Characterization of the receptor mediating the antianaphylactic effects of beta-adrenoceptor agonists in human lung tissue in vitro

An experimental exposure study revealing composite airway effects of physical exercise in a subzero environment

Exposure to a cold climate is associated with an increased morbidity and mortality, but the specific mechanisms are largely unknown. People with cardiopulmonary disease and winter endurance athletes are particularly vulnerable. This study aimed to map multiple domains of airway responses to exercise in subzero temperature in healthy individuals.

Thirty-one healthy subjects underwent whole-body exposures for 50 minutes on two occasions in an environmental chamber with intermittent moderate-intensity exercise in +10 °C and -10 °C. Lung function, plasma/urine CC16 , and symptoms were investigated before and after exposures.

Compared to baseline, exercise in -10 °C decreased FEV₁ (p=0.002), FEV₁/FVC (p<0.001), and increased R20Hz (p=0.016), with no differences between exposures. Reactance increased after +10 °C (p=0.005), which differed (p=0.042) from a blunted response after exercise in -10 °C. Plasma CC16 increased significantly within exposures, without differences between exposures. Exercise in -10 °C elicited more intense symptoms from the upper airways, compared to +10 °C. Symptoms from the lower airways were few and mild. 

Short-duration moderate-intensity exercise in -10 °C induces mild symptoms from the lower airways, no lung function decrements or enhanced leakage of biomarkers of airway epithelial injury, and no peripheral bronchodilatation, compared to exercise in +10 °C. 

The Use of Antiallergic and Antiasthmatic Drugs in Viral Infections of the Upper Respiratory Tract

Despite their frequency, upper respiratory tract infections (URTIs) constitute an area with few, if any, effective treatment remedies. Asthma and airway allergies share similar pathogenetic mechanisms to URTIs and it is not surprising, therefore, that agents used to treat allergic disorders have also been studied in URTIs. Their possible effects, limitations and hypothetical modes of action in URTIs are reviewed. In controlled clinical trials of satisfactory scientific standard, symptom reductions in both experimental rhinovirus infections and natural colds have occurred with topical anticholinergics, oral antihistamines and topical chromones. Future treatment alternatives for URTIs may include the intranasal anticholinergic ipratropium bromide, new nonsedating antihistamines and sodium cromoglycate (cromolyn sodium). The latter has a record of safety and an absence of adverse effects that would make it an attractive alternative for this common but not particularly serious condition in otherwise healthy individuals.

Do beta-blockers really enhance the risk of anaphylaxis during immunotherapy?

Both beta-blockers and allergen immunotherapy are frequently prescribed, and allergy/immunology physicians commonly encounter patients who are candidates for immunotherapy and are receiving beta-blockers. The evidence in the medical literature indicates that although anaphylaxis does not appear to be more frequent, beta-blocker exposure is associated with greater risk for severe anaphylaxis, and for anaphylaxis refractory to treatment. Use of beta-blocker suspension merits consideration to reduce risk for untoward outcomes, while supplanting the beta-blocker medication with an equally efficacious non-beta-blocker alternative. For patients who require a beta-blocker for an indication for which there is no equally effective substitute, a management decision by the physician prescribing allergen immunotherapy should be approached carefully from an individualized risk-benefit standpoint.

Influence of beta2-adrenoceptor gene polymorphisms on beta2-adrenoceptor-mediated responses in human lung mast cells

BACKGROUND AND PURPOSE

Previous studies have shown that beta(2)-adrenoceptor-mediated responses in human lung mast cells are highly variable. The aims of the present study were to establish whether polymorphisms of the beta (2)-adrenoceptor gene (ADRB2) influence this variability in (a) beta(2)-adrenoceptor-mediated inhibition and (b) desensitization of beta(2)-adrenoceptor-mediated responses in human lung mast cells.

EXPERIMENTAL APPROACH

Mast cells were isolated from human lung tissue. The inhibitory effects of the beta-adrenoceptor agonist, isoprenaline (10(-10)-10(-5) M), on IgE-mediated histamine release from mast cells were determined (n=92). Moreover, the inhibitory effects of isoprenaline were evaluated following a desensitizing treatment involving long-term (24 h) incubation of mast cells with isoprenaline (10(-6) M) (n=65). A potential influence of polymorphisms on these functional responses was determined by genotyping 11 positions, in the promoter and coding regions, of ADRB2 previously reported as polymorphic.

KEY RESULTS

There was no influence of any of the polymorphic positions of ADRB2 on the potency of isoprenaline to inhibit histamine release from mast cells with the exception of position 491C>T (Thr164Ile). There was no influence of any of the polymorphic positions of ADRB2 on the extent of desensitization of the isoprenaline-mediated response following a desensitizing treatment except for position 46G>A (Gly16Arg). Analyses at the haplotype level indicated that there was no influence of haplotype on beta (2)-adrenoceptor-mediated responses in mast cells.

CONCLUSIONS AND IMPLICATIONS

These data indicate that certain polymorphisms in ADRB2 influence beta(2)-adrenoceptor-mediated responses in human lung mast cells.

Regulation of mast cells by beta-agonists

The human lung mast cell is known to be a critical effector cell in the mediation of asthma. Activation of the mast cell by allergens and other stimuli leads to the release and generation of a wide variety of autacoids that cause bronchoconstriction, promote inflammation, and may influence airway remodeling. Therefore, the stabilization of mast cells has obvious value in the prevention of asthma. Among the drugs used to treat asthma, only beta-agonists are effective stabilizers of mast cells. Both short- and long-acting beta-agonists are effective against mast cells, but there are differences between agonists regarding the extent of inhibitory activity attained. Consequently, the type of beta-agonist prescribed influences the degree of mast cell stabilization possible. Despite the potential value of attenuating mast cell activity with beta-agonists, this benefit may diminish with time because of the development of tolerance. Both short- and long-acting beta-agonists can induce tolerance to mast cell stabilization, and generally, higher efficacy agonists tend to induce greater levels of tolerance; however, weaker agonists induce greater levels of tolerance than might be expected. Tolerance to the mast-cell-stabilizing effects of beta- agonists may be an issue clinically, because this occurs more readily than tolerance to smooth muscle relaxation. This could lead to a situation in which beta-agonists fail to prevent the release of mediators from mast cells but can still effectively relax airway smooth muscle. The continued ability to bronchodilate could mask the unfavorable consequences of unchecked mediator release from mast cells.

