Bronchial hypersensitivity to mecholyl and histamine in asthma subjects

Methacholine challenge testing: comparative pharmacology

Standardization of the methacholine inhalation challenge, the most common direct bronchoprovocation test, is important. One aspect of standardization is the appropriate washout period for pharmacologic agents which affect the response. This review summarizes the available data on pharmacologic inhibition of the methacholine response. Specific (anti-muscarinic) agents demonstrate marked bronchoprotection (up to 7 days for the long-acting drugs) which lasts longer than the duration of bronchodilation. The functional antagonist (beta 2 agonist class of medications) shows marked, but less, bronchoprotection which is relatively short lived and is similar to the duration of bronchodilator efficacy. Tolerance develops quickly, especially to the long-acting agents. Single doses of controller medications, such as inhaled corticosteroids (ICS) and leukotriene receptor antagonists, have no effect on the methacholine test, while regular use, at least for ICS, has a modest protective effect whose duration is uncertain and likely variable. Theophylline has a small effect and H1 blockers (all generations) have a negligible effect.

Testing airway responsiveness using inhaled methacholine or histamine

Airway responsiveness assessed using histamine and methacholine is safe, reproducible and relatively easily undertaken in adults and children. Results are similar for methacholine and histamine although methacholine is better tolerated. Responsiveness is increased in children and the elderly, and in women compared to men, possibly due to body size effects. Baseline lung function confounds the interpretation of airway responsiveness and may explain the effect of smoking in most studies. Results are most usefully expressed as the provocative dose producing a 20% fall in FEV1 (PD20FEV1) or the dose-response slope (DRS). When technical factors are controlled the reproducibility of the test is from one to two doubling doses. Measurements of airway responsiveness have been widely used in clinical and research practice. However, assessing their value in diagnosing asthma is limited by the lack of a gold standard for the definition of asthma. Using a cut-off value of 8 mg/mL or 8 mumol for PD20, the tests will discriminate asthmatic from non-asthmatic subjects (based on questionnaire definitions of asthma) with a sensitivity of around 60% and a specificity of around 90%. These properties of the test result in positive and negative predictive values of 86% and 69% when the prevalence of asthma is high (50%-as in the clinical setting) and 40% and 95% when the prevalence of asthma is low (10%, as in general population studies). In the usual clinical setting, assessing the significance of atypical or non-specific symptoms, the tests are of intermediate value in predicting the presence of asthma and less useful in excluding asthma. The additional benefit of testing airway responsiveness to measuring peak flows or to a trial of therapy has yet to be fully assessed. Testing of airway responsiveness may be of value in assessing occupational asthma, asthma severity and the effects of potential sensitizers or treatments. In research, tests of airway responsiveness are more useful for excluding cases of asthma. In population studies, they serve as an objective marker of abnormal airway function which may be genetically determined and, like allergy, are strongly associated with asthma. The predictive value of airway hyperresponsiveness for the development of airway disease is yet to be clearly established. In epidemiology the benefits of measuring airway responses must be weighed against the added inconvenience and cost that is incurred.

Inhaled lysine acetylsalicylate (L-ASA) attenuates histamine-induced bronchoconstriction in asthma

