Genetic factors in asthma severity

The development of asthma in an individual depends upon the interaction of genetic factors with the environment. Asthma is a polygenic disease and both genome screening and candidate gene strategies have identified a number of putative genes that may predispose to the development of asthma. However, there are few data regarding genes that may either dictate disease severity or chronicity and genes that dictate response to treatment. Analysing asthma as a categorical variable will fail to identify genes solely involved in determining disease severity, whereas studies designed to analyse asthma as a semiquantitative trait may identify these genes in addition to disease-initiating genes. However, identifying genes specifically involved in the determination of disease severity (e.g. in airway remodelling) will be ideally performed in cohorts of asthmatics specifically recruited and using appropriate end points. This review discusses methodological issues concerned with identifying disease-modifying genes in individuals with asthma, and summarizes the potential contribution of known candidate genes to the determination of disease severity.

Subsensitivity to bronchoprotection against adenosine monophosphate challenge following regular once-daily formoterol

Regular treatment with inhaled long-acting beta2-agonists leads to subsensitivity to their bronchoprotective effects, although the effect of dosing frequency on this subsensitivity is not known. The aim of this study was to assess whether a once-daily dosing regimen with formoterol might be associated with a lesser degree of subsensitivity. In a randomized placebo-controlled double-blind, double-dummy crossover study 10 asthmatics treated with inhaled steroids (mean age 31 yrs, forced expiratory volume in one second (FEV1) 82% predicted) received 1 week of treatment with: formoterol dry powder 24 microg twice daily (08:00 and 20:00 h); formoterol 24 microg once daily (20:00 h); or identical placebo. Adenosine monophosphate (AMP) bronchial challenge was performed 12 h after the first and the last dose of each treatment. There was significant loss of protection with formoterol twice daily between the first and last dose (geometric mean provocative concentration causing a 20% fall in FEV1 (PC20)): 475 versus 129 mg x mL(-1) (a 3.7-fold loss, p=0.006) and with formoterol once daily: 367 versus 127 mg x mL(-1) (a 2.9-fold loss, p=0.005), compared with placebo: 71 versus 75 mg x ml(-1) (nonsignificant). There was no significant difference in the degree of loss of protection between formoterol once and twice daily. For first-dose protection there was a significant difference between active treatments and placebo, but after the last dose the residual protection between active treatments and placebo was not significant. Thus, in patients taking inhaled corticosteroids, regular formoterol 24 micreog once daily induces a similar degree of subsensitivity to adenosine monophosphate bronchial challenge as with formoterol 24 microg twice daily. This in turn suggests that even with a 24-h dosing interval there is the development of tolerance to formoterol by prolonged occupancy of airway beta2-adrenoceptors.

Regulation of proliferation of human colonic subepithelial myofibroblasts by mediators important in intestinal inflammation

An increase in myofibroblast number may be necessary for wound healing but may also lead to postinflammatory scarring. We have, therefore, studied the role of mediators important in inflammatory bowel disease in regulating proliferation of human colonic myofibroblasts. Using primary cultures of these cells, we have shown increases in [3H]thymidine incorporation in response to platelet-derived growth factor (EC50 = 14 ng/ml), basic fibroblast growth factor (EC50 = 2.2 ng/ml), and epidermal growth factor (EC50 = 1.1 ng/ml). Coulter counting of cell suspensions demonstrated increases in cell number with these growth factors along with insulin-like growth factor-I and -II. In addition the proinflammatory cytokines IL-1beta and TNF-alpha produced increases in [3H]thymidine incorporation. IL-1beta and platelet-derived growth factor together produced an increase in [3H]thymidine greater than either agonist alone; this effect was not, however, seen when we examined changes in cell numbers. Finally, we demonstrate a mechanism whereby these responses may be downregulated: vasoactive intestinal peptide (1 microM) elevates cyclic AwMP in these cells 4. 2-fold over control and produces a dose-related inhibition of platelet-derived growth factor-driven proliferation with a maximum inhibition of 33% at 1 microM.

Carbachol-induced actin reorganization involves Gi activation of Rho in human airway smooth muscle cells

To determine whether M2 muscarinic receptors are linked to the monomeric G protein Rho, we studied the effect of carbachol on actin reorganization (stress fiber formation) in cultured human airway smooth muscle cells that expressed mainly M2 muscarinic receptors by dual-fluorescence labeling of filamentous (F) and monomeric (G) actin. F-actin was labeled with FITC-labeled phalloidin, and G-actin was labeled with Texas Red-labeled DNase I. Carbachol stimulation induced stress fiber formation (increased F-actin staining) in the cells and increased the F- to G-actin ratio 3.6 +/- 0.4-fold (mean +/- SE; n = 5 experiments). Preincubation with pertussis toxin, Clostridium C3 exoenzyme, or tyrosine kinase inhibitors reduced the carbachol-induced increase in stress fiber formation and significantly decreased the F- to G-actin ratio, whereas a mitogen-activated protein kinase inhibitor, a phosphatidylinositol 3-kinase inhibitor, and a protein kinase C inhibitor were without effect. This study demonstrates that in cultured human airway smooth muscle cells, muscarinic-receptor activation induces stress fiber formation via a pathway involving a pertussis-sensitive G protein, Rho proteins, and tyrosine phosphorylation.

Variations in the subunit content and catalytic activity of the cytochrome c oxidase complex from different tissues and different cardiac compartments

The composition and activity of cytochrome c oxidase (COX) was studied in mitochondria from rat liver, brain, kidney and heart and also in different compartments of the bovine heart to see whether any correlation exists between known oxidative capacity and COX activity. Immunoblot analysis showed that the levels of ubiquitously expressed subunits IV and Vb are about 8-12-fold lower in liver mitochondria as compared to the heart, kidney and brain. The heart enzyme with higher abundance of COX IV and Vb showed lower turnover number (495) while the liver enzyme with lower abundance of these subunits exhibited higher turnover number of 750. In support of the immunoblot results, immunohistochemical analysis of heart and kidney tissue sections showed an intense staining with the COX Vb antibody as compared to the liver sections. COX Vb antibody stained certain tubular regions of the kidney more intensely than the other regions suggesting region specific variation in the subunit level. Bovine heart compartments showed variation in subunit levels and also differed in the kinetic parameters of COX. The right atrium contained relatively more Vb protein, while the left ventricle contained higher level of subunit VIa. COX from both the ventricles showed high Km for cytochrome c (23-37 microM) as compared to the atrial COX (Km 8-15 microM). These results suggest a correlation between tissue specific oxidative capacity/work load and changes in subunit composition and associated changes in the activity of COX complex. More important, our results suggest variations based on the oxidative load of cell types within a tissue.