Influence of agonist intrinsic activity on the desensitisation of beta2-adrenoceptor-mediated responses in mast cells

1. The aim of the present study was to determine whether the intrinsic activity of an agonist influences the extent of desensitisation of beta(2)-adrenoceptor-mediated responses in human lung mast cells. 2. The effects of a wide range of beta-adrenoceptor agonists (10(-10)-10(-5) m) on the IgE-mediated release of histamine from mast cells were determined. The intrinsic activity of agonists was established by comparing the maximal inhibitory response (E(max)) of an agonist relative to the maximal response obtained with the full agonist, isoprenaline. The intrinsic activity order for the inhibition of histamine release was isoprenaline (1.0)>formoterol (0.94)>fenoterol (0.89)>terbutaline (0.84)>salbutamol (0.69)>clenbuterol (0.65)>salmeterol (0.30)>dobutamine (0.20). 3. There was a significant (P<0.05) positive correlation (r=0.81) between the extent to which beta-adrenoceptor agonists inhibited histamine release and the degree to which the agonists caused elevations in cAMP in mast cells. 4. Further studies investigated the effects of long-term (24 h) incubation of mast cells with beta-adrenoceptor agonists on the subsequent ability of isoprenaline to inhibit histamine release. At concentrations of agonists selected to occupy a large percentage (88%) of beta(2)-adrenoceptors, there was a significant (P<0.05) correlation (r=0.73) between the relative intrinsic activity of agonists as inhibitors of histamine release and the extent of functional desensitisation induced by the agonists. At lower receptor occupancies, however, there was no correlation between the relative intrinsic activity of agonists and the extent of agonist-induced desensitisation. 5. These data indicate that, under experimental conditions where high receptor occupancies prevail, agonist intrinsic activity influences the extent of desensitisation of beta(2)-adrenoceptor-mediated responses in mast cells.

Desensitisation of mast cell beta2-adrenoceptor-mediated responses by salmeterol and formoterol

1. The long-acting beta(2)-adrenoceptor agonist formoterol (10(-10)-10(-6) m) inhibited the IgE-dependent release of histamine from human lung mast cells in a concentration-dependent manner. Formoterol was more potent and a full agonist relative to the nonselective beta-adrenoceptor agonist isoprenaline. By contrast, the long-acting beta(2)-adrenoceptor agonist salmeterol (10(-10)-10(-6) m) was about two-thirds less efficacious than either formoterol or isoprenaline as an inhibitor of histamine release. 2. Isoprenaline, formoterol and salmeterol (all at 10(-5) m) increased total cell cAMP levels in mast cells over basal by 361+/-90 (P<0.05), 321+/-89 (P<0.05) and 64+/-24% (P>0.05), respectively. 3. Long-term (24 h) incubation of mast cells with formoterol (10(-6) m) or salmeterol (10(-6) m) essentially abolished the subsequent ability of isoprenaline to inhibit histamine release. Both formoterol and salmeterol were more effective at inducing the functional desensitisation than isoprenaline (10(-6) m) or the short-acting beta(2)-adrenoceptor agonist salbutamol (10(-6) m). 4. The desensitisation induced by long-term treatments with salmeterol and formoterol was specific for beta(2)-adrenoceptor-mediated inhibition of histamine release as the inhibitory effects of alternative cAMP-elevating compounds, prostaglandin E(2), a receptor-mediated activator of adenylate cyclase, and forskolin, a direct activator of adenylate cyclase, were unaffected by desensitising treatments. 5. Radioligand binding studies were performed to determine beta(2)-adrenoceptor density in cell membranes after pretreatment (24 h) of cells with agonists. Isoprenaline, formoterol and salmeterol (all at 10(-6) m) reduced beta(2)-adrenoceptor density by 13+/-5 (P>0.05), 49+/-13 (P<0.05) and 35+/-17% (P>0.05), respectively. 6. These data indicate that long-term exposure of mast cells to both salmeterol and formoterol can cause substantial levels of desensitisation to beta(2)-adrenoceptor-mediated responses in mast cells.

Desensitization of beta2-adrenoceptor-mediated responses by short-acting beta2-adrenoceptor agonists in human lung mast cells

1 The principal aim of the present study was to determine whether long-term treatment of human lung mast cells (HLMC) with the clinically-relevant beta(2)-adrenoceptor agonists, salbutamol and terbutaline, leads to desensitization of beta(2)-adrenoceptor-mediated responses in these cells. 2 The non-selective beta-adrenoceptor agonist, isoprenaline, and the selective beta(2)-adrenoceptor agonists, salbutamol and terbutaline, inhibited the IgE-mediated release of histamine from HLMC. Salbutamol (pD(2); 7.7+/-0.3) and terbutaline (pD(2); 7.3+/-0.2) were roughly equipotent as inhibitors of histamine release although both agonists were less potent than isoprenaline (pD(2); 8.6+/-0.2). 3 Isoprenaline (10(-5) M), salbutamol (10(-5) M) and terbutaline (10(-5) M) enhanced total cell cAMP levels in HLMC over basal by 361+/-90, 150+/-38 and 165+/-35%, respectively. 4 Long-term exposure (24 h) of HLMC to either salbutamol (10(-7) M) or terbutaline (10(-7) M) led to a subsequent reduction in the effectiveness of salbutamol and terbutaline (both 10(-9)-10(-4) M) to inhibit histamine release. However, salbutamol was significantly (P<0.05) more effective than terbutaline at promoting the functional desensitization. 5 Radioligand binding studies, using iodinated cyanopindolol, were performed to determine beta(2)-adrenoceptor density in cell membranes after pretreatment (24 h) of cells with either salbutamol (10(-6) M) or terbutaline (10(-6) M). Both agonists reduced beta(2)-adrenoceptor density in membranes to about the same extent (approximately 25% reduction) but these changes in receptor density were not statistically significant (P>0.05). 6 These data indicate that long-term exposure of mast cells to salbutamol causes greater levels of desensitization to beta(2)-adrenoceptor-mediated responses in HLMC than terbutaline. These findings may have wider clinical significance in the context of asthma treatment as compromised mast cell inhibition could result following long-term exposure of mast cells to short-acting bronchodilators.

Pharmacological characterisation of the beta-adrenoceptor expressed by human lung mast cells

The nonselective beta-adrenoceptor agonist, isoprenaline (pD2; 8.8 +/- 0.2), and selective beta2-adrenoceptor agonists, clenbuterol (9.2 +/- 0.4) and salbutamol (7.1 +/- 0.1), inhibited the immunoglobulin E-mediated release of histamine from human lung mast cells in a concentration-dependent manner. The beta2-adrenoceptor-selective antagonist, ICI118551 (erythro-(+/- )-1-(7-methylindan-4-yloyl)-3-isopropylaminobutan-2-ol HCl), antagonised the isoprenaline inhibition of histamine release from human lung mast cells with high affinity (apparent pK(B); 9.5 +/- 0.2), whereas high concentrations of the beta1-adrenoceptor-selective antagonist, CGP20712A (2-hydroxy-5-(2-(hydroxy-3-(4((1-methyl-4-trifluoromethyl)-1-H-imidazol-2-yl)-phenoxy)-propyl)-aminoethoxyl)-benzamide), were required to reverse the isoprenaline inhibition (apparent pK(B); 6.5 +/- 0.3). Radioligand binding studies using [125I]-iodocyanopindolol ([125I]CYP) were performed on membranes derived from purified mast cells (>90% purity). Binding of [125I]CYP to mast cell membranes was displaced from a single binding site with a high affinity for ICI118551 (pK(i); 8.9 +/- 0.1) and low affinity for CGP20712A (pK(i); 6.0 +/- 0.03), indicative of a homogeneous population of beta2-adrenoceptors. In contrast, in human lung membranes, these antagonists displaced [125I]CYP from two sites indicative of a heterogeneous population of beta1-adrenoceptors (20%) and beta2-adrenoceptors (80%). These data indicate that the beta-adrenoceptor expressed by human lung mast cells and mediating inhibition of mediator release from these cells is the beta2-adrenoceptor.

