The effects of interleukin-8 on airway smooth muscle contraction in cystic fibrosis

BACKGROUND

Many cystic fibrosis (CF) patients display airway hyperresponsiveness and have symptoms of asthma such as cough, wheezing and reversible airway obstruction. Chronic airway bacterial colonization, associated with neutrophilic inflammation and high levels of interleukin-8 (IL-8) is also a common occurrence in these patients. The aim of this work was to determine the responsiveness of airway smooth muscle to IL-8 in CF patients compared to non-CF individuals.

METHODS

Experiments were conducted on cultured ASM cells harvested from subjects with and without CF (control subjects). Cells from the 2nd to 5th passage were studied. Expression of the IL-8 receptors CXCR1 and CXCR2 was assessed by flow cytometry. The cell response to IL-8 was determined by measuring intracellular calcium concentration ([Ca2+](i)), cell contraction, migration and proliferation.

RESULTS

The IL-8 receptors CXCR1 and CXCR2 were expressed in both non-CF and CF ASM cells to a comparable extent. IL-8 (100 nM) induced a peak Ca2+ release that was higher in control than in CF cells: 228 +/- 7 versus 198 +/- 10 nM (p < 0.05). IL-8 induced contraction was greater in CF cells compared to control. Furthermore, IL-8 exposure resulted in greater phosphorylation of myosin light chain (MLC20) in CF than in control cells. In addition, MLC20 expression was also increased in CF cells. Exposure to IL-8 induced migration and proliferation of both groups of ASM cells but was not different between CF and non-CF cells.

CONCLUSION

ASM cells of CF patients are more contractile to IL-8 than non-CF ASM cells. This enhanced contractility may be due to an increase in the amount of contractile protein MLC20. Higher expression of MLC20 by CF cells could contribute to airway hyperresponsiveness to IL-8 in CF patients.

Role of the cystic fibrosis transmembrane conductance channel in human airway smooth muscle

Patients with cystic fibrosis (CF) suffer from asthma-like symptoms and gastrointestinal cramps, attributed to a mutation in the CF transmembrane conductance regulator (CFTR) gene present in a variety of cells. Pulmonary manifestations of the disease include the production of thickened mucus and symptoms of asthma, such as cough and wheezing. A possible alteration in airway smooth muscle (ASM) cell function of patients with CF has not been investigated. The aim of this study was to determine whether the (CFTR) channel is present and affects function of human ASM cells. Cell cultures were obtained from the main or lobar bronchi of patients with and without CF, and the presence of the CFTR channel detected by immunofluorescence. Cytosolic Ca(2+) was measured using Fura-2 and dual-wavelength microfluorimetry. The results show that CFTR is expressed in airway bronchial tissue and in cultured ASM cells. Peak Ca(2+) release in response to histamine was significantly decreased in CF cells compared with non-CF ASM cells (357 +/- 53 nM versus 558 +/- 20 nM; P < 0.001). The CFTR pharmacological blockers, glibenclamide and N-phenyl anthranilic acid, significantly reduced histamine-induced Ca(2+) release in non-CF cells, and similar results were obtained when CFTR expression was varied using antisense oligonucleotides. In conclusion, these data show that the CFTR channel is present in ASM cells, and that it modulates the release of Ca(2+) in response to contractile agents. In patients with CF, a dysfunctional CFTR channel could contribute to the asthma diathesis and gastrointestinal problems experienced by these patients.

MAP kinases mediate interleukin-13 effects on calcium signaling in human airway smooth muscle cells

Interleukin-13 (IL-13) has been strongly implicated in the pathogenesis of allergic asthma through animal models that have shown that IL-13 is both necessary and sufficient to cause airway hyperresponsiveness (AHR). Airway smooth muscle (ASM) is a primary effector of AHR, and IL-13 increases the responsiveness of ASM, by increasing Ca(2+) release intracellularly, to bronchoconstrictors such as histamine. The mechanisms and signaling pathways mediating this effect are incompletely understood. We have investigated the pathways through which IL-13 regulates the Ca(2+) response to histamine in primary human ASM cell cultures. Functional IL-13 receptors were demonstrated by IL-13-mediated phosphorylation of signal transducer and activator of transcription 6 (STAT6) and mitogen-activated protein kinases (MAPKs). IL-13 increased Ca(2+) responses to histamine. The augmentation of Ca(2+) signaling was not affected by inhibition of STAT6 or p38 MAPK signaling but was prevented by concurrent inhibition of c-jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) MAPKs. This inhibition did not affect the IL-13-induced increase in histamine receptors. We conclude that IL-13 induces potentiation of Ca(2+) responses to contractile agonists by affecting mechanisms downstream of receptors. JNK and ERK MAPKs modulate these mechanisms.

Effects of decorin and biglycan on human airway smooth muscle cell proliferation and apoptosis

Proteoglycans (PG) are altered in the asthmatic airway wall. Because PGs are known to affect cell proliferation and apoptosis, we hypothesized that alterations in PG might influence the airway smooth muscle (ASM) hyperplasia observed in the asthmatic airway. Human ASM cells were seeded on plastic or plates coated with decorin (Dcn), biglycan (Bgn), or collagen type I (Col I) (1, 3, and 10 microg/ml). Cells were stimulated with platelet-derived growth factor (PDGF), and cell number was assessed at 0, 48, and 96 h. Cell proliferation was measured by bromodeoxyuridine (BrdU) incorporation and apoptosis by annexin V and propidium iodide staining at 48 h post-PDGF stimulation. A significant decrease in cell number was observed with cells seeded on Dcn (10 microg/ml) at 0, 48, and 96 h (P < 0.01). Dcn induced both decreases in BrdU incorporation and increases in annexin V staining (P < 0.05). Bgn decreased cell number at time 0 only (P < 0.05) and affected neither proliferation nor apoptosis. Col I (10 mug/ml) caused a significant increase in cell number at 48 and 96 h (P < 0.01). Adding exogenous Dcn (1-30 microg/ml) to the medium had no effect on cell number. Exposing Dcn-coated matrices to chondroitinase ABC, an enzyme that degrades glycosaminoglycan side chains, reversed the Dcn-induced decrease in cell number. These studies demonstrate that different PGs have variable effects on ASM cell proliferation and apoptosis. Recently described decreases in Dcn in the asthmatic airway wall could potentially permit more exuberant ASM growth.

