Hypoxanthine in fetal umbilical venous blood and amniotic fluid from pregnancies complicated by rhesus isoimmunization

Concentrations of hypoxanthine (HX) was determined in umbilical venous blood and amniotic fluid obtained at 74 instances in 36 rhesus immunized patients before the onset of labor. HX concentrations were related to gestational age, concentrations of hemoglobin and lactate, pH, and partial oxygen pressure in umbilical venous blood. Multiple regression analysis revealed hemoglobin concentration to be the only variable that had any explanatory power to HX in amniotic fluid. No one of the studied variables gave any significant contribution to a regression model to explain HX in umbilical venous blood. We conclude that HX levels in umbilical venous blood and in amniotic fluid from rhesus immunized patients were not associated with fetal blood gases before the onset of labor.

Effect of ethanol ingestion on nucleotides and glycolytic intermediates in erythrocytes and purine bases in plasma and urine: acetaldehyde-induced erythrocyte purine degradation

The effect of ethanol on nucleotides and glycolytic intermediates in erythrocytes and purine bases in plasma and urine was investigated. Ethanol ingestion (0.45 mL/kg body weight) increased plasma concentrations and urinary excretion of oxypurines (hypoxanthine and xanthine) and concentrations of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and glyceraldehyde 3-phosphate+dihydroxyacetonephosphate in erythrocytes. In an in vitro incubation study using erythrocytes, acetaldehyde increased the concentrations of AMP, ADP, and glyceraldehyde 3-phosphate+dihydroxyacetonephosphate in erythrocytes as well as the concentration of hypoxanthine in the incubation medium. These results suggest that acetaldehyde (a metabolite of ethanol) induces an increase in purine degradation by erythrocytes and then contributes to the ethanol-induced enhanced purine degradation in vivo.

Respiratory gas exchange and metabolic responses during exercise in McArdle's disease

During normal progressive exercise, the gas exchange anaerobic threshold occurs when CO2 production (VCO2) and ventilation (VE) increase so as to depart from a linear relationship to O2 consumption (VO2). This is thought to represent a gas exchange response to metabolic acidosis due to lactate accumulation. Patients with McArdle's disease have previously been reported to exhibit a steepened ventilatory response relative to VCO2, despite an inability to produce lactate. However, the VCO2 response has not been studied. We therefore investigated the VCO2-VO2 and VE-VO2 relationships in seven McArdle's disease patients and seven control subjects during symptom-limited maximal treadmill exercise. Analysis of gas exchange showed that whereas all control subjects had an easily identifiable anaerobic threshold, four of the patients had none and the other three displayed an attenuated threshold. The occurrence of the threshold in one patient was associated with a small rise in lactate and in another patient with an abrupt rise in leg discomfort, suggesting a pain response. Ammonia and the purine metabolite hypoxanthine were elevated during exercise in all patients, suggesting that ammonia may be a product of adenosine monophosphate degradation. Free fatty acid levels were also elevated, and a shift toward utilization of lipid may contribute to abnormal gas exchange responses. It is concluded that lactic acidosis contributes to the gas exchange anaerobic threshold but that other factors, such as discomfort, may be involved in the excess Ve seen during heavy exercise.

[The concentration of end products of purine metabolism as possible signs of tissue hypoxia in critically ill surgical patients]

The study was performed on 26 critically ill patients with hemorrhagic pancreonecrosis and disseminated suppurative peritonitis. Central hemodynamic and oxygen transport parameters have been determined in all the patients. To assess the degree of tissue hypoxia end products of ATP catabolism (hypoxanthine, xanthine, and uric acid) have been studied. All the studies were performed at various stages of correction of volemic disturbances and oxygen transport function. It has been established that an increased blood plasma level of hypoxanthine and xanthine may serve as an additional criterion of tissue hypoxia in critically ill surgical patients. Changes in hypoxanthine, xanthine, and uric acid concentrations and oxygen transport parameters can be used to assess changes in the functioning of the microcirculatory bed.