Influence of genetic polymorphisms in the beta2-adrenoceptor on desensitization in human lung mast cells

The beta-adrenoceptor agonist, isoprenaline, inhibited the immunoglobulin E-mediated release of histamine from human lung mast cells (HLMC). Long-term (24 h) exposure of HLMC to isoprenaline reduced the subsequent effectiveness of isoprenaline to inhibit histamine release. The extent of this functional desensitization was variable with some HLMC preparations resistant and others highly susceptible. We sought to determine whether the variability in the degree of functional desensitization was influenced by genetic polymorphisms in the beta2-adrenoceptor. HLMC preparations were genotyped at two polymorphic loci, positions 16 (arg to gly) and 27 (gln to glu), and the effect of desensitizing conditions (24 h with 10(-6) M isoprenaline) on the subsequent ability of isoprenaline (10(-7) M) to inhibit histamine release from HLMC was determined (n = 72). In HLMC preparations expressing beta2-adrenoceptors with arg (wild-type) or gly (mutant) at position 16, desensitization was 71 +/- 5% (n = 18) or 43 +/- 5%, (n = 26), respectively, whereas the desensitization was 59 +/- 6% (n = 28) for heterozygotes at this position. In HLMC preparations expressing beta2-adrenoceptors with gln (wild-type) or glu (mutant) at position 27, desensitization was 65 +/- 5% (n = 25) or 28 +/- 7% (n = 17), respectively, whereas the desensitization was 61 +/- 5% (n = 30) for heterozygotes at this position. These data suggest that mutant (gly16 and glu27) forms of the receptor are resistant to desensitization compared to wild-type (arg16 and gln27) forms. However, analyses to determine the relative contributions of positions 16 and 27 suggest that position 27 is more important in influencing the degree of functional desensitization.

Regulation of human mast cell and basophil function by cAMP

1. Mast cells and basophils are important in mediating allergic disorders such as asthma. Activation of these cells results in the release of a wide variety of mediators that can promote inflammatory responses. 2. Receptor-mediated activators of adenylate cyclase such as the beta-adrenoceptor agonist, isoprenaline, and prostaglandin E2 (PGE2) are effective at inhibiting mediator release from human lung mast cells (HLMC) but not basophils. In HLMC, both isoprenaline and PGE2 elevate and sustain increases in cyclic adenosine 3',5'-monophosphate (cAMP) whereas in basophils, both compounds cause transient increases in cAMP. 3. Non-selective inhibitors of phosphodiesterase (PDE) such as theophylline and 3-isobutyl-1-methylxanthine are effective inhibitors of mediator release from both HLMC and basophils and both compounds cause elevations of cAMP that are sustained in both cell types. 4. Studies with selective inhibitors of PDE indicate that the cAMP-specific PDE, PDE 4, regulates the activity of basophils but not HLMC. The nature of the PDE regulating HLMC responses is uncertain. 5. These data indicate that agents that induce and sustain elevations in intracellular cAMP attenuate the stimulated release of mediators from mast cells and basophils. However, the responsiveness of HLMC and basophils to selected cAMP-active agents differs.

The complementary role of glucocorticosteroids and long-acting beta-adrenergic agonists

In summary, beta 2-adrenergic agonists and corticosteroids can interact to produce beneficial effects on airway function. The regular use of short-acting, beta 2-adrenergic agonists as relief therapy is safe and effective; however, some degree of caution may be required with the use of very high doses. Long-acting beta 2-adrenergic agonists provide further benefits in terms of asthma control in patients already established on inhaled corticosteroid therapy. The mechanism by which this interaction occurs remains to be elucidated, but may involve a protective effect of corticosteroids on dysfunctional beta-adrenergic receptor expression and function. In asthma, there may be a degree of uncoupling of the airway receptors, probably caused by cytokines such as IL-1 beta. However, this has not been established yet. Furthermore, beta-adrenergic receptor-mediated effects may be more quickly downregulated with beta-receptor stimulation, leading to a reduction in anti-inflammatory effects. The regular use of corticosteroids leads to an inhibition of cytokine production and prevents beta-adrenergic receptor downregulation, allowing beta 2-adrenergic agonists to be more effective. Further research, which may lead to a greater understanding of these mechanisms, may also lead to the development of more effective treatment regimens.

Influence of receptor reserve on beta-adrenoceptor-mediated responses in human lung mast cells

1. The effects of the beta-adrenoceptor agonists isoprenaline and salbutamol on IgE-mediated histamine release from human lung mast cells (HLMC) were evaluated. Both agonists (10(-10)-10(-5) M) inhibited histamine release in a dose-dependent manner and isoprenaline (pD2, 8.3+/-0.1, mean+/-s.e.mean) was more potent than salbutamol (7.3+/-0.1). Moreover, the mean data indicated that salbutamol was a partial agonist when compared with isoprenaline. However, there was a large degree of interexperimental variability because, in 11 of 32 experiments, salbutamol was a full agonist and, in 21 of 32 experiments, a partial agonist relative to isoprenaline. These data suggest that different HLMC preparations possess variable receptor reserves. 2. The effect of the irreversible beta-adrenoceptor antagonist, bromoacetylalprenolol menthane (BAAM), on the inhibition of IgE-mediated histamine release by both isoprenaline and prostaglandin E2 (PGE2) was assessed. Whereas BAAM (100 nM) antagonized the isoprenaline inhibition of histamine release from activated HLMC, BAAM had no effect on the PGE2 inhibition. Pretreatment of HLMC with the beta2-selective competitive antagonist, ICI 118551 (100 nM), protected against the loss in responsiveness to isoprenaline following treatment with BAAM. 3. Concentrations of 1, 10 and 100 nM of BAAM caused dose-dependent rightward shifts in the dose-response curve for the isoprenaline inhibition of histamine release. Furthermore, there was a dose-dependent reduction in the maximal inhibitory response obtained with isoprenaline following treatments with increasing concentrations of BAAM. Although the rightward shifts in the isoprenaline dose-response curves, with a given concentration of BAAM, were similar in all experiments, there was some variability in the depression of the maximal response in individual experiments. Thus, in 6 of 16 experiments, BAAM (1 nM) did not depress the maximal response to isoprenaline, whereas in 10 of 16 experiments there was a depression (7 to 49% reduction) in the maximal response. These data suggest that different HLMC preparations possess variable receptor reserves. 4. Isoprenaline was more potent as an inhibitor in those HLMC preparations in which there was a larger receptor reserve (i.e. preparations in which the maximal inhibitory response to isoprenaline was unaffected by pretreatment with 1 nM BAAM). 5. The influence of receptor reserve on the inhibition by salbutamol of histamine release from HLMC was evaluated. There was a good correlation (r=0.77) between receptor reserve and the maximal response (relative to isoprenaline) obtained with salbutamol. Thus, HLMC preparations with larger receptor reserves were more responsive to salbutamol. 6. Receptor reserve influenced the desensitization of beta-adrenoceptor-mediated responses in HLMC. Cells were incubated (24 h) with isoprenaline (1 microM), washed and then the ability of a second isoprenaline (10(-10)-10(-5) M) exposure to inhibit histamine release was assessed. The pretreatment caused a reduction in the isoprenaline inhibition of histamine release although the extent of desensitization was highly variable, ranging from essentially negligible levels in some preparations to substantial reductions (93% desensitization) in the ability of isoprenaline to inhibit histamine release. There was a reasonable correlation (r=0.59) between receptor reserve and desensitization. Preparations that possessed a larger receptor reserve were more resistant to desensitization. 7. Collectively, these data suggest that a receptor reserve exists for the beta-adrenoceptor-mediated inhibition of histamine release from HLMC but that the size of this reserve varies between HLMC preparations. Moreover, the size of this receptor reserve may influence the sensitivity of HLMC to beta-adrenoceptor agonists and the susceptibility of individual HLMC preparations to desensitization.

