Effect of alpha-receptor blocking drugs and disodium cromoglyate on histamine hypersensitivity in bronchial asthma

The effects of oral AH 5158, a combined α and β-adrenoceptor antagonist, in healthy volunteers

1 In healthy male volunteers after single oral doses, AH 5158 produced inhibition of exercise induced tachycardia, falls in systolic and diastolic pressure at rest and in response to exercise, which are probably related to combined β- and α-adrenoceptor antagonism. 2 At increasing doses from 100 mg to 400 mg there exists a dose related antagonistic effect, though the dominant effect of β-adrenoceptor antagonism is more easily demonstrable than is α antagonism. 3 As indicated by the pattern of pharmacological effects, absorption of the oral drug is good and the duration of action of a 400 mg dose is approximately 8 hours. 4 Despite being administered in β-adrenoceptor blocking doses, AH 5158 had no adverse effects upon peak expiratory flow at rest or in response to exercise. 5 It is concluded that the pharmacological profile of this combined α- and β-adrenoceptor antagonism suggests a potential therapeutic role as an antihypertensive drug.

The effects of topical sodium cromoglicate on itch and flare in human skin induced by intradermal histamine: a randomised double-blind vehicle controlled intra-subject design trial

BACKGROUND

Itch is a prominent feature of many skin diseases, particularly atopic dermatitis and cutaneous mastocytosis. Sodium cromoglicate (SCG), a chromone developed for the treatment of allergic disease has been shown to reduce the severity of itch when applied topically to subjects with atopic dermatitis. The aim of this study was to investigate whether topical sodium cromoglicate can reduce the severity of itch induced by intradermal histamine.

METHODS

SCG was introduced into the skin of healthy volunteers both by iontophoresis and by topical application using a new 4% cutaneous emulsion (Altoderm™). The skin was then challenged with intradermal histamine. Measurements were made of severity of itch, size of wheal and flare and change in blood flux

RESULTS

SCG significantly reduced the severity of itch (P = 0.0045) and flare (P = 0.0143) when delivered by iontophoresis. SCG 4% cutaneous emulsion significantly reduced severity of itch (P = 0.024) and flare (P = 0.015) in atopic subjects. Trend analysis showed increasing effect on itch with increased concentrations of SCG, which was significant (P = 0.046). There were no effects on wheal or blood flux.

CONCLUSIONS

Topically applied SCG, administered in a new cutaneous emulsion base, significantly reduced the itch and flare caused by intradermal histamine. The effect was greatest in atopic subjects and increased with the concentration of SCG in the emulsion.

TRIAL REGISTRATION

ISRCTN35671014.

Role of muscarinic acetylcholine receptors in a guinea pig model of asthma

We examined the density of muscarinic acetylcholine receptor (mACh-R) subtypes (M1R, M2R and M3R) in guinea pig lung. The density of M3R in the lung tissue of ovalbumin (OA)-sensitized guinea pigs was higher than that in the control group. However, no difference was observed in the affinity of M3R between the sensitized and the control lungs. No difference was observed in the density and affinity of M1R and M2R in sensitized and control lungs. Pilocarpine, which is an M2R stimulant, increased the density of M3R in the lung tissue and the rate of the increase in sensitized guinea pigs was less than that in the control group. In contrast, methoctranine, which is an M2R antagonist, decreased the density of M3R and the rate ofthis decrease was the same in the sensitized and control groups. These results suggest that, in OA-sensitized guinea pigs, a dysfunction of M2R leads to the abnormal density of M3R.

Allergic inflammation in upper and lower airways

OBJECTIVE

The primary reason for this review is to discuss the relationship between upper and lower airways at various levels with the emphasis on common pathophysiologic mechanisms, and how treatment of the upper airways will benefit the lower airways.

DATA SOURCES

The main source of information is derived from original articles and books, with an extensive bibliography included.

STUDY SELECTION

Studies were derived almost exclusively from articles and reviews in peer-reviewed journals.

RESULTS

The prevalence of rhinitis and asthma are both increasing. Common to both the upper and lower airways are the triggers, many of the inflammatory cells and mediators, and the treatment modalities. By contrast, there are organ-specific differences in the reaction to various stimuli in the nose or lung, with each organ manifesting its own vocabulary of response.

CONCLUSIONS

There are meaningful relationships between upper and lower airways at various levels of our understanding. Differential responses to medications help us better understand pathogenic mechanisms in rhinitis and asthma. Further, treatment of the upper airways provides additional benefit to the lower airways.

Effect of an alpha 2-adrenoceptor antagonist, midaglizole, on bronchial responsiveness to histamine in patients with mild asthma

The purpose of this study was to investigate the effects of midaglizole (MID) and interactions of MID with beta 2-agonists on bronchial hyperresponsiveness (BHR). Thirteen patients with mild asthma were randomized with respect to whether they were taking oral beta 2-agonists, and the investigators were blinded to patients' regular drug regimens. Histamine challenge test was performed before and after oral administration of MID for 1 week (300 mg/day). There was a significant increase in PC20 values in asthmatic subjects on regular therapy with beta 2-agonists (p < 0.05), whereas asthmatics not taking beta 2-agonists showed no significant change in PC20. These results suggest that MID may participate in improved BHR in the presence of beta 2-agonists and play some role in enhancing the effects of beta 2-agonists.

