PNPLA3 variant M148 causes resistance to starvation-mediated lipid droplet autophagy in human hepatocytes

The mechanism of how patatin-like phospholipase domain-containing protein 3 (PNPLA3) variant M148 is associated with increased risk of development of hepatic steatosis is still debated. Here, we propose a novel role of PNPLA3 as a key player during autophagosome formation in the process of lipophagy. A human hepatocyte cell line, HepG2 cells, expressing recombinant I148 or 148M, was used to study lipophagy under energy deprived conditions, and lipid droplet morphology was investigated using florescence microscopy, image analysis and biochemical assays. Autophagic flux was studied using the golden-standard of LC3-II turnover in combination with the well characterized GFP-RFP-LC3 vector. To discriminate between, perturbed autophagic initiation and lysosome functionality, lysosomes were characterized by Lysotracker staining and LAMP1 protein levels as well as activity and activation of cathepsin B. For validation, human liver biopsies genotyped for I148 and 148M were analyzed for the presence of LC3-II and PNPLA3 on lipid droplets. We show that the M148-PNPLA3 variant is associated with lipid droplets that are resistant to starvation-mediated degradation. M148 expressing hepatocytes reveal decreased autophagic flux and reduced lipophagy. Both I148-PNPLA3 and M148-PNPLA3 colocalize and interact with LC3-II, but the M148-PNPLA3 variant has lower ability to bind LC3-II. Together, our data indicate that PNPLA3 might play an essential role in lipophagy in hepatocytes and furthermore that the M148-PNPLA3 variant appears to display a loss in this activity, leading to decreased lipophagy.

Perilipin 1 binds to aquaporin 7 in human adipocytes and controls its mobility via protein kinase A mediated phosphorylation

Accumulating evidence suggests that dysregulated glycerol metabolism contributes to the pathophysiology of obesity and type 2 diabetes. Glycerol efflux from adipocytes is regulated by the aquaglyceroporin AQP7, which is translocated upon hormone stimulation. Here, we propose a molecular mechanism where the AQP7 mobility in adipocytes is dependent on perilipin 1 and protein kinase A. Biochemical analyses combined with ex vivo studies in human primary adipocytes, demonstrate that perilipin 1 binds to AQP7, and that catecholamine activated protein kinase A phosphorylates the N-terminus of AQP7, thereby reducing complex formation. Together, these findings are indicative of how glycerol release is controlled in adipocytes, and may pave the way for the future design of drugs against human metabolic pathologies.

ApoA-I Milano stimulates lipolysis in adipose cells independently of cAMP/PKA activation

ApoA-I, the main protein component of HDL, is suggested to be involved in metabolic homeostasis. We examined the effects of Milano, a naturally occurring ApoA-I variant, about which little mechanistic information is available. Remarkably, high-fat-fed mice treated with Milano displayed a rapid weight loss greater than ApoA-I WT treated mice, and a significantly reduced adipose tissue mass, without an inflammatory response. Further, lipolysis in adipose cells isolated from mice treated with either WT or Milano was increased. In primary rat adipose cells, Milano stimulated cholesterol efflux and increased glycerol release, independently of β-adrenergic stimulation and phosphorylation of hormone sensitive lipase (Ser563) and perilipin (Ser522). Stimulation with Milano had a significantly greater effect on glycerol release compared with WT but similar effect on cholesterol efflux. Pharmacological inhibition or siRNA silencing of ABCA1 did not diminish Milano-stimulated lipolysis, although binding to the cell surface was decreased, as analyzed by fluorescence microscopy. Interestingly, methyl-β-cyclodextrin, a well-described cholesterol acceptor, dose-dependently stimulated lipolysis. Together, these results suggest that decreased fat mass and increased lipolysis following Milano treatment in vivo is partly explained by a novel mechanism at the adipose cell level comprising stimulation of lipolysis independently of the canonical cAMP/protein kinase A signaling pathway.

Single injections of apoA-I acutely improve in vivo glucose tolerance in insulin-resistant mice

AIMS/HYPOTHESIS

Apolipoprotein A-I (apoA-I), the main protein constituent of HDL, has a central role in the reverse cholesterol-transport pathway, which together with the anti-inflammatory properties of apoA-I/HDL provide cardioprotection. Recent findings of direct stimulation of glucose uptake in muscle by apoA-I/HDL suggest that altered apoA-I and HDL functionality may be a contributing factor to the development of diabetes. We have studied the in vivo effects of short treatments with human apoA-I in a high-fat diet fed mouse model. In addition to native apoA-I, we investigated the effects of the cardioprotective Milano variant (Arg173Cys).

METHODS

Male C57Bl6 mice on a high-fat diet for 2 weeks that received a single injection of human apoA-I proteins (wild-type and Milano) were analysed for blood glucose and insulin levels during a 3 h incubation followed by glucose tolerance tests. Incorporation of injected human apoA-I protein into HDLs was analysed by native gel electrophoresis.

RESULTS

ApoA-I treatment significantly improved insulin secretion and blood glucose clearance in the glucose tolerance test, with an efficiency exceeding that of lean control animals, and led to decreased basal glucose during the 3 h incubation. Notably, the two apoA-I variants triggered insulin secretion and glucose clearance to the same extent.

CONCLUSIONS/INTERPRETATION

ApoA-I treatment leads to insulin- and non-insulin-dependent effects on glucose homeostasis. The experimental model of short-term (2 weeks) feeding of a high-fat diet to C57Bl6 mice provides a suitable and time-efficient system to unravel the resulting tissue-specific mechanisms of acute apoA-I treatment that lead to improved glucose homeostasis.

Expression and regulation of cyclic nucleotide phosphodiesterases in human and rat pancreatic islets

As shown by transgenic mouse models and by using phosphodiesterase 3 (PDE3) inhibitors, PDE3B has an important role in the regulation of insulin secretion in pancreatic β-cells. However, very little is known about the regulation of the enzyme. Here, we show that PDE3B is activated in response to high glucose, insulin and cAMP elevation in rat pancreatic islets and INS-1 (832/13) cells. Activation by glucose was not affected by the presence of diazoxide. PDE3B activation was coupled to an increase as well as a decrease in total phosphorylation of the enzyme. In addition to PDE3B, several other PDEs were detected in human pancreatic islets: PDE1, PDE3, PDE4C, PDE7A, PDE8A and PDE10A. We conclude that PDE3B is activated in response to agents relevant for β-cell function and that activation is linked to increased as well as decreased phosphorylation of the enzyme. Moreover, we conclude that several PDEs are present in human pancreatic islets.