Salmeterol inhibition of mediator release from human lung mast cells by beta-adrenoceptor-dependent and independent mechanisms

1. The long-acting beta2-adrenoceptor agonist, salmeterol (10(-9)-10(-5) M), inhibited the IgE-mediated release of histamine from human lung mast cells (HLMC) in a dose-dependent fashion. Additional beta-adrenoceptor agonists were studied and the rank order of potency for the inhibition of histamine release from HLMC was isoprenaline > salmeterol > salbutamol. Approximate EC50 values for the inhibition of histamine release were 10 nM for isoprenaline and 100 nM for salbutamol. An EC50 value for salmeterol could not be calculated because maximal responses to salmeterol were not observed over the concentration range employed. 2. Both salmeterol and isoprenaline inhibited the generation of sulphopeptidoleukotrienes (sLT) more potently and more efficaciously than the release of histamine from immunologically-activated HLMC. Salmeterol (EC50 < 0.1 nM) was more potent than isoprenaline (EC50 0.4 nM) at attenuating sLT generation. 3. The beta-adrenoceptor antagonist, propranolol (1 microM), and the selective beta2-adrenoceptor antagonist, ICI 118,551 (0.1 microM), both caused rightward shifts in the dose-response curve for the inhibition of histamine release by isoprenaline. The antagonism of salmeterol effects by propranolol and ICI 118,551 was more complex. At lower concentrations (< 1 microM) of salmeterol, both antagonists shifted the dose-reponse curve to salmeterol rightward. At a higher concentration (10 microM) of salmeterol, neither ICI 118,551 nor propranolol was an effective antagonist of the salmeterol-mediated inhibition of histamine release. 4. Prolonged exposure (4 h) of HLMC to isoprenaline (1 microM) caused an approximately 50% reduction in the effectiveness of a second exposure to isoprenaline (10 microM) at inhibiting the release of histamine. whereas this pretreatment did not affect the salmeterol (10 microM) inhibition of histamine release. 5. Isoprenaline (10(-9)-10(-5) M) caused a dose-dependent increase in total cell cyclicAMP levels in purified HLMC which paralleled the inhibition of histamine release. Salmeterol (10(-9)-10(-5) M) was considerably less potent than isoprenaline at increasing HLMC cyclicAMP levels. 6. In summary, these data indicate that salmeterol is an effective inhibitor of the stimulated release of mediators from HLMC. The present data also suggest that salmeterol may act to inhibit mediator release from HLMC by beta-adrenoceptor-dependent and independent mechanisms.

Protection by dexamethasone of the functional desensitization to beta 2-adrenoceptor-mediated responses in human lung mast cells

1. The beta-adrenoceptor agonist, isoprenaline, inhibited the IgE-mediated release of histamine from human lung mast cells (HLMC) in a dose-dependent manner. Maximal inhibitory effects were obtained with 0.1 microM isoprenaline. However, the inhibition of histamine release from HLMC by isoprenaline (0.1 microM) was highly variable ranging from 33 to 97% inhibition (mean, 59 +/- 3%, n = 27). 2. Long-term (24 h) incubation of HLMC with isoprenaline led to a subsequent reduction in the ability of a second exposure of isoprenaline to inhibit IgE-mediated histamine release from HLMC. The impairment in the ability of isoprenaline (0.1 microM) to inhibit histamine release following desensitizing conditions (1 microM isoprenaline for 24 h) was highly variable amongst HLMC preparations ranging from essentially negligible levels of desensitization in some preparations to complete abrogation of the inhibitory response in others (mean, 65 +/- 6% desensitization, n = 27). 3. The ability of HLMC to recover from desensitization was investigated. Following desensitizing conditions (1 microM isoprenaline for 24 h), HLMC were washed and incubated for 24 h in buffer and the effectiveness of isoprenaline (0.1 microM) to inhibit IgE-mediated histamine release from HLMC was assessed. The extent of recovery was highly variable with some HLMC preparations failing to recover and others displaying a complete restoration of responsiveness to isoprenaline (mean, 40 +/- 6% recovery, n = 23). 4. The effects of the glucocorticoid, dexamethasone, were also investigated. Long-term (24-72 h) treatments with dexamethasone (0.1 microM) had no effect on IgE-mediated histamine release from HLMC. Additionally, long-term (24-72 h) treatments with dexamethasone (0.1 microM) had no effect on the effectiveness of isoprenaline to inhibit histamine release. However, long-term (24-72 h) treatments with dexamethasone (0.1 microM) protected against the functional desensitization induced by incubation (24 h) of HLMC with isoprenaline (1 microM). The protective effect was time-dependent and pretreatment of HLMC with dexamethasone for either 24, 48 or 72 h prevented desensitization by either 15 +/- 7, 19 +/- 5 or 51 +/- 10%, respectively (n = 5-7). 5. HLMC preparations which were relatively refractory to isoprenaline even after withdrawal (24 h) from desensitizing conditions responded more effectively to isoprenaline (0.1 microM) if dexamethasone (0.1 microM) was also included during the recovery period (19 +/- 9% recovery after 24 h in buffer; 50 +/- 8% recovery after 24 h with dexamethasone, n = 5). 6. These data indicate that the responses of different HLMC preparations to isoprenaline, the susceptibility of HLMC to desensitization and the ability of HLMC to recover from desensitizing conditions varies markedly. Dexamethasone, which itself has no direct effects on IgE-mediated histamine release from HLMC, protected HLMC from the functional desensitization to beta-adrenoceptor agonists. Because beta 2-adrenoceptor agonists and glucocorticoids are important in the therapeutic management of asthma and as the HLMC is probably important in certain types of asthma, these findings may have wider clinical implications.

Current therapies for asthma. Promise and limitations

Effective treatments for asthma exist, but morbidity and mortality have continued to climb. Many attempts have been made to refine rather than change therapy over the past 20 years. Drugs currently used to treat asthma include beta 2-agonists, glucocorticoids, theophylline, cromones, and anticholinergic agents. For acute, severe asthma, the inhaled beta 2-agonists are the most effective bronchodilators. Short-acting forms give rapid relief; long-acting agents provide sustained relief and help nocturnal asthma; and serious adverse effects are rare when these drugs are used properly. First-line therapy for chronic asthma is inhaled glucocorticoids, the only currently available agents that reduce airway inflammation. Their side effects can be reduced by rinsing the mouth or by using large-volume spacers. Theophylline is a bronchodilator that is useful for severe and nocturnal asthma, but recent studies suggest that it may also have an immunomodulatory effect. Although theophylline is inexpensive, monitoring its plasma concentrations is both expensive and inconvenient. Cromones work best for patients who have mild asthma: they have few adverse effects, but their activity is brief, so they must be given four times daily. The anticholinergic bronchodilators are more useful for treating COPD than for chronic asthma. These drugs have virtually no side effects, and their onset is slower and their action longer than inhaled beta 2-agonists. The new direction in treating asthma will be orally administered medication that has few side effects and is targeted specifically to the pathogenesis of asthma.