Spectral analysis of heart rate variability in bronchial asthma

Sympathetic and parasympathetic activity was evaluated in ten healthy controls, nine asymptomatic, untreated asthmatic subjects and ten asthmatic patients during treatment for acute asthma, by measurement of the variation in resting heart rate using frequency spectrum analysis. Heart rate was recorded by ECG and respiratory rate by impedance plethysmography. Spectral density of the beat-to-beat heart rate was measured within the low frequency band 0.04 to 0.10 Hz (low frequency power) modulated by sympathetic and parasympathetic activity, and within a 0.12 Hz band width at the respiratory frequency mode (respiratory frequency power) modulated by parasympathetic activity. Acute asthmatics had higher heart rates than either of the other two groups; this was probably related to the effects of beta-adrenoceptor agonist medication. Sympathetically mediated heart rate variability (normalized low frequency power) was significantly lower in both asymptomatic (p less than 0.002) and acute (p less than 0.02) asthma subjects compared to controls. This is consistent with altered sympathetic/parasympathetic regulation of heart rate in subjects with bronchial asthma.

Effect of long-term treatment with sodium cromoglycate on nonspecific bronchial hyperresponsiveness in asthma

Several studies in the past have demonstrated a reduction in nonspecific bronchial hyperresponsiveness subjects with seasonal extrinsic asthma after long-term treatment with sodium cromoglycate. Since sodium cromoglycate is an effective drug in the prophylactic treatment of all types of asthma, we assessed the effect of a three-month treatment on nonspecific bronchial hyperresponsiveness in 11 patients with perennial asthma. Bronchial responsiveness was determined by histamine bronchoprovocation test, using SGaw as the index of lung function and expressed as PD35SGaw. During the run-in period of one month when sodium cromoglycate was not used, the histamine PD35SGaw decreased significantly from 0.15 +/- 0.30 to 0.09 +/- 0.29 mg/ml (p less than 0.001). After three months of treatment with the drug, bronchial hyperresponsiveness was reduced significantly; the PD35SGaw was 0.21 +/- 0.29 mg/ml (p less than 0.001). It was concluded that long-term treatment of patients with perennial asthma with sodium cromoglycate results in reduced bronchial hyperresponsiveness.

Corticosteroids and cromolyn sodium as modulators of airway inflammation

Heightened airway reactivity is a cardinal feature of asthma and correlates with many clinical features of the illness, such as the acute response to bronchodilator drugs, the magnitude of diurnal fluctuations in lung function, and the amount of therapy required to control symptoms. Data have accumulated indicating that a reduction in airway reactivity can decrease asthma morbidity, and many advocate treating asthmatic patients prophylactically to prevent acute exacerbations from developing, rather than responding to them after they have occurred. This approach is particularly effective if it is used when the airways are being exposed to stimuli to which they are sensitive. A number of drugs have been purported to reduce airway reactivity, but the most convincing evidence supports the effects of cromolyn and inhaled and oral steroids. Although each type of drug has its own advantages and disadvantages and different modes of action, the common denominator is believed to be a reduction in the state of airway inflammation.

Histamine and allergen induced changes in nasal airways resistance measured by anterior rhinomanometry: reproducibility of the technique and the effect of topically administered antihistaminic and anti-allergic drugs

1. Changes in nasal airways resistance (NAR) following the topical application of histamine and allergen solutions were measured by passive anterior rhinomanometry. 2. The repeatability of five consecutive measurements of resting NAR prior to provocation with histamine or allergen (expressed as the coefficient of variation) was 32.8% and following instillation of saline control solution 37.2%. 3. The repeatability of five consecutive measurements of NAR during the nasal obstruction produced by histamine and allergen was similar to that recorded prior to provocation; the coefficients of variation (median values) being 39.6% and 33.1% respectively. The degree of variability was not related to the dose of agonist or the degree of nasal obstruction. 4. The reproducibility of histamine or allergen induced changes in NAR on four separate weekly occasions showed no significant intra-subject differences. 5. The effects of sodium cromoglycate (SCG), clemastine and ketotifen administered to the nasal mucosa 30 min before provocation with histamine and allergen were compared in a random order, double-blind, placebo controlled study. 6. Clemastine and SCG, but not ketotifen, significantly inhibited the nasal response to increasing concentrations of histamine. None of the drugs administered in the concentrations used in this study significantly inhibited the nasal response to allergen.

