Methods for studying leukocyte filterability in undiluted blood from intermittent claudicants

Leukocytes are characterised from their influence on the filterability of undiluted blood from patients with PAOD (intermittent claudicants - Fontaine Stage II) and a group of sex and age-matched controls. Undiluted blood was filtered through 5 microm Nuclepore (Hemafil) filters for 300 s, at 711 Pa and room temperature, using a custom-made constant pressure filtrometer. Four populations of leukocytes are identified in both groups. In the control group, 94.4% of the leukocytes are identified as fast leukocytes with a transit time of 1.8 s. The remaining white cells are recognised as slow flowing leukocytes and subdivided into three further sub-populations. The first of these (SL1; 2.8% of total leukocyte count) is characterised by a transit time of 31.7 s, a second population (SL2; 1.5% of total leukocyte count) by a transit time of 145.8 s while the remaining cells are identified as pore blockers (PB) under these conditions. A similar rheological classification is valid in the patients but the sum of the three minor populations is elevated compared to controls (p = 0.001) although there is no overall leukocytosis. The only significant difference in flow properties of any blood cells, between the two groups of volunteers, is seen in the major population of leukocytes with an elevated transit time of 2.4 s. Stepwise regression analysis identifies the concentration of fast leukocytes, SL2 and PB as the major variables affecting blood flow through the filter. It is argued that the higher concentration of SL2 and PB probably reflect the increased sensitivity of neutrophils to physical stimuli.

13C NMR measurements of human gluconeogenic fluxes after ingestion of [U-13C]propionate, phenylacetate, and acetaminophen

Anaplerotic, pyruvate recycling, and gluconeogenic fluxes were measured by 13C isotopomer analysis of plasma glucose, urinary phenylacetylglutamine, and urinary glucuronide in normal, 24-h-fasted individuals after ingestion of [U-13C]propionate, phenylacetate, and acetaminophen. Plasma glucose isotopomer analysis reported a total anaplerotic flux of 5.92 +/- 1.03 (SD) relative to citrate synthase. This was not significantly different from glucuronide and phenylacetylglutamine analyses (6.08 +/- 1.16 and 7. 14 +/- 1.94, respectively). Estimates of pyruvate recycling from glucose and glucuronide isotopomer distributions were almost identical (3.55 +/- 0.99 and 3.66 +/- 1.11, respectively), whereas phenylacetylglutamine reported a significantly higher estimate (5.74 +/- 2.13). As a consequence, net gluconeogenic flux reported by phenylacetylglutamine (1.41 +/- 0.28) was significantly less than that reported by glucose (2.37 +/- 0.64) and glucuronide (2.42 +/- 0. 76). This difference in fluxes detected by analysis of phenylacetylglutamine vs. hexose is likely due to compartmentation of hepatic metabolism of propionate. Net gluconeogenic flux estimates made by use of this stable isotope method are in good agreement with recent measurements in humans with [14C]propionate.

Propofol preserves the viability of isolated rat hepatocyte suspensions under an oxidant stress

The purpose of this study was to investigate whether propofol protects rat hepatocyte suspensions against an oxidant attack by a free radical generator 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH). Rat hepatocyte suspensions (2 x 10(6) cells/mL) were prepared using Seglen's collagenase perfusion technique. Suspensions were treated with AAPH (50 mM) alone, propofol (28 microM) plus AAPH, or, in a separate experiment, with either AAPH alone or 10% intralipid (0.5 microL/mL) plus AAPH. Each experiment had untreated control suspensions. Cell viability was measured at 1, 2, and 3 h using the trypan blue exclusion test and expressed as a percentage of the initial number of viable cells. Cells taken from control at time 0 h and each experimental group at 1 h from five separate hepatocyte preparations were examined by electron microscopy. Control cell viability decreased with time. The addition of AAPH significantly reduced viability compared with control (P < 0.0001); pretreatment with propofol significantly attenuated this effect at 1 h (P = 0.0008), but 10% intralipid had no effect. Electron microscopy revealed structural changes in cell membranes that could have accounted for the inability to exclude trypan blue. In conclusion, a 28-microM concentration of propofol protects rat hepatocytes from an oxidant stress sufficient to cause cell death at 1 h.

IMPLICATIONS

Oxidants contribute to tissue injury in a variety of situations. We have shown that the anesthetic propofol improves survival of liver cells exposed to oxidant injury at blood concentrations achieved in anesthetized patients. These effects may be relevant during transplantation and critical illness.

