The determination of hypoxanthine and xanthine with a PO2 electrode

Oxygenation of the newborn. The impact of one molecule on newborn lives

Hypoxanthine is a purine metabolite which increases during hypoxia and therefore is an indicator of this condition. Further, when hypoxanthine is oxidized to uric acid in the presence of xanthine oxidase, oxygen radicals are generated. This was the theoretical basis for suggesting and studying, beginning in the 1990s, resuscitation of newborn infants with air instead of the traditional 100% O2. These studies demonstrated a 30% reduction in mortality when resuscitation of term and near term infants was carried out with air compared to pure oxygen. The mechanism for this is not fully understood, however the hypoxanthine -xanthine oxidase system increases oxidative stress and plays a role in regulation of the perinatal circulation. Further, hyperoxic resuscitation inhibits mitochondrial function, and one reason may be that genes involved in ATP production are down-regulated. Thus, the study of one single molecule, hypoxanthine, has contributed to the global prevention of an estimated 2-500,000 annual infant deaths.

Hyperoxia in the term newborn: more evidence is still needed for optimal oxygen therapy

It took more than 30 years from the first observations that oxygen may be toxic during resuscitation till international guidelines changed to recommend that term and near term newborn infants should be resuscitated with air instead of 100% oxygen. There are still a number of unanswered questions related to oxygen therapy of the newborn infant. The newborn brain, lungs and other organs are susceptible to oxygen injury, and newborns still develop injury caused by hyperoxia.

Release of hypoxanthine and phosphate from exercising human legs with and without arterial insufficiency

Release of hypoxanthine and phosphate from exercising legs was studied in eight subjects without known obstructive arterial disease and in 20 claudicants. Lower leg blood flow was measured with a thermodilution catheter in the popliteal/distal femoral vein. The catheter allowed blood sampling from the calf before, during and after exhaustive exercise on a bicycle ergometer at a stepwise increasing load. Resting plasma hypoxanthine levels were higher in claudicants than in normal subjects (p less than 0.05). Hypoxanthine concentrations increased 2-4-fold during exercise, amounting to values ten times higher than the resting levels 5 and 10 min post exercise, in the venous effluent of the normal legs. A similar rise was found in the claudicants despite half the exercise intensity at exhaustion. Popliteal venous concentrations of phosphate increased by approximately 25% during exercise without significant differences between the two groups. During exercise the release of hypoxanthine increased 38-fold and of phosphate 21-fold in the normal lower legs, while a ten-fold increase in both metabolites was recorded in the claudicating legs. The study demonstrated a high release of hypoxanthine and phosphate from the human lower leg during rhythmic, exhaustive exercise (with maximal vasodilation). The result is compatible with the assumption that metabolites from the catabolism of adenine nucleotides (adenosine) play a role in the autoregulation of blood flow in human skeletal muscle. Increased plasma hypoxanthine concentrations at rest may indicate peripheral arterial insufficiency.

Oxidative Stress in the Newborn – A 30-Year Perspective

In this review the development of the concept 'hypoxia-reoxygenation injury' is outlined. An update of some important factors and mechanisms related to oxidative stress injury in newborn infants is presented, including the metabolism of glutathione, the role of antioxidants, iron and nitric oxide, and how these may influence health and disease in the newborn and contribute to 'oxygen radical disease of the newborn'. New insight into how hyperoxia and hypoxia may induce changes leading to retinopathy of prematurity by vascular endothelial growth factor acting in concert with insulin-like growth factor is briefly summarized. Inflammation and oxidative stress seem to be two sides of the same coin in newborn babies both contributing to injury partly through similar mechanisms.

Room air resuscitation-two decades of neonatal research

Experimental as well as clinical studies have demonstrated that room air is as efficient as pure oxygen for newborn resuscitation. Recent data even indicate that outcome is improved if pure oxygen is avoided. Thus, in a meta-analysis, neonatal mortality was significantly lower in those newly born infants resuscitated with 21% than with 100% oxygen. Short-term recovery is also improved in the room air group since time to first breath is shorter, heart rate at 90 s and 5 min Apgar score are higher. Animal data indicate that injury in a number of organs, including the brain, is aggravated by giving pure oxygen to newly born depressed infants even for a brief period. Although the optimal oxygen concentration probably is not known for newborn infants in need of resuscitation, pure oxygen should be avoided. These data should be reflected in new guidelines that are under way.

