inosinic-acid and Coronary-Disease

1. A 5'-nucleotidase with a strong preference for AMP over IMP was characterized in homogenates and subcellular fractions of pigeon heart by using concentrations of ATP, ADP and AMP which mimicked those present in the ischaemic tissue. 2. The AMP-5'-nucleotidase had a neutral pH optimum and an apparent Km in the range 4.6-5.2 mM. It was stimulated by ATP plus ADP, and was inhibited by other nucleoside monophosphates, Pi and p-nitrophenyl phosphate, but not by ribose 5-phosphate or beta-glycerophosphate. The enzyme was not inhibited by [alpha beta-methylene] ADP or by 5'-deoxy-5'-isobutylthioadenosine, an inhibitor of the previously purified IMP-preferring cytosolic 5'-nucleotidase. 3. Subcellular-fractionation studies indicated that the enzyme has access to cytosolic AMP, although it may be associated by weak ionic interactions with an organelle present in the low-speed particulate fraction. 4. A 5'-nucleotidase was detected under similar conditions in homogenates of rat heart. 5. The activity of the pigeon heart AMP-5'-nucleotidase was sufficient to account for previously measured rates of ischaemia-induced adenosine formation. The similar activity in rat heart could, however, account for only part of ischaemia-induced adenosine formation in this tissue.

Topics: 5'-Nucleotidase; Adenosine; Adenosine Monophosphate; Animals; beta-N-Acetyl-Galactosaminidase; Columbidae; Coronary Disease; Deoxyadenosines; Enzyme Activation; Hexosaminidases; Hydrogen-Ion Concentration; Inosine Monophosphate; Myocardium; Nucleotidases; Subcellular Fractions; Substrate Specificity; Thionucleosides

After 25 minutes of ischemia, in the isolated rat preparation, hearts fail to reestablish adequate contractile function. To determine whether this failure was associated with a transmural variation in the metabolic response of myocardial cells to reperfusion, the authors subjected hearts to 25 minutes of global ischemia with and without 5 or 20 minutes of reperfusion. After freeze-drying the left ventricular myocardium was divided into subepicardial (EPI) and subendocardial (ENDO) regions before estimating the lactate, total adenine pool metabolites, and creatine phosphate (CP) and phosphate concentrations in each region. Other groups of hearts were perfusion-fixed with glutaraldehyde then injected with nuclear track emulsion to demonstrate that a high proportion of capillaries in both the subendocardial (89%) and subepicardial (95%) myocardium transmitted perfusate after 5 minutes of reperfusion. Reperfusion removed lactate equally from each region. Thus the differences in the capacity of reperfusion of these regions to recover CP (ENDO, 100%; EPI, 168% of preischemic values), to elevate adenosine triphosphate (ATP) (ENDO, 32%; EPI, 63%), or to retain adenosine monophosphate (AMP) (ENDO, 625%; EPI, 277%) were unlikely to be due to regional differences in microvascular function. Despite the better preservation of both structure and metabolism in the subepicardium, there was, during reperfusion, a progressive loss of purine precursors from cells in both regions of the myocardium. These results suggest that the loss of ability of the myocardium to recover significant function after relatively short periods of ischemia is due to their inability, on reperfusion, to synthesise sufficient ATP from the available precursors. This capacity for resynthesis of ATP is lost more rapidly in the subendocardial than in the subepicardial myocardium.

Topics: Adenine Nucleotides; Animals; Coronary Disease; Energy Metabolism; Hypoxanthine; Hypoxanthines; In Vitro Techniques; Inosine; Inosine Monophosphate; Male; Myocardium; Perfusion; Rats; Rats, Inbred Strains; Reference Values; Uric Acid; Xanthine; Xanthines

Myocardial energy metabolism during deep general hypothermia (20 degrees C) and multidose crystalloid cardioplegia, and also during subsequent reperfusion, was studied in eight patients undergoing isolated aortic valve replacement. Six serial transmural biopsy samples from the left ventricular apex were analyzed for high-energy phosphates and their degradation products. Reductions in ATP, total adenine nucleotide content and energy charge were insignificant during cardioplegia, as were changes in adenosine and uric acid concentrations. During reperfusion, however, there was slight but significant reduction in total adenine nucleotide content, despite adequate oxygenation as indicated by reversal of lactate accumulation. These observations suggest that the reperfusion phase is accompanied by metabolic aberrations which are not overcome by good oxygenation in relation to the metabolic rate.