Inhaled allergen-driven CD1c up-regulation and enhanced antigen uptake by activated human respiratory-tract dendritic cells in atopic asthma

BACKGROUND

Dendritic cells (DC) mediate inflammation in rodent models of allergic airway disease, but the role played by human respiratory-tract DC (hRTDC) in atopic asthma remains poorly defined. Recent data suggest that CD1 antigen presentation by hRTDC may contribute to asthma pathogenesis.

OBJECTIVE

To investigate the influence of hRTDC on the balance between atopy and allergic asthma in human subjects and to determine whether CD1 expression by hRTDC is modulated during asthmatic inflammation.

METHODS

Sputum cells were induced from steroid-naïve, allergen-challenged and allergen-naïve subjects (atopic asthmatics, atopic non-asthmatics and non-atopic controls). hRTDC were identified using monoclonal antibody labelling and analysis by flow cytometry.

RESULTS

hRTDC stained HLA-DR(+) (negative for markers of other cell lineages) were predominantly myeloid and comprised approximately 0.5% of viable sputum cells. Sputum cells were potent stimulators of allogeneic CD4(+) naïve T cells and enrichment/depletion experiments correlated stimulatory potency with DC numbers. Sputum contained cells that exhibited typical dendritic morphology when analysed by electron microscopy. Myeloid hRTDC were endocytically active, but uptake of FITC-dextran was enhanced in cells from asthmatics (P<0.001). Despite their increased endocytic capacity, asthmatic myeloid hRTDC appeared mature and expressed increased levels of maturation markers (P<0.05-P<0.001), CD1c, CD1d and langerin (P<0.05). CD1c expression by asthmatic myeloid hRTDC was enhanced upon in vivo allergen challenge (three to ninefold within 24 h; P<0.05). CD11c(-)CD123(high) hRTDC were only detected in asthmatic sputum and were increased in number following allergen challenge.

CONCLUSION

Despite limited cell numbers, it proved possible to analyse human RTDC in induced sputum, providing evidence that increased antigen uptake and enhanced CD1 presentation by activated hRTDC may contribute to allergic airway disease. CD1 presentation by hRTDC in atopic asthma may therefore constitute a novel target for future intervention strategies.

Recruitment of patients into an internet-based clinical trials database: the experience of OncoLink and the National Colorectal Cancer Research Alliance

PURPOSE

In March 2001, the National Colorectal Cancer Research Alliance (NCCRA) and OncoLink (http://www.oncolink.org) established a database to facilitate patient enrollment onto clinical trials. This study describes the population registering with the database and identifies discrepancies between individuals registering through the Internet and those registering through a telephone call center.

METHODS

Participants registered with the NCCRA/OncoLink database through the Internet or a telephone call center. All participants entering the database completed a questionnaire regarding basic demographics, colon cancer risk factors, and indicated how they became aware of the database. Comparisons were made between individuals registering through the Internet and those registering through the telephone call center.

RESULTS

A total of 2,162 participants registered during the first 16 months of the database. Most patients registered through the Internet rather than the telephone call center (88% v 12%; P < .001). More females than males registered (73% v 27%; P < .001). The majority (89%) were white. Participants registering through the Internet were younger than those registering through the call center (mean, 48.8 v 55.0 years; P < .001). There was no difference between the two groups with regard to sex or ethnicity.

CONCLUSION

The Internet has the potential to increase the likelihood that interested individuals find appropriate clinical trials. Some of the discrepancies that are known to exist for access to the Internet were also seen for those registering with the database through the Internet. Despite these differences, the potential to increase clinical trial enrollment with this type of Internet-based database is high.

In vivo assessment of lung inflammatory cell activity in patients with COPD and asthma

The involvement of inflammatory cells in the pathogenesis of chronic obstructive pulmonary disease (COPD) and asthma is well established. This study aimed to quantify differences in inflammatory cell function in situ in these patients as compared to normal subjects. Positron emission tomography was used to assess neutrophil activity (18F-fluorodeoxyglucose (18FDG)) and macrophage accumulation (11C-PK11195) in six patients with COPD, six chronic asthmatics and five age-matched normal control subjects. 18FDG uptake was greater in COPD than in normal subjects, with no increase in asthmatics. The mean slope of 18FDG uptake, corrected for volume of distribution, was 4.0 min(-1) in COPD patients compared with 1.5 min(-1) in control subjects and 1.7 min(-1) in asthmatics. Mean 11C-PK11195 uptake (plateau tissue:plasma) was higher in four of six COPD patients (10.8) and three of five asthmatics (11.8) than the maximum value in control subjects (6.2). From this preliminary study the authors conclude that positron emission tomography may be useful to assess polymorphonuclear neutrophil and macrophage activity in vivo in chronic obstructive pulmonary disease and asthma, and may reveal differences in cell behaviour between the study groups. In addition, positron emission tomography may provide indices of disease activity for future therapeutic studies.

Imaging atherosclerotic plaque inflammation with [18F]-fluorodeoxyglucose positron emission tomography

BACKGROUND

Atherosclerotic plaque rupture is usually a consequence of inflammatory cell activity within the plaque. Current imaging techniques provide anatomic data but no indication of plaque inflammation. The glucose analogue [18F]-fluorodeoxyglucose (18FDG) can be used to image inflammatory cell activity non-invasively by PET. In this study we tested whether 18FDG-PET imaging can identify inflammation within carotid artery atherosclerotic plaques.

METHODS AND RESULTS

Eight patients with symptomatic carotid atherosclerosis were imaged using 18FDG-PET and co-registered CT. Symptomatic carotid plaques were visible in 18FDG-PET images acquired 3 hours post-18FDG injection. The estimated net 18FDG accumulation rate (plaque/integral plasma) in symptomatic lesions was 27% higher than in contralateral asymptomatic lesions. There was no measurable 18FDG uptake into normal carotid arteries. Autoradiography of excised plaques confirmed accumulation of deoxyglucose in macrophage-rich areas of the plaque.

CONCLUSIONS

This study demonstrates that atherosclerotic plaque inflammation can be imaged with 18FDG-PET, and that symptomatic, unstable plaques accumulate more 18FDG than asymptomatic lesions.