Antioxidant effects of propofol in human hepatic microsomes: concentration effects and clinical relevance

Propofol is known to possess antioxidant properties. There is controversy regarding the mechanisms by which the drug produces its antioxidant effects and the significance of these effects in relation to plasma concentrations of propofol in clinical practice. We studied the effects of increasing concentrations of Intralipid, propofol, butylated hydroxytoluene (BHT) and a vitamin E analogue (Trolox C) in 0.9% saline on non-enzymic and enzymic lipid peroxidation in human hepatic microsomes, and on concentrations of antioxidant enzymes in a Hep G2 cell line. Propofol showed significant inhibition of lipid peroxidation, but was less potent than BHT or Trolox C. IC50 values for non-enzymic and enzymic lipid peroxidation were mean 9.47 (SD 0.86) and 7.39 (0.84) mumol litre-1 for propofol, 1.30 (0.57) and 0.32 (0.02) mumol litre-1 for BHT and 2.34 (0.68) and 0.35 (0.04) mumol litre-1 for Trolox C, respectively. The antioxidant activities of propofol were substantially retained in the presence of up to 30 g litre-1 of human serum albumin. Propofol at concentrations of up to 100 mumol litre-1 had no significant effect on the activities of antioxidant enzymes. Clinically relevant concentrations of propofol produced significant inhibition of both enzymic and non-enzymic lipid peroxidation in hepatic microsomal preparations, possibly as a result of accumulation in lipophilic environments. Measurement of antioxidant effects of drugs in aqueous media may have little relevance to their effects in protecting against lipid peroxidation in biological systems.

Measurement of hepatic glucose output, krebs cycle, and gluconeogenic fluxes by NMR analysis of a single plasma glucose sample

13C and 1H NMR spectroscopy of plasma glucose was used to resolve the isotopomer contributions from tracer levels of [1,6-13C2]glucose, a novel tracer of glucose carbon skeleton turnover, and [U-13C]propionate, a tracer of hepatic citric acid cycle metabolism. This allowed simultaneous measurements of hepatic glucose production and citric acid cycle fluxes from the NMR analysis of a single plasma glucose sample in fasted animals. Glucose carbon skeleton turnover, as reported by the dilution of [1,6-13C2]glucose, was 56 +/- 2 micromol/kg/min in the presence of labeling from [U-13C]propionate and 53 +/- 4 micromol/kg/min in its absence. Therefore, as expected, the labeling contributions from [U-13C]propionate metabolism did not have a significant effect on the measurement of glucose turnover. For the group infused with both tracers, citric acid cycle flux estimates from the analysis of glucose C2 isotopomer ratios were consistent with those from our recent experiments where only [U-13C]propionate was infused, verifying that the presence of [1,6-13C2]glucose did not interfere with these measurements. This integrated analysis of hepatic glucose output and citric acid cycle fluxes from plasma glucose isotopomers yielded a noninvasive estimate of hepatic citrate synthase flux of 74 +/- 12 micromol/kg/min for 24-h fasted rats.

Leucocyte filterability: comparing diluted with undiluted blood

Red blood cells and about 95% of white blood cells have an immediate and constant effect on the flow of undiluted or diluted blood through 5 microm filters. The remaining 5% of all leucocytes exert an increasing influence on flow such that the rate of flow of diluted and undiluted blood through these filters is continually declining over a period of 150 s. Analysis of this declining flow rate enables these cells to be counted and their rheological properties to be deduced. Approximately 50% of these slow leucocytes pass through the filters with a transit time of about 30 s and the remaining cells act as pore blockers for 150 s. The numbers and flow properties of slow leucocytes was approximately the same in blood from young women (25 years) and older men (65 years). However, the number of slow leucocytes was increased in a group of men (65 years) suffering from peripheral arterial occlusive disease. Dilution of the blood with phosphate-buffered saline increased the numbers of slow leucocytes in both of the older, but not the younger, group of volunteers. This effect was particularly noticeable in the patient group. It is recommended that filtration studies of the rheological profile of leucocytes can, and must, be performed with undiluted blood. The properties after dilution may sometimes, but not invariably, reflect changes ex vivo as well as inherent differences in the cells themselves.

Effects of a low concentration of isoflurane on contrast sensitivity in volunteers

The effects of 0.15% quasi steady-state end-tidal isoflurane on the contrast sensitivity of five healthy volunteers were investigated by measuring their performance in computer generated letter discrimination tasks. A series of letters were displayed on a computer screen so that the luminance of the letter differed from that of the background. Two protocols were used: in the static protocol, the letter remained displayed on the screen until the subject responded, whereas in the dynamic protocol, the letter was displayed for 1/72 s only. Isoflurane significantly decreased contrast sensitivity in both protocols in all subjects.