Asthma therapy with aerosols: clinical relevance for the next decade

Inhaled therapy is the mainstay of modern asthma management, as this optimizes the therapeutic ratio. Short-acting beta 2-agonists are the most effective bronchodilators and when given by inhalation give rapid relief of symptoms, without adverse effects, although there are concerns about overuse of these drugs. Inhaled long-acting beta 2-agonists are useful in some patients. Inhaled anticholinergics are particularly useful in patients with COPD and in the future long-acting drugs, such as tiotropium bromide, will be available. Inhaled glucocorticoids are the most effective therapy in controlling chronic asthma symptoms, and systemic effects are not a problem in the vast majority of patients. Improved inhalation devices and steroids with reduced oral bioavailability have resulted in reduced systemic side effects, which now arise largely from absorption from the lungs. In the future it is likely that new classes of drug will be developed, but whether they will be used by inhalation or given by mouth will depend on the frequency of side effects and the mode of action of the drugs. There are likely to be several improvements in inhaler delivery systems, so that the inhaled route will remain predominant for many years to come.

The effect of selective phosphodiesterase 3 and 4 isoenzyme inhibitors and established anti-asthma drugs on inflammatory cell activation

1. This study aimed to evaluate the effects of phosphodiesterase (PDE) inhibitors and currently prescribed anti-asthma drugs for their ability to inhibit inflammatory cell activation in vitro. 2. Alveolar macrophages and eosinophils were isolated from the bronchoalveolar lavage (BAL) fluid of ovalbumin (Ovalb)-sensitized guinea-pigs. Opsonized zymosan (OZ) and PAF stimulated leukotriene B4 (LTB4) release from eosinophils was measured by radioimmunoassay. Ovalb-induced superoxide generation was measured by reduction of cytochrome C. 3. Monocytes were separated from human peripheral venous blood and mast cells were dispersed from human lung fragments. Lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) release from monocytes was measured by ELISA and anti-IgE stimulated histamine release from mast cells was measured by a radioenzymatic method. 4. The beta 2 agonist, salbutamol inhibited TNF-alpha release from monocytes and histamine release from mast cells whilst having no effect on eosinophil-derived LTB4 release or macrophage superoxide generation. 5. The PDE 3 inhibitor, milrinone produced a concentration-related inhibition of TNF-alpha release from monocytes which achieved statistical significance at 10(-5) M but inhibited LTB4 release from eosinophils and superoxide generation from macrophages only at the highest concentration (10(-3) M) examined. Milrinone had no effect on histamine release from mast cells. 6. The selective PDE 4 inhibitors, denbufylline and rolipram and the corticosteroid, beclomethasone produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes and superoxide generation from alveolar macrophages whilst having no effect on histamine release from mast cells. 7. The mixed PDE 3/4 inhibitor, benzafentrine produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes, superoxide generation from alveolar macrophages and histamine release from mast cells. 8. In conclusion these data clearly show that both established anti-asthma medication as well as PDE inhibitors have the potential to inhibit inflammatory cell activation in vitro but that the anti-secretory actions of beta 2 agonists, corticosteroids and PDE inhibitors are distinct.

Anaphylactoid and anaphylactic reactions. Hazards of beta-blockers

Studies have demonstrated greater hazards associated with anaphylaxis in patients receiving beta-blockers. Serious anaphylaxis is more frequent. Evidence suggests this occurs via modulation of adenylate cyclase, which can influence release of anaphylactogenic mediators. Treatment of anaphylaxis in patients exposed to beta-blockers is complicated because therapeutic administration of epinephrine (adrenaline) may be ineffective or promote undesired alpha-adrenergic and vagotonic effects. Risk reduction efforts should be considered for patients receiving beta-blockers who are prone to experience anaphylaxis.

Pharmacological studies of allergic cough in the guinea pig

The pharmacological mechanisms of allergic cough in the guinea pig were studied. Actively sensitized guinea pigs were exposed to aerosols of antigen to elicit coughing. In separate experiments, naive guinea pigs were exposed to aerosols of capsaicin to elicit coughing. Both allergic and capsaicin-induced cough were inhibited by loratadine (0.3-10 mg kg-1 p.o.) and chlorpheniramine (0.1-3.0 mg kg-1 p.o.). Neither cimetidine (10 mg kg-1 s.c.), nor thioperamide (3-10 mg kg-1 s.c.), inhibited allergic or capsaicin-induced cough. Codeine (3-30 mg kg-1 p.o.), salbutamol (0.003-3.0 mg kg-1 s.c.) and ipratropium (0.03-1.0 mg kg-1 s.c.) inhibited both allergic and capsaicin-induced cough. Hexamethonium (10 and 30 mg kg-1 s.c.) inhibited allergic, but not capsaicin-induced cough. Allergic and capsaicin-induced cough were unaffected by phenidone (5.0 and 10.0 mg kg-1 s.c.). Indomethacin (5.0 and 10.0 mg kg-1 s.c.) had no effect on allergic cough but slightly inhibited capsaicin-induced cough. We conclude that allergic and capsaicin-induced cough are modulated by histamine H1 receptor and cholinergic mechanisms. Histamine H2 or histamine H3 receptor mechanisms, and lipoxygenase and cyclooxygenase products of arachidonic acid metabolism do not influence allergic and capsaicin-induced cough. Ganglionic mechanisms play a minor role in the production of allergic cough and no role in capsaicin-induced cough.

Effects of beta 2-adrenoceptor agonists on anti-IgE-induced contraction and smooth muscle reactivity in human airways

1. The beta 2-adrenoceptor agonists, salbutamol, salmeterol and RP 58802 relaxed basal tone of human isolated bronchial smooth muscle. Salmeterol- and RP 58802-induced relaxations persisted for more than 4 h when the medium was constantly renewed after treatment. 2. Salbutamol, salmeterol and RP 58802 reversed histamine-induced contractions in human airways (pD2 values: 6.15 +/- 0.21, 6.00 +/- 0.19 and 6.56 +/- 0.12, respectively). 3. Anti-IgE-induced contractions were significantly inhibited immediately after pretreatment of preparations with beta 2-adrenoceptor agonists (10 microM). However, when tissues were treated with beta 2-agonists and then washed for a period of 4 h, salmeterol was the only agonist which significantly inhibited the anti-IgE response. 4. Histamine response curves were shifted to the right immediately after pretreatment of tissues with the beta 2-adrenoceptor agonists (10 microM; 20 min), but maximal contractions were not affected. After a 4 h washing period, the histamine curves were not significantly different from controls. Concentration-effect curves to acetylcholine (ACh) or leukotriene C4 (LTC4) were not significantly modified after beta 2-agonist pretreatment. 5. These results suggest that beta 2-adrenoceptor agonists may prevent anti-IgE-induced contraction by inhibition of mediator release rather than alterations of those mechanisms involved in airway smooth muscle contraction.