Beta2-adrenoceptor polymorphisms are in linkage disequilibrium, but are not associated with asthma in an adult population

OBJECTIVE

To determine the association between the beta2-adrenoceptor polymorphisms at amino acids 16 and 27 and markers of allergic disease and asthma per se in a random adult population, and to determine the degree of linkage disequilibrium existing between polymorphisms at amino acid positions 16, 27, 164 and nucleic acid residue 523.

METHODS

We measured serum IgE, skin-prick test positivity, atopy, bronchial hyperreactivity, wheeze and asthma (self-reported and doctor-diagnosed), and determined beta2-adrenoceptor genotype by allele specific oligonucleotide hybridization, in 630 adults aged between 18 and 70, selected from the electoral role in a local health authority in Nottingham.

RESULTS

Homozygotes for the Glycine 16 polymorphism had a significantly higher incidence of atopy (chi2=6.44 (Pearson's), P=0.04). We also observed a significant association between the Glycine 16 allele and atopy (chi2=4.13 (Pearson's), P=0.04), when we assumed the Glycine 16 allele to operate in a dominant mode. No other significant associations between beta2-adrenoceptor polymorphisms and markers of allergic disease and asthma per se were observed. Marked linkage disequilibrium exists between the beta2-adrenoceptor polymorphisms at amino acid 16 and 27 (D=0.38, chi2 P<0.0001), and between the beta2-adrenoceptor polymorphisms at amino acid 27 and nucleic acid residue 523 (C-A) (D=0.36, chi2 P<0.0001).

CONCLUSION

There is no consistent association between beta2-adrenoceptor polymorphisms and the risk of developing allergic disease or asthma per se in this adult sample. Marked linkage disequilibrium exists between the amino acid 16 and 27 polymorphisms, and also between the amino acid 27 polymorphism and the nucleic acid residue 523 (C-A) polymorphism. This polymorphism accounts for the Ban 1 RFLP previously described at the beta2-adrenoceptor locus on chromosome 5q 31.

Beta2-adrenoceptor regulation and bronchodilator sensitivity after regular treatment with formoterol in subjects with stable asthma

OBJECTIVE

We have previously found that beta2-adrenoceptor downregulation and bronchodilator desensitization to albuterol occurred at 36 hours after stopping regular treatment with twice daily salmeterol. In this study we have evaluated these same effects with formoterol given once or twice daily on a regular basis.

METHODS

In a randomized, placebo-controlled, double-blind, double-dummy crossover study, 16 subjects with mild-to-moderate stable asthma (mean [SD] age, 32.5 [15.3] years; mean [SD] FEV1, 73.2 [12.1] percent predicted) receiving regular inhaled corticosteroid therapy received 1 week of treatment with formoterol dry powder (24 microg twice daily [8 AM/8 PM]), formoterol (24 microg once daily [8 PM]), or identical placebo. Lymphocyte beta2-adrenoceptor parameters and a dose-response curve to inhaled albuterol (200 to 1600 microg) were evaluated at 36 hours after the last dose of each treatment period.

RESULTS

There were no significant differences in the mean values for albuterol dose-response effects among the three treatment regimens. Comparison of maximal bronchodilator responses between treatments (mean and SEM as change from baseline) revealed no significant differences between treatments for FEV1 (0.47 L [0.06 L] for placebo vs 0.48 L [0.07 L] for 24 microg once daily formoterol vs 0.51 L [0.08 L] for 24 microg twice daily formoterol) or for forced expiratory flow, mid-expiratory phase (FEF25-75) (0.80 L/sec [0.12 L/sec] for placebo vs 0.80 L/sec [0.16 L/sec] for 24 microg once daily formoterol vs 0.89 L/sec [0.14 L/sec] for 24 microg twice daily formoterol). Formoterol also had no significant effect on mean lymphocyte beta2-adrenoceptor density. However, in five of seven patients with the homozygous Gly-16 polymorphism, beta2-adrenoceptor density was downregulated by twice daily formoterol, whereas only two such cases exhibited a reduction in maximal FEV1 response to albuterol.

CONCLUSIONS

The results of this study showed that for patients taking inhaled corticosteroids, overall beta2-adrenoceptor regulation and associated bronchodilator sensitivity to inhaled albuterol were unaltered at 36 hours after stopping regular treatment with formoterol. However, in a subset of patients who were Gly-16 homozygous, there was a tendency towards downregulation but not desensitization. Further studies in subjects with more severe asthma are required to assess the clinical relevance of these findings.

Improving communication between hospital and primary care increases follow-up rates for asthmatic patients following casualty attendance

Despite adequate access to primary care facilities, there is a group of patients who habitually present to hospital accident and emergency (A&E) departments when their asthma deteriorates. In Nottingham 50% of these patients are discharged from the A&E department without admission to hospital and are advised to inform and see their general practitioner (GP), but many fail to do so. We instituted a system of identifying all patients seen and discharged from our A&E department with asthma and informing their GPs and practice nurses within one working day of the event by fax. To determine whether any action had been taken following receipt of our fax, we contacted each general practice 1 month after the A&E attendance in 100 consecutive cases. Full data were available for 66 patients. Our faxes increased the notification of A&E attendances to GPs from 47 to 89%. This resulted in an increase in the number of follow-up appointments initiated by the practice, from 15 to 31. However, 29% of patients were not asked to attend for follow-up, in spite of the practice being aware of a recent A&E visit. Improving communication between hospital and general practice increases the rate of follow-up by GPs for patients with asthma who have been discharged from A&E. This has the potential to improve asthma management for this group of patients.

Association between beta 2-adrenoceptor polymorphism and susceptibility to bronchodilator desensitisation in moderately severe stable asthmatics

BACKGROUND

In-vitro studies have suggested that polymorphisms of the beta 2-adrenoceptor may influence the desensitisation induced by beta 2-agonists. We investigated the influence of beta 2-AR polymorphism on the development of bronchodilator desensitisation in asthma patients.

METHODS

We carried out an analysis of 22 moderately severe stable asthmatics, mean age 38 years, FEV1 63% of predicted and FEF25-75 38% of predicted, who received a median inhaled corticosteroid dose of 1000 micrograms/day. Patients were randomly assigned inhaled placebo or inhaled formoterol 24 micrograms bid for 4 weeks each in a crossover study. Bronchodilator dose-response curves were made at the end of each treatment period by use of cumulative doses of formoterol (6-108 micrograms) with FEV1 and FEF25-75 measured 30 min after each dose, and up to 6 h after the last dose. We calculated the degree of bronchodilator desensitisation by comparing the dose-response (for maximum and 6 h) after placebo with that after formoterol, and expressed this degree as a percentage of placebo response. Patients were divided into groups according to genotype at codon 16: homozygous Arg 16 (n = 4), heterozygous Arg 16/Gly 16 (n = 8), and homozygous Gly 16 (n = 10). At codon 27: homozygous Gln 27 (n = 5), heterozygous Gln 27/Glu 27 (n = 11), and homozygous Glu 27 (n = 6).