When administered by inhalation, histamine provokes dose-related bronchoconstriction in asthmatic subjects mainly by a direct activation of histamine H1-receptors on airway smooth muscle. However, little is known of the change in airway responsiveness to histamine after cyclooxygenase blockade. The aim of the study was to investigate the effect of the potent cyclooxygenase inhibitor, lysine acetylsalicylate (L-ASA), administered by inhalation on histamine-induced bronchoconstriction in a group of 16 asthmatic subjects. The subjects studied attended the laboratory on four separate occasions to receive nebulized L-ASA (solution of 90 mg/ml) or matched placebo (glycine solution of 30 mg/ml) 15 min before bronchoprovocation tests with histamine and methacholine in a randomized, double-blind order. Changes in airway caliber were followed as forced expiratory volume in 1 s (FEV1), and agonist responsiveness was expressed as the provocative concentration causing a 20% fall in FEV1 from baseline (PC20). Administration of both L-ASA and glycine solution caused a small but significant acute fall in FEV1 from baseline, which returned to normal within 15 min. When compared to placebo, inhaled L-ASA reduced the airway responsiveness to histamine in 13 of the 16 subjects studied, the geometric mean (range) values fro PC20 histamine increasing significantly (P < 0.001) from 1.72 (0.13-5.49) mg/ml to 3.31 (0.36-12.00) mg/ml after placebo and L-ASA, respectively. No significant change in airway responsiveness to methacholine was recorded after L-ASA. Acute administration of L-ASA by inhalation protects the asthmatic airways against histamine-induced bronchoconstriction, thus suggesting that endogenous prostaglandins may play a contributory role in the airways response to histamine in human asthma.

[Current use, methodology and evaluation of nonspecific bronchial provocation tests in our country]

With the aim of determining the current use of non-specific bronchial inhalation challenge (BIC) testing in Spain, 147 questionnaires were sent to hospitals with pneumology departments or units. The questionnaire covered general, technical and methodological aspects of this diagnostic procedure, as well as its assessment and interpretation. Of the 42 informants who returned questionnaires, mainly from large urban hospitals, 34 reported using BIC. The most widespread criterion applied in deciding to use BIC was the presence of atypical asthma symptoms (33/34). The stimulus most often used was methacholine inhalation (33/34). We found that technical preparation of the drug was highly standardized, but that administration and follow-up protocols differed greatly. There was also great variety in the PC20/PD20 value assigned to indicate bronchial hyperresponsiveness. This study contributes to our better understanding of the current use of BIC in Spain and highlights the need to work toward greater standardization for this diagnostic procedure, to enable us to assess and interpret the results more consistently.

Unimodal distribution of bronchial hyperresponsiveness to methacholine in asthmatic patients

Distribution of bronchial hyperresponsiveness to methacholine was assessed in 791 consecutive patients who were referred to the outpatient clinic of the pulmonary department due to asthmatic or persistent lower airway symptoms. Bronchial asthma was diagnosed in 319 patients. Clinical sensitivity of methacholine challenge for the disease was 89 percent and specificity, 76 percent. The degree of bronchial hyperresponsiveness in the entire group of asthmatic patients was unimodally log normal distributed. Of the 82 patients with allergic rhinitis without concurrent asthma, 27 percent had bronchial hyperresponsiveness, but of a markedly lesser degree than in the hyperresponsive asthmatic patients. In 49 patients with chronic bronchitis, 22 percent had hyperresponsiveness. The present data indicate that the degree of bronchial hyperresponsiveness in asthmatic patients is unimodally distributed, supporting the view that both genetic and environmental factors have an impact upon its development. Although the degree of bronchial hyperresponsiveness in asthma is more pronounced than in allergic rhinitis or in chronic bronchitis, a marked overlap exists.

The relationship between bronchial responsiveness to methacholine and bronchial responsiveness to histamine in asthmatic subjects

There is widespread belief that methacholine responsiveness in asthmatic subjects is closely related to histamine responsiveness, and that the two agents may be used interchangeably in the measurement of non-specific bronchial responsiveness (NSBR). Because this view has been challenged, we have examined the repeatability of measurements of bronchial responsiveness to methacholine and histamine and the relationship between them, in groups of 20 adult asthmatic subjects. Bronchial responsiveness was expressed as the cumulative dose (in both micrograms and mmols) provoking a 20% fall in FEV1 (PD20). The predicted 95% confidence limits for the second PD20 measurement of a further pair were within the range 0.5-2.0 x first PD20 for both agents. When the two agonists were compared in the same subjects, a significant difference in potency was noted (ratio of geometric means PD20.methacholine to PD20.histamine 2.19 [micrograms], 3.43 [mmols]; p = 0.0003). Furthermore, the variance of the differences of the pairs of log PD20.methacholine and PD20.histamine measurements was found to be significantly greater than that of either the paired methacholine measurements or the paired histamine measurements (p less than 0.01). We conclude firstly that methacholine is a less potent bronchoconstrictor than histamine and secondly that, while inhalation tests with either agent broadly reflect the degree of NSBR, they measure different phenomena and cannot be used interchangeably even after allowance is made for the difference in potency.