Selection of babies for intervention after birth asphyxia

Based on animal experiments, the therapeutic window for neonates with signs of perinatal hypoxia-ischaemia is probably less than 6 h, and early selection of patients is of utmost importance. In term neonates, fetal heart rate and blood flow patterns, the Apgar score, and other clinical scoring systems are insufficient to select patients for intervention, whereas umbilical artery pH<7.0 combined with umbilical arteriovenous differences in PCO(2), lactate/pyruvate ratios in cord blood, and CSF interleukin-1beta have a better predictive value. At present, neurophysiological methods such as (amplitude-integrated) EEG and evoked potentials have the best predictive value. In preterm neonates, lactate/pyruvate and uric acid measurements in cord blood, as well as neurophysiology appear to be helpful to predict brain injury, and might be used to select patients for intervention.

The importance of the measurement of ATP depletion and subsequent cell damage with an estimate of size and nature of the market for a practicable method: a review designed for technology transfer

ATP is the energy currency of cells. ATP depletion is a central process in pathogenesis, in particular ischaemia, hypoxia and hypoglycaemia. ATP depletion in cells can be indirectly measured from the increased concentrations of extracellular hypoxanthine, a central intermediate in the metabolism of ATP. Cell damage secondary to ATP depletion can also be measured from extracellular hypoxanthine. The relevant biochemistry and physiology is briefly reviewed. Since market size is needed for investment decisions that would allow technology transfer, the numbers of hypoxanthine analyses that are clinically justified from the extensive published evidence are calculated per million population from UK, Norwegian and other evidence. The concentration of oxygen in blood is measured to estimate whether mitochondrial oxidative phosphorylation is adequate. Measurements of bicarbonate are used to estimate anaerobic glycolysis. Since the indirect estimation of ATP depletion is a major objective of blood gas and acid-base analyses, the number of such analyses per million population provides a good estimate of potential market size for a more direct method of estimating ATP depletion. A method is required for the rapid, dispersed emergency analyses needed clinically. Routes for method development are indicated. Competition, risks, acceptability, consumer motivation and timetables are indicated for the development phase. There are medicolegal pressures, especially in the USA, for the proposed advances to be widely used.

Post-mortem concentrations of hypoxanthine in the vitreous humor--a comparison between babies with severe respiratory failure, congenital abnormalities of the heart, and victims of sudden infant death syndrome

Post-mortem hypoxanthine concentrations in the vitreous humor of human infants were investigated. Hypoxanthine is formed from hypoxic degradation of adenosine monophosphate. The concentrations in the vitreous humor can give information about antemortem hypoxia. The post-mortem levels were corrected for the time elapsing between death and the autopsy. Four groups of infants were compared: 17 babies who died of respiratory distress syndrome (RDS), 72 infants who died of sudden infant death syndrome (SIDS), 23 children dying of congenital heart disease (both cyanotic and acyanotic), and 15 children dying acutely in accidents without any known significant time of hypoxia before death. The corrected, median hypoxanthine levels in victims of SIDS (200 mumol/L) was significantly higher (p < 0.01) than in the accident group (0 mumol/L), but no clear difference was found between the SIDS group and the RDS group (101 mumol/L), or the heart group (54 mumol/L). A number of children with "normal" hypoxanthine levels (0 to 38 mumol/L) were found in all four groups, but the numbers were significantly lower (p < 0.005) in the RDS, SIDS and heart groups than in the accident group. It is concluded that SIDS is probably not a sudden event, but may be preceded by relatively long, or repeated intermittent periods of hypoxia (of unknown etiology).

Hypoxanthine, xanthine, and urate in synovial fluid from patients with inflammatory arthritides

As nucleotide catabolism increases during tissue injury the appearance of purine metabolites in inflamed synovial fluid might be of value in understanding the joint damage in inflammatory arthritides. In this study, therefore, synovial and plasma concentrations of hypoxanthine, xanthine, and urate in 16 patients with rheumatoid arthritis (three with psoriatic arthropathy) were analysed. It was found that their plasma concentrations of hypoxanthine were greater than those of a reference group of healthy subjects. The synovial fluid concentrations of hypoxanthine, xanthine, and urate were higher than corresponding concentrations in plasma. Positive correlations were found between the respective plasma and synovial fluid values of xanthine and urate. These findings indicate a local enhanced purine metabolism in inflamed joint tissue and diffusion of oxypurines from joint cavity to plasma. No relation was found between measured metabolites and disease duration, radiological joint findings, or synovial fluid cells. Except for a weak correlation between plasma urate and serum haptoglobin, measured purine metabolites were not related to laboratory measures of systemic inflammation.

