The Determination of Urinary Oxypurines as Markers of Gastrointestinal Tumors

Plasma levels and urinary excretion of oxypurines – hypoxanthine and xanthine – were evaluated by reverse-phase high-pressure liquid chromatography in 13 patients affected by gastric tumors and in 19 colorectal tumor-bearing patients. Preliminary results indicate higher values of urinary xanthine and an increase in the xanthine/hypoxanthine ratio in cancer patients. The increase was not generalized to all subjects, and did not appear related either to the stage of the disease or to CEA values. The limits within which the determination of urinary oxypurines can be employed as a tumor marker are discussed.

[A case of Xanthinuria in a patient with marked hypouricemia]

Xanthinuria is a rare autosomal recessive disorder associated with a deficiency of xanthine oxidoreductase (XOR), which normally catalyzes the conversion of hypoxanthine to uric acid. The effects of this deficit are an elevated concentration of hypoxanthine and xanthine in the blood and urine, hypouricemia, and hypouricuria. The deficit in XOR can be isolated (type I xanthinuria) or associated with a deficit in aldehyde oxidase (type II xanthinuria) and sulfite oxidase (type III xanthinuria). While the first two variants have a benign course, are often asymptomatic (20%), and clinically indistinguishable, type III xanthinuria is a harmful form that leads to infant death due to neurological damage. The clinical symptoms (kidney stones, CKD, muscle and joint pain, peptic ulcer) are the result of the accumulation of xanthine, which is highly insoluble, in the body fluids. We describe a case of type I xanthinuria in a 52-year-old woman who presented with hypouricemia, hypouricuria and kidney stones. The diagnosis was based on purine catabolite levels in urine and serum measured by 3 nonroutine methods: high-pressure liquid chromatography, mass spectrometry, and magnetic resonance imaging. To identify the type of xanthinuria the allopurinol test was used. We believe that these tests will facilitate the diagnosis of xantinuria especially in asymptomatic patients without the need for a biopsy of the liver or intestines, which is useful only for scientific purposes.

Plasma concentrations and urinary excretion of purine bases (uric acid, hypoxanthine, and xanthine) and oxypurinol after rigorous exercise

To investigate the effects of exercise on the plasma concentrations and urinary excretion of purine bases and oxypurinol, we performed 3 experiments with 6 healthy male subjects. The first was a combination of allopurinol intake (300 mg) and exercise (VO2max, 70%) (combination experiment), the second was exercise alone (exercise-alone experiment), and the third was allopurinol intake alone (allopurinol-alone experiment). In the combination experiment, exercise increased the concentrations of purine bases and noradrenaline in plasma, as well as lactic acid in blood and the urinary excretion of oxypurines, whereas it decreased the urinary excretion of uric acid and oxypurinol as well as the fractional excretion of hypoxanthine, xanthine, uric acid, and oxypurinol. In the exercise-alone experiment, exercise increased the concentrations of purine bases and noradrenaline in plasma, lactic acid in blood, and the urinary excretion of oxypurines, whereas it decreased the urinary excretion of uric acid and fractional excretion of purine bases. In contrast, in the allopurinol-alone experiment, the plasma concentration, urinary excretion, and fractional excretion of purine bases and oxypurinol remained unchanged. These results suggest that increases in adenine nucleotide degradation and lactic acid production, as well as a release of noradrenaline caused by exercise, contribute to increases in plasma concentration and urinary excretion of oxypurines and plasma concentration of urate, as well as decreases in urinary excretion of uric acid and oxypurinol, along with fractional excretion of uric acid, oxypurinol, and xanthine. In addition, they suggest that oxypurinol does not significantly inhibit the exercise-induced increase in plasma concentration of urate.

Ketamine Sedation During Spinal Anesthesia for Arthroscopic Knee Surgery Reduced the Ischemia-Reperfusion Injury Markers

We studied the effect of ketamine sedation on oxidative stress during arthroscopic knee surgery with tourniquet application by determining blood and tissue malonyldialdehyde (MDA) and hypoxanthine (HPX) levels. Thirty ASA I-II patients undergoing arthroscopic knee surgery with tourniquet were randomly divided into two groups. Spinal anesthesia induced with 12.5 mg bupivacaine was administered to all patients. In the ketamine group, after IV administration of 0.01 mg/kg midazolam, a continuous infusion of ketamine (0.5 mg . kg(-1) . h(-1)) was used until the end of surgery whereas the placebo group received a volume-equivalent placebo infusion. Ramsey Sedation Scale (RSS) was used for assessing the sedation level. Venous blood and synovial membrane tissue samples were obtained before ketamine infusion, at 30 min of tourniquet ischemia, and at 5 min after tourniquet deflation for MDA and HPX measurements. Tissue MDA and HPX levels were significantly less in the ketamine group than the control group after reperfusion. RSS scores were higher in the ketamine group without any adverse effect. We conclude that ketamine sedation attenuates lipid peroxidation markers in arthroscopic knee surgery with tourniquet application.

Newborn piglets with meconium aspiration resuscitated with room air or 100% oxygen

We investigated whether newborn piglets exposed to hypoxemia and severe meconium aspiration could be reoxygenated with room air as efficiently as with 100% O(2). Twenty-one 2- to 5-d-old piglets were randomly divided into three groups: 1) the room air group: hypoxemia, meconium aspiration, and reoxygenation with room air (n = 8); 2) the O(2) group: hypoxemia, meconium aspiration, and reoxygenation with 100% O(2) (n = 8); and 3) the control group: meconium aspiration, and reoxygenation with room air (n = 5). Hypoxemia was induced by ventilation with 8% O(2) until the mean blood pressure reached <20 mm Hg or the base excess reached <-20 mM. At this point, reoxygenation was started with either room air or 100% O(2). Three milliliters per kilogram of meconium 110 mg/mL was instilled into the trachea immediately before the start of reoxygenation. The O(2) tension in arterial blood was significantly lower in the room air group; at 5 min of reoxygenation it was 9.1 +/- 0.5 kPa versus 43.5 +/- 6 kPa in the O(2) group (p < 0.05). At 5 min of reoxygenation the tidal volume per kilogram was 12.1 +/- 0.7 mL/kg in the room air group and 13.1 +/- 0.9 mL/kg in the O(2) group (NS). There were no significant differences between the room air and the O(2) groups during 120 min of reoxygenation in mean arterial blood pressure, pulmonary arterial pressure, cardiac index, base excess, or plasma hypoxanthine. In conclusion, hypoxic newborn piglets with meconium aspiration were found to be reoxygenated as efficiently with room air as with 100% O(2).