FINDINGS

We found a significantly (p < 0.05) greater degree of bronchodilator desensitisation with homozygous Gly 16 than with homozygous Arg 16 for maximal FEV1 response: -8% (Arg 16) vs 46% (Gly 16); and for maximal FEF25-75 response: -32% (Arg 16) vs 74% (Gly 16; 95% CI 15-92% and 49-164%, respectively). Bronchodilator responses at 6 h were also significantly (p < 0.05) different for FEV1 and FEF25-75 when Arg 16 and Gly 16 were compared and values for heterozygous Arg 16/Gly 16 were intermediate. There was significantly greater desensitisation with Glu 27 than with Gln 27 for maximal FEF25-75 response: -7% (Gln 27) vs 68% (Glu 27), p = 0.05; and for 6 h FEF25-75 response: 43% (Gln 27) vs 93% (Glu 27), p < 0.05 (95% CI 2-147% and 5-94%, respectively). All patients who were homozygous Glu 27 were also homozygous Gly 16.

INTERPRETATION

We have found preliminary evidence that beta 2-adrenoceptor polymorphism is associated with altered beta 2-adrenoceptor expression in asthma patients. The homozygous Gly-16 form was significantly more prone to bronchodilator desensitisation than Arg 16, with the influence of Gly 16 dominating over any putative protective effects of Glu 27.

The glutamine 27 beta2-adrenoceptor polymorphism is associated with elevated IgE levels in asthmatic families

BACKGROUND

The beta2-adrenoceptor polymorphisms occurring at amino acid positions 16 (arginine to glycine) and 27 (glutamine to glutamate) are known to be functionally relevant and also disease-modifying in subjects with asthma. However, the contribution of these polymorphisms to the development of the asthmatic phenotype or other markers for allergic disease remains to be established.

OBJECTIVE

This large family study examines the contributions of these polymorphisms in determining the heritable component of markers for allergic disease in asthmatic families.

METHODS

Three hundred twenty-four individuals from 60 families multiplex for asthma selected by means of an asthmatic proband were characterized for the following markers of allergic disease: asthma, atopy, and serum IgE. The polymerase chain reaction was used to generate a 234 base pair fragment spanning the region of interest, and the beta2-adrenoceptor polymorphism was then defined by allele-specific oligonucleotide hybridization. Segregation analysis was then performed.

RESULTS

We found a significant association (p = 0.009) between the glutamine 27 beta2-adrenoceptor polymorphism and elevated levels of IgE, which was supported by the observation of linkage between IgE and beta2-adrenoceptor polymorphisms at locus 27 (p = 0.037). However, there was no association between either the arginine-glycine 16 or the glutamine-glutamate 27 beta2-adrenoceptor polymorphism and an increased risk of asthma or atopy per se.

CONCLUSION

The glutamine 27 beta2-adrenoceptor polymorphism appears to contribute to IgE variability in families with asthma. However, it seems that although both amino acid 16 and 27 beta2-adrenoceptor polymorphisms are disease-modifying in subjects with asthma, they do not contribute markedly to the development of the asthmatic phenotype.

Systemic corticosteriod rapidly reverses bronchodilator subsensitivity induced by formoterol in asthmatic patients

There is evidence that downregulation and desensitization of airway beta 2-adrenoceptors (beta 2-AR) develops after continuous exposure to long-acting beta 2-agonists such as formoterol and salmeterol. To investigate the facilitatory effects of acute administration of systemic corticosteroid on bronchodilator subsensitivity, as might occur in the setting of acute asthma, 12 subjects with moderately severe asthma, with a mean FEV1 of 66% predicted, of whom were all receiving inhaled corticosteriod, were randomized to receive either inhaled placebo (PL) or inhaled formoterol (FM) 24 micrograms twice daily for 4 wk in a double-blind crossover study. Subjects were also genotyped in terms of beta 2-Ar polymorphism at loci 16 and 27. A dose-response curve (DRC) and duration-time profile for FM (12 to 108 micrograms) was produced 1 h after administration of placebo tablets and after injection at 3 wk, and 1 h after administration of oral prednisolone, 50 mg, and intravenous hydrocortisone, 200 mg, at 4 wk. Comparisons between treatments were made with area-under-curve (AUC) measurements as the change from baseline. There was a significant rightward shift in the DRC after FM as opposed to placebo for delta FEV1 (as AUC, L.h): 2.51 versus 4.22 (95% CI: 0.54 to 2.89; p = 0.01) and delta FEF25-75 (as AUC, L x 10(3)): 11.30 versus 19.94 (95% CI: 2.12 to 15.12; p = 0.01). This was significantly reversed by steroid (S) for FEV1 (FM versus FM+5): 2.51 versus 3.57 (95% CI: 0.11 to 2.27; p = 0.03) and for FEF25-75: 11.30 versus 18.47 (95% CI: 2.52 to 11.70; p = 0.005). Lymphocyte beta 2-AR density (log Bmax; fmol/10(6) cells) showed significant upregulation 3 h after steroid (FM+5 versus FM): 0.34 versus 0.24 (95% CI: 0.02 to 0.18; p = 0.01). For heart-rate response (as AUC, beats), there was subsensitivity with FM versus PL: 2,700 versus 5,200 (95% CI: 40 to 5,000; p < 0.001), and this was reversed by steroid (FM+5 versus FM): 9,600 versus 2,700 (95% CI: 4,900 to 8,800; p < 0.001). This reversal by systemic corticosteroid appears to be generally independent of beta 2-AR polymorphism at loci 16 and 27. In conclusion, we have demonstrated that bronchodilator subsensitivity occurs after regular inhaled FM in asthmatic patients, and is rapidly reversed by systemic corticosteroid. Thus, in acute asthma, systemic corticosteroid should be administered a soon as possible, in order to restore normal airway beta 2-AR sensitivity, particularly in patients who are receiving regular long-acting beta 2-agonists.