Simultaneous determination of inosine, hypoxanthine, xanthine, and uric acid and the effect of metal chelators

We describe a sensitive, reproducible method for the simultaneous determination of the ATP catabolites inosine, hypoxanthine, xanthine, and uric acid in biological samples and organ perfusate using reverse-phase chromatography and multiwavelength detection at 254, 270, and 292 nm. Sample preparation includes precipitating proteins with perchloric acid, neutralizing the sample, passing the supernatant over a polyethyleneimine column, and analyzing the collected fractions by high-performance liquid chromatography. Addition of metal chelators to the perchloric acid resulted in increased values for xanthine, hypoxanthine, and uric acid. The method was sensitive (limit of detection, 0.08 nmol on column; S/N = 4) and linear over the range 0.5-30 microM. Precision and accuracy of the method were evaluated for lung tissue and lung perfusate. Coefficients of variation ranged from 2.8 to 6.1% for perfusate and from 1.7 to 12.6% for tissue. Recoveries for all compounds exceeded 90%. We applied this method to rat lung tissue, lung perfusate, and rat and human blood. Advantages of this method are simultaneous quantitation with excellent sensitivity of all compounds, simplified peak identification by using multiwavelength detection, and improved accuracy by preventing loss of compounds with metal chelators.

Plasma xanthine oxidase and resistance to hypoxia: effect of purines and alcohol administration

The administration of allopurinol significantly increased resistance to repeated hypobaric hypoxia, while hypoxanthine decreased it. The administration of adenine or inosine (25 mg/kg) was without effect. The results show pathogenic significance of xanthine oxidase-dependent production of free oxygen radicals in posthypoxic damage. In other experiments, the administration of 50% ethanol (12 ml/kg) by gastric catheter increased plasma xanthine oxidase activity in both rats and hamsters.

Renal excretion of hypoxanthine and xanthine in primary gout

PURPOSE

The renal excretion of uric acid is usually diminished in primary gout with respect to increased serum urate levels. To determine whether the renal excretion of uric acid precursors, hypoxanthine and xanthine, is also abnormal in primary gout, the concentrations of these purines were measured in plasma and 24-hour urine samples in normal subjects, in patients with primary gout and uric acid underexcretion, and in patients with enzyme deficiencies that are known to result in over-production of uric acid.

SUBJECTS AND METHODS

Three groups of subjects were studied: Group I consisted of 10 ambulatory healthy normal men; Group II consisted of 15 patients in whom primary gout was diagnosed; and Group III consisted of 10 patients with various enzyme defects known to produce an excessive synthesis of uric acid. In each subject, plasma and 24-hour urinary uric acid, hypoxanthine, xanthine, and creatinine concentrations were measured and the mean of three consecutive determinations was used. The fractional excretion of purine compounds was calculated from a formula. Hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, and hemoglobin were also measured in each subject.

RESULTS

Plasma hypoxanthine and xanthine were increased in the two groups of patients compared with the control subjects. Urinary hypoxanthine and xanthine levels were reduced in gouty patients compared with control subjects, whereas levels were increased in patients with uric acid overproduction. A positive correlation was found between the renal clearances of uric acid, hypoxanthine, and xanthine.

CONCLUSION

The results indicate that the renal excretion of hypoxanthine and xanthine is severely impaired in most patients with primary gout.