Metabolism of intravenously administered high-dose 6-mercaptopurine with and without allopurinol treatment in patients with non-Hodgkin lymphoma

PURPOSE

We investigated the metabolism of high dose 6 mercaptopurine (HD-6MP) infusions and its influence on the metabolism by allopurinol, an inhibitor of xanthine oxidase, the enzyme that catabolizes 6MP into thioxanthine and thiouric acid.

PATIENTS AND METHODS

Nine patients (aged 2-11 years) with non-Hodgkin lymphoma (NHL) were treated with HD-6MP (1300 mg/m(2).24h) within a therapeutic window after diagnosis. Four patients received oral allopurinol (200 mg/m(2).day) to prevent urate nephropathy, and five did not. Plasma and RBC were isolated before and 4, 20, 24, 28, and 48h after the start of the infusion. All measurements were performed with HPLC.

RESULTS

Considerable variations were found in the plasma levels of 6MP, thioxanthine, and thiouric acid and of RBC-MeTIN levels. 6MP-riboside was not detectable, and MeMP and MeMPR levels were <1.3 muM in the plasma. In general, 6MP, thioxanthine, and MeMP levels in plasma were higher, and thiouric acid plasma levels and RBC-MeTIN levels were lower in the patients treated with allopurinol compared to those who did not receive allopurinol.

CONCLUSIONS

6MP is extensively metabolized in patients with NHL treated with HD-6MP. Thiopurine methylation, at the levels of nucleotide, nucleoside, and base, is an important metabolic pathway after HD-6MP. Co-administration of allopurinol can result in both a decreased catabolism and anabolism of 6MP compared to treatment with HD-6MP alone. This observation may have consequences for the therapeutic efficacy and toxic effects of 6MP in combination with allopurinol.

Ammonia response to exercise in patients with congestive heart failure

OBJECTIVE

To assess energy depletion in skeletal muscle in patients with congestive heart failure by measuring blood purine metabolites during exercise and, at the same time, determine the implications of the ammonia response to exercise in these patients.

SETTING

Tottori University Hospital, Yonago, Japan.

PATIENTS

49 heart failure patients (New York Heart Association (NYHA) grades I-III) and 16 normal subjects.

MAIN OUTCOME MEASURES

Blood lactate, ammonia, and hypoxanthine levels were measured during exercise with expired gas analysis.

RESULTS

In normal exercising subjects as well as in each heart failure subgroup, the ammonia threshold was significantly higher than both the lactate threshold [control: 21.8 (SD 5.3) v 17.4 (3.3) ml/kg/min; NYHA class I: 18.9 (3.8) v 15.5 (2.6); class II: 14.8 (2.5) v 12.7 (2.4); class III: 13.5 (2.6) v 11.8 (2.5)] and the ventilatory threshold (P < 0.01). The difference between the ammonia and lactate thresholds was noted in all normal subjects and in all heart failure patients. The ammonia threshold, however, was significantly lower in heart failure patients than in normal subjects and it decreased with increasing NYHA class (P < 0.01). Maximum ammonia levels were lower in the heart failure group and decreased further with higher NYHA classifications [control: 198 (52) mg/dl; NYHA class I: 170 (74); class II: 134 (58); class III: 72 (15); P < 0.01]. There were significant correlations between maximum ammonia values and maximum lactate, oxygen consumption, and hypoxanthine levels (r = 0.74, 0.48, and 0.87, respectively; P < 0.001).

CONCLUSIONS

The ammonia threshold may reflect the onset of ATP depletion in exercising skeletal muscles, as opposed to the onset of anaerobic respiration. It seems therefore that energy depletion in skeletal muscles during exercise occurs after attaining the anaerobic threshold. Both aerobic and anaerobic capacities of skeletal muscle are reduced in patients with congestive heart failure.

[Urate production in a porcine model of myocardial ischemia-reperfusion]

OBJECTIVE

This study was designed to investigate urate production by swine hearts using an in vivo regionally ischemic-reperfused model.

ANIMALS AND METHODS

Ten female pigs underwent 60 minutes of myocardial ischemia by clamping of the left anterior descending artery and afterwards 120 minutes of reperfusion. Epicardial biopsies and blood samples from coronary sinus were taken before ligation, at the end of ischemic period and 5, 30, 60 and 120 minutes upon reperfusion.

RESULTS

During ischemia, tissue levels of ATP and ADP greatly declined with a subsequent increase in the concentration of AMP, inosine and hypoxanthine (33 +/- 12 vs 93 +/- 17, 26 +/- 8 vs 768 +/- 86 and 32 +/- 10 vs 219 +/- 26 nmol/g dry weight, p < 0.01 for each). Despite the great increase in the hypoxanthine levels, uric acid concentration remained constant (69 +/- 9 vs 32 +/- 12 nmol/g dry weight, NS). Hypoxanthine, xanthine and uric acid concentrations increased in blood samples obtained from the coronary sinus at the end of ischemic period (17.99 vs 31.03 nmol/ml, p < 0.01, 0.29 vs 1.45 nmol/ml, p < 0.05 and 1.20 vs 2.31 nmol/ml, p < 0.01 respectively) and were enhanced upon reperfusion (35.8 and 3.89 nmol/ml for hypoxanthine and uric acid respectively, p < 0.05) without any significant modifications in their concentrations at the arterial level.

CONCLUSION

These results demonstrate that the ischemic-reperfused swine heart produces urate probably outside the myocardium.

Erythrocyte nucleotides and blood hypoxanthine in patients with uremia evaluated immediately and 24 hours after hemodialysis

Using high-performance liquid chromatography, concentrations of erythrocyte adenine nucleotides and hypoxanthine were evaluated in patients undergoing regular acetate hemodialysis before dialysis, immediately following dialysis, and 24 hr after. It was shown that adenosine triphosphate concentration was maintained consistently high, not only just after hemodialysis but also 24 hr later. There was also no difference in concentration of mono- and diphosphates of adenosine. Hypoxanthine concentration decreased twofold after hemodialysis. However, it was still markedly higher than normal values. The level of hypoxanthine was maintained at the postdialysis level, 24 hr later. This suggests that hypoxanthine production could be stimulated during acetate dialysis.

Effect of amino acids on the excretions of purine bases and oxypurinol

To investigate whether or not amino acids affect the urinary excretion of purine bases and oxypurinol, a 12% amino acid solution was infused to 6 subjects who took allopurinol (300 mg) 6 h before the study. Amino acid infusion increased the urinary excretion and the fractional clearance of uric acid and oxypurinol and decreased the plasma concentration of oxypurinol. However, it affected neither the urinary excretion, the fractional clearance, the plasma concentration of oxypurines nor the plasma concentration of uric acid. These results indicate that amino acids affect the renal transport pathways of oxypurinol and uric acid but not those of oxypurines. In addition, it was suggested that the amino acid-induced increase in the urinary excretion of oxypurinol may be considered when allopurinol is administered to hyperuricemic patients with hypoproteinemia who have taken amino acids either orally or intravenously.