Effect of IL-1 beta on responses of cultured human airway smooth muscle cells to bronchodilator agonists

Decreased beta-adrenergic responsiveness is a characteristic feature of asthma. In order to determine whether cytokines released in the asthmatic airway contribute to this phenomenon, we measured changes in stiffness of cultured human airway smooth muscle (HASM) cells induced by isoproterenol (ISO) in control HASM cells and HASM cells pretreated with IL-1 beta (20 ng/ml for approximately 42 h). Stiffness was measured by magnetic twisting cytometry. HASM cells were obtained from normal tracheal tissue obtained at lung transplant, and studied in passages 4-7. In control cells, ISO caused a dose-related decrease in cell stiffness. IL-1 beta had no effect on baseline cell stiffness. However, IL-1 beta caused a rightward shift in the concentration-response curve to ISO and decreased the maximal effectiveness of this agonist. Decreased responses to ISO were also obtained with 2 ng/ml IL-1 beta, or when cells were pretreated with IL-1 beta (20 ng/ml) for 22 h. This effect of IL-1 beta was not altered by pretreatment of the cells with pertussis toxin (100 ng/ml throughout the IL-1 beta exposure period). IL-1 beta also significantly attenuated the ability of prostaglandin E2 (PGE2) to decrease cell stiffness. In contrast, IL-1 beta had no effect on cell stiffness responses to dibutryl cAMP, a cell permeant analog of cAMP suggesting that the cytokine does not influence either the ability of cAMP to activate kinases, or the targets of these kinases which ultimately mediate cell relaxation. IL-1 beta (20 ng/ml for 40 h) caused a small (30%) but significant (P < 0.02) increase in basal cAMP, but also resulted in a 2-3-fold decrease in the changes in cAMP formation induced by either ISO or PGE2. In contrast, IL-1 beta had no effect on cAMP formation in response to forskolin, suggesting that IL-1 beta does not mediate its effects via changes in the expression or activity of adenylyl cyclase. Pretreatment with IL-1 beta had no significant effect on beta 2 adrenoceptor number assessed by [125I]-CYP binding in these cells, nor was there any significant effect of IL-1 beta on Gsa expression assessed by Western blot. In summary, our results indicate that IL-1 beta causes a concentration- and time-dependent decrease in responses of HASM cells to ISO and are consistent with the hypothesis that the effects of IL-1 beta are mediated by uncoupling of beta-receptors from Gs-induced activation of adenylyl cyclase.

The future of asthma

Reports in the media describing the discovery of "the asthma gene" or "a new vaccine for asthma" may be inaccurate and often raise patients' hopes unjustifiably. This article is a personal view of key areas in current asthma research, and it examines how they may impinge on the care of asthmatic patients in the next decade. I have tried to explain the thinking behind some of the approaches under study. I discuss the potential contributions of genetic studies, immunological approaches, and new therapeutic approaches.

Regulation of histamine H1 receptor coupling by dexamethasone in human cultured airway smooth muscle

1. The regulation of histamine-induced [3H]-inositol phosphate and intracellular calcium responses in human cultured airway smooth muscle cells was studied. 2. Histamine induced concentration-dependent [3H]-inositol phosphate formation (EC50 4 microM). This response was inhibited by a range of selective H1 receptor antagonists but not by the H2-selective antagonist, tiotidone or the H3 receptor-selective antagonist, thioperamide, indicating that an H1 receptor is involved in this response in human cultured airway smooth muscle cells. 3. Preincubation of human cultured airway smooth muscle cells with concentrations of dexamethasone > 10 nM for 22 h produced concentration-dependent inhibition of histamine-induced inositol phosphate formation. The maximum inhibition observed was 45% of the response in control cells. The inhibitory effect of dexamethasone was itself reversed by prior exposure to the glucocorticoid receptor antagonist, RU38486 (10 microM). Preincubation for 22 h with 1 microM dexamethasone produced inhibition of the inositol phosphate response to histamine to all concentrations of histamine inducing significant inositol phosphate formation in these cells. In contrast, the response to the G protein activator, NaF (0.1-20 mM) was unaltered by preincubation with dexamethasone. 4. Preincubation of human airway smooth muscle cells with 1 microM dexamethasone for time periods of < 6 h failed to inhibit histamine-induced inositol phosphate formation in human airway smooth muscle cells. 5. Histamine also induced concentration-dependent elevation of intracellular calcium levels in Fura 2-loaded human airway smooth muscle cells. This response was inhibited by preincubation with 1 microM dexamethasone. 6. We conclude that signal transduction through the H1 receptor in human airway smooth muscle is subject to regulation by dexamethasone and that this may in part account for the protective effect of dexamethasone against spasmogen-induced contractile responses in the airways.

Beta 2 adrenoceptor polymorphisms: are they clinically important?

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alpha-Thrombin increases cytosolic calcium and induces human airway smooth muscle cell proliferation

In a variety of diseases including asthma, inflammation causes microvascular leakage and activates thrombin. In addition to cleaving fibrinogen to fibrin, thrombin may have other important cellular effects. Because airway inflammation and vascular permeability are important determinants of airway hyperreactivity, we have studied the effects of thrombin on airway smooth muscle. Using cultured human airway smooth muscle cells, we have examined whether alpha-thrombin can evoke calcium responses, phosphoinositide turnover, or cell proliferation. We have demonstrated that alpha-thrombin does increase cytosolic calcium and phosphoinositide hydrolysis in a dose- and time-dependent manner that may be inhibited by pretreating cells with r-hirudin. In addition, we have shown that thrombin stimulates airway smooth muscle cell proliferation. By contrast, bradykinin, which evoked comparable increases in cytosolic calcium and phosphoinositide turnover, did not stimulate airway smooth muscle cell growth. We conclude that thrombin effectively increases cytosolic calcium and induces PI hydrolysis and, in addition, is capable of stimulating airway smooth muscle cell growth. However, the lack of an effect of bradykinin on cell growth suggests that increases in calcium and PI turnover alone will not induce airway smooth muscle cell proliferation. We suggest that alpha-thrombin may be important in the pathogenesis of both increased airway resistance as well as the structural changes seen as a consequence of chronic asthma.