Valuable indicators of physical stress in porcine plasma

Various markers for stress were evaluated in the plasma of pigs. Treadmill exercise was chosen as a well defined and quantifiable stressor. One group of non-stress-susceptible pigs had to carry out two intense exercise bouts at a one-week interval, and another group remained in their pens and served as controls. Large interindividual differences in the performance and in the hormonal and metabolic responses to exercise were observed. The exercise stress resulted in an immediate increase in the plasma concentrations of cortisol, lactate and hypoxanthine, with a return to the pre-exercise levels within one hour. No direct effect of physical stress on CBG binding capacity or on the concentrations of xanthine and uric acid was observed. In two very nervous pigs, even mild stress in connection with the first blood sampling resulted in an elevated concentration of lactate, but the cortisol and hypoxanthine values remained at the basal level. It is concluded that plasma concentrations of cortisol, lactate and hypoxanthine are valuable markers for physical stress.

Ergometer exercise in myoadenylate deaminase deficient patients

Three patients with primary myoadenylate deaminase deficiency were subjected to exercise on a bicycle ergometer at 125 W for 30 minutes. Blood samples prior to, during, and at the end of exercise were analyzed for lactate, ammonia, and hypoxanthine. In addition, urinary hypoxanthine excretion was measured. In these patients the serum lactate level increased to concentrations between 7.9 and 9.0 mmol/l at the end of exercise whereas the mean lactate level in nine control subjects at the end of exercise was 3.3 mmol/l (range 1.1-8.1 mmol/l). There was no difference to control subjects in the exercise-induced increase in plasma levels of ammonia and hypoxanthine or in the increase in urinary hypoxanthine excretion. The findings support the hypothesis of a reduced substrate supply to the citric acid cycle in myoadenylate deaminase deficiency. The normal formation of ammonia and hypoxanthine excludes a marked loss of adenine nucleotides in working muscles in these patients.

A high-performance liquid chromatographic method for the determination of hypoxanthine, xanthine, uric acid and allantoin in serum

A method was developed for the simultaneous determination of hypoxanthine, xanthine, uric acid and allantoin based on isocratic reversed-phase chromatography. This HPLC-method additionally allows the direct determination with UV-detection of inosine-5'-phosphate, uridine, thymine, orotic acid, allopurinol and oxipurinol, besides hypoxanthine, xanthine and uric acid in the same chromatographic run. Allantoin elutes in this system near the void volume and a fraction is collected covering the retention time range for this substance. After hydrolysis allantoin is converted to glyoxylate-2,4-dinitrophenylhydrazone, rechromatographed and detected at 360 nm. The coefficient of variation for this method does not exceed 5.0% for a serum concentration of 0.3 mumol/l hypoxanthine and is not greater than 5.3% for a xanthine concentration of 0.3 mumol/l serum. Recoveries were 90-110% for both hypoxanthine and xanthine. The determination of uric acid had an imprecision and inaccuracy not exceeding 1.45% in the concentration range of 103-568 mumol/l. Due to the more complex procedure required for the determination of allantoin, the coefficient of variation between days was 13.6% for a sample containing 0.8 mumol/l allantoin and the recoveries for this analyte were in the range of 86-93%. Reference ranges (mean +/- SD) determined on 171 serum samples from healthy adults were 12.7 +/- 6.6 mumol/l for hypoxanthine, 3.3 +/- 1.4 mumol/l for xanthine, and 15.7 +/- 7.9 mumol/l for allantoin. No significant age or sex dependence was observed. Uric acid concentrations were 320 +/- 55 mumol/l serum for men and 206 +/- 55 mumol/l for women.

Decreased resting levels of adenine nucleotides in human skeletal muscle after high-intensity training