Thymoxamine: lack of antihistaminic effects in clinical doses in man

The purpose of this study was to investigate whether the alpha 1-adrenoceptor antagonist thymoxamine possesses antihistaminic activity in clinical doses in man, as has been reported on the guinea pig ileum in vitro. Five normal subjects were given on three separate occasions intravenous infusions of thymoxamine (0.15 mg kg-1 loading dose followed by 0.15 mg kg-1 h-1), chlorpheniramine (1.5 mg loading dose followed by 1.5 mg h-1) and normal saline (placebo). Intravenous bolus doses of histamine (1 and 2 micrograms kg-1) were given after pretreatment with propranolol 10 mg to block the beta-adrenoceptor agonist effects of the catecholamines released by the histamine injections. Histamine caused a dose-dependent reduction of FEV1 and FVC that was antagonised by chlorpheniramine but not by thymoxamine, suggesting that thymoxamine has no antihistaminic activity in the doses used in man. Thymoxamine caused a small enhancement of the bronchoconstrictor effect of the lower dose of histamine. The relatively selective action of thymoxamine makes it a suitable agent for the investigation of alpha 1-adrenoceptors.

An antiallergic activity of disodium cromoglycate unrelated to mast cell activation

The pharmacological effects of disodium cromoglycate (DSCG) were studied in rats during the development of reactions to various allergens or carrageenin. DSCG (10 mg/kg and 100 mg/kg, i.v.) showed pronounced inhibitory effects on type I and type III (passive Arthus) allergic reactions. An immunological degranulation of mast cells and a significant decrease in tissue histamine content were observed in type I allergic reactions but not in type III allergic reactions characterized by an apparent infiltration of neutrophils. An antihistaminic agent, promethazine (1 mg/kg, i.v.) was effective only against type I allergic reactions and totally ineffective against type III allergic reactions. Thus, the results obtained above strongly suggest that DSCG exhibits at least two mechanisms of antiallergic action; one is related to mediator release from mast cells and the other is unrelated to mast cell activation.

Influence of circulating alpha adrenoceptor agonists on lung function in patients with exercise induced asthma and healthy subjects

The influence of circulating noradrenaline (in this context primarily a non-selective alpha agonist) and the alpha 1 selective agonist phenylephrine on bronchial tone, blood pressure, and heart rate was studied in eight patients with exercise induced asthma and eight age and sex matched controls. All subjects refrained from taking treatment for at least one week before the trial. The agonists were infused intravenously in stepwise increasing doses of 0.04, 0.085, 0.17, and 0.34 micrograms/kg a minute for noradrenaline and 0.5, 1.0, 2.0, and 4.0 micrograms/kg a minute for phenylephrine. At the highest dose the plasma concentration of noradrenaline was about 30 nmol/l, resembling the concentrations found during intense exercise, and that of phenylephrine was about 400 nmol/l. Both agonists caused dose dependent and similar increases in blood pressure in the two groups. Despite clearcut cardiovascular effects (systolic and diastolic blood pressure increased by about 40-50/25-30 mm Hg), neither agonist altered lung function, as assessed by measurements of specific airway compliance (sGaw), peak expiratory flow (PEF), or end expiratory flow rate, in either group. It is concluded that circulating alpha agonists, whether alpha 1 selective (phenylephrine) or non-selective (noradrenaline), fail to alter basal bronchial tone in patients with exercise induced asthma or in healthy subjects.

Bronchial responsiveness to methacholine during airway cooling in normal subjects

In order to investigate the effects of airway cooling on bronchial responsiveness in normal subjects, we measured bronchial responsiveness to inhaled methacholine with and without the inhalation of cold air. Two out of seven subjects showed an increase in baseline respiratory resistance (Rrs) during cooling of the airway but the other five subjects showed little change in their baseline Rrs. All subjects increased bronchial responsiveness to methacholine. Additionally, the threshold dose of methacholine decreased to one-third of the control dose with cooling of the airway. We speculate that airway cooling increased bronchial responsiveness to methacholine in normal subjects presumably due to increased vagal tone, increased alpha-adrenergic activity and/or a release of chemical mediators.

Long-term modification on histamine-induced bronchoconstriction by disodium cromoglycate and ketotifen versus placebo

In order to compare long-term changes induced on a wide spectrum of bronchial hyperreactivity (BH) by the antiallergic drugs disodium cromoglycate (DSCG) and ketotifen, 56 asthmatic patients (age range 15-55 years) were studied. Patients were allocated to three groups with similar age and BH level. During 2 months, 15 individuals inhaled 20 mg DSCG four times a day, 14 took ketotifen 1 mg twice a day orally and 14 one placebo (lactose) capsule twice a day. After preliminary results, an additional group of 13 patients took clemastine 1 mg orally twice a day for 1 week. Only the ketotifen and clemastine groups differed significantly from the placebo group on shifting log dose-response curves of inhaled histamine. In addition, no significant difference was seen between the ketotifen and clemastine groups. These results suggest that changes induced by ketotifen were mainly related to its powerful antihistamine action; similarly, nonspecific BH is not wholly dependent on mediator release.