Recovery of FEV1 after histamine challenge in asthmatic children

Factors that influence the time necessary for complete recovery of FEV1 after inhaling histamine were analysed in forty-five children with asthma. These included the initial bronchial obstruction (baseline FEV1), the provocation dose of histamine producing a 20% fall in FEV1 (PD20) and the fall in FEV1 after the histamine challenge. In addition it was also investigated whether a second challenge carried out after complete recovery of FEV1 would produce a reproducible PD20-histamine value. The time for complete recovery varied widely from 15 to more than 75 min. The time needed for complete recovery of FEV1 after the histamine challenge seems to be mainly determined by the PD20 value. The other factors such as initial bronchial obstruction and the fall in FEV1 after the challenge showed no significant relationship with the recovery time. A second challenge with histamine resulted in a highly reproducible PD20 value. The clinical implication of this study is that other tests can only be performed when FEV1 has returned to 95% of baseline.

Blood leukotriene levels during the acute asthma attack in children

Leukotrienes (LT) have been proposed to be important mediators in the etiology of the acute asthma attack (AAA). We therefore studied blood LT levels in 18 children having AAA. Heparinized blood samples were obtained before and after treatment with epinephrine injections and/or metaproterenol inhalations in the emergency room. The samples were acidified and subjected to Sep-pak chromatography. Reverse phase high performance liquid chromatography (RP-HPLC), ultraviolet (UV) spectroscopy and bioassay on guinea pig ileum were used to identify the LT based on comparison to data produced by standard synthetic LT samples. Radioimmunoassay (RIA) was used to further confirm the presence of LT. LT C, D and E were detected in the plasma of children having AAA. Only LT C levels were significantly elevated over control values. The mean blood LT C level of control patients was 1.6 +/- 1.2 nanograms per milliliter (ng/ml, mean +/- SEM) while that of the asthma patients was 73.8 +/- 18.2 ng/ml prior to treatment. After emergency room treatment the asthma patients had a mean blood LT C level of 22.5 +/- 11.7 ng/ml. Lowered levels of LT C accompanied improved clinical condition of the patients. This finding indicates that the AAA in children is associated with elevated blood levels of LT C.

Nasal response of rhinitic and non-rhinitic subjects to histamine and methacholine: a comparative study

The nasal responses to provocation with histamine and methacholine were compared in 20 subjects with and 20 without rhinitis. Two variables were measured: nasal airways resistance and the development of rhinorrhoea. Histamine had a greater effect than methacholine in increasing nasal airways resistance while the converse was true for rhinorrhoea. Rhinitic subjects had a significantly greater response to histamine induced changes in nasal airways resistance (p less than 0.05), rhinorrhoea (p less than 0.05) and methacholine induced rhinorrhoea (p less than 0.01) than those without rhinitis. No significant differences were found between the two groups in methacholine induced changes in nasal airways resistance. The findings show that, like the lower airways of patients with asthma, the nasal mucosa of rhinitic subjects shows a greater responsiveness to non-specific agonists than that of non-rhinitic subjects.

Behavioral interventions as adjunctive treatments for chronic asthma

Results of this review of the behavioral literature on asthma therapy indicate that systematic desensitization, operant interventions, and biofeedback treatments have been successful in altering pulmonary functioning, asthma symptomatology, and/or asthma-related behaviors, whereas some evidence for the limited effectiveness of relaxation training has been demonstrated. The clinical usefulness of these techniques remains open to interpretation. It cannot be said, however, that the results reported represent the definitive statement regarding the usefulness of these interventions, due to the lack of methodological sophistication evident in this body of research. Behavioral investigators currently interested in this area have the opportunity to design and implement research strategies which attend to sound methodological considerations and which may present a clearer demonstration of the efficacy of the adjunctive behavioral treatments which have been used with asthma patients for the past several decades.