Responses of blood and plasma lactate and plasma purine concentrations to maximal exercise and their relation to performance in standardbred trotters

OBJECTIVE

To study whether end products of 2 pathways of anaerobic energy metabolism, lactate and purines, that accumulate in the blood after intense exercise indicate any relation to exercise performance.

DESIGN

Venous blood samples were taken within 1 and 15 minutes after a trotting race of 2,100 m.

ANIMALS

16 Clinically healthy Standardbred trotters.

PROCEDURE

Blood and plasma lactate concentrations were measured by enzymatic analyzer, and purines, uric acid and allantoin, were determined by high-performance liquid chromatography. The concentrations of metabolites were then correlated to racing time and individual performance indexes that are annually calculated from the percentage of winnings, placings, and starts rejected, average earnings per start, and the racing record.

RESULTS

Blood lactate concentration immediately and calculated cell lactate concentration immediately and 15 minutes after the race correlated positively (P < 0.05 to P < 0.01) with the individual performance indexes. Plasma lactate concentration was not correlated to the individual performance indexes. Uric acid concentration, immediately and 15 minutes after the race, was negatively correlated (P < 0.05) to the individual performance indexes, and a positive relation (P < 0.05) was found between the highest concentration of uric acid and the racing time. Concentration of allantoin immediately or 15 minutes after the race did not have any significant correlation to the individual performance indexes.

CONCLUSIONS

Accumulation of lactate in the blood, which was greater in the superior performing horses, may prove to be an useful predictor of anaerobic capacity. The results also indicate that the loss of purine nucleotides was less in the superior performing horses, although further studies are needed to confirm this.

Regional generation of free oxygen radicals during cardiopulmonary bypass in children

Studies on free radical generation during cardiopulmonary bypass have focused mainly on the heart and the lungs. However, low pumping pressure, nonpulsatile perfusion, and hypothermia affect the entire circulation, resulting in decreased splanchnic blood flow, increased intestinal permeability, and endotoxemia. To evaluate regional phenomena, we studied 16 children undergoing cardiopulmonary bypass. Free radical production, granulocyte activation, and hypoxanthine metabolism were assessed separately in the circulations drained by the inferior and superior venae cavae, as well as in the oxygenator. Three minutes after the onset of cardiopulmonary bypass, significant gradients between the inferior vena cava and the arterial line of the oxygenator existed in malondialdehyde (+0.60 +/- 0.12 mumol/L, lactoferrin (+18.21 +/- 7.65 micrograms/L), myeloperoxidase (+53.75 +/- 16.50 micrograms/L), hypoxanthine (-0.62 +/- 0.15 mumol/L), and urate (+8.87 +/- 4.03 mumol/L). These gradients decreased in parallel with decreasing body temperature. Except for a transient gradient in malondialdehyde at 3 minutes after the onset of cardiopulmonary bypass (+0.23 +/- 0.08 mumol/L), no changes were detected between the superior vena cava and the arterial line. In the oxygenator, granulocyte activation was observed only after aortic declamping. We conclude that during cardiopulmonary bypass, significant free radical generation, granulocyte activation, hypoxanthine elimination, and urate production take place in the region drained by the inferior vena cava. In the oxygenator, granulocyte activation occurs only after aortic declamping.

Simultaneous determination of guanine, uric acid, hypoxanthine and xanthine in human plasma by reversed-phase high-performance liquid chromatography with amperometric detection

A reversed-phase high-performance liquid chromatographic method with amperometric detection is described for the separation and quantification of uric acid, guanine, hypoxanthine and xanthine. The isocratic separation of a standard mixture of the compounds was achieved in 5 min on a Spherisorb 5 C18 reversed-phase column, with a mobile phase of NaH2PO4 (300 mmol dm-3, pH 3.0)-methanol-acetonitrile-tetrahydrofuran (97.8 + 0.5 + 1.5 + 0.2). Uric acid, guanine, hypoxanthine and xanthine were completely separated, with detection limits in the range 2-20 pmol per injection. The effect of pH and the composition of the mobile phase on the separation are described. The hydrodynamic voltammograms of these compounds were recorded at a glassy carbon electrode. The linear range of the calibration graph for each compound was: uric acid, 1-5000 mumol dm-3; guanine, 0.5-2000 mumol dm-3; hypoxanthine, 0.1-500 mumol dm-3 and xanthine, 0.5-5000 mumol dm-3. The within- and between-day precision was good. The uric acid and hypoxanthine content in human plasma was measured using the proposed method. Good recoveries of uric acid (97.9-103%), hypoxanthine (98.0-99.2%), guanine (96.0-98.3%) and xanthine (96.0-102%) were obtained from human plasma. The results of electrochemical detection were in good agreement with those of UV detection.

Randomised controlled trial of allopurinol prophylaxis in very preterm infants

Allopurinol, an inhibitor of xanthine oxidase (an enzyme capable of generating superoxide radicals following hypoxiaischaemia), was investigated in preterm infants to determine its ability to prevent the complications of neonatal intensive care which may be associated with oxidative injury. Four hundred infants of between 24 and 32 weeks' gestation were randomly allocated to receive enteral allopurinol (20 mg/ml) or an equivalent dose of placebo for seven daily doses. At admission, plasma hypoxanthine concentrations were significantly higher in infants who subsequently developed periventricular leucomalacia (PVL), bronchopulmonary dysplasia (BPD), or retinopathy of prematurity (ROP), but there was no difference in the primary endpoint (PVL) between the treated and control groups. The failure of allopurinol prophylaxis in this group of infants is probably related to the complex nature of the pathological processes and to the timing of treatment. If oxidant injury is an important mechanism of cellular injury in these preterm infants, an alternative biochemical modulator would be required, or a combination of agents might be effective.