Comparative treatment planning between proton and X-ray therapy in pancreatic cancer

With the utilization of new biologic agents and experimental chemotherapy in the treatment of pancreatic cancer, the issue of local-regional control will become increasingly important. This study was undertaken to determine the feasibility of dose escalation using proton therapy, as compared to conventional 3-dimensional conformal radiation, by minimizing the dose to normal tissues. The photon treatment plans of 4 patients with unresectable pancreatic cancer treated on a biologic therapy trial were utilized. Each patient was treated using a 3- or 4-field photon plan with 45 Gy to the clinical target volume (CTV), followed by a boost of 14.4 Gy to the gross target volume (GTV). Using a Helax treatment planning system, proton plans were generated to encompass the same CTV and GTV to the same prescribed dose. Dose-volume histograms (DVHs) were generated for the GTV, CTV, spinal cord, liver, and right and left kidneys. Each DVH was compared between the photon and proton plans. Proton plans utilized either a 2- or 3-field technique. Available energies included 130 or 180 MeV. Range modulators and bolus were used as needed to conform to the target volume. With the CTV and GTV receiving the same dose from the proton and photon plans, all individual proton plans were superior to the photon plans in reduction of normal tissue dose. For the 4 patients, the average dose reduction to 50% of the organ at risk was 78% to spinal cord (p = 0.003), 73% to left kidney (p = 0.025), 43% to right kidney (p = 0.059), and 55% to liver (p = 0.061). These comparative treatment plans show proton therapy results in significant reductions of dose to normal tissue compared to conventional photons while treating the same target volumes. This allows for the design of dose-escalation protocols using protons in combination with new biologic therapies and chemotherapy.

Ras inhibitors and radiation therapy

Local recurrence after a definitive course of radiation therapy remains a significant clinical problem and represents a common pattern of failure for many solid tumors. The sensitivity of tumor cells to the cytotoxicity of ionizing radiation is thought to be one of the major determinants of local control for tumors in patients treated with radiation therapy. There is substantial experimental evidence to demonstrate that increased radiation resistance is associated with the expression of activated oncogenes, including Ras. Mutated forms of Ras are found in 30% of human cancers including a substantial proportion of pancreatic and colon adenocarcinomas. Mutated Ras produces proteins that remain locked in a constitutively active state, thereby relaying uncontrolled signals. Ras proteins are guanosine triphosphate-binding proteins that play a pivotal role in the control of many cellular processes, including growth and differentiation. Preclinical studies have shown that expression of mutant Ras increases cellular radioresistance. Ras function is dependent on its localization to the plasma membrane. This is achieved by posttranslational modifications, including the addition of a farnesyl isoprenoid moiety in a reaction catalyzed by the enzyme protein farnesyltransferase (FTase). This enzyme has become an important target for the design of new agents that target Ras. FTase inhibitors (FTIs) block the farnesylation of Ras and reverse Ras-mediated radioresistance in human cell lines. FTIs have been well tolerated in animal studies and appear not to cause generalized cytotoxicity. There are ongoing clinical trials to determine the optimal therapeutic schedules and dose for FTIs. A phase 1 trial of the FTI L778-123 and radiotherapy has recently been completed.

Invasion of epithelial cells by Yersinia pestis: evidence for a Y. pestis-specific invasin

The causative agent of plague, Yersinia pestis, is regarded as being noninvasive for epithelial cells and lacks the major adhesins and invasins of its enteropathogenic relatives Yersinia enterocolitica and Yersinia pseudotuberculosis. However, there are studies indicating that Y. pestis invades and causes systemic infection from ingestive and aerogenic routes of infection. Accordingly, we developed a gentamicin protection assay and reexamined invasiveness of Y. pestis for HeLa cells. By optimizing this assay, we discovered that Y. pestis is highly invasive. Several factors, including the presence of fetal bovine serum, the configuration of the tissue culture plate, the temperature at which the bacteria are grown, and the presence of the plasminogen activator protease Pla-encoding plasmid pPCP1, were found to influence invasiveness strongly. Suboptimal combinations of these factors may have contributed to negative findings by previous studies attempting to demonstrate invasion by Y. pestis. Invasion of HeLa cells was strongly inhibited by cytochalasin D and modestly inhibited by colchicine, indicating strong and modest respective requirements for microfilaments and microtubules. We found no significant effect of the iron status of yersiniae or of the pigmentation locus on invasion and likewise no significant effect of the Yops regulon. However, an unidentified thermally induced property (possibly the Y. pestis-specific capsular protein Caf1) did inhibit invasiveness significantly, and the plasmid pPCP1, unique to Y. pestis, was essential for highly efficient invasion. pPCP1 encodes an invasion-promoting factor and not just an adhesin, because Y. pestis lacking this plasmid still adhered to HeLa cells. These studies have enlarged our picture of Y. pestis biology and revealed the importance of properties that are unique to Y. pestis.

Molecular characterization of the hemin uptake locus (hmu) from Yersinia pestis and analysis of hmu mutants for hemin and hemoprotein utilization

Sequence analysis of the hemin uptake locus (hmu) of Yersinia pestis revealed five genes, hmuRSTUV, required for use of hemin and hemoproteins as iron sources. The translated gene products have homologies with proteins of the hemin transport genes of several gram-negative bacteria. Promoters were identified upstream of hmuP'R (p1) and upstream of hmuS (p2); p1, which contains a Fur box, is regulated by iron and Fur, while p2 exhibits weak, but constitutive, activity. HmuR, which has homology with TonB-dependent outer membrane (OM) receptors, is localized to the OM of Y. pestis and is required for utilizing hemin and all hemoproteins under iron-depleted conditions. The proposed ABC transporter, HmuTUV, is necessary for use of hemin, hemin-albumin, and myoglobin, but not hemoglobin, hemoglobin-haptoglobin, or heme-hemopexin, as iron sources. In the absence of HmuTUV, HmuS, a cytoplasmic protein, is involved in use of hemoglobin and heme-hemopexin. In mice, the 50% lethal doses of Y. pestis DeltahmuP'RSTUV mutants injected subcutaneously or retro-orbitally did not differ from that of the Hmu(+) parent strain. Thus, the hmu system is not essential for infection in mice via these routes. Growth studies showed that a DeltahmuP'RSTUV mutant could grow in iron-depleted medium containing high concentrations of hemoglobin, suggesting that an Hmu-independent, lower-affinity hemoglobin uptake system may exist.