Prevalence of post traumatic stress disorder and other psychiatric diagnoses in three groups of abused children (sexual, physical, and both)

OBJECTIVE

The purpose of this study was to compare the prevalence of Post Traumatic Stress Disorder and other diagnoses in three groups of abused children, sexual only (N = 127), physical only (N = 43), and BOTH (N = 34).

METHOD

The children, aged 7 to 13 years, were referred to the project from several sources at Arkansas Children's Hospital and from associated local agencies. The victims and caregivers were separately administered the Diagnostic Interview for Children and Adolescents, Revised Version (DICA). Additionally, caregivers and classroom teachers completed the Child Behavior Checklist (CBCL). Characteristics of the abuse were obtained from an investigative questionnaire.

RESULTS

Both victims and caregivers endorsed high rates of disorders, with caregivers generally giving higher rates than children and boys having more externalizing diagnoses than girls. Children in the BOTH group had more diagnoses overall. Concordance between victims and caregivers was modest. PTSD was significantly comorbid with most affective disorders. On the CBCL, caregivers rated girls less disturbed than boys and the sexually abused only group less disturbed than the other groups. Teachers rated the boys more adversely than girls but did not see differences by abuse group. A younger age of onset of sexual abuse and coercion to maintain secrecy predicted a higher number of total diagnoses. Also, children who were physically abused by males had more diagnoses than those physically abused by females.

CONCLUSIONS

Children who have been both physically/sexually abused appear to be at highest risk of psychiatric disturbance. PTSD, though common (circa one-third of victims), is generally comorbid with other affective disorders.

Impairment of gas exchange due to alveolar oedema during xylazine sedation in sheep; absence of a free radical mediated inflammatory mechanism

We studied the mechanism of impairment of gas exchange following sedation with the alpha2 adrenoreceptor agonist, xylazine, in Suffolk cross-bred sheep spontaneously breathing room air. Xylazine caused a significant fall in PaO2 from a mean (pre-xylazine) of 97.9 mm Hg (6.7 mm Hg SEM) to a mean of 38.1 mm Hg (3.2 mm Hg SEM) one minute after injection with a transient increase in PaCO2 from a mean (pre-xylazine) of 32.6 mm Hg (1.9 mm Hg SEM) to a mean of 40.2 mm Hg (3.0 mm Hg SEM). There was no significant fall in mean arterial pressure or in white cell count. There was no significant change in a number of indices of free radical release which included ascorbyl radical, plasma antioxidant potential and alpha-tert-butyl phenyl nitrone (PBN) spin adduct measured simultaneously in both arterial and venous blood. In all sheep given xylazine there was no histological evidence of platelet emboli but lung histopathology showed evidence of pulmonary oedema and intense microvascular congestion with red cells extravasated into alveoli. No such histological changes were seen in the lungs of normal sheep. The impaired gas exchange during sedation with xylazine in sheep is caused, not by an oxidant mediated inflammatory mechanism or by platelet emboli, but by intense alveolar oedema which is probably due to pulmonary venospasm.

Cell motility of tumor cells visualized in living intact primary tumors using green fluorescent protein

Metastasis is the leading cause of death in cancer patients. Cell motility is believed to be a necessary step in the metastatic process (L. Liotta and W. G. Stetler-Stevenson, In: Cancer: Principles and Practice of Oncology, pp. 134-149, 1993). Currently, most methods available to study the behavior of metastatic tumor cells are indirect, e.g., cell motility is examined in vitro and the results are correlated with metastatic capability (A. W. Partin, et al., Cancer Treat. Res., 59: 121-130, 1992). We have developed a model that directly examines the motility of metastatic primary tumor cells in situ. A metastatic rat breast cancer cell line was established that constitutively expresses green fluorescent protein. Upon s.c. injection of these cells into the mammary fat pad of female Fischer 344 rats, primary and metastatic tumors form that fluoresce when they are excited with FITC-filtered light. Animations of metastatic tumor cells moving in live rats were generated by intravital imaging of the primary tumor in situ on a laser scanning confocal microscope. With this model, the behavioral phenotype of metastatic and nonmetastatic tumor cells can be described and determined. This information will allow the effects of genetic manipulations or therapeutic treatments on this phenotype to be determined (D. R. Soll, Int. Rev. Cytol., 163: 43-104, 1995). This is the first time that living primary tumor cells in a live animal have been visualized as part of a clinically relevant model.

