Release of leukotrienes, induced by the Ca++ ionophore A23187, from human lung parenchyma in vitro

When chopped human lung is stimulated with the Ca++ ionophore A23187 (0.25-10 microM) leukotriene (LT) B4, LTD4 and LTE4 are found in the incubation medium according to different patterns. LTD4 is released promptly and its levels increase up to 45 min after the stimulus (A23187, 10 microM) and decline later (120 min); LTE4 formation follows a sigmoidal shape and continues to accumulate even 2 hr after the challenge; LTB4 levels reach a plateau at 45 min. LTC4 was undetectable in most experiments but it was found to accumulate when reduced glutathione (10 mM) was added. Addition of exogenous LTC4 to unstimulated fragments of human lung shows that an effective interconversion to LTD4 and LTE4 takes place: A23187 stimulates formation of LT and cyclo-oxygenase products dose dependently; a statistically significant formation of LT occurs at A23187 concentration of 1 microM whereas thromboxane B2 (TXB2) and 6-K-prostaglandin F1 alpha levels increased significantly only at 2.5 microM A23187. Pretreatment with U-60257 (100 microM) prevented formation of LT without a concomitant increase of TXB2 levels. Indomethacin (1.5 microM) blocked the release of 6-K-prostaglandin F1 alpha and TXB2 without a shift of arachidonic acid towards LT-like activity. Addition of exogenous LTC4 did not trigger synthesis of TXB2 or 6-K-prostaglandin F1 alpha. Our results indicate that reduced glutathione levels and the activity of the enzymes involved in LT biosynthesis and/or metabolism play an important role in controlling the pattern of LT release from human lung.     

Aggregated low density lipoprotein induces tissue factor by inhibiting sphingomyelinase activity in human vascular smooth muscle cells

Summary. Background: Our previous results demonstrated that aggregated low density lipoprotein (agLDL) induces tissue factor (TF) expression and activation through Rho A translocation in human vascular smooth muscle cells (VSMC). We also previously demonstrated that membrane sphingomyelin (SM) content is higher in agLDL‐exposed VSMC than in control cells. The main enzymes regulating cellular SM content are the family of sphingomyelinases (Smases) that hydrolize SM to phosphorylcholine and ceramide (CER). Objectives: We wished to investigate whether agLDL has the ability to modulate acidic‐ (A‐) and neutral (N‐) Smase activity and whether or not this effect is related to the upregulatory effect of agLDL on Rho A translocation and TF activation in human VSMC. Methods and Results: By measuring generated [¹⁴C]‐phosphorylcholine, we found that agLDL significantly decreased A‐Smase and specially N‐Smase activity. Pharmacological Smase inhibitors increased Rho A and TF. Specific loss‐of‐function of A‐Smase or N‐Smase 1 (N1‐Smase) by siRNA treatment (500 nmol L^?1, 12 hours) dramatically increased membrane Rho A protein levels (5‐ and 3‐fold, respectively). Concomitantly, TF protein expression and TF procoagulant activity were also increased. Inhibition of A‐Smase or N‐Smase activity by agLDL, siRNA‐anti A‐ or N1‐Smase or pharmacological treatment significantly increased the SM content of vascular cells. The inhibition of SM synthesis by fumonisin B₁ (FB₁) prevented the upregulatory effect of agLDL on TF. Conclusions: These results demonstrate that inhibition of both A‐ and N1‐Smase might explain the upregulatory effect of agLDL on TF activation, and suggest that this effect is related, at least in part, to membrane SM enrichment.     

TxA2-mediated myocardial ischemia as a consequence of an acute lung inflammatory reaction in the rabbit