Interleukin-8: novel roles in human airway smooth muscle cell contraction and migration

In patients with cystic fibrosis (CF) and asthma, elevated levels of interleukin-8 (IL-8) are found in the airways. IL-8 is a CXC chemokine that is a chemoattractant for neutrophils through CXCR1 and CXCR2 G protein-coupled receptors. We hypothesized that IL-8 acts directly on airway smooth muscle cells (ASMC) in a way that may contribute to the enhanced airway responsiveness and airway remodeling observed in CF and asthma. The aim of this study was to determine whether human ASMC (HASMC) express functional IL-8 receptors (CXCR1 and CXCR2) linked to cell contraction and migration. Experiments were conducted on cells harvested from human lung specimens. Real-time PCR and fluorescence-activated cell sorting analysis showed that HASMC expressed mRNA and protein for both CXCR1 and CXCR2. Intracellular Ca2+ concentration ([Ca2+]i) increased from 115 to 170 nM in response to IL-8 (100 nM) and decreased after inhibition of phospholipase C (PLC) with U-73122. On blocking the receptors with specific neutralizing antibodies, changes in [Ca2+]i were abrogated. IL-8 also contracted the HASMC, decreasing the length of cells by 15%, and induced a 2.5-fold increase in migration. These results indicate that HASMC constitutively express functional CXCR1 and CXCR2 that mediate IL-8-triggered Ca2+ release, contraction, and migration. These data suggest a potential role for IL-8 in causing abnormal airway structure and function in asthma and CF.

Immunotherapy as a disease modifier

Immunotherapy was formerly the treatment of allergic disease by repeated exposure to allergen. Other approaches to immune modulation have emerged using new knowledge of T cell function. The so-called hygiene hypothesis argues that alterations in our environment have resulted in a failure of the immune system to develop normally, such that excessive Th2 type responses to antigen exposures occur. These observations have prompted therapies designed to promote a shift from Th-2 to Th-1 responses. These therapies include bacterial vaccines and stimulation of the immune system with Toll like receptor ligands or bacterial nucleotide immunostimulatory sequences (CpG motifs). Traditional desensitization immunotherapy is being re-examined and anti-IgE therapy is also enjoying a measure of success.

The effects of extracellular purines and pyrimidines on human airway smooth muscle cells

Extracellular ATP and UTP modulate the function of many cell types through the stimulation of specific P2 receptors, and the inhalation of UTP has been proposed as a therapeutic means of increasing mucociliary clearance in cystic fibrosis patients. The aim of this study was to determine whether P2 receptors are present and functional in human airway smooth muscle (HASM) cells. Experiments were conducted on primary cultures of HASM cells. Reverse transcription-polymerase chain reaction and Western blot analysis showed that P2Y(1), P2Y(2), P2Y(4), and P2Y(6) receptor subtypes are expressed. Exposure to extracellular ATP, UTP, ADP, and UDP at concentrations ranging from 10(-6) to 10(-4) M, produced significant increases in intracellular Ca(2+) that peaked to 491 +/- 51 nM (p < 0.001) with ATP 10(-5) M and to 321 +/- 30 nM with UTP 10(-4) M. ATP and UTP also induced HASM cell contraction, decreasing cell length by 9.9 +/- 4.3 and 5.6 +/- 2.0%, respectively. Pretreatment of the cells with UTP for short periods of time (10 and 30 min) enhanced the peak Ca(2+) release to UTP, whereas repeated and prolonged pretreatment with UTP decreased it. These results indicate that several subtypes of P2Y receptors are present and functional in HASM cells. They also show that the response of the receptors is increased after short periods of exposure to UTP and decreased after prolonged and repeated exposure. Considering that ATP and UTP are endogenous mediators and that analogs of UTP could be used as a therapeutic modality, the role of extracellular triphosphate nucleotides in physiological and pathophysiological processes in the airways warrants further investigation.

Effects of hypoxia on rat airway smooth muscle cell proliferation

Although it is well known that hypoxemia induces pulmonary vasoconstriction and vascular remodeling, due to the proliferation of both vascular smooth muscle cells and fibroblasts, the effects of hypoxemia on airway smooth muscle cells are not well characterized. The present study was designed to assess the in vitro effects of hypoxia (1 or 3% O(2)) on rat airway smooth muscle cell growth and response to mitogens (PDGF and 5-HT). Cell growth was assessed by cell counting and cell cycle analysis. Compared with normoxia (21% O(2)), there was a 42.2% increase in the rate of proliferation of cells exposed to 3% O(2) (72 h, P = 0.006), as well as an enhanced response to PDGF (13.9% increase; P = 0.023) and to 5-HT (17.2% increase; P = 0.039). Exposure to 1% O(2) (72 h) decreased cell proliferation by 21.0% (P = 0.017) and reduced the increase in cell proliferation induced by PGDF and 5-HT by 16.2 and 15.7%, respectively (P = 0.019 and P = 0.011). A significant inhibition in hypoxia-induced cell proliferation was observed after the administration of bisindolylmaleimide GF-109203X (a specific PKC inhibitor) or downregulation of PKC with PMA. Pretreatment with GF-109203X decreased proliferation by 21.5% (P = 0.004) and PMA by 31.5% (P = 0.005). These results show that hypoxia induces airway smooth muscle cell proliferation, which is at least partially dependent on PKC activation. They suggest that hypoxia could contribute to airway remodeling in patients suffering from chronic, severe respiratory diseases.