Influence of beta 2-adrenergic receptor genotypes on signal transduction in human airway smooth muscle cells

The phenotypic relevance of allelic variation in the structure of the beta 2-adrenergic receptor (beta 2AR) expressed in lung cells is unknown. In particular, altered responsiveness of the beta 2AR expressed on airway smooth muscle, which are responsible for bronchodilation in the treatment of asthma, may be an important factor in the ultimate physiologic response to agonist. To approach this, we established primary cultures of human airway smooth muscle cells obtained at autopsy and developed a method to determine the beta 2AR genotype at the polymorphic loci of codons 16 and 27, using allele-specific polymerase chain reactions. Radioligand binding studies revealed that these cells expressed approximately 70 fmol/mg of receptor which was exclusively of the beta 2AR subtype. All cell lines obtained (n = 10) exhibited normal agonist binding and receptor-mediated activation of the adenylyl cyclase second messenger pathway. However, distinct differences were found in the response to long-term agonist exposure between the different beta 2AR genotypes. Cells expressing Arg at codon 16 (Arg16) traditionally referred to as wild-type, underwent 77.8 +/- 8.1% downregulations of beta 2AR following prolonged (24-h) exposure to the beta 2AR agonist isoproterenol (10 microM). In contrast, cells expressing Gly16 beta 2AR underwent enhanced agonist-promoted downregulation (95.6 +/- 1.7%, P < 0.05 versus Arg16), whereas cells expressing Glu27 beta 2AR were relatively resistant to such downregulation (29.5 +/- 12.7%, P < 0.01 versus Arg16). For cells expressing Glu27 beta 2AR, this difference resulted in a significant attenuation of agonist-promoted functional desensitization (33 +/- 7 versus 90 +/- 5% desensitization for Arg16, P < 0.001) following preincubation with 1 microM isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)

Association of Glu 27 beta 2-adrenoceptor polymorphism with lower airway reactivity in asthmatic subjects

Cells expressing the Glu 27 beta 2-adrenoceptor polymorphism show attenuated down-regulation of the receptor after long-term exposure to agonist. We studied beta 2-adrenoceptor genotype for the Gln/Glu 27 polymorphism and airway reactivity in 65 patients with mild to moderate asthma. Glu 27 homozygotes had a four-fold higher geometric mean methacholine PD20 (provocative dose) than individuals who were homozygous for the wild-type (Gln 27) form of the receptor; heterozygotes had an intermediate value (3.23, 0.86, 1.96 mumol, respectively). These data suggest that beta 2-adrenoceptor genotype is important in the establishment of the asthmatic phenotype.

Use of cultured airway myocytes for study of airway smooth muscle

Cultured airway smooth muscle cells provide a convenient model system for studying the regulation of a wide range of airway responses at the cellular level. This review describes the characteristics of cultured airway smooth muscle cells and differences that exist between cultured cells and acutely dissociated cells or muscle strips. Receptor and ion-channel expression and control of coupling in cultured airway smooth muscle are reviewed. The methodology for airway smooth muscle culture is discussed. The main advantage of using cultured airway smooth muscle cells is that studies can be performed to examine long-term control of cell responses. Studies of the regulation of receptor expression and coupling, desensitization of receptor or channel-mediated responses, or regulation of the expression of important enzymes or muscle proteins can be readily performed in cell culture. In addition, cultured airway myocytes provide a useful secondary screening system for the development of novel therapeutic agents targeted at airway receptors that are expressed upon these cells.

Agonist-induced desensitization of histamine H1 receptor-mediated inositol phospholipid hydrolysis in human umbilical vein endothelial cells

1. The regulation of histamine-induced [3H]-inositol phosphate formation was studied in human cultured umbilical vein endothelial cells (HUVEC). 2. Histamine (EC50 4.8 microM) produced a 12.7 fold increase in [3H]-inositol phosphate formation over basal levels. Prior exposure to 0.1 mM histamine (2 h) produced a 78% reduction in the response to subsequent histamine (0.1 mM) challenge. The IC50 for this histamine-induced desensitization was 0.9 microM. 3. The inositol phosphate response to histamine (0.1 mM) was inhibited by phorbol dibutyrate (IC50 40 nM; maximal reduction 64%). This effect was antagonized by both staurosporine (100 nM) and Ro 31-8220 (10 microM). However, the histamine-induced desensitization of the H1-receptor-mediated inositol phosphate response was insensitive to the protein kinase inhibitors, staurosporine, Ro 31-8220, K252a and KN62. 4. Prior exposure to sodium nitroprusside (100 microM), forskolin (10 microM) or dibutyryl cyclic AMP (1 mM) had no effect upon histamine-induced [3H]-inositol phosphate formation. 5. NaF (20 mM) and thrombin (EC50 0.4 u ml-1) also induced inositol phosphate formation in HUVEC. Histamine pretreatment (0.1 mM, 10-120 min) failed to modify the inositol phosphate response to a subsequent NaF or thrombin challenge. 6. We conclude that the desensitization of histamine H1-receptor-mediated [3H]-inositol phosphate formation occurs at the level of the receptor and involves a mechanism independent of activation of protein kinase A, G, or C, or calcium calmodulin-dependent protein kinase II.

Audit of a complete home nebulizer service provided by a respiratory nurse specialist

A retrospective audit was performed of a home nebulizer service managed entirely by a Respiratory Nurse Specialist (RNS). We examined (i) the role and workload of the RNS, (ii) the outcome of referrals to the service and (iii) the subsequent compliance with treatment of patients prescribed home nebulized bronchodilators. The case notes and RNS records of all patients referred for consideration of home nebulized bronchodilators over a 9-month period were reviewed. The nebulizer service encompassed patient assessment, trials of nebulized therapy, nebulizer tissue and patient registration and an exchange and servicing system. The non clerical aspects of the service took 9 h per week, 24% of total RNS time. A further 15 h weekly of clerical time was also required. Of 76 referrals, 57 (75%) patients had chronic airflow obstruction (CAO). In CAO patients, 41 had a trial of nebulized therapy and in 27 (66%) such therapy was considered beneficial. In the other 16 CAO patients the RNS deemed a trial inappropriate or impractical and 12 such patients were prescribed nebulized therapy. Overall, therefore 39/57 (68%) of CAO referrals were prescribed home nebulized therapy. At 3-6 months, seven (18%) patients were using their nebulizer infrequently or not at all, 25 (64%) one to four times daily, and seven (18%) four times daily. We conclude that a RNS can manage a complete nebulizer service, but at a considerable cost in professional time. Clerical assistance is essential if appropriate use is to be made of the skills of an RNS.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of high-dose salbutamol on cardiac rhythm in severe chronic airflow obstruction: a controlled study

Despite concern over possible adverse cardiac effects of high-dose beta-agonists there have been no controlled studies of the effects of such a therapy in patients with severe chronic airflow obstruction (CAO). We therefore studied 22 CAO patients (FEV < 1 litre) with continuous ambulatory cardiac monitoring. Patients received either nebulised salbutamol (5 mg) or saline each given 4 times daily for 24 h on 2 consecutive days, single blind, in random order. Supraventricular arrhythmias were common on both saline and salbutamol days (8 vs. 9 patients, p = NS), but none were clinically apparent. There were no episodes of ventricular tachycardia. Ventricular ectopic activity was highly variable but did not significantly differ between the two study days overall or between specific periods after nebulised salbutamol or saline. Serum potassium (mean) fell by 0.23 (SD 0.06) mmol/l in 10 patients after salbutamol. Baseline FEV1, PaO2, PCO2 were not predictive of arrhythmias or ectopic activity. While occasional adverse effects cannot be excluded, we conclude that high-dose salbutamol does not lead to any general increase in arrhythmogenic potential in severe CAO.