Bronchial hyperreactivity after treatment with sodium cromoglycate in atopic asthmatic patients not exposed to relevant allergens

The bronchial hyperreactivity, measured as the responsiveness to histamine, was studied in 14 atopic patients before, during, and after 4 wk of treatment with sodium cromoglycate (SCG) and placebo in a double-blind, randomized, crossover study. The patients were not exposed to relevant allergens during the study. The variations in provocation concentrations corresponding to 20% decrease in FEV1 (PC20) were small during both placebo and active drug treatment. After SCG treatment, PC20 increased (less responsiveness) in nine of the 14 patients, especially in those with low PC20 values. The difference between placebo and active drug treatment was not statistically significant. Although SCG has a mediator-inhibiting effect, this study gave no support for the assumption that inhibition of mediator release leads to a reduction of the bronchial hyperreactivity in atopic asthmatic subjects who are not exposed to relevant allergens.

The action of prazosin and propylene glycol on methoxamine-induced bronchoconstriction in asthmatic subjects

The effect of 1 mg inhaled prazosin on bronchoconstriction induced by methoxamine was investigated in seven asthmatic subjects. Prazosin caused significant inhibition of the methoxamine-induced bronchoconstriction in six of the seven patients. These findings suggest that methoxamine produces bronchoconstriction in asthmatic subjects via stimulation of alpha-adrenoceptors. In previous studies propylene glycol has been used as a vehicle for delivery of prazosin. This substance was found to cause significant inhibition of methoxamine effects and to shift the dose response curve to histamine to the right in four of seven patients.

Effect of antihistamines and antiallergic drugs on responses to allergen and histamine provocation tests in asthma

The inhibition of immediate allergen or histamine induced airflow obstruction by inhaled ketotifen, clemastine, sodium cromoglycate, and placebo was studied in two groups of asthmatic subjects. Single doses of ketotifen (0.5 mg), clemastine (0.5 mg), sodium cromoglycate (20 mg), or placebo were administered by inhalation 45 minutes before bronchial provocation testing at weekly intervals, double blind and in random order. Inhalation of ketotifen and clemastine, but not sodium cromoglycate, caused an increase in the amount of histamine which had to be administered to cause a 20% fall in FEV1 from control levels (PD20-FEV1) compared with placebo. The PD20-FEV1 for allergen increased significantly after inhalation of clemastine and sodium cromoglycate. Clemastine, primarily an H1 receptor antagonist, inhibited airflow obstruction after inhalation of both histamine and allergen. Its inhibitory effect on allergen induced asthma did not differ significantly from that of sodium cromoglycate. Ketotifen, when inhaled in a single dose of 0.5 mg before bronchial provocation testing, showed potent antihistamine activity, but there was no evidence of any additional "antianaphylactic" activity.

Haemophilus influenzae and the beta-adrenergic system: a review

Haemophilus influenzae is a bacterium that often can be isolated from the deeper respiratory airways of patients with chronic asthmatic bronchitis. In the present study the effects of H. influenzae vaccination on guinea pig pulmonary beta-adrenoceptor number and function (in vitro and in vivo) have been evaluated. Functioning of beta-adrenoceptors is determined by measuring the beta-mimetic effect of isoprenaline on the inhibition of anaphylactic mediator release and isolated tracheal strip relaxation. The number of beta-adrenoceptor binding sites was measured by means of a 3H-dihydroalprenolol binding assay. Also the mechanism of action underlying the changes in beta-adrenoceptor functioning was evaluated. Furthermore, it was established that the effect on the beta-adrenoceptor system was not specific for H. influenzae and that other respiratory pathogens were also biologically active in this respect.

Dual modes of action for disodium cromoglycate in inhibition of antigen-induced contractions of guinea-pig isolated airways smooth muscle

Disodium cromoglycate (DSCG; 10 mumol/l-1 mmol/l) relaxed the tone induced in the guinea-pig isolated trachea by histamine (5 mumol/l). Both isoprenaline and fenoterol were approximately 1000 times more potent than DSCG in relaxing tracheal smooth muscle. Ovalbumin (1 microgram/ml) contracted isolated tracheal and parenchymal strips from sensitized guinea-pigs. The sensitization procedure used was selective for eliciting IgG antibody production. In concentrations equieffective for relaxation of the isolated trachea, fenoterol (20 nmol/l), isoprenaline (60 nmol/l) and DSCG (100 mumol/l) inhibited ovalbumin-induced contractions of both tracheal and parenchymal strip preparations. DSCG produced a significantly greater (P less than 0.05) inhibition of ovalbumin-induced contractions of isolated trachea than did isoprenaline, suggesting that at 100 mumol/l DSCG produced a greater inhibition of mediator release than that produced by isoprenaline. Compound 48/80 (200 micrograms/ml) contracted the isolated trachea whereas this concentration had no contractile effect on the parenchymal strip. The failure of DSCG to inhibit compound 48/80 induced contractions of the isolated trachea together with the lack of contractile effect of compound 48/80 on the parenchymal strip suggest that compound 48/80 is inferior to antigenic stimulation as a reliable analogue of immunological activation of mast cells and consequent mediator release.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison between an alpha-adrenergic antagonist and a beta 2-adrenergic agonist in bronchial asthma