Skeletal muscle metabolism during short duration high-intensity exercise: influence of creatine supplementation

Seven male subjects performed repeated bouts of high-intensity exercise, on a cycle ergometer, before and after 6 d of creatine supplementation (20 g Cr H2O day-1). The exercise protocol consisted of five 6-s exercise periods performed at a fixed exercise intensity, interspersed with 30-s recovery periods (Part I), followed (40 s later) by one 10 s exercise period (Part II) where the ability to maintain power output was evaluated. Muscle biopsies were taken from m. vastus lateralis at rest, and immediately after (i) the fifth 6 s exercise period in Part I and (ii) the 10 s exercise period in Part II. In addition, a series of counter movement (CMJ) and squat (SJ) jumps were performed before and after the administration period. As a result of the creatine supplementation, total muscle creatine [creatine (Cr) + phosphocreatine (PCr)] concentration at rest increased from (mean +/- SEM) 128.7 (4.3) to 151.5 (5.5) mmol kg-1 dry wt (P < 0.05). This was accompanied by a 1.1 (0.5) kg increase in body mass (P < 0.05). After the fifth exercise bout in Part I of the exercise protocol, PCr concentration was higher [69.7 (2.3) vs. 45.6 (7.5) mmol kg-1 dry wt, P < 0.05], and muscle lactate was lower [26.2 (5.5) vs. 44.3 (9.9) mmol kg-1 dry wt, P < 0.05] after vs. before supplementation. In Part II, after creatinine supplementation, subjects were better able to maintain power output during the 10-s exercise period (P < 0.05). There was no change in jump performance as a result of the creatine supplementation (P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Capillary electrophoresis as a clinical tool. Determination of organic anions in normal and uremic serum using photodiode-array detection

We report the use of free solution capillary electrophoresis to identify and quantify low-molecular-mass compounds found in normal and uremic serum as well as in hemodialysate fluid. The method reported provides a multicomponent analysis, allowing a single-step screening for more than 19 metabolites in less than 16 min. Serum samples from healthy individuals and from patients who have been diagnosed with chronic renal failure are analyzed using a borate buffer system at pH 9.0, and an extended light path capillary. Several ionic sample constituents are identified by electrophoretic mobility, UV spectra, and spiking with authentic standards. An analysis of the relative concentration of several metabolites, including hypoxanthine, pseudouridine, hippuric acid, and uric acid is presented. Each of these four metabolites is found in both normal and uremic serum samples (limits of detection 1 to 6 microM). Moreover, each of these metabolites is present at significantly elevated levels in uremic patients. The method reported is shown to have promising clinical utility for profiling serum sample constituents, and for quantitative determination of a few important metabolites.

Creatine and its application as an ergogenic aid

Phosphocreatine (PCr) availability is likely to limit performance in brief, high-power exercise because the depletion of PCr results in an inability to maintain adenosine triphosphate (ATP) resynthesis at the rate required. It is now known that the daily ingestion of four 5-g doses of creatine for 5 days will significantly increase intramuscular creatine and PCr concentrations prior to exercise and will facilitate PCr resynthesis during recovery from exercise, particularly in those individuals with relatively low creatine concentrations prior to feeding. As a consequence of creatine ingestion, work output during repeated bouts of high-power exercise has been increased under a variety of experimental conditions. The reduced accumulation of ammonia and hypoxanthine in plasma and the attenuation of muscle ATP degradation after creatine feeding suggest that the ergogenic effect of creatine is achieved by better maintaining ATP turnover during contraction.

Xylitol-induced increase in the concentration of oxypurines and its mechanism

We investigated the effect of xylitol on the plasma concentration and the urinary excretion of purine bases, 5-hydroxypyrazinamide and 5-hydroxypyrazinoic acid in subjects who had ingested pyrazinamide (60 mg/kg weight). One liter of 10% xylitol was infused intravenously over 2 hours to 5 subjects to whom pyrazinamide had been administered 10 hours before. Xylitol increased the plasma concentration of uric acid, hypoxanthine and xanthine, the urinary excretion of hypoxanthine and a ratio of lactic acid/pyruvic acid in blood, while it decreased the plasma concentration and the urinary excretion of inorganic phosphate, 5-hydroxypyrazinamide and 5-hydroxypyrazinoic acid. These results suggested that in addition to an increase in purine degradation by xylitol, xylitol-induced increase in the cytosolic NADH inhibited xanthine dehydrogenase activity in the liver and the small intestine.

Intrauterine exposure to cocaine increased plasma ANP (atrial natriuretic peptide) but did not alter hypoxanthine concentrations in the sheep fetus

To assess the effects of cocaine, administered to the ewe, on the secretion of atrial natriuretic peptide (ANP), Plasma Renin Activity (PRA) and hypoxanthine in the fetus we studied 6 chronically cannulated sheep fetuses late in gestation. The ewe was given an intravenous injection of cocaine (2 mg/kg). Maternal and fetal arterial blood samples were withdrawn prior to the injection and at 2, 5, 10, 15, 45 and 60 min after the injection for the measurement of ANP, PRA and hypoxanthine. Fetal arterial blood pressure (MAP), plasma ANP and protein levels increased and pH and pO2 decreased after cocaine was administered to the ewe. Fetal plasma hypoxanthine and PRA did not change. These results suggest that cocaine administration to the ewe is associated with fetal hypertension, hypoxemia and acidemia all of which may serve as stimuli for the secretion of ANP.

Markers of acute and chronic asphyxia in infants with meconium-stained amniotic fluid

OBJECTIVE

Cord blood pH, lactate, hypoxanthine, and erythropoietin levels have all been used as markers of either acute or chronic asphyxia. We sought to determine whether these index values were significantly different in infants with or without meconium-stained amniotic fluid.

STUDY DESIGN

Fifty-six pregnant women in spontaneous labor at term were divided into two groups on the basis of the presence or absence of meconium-stained amniotic fluid. All meconium-stained fluid was centrifuged, and the volume percentage of particulate matter (i.e., meconium) was recorded. Umbilical artery blood and mixed arterial and venous cord blood were obtained at each delivery. Lactate, hypoxanthine, and erythropoietin levels were measured. Statistical analysis included Student t test and rank sum statistics where appropriate. Normal and Spearman correlation coefficients were also used.

RESULTS

There were no significant differences in mean umbilical artery pH (7.26 +/- 0.06 vs 7.25 +/- 0.10), lactate levels (32.8 +/- 10 mg/dl vs 30.4 +/- 14.2 mg/dl), and hypoxanthine levels (13.4 +/- 6.7 mumol/L vs 14.0 +/- 6.0 mumol/L) in newborns with meconium (n = 28) compared with controls (n = 28). Erythropoietin levels were significantly greater in newborns with meconium (median 39.5 mIU/ml vs 26.8 mIU/ml, p = 0.039). There was no correlation between the amount of particulate matter and any marker of asphyxia.

CONCLUSIONS

There was no correlation between markers of acute asphyxia (i.e., umbilical artery blood pH, lactate, or hypoxanthine) and meconium. However, erythropoietin levels were significantly elevated in newborns with meconium-stained amniotic fluid. This latter marker may better correlate with chronic asphyxia.

Breakdown of adenine nucleotides, formation of oxygen free radicals, and early markers of cellular injury in endotoxic shock

OBJECTIVE

To study the influence of shock on muscle and plasma adenine nucleotide and creatine pools and their metabolites, and to identify early markers of cellular injury in shock.

SETTING

Surgical research laboratory, Kuwait and UAE.

DESIGN

Experimental study.