Atopic disposition and bronchial reactivity to inhaled acetylcholine in young adults with a history of asthma in childhood

The atopic disposition, indicated by positive skin reactions and IgE antibody titers etc., and the bronchial reactivity to inhaled acetylcholine were examined on the following three groups: (1) 20 young adults with a history of childhood asthma who have been symptom-free for more than 4 yr; (2) 20 current asthmatics, and (3) 20 healthy young adults. Young adults with a history of childhood asthma remained atopic in their disposition even after complete clinical remissions of their childhood asthma. However, they had a lower bronchial reactivity as compared with current asthmatics, although the bronchial reactivities of both groups were apparently higher than the control group.

Effect of prior bronchoconstriction on the airway response to histamine in normal subjects

We have examined the effect of prior bronchoconstriction on the bronchial responsiveness to inhaled histamine in nine normal subjects. The airway response to increasing concentrations of histamine aerosol was assessed by measurement of specific airways conductance (sGaw) in a body plethysmograph. The threshold provocative dose of histamine needed to cause a 35% fall in starting sGaw (PD35) and the steepest slope of the response were measured from cumulative log dose response curves. Histamine challenges were performed in duplicate after premedication with 0.9% sodium chloride (control) or methacholine aerosol on separate days. The mean starting sGaw did not change significantly after inhalation of 0.9% sodium chloride but methacholine caused a mean reduction in sGaw of 42%. Mean control PD35 values did not differ significantly from mean PD35 values after methacholine. The mean steepest slope of the response after methacoline was 47% lower than the mean control value. There was a significant linear relationship between starting sGaw and the steepest slope for the control and for the methacholine premedicated challenges. The reduction in slope after methacholine was accounted for by the fall in starting sGaw. Because histamine PD35 was not altered by prior bronchoconstriction, it is concluded that the bronchial hyperresponsiveness of asthmatic subjects to non-specific bronchoconstrictor stimuli is unlikely to be a direct consequence of their low starting airway calibre.

Histamine bronchial challenge: effect on regional ventilation and aerosol deposition

We studied regional changes in ventilation and aerosol deposition after histamine challenge in six patients with asthma and two with rhinitis and a history of wheezing. All were known to have bronchial hyperreactivity and all showed an increased response to histamine. Ventilation and aerosol deposition studies, using xenon-133 and an aerosol of sulphur colloid tagged with technetium 99m, were performed while they were sitting. Before administration of histamine radioaerosol scintiscans were abnormal in five of six patients; after histamine challenge all were abnormal and central deposition was significantly greater in all of them. The decrease in aerosol penetration correlated with the percentage decrease in FEV1, indicating that the efficiency of aerodynamic filtration depends on the degree of airway narrowing. In six of the eight subjects the distribution of ventilation changed from predominantly basal to predominantly apical after histamine, which suggests the airways response was greater, at least initially, in the better ventilated regions. This indicates a close relationship between regional ventilation and the site of histamine deposition and has implications for the delivery of aerosolised agents in general.

Diagnosis of bronchial asthma by clinical evaluation. An unreliable method

To determine the predictive value of wheeze compared to methacholine inhalation challenge (MIC) in diagnosing asthma, we prospectively evaluated 34 patients considered to be difficult diagnostic problems, referred with a history of wheeze. On the basis of MIC results, 12 patients had hyperreactive airways consistent with asthma, while 22 had airways that were no more reactive than those of normal controls. Compared to MIC, a history of wheeze was predictive of hyperreactive airways 35 percent of the time, a prior clinical diagnosis of asthma 62 percent, and scattered monophonic expiratory wheeze 43 percent. We conclude that: (1) a history of wheeze, a prior clinical diagnosis of asthma, and expiratory wheezing on physical examination are much less reliable than MIC in predicting the presence or absence of asthma; (2) these parameters cannot be used as reliable epidemiologic markers for asthma; and (3) the clinical suspicion of asthma should be confirmed by bronchoprovocation challenge or the demonstration by spirometry of reversible expiratory airflow obstruction.