Summary. Epidemiological studies link acute infection of the respiratory tract to a transient increased risk of acute myocardial infarction. The underlying mechanisms remain unknown. We hypothesized that vasoactive mediators produced by inflammatory cells in the lungs and drained in the coronary circulation may trigger acute myocardial ischemia. To test this hypothesis we used an experimental model in the rabbit. Injection of the bacterial‐derived peptide N‐formyl‐Met‐Leu‐Phe (or N‐formyl‐Methionyl‐Leucyl‐Phenylalanine)(fMLP) in the jugular vein induced massive recruitment of both polymorphonuclear leukocytes (PMN) and platelets in the microcirculation of the lungs, accompanied by rapid and marked increase of leukotriene B4, cysteinyl leukotrienes and thromboxane (Tx) A2 in the aortic blood. In all animals, fMLP evoked ischemic electrocardiographic changes: within the first minute of infusion a profound depression of the ST segment and inversion of the T wave were observed. Mean aortic pressure and heart rate fell to 64.0 ± 6.9 and 83.5 ± 3.1% of the basal levels at 3 and 10 min, respectively. All these alterations were transient. Aspirin, prevented electrocardiographic ischemic changes, reverted bradycardia and hypotension but did not significantly modify either PMN or platelet recruitment nor leukotriene synthesis. Ridogrel, a Tx‐synthase and receptor inhibitor, prevented ECG alterations and bradycardia, but did not prevent and even worsened hypotension; it blocked platelet, but not PMN, sequestration. Pretreatment of animals with intravenous high dose of aspirin prevented ridogrel‐dependent hypotension and platelet inhibition, suggesting that PGI2 contributes to the effects of Tx‐synthase and receptor inhibitor. In hypercholesterolemic rabbits, ECG alterations persisted longer than in normal controls. In summary, our results indicate that acute activation of PMN and platelets in the lungs provokes transient myocardial ischemia, in normal animals that is exacerbated in hypercholesterolemic rabbits. TxA2 appears to be the major mediator of this phenomenon. Moreover the data suggest that a balance between TxA2 and PGI2 plays a pivotal role in platelet activation and recruitment in our model.     

前列环素和血栓素A2在急性坏死性胰腺炎并发肾损害发病机制中的作用

目的：探讨前列环素（ＰＧＩ２）、血栓素Ａ２（ＴＸＡ２）在急性坏死性胰腺炎并发肾损害发病机制中的作用。方法：采用胰胆管结扎、胰腺被膜下注射５％牛磺胆酸钠复制急性坏死性胰腺炎肾损害大鼠模型,以放射免疫方法动态测定术后２４、４８小时肾静脉血浆和肾组织中血栓素Ｂ２（ＴＸＢ２）、ＰＧＩ２水平,并观察尿素氮（ＢＵＮ）、血肌酐（ＳＣｒ）的改变。结果：随着急性坏死性胰腺炎病程进展,肾静脉血浆和肾组织中ＴＸＢ２、６酮前列腺素１α（６ｋｅｔｏＰＧＦ１α）水平逐渐升高,ＴＸＢ２水平升高较６ｋｅｔｏＰＧＦ１α为甚,ＴＸＢ２／６ｋｅｔｏＰＧＦ１α比值增大,ＢＵＮ、Ｃｒ亦显著提高。结论：ＴＸＡ２和ＰＧＩ２平衡紊乱是急性坏死性胰腺炎并发肾损害的主要因素之一。     

Effects of SCA40 on human bronchi and on guinea pig main bronchi in vitro. Comparison with cromakalim

Summary— The aim of this study was to examine the activity of SCA40, a novel charybdotoxin-sensitive potassium channel opener, against a variety of spasmogens or against electrical field stimulation in guinea pig isolated main bronchi and in human isolated bronchi; the effects of SCA40 were compared with those of cromakalim. Like cromakalim, SCA40 reduced the contractility of guinea pig and human isolated bronchi precontracted with acetylcholine 10^?6 M or neurokinin A 10^?6 M, SCA40 being more efficient and more potent than cromakalim. Moreover, on guinea pig isolated main bronchi, SCA40 can exert a preventive effect on contractions induced by acetylcholine, neurokinin A or capsaicin, that is, it shifts to the right the concentration-effect curves of these substances, whereas cromakalim has no such effect. The effects of cromakalim were antagonized by glibenclamide 10^?5 M, whereas the effects of SCA40 were inhibited by tetraethylammonium (TEA 10^?2 M) and charybdotoxin (3 × 10^?8 M), but this inhibitory effect of TEA was reversed by nifedipine (10^?6 M). Electrical field stimulation of guinea pig isolated main bronchi induced two successive contractile responses. Both contractions were significantly reduced by SCA40 (10^?6 and 10^?5 M) and cromakalim (10^?5 M). Since cromakalim was unable to inhibit the effects of acetylcholine or neurokinin A, it might be suggested that for this latter compound the inhibition seems to take place prejunctionally and to affect the release of neuromediators produced by electrical field stimulation. In contrast, in the case of SCA40, a postjunctional effect seems to be likely, owing to its preventive effects, although a prejunctional effect cannot be excluded. Finally, on guinea pig isolated main bronchi, SCA40 (10^?8-10^?6 M) did not potentiate the relaxant effect of isoprenaline or sodium nitroprusside, suggesting a lack of functional manifestation of inhibition of phosphodiesterase for these concentrations. In conclusion, these results demonstrate that SCA40 is a potent and efficient relaxant of guinea pig and human airway smooth muscle, and is able to inhibit, in the guinea pig isolated main bronchi, the contractions induced by electrical field stimulation. It has an effect on TEA-sensitive K+ channels, but this effect is probably not involved in its relaxant effect which does not also rest on an inhibitory effect of phosphodiesterase.     