The effect of high-intensity intermittent training on the adenine nucleotide content of skeletal muscle was studied. Eleven male subjects (group A) performed high-intensity intermittent training on a cycle ergometer three times per week for 6 wk, followed by 1 wk of the same kind of training with two sessions per day. Nine males (group B) exclusively performed 1 wk of training with two sessions per day. In group A, skeletal muscle total adenine nucleotide (TAN) levels decreased from 25.1 +/- 0.7 (SE) to 22.0 +/- 0.6 mmol/kg dry wt over the 6-wk period (P < 0.01). The subsequent intensive week did not further alter TAN levels. In group B, the intensive week of training reduced TAN levels from 25.1 +/- 0.5 to 19.4 +/- 0.6 mmol/kg dry wt (P < 0.001). The decrease was sustained 72 h after training (P < 0.001). During the intensive week, there was no change in plasma creatine kinase activity in either group A or group B. The plasma activity was, however, higher in group B than in group A on days 4 and 7 of the intensive week (P < 0.05). The results from this study indicate that high-intensity intermittent exercise causes a decrease in resting levels of skeletal muscle adenine nucleotide without a concomitant indication of muscle damage. A training-induced adaptation appears to occur with training by which a further loss of adenine nucleotides is prevented despite an increased training dose.

Nucleosides and glutamine are primary energy substrates for embryonic and adult chicken red cells

It has been assumed that glucose is a major energy yielding substrate for chicken red blood cells. In this report we show that glucose fails to maintain cellular ATP levels in embryonic and mature chicken erythrocytes during overnight incubation. Of over a dozen metabolites tested, inosine, guanosine, and glutamine were the most efficacious ATP-sustaining substrates. Of seven potential citric acid cycle substrates, only glutamine significantly sustained ATP levels. Incubation with inosine plus glutamine sustained the ATP level at over 70% of the initial value found in embryonic chicken red cells. Uridine, cytidine, xanthosine, glutamate, and pyruvate were ineffective substrates. Similar results were obtained with adult erythrocytes, except that glutamine plus inosine fully sustained ATP levels during long-term incubation. Adenosine did not sustain ATP levels. Below 1 mM, the adenosine level was rapidly exhausted and above 1 mM its presence led to cell lysis. The ability of some nucleosides to maintain ATP levels is consistent with the high numbers of nitrobenzylthioinosine binding sites (nucleoside transporter sites) both in mature chicken red cells (approximately 10,000 sites/cell) and in embryonic red cells (approximately 30,000 sites/cell). Unlike pig red cells which switch from glucose to nucleosides at the erythrocyte stage, chicken cells show primary dependence on nucleoside metabolism at the embryonic stage.

Effectiveness of thrombolysis is associated with a time-dependent increase of malondialdehyde in peripheral blood of patients with acute myocardial infarction

By using a highly sensitive, high-performance liquid chromatographic technique, plasma values of malondialdehyde (MDA), adenosine and oxypurines were determined in 10 healthy subjects, 10 patients with noncardiac illness, and 20 patients with acute myocardial infarction (AMI) observed within 6 hours from the onset of symptoms. Patients with AMI received fibrinolytic treatment. Peripheral blood was obtained before and serially after thrombolysis (1, 2, 3, 6 and 24 hours). Coronary patency was assessed by timing of peak creatine phosphate kinase and by predischarge angiography. MDA (mean +/- SD) in healthy subjects, noncardiac patients, and immediately before thrombolytic treatment in patients with AMI was 0.051 +/- 0.013, 0.066 +/- 0.020 and 0.397 +/- 0.326 mumol/liter of plasma, respectively. A progressive increase in plasma MDA after thrombolysis was observed only in reperfused patients, whose values at the third, sixth and 24th hours were also significantly greater than those of nonreperfused patients. Time-dependent variations of xanthine and adenosine were also observed in the same group after thrombolysis. The data appear to indicate that a relevant increase in plasma MDA, mostly originating due to phospholipid derangement of postischemic myocytes, occurs only in patients with successful thrombolysis, thus suggesting that if properly assayed, it may represent reliable biochemical evidence of tissue injuries after myocardial reperfusion in humans.

Biochemical indicators of hazardous shoulder-neck loads in light industry

Prolonged, repetitive handling of light material is known to increase the risk of shoulder-neck disorders. Biological risk indicators related to musculoskeletal exposure, applicable by the general practitioner in the workplace, could provide an instrument for early intervention and rehabilitation. Eight women were studied, all full-time workers performing assembly tasks associated with a high prevalence of shoulder-neck complaints. All subjects were more tender in the shoulder region than young women in low-risk occupations. Heart rate recordings indicated a low general metabolic load during work. Concentrations in antecubital venous blood of several markers for metabolic stress and cellular damage (lactate, ammonia, hypoxanthine, urate, malondialdehyde, potassium, creatine kinase) were normal for all subjects, and showed no increase during 3 consecutive working days. Thus, the blood markers did not reflect hazardous shoulder-neck exposure.