Fifteen patients suffering from asthma received inhalations of phentolamine, albuterol (salbutamol), a combination of phentolamine and albuterol, and placebo, in a single-blind fashion; the changes in the pulmonary function tests were recorded over a three-hour period. Three patients responded to phentolamine with marked bronchodilatation, whereas severe bronchoconstriction was induced by the drug in two patients. Five patients improved more with phentolamine than with placebo, while all patients improved more markedly with albuterol and still more following inhalation of the combination of both drugs. As a group, there were no statistically significant differences between the responses to phentolamine compared with placebo, or between albuterol alone compared with the combination of both drugs. We concluded that both alpha-antagonist and beta 2-agonist agents act in the same direction in most patients, the beta 2-agonist being the dominant. These results do not offer convincing proof that enhanced alpha-adrenergic activity is the main bronchoconstrictor mechanism even in those few with good response to phentolamine, who also showed very good responsiveness to albuterol. The mechanism of phentolamine-induced bronchoconstriction was discussed, but in the light of presently accepted theories, we were unable to evolve a reasonable explanation.

Sodium cromoglycate, verapamil and nicardipine antagonism to leukotriene D4 bronchoconstriction

1--The effects of nicardipine, verapamil and sodium cromoglycate (SCG) on the increase in pulmonary airway resistance(RAw) and decrease in pulmonary dynamic compliance (CDyn) induced by leukotriene D4 (LTD4) 0.5 micrograms kg-1 and acetylcholine (ACh) 3 micrograms kg-1 were investigated in anaesthetized guinea-pigs. The effects of these three agents on the contractile effects of LTD4 and ACh were tested on isolated tracheal preparations of the guinea-pig. 2--Nicardipine and verapamil (0.3 and 1 mg kg-1), as well as SCG (3 and 10 mg kg-1), partially but significantly inhibited the effects of LTD4 on RAw. Partial inhibition of the effect of LTD4 on CDyn was only observed with verapamil (0.3 and 1 mg kg-1). Nicardipine and verapamil had no effect on ACh-induced bronchoconstriction in vivo. 3--In concentrations higher than 10(-5) M, nicardipine and verapamil inhibited the contractile effects of LTD4 and ACh on guinea-pig isolated trachea. SCG had no effect on this preparation. 4--These results suggest that nicardipine, verapamil and SCG partially reduce the component of bronchoconstriction associated with stimulation of irritant receptors by LTD4. However, the site and mechanism of action of Ca2+-entry antagonists remain uncertain.

The modulation of adrenergic airway tone in normal and ascaris-sensitive beagle dogs

The airway effects of adrenergic receptor stimulation/inhibition were investigated in sets of normal (N) and natively ascaris-sensitized (S) beagle dogs. In one group, the effect of beta-adrenergic stimulation/alpha-adrenergic inhibition in airway conductance (Gaw) and dynamic lung compliance (CDYN) were observed. For both N and S dogs, thymoxamine pretreatment served to enhance an isoproterenol inhibition of PGF2 alpha-induced Gaw decreases. No effect was observed in CDYN. In another set of animals, the effects of i.v. administration of norepinephrine (NE), epinephrine (EPI) and phenylephrine (PE), before and after pretreatment with propranolol/indomethacin were observed. For N dogs, all three alpha-adrenergic agents failed to produce bronchospasm; however, propranolol/indomethacin pretreatment significantly potentiated the effects of all three alpha-agents. No significant changes were observed in the CDYN response either prior to or after pretreatment with propranolol/indomethacin. In contrast, for S dogs, all three alpha-agonists produced moderate bronchoconstriction with or without propranolol/indomethacin pretreatment. In addition, the Gaw response to i.v. PE was statistically greater in S dogs than that observed in the N group. Finally, only i.v. PE produced significant decreases in the CDYN response in the S group of animals. These data suggest the presence of alpha-adrenergic influence in the canine airways and elaboration of this action appears to occur best in propranolol/indomethacin-pretreated animals.

Sympathoadrenal reactivity in exercise-induced asthma

The possibility that sympathoadrenal activity is altered in asthma was examined in eight patients with a history of exercise-induced asthma (EIA), eight matched patients with nonexercise induced asthma (NEIA), and eight matched healthy control subjects. No medication was allowed for at least one week before examination. In a pretrial exercise test diagnosis of EIA was confirmed and each individual's work capacity (Vo2 max) was determined. The trial consisted of an orthostatic test and a standardized exercise test at 80 to 90 percent of VO2 max on a treadmill. The trial exercise test caused a decrease in FEV1 in EIA patients only, whereas measurements of Sgaw revealed a significant but less pronounced postexercise bronchoconstriction in NEIA-patients as well. Basal plasma catecholamine levels were similar in all groups. Noradrenaline and adrenaline levels were approximately doubled by the orthostatic test and increased approximately ten-fold following exercise, with no differences between the groups. Plasma cAMP levels were approximately doubled by the exercise test. In the EIA patients there was an inverse correlation between increases in plasma cAMP and decreases in Sgaw. Our study does not support earlier claims that exaggerated catecholamine response to exercise causes postexercise bronchoconstriction by alpha-adrenoceptor stimulation in EIA. Differences in study results appear to have methodologic explanations.