Experiences and attitudes of consultant and nontraining grade anaesthetists to continuing medical education (CME)

A questionnaire survey was sent to 164 consultant anaesthetists with the aim of investigating their experiences and attitudes to continuing medical education. The response rate was 79%. Most anaesthetists were motivated to achieve the required number of credits and for the majority of anaesthetists, regional, national and internal departmental discussion meetings were the mainstay of educational activities. The educational standard of available activities could be improved to include more workshop-style learning opportunities and to make journal reading a creditable continuing medical education activity. The place of research is questioned. There was doubt as to whether sanctions such as withdrawing recognition for training should be imposed on departments where some anaesthetists fail to achieve the required number of credits and whether this would motivate anaesthetists to achieve the set standards. Continuing medical education was felt to be effective and the main barriers to attending educational activities are discussed.

Sequential changes in gas exchange following traumatic fat embolism

We present a young man who developed fat embolism syndrome following a fractured femoral shaft. By intermittently measuring oxygen saturation with a pulse oximeter and varying the inspired partial pressure of oxygen we were able to quantify the development of shunt and ventilation/perfusion (V/Q) mismatch over the course of his illness. Shunt and low V/Q gradually improved in the week following admission but deteriorated following general anaesthesia for nailing of the femur.

The filterability of leukocytes in undiluted blood

A filtrometer is described for measuring the flow of fluids through microfilters. The flow of Newtonian fluids through the filters can be predicted from the diameter, length and number of pores. There are no physical artefacts such as turbulent flow or a significant lag period before steady-state flow is achieved. The instrument has been used as a viscometer and has been used to record and analyse the flow of undiluted blood through 5 microns polycarbonate filters. The calculated viscosity of Newtonian fluids agrees well with those measured by a more conventional viscometer (Ostwald). Flow profiles of blood have been analysed to give both the numbers and the flow properties of a small population of slow leukocytes which equate numerically with the monocytes. They are subdivided into three distinct sub-populations, according to their rheological properties, and these are termed SL1, SL2 and PB. The concentration of these cells, in blood, are 0.12 +/- 0.02 x 10(6) ml-1, 0.11 +/- 0.02 x 10(6) ml-1, 0.09 +/- 0.02 x 10(6) ml-1 in young females aged about 25 years. The transit time of these cells, through 5 microns pores, is 34.8 +/- 1.4 s, 147.5 +/- 2.5 s and > 300 s, respectively. Analysis of blood from older men (53-79 years) gives essentially the same results although the concentration of SL1 is slightly higher at 0.19 +/- 0.09 x 10(6) ml-1.

Ad HoC conferences of hospital and community professionals in cases of hospitalized physically abused children

OBJECTIVE

Although community interagency child protection teams are common and well described in the literature, they may not meet the needs of investigating agencies when children are hospitalized in tertiary medical facilities some distance from their homes. Sometimes, the communities in which they live do not have effective teams, or the information to be conveyed is highly technical. This report describes and assesses ad hoc multi-agency conferences with varying hospital and community agency participants, each conference devoted to a single hospitalized child suspected of having been abused.

METHOD

A questionnaire devised by the authors was administered by telephone to 22 former conference participants from state social agencies, law enforcement units, and prosecuting attorney's offices.

RESULTS

Most of the surveyed participants reported the case-specific conferences to have been helpful, meeting their goals and affecting the outcomes of their cases.

CONCLUSION

The conferences appear to have been worthwhile. Although they were associated with some disadvantages for the involved professionals and the sponsoring hospital, the disadvantages appeared to have been offset by the potential benefits for the children, families, participants, and hospital.

Errors on anaesthetic record charts as a measure of anaesthetic performance during simulated critical incidents

We have measured the performance of 10 trainee anaesthetists during a single simulated anaesthetic during which there was a complex critical incident. Errors in the recording on the anaesthetic charts of the "patient's" oxygen saturation, heart rate, systolic and diastolic arterial pressures and end-tidal carbon dioxide concentrations were used as a measure of mental workload and hence performance. The critical incident was designed to be stressful and contained, in sequence, episodes of hypotension, arrhythmia and bronchospasm. Chart recording errors increased markedly during the critical incident (P < 0.01) and decreased subsequently when the "patient" had stabilized. More than 22% of the values charted during the simulation were in error by more than 25% of the real value, and errors in excess of 100% of the actual value were recorded. There was no evidence of a tendency to consistently underestimate the magnitude of abnormal values. This method is appropriate for assessing the performance of groups of anaesthetists during simulated critical incidents. It also raises questions on the accuracy of anaesthetic record charts when recording critical incidents.