Beta 2-adrenoceptors mediate a reduction in endothelial permeability in vitro

The permeability of bovine pulmonary artery endothelial (CPAE) monolayers to Evans blue-labelled albumin (Evans blue-albumin) has been measured in vitro. Thrombin caused a concentration-dependent increase in Evans blue-albumin clearance across endothelial monolayers. Isoprenaline inhibited thrombin-induced Evans blue-albumin clearance in a concentration-dependent manner (EC50 21 nM). This effect was mimicked by the selective beta 2-adrenoceptor agonists salbutamol (EC50 64 nM) and salmeterol (EC50 2.7 nM), but not by the selective beta 1-adrenoceptor agonist, RO-363 ((1-[3',4'-dihydroxyphenoxy]-2-hydroxy-[3",4"- dimethoxyphenethylamino]-propane)oxalate), nor by the selective beta 3-adrenoceptor agonist, CL-316,243 (disodium (R,R)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]propyl]-1,3- benzodioxole-2,2-dicarboxylate). Isoprenaline, salbutamol and salmeterol, but not RO-363 or CL-316,243 produced small, but significant reductions in Evans blue-albumin clearance across unstimulated endothelial monolayers. Inhibition of the response to thrombin by isoprenaline was antagonised by the selective beta 2-adrenoceptor antagonist, ICI-118,551 ((erythro-DL-1(7-methylindan-4- yloxy)3-isopropylaminobutan-2-ol), pKB 8.4). Salmeterol also inhibited hydrogen peroxide-stimulated Evans blue-albumin clearance. Hence, the widely used beta 2-adrenoceptor agonists, salbutamol and salmeterol, are able to reduce endothelial permeability at nanomolar concentrations.

Formoterol on airway smooth muscle and human lung mast cells: a comparison with salbutamol and salmeterol

Formoterol, like salbutamol and salmeterol, relaxed isolated preparations of guinea-pig trachea and human bronchus, and inhibited antigen-induced mediator release from human lung fragments in a concentration-related fashion. In each case, these actions were mediated through beta 2-adrenoceptors, with formoterol being 50-120-fold more potent than salbutamol, and 2-27-fold more potent than salmeterol. The duration of action of formoterol was longer than that of salbutamol in all preparations, but was markedly shorter than that of salmeterol, whose actions persisted for many hours despite continuous or extensive washing of the tissues. In conscious guinea-pigs, inhaled formoterol, salbutamol and salmeterol all caused dose-related inhibition of histamine-induced bronchoconstriction. Formoterol was again more potent (10-20-fold) than either salbutamol or salmeterol. However, while the actions of a threshold-effective dose of formoterol persisted for less than 3 h, somewhat longer than those of salbutamol (< 1.5 h), an equivalent dose of salmeterol was active for at least 6 h. Therefore, while formoterol is a potent beta 2-adrenoceptor agonist in vitro and in vivo, and is consistently longer-acting than salbutamol, its duration of action is markedly shorter than that of salmeterol.

Ageing, late-onset asthma and the beta-adrenoceptor

Late-onset asthma in old age is a common clinical problem. There are similarities between receptor and post-receptor beta 2-adrenoceptor abnormalities reported in young asthmatics and in elderly normal subjects. Recent evidence lends some support to the idea of the 'aging' beta 2-adrenoceptor as a contributory factor in the development of late-onset asthma, although questions of the validity of the peripheral mononuclear cell model and of receptor tachyphylaxis to intrinsic and extrinsic beta-adrenoceptor agonists remain unresolved. Further work should focus on in vivo studies of airway receptor function and on beta 2-adrenoceptor-mediated pathways other than smooth muscle-related bronchoconstriction.

Roles of eosinophils and catecholamines in pathophysiology of exercise-induced asthma

To study the roles of eosinophils and catecholamines in the pathophysiology of exercise-induced asthma (EIA), an exercise challenge test was performed in 22 asthmatic children, using a bicycle ergometer, and the changes in lung function, plasma norepinephrine (NE), epinephrine (E) and eosinophil cationic protein (ECP) levels with exercise were evaluated. Subjects were classified into three groups from the results of lung function test, respectively: EIA-negative group. EIA-positive groups with good recovery and poor recovery. Eosinophil counts before exercise in the EIA-positive groups were significantly higher than those in the EIA-negative group. The ECP levels rose with exercise in all groups. Five minutes after exercise, ECP values fell to the pre-exercise level in the EIA-negative group, but rose to higher levels in EIA-positive groups. Plasma E levels rose with exercise and showed 4-fold increase in the EIA-negative group, whereas only 1.5-fold increase of plasma E levels was observed in the EIA-positive group with poor recovery. From these findings, a possible contribution of sympathoadrenal hypofunction and a probable involvement of eosinophils in the pathophysiology of EIA have been suggested.

Beta-adrenoceptors on smooth muscle, nerves and inflammatory cells

Although the bronchodilator action of beta 2-adrenoceptor agonists in asthma is largely due to relaxation of airway smooth muscle, these agents have other effects which may contribute to their anti-asthma action. Human airway smooth muscle contains only beta 2-receptors which, when stimulated, stimulate a rise in intracellular cAMP and activation of PKA (protein kinase A), which in turn phosphorylates several cellular proteins, resulting in relaxation. However, beta-agonists also influence membrane K+ channels and induce smooth muscle relaxation without a rise in cAMP, and this mechanism appears to be the major feature of bronchodilatation in asthma. There is also evidence that beta-agonists may modulate neurotransmission in airways via prejunctional receptors on airway nerves, both sensory and motor. Blockade of prejunctional beta 2-receptors in asthma patients may lead to marked rise in acetylcholine release, with severe bronchoconstriction. Although beta-agonists have little or no effect on the chronic inflammatory response which underlies chronic airway hyper-responsiveness, they do inhibit the release of histamine from mast cells in vitro. The presence of beta-receptors has also been detected not only on mast cells but also on eosinophils, macrophages, lymphocytes and neutrophils, but beta-agonists have little or no inhibitory action on the activities of all these cells due to rapid tachyphylaxis.