Developing a tissue‐engineered model of the human bronchiole

Scientists are always looking for new tools to better mimic human anatomy and physiology, especially to study chronic respiratory disease. Airway remodelling is a predominant feature in asthma and occurs in conjunction with chronic airway inflammation. Both the inflammatory and repair processes alter the airway wall which is marked by anatomical, physiological and functional changes. A tissue‐engineered model of bronchiole remodelling presents a novel approach to investigating the initiation and progression of airway remodelling. By developing a unique bioreactor system, cylindrical‐shaped bronchioles constructed from well‐characterized human lung primary cells have been engineered and examined with a much greater control over experimental variables. We have grown human bronchioles composed of fibroblasts, airway smooth muscle cells, small airway epithelial cells and extracellular matrices. The various cell types are in close proximity to one another for cell–cell signalling and matrix interactions. The cylindrical geometry of the tissue applies radial distension for mechanotransduction and the air interface provides a natural environment for the epithelial cells. Optimal cell density, extracellular matrix concentration and media composition were determined. Immunohistochemistry verified bronchiole phenotypic stability. Quiescence was gauged by protein expression which verified a change in phenotype after the initial fabrication stage and implementation of the air interface. A fabrication timeline was devised for repeatable bronchiole fabrication and to understand tissue contraction and cell‐seeding duration. The stability of the bronchiole structures and their cellular composition lends these bronchioles to study cell–cell interactions and remodelling events while maintaining in vivo geometrical dimensions and relationships. Copyright © 2010 John Wiley & Sons, Ltd.     

Modulation of the calcium sensitivity of the smooth muscle contractile apparatus: molecular mechanisms, pharmacological and pathophysiological implications

Summary— Smooth muscle contraction is the basis of the physiological reactivity of several systems (vascular, respiratory, gastrointestinal, urogenital…). Hyperresponsiveness of smooth muscle may also contribute to a variety of problems such as arterial hypertension, asthma and spontaneous abortion. An increase in cytoplasmic calcium concentration ([Ca²⁺]_i) is the key event in excitation-contraction coupling in smooth muscle and the relationship linking the [Ca²⁺]_i value to the force of contraction represents the calcium sensitivity of the contractile apparatus (CaSCA). Recently, it has become evident that CaSCA can be modified upon the action of agonists or drugs as well as in some pathophysiological situations. Such modifications induce, at a fixed [Ca²⁺]_i value, either an increase (referred to as sensitization) or a decrease (desensitization) of the contraction force. The molecular mechanisms underlying this modulation are not yet fully elucidated. Nevertheless, recent studies have identified sites of regulation of the actomyosin interaction in smooth muscle. Sensitization primarily results from the inhibition of myosin light chain phosphatase (MLCP) by intracellular messengers such as arachidonic acid or protein kinase C. In addition, phosphorylation of thin filament-associated proteins, caldesmon and calponin, increases CaSCA. Activation of small (monomeric) G-proteins such as rho or ras is also involved. Desensitization occurs as a consequence of phosphorylation of myosin light chain kinase (MLCK) by the calcium-calmodulin activated protein kinase II, or stimulation of MLCP by cyclic GMP-activated protein kinase. In the present review, examples of physiological modulation of CaCSA as well as pharmacological and pathophysiological implications are illustrated for some smooth muscles.     

Flow-cytometric analysis of human basophil degranulation. II. Degranulation induced by anti-IgE, anti-IgG4 and the calcium ionophore A23187

Quantification of human basophil degranulation induced by anti-IgE, anti-IgG4, and by ionophore was performed using a flow-cytometric system. It was shown that these antibodies and ionophore can degranulate basophils in a dose-dependent manner, and that there is a wide variation in the response of basophils obtained from different individuals to these stimuli. A significant correlation was observed between the degree of degranulation induced by anti-IgE and anti-IgG4, while this was not the case for anti-IgE and ionophore. It was also shown that IgG4 myeloma protein can passively sensitive basophils. In general, degranulating efficacy was in the order of ionophore greater than anti-IgE greater than anti-IgG4, both in allergic and non-allergic individuals.     