Pulmonary fibrosis correlates with duration of tissue neutrophil activation

The role of inflammatory cells such as neutrophil granulocytes in the pathogenesis of pulmonary scarring is unclear. We determined the metabolic activity of neutrophils with positron emission tomography (PET) to measure regional uptake of (18F)-2-fluoro-2-deoxy-D-glucose (18FDG) following its intravenous injection. Fibrogenic or nonfibrogenic substances were instilled into the right upper lobe of rabbit lungs. Time course and intensity of the 18FDG signal in the affected region varied markedly, depending on the stimulus. Time to peak signal (Tmax) and rate constant for its decline (k) for the test substances were, respectively: C5a 10 h (Tmax), 0.045 +/- 0.030 h-1 (k); Streptococcus pneumoniae 15 h, 0.068 +/- 0.012 h-1; bleomycin 28 h, 0.002 +/- 0.001 h-1; microcrystalline silica (microXSiO2), 90 h, 0.0012 +/- 0.0007 h-1; amorphous silica (aSiO2), no response. Response to the nonfibrogenic agents C5a, S. pneumoniae and aSiO2 was brief or nonexistent, falling to baseline values within 3 d, whereas that to the fibrogenic agents bleomycin and microXSiO2 persisted for up to 4 wk. Neutrophil numbers in the lung were proportional to the 18FDG signal following C5a and S. pneumoniae, but not bleomycin and microXSiO2. Autoradiography of lungs following administration of (3H)-deoxyglucose [(3H)-DG] showed specific localization to neutrophils in all models. Thus, 18FDG uptake provides a remarkably specific measure of neutrophil activity in situ, and the development of pulmonary fibrosis may be related to persistence of this activity.

Dissociation of neutrophil emigration and metabolic activity in lobar pneumonia and bronchiectasis

In animal models of pulmonary inflammation, neutrophils exhibit a dramatic influx of glucose in periods of high metabolic activity. This information was utilized to develop a technique, involving positron emission tomography (PET) of 2-[18F]-fluoro-2-deoxy-D-glucose (18FDG), which measures neutrophil activity in situ. This technique was applied in a comparative study of neutrophil function in patients with acute lobar pneumonia or bronchiectasis. Neutrophil emigration was measured by gamma-scintigraphy of intravenously injected 111In-labelled granulocytes and neutrophil activity determined by PET of 18FDG. Neutrophil emigration was evident in 4 out of 5 bronchiectasis patients, whilst no emigration was apparent in the two pneumonia patients studied, consistent with animal studies showing maximum emigration soon after challenge. In contrast, 18FDG uptake was markedly increased in 4 out of 5 pneumonia patients but not in the patients with bronchiectasis. Localization of radioactivity to neutrophils was confirmed by microautoradiography of lavage fluid in a patient with pneumonia. These results suggest that the elevated uptake of glucose by neutrophils during the inflammatory response is a postmigratory event, most likely reflecting the respiratory burst, and that high levels of neutrophil emigration are not necessarily associated with significantly increased metabolic activity of these cells.

A comparison of the dual lumen and coaxial catheters for temporary hemodialysis access

Percutaneous central venous catheterization can provide reliable temporary hemodialysis access. The current study compared the hemodynamic performance of 28 coaxial catheters to 27 side by side catheters. A total of 675 dialysis sessions were evaluated to assess the flow characteristics of these two designs. The results demonstrated that the side by side catheter provided greater cumulative blood flow with more favorable venous and arterial pressures. Nevertheless, the coaxial catheter performed satisfactorily and met the minimum standards for these devices.

Dissociation of neutrophil emigration and metabolic activity in lobar pneumonia and bronchiectasis

In animal models of pulmonary inflammation, neutrophils exhibit a dramatic influx of glucose in periods of high metabolic activity. This information was utilized to develop a technique, involving positron emission tomography (PET) of 2-[18F]-fluoro-2-deoxy-D-glucose (18FDG), which measures neutrophil activity in situ. This technique was applied in a comparative study of neutrophil function in patients with acute lobar pneumonia or bronchiectasis. Neutrophil emigration was measured by gamma-scintigraphy of intravenously injected 111In-labelled granulocytes and neutrophil activity determined by PET of 18FDG. Neutrophil emigration was evident in 4 out of 5 bronchiectasis patients, whilst no emigration was apparent in the two pneumonia patients studied, consistent with animal studies showing maximum emigration soon after challenge. In contrast, 18FDG uptake was markedly increased in 4 out of 5 pneumonia patients but not in the patients with bronchiectasis. Localization of radioactivity to neutrophils was confirmed by microautoradiography of lavage fluid in a patient with pneumonia. These results suggest that the elevated uptake of glucose by neutrophils during the inflammatory response is a postmigratory event, most likely reflecting the respiratory burst, and that high levels of neutrophil emigration are not necessarily associated with significantly increased metabolic activity of these cells.

The hmu locus of Yersinia pestis is essential for utilization of free haemin and haem--protein complexes as iron sources

Yersinia pestis strains utilize haem and several haem-protein complexes as sole sources of iron. In this study, the haemin uptake locus (hmu) of Y. pestis KIM6+ was selected from a genomic library by transduction into an Escherichia coli siderophore synthesis (entC) mutant. Recombinant plasmids containing a common 16 kb BamHI insert were isolated that allowed E. coli entC to use haemin as an iron source. An 8.6 kb region of this insert was found to be essential for haemin utilization and encoded at least five proteins with molecular masses of 79/77, 44, 37, 35, and 30/27.5 kDa. A 10.9 kb Clal fragment containing the hmu locus showed varying degrees of homology to genomic DNA from Yersinia pseudotuberculosis, Yersinia enterocolitica, and other genera of Enterobacteriaceae. An E. coli hemA aroB strain harbouring cloned hmu genes used haemin as both an iron and porphyrin source but only on iron-poor medium, suggesting that haemin uptake is tightly iron regulated. Additionally, haemoglobin and myoglobin were used as iron sources by an E. coli entC (pHMU2.2) strain. Deletion of the hmu locus from Y. pestis KIM6+ chromosome generated a mutant that grew poorly on iron-depleted medium containing free haemin as well as mammalian haem-protein complexes including haemoglobin, haemoglobin-haptoglobin, myoglobin, haem-haemopexin, and haem-albumin unless it was complemented with cloned hmu genes.