Inhibition by salmeterol of increased vascular permeability and granulocyte accumulation in guinea-pig lung and skin

1. The long-acting beta 2-adrenoceptor agonist, salmeterol has been evaluated for its anti-inflammatory effects in the guinea-pig lung and skin. 2. Salmeterol, administered in bronchodilator doses to conscious guinea-pigs by both oral (0.01-1.0 mg kg-1) and inhaled (nebulizer concentration, 0.001-1.0 mg ml-1) routes, inhibited histamine-induced plasma protein extravasation (PPE) into the airway lumen. 3. Inhibition of PPE by salmeterol was long-lasting (greater than 6 h) and was inhibited by prior administration of propranolol (1 mg kg-1, s.c.), indicating an effect mediated by beta-adrenoceptors. 4. Inhaled salbutamol (nebulizer concentration, 0.001-1.0 mg ml-1) also inhibited PPE in guinea-pig lung but, in contrast to salmeterol, this effect was short-lived with substantial loss of activity 2 h after administration. 5. Inhaled salmeterol (0.1 mg ml-1) and salbutamol (1.0 mg ml-1) inhibited the accumulation of neutrophils in guinea-pig lung in response to lipopolysaccharide (100 micrograms ml-1). Salmeterol, but not salbutamol, inhibited the infiltration of eosinophils into the airway lumen in response to platelet activating factor (100 micrograms ml-1). These effects of salmeterol were blocked by prior administration of propranolol (5 mg kg-1, s.c.), indicating that they were also beta-adrenoceptor-mediated. 6. Oral salmeterol (10 mg kg-1, p.o.), but not salbutamol (10 and 100 mg kg-1, p.o.), inhibited zymosan-induced granulocyte accumulation and PPE in guinea-pig skin. Lower doses of salmeterol (0.1 and 1 mg kg-1) inhibited PPE, but not granulocyte accumulation.The effects of salmeterol were blocked by prior administration of propranolol (1mgkg-', s.c.). Both salmeterol and salbutamol inhibited histamine-induced PPE in guinea-pig skin.7. Intradermal salmeterol (10-'mol per site), but not salbutamol, was also effective in inhibiting zymosan-induced granulocyte accumulation and PPE in guinea-pig skin.8. It is concluded that salmeterol, at bronchodilator doses in the guinea-pig, inhibits granulocyte accumulation and PPE, possibly by an action on the vasculature. As this profile of activity is not shared by the shorter-acting compound, salbutamol, it would seem that anti-inflammatory activity is associated with beta-adrenoceptor agonism of long duration. The implications of these findings for the use of salmeterol in the treatment of bronchial asthma are discussed.

Beta 2 adrenergic receptors in asthma: a current perspective

The role of the beta 2-adrenergic receptor in both the pathogenesis and treatment of asthma has been a subject of intense speculation and investigation for 25 years. The physiological effects of endogenous circulating catecholamines and exogenous adrenergic agonists in the lung are mediated by the beta 2-adrenergic receptor, which is present on a variety of cell types. Documented effects of beta 2-adrenergic receptor activation in the human lung include smooth muscle relaxation, inhibition of acetylcholine release from cholinergic nerve terminals, stimulation of serous and mucous cell secretion, increases in ciliary beat frequency, promotion of water movement into the airway lumen by stimulation of ion secretion across the apical membrane of epithelial cells, increase in bronchial blood flow, reduction in venular permeability, and inhibition of mediator release from some, but not all, inflammatory cells. Beta 2-Adrenergic receptors are present in normal or increased numbers on asthmatic airway smooth muscle but are uncoupled in severe asthma, leading to functional hyporesponsiveness, probably due to the effects of inflammatory mediators. There is also evidence for dysfunction of beta 2-adrenergic receptors on circulating inflammatory cells following mediator release. However, dysfunction of the receptors on airway smooth muscle and inflammatory cells is unlikely to be of primary importance in the pathogenesis of asthma. There is increasing concern that regular beta 2-adrenergic receptor agonist use in the therapy of asthma is deleterious. Although a number of theories have been advanced to explain such an effect, none is well established and further research is urgently required.

Salmeterol: a potent and long-acting inhibitor of inflammatory mediator release from human lung

1. The effects of salmeterol, a novel long-acting beta 2-adrenoceptor agonist, have been investigated on antigen-induced mediator release from passively sensitized fragments of human lung in vitro. 2. Salmeterol was a potent inhibitor of the release of histamine (-log IC50 = 8.54), leukotriene C4 (LTC4)/LTD4 (-log IC50 = 9.07) and prostaglandin D2 (-log IC50 = 8.81). It was slightly less potent (1-3 fold) than isoprenaline, but significantly more potent (10-35 fold) than salbutamol. 3. Propranolol competitively antagonized the inhibitory effects of salmeterol on histamine release (pA2 = 8.41) and LTC4/LTD4 release, (pA2 = 8.40) indicating an action via beta-adrenoceptors. 4. The inhibitory effects of isoprenaline (20 nM) and salbutamol (200 nM) were removed after washing the lung tissue for 2 h and 4 h respectively. In contrast, the inhibitory effects of salmeterol (40 nM) were much longer-lasting, and were still evident after 20 h. 5. Salmeterol therefore exhibits potent and persistent inhibition of anaphylactic mediator release from human lung. This anti-inflammatory effect may be important for the therapeutic potential of salmeterol in the treatment of bronchial asthma.

IgG- and IgE-mediated histamine release from superfused guinea-pig airway tissues

Anaphylactic histamine release and the inhibition by the beta-adrenoceptor agonist fenoterol has been investigated using lung and tracheal tissues from two groups of guinea-pigs, differently sensitized to respond with IgG or IgE antibodies, respectively. A superfusion method was introduced and compared with classical batch incubation. The difference between IgG- and IgE-mediated histamine release during superfusion of both tissues was much greater than the difference obtained during batch-incubations. Fenoterol inhibited IgG-mediated histamine release during superfusion at lower concentrations and to a larger extent than the release from IgE-sensitized tissues. The inhibition by fenoterol was less pronounced after batch-wise incubations, preincubation at 0 degrees C abolished the quantitative difference of IgG- and IgE-mediated histamine release from lung slices as well as the difference in beta-adrenergic inhibition. It is concluded that the new superfusion procedure for airway tissues enhances the sensitivity of antigen-induced histamine release for pharmacological modulation, compared with batch-wise incubation. In addition, the effects of 0 degrees C pretreatment show that cooled transport and storage of airway tissue should be considered with care.

Biological properties of human skin mast cells

Mast cells and basophils, although sharing many constitutive properties, are quite distinct in their development, functions and biological properties. Mast cell granules are composed of a macromolecular matrix of proteoglycan and neutral protease of which heparin and tryptase, respectively, are predominant. The distribution of the other major neutral protease, chymase, allows human mast cell subpopulations to be subdivided immunocytochemically. All human mast cells respond to IgE-dependent stimulation with the secretion of the preformed mediator, histamine, and the newly generated lipid-derived eicosanoids PGD2 and LTC4. Although amounts of these products vary between mast cells dispersed from different tissues, it is uncertain whether this reflects true heterogeneity. Mast cells of the human skin, but not those of other tissues, are sensitive to stimulation by substance P, compound 48/80 and other basic non-immunological stimuli. The mechanism of mediator secretion induced by these agents is distinct from that induced by IgE-dependent stimulation. However, the morphological characteristics of degranulation are similar, suggesting that the distinct biochemical pathways merge into a common pathway before effecting degranulation.

A new approach to the treatment of asthma

Asthma is a chronic inflammatory condition. The previous emphasis on bronchodilator therapy, which does not treat the underlying inflammation, may be misplaced. Earlier introduction of antiinflammatory agents, such as corticosteroids or cromolyn sodium, is strongly recommended. Effective suppression of airway inflammation reduces the need for bronchodilator therapy and may reduce the morbidity and, perhaps, mortality of asthma.

Beware beta-adrenergic blockers in patients with severe urticaria!