Beta-adrenergic agonists regulate KCa channels in airway smooth muscle by cAMP-dependent and -independent mechanisms

Stimulation of calcium-activated potassium (KCa) channels in airway smooth muscle cells by phosphorylation-dependent and membrane-delimited, G protein actions has been reported (Kume, H. A. Takai, H. Tokuno, and T. Tomita. 1989. Nature [Lond.]. 341:152-154; Kume, H., M. P. Graziano, and M. I. Kotlikoff. 1992. Proc. Natl. Acad. Sci. USA. 89:11051-11055). We show that beta-adrenergic receptor/channel coupling is not affected by inhibition of endogenous ATP, and that activation of KCa channels is stimulated by both alpha S and cAMP-dependent protein kinase (PKA). PKA stimulated channel activity in a dose-dependent fashion with an EC50 of 0.12 U/ml and maximum stimulation of 7.38 +/- 2.04-fold. Application of alpha S to patches near maximally stimulated by PKA significantly increased channel activity to 15.1 +/- 3.65-fold above baseline, providing further evidence for dual regulatory mechanisms and suggesting that the stimulatory actions are independent. Analysis of channel open-time kinetics indicated that isoproterenol and alpha S stimulation of channel activity primarily increased the proportion of longer duration events, whereas PKA stimulation had little effect on the proportion of short and long duration events, but resulted in a significant increase in the duration of the long open-state. cAMP formation during equivalent relaxation of precontracted muscle strips by isoproterenol and forskolin resulted in significantly less cAMP formation by isoproterenol than by forskolin, suggesting that the degree of activation of PKA is not the only determinant of tissue relaxation. We conclude that beta-adrenergic stimulation of KCa channel activity and relaxation of tone in airway smooth muscle occurs, in part, by means independent of cyclic AMP formation.

Expression of muscarinic M2 receptors in cultured human airway smooth muscle cells

[3H]-inositol phosphate formation and the inhibition of isoproterenol-induced [3H]-cyclic adenosine monophosphate (AMP) formation in response to the muscarinic agonist carbachol were studied in cultured human airway smooth muscle cells. Stimulation with carbachol produced concentration-dependent inhibition of isoproterenol (1 microM)-induced cyclic AMP formation (EC50, 0.15 microM; maximal inhibition, 60%). This response was itself reversed by pertussis toxin (100 ng/ml) and was competitively inhibited by the muscarinic antagonists pirenzepine (pA2, 6.5), methoctramine (pA2, 8.0), 4-diphenylacetoxy-N-methyl-piperidine (pA2, 8.0), and parafluorohexahydrosiladifenidol (pA2, 6.5), indicating that the M2 receptor subtype was mediating this response. In addition, carbachol also induced [3H]-inositol phosphate formation in these cells (EC50, 11 microM; 2.1-fold stimulation over basal), although the response observed was markedly down-regulated compared with the response seen in noncultured airway smooth muscle preparations. Growth arrest of cells failed to increase the magnitude of the inositol phosphate response to carbachol. These results demonstrate that cultured human airway smooth muscle cells express functionally coupled M2 receptors and probably also low levels of coupled M3 receptors.

Control of histamine induced inositol phospholipid hydrolysis in cultured human tracheal smooth muscle cells

[3H]Inositol phosphate responses to histamine and a range of other agonists were studied in cultured human tracheal smooth muscle cells. Histamine (EC50 6.5 microM), bradykinin (EC50 9.7 nM), carbachol (EC50 10 microM), substance P and NaF all produced concentration dependent [3H]inositol phosphate formation in these cells. The response to histamine was inhibited by mepyramine (KA 4.3 x 10(9) M-1), indicating the involvement of the histamine H1 receptor in this response. The inositol phosphate response to histamine was apparently desensitized following prolonged agonist exposure. The response to histamine was inhibited by phorbol dibutyrate (IC50 6 nM), and this inhibitory effect was reversed by staurosporine (150 nM). Isoprenaline (1 microM), rolipram (0.1-100 microM) and 3-isobutyl-1-methylxanthine (0.1 mM) all produced small inhibitory effects upon histamine induced inositol phosphate formation. These results demonstrate that cultured human tracheal smooth muscle cells express histamine H1 receptors coupled to phosphoinositidase C and suggest that the inositol phosphate response induced by stimulation of this receptor subtype is inhibited by activation of protein kinase C and, to a lesser extent, by elevation of cell cyclic AMP content.

Beta 2-adrenoceptor desensitization in cultured human airway smooth muscle

1. The mechanisms underlying control of cyclic AMP responses to isoprenaline were studied in primary cultures of human airway smooth muscle cells. In these cells, isoprenaline induced concentration-related cyclic AMP formation via beta 2-adrenoceptor stimulation. 2. Prior incubation of cells with varying concentrations of isoprenaline (1-16 h), forskolin, prostaglandin E2 or a stable analogue of cyclic AMP all produced concentration-related desensitization of cyclic AMP responses to subsequent challenge with isoprenaline (maximum reduction with 1 mumol/l isoprenaline, 85% after 16 h). The desensitization induced over 2 h (44%) by a concentration of prostaglandin E2 which gave a similar rise in cyclic AMP levels to 1 mumol/l isoprenaline was significantly less (P < 0.05) than the desensitization (62%) induced over 2 h by 1 mumol/l isoprenaline itself. 3. Isoprenaline-induced desensitization of beta 2-adrenoceptor-induced cyclic AMP formation was insensitive to prior exposure of cells to dexamethasone. 4. These findings suggest that isoprenaline-induced desensitization of beta 2-adrenoceptor-induced cyclic AMP formation in primary cultures of human airway smooth muscle cells is mediated through both a cyclic AMP-dependent and probably an additional cyclic AMP-independent pathway, and that these pathways are insensitive to inhibition by glucocorticoids.