Release of platelet-activating factor (PAF-acether) from alveolar macrophages by the calcium ionophore A 23187 and phagocytosis

Platelet-activating factor (PAF-acether) was recovered from rabbit, rat and human alveolar macrophages stimulated with the Ca++ ionophore A23187. PAF-acether release was also obtained from rat and rabbit macrophages in the presence of zymosan, but not from human alveolar preparations in spite of the phagocytic activity exhibited by the latter cells. Observed releases were active, Ca++ dependent, and plateaued at 45 min. No PAF-acether was released from lungs washed out of their macrophages, another argument against the mastocyte origin of this mediator. Given the potent bronchoconstrictive activity of PAF-acether, its release from alveolar macrophages may provide an alternative explanation for non IgE-dependent asthmas and the implication of platelets in pulmonary diseases.     

急性心肌梗死患者溶栓治疗过程中血浆前列环素和血栓素A2的变化及其意义

目的：探讨急性心肌梗死（ＡＭＩ）患者溶栓治疗过程中血浆前列环素（ＰＧＩ２）及血栓素Ａ２（ＴＸＡ２）变化与再灌注损伤的关系。方法：将发病２４小时内入院的１０４例ＡＭＩ患者随机分为溶栓组６０例与未溶栓组４４例;溶栓组连续３日测定外周血ＰＧＩ２和ＴＸＡ２的代谢产物６酮前列腺素Ｆ１α（６ｋｅｔｏＰＧＦ１α）和血栓素Ｂ２（ＴＸＢ２）的浓度;并计算６ｋｅｔｏＰＧＦ１α／ＴＸＢ２比值（Ｋ／Ｔ）。结果：溶栓血管再通组（４２例）的６ｋｅｔｏＰＧＦ１α和ＴＸＢ２水平均高于溶栓血管未通组（１８例）和未溶栓组,以ＴＸＢ２增加的幅度更大,表现为溶栓血管再通组Ｋ／Ｔ比值显著低于后２组（Ｐ＜０．０１）;而溶栓血管未通组与未溶栓组间上述指标无显著性差异（Ｐ均＞０．０５）。另外,溶栓血管再通组中有再灌注心律失常者的Ｋ／Ｔ比值（０．７７±０．０７）显著低于无再灌注心律失常者（０．８８±０．１４,Ｐ＜０．０５）。结论：ＡＭＩ时ＰＧＩ２与ＴＸＡ２平衡失调,其与再灌注心律失常的发生和冠状动脉再通的病理生理过程有关。溶栓治疗时,使用药物纠正ＰＧＩ２与ＴＸＡ２平衡失调可能有一定意义     

非小细胞肺癌患者血清人类表皮生长因子受体-2和环氧化酶-2水平及临床意义

目的探讨非小细胞肺癌患者血清人类表皮生长因子受体2（humanepidermalgrowthfactorreceptor2,HER2）和环氧化酶2（cycl00xygenase-2,COX2）水平相关性及与预后的关系。方法非小细胞肺癌患者221例（观察组）与肺部良性疾病患者41例（对照组）,2组采用双抗体夹心ELISA法检测血清HER2和COX2水平,分析二者相关性及与生存时间的关系。结果观察组HER-2和COX-2水平明显高于对照组（P〈0．05）;观察组HER2阳性表达者中位生存时间（48．7周）较HER-2阴性表达者（62．3周）短;COX2阳性表达者中位生存时间（67．0周）较COX-2阴性表达者（83．1周）短（P〈0．05）;观察组HER2与CoX2水平呈正相关（r=0．717,P=0．007）;观察组HER-2和COX-2水平不是影响预后的独立危险因素,但二者联合检测可预测患者预后（OR=1．5,95％CI：1．08～2．09）。结论非小细胞肺癌与HER-2和COX2阳性表达明显相关,二者联合检测有助于非小细胞肺癌的预后评估。     