The risks of beta-blockers in asthmatics are well known. However, there are increasing reports of severe, and often refractory, anaphylaxis in patients taking beta-blockers who experience other allergic phenomena. We describe the case of a 69-year-old lady with long-standing recurrent angio-oedema and giant urticaria who was placed on atenolol. Mechanisms whereby beta-blockers may precipitate or exacerbate anaphylaxis are outlined and the treatment of patients with anaphylaxis, taking beta-blockers, is discussed.

Circulating adrenaline and noradrenaline concentrations during exercise in patients with exercise induced asthma and normal subjects

A failure of the usual increase in plasma adrenaline and noradrenaline concentrations during submaximal exercise has been suggested as a contributory cause of exercise induced asthma. Six normal subjects and six asthmatic patients underwent a standard graded maximal exercise test. Measurements of oxygen consumption, minute ventilation, exercise time, blood lactate concentration, and heart rate indicated that the two groups achieved similarly high work loads during exercise. Mean FEV1 fell by 20% in asthmatic patients after exercise. Basal plasma adrenaline concentrations (nmol/l) increased in normal subjects from 0.05 to 2.7 and in asthmatic patients from 0.12 to 1.6 at peak exercise. Noradrenaline concentrations (nmol/l) increased in normal subjects from 2.0 to 14.3 and in asthmatic patients from 1.9 to 13.7 at peak exercise. The increases in adrenaline and noradrenaline in the asthmatic patients did not differ significantly from the increases in normal subjects. Thus a reduced sympathoadrenal response to exercise seems unlikely to be an important mechanism in the pathogenesis of exercise induced asthma.

Systemic adrenaline attenuates skin response to antigen and histamine

Six atopic subjects received either adrenaline (0.3 ml of 1 mg/ml), subcutaneously over the deltoid muscle, or saline on 2 separate days. After 10 min, histamine and antigen were injected intradermally in the forearm. Adrenaline significantly inhibited the flare of histamine and both the flare and weal of antigen (P less than 0.05). This anti-allergic action of adrenaline occurred with a dose that we have previously shown produces plasma concentrations at the upper limit of the physiological range in resting normal subjects.

Effect of prednisolone and ketotifen on beta 2-adrenoceptors in asthmatic patients receiving beta 2-bronchodilators

In 13 patients with bronchial asthma, who were on beta 2-adrenergic bronchodilator therapy, the effects of prednisolone and ketotifen on lymphocyte beta 2-adrenoceptor density and -responsiveness were investigated. The mean lymphocyte beta 2-adrenoceptor density and -responsiveness was significantly lower than in healthy controls, presumably due to the long-term beta 2-adrenergic bronchodilator treatment. Both prednisolone 100 mg i.v. and ketotifen 1 mg b.d.p.o. for 6 days rapidly improved lymphocyte beta 2-adrenoceptor function. 16 h after prednisolone and about 6 days after the first dose of ketotifen lymphocyte beta 2-adrenoceptor density and -responsiveness had risen to values within the range in normal volunteers. The improvement of lymphocyte beta 2-adrenoceptor function was accompanied by a significant increase in peak expiratory flow rate before and after inhalation of salbutamol. It is concluded that prednisolone and ketotifen may act beneficially on the recovery of beta 2-adrenoceptor responsiveness to beta 2-adrenergic bronchodilators in tolerant asthmatic patients.

The ability of salbutamol and theophylline to suppress immediate allergic conjunctivitis in the guinea pig

Topically administered salbutamol was extremely effective in suppressing immediate allergic conjunctivitis in the guinea pig; a dose as low as 0.1% elicited 98% inhibition. Topical pretreatment with 1% propranolol completely blocked the suppressant action of 0.1% salbutamol. This was also the case after systemic propranolol (1 mg/kg SC); the beta-adrenoceptor antagonist itself has no effect on antigen-induced inflammation. The effect of 0.1% salbutamol was unaltered by pretreatment with the specific beta 1-adrenoceptor antagonist betaxolol (1 mg/kg SC). In marked contrast, the suppressant action of 0.1% salbutamol was profoundly inhibited by pretreatment with the selective beta 2-adrenoceptor antagonist ICI-118,551 (0.5 mg/kg SC). The experiments employing beta-adrenoceptor antagonists unequivocally demonstrate that the salbutamol suppression of immediate allergic conjunctivitis in the guinea pig is mediated via the activation of beta 2-adrenoceptors. The methylxanthine phosphodiesterase inhibitor theophylline was active after oral administration, 50 mg/kg eliciting an 80% inhibition. Theophylline was inactive topically at 1% and 5%, but this could be due to the fact that the compound was insoluble at these concentrations. Thus, procedures that elevate cyclic-AMP levels suppress immediate hypersensitivity reactions in the guinea pig conjunctiva. Whether or nor this offers an alternative approach to treat allergic conjunctivitis in humans remains to be determined.

Beta-blocker therapy and the risk of anaphylaxis

Beta-blocker therapy is associated with an increase in the severity and, possibly, the incidence of acute anaphylaxis. The population at risk consists of people with allergic conditions who are given a beta-blocker for an unrelated condition. Anaphylaxis under these conditions may be severe, protracted and resistant to conventional treatment because of the beta-adrenergic blockade. Severe or fatal attacks have been triggered by insect stings, the ingestion of allergenic foods or drugs, and injections of radiocontrast media, antisera or immunotherapy antigens. These occurrences are probably infrequent, but their incidence is unknown. At least two fatal cases have recently occurred in Canada. Clinical allergists, internists and family practitioners in particular should be aware of the need for aggressive and prolonged support in patients who experience anaphylaxis while receiving beta-blocker therapy and should report all such occurrences to the federal registry of adverse drug reactions. Allergy skin testing or immunotherapy is inadvisable in patients who take a beta-blocker orally or in the form of ophthalmic eyedrops. The list of relative contraindications to beta-blocker use should be extended to include susceptibility to recurrent anaphylaxis, whether it is idiopathic or due to an identifiable cause.

Pulmonary anti-anaphylactic activity of clenbuterol tested on actively and passively sensitized guinea-pigs

Clenbuterol, an adrenergic beta-mimetic agent free of cardiostimulant effects, prevents the release of histamine from isolated rat mast cells. We studied its anti-anaphylactic activity in guinea-pigs and compared it with that of isoprenaline. At doses inactive against the bronchoconstriction caused by 5HT, clenbuterol (3 micrograms/kg) and isoprenaline (0.1-0.3 micrograms/kg) prevented the bronchoconstriction due to 1 mg/kg ovalbumin infused into passively sensitized animals. Clenbuterol and isoprenaline (0.5-1 microM) inhibited by 40% the contractions of superfused parenchyma lung strips from actively sensitized animals, stimulated with 0.3, 1 and 10 micrograms of ovalbumin. When strips from passively sensitized animals were challenged in the organ bath, clenbuterol and isoprenaline (0.01 microM) reduced by 50% the contraction triggered by 10 micrograms/ml of ovalbumin. These concentrations of clenbuterol were ineffective against contractions caused by acetylcholine. Clenbuterol and isoprenaline (0.001-0.01 microM) inhibited the release of histamine and of thromboxane A2 triggered by ovalbumin (0.1, 1 and 10 micrograms) injected into isolated lungs from actively sensitized guinea-pigs indicating that the anti-anaphylactic properties of clenbuterol are independent from its smooth muscle relaxing activity.