Imaging allergen-invoked airway inflammation in atopic asthma with [18F]-fluorodeoxyglucose and positron emission tomography

BACKGROUND

Airway inflammation is a feature of asthma and can be quantified invasively with bronchial lavage and endobronchial histology. Inflammatory foci can be imaged non-invasively with positron emission tomography (PET) and [18F]-fluorodeoxyglucose (18FDG) to quantify glucose uptake in activated granulocytes. We used this technique to study airway inflammation in asthma.

METHODS

Nine men with mild atopic asthma were studied. In five, we studied the effect of bronchoscopic segmental allergen challenge on 18FDG uptake. Allergen was instilled into the posterior segment of the right upper lobe; a similar volume (20 mL) of isotonic saline was instilled into the posterior segment of the left upper lobe. At 1-32 h after instillation, PET with 18FDG was done. In the other four patients, we administered aerosolised allergen.

FINDINGS

18FDG uptake was increased four-fold in the right compared with the left upper lobe (geometric mean of ratios 4.30, 95% Cl 2.39-7.72, p=0.002). Aerosolised administration of allergen did not significantly increase 18FDG uptake.

INTERPRETATION

These data show that local allergen-invoked airway inflammation can be visualised with 18FDG and PET in asthma. The cellular localisation of the 18FDG signal remains to be determined.

An experimental analysis of a neurobehavioral motor intervention

This study reports the effects of a neurobehavioral intervention approach on the motor skills of four children with cerebral palsy between 21 and 34 months of age. The intervention is based on the merging of neuromotor and behavioral approaches. The behavioral approach, using principles of 'how to teach', addressed motivational issues and allowed for precise definitions of expected outcomes which assisted in measuring acquisition and generalization of behaviors. The neuromotor approach provided 'what to teach' by focusing the intervention on underlying movement components (e.g., trunk rotation, weight bearing) rather than discrete milestone skills. The impact of the approach was assessed using a multiple-baseline design replicated three times. The children demonstrated the movement component by using it to perform both a treated exemplar skill (i.e. a motor skill requiring the movement component for execution) and an untreated exemplar skill.

Changes in the generativity and use of semantic relationships concurrent with milieu language intervention

Changes associated with a milieu language intervention implemented to teach productive semantic relationships (e.g., action-object combinations) were investigated. Subjects were 11 young children with borderline to moderate levels of mental retardation, all in the early stages of language development. Following a baseline period, each subject received three to four training sessions per week in a small group interactive play situation. Measures of generativity were analyzed via pre/post group comparisons. Concurrent with the intervention subjects showed substantial gains in their ability to generatively produce semantic relationships in the intervention context and across settings, adults, and interaction styles. Subjects also correctly responded to an increasing proportion of target probe questions in both the intervention and generalization settings. The results suggest that, for most of the subjects, milieu teaching was associated with enhanced generativity and use of semantic relationships.

In vivo measurement of neutrophil activity in experimental lung inflammation

Positron emission tomography (PET) was used to quantify 18fluorodeoxyglucose (18FDG) uptake in rabbits with experimental pneumonitis localized to the right upper lobe. In Streptococcus pneumoniae-induced pneumonia, which causes a profound inflammatory response lasting several days before it resolves, 18FDG uptake was pronounced at 15 h after the onset of inflammation, but by 48 h there was little uptake. In bleomycin injury, which progresses from an acute inflammatory stage to chronic inflammation and scarring, 18FDG uptake detectable by PET persisted for up to 21 d. Autoradiography of histologic sections after intravenous administration of [3H]deoxyglucose 15 h after streptococcal instillation and 2 wk after bleomycin instillation showed that, in both models, deoxyglucose uptake was localized to neutrophils. In the streptococcal model there was little 18FGD signal at 6 h, when major neutrophil migration occurs. At 15 h, [3H]deoxyglucose-labeled neutrophils were present in the airspaces but not in the alveolar septa, suggesting that the deoxyglucose signal reflected a postmigratory neutrophil event, probably the respiratory burst. Thus, PET of 18FDG uptake may provide a novel and readily repeatable, noninvasive approach to the in vivo study of neutrophil activity at otherwise inaccessible sites.

Cardiopulmonary response to exercise in patients with intrapulmonary vascular shunts

The majority of patients with intrapulmonary right-to-left shunting due to pulmonary arteriovenous malformations-exhibit good maximum exercise capacity (> 70% predicted) despite profound arterial oxygen desaturation. We studied seven such patients to assess tissue oxygen delivery during steady-state exercise. From rest to exercise [50 +/- 7 (SE) W] arterial saturation fell from 80 +/- 3 to 74 +/- 3%, and mean right-to-left shunt increased slightly from 31 +/- 4 to 34 +/- 5% (P = NS). Minute ventilation was high for oxygen uptake, and the ventilatory equivalent was raised (174 +/- 19% predicted) and was correlated with shunt size (r = 0.93). The majority of the patients maintained pulmonary alveolar blood flow within the predicted range for their power output, but total cardiac output was increased to 142 +/- 11% predicted due to flow through the shunt. Consequently, on exercise, oxygen delivery per unit oxygen consumption [2.3-3.3 (normal range 1.6-2.4)] and calculated mixed venous oxygen tension (27.0 +/- 0.8 Torr) were preserved. Arterial PCO2 rose on exercise by 2.8 +/- 1.2 Torr, in proportion to the ratio of flow through the shunt to total cardiac output (r = 0.73), but remained low (33.1 +/- 1.4 Torr) in absolute terms. The high cardiac output on exercise may be facilitated by a low pulmonary vascular resistance (0.33 +/- 0.08 mmHg.1-1.min, measured at rest), which may explain why exercise performance is better in these patients than in patients with equivalent hypoxemia from other causes.

Facilitating prelinguistic communication skills in young children with developmental delay

Very little research has focused on the development and evaluation of intervention strategies designed to facilitate the acquisition of prelinguistic communication skills. We conducted two experiments to determine the effects of a milieu teaching approach on the acquisition and generalization of specific prelinguistic communication skills. In the first experiment, we utilized this intervention approach within a multiple baseline design to teach prelinguistic requesting, commenting, and vocal imitation to a single subject with Down syndrome and language delay. The results indicated that the intervention approach was effective at facilitating the child's use of these skills within the treatment setting. Therefore, in the second experiment we conducted a more comprehensive analysis of this approach with 4 subjects with mental retardation. Three of these subjects were taught to request, and 1 subject was taught both to request and to comment. The effects were experimentally evaluated with multiple baseline across subjects design. The results indicated that the intervention was effective in eliciting the intervention targets within the training setting for all 4 subjects. All 4 subjects showed evidence of generalization across stimulus materials, setting, teachers, and interaction style. There was also evidence of reciprocal effects on how classroom teachers in the generalization setting interacted with the subjects as a result of changes in the child's communication behavior.