Airway smooth muscle cells express functional neurokinin-1 receptors and the nerve-derived preprotachykinin-a gene: regulation by passive sensitization

Preprotachykinin-A (PPT-A) gene-derived neuropeptides, namely substance P (SP) and neurokinin (NK)A, and their receptors participate in allergen-induced airway responses. Whether airway smooth muscle cells (ASMC) may react directly to SP through expression of the NK-1 receptor or express the gene for the synthesis of SP, the PPT-A gene, is unknown. We demonstrated using reverse transcription-polymerase chain reaction that tracheal SMC (TSMC) from atopic Brown Norway rats contained mRNA transcripts for the full-length isoform of the NK-1 receptor. Flow cytometric analysis indicated that the NK-1 receptor was expressed on the surface of TSMC. This receptor was functional as demonstrated by calcium mobilization in response to SP stimulation. The expression of the NK-1 receptor was not altered in passively sensitized TSMC in response to antigenic stimulation, although this stimulation increased the expression of the chemokine RANTES (regulated on activation, normal T cells expressed and secreted). Using different sets of PCR primers, we showed that TSMC also express the beta, alpha, and its alternative splicing product delta, and possibly the gamma mRNA transcript isoforms of the PPT-A gene. Gene sequencing of the PCR-amplified beta isoform confirmed that it is a transcript product of the rat PPT-A gene, and the production of SP by TSMC was confirmed by enzyme immunoassay. We also showed the beta isoform increased after cell stimulation with rat sera, whether sensitized or not. In conclusion, both the PPT-A gene and NK-1 receptors are expressed by TSMC, which suggests the possibility of autocrine neuropeptidergic mechanisms in these cells. However, these mechanisms are not upregulated by passive sensitization.

Effects of extracellular triphosphate nucleotides and nucleosides on airway smooth muscle cell proliferation

Extracellular ATP and uridine triphosphate (UTP) have a range of effects on a wide variety of cells through the activation of P(2) receptors. The aim of this work was to establish if stimulation with ATP and UTP enhances airway smooth muscle (ASM) cell proliferation and to determine the type of receptor mediating this effect. Proliferation of rat ASM cells was assessed through bromodeoxyuridine (BrdU) uptake and by cell counting. At concentrations of 10(-6) and 10(-5) M, ATP and UTP induced significant increases in BrdU incorporation. ATP analogs specific for the P(2X) and P(2Y1) receptor subtypes had no effect. UDP (a P(2Y6) receptor agonist) produced significant decreases in BrdU incorporation and cell counts. Adenosine, the metabolite of ATP, produced an increase in cell proliferation through stimulation of the A(1) receptor. A(2) and A(3) receptor stimulation had no effect. Reverse transcription and polymerase chain reaction analysis showed that mRNA transcripts for the P(2Y2), P(2Y4), P(2Y6), A(1), A(2), and A(3) receptor subtypes were present in cultured ASM cells. These data show that extracellular UTP, ATP, and their metabolites may affect airway remodeling by increasing or by reducing (P(2Y6) receptor) ASM cell proliferation.

Mechanisms of the potentiation by adenosine of adenosine triphosphate-induced calcium release in tracheal smooth-muscle cells

The effects of concomitant P1-receptor stimulation on peak intracellular Ca2+ release by extracellular adenosine 5'-triphosphate (ATP) and 5-hydroxytryptamine (5-HT) were investigated in cultured airway smooth-muscle (ASM) cells. The results show that peak Ca2+ release to ATP is enhanced by preincubation with adenosine (ADO) and with the specific A3 receptor agonist 1-Deoxy-1-(6-([(3-iodophenyl)methyl] amino)-9H-purin-9-yl)-N-methyl-beta-D-ribofuranuronamide (1B-MECA). The response to 5-HT, a smooth-muscle contractile agonist, was also enhanced after preincubation with ADO. Further measurements showed that this enhancement of the response to ATP was dependent on extracellular calcium because it was abolished by the removal of Ca2+ from the extracellular fluid and by incubation with the calcium channel blocker nifedipine. In addition, there was no difference between the levels of total inositol phosphates measured in the presence of ATP alone or of ADO + ATP. AACOCF3, a specific blocker of phospholipase A2, decreased the peak Ca2+ response to ATP and abolished the enhanced response to ATP and 5-HT produced by ADO. We conclude that stimulation of P1 and P2 receptors in ASM cells activates not only phospholipase C but also phospholipase A2. The enhancement of ATP-induced and 5-HT-induced Ca2+ release is due to Ca2+ influx from the extracellular fluid through a Ca2+ channel presumably modulated by arachidonic acid. These data show that endogenous ADO may modulate airway hyperresponsiveness by enhancing the ASM response to contractile agonists.