Effects of acute physical stress on immune competence in pigs

Some interrelations between physical stress and immune competence were studied in pigs. One group of pigs underwent 2 intense short-term treadmill exercise tests, separated by an interval of 1 week, and another group served as controls. In vitro production of interferon alpha by blood mononuclear cells and the ability of lymphocytes to proliferate and produce interleukin 2 were chosen as markers of immune competence; plasma concentrations of cortisol, lactate, and purines were used as markers of physical stress. Blood samples were drawn from a catheter in situ 60 minutes before, immediately after, and at 10, 30, and 60 minutes, and 7, 24, and 72 hours after exercise. Physical stress resulted in immediate increase in the plasma concentrations of cortisol, lactate, and hypoxanthine, but had no effect on the blastogenic capability of lymphocytes or on their interleukin-2 production on either of the test occasions. Ability of blood mononuclear cells to produce interferon alpha in vitro was not affected by exercise stress.

In vitro changes in platelet function and metabolism following increasing doses of ultraviolet-B irradiation

Ultraviolet-B (UV-B) irradiation of platelet concentrates (PCs) may prevent the development of posttransfusion HLA alloimmunization. This study evaluated the effect of increasing doses of UV-B radiation on stored PCs. Pooled PCs were irradiated at UV-B doses of 600, 2400 or 10,000 mJ per cm2 and stored up to 96 hours under standard blood bank conditions. Compared to nonirradiated room-temperature and 37 degrees C controls, the irradiated units showed no significant changes in platelet count, white cell count, discharge of lactate dehydrogenase, release of beta-thromboglobulin, metabolism of ATP, ADP, ammonia, glutamine, glutamate, hypoxanthine, pCO2, or pO2 at any time of storage following any of the three UV-B doses. However, after a dose of 10,000 mJ per cm2, there were significant decreases in in vitro assays of platelet function-specifically, osmotic recovery and morphology score. Some metabolic systems were also affected by the 10,000 mJ per cm2 radiation dose, as shown by a decline in pH and bicarbonate and an increase in glucose consumption and lactate production (p < 0.05). The changes in these latter assays appeared only after 96 hours of postirradiation storage. Such changes were not seen in either the room-temperature or 37 degrees C control groups. Thus, heat generated during irradiation, per se, did not appear responsible for the observed in vitro changes in platelet function and metabolism. On the basis of the assays analyzed, it is concluded that UV-B irradiation of PCs at doses up to 10,000 mJ per cm2 does not induce significant metabolic or functional derangements following short-term storage (24-48 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

O2 uptake kinetics in response to exercise. A measure of tissue anaerobiosis in heart failure

Oxygen uptake (VO2) reflects the rate of aerobic regeneration of high-energy phosphate compounds (primarily adenosine triphosphate [ATP]). Since lactate increase is thought to result from an inadequate rate of aerobic ATP regeneration, it might be expected that lactate increase would be associated with a delayed attainment of steady state for VO2 in response to constant load exercise. Similarly if mitochondrial ATP regeneration during exercise is inadequately supported by O2 transport mechanisms, adenosine diphosphate (ADP) and purine nucleotide by-products, such as hypoxanthine, should increase. This study investigated the relationship between VO2 kinetics during exercise and accompanying changes in blood lactate and hypoxanthine values in heart failure patients, as a model of compromised O2 transport. Twenty-five patients with chronic heart failure performed cycle ergometry for 6 min at 25 W and at a work rate midway (50 percent delta) between their lactic acidosis threshold (LAT) and peak VO2. Ventilation and gas exchange were measured breath by breath, and venous lactate, hypoxanthine, norepinephrine, and epinephrine were determined at rest and 2 min after each test. The slow component of VO2 kinetics was quantified as the rise in VO2 from the third to the sixth minute of exercise (delta VO2 [6-3]). Ten age- and size-matched normal subjects served as control subjects. delta VO2 (6-3) was correlated with the increase in lactate (r = 0.71, p < 0.001), hypoxanthine (r = 0.61, p < 0.001), and norepinephrine (r = 0.41, p < 0.01) but not epinephrine in response to exercise in the heart failure patients. The delta VO2 (6-3) and delta lactate were both greater in the patients than in the control subjects at similar absolute work rates (54 +/- 20 and 60 W, respectively). However, the slope of the relationship between delta La and delta VO2 (6-3) for the patient and normal groups was indistinguishable. The lactate increase was correlated with hypoxanthine increase (r = 0.66, p < 0.001), but not norepinephrine or epinephrine. In summary, VO2 kinetics in response to exercise reflects delayed attainment of the steady state in heart failure patients, which is correlated with increases in lactate and hypoxanthine, markers of increased anaerobic metabolism.