The effect of pancreatic polypeptide on glucose disposal after surgical alterations of the pancreas

Surgical alterations of the pancreas result in anatomic changes that can affect postoperative glucose metabolism. Pancreas transplantation results in reduction of beta-cell mass, systemic release of insulin, and denervation. The authors hypothesized that such alterations affect peripheral glucose disposal to induce an "insensitivity" to endogenously (systemically) released insulin. Additionally, they hypothesized that surgically induced deficiency of the postprandial hormone, pancreatic polypeptide, might contribute to altered glucose disposal. The authors studied two surgical models in dogs known to be devoid of pancreatic polypeptide--70% proximal pancreatectomy (PPx) and PPx plus distal pancreas autotransplantation (PAT/B). Oral glucose challenge and euglycemic hyperinsulinemic clamp studies were performed before and after a 16-day "pulsed" infusion of pancreatic polypeptide. Both surgical procedures resulted in elevations in the integrated glucose response after oral glucose, which was not affected by pancreatic polypeptide infusion. Euglycemic clamp studies showed decreased hepatic glucose output (Ra) and overall glucose disposal (Rd) in the fasted state for both surgical groups. The transplant animals demonstrated significant decreases in Rd during the hyperinsulinemic challenge (3.2 +/- 0.01 versus 5.7 +/- 0.01 mg/kg/minute at 60 to 120 minutes for PAT/B versus control). After 16 days of pancreatic polypeptide infusion, however, basal Ra, as well as basal and 60- to 120-minute Rd values, were returned to control values in the transplant group. The authors conclude that pancreas transplantation results in altered glucose disposal, possibly due to an altered effectiveness of systemically released insulin. They conclude that pancreatic polypeptide is an important modulator of peripheral insulin action. Therefore, the role of pancreatic polypeptide must be taken into account when evaluating postoperative glucose metabolism in canine models of pancreas transplantation.

Rapid analysis for metabolites of 11C-labelled drugs: fate of [11C]-S-4-(tert.-butylamino-2-hydroxypropoxy)-benzimidazol-2-one in the dog

Positron emission tomography (PET) requires the use of compounds labelled with short-lived, positron-emitting isotopes (e.g., t1/2 of 11C approximately 120 min). As the concentration of unbound, non-metabolised drug is required as the input function for modeling, this presents particular problems for the study of the kinetics and metabolism of such compounds. We have now developed a rapid extraction procedure, followed by high-performance liquid chromatography using a short analytical column coupled to an on-line gamma-detector to determine the metabolism and kinetics of a non-selective beta-adrenergic antagonist of high affinity, S-4-(tert.-butylamino-2-hydroxypropoxy)benzimidazol-2-one. This antagonist is potentially well suited to the non-invasive localisation of beta-receptors in vivo. The ligand was rapidly taken up into the beta-receptor pool or excreted in urine, with less than 5% of the drug converted to metabolites. Plasma protein binding was only 16%. No significant metabolism of the ligand was observed in the anaesthetised dog, and, therefore, no correction for blood metabolite concentration is required for kinetic analysis of the 11C-labelled ligand during PET studies in this species. The analytical method reported here should be widely applicable: quantification of metabolites enables accurate estimation of the input function and is critical to the interpretation of PET data.

Comparison of estimates of cardiac output by indicator dilution and freon 22 uptake during gas mixing in dogs

STUDY OBJECTIVE

The aim was to measure cardiac output while rebreathing tidal volumes, by correction of soluble gas uptake for gaseous mixing.

DESIGN

Simultaneous measurements of cardiac output by indocyanin green and freon 22 uptake during rebreathing were made. Mixing for a hypothetical gas of identical gaseous diffusivity to freon 22 was calculated by interpolation between concentrations of two insoluble gases, helium and sulphur hexafluoride. Mixing efficiency was estimated by the number of breaths for helium to become 99% equilibrated with lung gas (n99-He).

EXPERIMENTAL MATERIAL

Five anaesthetised dogs rebreathed at intervals with 300 ml of test gas.

MEASUREMENTS AND MAIN RESULTS

63 comparisons of cardiac output using indocyanin green and freon 22 uptake (over breaths 7-13 using the mean mixed volume of distribution), gave a mean (95% confidence interval) underestimation of 0.345 (0.093-0.597) litre.min-1 (14%). Exclusion of 12 points in which n99-He was greater than 15 resulted in a mean underestimation of 0.052(-0.163-0.267) litre.min-1 (2%). Without correction for gaseous mixing, freon 22 uptake for these data overestimated blood flow by a mean of 1.31 litre.min-1 (overestimation = 2.7 over breaths 5-11). Use of the equilibrium volume of distribution resulted in an overestimation of blood flow relative to green dye of 1.2 litre.min-1 (breaths 5-11) and 0.76 litre.min-1 (breaths 7-13).

CONCLUSIONS

Estimates of cardiac output by soluble gas uptake are optimal when correction is made for mixing of gas of identical diffusivity. The mean mixed gas volume gives the best correlation with the reference method, implying a selective distribution of blood flow to the better ventilated areas.

DLCO/Q and diffusion limitation at rest and on exercise in patients with interstitial fibrosis

Pulmonary diffusing capacity for carbon monoxide (DLCO) and pulmonary capillary blood flow (Qp) were measured on exercise in patients with a low DLCO with the aim of predicting, from the overall DL/Qp ratio, diffusion limitation for oxygen and relating it to the fall in arterial oxygen saturation actually observed. Five patients with cryptogenic fibrosing alveolitis (DLCO ranging from 20-54% predicted normal) exercised for 5 min at a work load equal to 60% of their maximum (45 to 90 watts). At 5 min (and previously at rest) they rebreathed rapidly for 15 sec from a 1.0 L bag containing helium (He), sulphur hexafluoride (SF6) and freon-22, 30% oxygen in argon and less than 1 ppm 11C-labelled carbon monoxide. Pulmonary capillary blood flow (Qp) and diffusing capacity (DLCO) were measured from flow-weighted breath-by-breath concentrations of freon-22 and 11CO, after correction for gas mixing delays (using He and SF6). Oxygen saturation (SaO2) (ear oximetry), MO2 and MCO2 and cardiac frequency were measured. PAO2 (ideal) was derived and mixed venous O2 saturation and content were calculated (Fick); PaO2 and PVO2 were derived from standard dissociation curves. For comparison, DLCO and Qp were measured in a similar fashion in five normal subjects exercising at 60 watts. Mean DLCO in patients with fibrosis was 9.62 (SD 2.88) ml.min-1, mm Hg-1 on exercise and mean Qp was 10.48 (SD 1.79) L.min-1 giving mean DLCO/Q ratios of 0.92 (SD 0.28). At 60 watts mean DLCO/Qp in normal subjects was 2.54 (SD 0.3), 2.76-times greater than in patients. SaO2% fell in patients by 3-15% on exercise. Predictions of alveolar-end capillary PO2 gradients from these overall DL/Q gradients showed that diffusion limitation accounted for 99% of the alveolar-arterial PO2 gradient on exercise in fibrosing alveolitis. Hughes (1991 Respir. Physiol. 83:167-178) [corrected] suggests that this simple approach overestimates the contribution of diffusion limitation by about 30%.