MATERIAL

19 New Zealand rabbits.

INTERVENTIONS

15 rabbits were injected with Escherichia coli endotoxin, and an additional 4 rabbits acted as controls.

MAIN OUTCOME MEASURES

Blood and muscle energy metabolites, platelet count, arterial blood gas tensions, and arterial pressure were followed until the animals died.

RESULTS

Five minutes after injection of endotoxin muscle ATP, creatine phosphate, and total adenine purine concentration decreased. This decrease was later reversed, but again decline to a critical level in the terminal phase. Loss of the muscle creatine pool indicated cellular damage after 3 hours. Plasma hypoxanthine, creatine, and lactate concentrations increased continuously throughout the study.

CONCLUSION

Hypoxanthine formation is a possible source of oxygen free radicals in shock. The rise of hypoxanthine, creatine, and lactate concentrations in plasma during septic shock may reflect early high energy nucleotide failure, membrane injury, and anaerobic metabolism, respectively.

Effects of oxygen radicals on cysteinyl leukotriene metabolism and pulmonary circulation in young pigs

The effects of oxygen radicals, generated by the hypoxanthine-xanthine oxidase (XO) system, on pulmonary circulation and release of cysteinyl-containing leukotrienes (LTs) were studied in pigs after XO infusion into the right atrium. A 2.3-fold increase in pulmonary vascular resistance (PVR) (p < 0.05 vs. baseline) and a 2.1-fold increase in LT release (p < 0.05 vs. baseline) was observed. Pretreatment with indomethacin and allopurinol attenauted the vascular response (p < 0.01 and p < 0.05 vs. XO), and the LT release was inhibited by allopurinol and catalase (p < 0.01 and p < 0.02 vs. XO). We conclude that oxygen radicals stimulate lipoxygenase metabolism. This coincides with the observed increase in PVR, however, no causal relationship can be derived from the data presented.

Analysis of the genotypes for aldehyde dehydrogenase 2 in Japanese patients with primary gout

Alcoholic ingestion is one of the major factors for increasing serum uric acid levels. Genotypes of aldehyde dehydrogenase 2 (ALDH2, E.C.1.2.1.3), which regulates the sensitivity of an individual to ethanol, were determined in Japanese patients with gout and control subjects by allele specific oligonucleotide hybridization using PCR amplified gene. The most common allele ALDH2*1 codes for normal ALDH2 activity, while the less common allele ALDH2*2 codes for a lower enzyme activity. The frequency of homozygotes of ALDH2*2 was significantly lower in patients with gout than those with rheumatoid arthritis or a normal population. Plasma and urinary hypoxanthine levels were strikingly increased after ethanol drinking in homozygotes for ALDH2*1 but not in heterozygotes for ALDH2*1/ALDH2*2, indicated extensive purine nucleotide degradation in homozygote for ALDH2*1. These data indicated that alcohol ingestion may not be the requisite factor but is deeply involved in the pathogenesis of gout and hyperuricemia.

Glucose infusion paradoxically accelerates degradation of adenine nucleotide in working muscle of patients with glycogen storage disease type VII

We investigated the effect of glucose infusion on adenosine triphosphate degradation in skeletal muscle of patients with glycogen storage disease type VII. Three patients and six healthy subjects exercised on a bicycle ergometer twice, once with 20% glucose infusion and once with saline infusion. The glucose infusion increased plasma glucose levels to 170 to 182 mg/dl and serum insulin levels to 30 to 50 microU/ml, while it markedly decreased plasma free fatty acid levels. The exercise-induced increases in plasma ammonia, inosine, and hypoxanthine were much larger with glucose than with saline infusion in the patients. Urinary excretion of inosine and hypoxanthine with glucose infusion was twice as high as that with saline infusion. No such differences were present between glucose and saline infusion in the healthy subjects. Glucose infusion therefore accelerates the energy crisis in working muscle of patients with glycogen storage disease type VII, probably due to a decrease in fatty acid utilization.

The pharmacokinetics of injectable allopurinol in newborns with the hypoplastic left heart syndrome

OBJECTIVE

The purpose of this investigation was to determine the pharmacokinetic disposition of intravenous allopurinol and its metabolite oxypurinol in neonates with the hypoplastic left heart syndrome (HLHS) and to evaluate the subsequent degree of xanthine oxidase inhibition using serum uric acid as a marker.

METHODS

Pharmacokinetic data were evaluated in 12 stable preoperative neonates with HLHS after a single intravenous allopurinol administration of 5 mg/kg or 10 mg/kg. Pharmacokinetic parameters were determined for elimination half-life, clearance, volume of distribution, and mean residence time. Xanthine oxidase inhibition, measured by serum uric acid reduction, was also measured.

RESULTS

Pharmacokinetic parameters revealed no statistically significant differences between a 5-mg/kg and 10-mg/kg dose of intravenous allopurinol on elimination half-life, clearance, volume of distribution, and mean residence time. Mean serum uric acid levels were significantly reduced from baseline by 39.99 and 42.94%, respectively, in the 5- and 10-mg/kg treatment groups.

DISCUSSION

The enzyme xanthine oxidase plays a key biochemical role in the generation of toxic oxygen-derived free radicals during ischemia-reperfusion conditions. Allopurinol and its active metabolite oxypurinol inhibit xanthine oxidase, and significantly reduce the conversion of hypoxanthine to xanthine and xanthine to uric acid. Cell injury may be caused by toxic oxygen free radicals produced by ischemia-reperfusion injury such as could occur during the repair of HLHS under hypothermic total circulatory arrest. We hypothesize that allopurinol may provide protection from cellular injury in this clinical context.

Reduced oxygen availability during high intensity intermittent exercise impairs performance

This study examined the influence of reduced oxygen availability on the ability to perform repeated bouts of high intensity exercise on a cycle ergometer. Seven male physical education students performed 10 exercise bouts (of 6 s each), interspersed with 30-s recovery periods, under hypoxic and normoxic conditions. The hypoxic condition was carried out in a low pressure chamber at 526 mmHg. Subjects were instructed to try to maintain a target pedalling speed of 140 rev min-1 during each exercise period. The mean power output of the first exercise bout was approximately 950 W. In both experimental conditions, all subjects were able to maintain the target speed for the first 3 s of each of the 10 exercise bouts. During the last 3-s interval of each exercise period the target speed was not maintained in both conditions over the 10 sprints. However, the reduction was greater in the hypoxic condition (P < 0.05). Post-exercise blood lactate accumulation was higher with hypoxia [10.3 (0.7) vs. 8.5 (0.8) mmol l-1, P < 0.05]. Oxygen uptake, measured during the exercise and recovery periods of sprints 6-9, was lower in the hypoxic condition [3.03 (0.2) vs. 3.19 (0.2) 1 min-1, P < 0.05]. These results indicate that a reduction in oxygen availability during high intensity intermittent exercise results in a higher accumulation of blood lactate and a lower oxygen uptake. The ability to maintain a high power output is impaired.