Hypoxanthine, xanthine and uridine in body fluids, indicators of ATP depletion

Measurements of hyp, xan and urd in body fluids can provide evidence of energy, ATP, depletion in the body, in organs or in cells. Such information is clinically useful in the many diseases in which cellular energy supplies cannot be maintained like perinatal asphyxia, hydrocephalus and vascular insufficiency in brain, heart, limbs, kidneys or other organs. Similar HPLC methods using reversed-phase C18 columns and quantitation by UV absorption have been employed in a variety of centres to yield almost identical results. These have been assembled in this review to form a series of reference values. The current analytical problems are reviewed. Since concentrations of hyp and xan may alter independently situations are discussed in which separate measurements rather than their summed, total oxypurine concentrations are needed. The biochemistry and physiology underlying the use of such analyses is examined to guide sampling of the appropriate body fluid at a relevant time and to avoid oversimplified interpretation of results as well as unnecessary arguments. Specifically: (1) Intracellular concentrations of hyp and xan are inversely related to adenylate energy change and therefore to the energy currency of the cell ATP. Uridine in tissues is similarly 'controlled'. (2) There is extensive evidence that large increases in hyp, xan and urd in body fluids indicate ATP depletion. (3) Small changes in hyp probably reflect alterations of ATP turnover. (4) Xanthine arises mainly from guanine and can change independently of hyp. (5) Clinically useful information is obtainable from hyp and xan concentrations in CSF, amniotic fluid, urine and plasma. Extensive clinical correlations are reviewed. At present we are in a development phase for which HPLC is ideal but the most efficient way to perform and use such analyses in routine clinical practice remains to be established.

Hypoxanthine and xanthine in stored SAGM-blood

The concentration of xanthine and hypoxanthine was measured in 8 portions of SAGM red cell concentrates during 4 wk storage. The concentration of xanthine increased from 4.2 to 35.1 mumol/l and the concentration of hypoxanthine increased from 16.8 to 165.2 mumol/l (mean values). Previous studies have demonstrated several important effects of purine bases--among these a reduced cytotoxicity of purine antimetabolites. It is concluded that further studies are necessary to investigate the clinical role of purines in stored blood products.

The concentrations of xanthine and hypoxanthine in cerebrospinal fluid as therapeutic guides in hydrocephalus

Xanthine, hypoxanthine, and total oxypurine levels were determined in the cerebrospinal fluid of 18 hydrocephalic patients and 8 healthy controls by high-performance liquid chromatography (HPLC). Eight of the hydrocephalic patients were self-compensated and 10 had shunts implanted during the course of the study. The mean xanthine, hypoxanthine, and total oxypurine levels in the normal children were 5.20, 5.94 and 11.29 mumol/l, respectively. In self-compensated hydrocephalics these levels were respectively 6.06, 6.50 and 12.57 mumol/l. In noncompensated hydrocephalics, they were 11.40, 10.79 and 22.19 mumol/l. The differences between the latter group and the first two are statistically significant (P less than 0.001). Fifteen days after implantation of shunts in the noncompensated hydrocephalics, the mean xanthine levels had fallen to 4.61 mumol/l, the mean hypoxanthine levels to 5.03 mumol/l, and the mean total oxypurine levels to 9.64 mumol/l. The change is statistically significant (P less than 0.001). In light of these findings we propose that xanthine, hypoxanthine, and total oxypurine levels be used in cases of hydrocephalus as guides for therapeutic action and to monitor progress.

Accuracy of Apgar score and arterial cord-blood pH in diagnosis of perinatal brain-damage assessed by CK-BB isoenzyme measurement

This study was carried out on 45 newborns to evaluate the accuracy of 1 minute Apgar score and umbilical arterial pH for prediction of the risk of perinatal brain damage. Using a new and very sensitive method for CK-BB determination, which is considered a good indicator of brain damage, CK-BB was used as reference. Patients with low Apgar score at one minute of life had significantly higher cord blood CK-BB values than the control group (p less than 0.01). No difference was found between the control group and the group with umbilical cord blood acidosis (p less than 0.2).

Cerebrospinal fluid hypoxanthine and xanthine concentrations as indicators of metabolic damage due to raised intracranial pressure in hydrocephalic children

Intracranial pressure and cerebrospinal fluid hypoxanthine and xanthine concentrations were measured in hydrocephalic children with suspected raised intracranial pressure. There was a highly significant correlation between intracranial pressure and cerebrospinal fluid hypoxanthine and xanthine levels.

Increased hypoxanthine concentrations in cerebrospinal fluid of infants with hydrocephalus

Hypoxanthine, the end product of purine metabolism, is usually very elevated in body fluids during severe hypoxia. We measured hypoxanthine in the cerebrospinal fluid of hydrocephalic preterm infants (12 with posthemorrhagic, one with congenital hydrocephalus) to determine whether hydrocephalus is associated with anaerobic metabolism of brain tissue. Cerebrospinal fluid hypoxanthine was undetectable in normal infants. In hydrocephalic infants, the concentration of hypoxanthine ranged from 7.5 mumol/L to 28 mumol (means = 14.3 mumol/L). The hypoxanthine concentrations fell from a mean of 12.8 mumol/L to a mean of 2.0 mumol/L (P less than 0.05) with successful treatment of the ventriculomegaly by lumbar puncture or by ventriculoperitoneal shunt. Patients with acute posthemorrhagic hydrocephalus had similar concentrations of hypoxanthine (means = 14.5 mumol/L) as patients with late or with congenital hydrocephalus (means = 13.8 mumol/L), indicating that brain hypoxia is probably a consequence of the ventriculomegaly and not of the hemorrhagic insult.