Modification of pulmonary gas mixing by postural changes

Mixing for two gases of markedly different gaseous diffusivity, helium (He) (mol wt = 4) and sulfur hexafluoride (SF6) (mol wt = 146) has been studied by a rebreathing method in different postures. In nine normal subjects duplicate measurements were made in the erect (seated), supine, and lateral decubitus posture, at a constant tidal volume (700 ml) and frequency (1 Hz) starting from functional residual capacity (FRC). Additional measurements were made on four of the subjects, rebreathing seated erect at a volume similar to the relaxed FRC supine and supine at a volume similar to the relaxed FRC seated. In the supine posture the mean breath number to reach 99% equilibrium (n99), was not significantly different for the two gases, 8.9 for He and 9.8 for SF6. There was a difference (P less than 0.01) when erect; n99 (He) = 8.2 and n99 (SF6) = 10.9. The greatest He-SF6 difference (P less than 0.001) was in the lateral decubitus position n99 (He) = 10.1 and n99 (SF6) = 15.9. The mean relaxed FRC as percent of seated was 71% supine and 75% in lateral decubitus posture. Rebreathing seated at a lower volume did not abolish the He-SF6 mixing difference nor did rebreathing at a higher volume when supine induce a He-SF6 mixing difference. Thus the effect of posture on gas mixing cannot be due solely to lung volume and must represent a convective and diffusive dependent change in the distribution of ventilation per unit lung volume.

A rapid rebreathing method for measurement of pulmonary gas volume in humans

We have developed a rapid gas-dilution technique, with which pulmonary gas volume can be measured in only 20 s, even in the presence of maldistribution of ventilation. The subject rebreathes from a 0.75-liter anesthetic bag filled with 10% He and 30% O2 in argon. Breath-by-breath flow-weighted inspired concentrations of all gases present are calculated from continuous measurement by mass spectrometry. Insoluble gas concentrations are corrected continuously for shrinkage of the system volume. By use of these corrected values a mathematical extrapolation predicts the equilibrium concentration for He in the absence of complete mixing. Validation of the technique was carried out by comparing volumes calculated from the predicted equilibrium value with those obtained by whole-body plethysmography in 7 normal subjects and 12 patients with lung disease. In normal subjects equilibrium was usually attained within the 20 breaths and no extrapolation was required. In most of the patients, however, equilibrium was not reached and the use of the extrapolation technique increased the proportion of the lung volume measured by gas dilution from 0.82 +/- 0.16 (SD) to 0.95 +/- 0.12 of that measured by plethysmography.

Measurement of functional residual capacity and pulmonary carbon monoxide uptake in conscious Greyhounds

A simplified rebreathing method was developed for measurement of functional residual capacity (FRC) and pulmonary diffusing capacity for CO in nonanesthetized standing Greyhounds. The FRC was related to body weight according to the equation: FRC = 0.04 (body weight in kg)1.22 whereas pulmonary diffusing capacity for CO in nonanesthetized standing Greyhounds (ml/min/mm of Hg) = 2.34 (body weight in kg).0.66 The large FRC per unit of body weight in the Greyhound emphasizes the need for breed specific prediction equations in veterinary respiratory physiologic studies and may reflect selection for exercise performance in the development of the Greyhound breed.

Performance of the large-reservoir oxygen mask (Ventimask)

The performance of large-reservoir Venturi masks ('Ventimask') giving nominal inspired oxygen (O2) concentrations ranging from 24% to 60% was assessed in a face model, in six normal subjects, and in ten patients with severe chronic airflow obstruction at the O2 flow rates recommended. Instantaneous oxygen concentrations were measured with a mass spectrometer ('Centronics MGA200') and volume-weighted to give mean inspired concentrations (FiO2). In human studies volume-weighting was achieved by simultaneous measurement of tidal volume from chest and abdominal motion by the use of a respiratory inductance plethysmograph ('Respitrace'). Reinspiration of dead space from the mask was assessed by measuring FiCO2, which varied from 0.2 to 0.4% (normals) and was 0.6 +/- 0.4% in patients. In normal subjects and patients breathing at rest the FiO2% in 24, 28, 35, and 40% ventimasks was within 1.9% absolute of nominal (range-1.2 to +1.9%) but the 60% mask read low (50.3%). Various factors can make FiO2 less than nominal but the human and model studies indicated that reinspiration of dead space from the mask was more important than hyperventilation. In tachypnoeic patients (frequency greater than 30/min), the O2 flow should be increased to 50% above recommended.

Effect of posture on inter-regional distribution of pulmonary ventilation in man

Regional ventilation per unit alveolar volume (V/VA) and regional lung expansion (FRCR/TLCR) were measured in twelve normal male human subjects in seated, supine, lateral decubitus and prone postures using a gamma camera and inhalation of the radioactive gases 81Krm (half-life 13 sec) and 85Krm (half-life 4.4 h). FRCR/TLCR decreased from superior to inferior in all postures except prone where it was uniform; V/VA increased from superior to inferior except in the prone position where it was uniform. In the horizontal axis FRCR/TLCR and V/VA were uniformly distributed except for cranial to caudal gradients (with lower values caudally) in supine and lateral decubitus postures. In the prone posture V/VA tended to be higher in caudal lung zones.