Control of cyclic AMP levels in primary cultures of human tracheal smooth muscle cells

1. [3H]-adenosine 3':5'-cyclic monophosphate ([3H]-cyclic AMP) responses were studied in primary cultures of human tracheal smooth muscle cells derived from explants of human trachealis muscle and in short term cultures of acutely dissociated trachealis cells. 2. Isoprenaline induced concentration-dependent [3H]-cyclic AMP formation with an EC50 of 0.2 microM. The response to 10 microM isoprenaline reached a maximum after 5-10 min stimulation and remained stable for periods of up to 1 h. After 10 min stimulation, 1 microM isoprenaline produced a 9.5 fold increase over basal [3H]-cyclic AMP levels. The response to isoprenaline was inhibited by ICI 118551 (10 nM), (apparent KA 1.9 x 10(9) M-1) indicating the probable involvement of a beta 2-adrenoceptor in this response in human cultured tracheal smooth muscle cells. However, with 50 nM ICI 118551 there was a reduction in the maximum response to isoprenaline. Prostaglandin E2 also produced concentration-dependent [3H]-cyclic AMP formation (EC50 0.7 microM, response to 1 microM PGE2 6.4 fold over basal). 3. Forskolin (1 nM - 100 microM) induced concentration-dependent [3H]-cyclic AMP formation in these cells. A 1.6 fold (over basal) response was also observed following stimulation with NaF (10 mM). 4. The nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) (0.1 mM) and the type IV, cyclic AMP selective, phosphodiesterase inhibitor rolipram (0.1 mM) both elevated basal [3H]-cyclic AMP levels by 1.8 and 1.5 fold respectively. IBMX (1-100 microM) and low concentrations of rolipram (< 10 microM), also potentiated the response to 1 microM isoprenaline. Inhibitors of the type III phosphodiesterase isoenzyme (SK&F 94120 and SK&F 94836) were without effect upon basal or isoprenaline-stimulated cyclic AMP responses in these cells.5. Carbachol (1 nM-I 00 microM) produced concentration-dependent inhibition of the [3H]-cyclic AMP response to 1 microM isoprenaline in human cultured tracheal smooth muscle cells (IC50 0.24 JM). Carbachol(1 JM) inhibited the [3H]-cyclic AMP response to 1 JM isoprenaline by 60%. This effect of carbachol was itself inhibited by atropine (50 nM) (KA 2.3 x 109 M-') indicating the involvement of a muscarinic receptor.6. These results show that primary cultures of human tracheal smooth muscle cells demonstrate cyclic AMP responses to direct receptor stimulation, adenylyl cyclase activation and inhibition with nonselective and type IV-selective cyclic AMP phosphodiesterase isoenzyme inhibitors, and that the cyclic AMP response to isoprenaline can be inhibited by muscarinic receptor stimulation.

Effect of oral lithium on bronchial reactivity in asthma

1. Recognition that inositol phospholipid-derived second messengers are involved in the initiation and maintenance of airway smooth muscle contraction raises the possibility of new therapeutic approaches to the treatment of asthma. We anticipated that lithium, through its effects on cell signal transduction and ion-transport pathways, would be likely to protect the airways against constrictor stimuli. 2. We carried out a randomized, double-blind study of lithium carbonate in asthmatic patients. 3. After a 1 week run-in period, 27 patients were allocated lithium carbonate (800 mg) or placebo for 21 days with measurement of forced expiratory volume in 1 s, the dose of histamine causing a 20% fall in the forced expiratory volume in 1 s and serum lithium concentration on days 3, 7, 14 and 21. 4. Twenty-one patients completed the study (10 on lithium, 11 on placebo). Mean serum lithium levels for patients on active treatment were in the therapeutic range on all four occasions. 5. Lithium did not alter the forced expiratory volume in 1 s (P = 0.8) or the twice-daily peak expiratory flow (P = 0.15). It did, however, reduce histamine reactivity (the maximum difference between lithium and placebo was 1.2 doubling doses of histamine on day 21; 95% confidence interval 0.2-2.2 doubling doses), improve symptom scores (P less than 0.05) and reduce usage of beta-adrenoceptor agonist inhalers (P less than 0.05). 6. We conclude that lithium reduces bronchial reactivity in airway smooth muscle; this finding raises new therapeutic possibilities for the treatment of asthma.

Agonist-induced inositol phosphate responses in bovine airway submucosal glands

Agonist-induced inositol phosphate responses were investigated in bovine airway submucosal glands prelabeled with [3H]inositol. The agents used included muscarinic, adrenergic, and histaminergic agonists and NaF as a direct stimulant of phosphoinositidase C. Carbachol (1 microM-1 mM) produced concentration-related [3H]-inositol phosphate formation [maximal response 7.3-fold, half-maximal effective concentration (EC50) 47 microM]. This response was inhibited by atropine [affinity constant (Ka) 1.5 x 10(9) M-1], suggesting the involvement of a muscarinic receptor. Histamine (EC50 66 microM, 2.4-fold stimulation) and norepinephrine (EC50 28 microM, 2.7-fold stimulation) also produced concentration-dependent [3H]inositol phosphate responses. The response to histamine was inhibited by mepyramine (Ka 1.9 x 10(8) M-1), and the response to norepinephrine was inhibited by phentolamine (Ka 1.3 x 10(8) M-1) and prazosin (Ka 2.3 x 10(8) M-1), indicating the involvement of H1 and alpha 1-receptors, respectively, in these responses. NaF also produced concentration-dependent [3H]inositol phosphate formation compatible with the involvement of a G protein in this response. These results demonstrate that a range of secretagogues induce inositol phosphate responses in bovine airway submucosal glands. This response may underlie stimulus response coupling in this tissue.

Modulation of fluoroaluminate-induced inositol phosphate formation by increases in tissue cyclic AMP content in bovine tracheal smooth muscle

1. The effect of fluoroaluminate complexes (AlCl3 plus NaF) upon smooth muscle tone, [3H]-inositol phosphate accumulation and [3H]-cyclic AMP accumulation has been investigated in slices of bovine tracheal smooth muscle. 2. Fluoroaluminate (10 microM AlCl3 + various concentrations of NaF) elicited concentration-dependent contractions of bovine tracheal smooth muscle strips at concentrations of NaF in the range 1-10 mM. The resultant contractile response was reversed by isoprenaline (50 nM) and was preserved in calcium-free medium. 3. Fluoroaluminate stimulated [3H]-inositol phosphate formation at concentrations of NaF over 1 mM. The response to 20 mM NaF + 10 microM AlCl3 was 164 +/- 29% of the response to 1 mM histamine. Fluoroaluminate also increased the incorporation of [3H]-myo-inositol into membrane phospholipids. 4. Fluoroaluminate produced a small rise in [3H]-cyclic AMP levels (2.1 fold increase over basal with 20 mM NaF). The response to forskolin (1 microM, 8.6 fold over basal) was reduced by fluoroaluminate in a concentration-dependent manner, but still remained significantly (P less than 0.05) elevated over the response to fluoroaluminate alone. 5. The [3H]-inositol phosphate response to fluoroaluminate was inhibited by salbutamol (maximum inhibition 60%, IC50 = 0.08 microM), forskolin (1 microM, 46% inhibition) and isobutylmethylxanthine (1 mM, 73% inhibition). 6. These data suggest that inhibition of agonist-induced inositol phospholipid turnover by cyclic AMP in this tissue can occur at the post-receptor level.