Mechanisms of sulphur dioxide induced bronchoconstriction in normal and asthmatic man

We have examined the inhibitory effect of atropine and sodium cromoglycate (SCG) on the bronchial response to sulphur dioxide (SO2) in groups of normal and asthmatic subjects. Eleven normal subjects were premedicated with propranolol (100 mg orally) one hour before each experiment. After baseline measurements of specific airways conductance (sGaw) the subject inhaled an aerosol from a Wright nebuliser for five minutes. In separate experiments this contained water (control), atropine methonitrate (0 . 2%), or SCG (1%). Fifteen minutes later sGaw was remeasured and the subject then breathed SO2 (8 ppm) for three minutes through the mouth. Specific airways conductance was measured for the duration of the subsequent response. Intervals between experiments on any one subject were one week or more. After control SO2 inhalation sGaw decreased in all subjects (mean 34 +/- 17 (SD)%). Atropine and SCG significantly inhibited the SO2 response (p less than 0 . 01 for both). After atropine the mean decrease in sGaw was 13 +/- 24%; after SCG 16 +/- 12% (range -3- + 55%). With atropine the degree of inhibition was inversely related to the subject's responsiveness to the control SO2 inhalation (r = 0 . 75; p less than 0 . 01). In four asthmatics (without beta-blockade and with lower SO2 exposure) atropine did not inhibit the SO2 response; SCG had a similar effect to that seen in normal subjects. Therefore, vagal efferent mechanisms are involved in the bronchial response to SO2 in normal subjects, but the lack of inhibition caused by atropine in hyperreactive normal and asthmatic subjects suggests that vagal mechanisms are not important in the causation of hyperreactivity to SO2. The mechanism of inhibition with SCG is unknown.

Pathogenesis of asthma. Neurophysiology and pharmacology of bronchospasm

Asthma results from variable and often sudden changes in airway smooth muscle tone. Allergy is not an essential component of the asthmatic response; however, mediator release plays an important role in the human asthmatic response. Histamine may act directly to cause bronchoconstriction by stimulating the H1-receptor on airway smooth muscle or indirectly by stimulation of afferent vagal fibers in airways. Histamine may also act locally on airways to augment cholinergic and, possibly, alpha-adrenergic constrictor effects, or to antagonize beta-adrenergic relaxation of airway smooth muscle. Cholinergic neural output promotes bronchoconstriction in non-atopic asthma, but parasympathetic reflexes are not a major component of human bronchial responses to inhaled allergen. The physiologic significance of the sympathetic nervous system in relaxing airway smooth muscle is incompletely defined. Recent studies suggest that direct sympathetic innervation of airways is relatively unimportant and that purinergic fibers may be the predominant inhibitory neurons in human airways. Investigations focusing on intracellular calcium metabolism in airway smooth muscle have implicated the adenyl cyclase-cyclic adenosine monophosphate system in the regulation of bronchomotor tone. Cyclic nucleotides may modulate but do not mediate respiratory muscle contraction, and their precise role in regulating bronchomotor tone remains uncertain.

Prazosin, an alpha 1-adrenoceptor antagonist, partially inhibits exercise-induced asthma

The effect of prazosin, a potent and specific alpha 1-adrenoceptor antagonist given by inhalation (total nebulized 2 mg) was compared with placebo in a double-blind randomized study of 10 atopic asthmatic children. Prazosin significantly (p less than 0.01) reduced the severity of post-exercise bronchoconstriction (maximum fall in peak expiratory flow after exercise 21.4% +/- SEM 6.3% after prazosin compared with 42.5% +/- 7.3% after placebo). This protective action of prazosin suggests that activation of alpha 1-adrenoceptor may be involved in the pathogenesis of exercise-induced asthma either by facilitation of mast-cell mediator release or by direct contraction of bronchial smooth muscle. Prazosin did not significantly change resting bronchomotor tone or histamine-induced bronchoconstriction, suggesting no effect on bronchial smooth muscle contractility.

Exercise-induced bronchoconstriction as an expression of bronchial hyperreactivity: a study of its mechanisms in children

The mechanism of exercise-induced bronchoconstriction (EIB) was studied by observing the protective effects of several aerosol agents in a double-blind, randomised trial. Exercise-induced bronchoconstriction was not affected by placebo, but was reduced by each agent used (p less than 0.001). Blocking the parasympathetic system had the weakest effect, while beta 2 adrenergic stimulation produced the strongest effect which was significantly different from the parasympatholytic (p less than 0.02). The effect of the mast cell stabilizer, sodium cromoglycate (SCG) was found to be intermediate. However in some patients SCG had a stronger effect than the beta 2 adrenergic agonist. A relationship was found between EIB and bronchial hyperreactivity induced by histamine (p less than 0.05).