Xylitol-induced increase in purine degradation: a role of erythrocytes

We administered xylitol intravenously to normal subjects to investigate the mechanism of xylitol-induced increase in the purine degradation in humans. Xylitol increased the plasma concentrations of hypoxanthine, xanthine and uric acid but decreased the blood concentration of pyruvic acid. The erythrocyte concentrations of IMP, AMP, ADP, glyceraldehyde 3-phosphate and fructose 1,6-diphosphate as well as the urinary excretion of hypoxanthine and xanthine were increased, while the erythrocyte concentration of ATP was decreased. In addition, the in vitro incubation studies using erythrocytes demonstrated that both xylitol-induced purine degradation and xylitol-induced inhibition of the conversion of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate were protected by pyruvic acid. These results indicate that xylitol-induced impairment of glycolysis in erythrocytes contributes to the observed xylitol-induced increase in the purine degradation in the body.

Transport of hypoxanthine from plasma to cerebrospinal fluid and vitreous humor in newborn pigs

To determine whether an elevated level of hypoxanthine in cerebrospinal fluid or vitreous humor might reflect a high plasma hypoxanthine concentration, or whether it necessarily represents local tissue hypoxia, we infused hypoxanthine intravenously to normoxemic and normotensive piglets (n = 6). Hypoxanthine was measured in different body fluids using HPLC. During the 8 hours of infusion hypoxanthine increased in plasma (from 30 +/- 6 mumol/l (mean +/- SD) before the infusion to 68 +/- 20 mumol/l at the end of the infusion, p < 0.01), cerebrospinal fluid (CSF) (19 +/- 8 to 43 +/- 9 mumol/l, p < 0.05) and vitreous humor (15 +/- 5 to 30 +/- 6 mumol/l, p < 0.05). After infusion, hypoxanthine values in all three fluids were similar to those seen in pigs after severe hypoxia. Hypoxanthine in vitreous humor and plasma were significantly correlated (r = 0.80, 95% confidence interval 0.47-0.93, p < 0.001). Urinary excretion of hypoxanthine increased almost 40 times from 0.12 +/- 0.14 to 4.6 +/- 2.9 mumol/kg/h indicating that renal excretion of hypoxanthine is not achieved just by passive filtration. We conclude that in newborn piglets hypoxanthine can pass from plasma to CSF and vitreous humor. Thus an increased CSF hypoxanthine concentration is not definite proof that significant cerebral hypoxia has occurred.

Effect of high-dose methotrexate on plasma hypoxanthine and uridine levels in patients with acute leukemia or non-Hodgkin lymphoma in childhood