Effects of purine nucleotides and nucleoside on cytosolic calcium levels in rat tracheal smooth muscle cells

Extracellular adenosine triphosphate (ATP) has a range of effects on a wide variety of cells through the activation of specific purinoceptors. The aim of this study was to establish whether P2 purinoceptors are present on airway smooth muscle cells. Experiments were conducted on cultured rat tracheal smooth-muscle cells (first through third passage). Intracellular Ca2+ ([Ca2+]i) was measured using Fura-2 and dual-excitation wavelength microfluorometry. The effects of ATP, adenosine diphosphate (ADP), uridine triphosphate (UTP), and adenosine (ADO) were measured in concentrations from 10(-6) to 10(-3) M. At a concentration of 10(-4) M, the peak [Ca2+]i was 502 +/- 92 nM for ATP and 543 +/- 76 nM for UTP (mean +/- standard error of the mean). ADO had no significant effect on Ca2+ release. Peak [Ca2+]i induced by ATP was not dependent on extracellular Ca2+ but was blocked by U-73122, an inhibitor of phospholipase C. Pretreatment with adenosine deaminase and desensitization with alphabeta-MeATP had no effect on ATP-induced Ca2+ release. The effects of ATP (10(-4) M) on peak [Ca2+]i were potentiated by the presence of ADO 10(-5) M (969 +/- 257 nM; P < 0.05). The presence of XAC, a blocker of A1 and A2 ADO receptors did not prevent this effect. In the presence of XAC, ADO 10(-6) M potentiated the effects of ATP (peak [Ca2+]i: 1,300 +/- 229 nM). The addition of 1433U83, a blocker of A3 ADO receptors, blocked the synergistic effect of ADO 10(-6) M on ATP. These data show that P2 purinoceptors, most likely of the P2U subtype, are present on airway smooth muscle cells and that the newly discovered A3 ADO receptor appears to be also present.

Maternal asthma and idiopathic preterm labor

Previous studies suggest that women with asthma are at increased risk of preterm birth. Moreover, drugs (especially beta-agonists) used to treat asthma are also used to treat preterm labor. The authors carried out a case-control study of 555 women from three hospital centers with idiopathic preterm labor (< 37 weeks), including two overlapping (i.e., non-mutually exclusive) subsamples: cases with early idiopathic preterm labor (< 34 weeks) and cases with idiopathic recurrent preterm labor (< 37 weeks plus a previous history of preterm delivery or second-trimester miscarriage). Controls were matched to cases according to race and smoking history prior to and during pregnancy. All subjects responded in person to questions about atopic, respiratory, obstetric, and sociodemographic histories. Subjects in the early and recurrent preterm labor subsamples were also asked to undergo spirometric testing with methacholine challenge 6-12 weeks after delivery. Cases were significantly more likely to report histories of asthma symptoms and physician-diagnosed asthma (matched odds ratios of 2-3) than controls, particularly those cases with recurrent preterm labor. No significant associations were observed, however, with methacholine responsiveness. These results could not be explained by residual confounding by smoking or other variables, nor by selective recall of asthma symptoms and histories by cases. Women with asthma are at increased risk of idiopathic preterm labor. The fact that no such association was seen with methacholine responsiveness suggests that nonatopic, noncholinergic mechanisms may link bronchial and uterine smooth muscle lability.

Maternal anthropometry and idiopathic preterm labor

OBJECTIVE

To assess the etiologic role of maternal short stature, low pre-pregnancy body mass index (BMI), and low rate of gestational weight gain in idiopathic preterm labor.

METHODS

We carried out a three-center case-control study of 555 women with idiopathic onset of preterm labor (before 37 completed weeks), including two overlapping (ie, nonmutually exclusive) subsamples: cases with early preterm labor (before 34 completed weeks) and cases with recurrent preterm labor (before 37 completed weeks plus a history of prior preterm delivery or second-trimester miscarriage). Controls were matched to cases by race and smoking history. All subjects responded in person to questions about height, pre-pregnancy weight, gestational weight gain, and obstetric and sociodemographic histories.

RESULTS

Maternal height, pre-pregnancy weight, and gestational weight gain demonstrated excellent test-retest reliability, with intra-class correlation coefficients of 0.97, 0.99, and 0.91, respectively. Based on matched analyses, women with a height of 157.5 cm or less had an increased risk of idiopathic preterm labor (odds ratio [OR] 1.85, 95% confidence interval [CI] 1.25-2.74), as did those with a pre-pregnancy BMI less than 19.8 kg/m2 (OR 1.63, 95% CI 1.09-2.44) or a gestational weight gain rate less than 0.27 kg/week (OR 1.74, 95% CI 1.16-2.62). Conditional logistic regression models containing all three anthropometric variables and controlling for parity, marital status, language, age, and education yielded virtually identical point estimates and CIs.

CONCLUSION

Maternal short stature, low pre-pregnancy BMI, and low rate of gestational weight gain may lead to shortened gestation by increasing the risk of idiopathic preterm labor.

Plasma concentrations and effects of salbutamol administered orally to patients with cystic fibrosis

1. To test whether cystic fibrosis (CF) altered the kinetics and dynamics of oral salbutamol, 11 patients with CF (19-33 years old; five females; FEV1: 37 +/- 12% of predicted value) and 10 healthy volunteers (20-41 years old; five females; FEV1: 99 +/- 14% of predicted value) received orally 4 mg salbutamol. 2. The estimated pharmacokinetic parameters of salbutamol in patients with CF were identical to those in healthy subjects. For instance, peak plasma concentrations of salbutamol were 10.5 +/- 2.6 (mean +/- s.d.) and 10.2 +/- 2.9 ng ml-1 (NS), and the area under salbutamol plasma concentrations as a function of time (AUC (0, 7 h)) was 43.0 +/- 9.3 ng ml-1 h and 43.3 +/- 12.7 ng ml-1 h (NS) in CF patients and in healthy subjects, respectively. Since on a mg kg-1 dose basis, CF patients received a dose 28% greater than healthy subjects, this lack of differences implies a decrease in the amount of salbutamol absorbed, or alternatively, an increase in both clearance and volume of distribution of salbutamol. 3. Salbutamol did not elicit bronchodilation in CF patients, but increased heart rate from 77 +/- 2 to 103 +/- 3 beats min-1 (P < 0.05). 4. Salbutamol decreased plasma potassium concentrations from 4.5 +/- 0.1 to 3.8 +/- 0.1 mmol l-1 in the CF group (P < 0.05) and from 4.1 +/- 0.2 to 3.4 +/- 0.1 mmol l-1 in the controls (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma atrial natriuretic peptide during spontaneous bronchoconstriction in asthmatics