磷脂酶A2对肺挫伤兔肺微循环障碍和肺水肿的作用

通过将兔肺挫伤后胸壁“开窗”方法，直接在显微镜下观察肺挫伤后肺微循环障碍和肺水肿的发生、发展过程，以及血清、肺组织和支气管肺泡灌洗液（ＢＡＬ）中磷脂酶Ａ２（ＰＬＡ２）变化，探讨肺挫伤后ＰＬＡ２在肺微循环障碍和肺水肿中的作用机制。实验发现：肺挫伤后１～２小时肺表面小动脉收缩，继之扩张、充血，个别肺小动脉栓塞。肺水肿可在肺挫伤后１～２小时出现，其发展形式有两种：一种是以肺泡水肿为主，另一种是以间质水肿为主。ＰＬＡ２在肺挫伤后２小时开始升高，４～５小时达到高峰，肺组织和ＢＡＬ中ＰＬＡ２活性亦升高。肺内的细胞浸润、聚集。应用ＰＬＡ２抑制剂氯喹后，ＰＬＡ２活性降低，肺微循环改善，肺水肿减轻。提示：ＰＬＡ２在肺挫伤后肺微循环障碍和肺水肿的形成、发展中起重要作用     

磷脂酶A2在小儿急性肺损伤中的作用及意义

目的探讨磷脂酶A2在急性肺损伤(ALI)恶化进程中的作用及意义.方法结合危重病例评分,采用ELISA检测28例ALI患儿血清PLA2含量,并监测患儿脏器功能及动脉血气.结果 ALI患儿血清PLA2含量明显高于正常组(P＜0.001),低于多脏器功能衰竭(MOF)组(P＜0.01).结论 PLA2参与ALI的病理生理过程,与ALI的病情有关,并可作为早期警示ALI及MOF的实验室参数.     

转录因子Sox2在人肺癌中的表达及其临床意义

目的通过观察干细胞转录因子Sox2在鳞癌中的表达,分析其表达情况与病理类型、分化程度和淋巴结转移等的相关性,探讨Sox2在肺癌中的临床意义。方法应用免疫组织化学方法检测48例已确诊的不同类型肺癌组织和10例正常肺组织病理标本中Sox2的表达水平。结果 Sox2蛋白在肺鳞癌组织中的阳性表达率为69%,在肺腺癌组织中表达为4.5%,在小细胞肺癌组织中表达为70%,正常组织中无表达,差异具有显著性。Sox2蛋白表达与患者的年龄、性别、分化程度、有无淋巴结转移无明显相关性。结论 Sox2在鳞癌中高表达,在腺癌中几乎不表达,可作为非小细胞肺癌鉴别诊断的辅助指标。     

In vitro cellular response to oxidized collagen–PLLA hybrid scaffolds designed for the repair of muscular tissue defects and complex incisional hernias

Unique poly(l ‐lactic acid) (PLLA)‐based scaffolds were constructed by embedding knitted PLLA yarns within a bioresorbable and differentially crosslinked three‐dimensional (3D) oxidized collagen scaffold. The scaffolds were designed specifically for the repair of complex incisional abdominal wall hernias and the repair of defects within planar muscular tissues, such as the bladder. The chemical composition of the collagen matrix and the percentage of scaffold infiltration were compared for the different scaffold compositions. The results demonstrate that the incorporation of the collagen sponge within the PLLA scaffold facilitated bladder smooth muscle cell (bSMC) adhesion and proliferation. The highest dose of oxidized collagen (Oxicol) demonstrated better cell adhesion, resulting in the largest cell densities and most uniform distribution throughout the 3D collagen sponge. This formulation promoted the greatest α‐smooth muscle actin (αSMA) expression detected through immunohistochemical staining and western blotting. For abdominal wall repair applications, the proliferation and differentiation of C2C12 myoblasts and myotube formation were studied. Following 7 days of myogenic induction, the greatest expression of mRNA of the myogenic markers myogenin and MRF4 was observed within the scaffolds with the highest dose of oxidized collagen, 1.5‐ and 3.85‐fold greater expressions, respectively, compared to PLLA with unmodified collagen. Furthermore, in vitro myotube formation and MyMC expression were enhanced in the Oxicol scaffolds. We conclude that the Oxicol scaffold formulation with a high‐dose oxidized collagen ratio provides enhanced myogenesis and αSMA, and the biological induction cues necessary to achieve better tissue integration, than standard PLLA scaffolds in the treatment of complex abdominal wall hernias. Copyright © 2013 John Wiley & Sons, Ltd.     