Modulation of carbachol-induced inositol phosphate formation in bovine tracheal smooth muscle by cyclic AMP phosphodiesterase inhibitors

An investigation was made of a range of agents capable of elevating tissue cyclic AMP levels, or acting as a stable analogue of cyclic AMP, upon carbachol induced inositol phosphate responses in bovine tracheal smooth muscle slices. Whereas the beta 2 adrenoceptor agonist salbutamol (1 microM) and the membrane permeable analogue of cyclic AMP, 8-bromo-cyclic AMP (1 mM) were without effect upon total [3H]inositol phosphate formation induced by carbachol, 3-iso-butyl-1-methylaxanthine (IBMX) (EC50 140 microM), the high Km, cyclic AMP selective phosphodiesterase inhibitor rolipram (EC50 41 microM) and theophylline (EC50 76 microM) all inhibited the inositol phosphate response to low (1 microM) concentrations of carbachol. IBMX (IC50 13 microM), rolipram (IC50 4.6 microM) and theophylline (IC50 180 microM) all relaxed bovine tracheal muscle strips precontracted with methacholine (1 microM). The adenylate cyclase activator forskolin (1 microM), produced a much smaller (10% inhibition) effect upon inositol phosphate formation induced by carbachol. Carbachol (1 microM-1 mM) did not inhibit forskolin induced [3H]cyclic AMP formation. An inhibitor of the cyclic GMP preferring phosphodiesterase isozyme, M&B 22948 (1-100 microM), was without effect upon either carbachol induced inositol phosphate formation or trachealis tone. It is concluded that IBMX, rolipram and theophylline inhibit carbachol stimulated inositol phosphate formation, possibly through a cyclic AMP independent mechanism.

Purulent pericarditis

Purulent pericarditis is an infrequent, but important complication of infective illnesses, in particular pneumonia, which if diagnosed early has a good prognosis. The incidence of the condition is probably increasing, particularly in the immuno-compromised group of patients. 'Classical' symptoms and signs are often absent, and a high index of awareness is required to diagnose the condition. This review deals with the epidemiology, microbiology, clinical features, treatment and prognosis of purulent pericarditis with two illustrative examples of typical cases.

Inhibition of histamine-stimulated inositol phospholipid hydrolysis by agents which increase cyclic AMP levels in bovine tracheal smooth muscle

1. The effect on histamine-stimulated [3H]-inositol phosphate accumulation of a range of agents which increase the accumulation, or mimic the actions, of cyclic AMP has been investigated in bovine tracheal smooth muscle. 2. Salbutamol (1 microM), forskolin (1 microM) and vasoactive intestinal peptide (VIP, 1 microM) inhibited the inositol phosphate response to 0.1 mM histamine and increased the accumulation of [3H]-cyclic AMP in [3H]-adenine-labelled slices of bovine tracheal smooth muscle. The effect on inositol phospholipid hydrolysis was mimicked by the membrane permeant analogues of cyclic AMP, dibutrylcyclic AMP (1 mM) and 8-bromo-cyclic AMP (1 mM). 3. In contrast to salbutamol, which was equally effective at producing the two effects, forskolin produced large increases in [3H]-cyclic AMP accumulation (EC50 = 1.2 microM) at much higher concentrations than those required for inhibition of histamine-stimulated [3H]-inositol phosphate accumulation (EC50 = 0.09 microM). However, significant increases in [3H]-cyclic AMP accumulation, of similar magnitude to those obtained with salbutamol and VIP, were observed over the concentration range appropriate for inhibition of the inositol phosphate response to histamine. 4. In the presence of histamine (0.1 mM), isobutylmethylxanthine (IBMX, 1 mM) and rolipram (0.1 mM) both significantly (P less than 0.05) elevated tissue [3H]-cyclic AMP levels. IBMX, rolipram and (to a lesser extent) SKF 94120 significantly (P less than 0.05) reduced histamine-stimulated [3H]-inositol phosphate accumulation by 81%, 68% and 20%, respectively. M&B 22948 was without a significant effect on either [3H]-cyclic AMP or histamine-induced [3H]-inositol phosphate accumulation. 5. Both rolipram and forskolin reduced the increase in incorporation of [3H]-inositol into membrane phospholipids which followed stimulation with histamine. However, a significant inhibition of [3H]-inositol phosphate accumulation could be demonstrated under conditions in which there was no change in the level of [3H]-inositol incorporation.

Beta-adrenoceptor stimulation inhibits histamine-stimulated inositol phospholipid hydrolysis in bovine tracheal smooth muscle

1. Histamine and carbachol produced concentration-related increases in the accumulation of 3H-inositol phosphates in slices of bovine tracheal smooth muscle. 2. Noradrenaline alone produced a small stimulation of 3H-inositol phosphate accumulation which was inhibited by the alpha-adrenoceptor antagonist phentolamine. In contrast, when noradrenaline (0.1 mM) was added simultaneously with histamine it significantly reduced the inositol phosphate response to high (greater than or equal to 0.1 mM) concentrations of histamine. However, noradrenaline had no inhibitory effect on the carbachol-induced inositol phosphate response. 3. The non-selective beta-agonist isoprenaline (IC50 = 0.08 microM) and the beta 2-selective agonist salbutamol (IC50 = 0.29 microM) both produced a dose-related inhibition of the inositol phosphate response to 0.1 mM histamine. The inhibitory effect of salbutamol was antagonized by propranolol (KA = 2.4 x 10(9) M-1) and the beta 2-selective adrenoceptor antagonist ICI 118551 (KA = 1.7 x 10(9) M-1). 4. The accumulation of 3H-inositol phosphates induced by histamine increased steadily over a 40 min period after an initial lag period of 3-4 min. Following the simultaneous addition of histamine and salbutamol there was a further delay of 3-4 min before the appearance of the inhibitory effect of salbutamol. 5. The effect of histamine on inositol phosphate accumulation was accompanied by a stimulation of [3H]-inositol incorporation into membrane phospholipids which was reduced by the presence of salbutamol. However, when histamine was used to stimulate maximally [3H]-inositol incorporation during the prelabelling period, salbutamol produced a marked inhibition of histamine-stimulated 3H-inositol phosphate accumulation under conditions in which there was no change in the level of incorporation.