The aim of this work was to establish the role of endogeneous ANP during a spontaneous asthma attack. Forced expiratory lung volume in 1 s (FEV1), cardiovascular parameters, and plasma ANP, cAMP, and cGMP were measured for 60 min before and 10 min after treatment with a bronchodilator in 10 asthmatics. The results show that in the presence of moderate bronchoconstriction, FEV1 was 54 +/- 3% (+/-SE); ANP levels initially were slightly elevated at 47 +/- 10 pg/ml and decreased to 26 +/- 3 pg/ml (p < 0.05) over 60 min, with no change in FEV1. Following salbutamol inhalation, FEV1 increased to 77 +/- 4% with no change in ANP. We conclude that endogenous ANP does not act as a bronchodilator in asthmatics with moderate bronchospasm.

Effect of intravenous atrial natriuretic peptide on gas exchange in humans

The aim of this work was to establish whether a physiological increase in atrial natriuretic peptide (ANP) plasma levels affects pulmonary gas exchange in humans. Ten volunteers received an infusion of either ANP (4 pmol.kg-1.min-1) or physiological saline, for 60 min. Baseline measures of the alveolar-arterial PO2 difference and of the physiological dead space were within normal limits and remained stable during and after the infusion of ANP or saline, although plasma ANP and cGMP rose significantly (p < 0.01) (mean +/- SEM: ANP: 13.4 +/- 3.9 to 56.0 +/- 10.4 pmol/l; cyclic GMP: 3.8 +/- 0.3 to 17.0 +/- 3.8 nmol/l). We conclude that a physiological increase in plasma ANP does not affect pulmonary gas exchange significantly in humans.

Effect of atrial natriuretic peptide on bronchial tone in anesthetized rabbits

The effect of atrial natriuretic peptide (ANP) on histamine-induced bronchoconstriction was studied in vivo (in normoxic and in hypoxic rabbits) and in vitro. Thirty-two anesthetized rabbits, spontaneously breathing room air or 10% O2, received infusions of ANP (20, 40, or 80 ng/min/kg normoxia; 20 ng/min/kg hypoxia) or the vehicle for 100 min. After 75 min of ANP infusion, bronchoconstriction was induced inhaling histamine; respiratory resistance (Rrs) was measured prior to and until 20 min posthistamine. The results show that the histamine-induced increase in Rrs was significantly reduced by ANP 80 ng/kg/min in normoxia, and by ANP 20 ng/kg/min in hypoxia. In vitro, ANP had no effect on tracheal and bronchial smooth muscle precontracted with histamine or acetylcholine. These results show that ANP can decrease a histamine-induced bronchoconstriction in vivo but not in vitro, suggesting an indirect mechanism of action.

Muscarinic effect of atrial natriuretic peptide on rabbit airways

1. The aim of the present work was to investigate under which circumstances atrial natriuretic peptide (ANP) modulates airway resistance. 2. Of the six groups of rabbits (n = 5) studied, three received an infusion of ANP (80 ng min-1 kg-1 i.v.) for a period of 100 min, while the other three were infused with the vehicle. Before receiving the infusion of ANP or the vehicle, the animals were pretreated with atropine (0.5 mg kg-1 i.v.), propranolol (2 mg kg-1 i.v.) or not pretreated. After 75 min of infusion of ANP, bronchoconstriction was induced by inhalation of histamine. Respiratory resistance (Rrs) was measured before and 3, 5, 10, 15 and 20 min post-histamine challenge. 3. Following 75 min of ANP infusion, plasma ANP concentration increased from 153 +/- 52 (mean +/- s.e.mean) to 1441 +/- 203 pg ml-1 (P < 0.05) without affecting baseline Rrs. Control Rrs values (12.5-20.4 cmH2O l-1 s) were significantly increased following the inhalation of histamine (P < 0.001). By themselves, atropine, propranolol or ANP did not modify the histamine-induced increase in Rrs. However, when the animals were pretreated with atropine, ANP infusion significantly reduced the increase in Rrs induced by histamine (30 +/- 2 vs 51 +/- 6 cmH2O l-1 s; P < 0.05). 4. These data suggest that ANP has an indirect modulating effect on the airway smooth muscle and will decrease Rrs when muscarinic receptors are blocked.

Effect of salbutamol on gastroesophageal reflux in healthy volunteers and patients with asthma

The aim of this work was to establish whether beta-adrenergic agonists promote or increase gastroesophageal reflux in patients with asthma. Ten healthy individuals and eight patients with asthma were studied on 2 different days. One day they received a placebo, and the other day they received 4 mg of salbutamol by mouth. Complete measurements of esophageal manometry were performed before and every 30 minutes for 210 minutes after the administration of the drugs. Esophageal pH was measured continuously for the duration of the experiment. The results demonstrate that (1) salbutamol had no effect on the lower esophageal sphincter pressure gradient, the peak esophageal contraction pressure, or the number and duration of reflux episodes in patients with asthma and normal individuals, and (2) patients with asthma have a resting lower esophageal sphincter pressure higher than healthy subjects. We conclude that the administration of salbutamol does not affect esophageal function.

Release of atrial natriuretic factor (ANF) induced by acute airway obstruction

The aim of this study was to measure the effects of an increase in negative intrathoracic pressure on the release of ANF. With the subjects seated comfortably, 3 control blood samples were obtained over 30 minutes. Eight subjects then breathed for 30 min. through an inspiratory resistance in such a way that maximal inspiratory pleural pressures were between -30 to -40 cmH2O. Three blood samples were withdrawn after 20, 25, and 30 min., with the subject still breathing against the artificial resistance. Plasma concentrations of ANF were analysed by RIA. They measured: control value 24.6 +/- 3.7 pg ANF/mL (X +/- SE); with resistance 37.1 +/- 8.1 pg/mL (p less than or equal to .05). These results suggest that ANF could be released during an asthma attack.