Differences in heparin-released lipolytic activity in the superficial and deep veins of the human forearm

Various doses of heparin were given as a single injection into the brachial artery of each of twelve fasting healthy males. Plasma lipolytic activity was measured in samples obtained before and at frequent time intervals after heparin injection, in the artery and the deep and superficial veins of the same forearm. As little as 0.15 U heparin produced a rapid and detectable release of lipolytic activity in both deep and superficial veins. A series of tenfold increases in the dose produced correspondingly greater releases in the veins but the increments in the release were smaller than the increments in the dose. Three repeated 15 U doses of heparin, separated by 30 min, in the same subject gave a high degree of reproducibility of the release of lipolytic activity in both deep and superficial veins. 90% of the lipase activity in the vein was inhibited by 1 M NaCl. In all subjects the release of lipolytic activity was higher in the deep vein, which predominantly drains muscle, than in the superficial vein, which drains mostly subcutaneous tissues such as skin and adipose tissue. This indicates that muscle is a tissue of considerable importance as a source of post heparin plasma lipolytic activity.     

Adenosine reduces airway excitatory non-cholinergic (e-NC) contraction through both A1 and A2 adenosine receptor activation in the guinea pig

Summary— The influence of adenosine and selective A₁ and A₂ agonists and antagonists was investigated on the cholinergic and the excitatory non-cholinergic (e-NC) contractions induced by electrical field stimulation in the guinea-pig bronchi. Adenosine (10 nM-1 mM) induced a concentration-dependent inhibition of the e-NC contraction (EC₅₀ = 90 ± 14 μM), whereas the cholinergic peak was only slightly affected. Preincubation of the tissue with the adenosine uptake blocker dipyridamole (10 μM) significantly shifted the concentration-inhibition curve to adenosine to the left (EC₅₀ = 10 ± 1 μM), suggesting an interaction with extracellular adenosine receptors of A₁ and/or A₂ subtype. To characterize the receptor type involved in this effect, selective adenosine derivatives were studied. The agonist to both A₁ and A₂ adenosine receptors, 5′-N-ethylcarboxamidoadenosine (NECA) was more potent than the selective A₁ agonist, (-)-R-6-phenylisopropyladenosine (R-PIA), in inhibiting the e-NC contraction (EC₅₀ = 0.10 ± 0.04 and 0.60 ±0.12 μM, respectively, with a maximal inhibition of 70 and 45%, respectively). The concentration-response curve to NECA was shifted to the right by the A₂ receptor selective antagonist 3,7-dimethyl-1-propargylxanthine (DMPX) (10 μM) (EC₅₀ = 1.4 ± 0.5 μ) as well as by the specific A₁ receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (10 μM) (EC₅₀ = 0.7 ± 0.3 μM). The inhibitory effect induced by the association of both antagonists, DPCPX and DMPX, was considerably potentiated (EC₅₀ > 22 ± 2.5 μM). The effect of R-PIA was also shifted to the right by DPCPX (EC₅₀ = 8.2 ± 1.6 μM) but was not modified by DMPX. The contractile response to exogenous substance P was unaffected by NECA pretreatment (0.3 μM). Altogether, these results suggest that adenosine-induced inhibition of e-NC contraction of guinea-pig bronchi is mediated through activation of both A₁ and A₂ adenosine receptors linked to inhibition of the release of neuropeptides from C-fibre nerve endings.     

Total lung capacity measured by body plethysmography and by the helium dilution method. A comparative study in different patient groups

Summary. The helium dilution method is known to underestimate the total lung capacity (TLC) in patients with poorly or non-ventilated areas in the lungs. The standard plethysmographic method has been reported to overestimate TLC in patients with severe airway obstruction. To determine the magnitude of the difference between the two methods, a comparison was made in different patient groups. In a group of patients with normal lung function tests (n= 20) there was a small but significant average difference in TLC between plethysmography and the helium dilution method, the larger values being obtained with the latter. In patient groups with moderately obstructed airways (n= 23), severely obstructed airways (n= 20), or emphysema (n= 19), there were no significant average differences, although in two patients in the emphysema group the plethysmographic values were considerably larger than those obtained by helium dilution. We conclude that the gas dilution methods and plethysmography with a pressure-compensated volume displacement plethysmograph gave estimates of TLC which agreed even in patients with airway obstruction or emphysema, except in patients with very severe lung disease.