Cerebral arterio-venous difference for hypoxanthine and lactate during graded asphyxia in the fetal lamb

Hypoxanthine (HX) and lactate are degradation products from energy-rich intracellular substrates (ATP and glycogen), and their concentration will increase during anaerobic conditions, such as fetal asphyxia. In this study the accumulation of the two metabolites in blood during asphyxia was studied in 7 acutely exteriorized fetal lambs. The arterio-venous difference of HX and lactate over the brain was related to the function of the fetal brain as reflected by the somato-sensory evoked electroencephalogram potentials (SEP). Increased concentrations of HX in plasma and lactate in blood occurred simultaneously with deterioration of the SEP and the 3 variables correlate highly significantly. During normoxia, a net cerebral influx was found for HX, which in combination with severe asphyxia gradually changed to a net efflux. A linear correlation was found between the cerebral arterio-venous differences of HX and the impairment of the SEP. No such correlation existed for lactate. The results suggest, that the fetal brain has a high threshold for degrading its energy-rich intracellular purines.

High-performance liquid chromatographic methods for base and nucleoside analysis in extracellular fluids and in cells

High-performance liquid chromatography based methods for the study of the metabolism of purine and pyrimidine bases and nucleosides have been developed. These methods, using 200--50 microliter samples of extracellular fluids and employing isocratic separations, can measure a wide range of compounds. Hypoxanthine, xanthine and uridine concentrations in plasma from normal men are relatively stable. Species differences have been detected: concentrations of cytidine are higher in rat and mouse serum than in man, since the concentrations of uridine are similar; purine/pyrimidine ratios may be different. Fetal calf serum used for tissue culture contains about a 40 times higher concentration of hypoxanthine than the less-effective calf serum. Use of the methods appears to be justified in the assessment of the metabolic damage due to severe hypoxia and/or ischaemia.

The measurement of hypoxanthine, xanthine, inosine and uridine in umbilical cord blood and fetal scalp blood samples as a measure of fetal hypoxia

Hypoxanthine, xanthine, inosine, urate and uridine, were measured in 149 samples of umbilical cord plasma using high pressure liquid chromatography. In spite of a good correlation with the simpler oxygen consumption method for measuring hypoxanthine, there was no clear discrimination between hypoxic and well oxygenated infants, although mean concentrations were higher in infants with well defined criteria of intrapartum hypoxia or bith asphyxia, there was overlap with the normal range. Fetal scalp blood samples were also found to be clinically unhelpful in the diagnosis of intrapartum hypoxia, at least in part due to variable degrees of haemolysis in the specimens. There were poor correlations between hypoxanthine concentrations and those of hydrogen ion, base deficit and lactate. Uridine concentrations were significantly higher in arterial cord blood than in venous cord blood but hypoxanthine or xanthine concentrations did not show this difference.

Reverse phase partition HPLC for determination of plasma purines and pyrimidines in subjects with gout and renal failure

A reverse phase partition mode of high pressure liquid chromatography was developed for the estimation of purine, pyrimidine and pyrazolopyrimidine nucleosides and bases. This method has been applied to the investigation of purine and pyrimidine metabolism in subjects with gout and/or renal failure during allopurinol therapy. Plasma levels of hypoxanthine and xanthine were quantitated in all subjects. No significant differences were observed between healthy males and gouty subjects with or without allopurinol medication. There was a significant increase in xanthine levels in patients with gout and renal failure, or renal failure on allopurinol, and plasma levels of oxipurinol were increased, but no correlation with glomerular filtration rate (GFR) was observed. The separation method was also used to examine urines from patients with known abnormalities of purine and pyrimidine metabolism in an attempt to evaluate its usefulness as a urine screening technique.