Reflex decrease of histamine-induced bronchoconstriction after laryngeal stimulation in asthmatic patients

The aim of this work was to determine if the nonadrenergic noncholinergic nervous system can be reflexly activated in asthmatic patients by stimulating the vocal cords. The stimulation was produced by a cytology brush passed through a bronchoscope previously introduced transnasally and positioned just above the epiglottis. The subjects were premedicated with cholinergic blockers, and bronchoconstriction was induced by inhalation of histamine. In 11 experiments performed on six patients, vocal cords stimulation resulted in a decreased RL from 8.4 +/- 1.0 to 6.3 +/- 0.8 cm H2O.L-1.s (mean +/- SE) (p less than 0.01). To assess the possible contribution of circulating catecholamines to this decrease, plasma epinephrine and norepinephrine levels were measured in six experiments, before and 30 s, 1, 3, and 5 min after the stimulation. Pulmonary resistance fell from 10.0 +/- 1.3 to 7.6 +/- 0.9 cm H2O.L-1.s (mean +/- SE) (p less than 0.05) 30 s and to 7.9 +/- 0.9 cm H2O.L-1.s (p less than 0.05) 60 s after stimulation. Epinephrine and norepinephrine levels increased slightly but not significantly throughout the experiment. We conclude that in asthmatic patients, as in normal subjects, stimulation of the vocal cords produces a reflex decrease in histamine-induced bronchoconstriction which is modulated by the nonadrenergic noncholinergic nervous system.

Sampling technique and rheology of human tracheobronchial mucus

The aims of this work were: (1) to establish a technique for the sampling of human tracheobronchial mucus not contaminated by saliva or topical anesthesia, and (2) to measure its viscoelastic properties. After local anesthesia of the hypopharynx by topical application of 4% xylocaine, a double-sleeve microbiology specimen brush was introduced into a flexible bronchoscope placed in the trachea. The brush was left in direct contact with the bronchial mucosa for 20 to 30 s to allow mucus to collect on it. The mucus sample was then scraped from the brush and immediately covered with paraffin oil. Its viscoelastic properties were determined by the magnetic microrheometer technique. Excluding the time to anesthetize, the whole procedure took less than 1 min (thus minimizing the effect of cough) and resulted in sufficient mucus for rheologic analysis in approximately 90% of trials, i.e., 2.1 +/- 1.5 (SD) mg. Mucus specimens were collected from 20 fasting healthy nonsmoking subjects; 17 of them returned for a second collection several days later. Values for mucus mechanical impedance (vector sum of elasticity and viscosity) at 1 rad/s were: Control 1, 141 +/- 41 (SE); Control 2, 155 +/- 58 dyn/cm2. There was a large variation in mucus viscoelasticity, both between subjects (CV, 130%) and within the same subject (CV, 55%) on different days. In 7 subjects, mucus samples were collected 15 min after intravenous injection of 0.6 mg atropine. Viscoelasticity in these samples was 708 +/- 147 dyn/cm2, a value significantly different from Control 1 (p less than 0.05) and Control 2 (p less than 0.05) values.(ABSTRACT TRUNCATED AT 250 WORDS)

Reflex decrease of histamine-induced bronchoconstriction after laryngeal stimulation in humans

The aim of this work was to determine whether the nonadrenergic, noncholinergic, inhibitory nervous system can be reflexly activated in humans by laryngeal stimulation. The stimulation was achieved with a cytology brush passed through a bronchoscope previously introduced transnasally and positioned just above the epiglottis. In one series of experiments, subjects were premedicated with beta-adrenergic and cholinergic blockers, and bronchoconstriction was induced by histamine inhalation. The results showed that mechanical irritation of the vocal cords with the cytology brush produced a sharp, short-lasting (less than 1 min) decrease in RL from (mean +/- SE) 6.8 +/- 2.1 to 4.8 +/- 1.5 cm H2O.L-1.s, and in the absence of parasympathetic blockade, laryngeal irritation produced a fall in RL from (mean +/- SE) 9.0 +/- 3.7 to 5.4 +/- 2.0 cm H2O.L-1.s (p less than 0.0001) (ANOVA). This decrease in RL was independent of the slight cough produced by laryngeal stimulation and reflects a change in lower and not upper airway resistance. Adequacy of the beta-adrenergic and cholinergic blockade was checked with an intravenous infusion of isoproterenol and inhaled methacholine, respectively. In 2 subjects, the fall in RL was abolished by a block of the superior laryngeal nerves and direct local anesthesia of the vocal cords. We conclude that mechanical irritation of the larynx produces a partial reversal of histamine-induced bronchoconstriction that is mediated through nervous pathways that are neither beta-adrenergic nor cholinergic in origin. We suggest that this decrease in bronchoconstriction is modulated by the nonadrenergic, noncholinergic, inhibitory nervous system.