Inhaled prazosin in asthma

Prazosin, a potent and selective alpha-adrenergic antagonist, was given by inhalation to nine asthmatic subjects aged 25-48 years (six with positive skin tests). Prazosin 0.5 mg, salbutamol 1 mg, or placebo were given by nebuliser in randomised double-blind fashion on separate days. Although all subjects showed a significant increase in FEV1, vital capacity, and maximum expiratory flow at 70% of total lung capacity after salbutamol, there was no significant difference between prazosin and placebo. This suggests that alpha-adrenergic receptors are not important in the control of bronchial tone in asthma. The weak bronchodilatation ascribed to alpha-antagonists in previous studies could be explained by other pharmacological actions of the drugs used.

New light on the mechanism of action of disodium cromoglycate

Disodium cromoglycate (DSCG) shows a prolonged protective effect against histamine on the smooth muscle of guinea pig ileum. Preventing allergen-induced mediator release from mast cells as well as protection of smooth muscle against mediators already released can both explain a beneficial effect of DSCG in the treatment of bronchial asthma and food allergy. It is believed that disappointing clinical trials with many new anti-allergic drugs, e.g. RS 7540, can be explained by the lack of protective effect on the smooth muscle of target organs.

Inhibition of allergen-induced asthma by three forms of sodium cromoglycate

The effect of three forms of sodium cromoglycate (SCG), 20 mg, on allergen-induced early asthmatic responses was examined in ten stable asthmatics. Dose response allergen inhalation tests were performed on five occasions at intervals of from 1 to 2 weeks to determine the provocation concentration producing a 20% reduction (PC20 allergen) in FEV1. Placebo was given before the first and the last tests to determine the reproducibility of responses to allergen over the study period; reduced responsiveness was observed in eight of the ten subjects. Major changes in levels of specific serum antibodies of the IgE and IgG classes did not serve to explain the changes in bronchial responses although there was a trend which suggested IgG-related desensitization. The observed changes in bronchial responses and antibody levels illustrate the requirement for tests of reproducibility of responses by the use of placebo controls at the beginning and end of a series of allergen inhalation challenges. SCG as (i) a micronized powder with lactose, (ii) micropellets without lactose, or (iii) an aerosol, were inhaled double-blind, in random order, 5 min before the additional three allergen inhalation tests. PC20 allergen was reduced following SCG in seven subjects; the differences were statistically significant for the group. There was no observed difference in efficacy between the different forms of SCG. In this study, the efficacy of SCG could not be related to age, atopic status, the initial level of allergen-specific IgE antibody, baseline FEV1, level of bronchial responsiveness to inhaled histamine or an effect of SCG on responsiveness to histamine.

Plasma catecholamines during exercise-induced bronchoconstriction in bronchial asthma

Plasma levels of adrenaline and noradrenaline during and after submaximal exercise in patients with bronchial asthma were investigated. Three groups were studied comprising 10 patients with exercise-induced bronchoconstriction (EIB), 10 asthmatic patients without EIB and four normal control subjects. Plasma catecholamines were measured at rest, at the end of exercise, and five and 15 minutes after exercise. Changes in airway resistance were assessed by measuring peak expiratory flow rate. Significant differences in catecholamine levels between reacting and non-reacting patients were found. In 10 patients developing EIB adrenaline and noradrenaline levels had risen significantly by the end of exercise and remained elevated up to the fifth minute of recovery. The rise in catecholamine levels in non-reacting asthmatics was insignificant. In control subjects noradrenaline had increased significantly by the end of exercise.

A protective action of disodium cromoglycate against the contraction of guinea-pig ileum induced by various pharmacological stimulants

The effect of disodium cromoglycate (DSCG) on the contraction of isolated guinea-pig ileum induced by histamine, acetylcholine and serotonin has been investigated. DSCG protected ileum against all agents tested. The action of DSCG at concentrations of 10(-3) to 10(-2) M was both dose- and time-dependent. Furthermore, DSCG inhibited compound 48/80-induced histamine release from isolated mast cells over the same range of concentrations. The anti-histaminic action of DSCG was reversible and after 2 h the ileum responded normally to histamine. DSCG-induced inhibition of the contractile response to histamine could be overcome by increasing concentrations of histamine but not by extracellular calcium. A mechanism of the action of DSCG, either against the contraction of ileal smooth muscle or against histamine release from mast cells, is discussed with a view to the inhibition of the utilization of calcium ions by both cells.

Inhibition of idiosyncratic reactions to aspirin in asthmatic patients by clemastine

An H1-receptor blocking antihistamine, clemastine, taken before aspirin gave complete or partial protection against flushing, rhinorrhea, cough, and headache in ten asthmatic patients with idiosyncrasy to aspirin. In five of the ten patients aspirin-precipitated bronchoconstriction was also reduced or prevented after pretreatment with clemastine. Thus histamine appears to play a part in the production of most non-respiratory symptoms occurring after aspirin ingestion in intolerant patients with asthma. Bronchial reactions might depend partly on histamine and partly on the action of other spasmogens. It is suggested that inhibition of prostaglandins of the E series by aspirin-like drugs plays a crucial part in the release of histamine from tissue stores in aspirin-sensitive asthmatic patients. Clemastine might be of use in the treatment of acute reactions to aspirin.

