear magnetic resonance (NMR) we measured energy stores and intracellular pH at 10-min intervals in the myotome of unanesthetized carp and goldfish before, during, and after a period of anoxia (1 h for carp and 4 h for goldfish). The fish were mounted in a modified bioprobe, and their gills were irrigated with a constant flow of aerated or anoxic water. Anoxia caused a steep decline of phosphocreatine and intracellular pH in carp muscle. After the phosphocreatine stores had been exhausted by greater than 85%, [ATP] fell, whereas IMP and phosphodiesters accumulated. In goldfish muscle, initial changes followed the same pattern, but after 20 min a steady state of high-energy phosphates was reached and the development of acidosis was dampened. The resistance of goldfish to anoxia is due to metabolic suppression and a switch from lactate to ethanol and CO2 as the anaerobic end products. In both species, recovery was complete within 3 h. The fast pH recovery seems to be mainly caused by H+ and lactic acid efflux.

Topics: Adenosine Triphosphate; Anaerobiosis; Animals; Cyprinidae; Energy Metabolism; Hydrogen-Ion Concentration; Hypoxia; Inosine Monophosphate; Magnetic Resonance Spectroscopy; Muscles; Phosphates; Phosphocreatine

The effect of hypoxaemia on the muscle content of inosine monophosphate (IMP) during short-term, low-intensity exercise has been investigated. Six men cycled twice for 5 min at 120 +/- 6 W (mean +/- SE), which corresponded to approximately 50% of their maximal normoxic O2 uptake, breathing air (N) on one occasion and 11% O2 in N2 (H) on the other. Oxygen uptake at the end of the exercise period was similar between treatments. No significant difference was observed between H and N in the muscle metabolite contents at rest. Muscle content of phosphocreatine (PCr) decreased and lactate increased during exercise. Post-exercise PCr during H was 80% of the value during N (P greater than 0.05) and post-exercise muscle lactate was fourfold higher during H than during N (P less than 0.001). Post-exercise muscle content of ADP was significantly higher during H than during N (P less than 0.01), while ATP and AMP remained constant under both H and N exercise (P greater than 0.05 H vs N). IMP was not detectable in pre-exercise muscle samples (less than 0.01 mmol kg-1 dry wt) but increased during N exercise (0.03 +/- 0.01 mmol kg-1 dry wt, wt, P less than 0.05) and even more during H exercise (0.16 +/- 0.05 mmol kg-1 dry wt, P less than 0.05, H vs N). Post-exercise IMP was negatively related to PCr (r = -0.90) and positively related to lactate (r = 0.88). It is concluded that hypoxaemia results in an enhanced accumulation of IMP during submaximal exercise and that the IMP level is related to the degree of anaerobic energy utilization.

Topics: Adult; Exercise; Humans; Hypoxia; Inosine Monophosphate; Inosine Nucleotides; Male; Muscle Contraction; Muscles; Phosphocreatine

The regional distribution of energy-related metabolites was determined for the normal dog heart by using high performance liquid chromatography to analyse the levels of ATP, ADP, AMP, IMP, adenosine, inosine, hypoxanthine/xanthine, uric acid and NAD in tissue samples from 7 defined areas of the myocardium and 2 of the conduction system, and calculating the overall concentration of these metabolites in each area. From 8 of the 20 hearts used, additional samples were taken and allowed to undergo autolysis in vitro at 37 degrees C for up to 2 h before being analysed in the same manner. The total concentration of the metabolites assayed ("adenine/oxypurine" pool) did differ from one area to another, most notably between ventricles (left = 6.08, right = 5.93, apex = 6.08 microM/g wet tissue weight) and atria (left wall = 4.44, left appendage = 4.12, right wall = 4.34, right appendage = 3.57 microM/g wet tissue weight), but for each area remained essentially constant during the period of autolysis studied.

Topics: Adenine Nucleotides; Adenosine; Animals; Chromatography, High Pressure Liquid; Dogs; Energy Metabolism; Female; Hypoxanthine; Hypoxanthines; Hypoxia; Inosine Monophosphate; Male; Myocardium; NAD; Uric Acid; Xanthine; Xanthines

Metabolic changes in the myocardial adenine and hypoxanthine pools of isolated rat hearts subjected to global ischemia, hypocalcemic global ischemia, and global substrate-free anoxia were compared. At timed intervals between 0 and 60 min separate aliquots of extracts of the ventricles were used to determine either tissue pH, or the components of the adenine pool and their catabolites by reverse phase high performance liquid chromatography (HPLC). The coronary perfusate draining from anoxically perfused hearts was collected over perchloric acid, neutralised and chromatographed by HPLC. The development of left ventricular resting tension (contracture) was recorded in the three groups of hearts. After 60 min ischemia the major catabolites, (AMP, inosine and hypoxanthine) comprised 70% of the total pool (11, 7 and 4 mumol/g dry wt, respectively). After the same period of anoxia 50% of the total pool, comprising adenosine, inosine, hypoxanthine and uric acid in approximately equal proportions, was recovered from the coronary perfusate. The major products remaining in the tissue were IMP and, to a lesser extent AMP (8 and 5 mumol/g dry wt, respectively). Left ventricular contracture developed at different rates in the three groups of hearts but always correlated closely with the maximum rate of adenine pool catabolism. The loss of components from the tissue and the divergence in pathway from adenosine to IMP production which occurs during anoxic perfusion should possibly be considered when assessing the biochemical events occurring in regionally ischemic heart muscle with significant residual flow.

Topics: Adenine; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Calcium; Chromatography, High Pressure Liquid; Contracture; Coronary Disease; Energy Metabolism; Hypoxanthine; Hypoxanthines; Hypoxia; Inosine; Inosine Monophosphate; Male; Myocardium; Rats; Rats, Inbred Strains; Uric Acid