Topics: Adenine Nucleotides; Aged; Aortic Valve; Biopsy, Needle; Coronary Disease; Energy Metabolism; Heart Arrest, Induced; Humans; Hypothermia, Induced; Inosine Monophosphate; Inosine Nucleotides; Middle Aged; Myocardium; Perfusion; Uric Acid

It is generally assumed that myocardial adenine nucleotides are broken down (e.g., during ischemia) via AMP----adenosine----inosine, but contribution of the pathway AMP----IMP----inosine cannot be excluded. The catabolism of exogenously added adenosine (1-20 microM) was studied in isolated rat hearts. All catabolites (i.e., inosine, hypoxanthine, xanthine, and uric acid) were measured together with nonmetabolized adenosine. Even at low (1 microM) adenosine concentrations, deamination accounted for 60% of adenosine disappearing from the perfusate. The adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) (5 and 50 microM) was infused together with adenosine (5 microM). These two concentrations of EHNA inhibited deamination of exogenous adenosine by 65 and 91%, respectively. When hearts were made ischemic by reduction of perfusion pressure, addition of EHNA raised the adenosine release from 1.4 to 9.8 nmole/min per gram wet wt., but surprisingly, the release of inosine and oxypurines (8 nmole/min per g wet wt.) did not change. These results suggest that considerable breakdown of myocardial adenine nucleotides can occur via the AMP----IMP----inosine pathway instead of AMP----adenosine----inosine. The rate of total purine release is probably not a good measure of intracellular adenosine formation.

Topics: Adenine; Adenosine; Adenosine Deaminase Inhibitors; Adenosine Monophosphate; Animals; Coronary Circulation; Coronary Disease; Inosine Monophosphate; Male; Myocardial Contraction; Myocardium; Nucleoside Deaminases; Purines; Rats; Rats, Inbred Strains

Langendorff perfused rat hearts show synchronous, statistically significant, systematic variations in ATP and ADP. Here we show that AMP and IMP also vary in register with ATP and ADP and we suggest that the synchronizing trigger for these oscillations may be ischaemia. Oscillations in the ATP/ADP ratio were found to be significantly correlated with creatine phosphate content but by contrast these quantities vary quite differently from the GTP/GDP ratio. Cyclic GMP oscillations showed a significant negative correlation with variations in ADP. Epinephrine raised mean cyclic AMP content and stabilized cyclic GMP oscillations, but had little other effect on the purine nucleotide variations.

Topics: Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Coronary Disease; Cyclic AMP; Cyclic GMP; Epinephrine; Guanosine Diphosphate; Guanosine Triphosphate; Heart; Inosine Monophosphate; Kinetics; Male; Myocardium; Perfusion; Purine Nucleotides; Rats; Rats, Inbred Strains

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

The isolated perfused rat heart was utilized to determine the maximum rate of adenosine incorporation into adenine nucleotides and the effect of ischemia on this rate. In aerobic hearts, the rates of [8-14C]adenosine incorporation into nucleotides in nanomoles/minute per gram dry tissue were ATP 34 +/- 2, ADP 6 +/- 0.4, AMP 3 +/- 0.3, and IMP, 1 +/- 0.2. Following ischemia these values were not significantly different except for the rate of incorporation into IMP, which doubled. The extent of adenosine deamination with one pass through the coronary vasculature was the same in aerobic and postischemic hearts: 2% and 7% of the perfusate adenosine was converted to hypoxanthine and inosine, respectively. These percentages were similar at 50, 100, and 200 micron adenosine. Perfusion of aerobic hearts for 5 h with adenosine did not change ATP concentrations. Therefore, [8-14C]adenosine incorporation into ATP in these hearts appeared to represent ATP turnover. In contrast, 5 h perfusion of postischemic hearts with adenosine restored ATP concentrations to control values. The synthesis rate calculated from the increase in ATP concentration was comparable to the synthesis rate calculated from [8-14C]adenosine incorporation. Thus, incorporation of [8-14C]adenosine into ATP in postischemic hearts represented net ATP synthesis.

Topics: Adenosine; Adenosine Diphosphate; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Coronary Disease; Inosine Monophosphate; Kinetics; Male; Myocardium; Rats