A comparative study of the concentrations of hypoxanthine, xanthine, uric acid and allantoin in the peripheral blood of normals and patients with acute myocardial infarction and other ischaemic diseases

The aim of this study was the elucidation of the role of the xanthine oxidoreductase in the purine metabolism in ischaemic diseases of man. The serum concentrations of hypoxanthine, xanthine, uric acid and allantoin were determined in peripheral blood samples from patients with angina pectoris, cerebral insult and myocardial infarction with thrombolytic therapy and were compared with the concentrations obtained for healthy males and females. No significant differences were observed for the serum hypoxanthine concentrations, xanthine concentrations, the sum (hypoxanthine+xanthine) and the ratio (xanthine/hypoxanthine) between the healthy males, healthy females, the patients suffering from angina pectoris and the patients suffering from cerebral insult. An increase of the serum xanthine concentration in patients with myocardial infarction indicates a significant metabolic involvement of xanthine oxidoreductase in this disease and therefore a possible role in the development of tissue damage in the postischaemic phase due to oxygen radicals generated by the oxidase activity of this enzyme. The serum concentrations of uric acid and allantoin showed no differences between any of the studied groups. Study of the non-enzymatic oxidation of uric acid to allantoin by oxygen radicals, a relevant radical-scavenging mechanism in other diseases, provided no indication of an increased concentration of oxygen radicals due to the xanthine oxidoreductase reaction or other radical-producing mechanisms.

Effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides

The effect of muscular exercise by bicycle ergometer on erythrocyte purine nucleotides was investigated in 6 athletes. Muscular exercise increased the concentration of inosine monophosphate from 5.9 +/- 1.1 to 7.3 +/- 1.3 nmol/ml in venous erythrocytes and from 5.7 +/- 1.0 to 6.8 +/- 1.4 nmol/ml in arterial erythrocytes, respectively, while it decreased the concentrations of adenosine diphosphate and adenosine monophosphate from 189.3 +/- 42.7 to 141.2 +/- 26.9 and from 26.0 +/- 7.8 to 15.7 +/- 4.3 nmol/ml in venous erythrocytes and also decreased their concentrations from 195.1 +/- 51.0 to 141 +/- 29.2 and from 26.5 +/- 9.6 to 14.8 +/- 3.0 nmol/ml in arterial erythrocytes, respectively. The muscular exercise also increased the concentration of inorganic phosphate in venous plasma from 1.12 +/- 0.12 to 1.46 +/- 0.22 mmol/l, that of NH3 in blood from 41.90 +/- 6.91 to 150.22 +/- 50.80 mumol/l, that of lactic acid in blood from 7.90 +/- 1.71 to 61.03 +/- 18.43 mg/dl and that of hypoxanthine in venous plasma from 1.32 +/- 0.36 to 18.14 +/- 4.87 mumol/l, respectively. Therefore, in vitro study was performed to investigate whether inorganic phosphate, NH4Cl, lactic acid or hypoxanthine affects nucleotides in erythrocytes. After 2 hour-incubation, 2 mM inorganic phosphate increased the erythrocyte concentration of inosine monophosphate 1.6 fold but decreased the erythrocyte concentrations of adenosine monophosphate and adenosine diphosphate 0.72 and 0.89 fold, respectively, in the suspension (pH 7.35), as compared with 1 mM inorganic phosphate. However NH4Cl, lactic acid or hypoxanthine did not affect erythrocyte purine nucleotides.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow and plasma hypoxanthine in relation to surfactant treatment

We have previously reported reduction in EEG activity in preterm babies after tracheal instillation of Curosurf. To elucidate the cause of EEG depression, we have examined cerebral blood flow (CFB), amplitude-integrated EEG (aEEG), mean arterial blood pressure (MABP) and plasma hypoxanthine (Hx) concentration in a group of preterm babies before and immediately after administration of surfactant. No change occurred in CBF immediately after surfactant treatment despite a significant decrease in MABP. At 60 min after surfactant administration, a significant reduction in CBF occurred (p < 0.05). However, when CBF values were corrected for changes in PaCO2, no reduction in CBF was observed. Mean plasma Hx concentration was 11.6 (SD 7.3) mumol/l before surfactant therapy, which decreased significantly to 8.1 (5.8) mumol/l (p < 0.05) 15-30 min after treatment. No correlations were found between plasma Hx concentration and FiO2, a/A pO2, PaCO2, SaO2, arterial blood pressure, CBF or the degree of EEG depression. This study indicates that EEG depression observed after surfactant instillation is not caused by cerebral ischemia.

Effects of L-propionylcarnitine on ischemia-induced myocardial dysfunction in men with angina pectoris

To identify the effect of L-propionylcarnitine (LPC) on ischemia, 31 fasting, untreated male patients with left coronary artery disease were studied during 2 identical pacing stress tests 45 minutes before (atrial pacing test I [APST I]) and 15 minutes after (APST II) administration of 15 mg/kg of LPC or placebo. Hemodynamic, metabolic, and nuclear angiographic variables were studied before, during, and for 10 minutes after pacing. After LPC administration, arterial total carnitine levels increased from 47 +/- 1.7 mumol/liter (control) to 730 +/- 30 mumol/liter. Hemodynamic and metabolic variables were comparable in LPC and placebo during APSI I, and reproducible in placebo during both tests. Although LPC did not affect myocardial oxygen demand and supply, it diminished myocardial ischemia, indicated by a significant 12% and 50% reduction in ST-segment depression and left ventricular end-diastolic pressure, respectively, during APST II. Moreover, during APST II, left ventricular ejection fraction increased by 18% (p < 0.05 vs APST I). Furthermore, LPC improved recovery of myocardial function after pacing, with a reduction in the time to peak filling and a 21% increase in both peak ejection and filling rates 10 minutes after pacing (all p < 0.05). Thus, LPC prevents ischemia-induced ventricular dysfunction, not by affecting the myocardial oxygen supply-demand ratio but as a result of its intrinsic metabolic actions, increasing pyruvate dehydrogenase activity and flux through the citric acid cycle. Because it is well tolerated, it may be a valuable alternative or addition to available antiischemic therapy.