The need for basic sciences in the understanding and practice of anaesthesia

We conducted a survey using an unstructured, then a structured, questionnaire to determine the attitudes of 78 postfellowship anaesthetists to the Basic Sciences component of the part I examination for the FRCA. Seventy-two per cent replied. These anaesthetists felt that about 65% of the basic science syllabus was essential to the understanding and practice of everyday anaesthesia, but there was varying opinion as to the importance of specific topics. Cardiovascular, respiratory, central nervous system and renal physiology were all regarded as essential, as was the pharmacology of anaesthetic drugs. Topics regarded as irrelevant included biochemistry, endocrinology, membrane theory and immunology. Paradoxically, there were many topics which anaesthetists regarded as essential but on which they were unable to give a tutorial. There was little difference between the responses of consultants and trainees. This survey may help to identify a core syllabus on which the majority of anaesthetists agree but also suggests that the current syllabus is overloaded with detail that has no place in clinical practice.

Thresholds for hypoxic cerebral vasodilation in volunteers

The effects of hypoxemia on the cerebral vasculature have been described in animal models, but data from human studies are limited and have often relied on invasive methodology. The ability to detect a threshold for hypoxic vasodilatation in humans may be clinically useful, particularly in patients with impaired intracranial compliance. Because physiology may differ among subjects, it would be advantageous to measure such thresholds using noninvasive bedside techniques that could be readily applied to individual patients. We have attempted to identify thresholds of hypoxic vasodilatation in volunteers using noninvasive methods of measurement. Thirteen healthy volunteers were studied using transcranial Doppler sonography. Time-averaged middle cerebral artery maximal flow velocity (MCA FVx), mean arterial blood pressure, peripheral oxygen saturation (Spo2), and partial pressure of endtidal CO2 were measured at baseline and during graded reduction in arterial Spo2 to 85%, at normocapnia. Flow velocity and estimated cerebrovascular resistance (CVRe) were indexed and plotted against Spo2. There was no significant change in mean arterial pressure during desaturation to 85%, although the mean heart rate increased from 65 to 82 bpm. An increase in MCA FVx and reciprocal decrease in CVRe were observed when Spo2 decreased to below 90%. These results suggest that hypoxemic cerebral vasodilatation may be measured noninvasively and that in normal human volunteers, the threshold is at an Spo2 of 90%, which is greater than that previously reported.

IMPLICATIONS

The ability to detect the point at which cerebral blood vessels dilate using noninvasive techniques is clinically advantageous. We have attempted to do this using transcranial Doppler sonography in volunteers whose inspired oxygen concentrations were gradually decreased. Thresholds of cerebral vasodilatation were found to be higher than those previously reported. These thresholds are important with regard to adequate perfusion in various pathologic states.

Clinical and toxicological findings in two young siblings and autopsy findings in one sibling with multiple hospital admissions resulting in death. Evidence suggesting Munchausen syndrome by proxy

A 15-month-old girl underwent several emergency department (ED) visits and two admissions for parent-reported histories of ingestions, apnea, and seizures. She was initially admitted following reports of several unusual episodes of syncope accompanied by convulsive movements and was discharged on mephobarbital with a diagnosis of atypical seizure disorder. The day after discharge, she was brought to the ED in cardiopulmonary arrest and was resuscitated after a prolonged period. She was declared brain dead 2 days later. Ante- and postmortem toxicology produced several inconclusive findings, none of which explained death. Autopsy findings, including neuropathology, failed to demonstrate any significant disease processes. Approximately 3 months later, a 4-month-old female sibling was brought to the ED with a parent-reported history of apnea and seizures similar to the deceased child. A stool specimen obtained 2 days after admission contained numerous tiny seeds, which were found by gas chromatography-mass spectrometry analysis to contain lorazepam and temazepam. The role of these benzodiazepines in the apnea episodes in this infant was unknown, but the presence of the seeds in such a young infant coupled with the parent's aberrant behavior, led to the tentative diagnosis of Munchausen syndrome by proxy. This diagnosis was strengthened when results from these studies persuaded legal authorities to remove the surviving sibling from the parents, resulting in an asymptomatic recovery.