We investigated the effect of high dose methotrexate (HDMTX) therapy on plasma hypoxanthine (Hx) and uridine (UR) concentrations in 12 children with acute lymphoblastic leukemia (ALL) or non-Hodgkin lymphoma (NHL). The initial plasma Hx level before the first administration of HDMTX (1 g/m2) was significantly higher in patients (25.5 +/- 17.5 microM) than that in healthy adult controls (4.0 +/- 1.4 microM). By 48 or 72 hours after the beginning of MTX infusion, the Hx concentration had decreased to 7.9 +/- 7.7 microM and 4.7 +/- 4.1 microM, respectively. This decrease of plasma Hx concentration after MTX infusion was also observed with the second course of HDMTX (3 g/m2) therapy. On the other hand, the plasma UR level did not change significantly. The in vitro treatment with 2 microM MTX of hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient mutant cells selected from HL-60 lowered the excretion of Hx into the culture medium. These data suggest a possible new explanation of the synergism of HDMTX and 6-thiopurines, for example 6-mercaptopurine and 6-thioguanine, since plasma Hx is considered to counteract 6-thiopurine toxicity through competition at the level of HGPRT.

Myocardial metabolism and adaptation during extreme hemodilution in humans after coronary revascularization

OBJECTIVE

This study was designed to evaluate the oxygen transport adjustments and myocardial metabolic adaptation that occurs with different levels of hemodilution during normothermia after cardiopulmonary bypass.

DESIGN

Prospective, nonrandomized study.

SETTING

Operating room in a university hospital.

PATIENTS

Eight patients with ejection fractions (> 40%) undergoing elective coronary artery bypass grafting.

METHODS

Before the institution of cardiopulmonary bypass, blood was withdrawn from patients to a target hematocrit of 15%. After coronary artery bypass grafting, a catheter was inserted directly into the coronary sinus. After the patients were rewarmed to 37 degrees C, they were weaned from cardiopulmonary bypass. Hemodynamic indices were measured, as well as measurements of myocardial oxygen consumption (VO2) and myocardial metabolism (lactate extraction and coronary sinus hypoxanthine). Measurements were made at three different hematocrit values: 15%, 20%, and 25%. Hematocrit was increased by autologous blood transfusion.

MEASUREMENTS AND MAIN RESULTS

The three levels of hemodilution (hematocrit: 17.4 +/- 3.4%; 23.0 +/- 3.7%; 27.8 +/- 4.8%) were significantly different from baseline (hematocrit 37 +/- 2.6%; p < .05). Oxygen delivery, which increased with autologous transfusion, exceeded 350 mL/min/m2 at each level of dilution. The myocardial VO2 increased significantly after autologous transfusion compared with the most dilute condition (7.0 +/- 3.7 mL/min at hematocrit 17.4% vs. 11.2 +/- 4.8 mL/min at hematocrit 23.0% and 12.4 +/- 4.0 mL/min at hematocrit 27.8%). This transfusion-induced increase was also true of myocardial oxygen extraction. Lactate extraction and hypoxanthine release were normal and unchanged at each level of hemodilution. Systemic oxygen extraction ratio increased with hemodilution and decreased with autologous transfusion.

CONCLUSIONS

Hemodilution to a hematocrit of approximately 15% is tolerated in anesthetized humans after coronary artery bypass surgery. There was no evidence of myocardial ischemia, as demonstrated by absence of S-T depression on the electrocardiogram, lactate extraction, or hypoxanthine release. In selected patients, postoperative transfusion may be based on systemic physiologic end-points, such as oxygen extraction ratio, rather than set hematocrit values.

Contrast in adenine uptake by chicken and rabbit erythrocytes in vitro

1. Relative to rabbit erythrocytes, chicken red blood cells exhibit a much greater capacity to utilize [3H]adenine for nucleotide synthesis in vitro, even at 5 degrees C and in the absence of added inorganic phosphate. 2. This difference is largely due to a higher concentration of phosphoribosylpyrophosphate and greater activity of adenine phosphoribosyltransferase in the avian cells. 3. The capacity of avian erythrocytes for utilization of guanine and hypoxanthine is several fold less than that of adenine. 4. The data are consistent with lower activity for hypoxanthine/guanine phosphoribosyltransferase than for adenine phosphoribosyltransferase in intact chicken erythrocytes. 5. The results indicate that reutilization of adenine by chicken erythrocytes may be physiologically significant.