Isolation and identification of a small molecular weight inhibitor of cyclic nucleotide phosphodiesterase from bovine brain

In a search for endogenous regulators for cyclic nucleotide phosphodiesterase (3':5'-cyclic-AMP 5'-nucleotidohydrolase, EC 3.1.4.17), we found that the ultrafiltrate of bovine brain homogenate contained a cyclic nucleotide phosphodiesterase inhibitor. The inhibitor-containing fraction was further purified by ion-exchange column chromatography and gel filtration chromatography. The purified inhibitor was found to be a small molecular weight compound which had a maximum absorption at 248 nm. This compound was identified by thin-layer chromatography and high-pressure liquid chromatography as hypoxanthine. We suggest that hypoxanthine may serve as an endogenous regulator for the hydrolysis of cyclic nucleotide by cyclic nucleotide phosphodiesterase.

Hypoxanthine in cerebrospinal fluid in children

In forty-five children the hypoxanthine concentration in cerebrospinal fluid (CSF) was measured (fifty-two samples). In newborn infants (nineteen patients) the hypoxanthine levels were higher in patients with clinical conditions associated with hypoxia (idiopathic respiratory distress syndrome, asphyxia, apneic attacks) than in patients without clinical hypoxia (P less than 0.01). In hypoxic patients the hypoxanthine concentration varied between 5 and 28 mu mol/l. In children outside the neonatal period the hypoxanthine concentration in CSF varied considerably in different diseases. High levels were registered in meningitis prior to treatment, febrile convulsions and in lymphoblastic leukaemia, probably reflecting tissue hypoxia and an increased tissue catabolism.

Post-mortem hypoxanthine levels in the vitreous humour. An introductory report

Post-mortem hypoxanthine levels in vitreous humour were determined in 86 consecutive legal autopsy cases. In cases of sudden death caused by trauma or by myocardial infarction, levels ranging from 0 to 540 mumol/l were found. The mean value was about ten times higher than normal in vivo plasma levels. The hypoxanthine levels seem to be independent of time post-mortem, at least during the first 48 hours. It is known that augmentation of the hypoxanthine plasma, cerebrospinal fluid, and urine levels reflects tissue hypoxia. In the present material no elevation of hypoxanthine levels in the vitreous humour was found in cases of strangulation or suspension, while statistically significant elevation was found in cases of drug intoxication. It is concluded that this may reflect the effect of drug-induced prolonged tissue hypoxia caused by respiratory depression.

Plasma hypoxanthine in neonatal hypoxia: a comparison of two methods

Hypoxanthine levels were determined in both venous and arterial cord blood of 42 neonates. Two methods were compared, a PO2 electrode determination and an HPLC (high-pressure liquid chromatography) method. A good correlation was found between the two methods. However, the HPLC method was more sensitive, more reproducible and easier to perform. Hypoxanthine levels in the umbilical artery were found to be higher than in the vein. A significant negative correlation between pH and hypoxanthine level was established. The studies showed that plasma hypoxanthine levels by themselves did not provide an absolute diagnosis of intrauterine hypoxia.

Urinary hypoxanthine, xanthine and uric acid excretion in newborn infants with perinatal complications

The concentration of hypoxanthine, xanthine and uric acid in the first 24-h urine of 105 newborn infants was measured densitometrically by thin-layer chromatography. 45 of them had moderate or severe perinatal complications. Among these newborns, 26 infants with perinatal complications (58%) and 4 infants without perinatal complications (7%) had an elevated urinary excretion rate of hypoxanthine. Urinary xanthine was not increased, uric acid was slightly higher in the group of infants with perinatal complication. It seems that a crucial mark is involved, if the rate of hypoxanthine exceed 15% of the total urinary oxypurine excretion, or, if related to urinary creatinine, more than 0.075 mumol hypoxanthine/mumol creatinine. Apparently, with hypoxic newborns increased values of urinary hypoxanthine excretion can be used to quantify the lack of oxygen retrospectively.

Alteration of plasma hypoxanthine concentration during ischaemia in the forelimb of the pig

Ischaemia in the forelimb of pigs was induced by clamping the main artery of an 'isolated leg' preparation. In plasma from the brachial vein the hypoxanthine concentration increased linearly between 10 and 25 min of ischaemia. The average increase in plasma hypoxanthine concentration in ten experiments was 25-0 micromol/1 after 30 min of ischaemia. It is concluded that the plasma hypoxanthine level might be a useful indicator of tissue hypoxia caused by impairment of peripheral blood flow.