Effect of posture on inter-regional distribution of pulmonary perfusion and VA/Q ratios in man

Using a gamma camera regional pulmonary perfusion per unit alveolar volume (Q/VA) and ventilation-perfusion ratios (VA/Q) were measured in fourteen normal male volunteers in upright, supine, lateral decubitus, prone and prone suspended postures with inhalation and intravenous infusion of radioactive 81Krm (half-life 13 sec) and inhalation of radioactive 85Krm (half-life 4.4 h). In the vertical axis, Q/VA increased from upper to lower lung regions in upright, lateral decubitus, prone and prone suspended postures but was uniform in supine and within the dependent lung in decubitus postures. Horizontally, Q/VA decreased from cranial to caudal in lateral decubitus, prone suspended, and near the diaphragm in supine. Vertically, VA/Q decreased from upper to lower in all postures except in supine and within the dependent decubitus lung where it increased. VA/Q tended to increase from cranial to caudal in horizontal postures. The effects of gravity on Q/VA and VA/Q vertical distributions are modified when FRC is low (supine, lower decubitus lung) because perfusion is more uniformly distributed. Horizontal gradients of Q/VA and VA/Q are more pronounced under conditions of high local lung volume but also occur in postures where FRC is low.

Genital clear cell adenocarcinoma

Genital clear cell adenocarcinoma is a rare cancer in young women related to prenatal exposure to diethylstilbestrol (DES). From the Diethylstilbestrol Registry, an analysis of 57 cases of genital clear cell adenocarcinoma is presented from the state of California, the most populous state in the United States. Approximately two-thirds of these patients have positive histories of prenatal diethylstilbestrol exposure. The majority of patients had early-stage genital cancer. Generally, early-stage clear cell cancer is successfully treated with radical pelvic surgery. A carefully structured screening program of the DES exposed patient is advised.

Quantitative measurement of intrapulmonary and extrapulmonary right-to-left shunt

We have developed a new technique that enables the shunting of blood from the right to the left side of the circulation to be partitioned into a cardiac and a lung component. The effects of recirculation are minimal, and the method does not require on-line data analysis. Quantitative estimates of these components have been made in two normal dogs and in five patients with raised pulmonary arterial pressures, some of whom were known to have a patent foramen ovale. The results were compared with oxygen shunt measured during air breathing. A poorly soluble gas, nitrogen, radiolabelled with 13N in solution is injected first into a central vein while matched samples of blood are drawn from the pulmonary artery and the aorta. A second solution containing 13N is injected into the right ventricle and sampled from the aorta only. Standardized gamma-counting techniques were used to analyze both the injected radioactivity and the radioactivity in the samples. These two measurements enable us to calculate the total right-to-left shunt, the pulmonary shunt, and by subtraction the extrapulmonary cardiac shunt.

The contribution of heart beat to gas mixing in the lungs of dogs

The mixing efficiency for two gases of different gaseous diffusivity, helium (He) and sulphur hexafluoride (SF6) have been studied in anaesthetised dogs, closed and open chested, with and without the heart beating. Equilibration of He and SF6 was studied during rebreathing at frequency of 0.5 Hz and a tidal volume of either 0.3 or 0.5 L. Circulation and gas exchange were taken over by a complete heart and lung bypass circuit during the periods when the heart was stopped. The number of breaths required to reach 99% equilibration (n99) ranged from 4 to 14 for He and from 6 to 17 for SF6. There was no significant change in mixing efficiency in any situation. Stopping the heart increased the n99 for He by only 0.4 +/- 11% (1 SD) (n = 21). Opening the chest increased n99 by 1.4 +/- 13% with the heart beating and 2.5 +/- 19% with the heart stopped. The n99 for SF6 was 30 +/- 22% higher than that for He with the chest closed with or without the heart beating. This increased to 37% with the chest opened but was not altered by stopping the heart. The findings for the final phase equilibration rate constant were similar. We conclude that the beating action of the heart does not affect gas mixing in the lungs in the tidal breathing range.

A conscious dog model for study of regional lung function

Using a specially designed mask and steady-state administration of the short-lived radioactive gas 81mKr, we measured the distribution of the ventilation-perfusion ratio (VA/Q) in the lungs of normal conscious standing greyhound dogs during tidal breathing. This model allows measurement of regional lung function unaffected by anesthesia and mechanical ventilation. An assessment of the distribution of VA/Q in the lungs of normal greyhound dogs revealed that topographically, ventilation and blood flow are well matched in the conscious dog.

Lung tissue volume estimated by simultaneous radiographic and helium dilution methods

The pulmonary total tissue volume (blood, extravascular water, and dry tissue volume) was measured by finding the difference between the radiographic displacement volume of the thorax (RDVT) and the lung gas volume. Simultaneous determinations of RDVT and gas volume were made in 10 healthy subjects sitting upright. RDVT was determined from posteroanterior and lateral chest radiographs, a computerised modification of the Barnhard method being used; and gas volume was measured by helium dilution with each radiographic exposure. At functional residual capacity pulmonary total tissue volume was 843 +/- 110 ml (1 SD). The density of the lung (ml tissue per ml tissue and gas) was 0.19 +/- 0.03 (1 SD). This method, different in principle from indicator-dilution and acetylene rebreathing studies, provides measurements of total tissue volume.

Glassy cell carcinoma of the cervix: report of three cases

Glassy cell carcinoma is a poorly differentiated adenosquamous carcinoma of the cervix, hallmarked by aggressive behavior, occurrence in association with pregnancy, and a poor patient survival rate. Three of these very rare cervical, primary malignancies are reported. At the time of this writing, only one patient has survived.

Rate of uptake of carbon monoxide at different inspired concentrations in humans

The rate of uptake of carbon monoxide (CO) in the lungs of normal subjects were measured at inspired concentrations of less than 1, 300, and 3,000 ppm (less than 0.0001-0.3%) using radioactive CO (11CO). In nine subjects the rate of uptake was monitored at the mouth during rebreathing. At inspired CO concentrations of approximately 1, 300, and 3,000 ppm and a mean alveolar O2 fraction of 0.15, the mean lung diffusing capacity was 25.8, 26.4, and 25.3 ml . min-1. Torr-1, respectively. In seven subjects the measurements were repeated after a period of O2 breathing, giving a mean alveolar O2 fraction of 0.78. The calculated membrane diffusing capacity was 31.9, 33.7, and 32.0 ml . min-1. Torr-1 at less than 1, 300, and 3,000 ppm inspired CO. We conclude that there is no difference in the rate of uptake of CO over the range of concentrations studied in these experiments. No evidence for the presence of a facilitated transport system for CO in the normal human lung was found.