Role of adenosine in dialysis-induced hypotension

First, this investigation showed that plasma levels of inosine, hypoxanthine, and xanthine, which are metabolites of adenosine, rose sharply when blood pressure dropped suddenly along with symptoms during a hemodialysis session (sudden hypotension), but not when it decreased gradually with eventual symptoms (gradual hypotension). Because adenosine has an action to dilate vessels, this result indicates the possibility that the increased release of adenosine would be a cause of sudden hypotension. Second, it was found that the frequency of sudden hypotension decreases with the administration of caffeine, which is an adenosine-receptor antagonist, whereas the frequency of gradual hypotension did not change. This result supports the above-mentioned hypothesis that adenosine may well be a mediator of sudden hypotension, but not of gradual hypotension. Third, our investigation demonstrated no significant differences in plasma norepinephrine level, in plasma renin activity, or in mean blood pressure between the hemodialysis session in which caffeine was administered and the session in which a placebo was given. These findings suggest that the effect of caffeine administration to prevent sudden hypotension is not mediated by the stimulation of the sympathetic nervous system or activation of the renin-angiotensin system, but by the adenosine-receptor antagonism.

Influence of daily drinking habits on ethanol-induced hyperuricemia

We examined the influence of alcohol drinking habits on the serum uric acid level after the ingestion of a small amount of ethanol. Subjects were divided into two groups according to their alcohol drinking habits--regular drinkers, who consume more than 60 g ethanol every day, and nondrinkers/occasional drinkers, who consume less than 20 g ethanol occasionally. Drinking 0.5 g ethanol/kg increased serum uric acid levels in regular drinkers by 52.6 +/- 26.3 mumol/L (0.8 +/- 0.4 mg/dL), whereas it did not in nondrinkers/occasional drinkers. Urinary excretion of uric acid was unaltered in both groups. Hypoxanthine and xanthine in both plasma and urine and serum acetate were increased more in regular drinkers than in nondrinkers/occasional drinkers. Accelerated adenine nucleotide degradation secondary to enhanced ethanol oxidation likely explains the ethanol-induced hyperuricemia in regular drinkers.

Adenosine: a sensitive marker of myocardial ischaemia in man

OBJECTIVE

In the human heart, the significance of adenosine as an indicator of myocardial ischaemia is controversial. Since adenosine fulfils key functions in the regulation of cardiac metabolism, its sensitivity as a marker of tissue ischaemia was investigated in this study in relation to other metabolites such as hypoxanthine and lactate.

METHODS

Cardiac metabolite production was studied in 18 patients with left coronary obstruction (> 90%) undergoing percutaneous transluminal coronary angioplasty (PTCA). Three balloon inflation procedures per patient were performed for 30, 60, and 90 s (+/- 5 s each) and coronary sinus adenosine, hypoxanthine, uric acid, and lactate were determined.

RESULTS

Before PTCA, coronary sinus concentrations of adenosine and hypoxanthine were 176(SEM 34) and 723(73) nM, respectively, and the lactate concentration was 0.47(0.07) mM. Lactate was extracted by cardiac tissue during normoxia, and adenosine and hypoxanthine were in the physiological range of healthy volunteers. During reperfusion the concentrations of all myocardial metabolites were temporarily increased. In particular, adenosine was enhanced in close proportion to the duration of coronary occlusion. Moreover, coronary sinus adenosine, but not lactate, was significantly lowered during reperfusion when nifedipine (0.2 mg) was given by intracoronary injection before PTCA.

CONCLUSIONS

With longer periods of coronary occlusion (> 30 s) the relative rank order of sensitivity indicating myocardial ischaemia was adenosine > lactate > hypoxanthine > uric acid. Coronary sinus concentrations of adenosine are quantitatively sufficient to be responsible for some of the changes in coronary blood flow occurring during reactive hyperaemia.

Influence of sprint training on human skeletal muscle purine nucleotide metabolism

To examine the effect of sprint training on human skeletal muscle purine nucleotide metabolism, eight active untrained subjects completed a maximal 30-s sprint bout on a cycle ergometer before and after 7 wk of sprint training. Resting muscle ATP and total adenine nucleotide content were reduced (P < 0.05) by 19 and 18%, respectively, after training. Training resulted in a 52% attenuation (P < 0.05) in the magnitude of ATP depletion after exercise and a similar reduction (P < 0.05) in the accumulation of inosine 5'-monophosphate and ammonia. During recovery, muscle inosine 5'-monophosphate (P < 0.05) and inosine (P < 0.01) content were reduced after training, as was the accumulation of inosine (P < 0.05). Plasma ammonia was higher (P < 0.05) after training early in recovery; in contrast, plasma hypoxanthine concentrations were reduced (P < 0.05) during the latter stages of recovery. The attenuated resting ATP and total adenine nucleotide contents after training probably result from the acute effects of prior training sessions. The reduction in the magnitude of ATP depletion during a 30-s sprint bout after training must reflect an improved balance between ATP hydrolysis and resynthesis. It is unclear which mechanism(s) is responsible for the reduction in the magnitude of ATP degradation after training.

Detection of liver ischemia using microdialysis during experimental peritonitis in pigs

The liver oxygen delivery (DO2) and consumption (VO2) were measured in a porcine model of septic shock induced by fecal peritonitis. Lactate and hypoxanthine were simultaneously monitored in hepatic extracellular fluid and in central venous blood using a microdialysis technique. Animals were divided into a control group (n = 6) and a peritonitis group (n = 6). Peritonitis was induced by installation of a standardized amount of autologous feces into the abdominal cavity. The animals were followed for 5 h. The changes in the liver during peritonitis were, a decreased DO2, a increased, maintained, or decreased VO2, an increased oxygen extraction, and a loss of net hepatic lactate uptake. Parallel to these changes, systemic lactic acidosis developed. Intrahepatic lactate and hypoxanthine increased during peritonitis reflecting liver ischemia. The increase of these metabolites was seen concomitantly in the liver and in central venous blood. There was a wide variability of the individual response to the septic challenge among the animals. The limited hepatic oxygen delivery, and the increased needs for oxygen led to flow-dependent oxygen consumption, and signs of liver ischemia in severe sepsis. Intrahepatic and intravenous microdialysis may be useful for monitoring of the individual time course of hepatic and systemic ischemia in sepsis.

Variations of adenine nucleotide levels in normal and pathologic human erythrocytes exposed to oxidative stress

Normal human erythrocytes suspended in isotonic saline at 0.5 haematocrit displayed, after 30 min exposure to 1 mM tert-butylhydroperoxide at 37 degrees C, a marked increase of NADPH, while the concentration of the other adenine nucleotides was almost unchanged. Hereditary Spherocytosis and glucose-6-phosphate dehydrogenase-deficient red blood cells exhibited, under basal conditions, higher levels of most of the nucleotides assayed and significant amounts of hypoxanthine. Treatment with tert-butylhydroperoxide caused, in glucose-6-phosphate dehydrogenase-deficient erythrocytes, a pronounced decrease of ADP and of AMP levels, a substantial invariance of other adenine nucleotides and a considerable raise of hypoxanthine. On the contrary, Hereditary Spherocytosis erythrocytes exhibited, after oxidative stress, increased levels of ADP and of AMP, a slight decrease of ATP and an accumulation of hypoxanthine similar to that found in enzyme-deficient red cells. In both the pathologic erythrocytes the addition of phosphate during the oxidative treatment resulted in a lower formation of hypoxanthine, while the presence of 10 mM glucose, fully prevented its appearance.