Prolonged hyporesponsiveness of airway smooth muscle to histamine following general anesthesia

The prolonged effect of barbiturates and inhalation anesthesia on airway response to histamine was studied in five groups of dogs. Group B (n = 10), H24 (n = 5), and H72 (n = 5) were anesthetized with sodium thiamylal (B) or halothane and N2O (H24, H72) for 3 h, during which a dose-response curve to histamine was obtained. The animals were then allowed to recover; 24 h (B and H24) or 72 h later, the animals were killed and an in vitro dose-response curve to histamine was obtained on a tracheal smooth muscle (TSM) specimen. Group C (n = 5), the control group, had no prolonged exposure to anesthesia. The dogs were immediately killed and the in vitro histamine response of the TSM was measured. The results (mean +/- SE) showed that the smooth muscle contractile properties (i.e., the maximum contraction to electrical field stimulation) were comparable in all four groups: 111 +/- 12 g (B); 168 +/- 23 g (H24); 106 +/- 32 g (H72); and 107 +/- 31 g (C). The maximum response (mean +/- SE) to histamine (as % of maximum electrical contraction) was: 15 +/- 6% (B), 30 +/- 9% (H24), 32 +/- 12% (H72), and 50 +/- 8% (C). Statistical analysis of the data showed that the histamine response of Group B and Group H24 was significantly decreased compared to Group C (P less than 0.01 and less than 0.05, respectively); in Group H72 the results were not significantly different from Group C (0.1 greater than P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of dopamine on tracheal smooth muscle

Dose-response curves to dopamine were obtained on guinea-pig, dog and human tracheal smooth muscle. Dopamine produced a relaxation of the guinea-pig tracheal chain, and this relaxation was completely blocked by propranolol. The potency of dopamine as a beta-agonist was 1/10 000 that of isoprenaline, 1/250 that of adrenaline and 1/50 that of noradrenaline. In human and dog tracheal smooth muscle, dopamine induced a contraction which could be entirely abolished by alpha-adrenoceptor antagonists. As an alpha-agonist, the potency of dopamine was 1/20 that of adrenaline and noradrenaline. Our data also show that a dopamine induced contraction is greatly potentiated if the smooth muscle specimen has been previously slightly contracted with histamine. We conclude that there are few, if any, specific dopaminergic receptors in the airways. Dopamine acts on both alpha- and beta-adrenoceptors, but in humans and dogs, its effect is predominantly on alpha-adrenoceptors.

Dopamine effect on bronchomotor tone in vivo

The effect of increasing doses of dopamine (inhaled or infused) on pulmonary resistance (RL) was measured in 4 normal and in 4 asthmatic subjects. Dopamine, in doses sufficient to raise systolic blood pressure 25 mmHg, did not change RL. However, dopamine, inhaled and infused, significantly decreased histamine-induced bronchoconstriction both in normal and in asthmatic subjects. Thus, we conclude that if dopamine is released by the adrenal medulla during an asthmatic attack, it should have a beneficial rather than a deleterious effect.

Comparison of steady state pulmonary diffusing capacity estimates for O2 and CO in dogs

In view of the fact that the inhomogeneity effects on pulmonary diffusing capacity (DL) estimates are quite different for O2 and for CO, simultaneous determinations of steady-state DLCO and DLO2 were attempted and compared. To this end, pulmonary gas exchange was measured in 17 anesthetized and artificially ventilated dogs, in hypoxia with and without carbon monoxide in inspired gas (FIO2 = 0.12, FICO = 0.0009 to 0.0016). The diffusing capacity estimates were computed by two conventional procedures, the first (Dapp) taking into account the mean alveolar partial pressures and the second (DVDA) the ideal alveolar partial pressures. It was found that the presence of COHb in blood, inevitable in the steady-state DLCO procedure, leads to a marked underestimation of DLO2; therefore DLCO values could only be adequately compared to DLO2 values obtained in the absence of CO from inspired gas. These DLO2 were 18.5 and 33.4 mumol . min-1 . Torr-1 . kg-1 for the mean DappO2 and DVDAO2, respectively, whereas the DLCO values obtained after 15 to 25 min CO inspiration were 30.0 and 83.4 mumol . min-1 . Torr-1 . kg-1 for the mean DappCO and the mean DVDACO, respectively. The salient feature is that with both procedures the mean value of DLCO estimate is higher than the corresponding DLO2 estimate. This finding suggests that in anesthetized, artificially ventilated dogs DappO2 and DVDACO estimates obtained by steady-state procedures in hypoxia are largely influenced by inhomogeneity effects and of limited value for assessment of the diffusing properties of the lung. DappCO and DVDAO2 are also affected by inhomogeneities but to a lesser degree.

The pathophysiology of asthma

Because postmortem studies of humans provide little information on the initial pathophysiologic events in asthma, animal models have been developed. Recently the Ascaris-allergic rhesus monkey has provided an opportunity to examine the onset of pathophysiologic changes following challenge and to correlate them with airway structure. These studies have suggested that the initial interaction between antigen and mast cells may occur in the bronchial lumen or in the epithelium superficial to the tight junctions, where a small but significant percentage of airway mast cells exist. It also appears that this initial antigen-antibody interaction results in the release of mediators that both stimulate the rapidly adapting stretch receptors in the mucosa and alter the mucosal barrier so that proteins of large molecular weight can penetrate. The fact that antigen challenge results in hyperresponsiveness to a subsequent dose of inhaled histamine and increased systemic absorption of histamine suggests that the airway hyperresponsiveness could be related to increased penetration of histamine into the bronchial wall. These observations suggest that the initial event in an acute asthmatic attack is the release of mediators from superficial mast cells, and that this amplifies the allergic response by altering the mucosal permeability so that more antigen reaches the submucosal mast cells. This altered permeability may also help explain the hyperreactivity of the airways to nonspecific airway stimulants in persons with asthma.

Airway sensitivity to slow-reacting substance of anaphylaxis, histamine, and antigen in Ascaris sensitive monkeys

The effects of Ascaris suum antigen, histamine, and slow-reacting substance of anaphylaxis (SRS-A) on the respiratory system were compared in 3 anesthetized rhesus monkeys. The agents were administered by instillation into the trachea, and the animals were studied in a volume displacement body plethysmograph. Two of the animals showed skin and bronchial sensitivity to Ascaris suum antigen and responded to it with increased pulmonary resistance and decreased dynamic compliance. A similar response was seen in all 3 animals after instillation of histamine, but SRS-A at 2 concentrations produced a predominant effect of decreased dynamic compliance with lesser alterations in pulmonary resistance. The effects of SRS-A were slow in onset and prolonged, as compared to the abrupt and short-lived effects of Ascaris suum antigen and histamine. The predominant effect of SRS-A on dynamic compliance suggests a more peripheral site of action of this mediator. In 5 monkeys allergic to Ascaris, no SRS-A could be detected in the blood at one and 5 min after antigen challenge, using the bioassay techniques.