Measurement of gluconeogenesis and pyruvate recycling in the rat liver: a simple analysis of glucose and glutamate isotopomers during metabolism of [1,2,3-(13)C3]propionate

Simple equations that relate glucose and glutamate 13C-NMR multiplet areas to gluconeogenesis and pyruvate recycling during metabolism of [1,2,3-(13)C3]propionate are presented. In isolated rat livers, gluconeogenic flux was 1.2 times TCA cycle flux and about 40% of the oxaloacetate pool underwent recycling to pyruvate prior to formation of glucose. The 13C spectra of glucose collected from rats after gastric versus intravenous administration of [1,2,3-(13)C3]propionate indicated that pyruvate recycling was slightly higher in vivo (49%) while glucose production was unchanged. This indicates that a direct measure of gluconeogenesis and pyruvate recycling may be obtained from a single 13C-NMR spectrum of blood collected after oral administration of enriched propionate.

Oxidation of lactate and acetate in rat skeletal muscle: analysis by 13C-nuclear magnetic resonance spectroscopy

The balance between carbohydrate and fatty acid utilization in skeletal muscle previously has been studied in vivo by using a variety of methods such as arteriovenous concentration differences and radioactive isotope tracer techniques. However, these methodologies provide only indirect estimates of substrate oxidation. We used 13C-nuclear magnetic resonance (NMR) spectroscopy and non-steady-state isotopomer analysis to directly quantify the relative oxidation of two competing exogenous substrates in rat skeletal muscles. We infused [1,2-13C]acetate and [3-13C]lactate intravenously in anesthetized rats during the final 30 min of 35 (n = 10) or 95 (n = 10) min of intense, unilateral, rhythmic hindlimb contractions. 13C-NMR spectroscopy and isotopomer analysis were performed on extracts of gastrocnemius and soleus muscles from both the contracting and contralateral resting hindlimbs. We found that 1) [13C]lactate and [13C]acetate were taken up and oxidized by both resting and contracting skeletal muscles; and 2) high-intensity muscle contractions altered the pattern of substrate utilization such that the relative oxidation of acetate decreased while that of lactate remained unchanged or increased. Based on these findings, we propose that 13C-NMR spectroscopy in combination with isotopomer analysis can be used to study the general dynamics of substrate competition between carbohydrates and fats in rat skeletal muscle.

A noninvasive method for evaluating the effect of thoracotomy on shunt and ventilation perfusion inequality

A new noninvasive method was used to evaluate gas exchange in 12 patients undergoing thoracotomy for a variety of surgical procedures. A plot of inspired oxygen partial pressure versus oxygen saturation was analysed to calculate the independent contribution of shunt and intermediate ventilation/perfusion ratio which occurs during general anaesthesia for thoracotomy. A model based on the inspired to arterial oxygen difference involving the shunt equation was used to show how the relationship between inspired oxygen partial pressure and oxygen saturation could be used to derive two parameters of oxygen exchange, the virtual shunt and an index of low ventilation/perfusion ratio. In all cases, there was a very good fit of the data to the model. Thoracotomy caused a mean increase in shunt from 13.8% to 20.8% and a worsening ventilation/perfusion ratio from 0.5 to 0.2, the magnitude of which depended on the underlying pathology. In two patients, the ventilation/perfusion ratio decreased to less than 0.1. The method enables the prediction of oxygen saturation at different inspired oxygen partial pressures and allows the two components of gas exchange to be isolated using simple routine measurements of inspired oxygen and pulse oximetry.

Determination of acetyl-CoA enrichment in rat heart and skeletal muscle by 1H nuclear magnetic resonance analysis of glutamate in tissue extracts

The contribution of a 13C-enriched substrate to the acetyl-CoA pool in animal tissues is typically measured by analysis of glutamate enrichment from tissue extracts. 13C NMR analysis offers the advantages of minimal sample processing and high information content, but has a low analytical sensitivity compared to other methods of tracer analysis such as GC/MS. We present a sensitive, simple, and direct 1H NMR measurement of glutamate C4 enrichment from tissue extracts. The method is demonstrated with heart and hindlimb muscle tissue extracts of rats infused with [2,4,6,8-13C4]-octanoate, a source of [2-13C]acetyl-CoA. Glutamate C4 enrichment in extracts of individual hindlimb soleus muscles weighing approximately 150 mg and containing approximately 0.3 mumol of glutamate was quantified by 1H NMR within about 40 min. Glutamate C4 enrichment measurements by 1H NMR in heart and gastrocnemius muscle were also highly correlated with independent measurements obtained from 13C NMR isotopomer analysis.