The effect of high-intensity training on purine metabolism in man

The effect of intermittent high-intensity training on the activity of enzymes involved in purine metabolism and on the concentration of plasma purines following acute short-term intense exercise was investigated. Eleven subjects performed sprint training three times per week for 6 weeks. Muscle biopsies for determination of enzyme activities were obtained prior to and 24 h after the training period. After training, the activity of adenosine 5'-phosphate (AMP) deaminase was lower (P < 0.001) whereas the activities of hypoxanthine phosphoribosyl transferase (HPRT) and phosphofructokinase were significantly higher compared with pre-training levels. The higher activity of HPRT with training suggests an improved potential for rephosphorylation of intracellular hypoxanthine to inosine monophosphate (IMP) in the trained muscle. Before and after the training period the subjects performed four independent 2-min tests at intensities from a mean of 106 to 135% of VO2max. Venous blood was drawn prior to and after each test. The accumulation of plasma hypoxanthine following the four tests was lower following training compared with prior to training (P < 0.05). The accumulation of uric acid was significantly lower (46% of pre-training value) after the test performed at 135% of VO2max (P < 0.05). Based on the observed alterations in muscle enzyme activities and plasma purine accumulation, it is suggested that high intensity intermittent training leads to a lower release of purines from muscle to plasma following intense exercise and, thus, a reduced loss of muscle nucleotides.

Metabolic response to standardised exercise test in standardbred trotters with red cell hypervolaemia

Plasma concentrations of lactate, amino acids, ammonia and products of purine catabolism were studied before, during and after a standardised incremental exercise test in 29 Standardbred trotters admitted to the clinic for exercise tolerance testing. According to their red cell volume the horses were divided into red cell normovolaemic and red cell hypervolaemic (polycythaemic) groups. The exercise-response curve for taurine differed significantly in the two groups, whereas all the other amino acids behaved similarly. The [branched-chain amino acid]/[alanine] ratio, a proposed indicator for the use of amino acids in gluconeogenesis, was at rest significantly higher in the polycythaemic horses. Post-exercise concentrations of ammonia and allantoin, both end products of ATP breakdown, were lower in the polycythaemic horses. No differences were observed in the VLA4 and V200 markers for lactate and heart rate responses to incremental exercise, the oxidative capacity of the gluteus medius muscle, the enzyme activities or the post-exercise concentration of lactate, uric acid and hypoxanthine. It is concluded that horses with red cell hypervolaemia behave in a submaximal standardised exercise test on a treadmill in the same way as do red cell normovolaemic horses. The results suggest that the rate of amino acid utilisation in gluconeogenesis and the ability of amino acids to produce energy aerobically may be elevated in polycythaemic horses.

Accumulation of allantoin and uric acid in plasma of exercising trotters

Plasma concentrations of hypoxanthine, uric acid, and allantoin, which are breakdown products of adenine nucleotides, were measured in Standardbred and Finnhorse trotters during and after an exercise test on a high-speed treadmill, after an incremental exercise test performed on a racetrack, and after a racing competition. Fiber-type composition of the middle gluteal muscle and the muscle concentrations of adenine nucleotides and inosine monophosphate were measured after the racetrack test. Changes in the concentration of hypoxanthine were not observed in any of the tests. Peak concentration of uric acid was measured between 5 and 30 minutes after exercise, and it was three- to tenfold higher than the value at rest. The variability can be explained by intensity of the exercise test and variation among horses. The concentration of allantoin after exercise was 2 to 3 times as high as that at rest, depending on the intensity of the exercise, although the absolute increase was about 10 times as high as the increase in the concentration of uric acid. Peak values of allantoin for the treadmill and the racetrack tests were obtained 4 to 6 minutes after exercise and < 30 minutes after the races. Peak concentration of allantoin correlated positively with the percentage of type-II (IIA+IIB) fibers in the middle gluteal muscle. Significant correlations were not observed between plasma concentration of uric acid or allantoin and muscle concentrations of adenosine triphosphate (ATP) or inosine monophosphate. It can be concluded that in horses, breakdown of ATP during and after exercise continues until allantoin is produced.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy economy in the pregnant human uterus at term: studies on arteriovenous differences in metabolites of carbohydrate, fat and nucleotides

Metabolic regulation was studied in the pregnant human uterus by determining its uptake and release of various substrates, some of which are commonly used as a fuel and some are markers of disturbed energy status in cells. Ten healthy women with normal pregnancy were examined when undergoing elective Caesarean section at term, before onset of labour. Carbohydrate metabolites (glucose, lactate and pyruvate), fat metabolites (free fatty acids (FFA) and glycerol) and nucleotide metabolites (hypoxanthine, xanthine and urate) were determined in arterial (radial artery) and venous (plexus of the uterine and ovarian veins) blood. In addition the arteriovenous difference in each substance across the uterus was calculated. A distinct uptake of glucose was a typical finding in the pregnant uterus as reflected by a positive difference. On the other hand, glycerol and FFA were released from the pregnant uterus. Similarly, a degradation of adenine-containing nucleotides seemed to be continuously ongoing in the pregnant uterus, since oxypurines displayed a negative difference as well.

High-performance liquid chromatographic assay for N2-[5-(hypoxanthin-9-yl)pentyloxycarbonyl]-L-arginine (ST 789) in plasma by cyclization with benzoin and fluorimetric detection

This paper describes a new highly sensitive assay for N2-[5-(hypoxanthin-9-yl)pentyloxycarbonyl]-L-arginine, an immunomodulatory agent, required for clinical pharmacokinetic investigation. A pre-column derivatization by cyclization with benzoin in aqueous medium produces the fluorescent 2-substituted amino-4,5-diphenylimidazole fluorescing at 450 nm (excitation wavelength 310 nm). L-Arginine-acetyl-L-carnitinamide chloride (ST 857, II), another arginine derivative, was used as an internal standard. A C18 DB column (5 microns, 250 mm x 4.6 mm I.D.) and a 45:55 (v/v) mixture of 0.05 M ammonium phosphate at pH 7.2 and methanol as mobile phase were used. Linearity was ascertained in the range 5-100 ng. Extraction recovery from plasma proved to be higher than 90% in the range 5-50 ng/ml. Intra-day precision, expressed as coefficient of variation, was in the range 4.7-6.0%. The limit of quantification proved to be 5 ng/ml and the limit of detection 2 ng/ml at a signal-to-noise ratio of 5. The method is specific.