Pulmonary effects of acute and chronic antigen exposure of immunized guinea pigs

Subdivisions of lung volume and pressure-volume (PV) curves of the lung and chest wall were measured in guinea pigs immunized to ovalbumin before and after acute (group 1) and chronic (group 2) antigen exposure. The histopathology produced in chronically exposed animals was also assessed. Animals were anesthetized with pentobarbital sodium and studied in a pressure-sensitive body plethysmograph, using a fluid-filled esophageal catheter to measure transpulmonary pressure (PL). Functional residual capacity (FRC) was determined by the Boyle's law technique; total lung capacity (TLC) was defined as the lung volume at a PL of 30 cmH20, and residual volume (RV) was defined as the lung volume at a transrespiratory pressure of -50 cmH2O. Acute antigen challenge of group 1 animals resulted in a decrease in TLC (22%), and increases in FRC (20%) and RV (110%), suggesting combined bronchoconstriction and alveolar duct constriction. Chronic antigen exposure of group 2 animals resulted in minimal changes in subdivisions of lung volume and PV curves, and produced a histological lesion resembling allergic alveolitis rather than asthma.

The number and distribution of mast cells in monkey lungs

We estimated the number of mast cells in monkey lungs by both quantitative histologic examination and measurement of total lung histamine, and showed that monkey lungs contain between 10(7) and 10(8) mast cells, with approximately 83% of these being located in conducting airways, and 17% in the parenchyma. The number of mast cells found in each airway generation increased from approximately 60,000 in the trachea to 8 million in the terminal bronchioles. In airways from different generations the number of mast cells superficial to the basement membrane in the epithelium and lumen (EMC) was compared to the number of mast cells found in the submucosa between basement membrane and cartilage and to the number of those found outside the cartilage. The number of EMC varied between animals and ranged from 0-0.4% of the total number of mast cells in the trachea, to 0-27% of the total in the terminal bronchioles. On the average, EMC accounted for 12% of the total number of mast cells in conducting airways, where we calculate that there is approximately one EMC for every 100,000 epithelial cells. Eosinophils were distributed in close relation to mast cells in the mucosa and submucosa, but were rare outside the cartilage. We conclude that the number of mast cells increases from central to peripheral airways and that this may account for the marked peripheral airway response observed after antigen challenge.

Airway responses to histamine and methocholine in Ascaris suum-allergic rhesus monkeys

We performed dose-response curves to inhaled histamine (H) and methacholine (MC) in a group of eight rhesus monkeys, with and without natural allergy to Ascaris suum antigen (AA). The animals were anesthetized with pentobarbital sodium, 25 mg/kg im and studied in a volume-displacement body plethysmograph. The dose of H or MC producing a 50% increase in pulmonary resistance (RL) was used to determine sensitivity to these agents and the increase in RL at a given dose was employed as a measure of reactivity. Sensitivity and reactivity to H and MC were then compared with AA responsiveness. A wide range of responses was observed but allergic animals were not more sensitive or reactive to H or MC than nonallergic animals. In addition, we studied the changes in breathing pattern that occurred during the inhalation of AA, H, and MC in four AA-sensitive animals. AA and H produced rapid shallow breathing within 30 s of starting inhalation, but MC, despite causing an equal degree of bronchoconstriction, did not produce alterations in breathing pattern.

Static lung mechanics of intact and excised rhesus monkey lungs and lobes

Subdivisions of lung volume and pressure-volume (PV) curves of the lung and chest wall (CW) were measured in 12 rhesus monkeys (Macacca mulatta) under pentobarbital anesthesia. In addition, volumes and PV curves were obtained on the excised lungs and lobes of 12 cynomolgus monkeys (M. fasicularis). Boyle's law was used to determine functional residual capacity (FRC) in the intact animals and water displacement to determine minimal volume (MV) in the excised lungs. Total lung capacity (TLC = lung volume at a transpulmonary pressure of 30 cmH2O) was similar in vivo and in vitro (90 + 83 ml/kg) but residual volume (RV = volume at airway pressure of -50 cmH2O) and MV differed markedly (16.5 + 5.9 ml/kg). In the intact animals a very stiff CW appeared to determine RV, whereas airway closure determined MV in excised lungs. PV curves of upper and lower lobes were not different when expressed as %TLC but when expressed as milliliters of gas per gram of lung, the upper lobes contained significantly more gas per unit weight.

Effect of indomethacin and atropine in experimental asthma in conscious guinea pigs

Pulmonary mechanics were measured in unanesthetized guinea pigs sensitized to horseradish peroxidase (HRP) before and during two aerosolized challenges of this antigen. During the first challenge the pulmonary resistance increased in all animals. Prior to second challenge the animals received either atropine (0.2 mg/kg) or indomethacin (10 mg/kg) intraperitoneally. We found that during the second challenge the indomethacin group had an increase in pulmonary resistance slightly greater or similar to that during the first exposure to the antigen, while the animals treated with atropine had a significantly diminished response (P less than 0.05). In five guinea pigs sensitized to HRP but challenged with a nonspecific aerosal made up of rabbit albumin, we found that pulmonary resistance increased in some animals and that this increase could be partially blocked by atropine. These results show that indomethacin has no effect on this model of allergic airways disease. They also confirm the importance of the vagus nerves in allergic bronchoconstriction and in addition show that nonspecific hyperirritability can be induced in some animals by immunization.