A comparison of the anti-anaphylactic activities of salbutamol and disodium cromoglycate in the rat, the rat mast cell and in human lung tissue

1 Salbutamol and disodium cromoglycate were compared for anti-anaphylactic activity against passive anaphylaxis in rat skin and peritoneum in vivo and in rat mast cells and human lung fragments in vitro.2 Salbutamol administered intravenously to rats inhibited cutaneous anaphylaxis, but also inhibited cutaneous responses to histamine and 5-hydroxytryptamine. Salbutamol administered intraperitoneally inhibited the release of slow reacting substance of anaphylaxis (SRS-A) but not the release of histamine in the peritoneum. It was a very weak inhibitor of histamine release from rat mast cells in vitro.3 Disodium cromoglycate administered intravenously to rats inhibited cutaneous anaphylaxis. Disodium cromoglycate administered intraperitoneally to rats inhibited the release of histamine and, to a lesser extent, SRS-A in the peritoneum. It was an effective but short-acting inhibitor of histamine release from rat mast cells in vitro.4 Salbutamol was a potent inhibitor of the anaphylactic release of histamine and SRS-A from fragments of human lung.5 Disodium cromoglycate was a weak inhibitor of the anaphylactic release of histamine and SRS-A from fragments of human lung. The inhibition was variable and not dose-related.6 The concentration of salbutamol required to inhibit anaphylaxis in human lung is of the same order as that required to relax human bronchial muscle. It is suggested that salbutamol may be more effective in allergic asthma if given in a prophylactic regimen.

Alpha-adrenergic hyper-responsiveness in asthma

Because alpha-adrenergic stimulation causes bronchoconstriction, the alpha-adrenergic responsiveness of 21 subjects with allergic asthma was compared with that of 16 subjects with allergic rhinitis and 38 normal control subjects. None of the patients had taken medications for at least 30 days before study. Alpha-adrenergic responsiveness was measured by the capacity of phenylephrine to constrict the cutaneous vascular bed and to dilate the pupillary sphincter muscle. Asthmatic subjects required 4.0 +/- 0.6 ng to reduce their cutaneous blood flow by 50 per cent, whereas normal controls required 32.0 +/- 7.5 ng (P less than 0.005) and subjects with allergic rhinitis required 23.7 +/- 9.4 ng (P less than 0.02). The pupils of asthmatic subjects dilated by greater than 0.5 mm in response to 1.8 +/- 0.14 per cent phenylephrine, patients with allergic rhinitis required 2.4 +/- 0.16 (P less than 0.01), and normal controls needed 2.7 +/- 0.07 (P less than 0.00001). Therefore, the patients with allergic asthma had significantly enhanced alpha-adrenergic responses when compared both to normal subjects and patients with allergic rhinitis; the possibility that increased alpha-adrenergic activity contributes to the asthmatic diathesis warrants further exploration.

Interaction of cromolyn sodium in aqueous solution with magnesium ions

The interaction of the antiasthmatic drug cromolyn sodium with Mg2+ ions in solution was studied. Selective ion electrode and torsion viscometer measurements were used to establish the degree of interaction. At the concentrations studied, the cromolyn ion had no more affinity for Mg2+ than SO42-. However, thixotropic gels were formed between 4 X 10(-2) M cromolyn sodium and 4 X 10(-4) Mg2+. At lower concentrations of Mg2+, viscosity still increased significantly. However, when the cromolyn concentration was lowered, the increase in viscosity was much less marked.

Adrenergic responses of asthmatic and normal subjects to submaximal and maximal work levels

The response of the adrenergic system of asthmatic subjects to exercise and the role of plasma catecholamines in exercise-induced asthma were investigated. Plasma levels of norepinephrine and epinephrine were measured at rest, during and after exercise in 7 asthmatic and 9 matched normal subjects. Exercise-induced bronchospasm occurred in all asthmatic subjects following exercise, while no significant change was observed in the normal subjects. The results showed that plasma levels of norepinephrine and epinephrine at rest and changes that occcurred during and after exercise were similar in both normal and asthmatic subjects. These data suggest that the adrenergic response of asthmatics to the same relative exercise stress as reflected in plasma catecholamine levels does not differ from that of normal subjects. It appears that changes in the circulating catecholamines do not play a significant role in the pathogenesis of exercised-induced asthma.

[Relations between cell-bound lipids and disodium cromoglycate (author's transl)]

Disodium cromoglycate binds in vitro and in vivo to lipids in white cells. Smears of cells from lymphocyte cultures and from bone marrow aspirates treated with DNCG and subsequently stained with pseudoisocyanine show a characteristic green fluorescence (515 nm) of membrane- and intracellular-lipids. It is suggested that the mode of action of DNCG in the prophylaxis of bronchial asthma could be the binding of DNCG to membrane lipids. This binding might block the IgE-mediated reaction on the surface of mast cells which otherwise would lead to degranulation and release of vasoactive substances.