Maximal-intensity intermittent exercise: effect of recovery duration

Seven male subjects performed 15 x 40m sprints, on three occasions, with rest periods of either 120 s (R120), 60 s (R60) or 30 s (R30) between each sprint. Sprint times were recorded with four photo cells placed at 0, 15, 30 and 40 m. The performance data indicated that whereas running speed over the last 10 m of each sprint decreased in all three protocols (after 11 sprints in R120, 7 sprints in R60 and 3 sprints in R30), performance during the initial acceleration period from 0-15 m was only affected with the shortest rest periods increasing from (mean +/- SEM) 2.58 +/- .03 (sprint 1) to 2.78 +/- .04 s (spring 15) (p < .05). Post-exercise blood lactate concentration was not significantly different in R120 (12.1 +/- 1.3 mmol.l-1) and R60 (13.9 +/- 1.2 mmol.l-1), but a higher concentration was found in R30 (17.2 +/- .7 mmol.l-1) (p < .05). After 6 sprints there was no significant difference in blood lactate concentration with the different recovery durations, however, there were significant differences in sprint times at this point, suggesting that blood lactate is a poor predictor of performance during this type of exercise. Although the work bouts could be classified primarily as anaerobic exercise, oxygen uptake measured during rest periods increased to 52, 57 and 66% of maximum oxygen uptake in R120, R60 and R30, respectively. Evidence of adenine nucleotide degradation was provided by plasma hypoxanthine and uric acid concentrations elevated post-exercise in all three protocols. Post-exercise uric acid concentration was not significantly affected by recovery duration.(ABSTRACT TRUNCATED AT 250 WORDS)

[Studies on purine-pyrimidine metabolism (1)--Quantitation of purine-pyrimidine metabolites and allopurinol-oxipurinol in biological fluids]

A reversed-phase high-performance liquid-chromatography method for determining simultaneous quantitation of purine-pyrimidine metabolites, allopurinol and oxipurinol in plasma and urine samples was studied. Separation was optimal with phosphate buffer (10 mmol/l, pH 5.0) containing 1% methanol as an eluent and mu Bondapak C18 as a column. An isocratic separation of a standard mixture of 13 compounds was achieved within 40 minutes with adequate reproducibilities (coefficient of variation: 2.49% for 1.63 mumol/l orotidin-0.12% for 50 mumol/l uridine). A simple ultrafiltration of plasma yielded quantitative recoveries (uric acid: 101.7-107.5%, hypoxanthine: 90.4-102.8%, xanthine: 95.9-99.5%, oxipurinol: 104.4-107.1%, allopurinol: 97.4-103.4%). Compounds were identified by their retention times, absorbance ratios, co-elution with standards and enzymic shifts. In addition to the above compounds, simultaneous quantitation of pseudouridine, uridine, adenine and inosine in the plasma would be possible under the same conditions.

Cerebral blood flow fluctuation in low-risk preterm newborns

Cerebral blood flow (CBF) fluctuation was studied by analyzing Doppler internal carotid blood velocity recordings of 13 healthy preterm newborns obtained in the course of their first 5 days of life. As measures of fluctuation we used the interquartile range (IQR) and the coefficient of variation (CV) of the ensemble of heart beats of a 20-s recording. In this way we determined fluctuation of the following velocity curve parameters (VCPs): end diastolic velocity; mean velocity; peak systolic velocity and pulsatility index (PI). The pooled data 5-95% intervals for fluctuation thus measured, were: 93-281% for CV; 0.6-3.7 cm/s for the IQR of the velocities; and 4-19% for the PI-IQR. Multiple regression analysis of IQR revealed significant relationships with: the VCP level; with restlessness; and with patency of the ductus arteriosus. Our findings imply that: (1) CBF has various qualities with different stability, mean velocity being the most stable; (2) for all the VCPs investigated, fluctuation is physiological in the early days after preterm birth; (3) most likely, there exists no age trend; (4) restlessness rather than wakefulness, enhances fluctuation; (5) patent ductus arteriosus destabilizes CBF; and (6) for a proper insight into fluctuation, the level of the VCP in question must be taken into account. We suggest that, the enhancing effect that patent ductus arteriosus has on fluctuation pays a contribution to the pathogenesis of brain damage. Finally, we conclude that the IQR represents fluctuation better than does the more commonly used CV.