Reproducibility of histamine challenge tests in asthmatic children

The measurement of bronchial reactivity by histamine challenge testing is of increasing clinical importance in paediatrics. By means of a simple tidal breathing technique for the measurement of histamine sensitivity (expressed as PC20--the concentration of histamine which produces a 20% fall in peak flow rate) in childhood asthma, the reproducibility of pairs of tests was estimated over one hour and 24-hour intervals in 22 children. Under carefully controlled conditions the 95% confidence limits of PC20 were 0.8-1.25 X baseline PC20 after one hour and 0.36-2.8 X baseline PC20 after 24 hours.

Autacoid and autonomic reactivity of sheep lung parenchymal strip and its modification by antigenic sensitization

Lung parenchymal strips (LPS) of horse plasma-sensitized and control sheep were studied isometrically in isolated organ baths and their responses to autacoid and autonomic agents were compared. Control LPS responded with contractions to histamine greater than carbachol greater than 5HT and relaxed to isoproterenol greater than adrenaline greater than phenylephrine. In sensitized LPS, adrenaline and phenylephrine-induced relaxations were converted to contractions and a new order of potency and efficacy for spasmogens was observed i.e. histamine greater than carbachol greater than adrenaline greater than phenylephrine greater than 5HT. Isoproterenol was also significantly (P less than 0.05) less potent and less effective in relaxing sensitized LPS compared to controls. Mepyramine, atropine and propranolol competitively antagonized their respective agonists (i.e. histamine, carbachol and isoproterenol) confirming the presence of H1-histaminergic, muscarinic-cholinergic and beta-adrenergic receptors respectively. The conversion of the relaxant effect of adrenaline and phenylephrine to a contraction supplemented by a significant reduction in isoproterenol activity suggests an impairment in the effective ratio of beta: alpha adrenoceptors in ovine LPS subsequent to antigenic sensitization.

Effects of Freund's complete adjuvant and ovalbumin sensitization on the pharmacological reactivity of isolated guinea-pig trachea

Tracheal strips were obtained from guinea-pigs injected with ovalbumin alone, ovalbumin incorporated into Freund's complete adjuvant (FCA), or FCA alone. There was no difference (P greater than 0.05) in amplitude of ovalbumin-induced contractile responses in tracheas from antigen sensitized and antigen + FCA sensitized animals. Although partial contraction of the muscle with carbachol (ED50) was unaffected by the various treatments, the relaxation responses to isoprenaline, histamine (H2-stimulation) and theophylline were impaired in the group receiving the ovalbumin + FCA sensitization regimen. These results are suggestive of an abnormal response associated with a defective cAMP system in this group.

Comparison of bronchial reactivity to histamine and methacholine in asthmatics

Eight subjects with asthma underwent bronchial challenge with histamine and methacholine. Dose-response curves were drawn on a scale which made the dosage equivalent in molecular weight. The results were analysed in terms of both the slope of the dose-response curve and the dose required to elicit a 20% fall in FEV1. No significant difference between methacholine and histamine was found in either measurement. Because of the similarity of the responses we conclude that the two agents are similar in action and may be used with equal effectiveness in bronchial challenges.

Reversed response to histamine following local anaphylaxis in blood-perfused calf trachea in situ

Tracheas of calves were perfused via the tracheal artery in situ. An endotracheal tube recorded tracheal muscle contractions. Carbachol, histamine or antigen caused tracheal vascular depressor responses. Carbachol caused contraction; histamine, 2-methylhistamine and antigen relaxed the tracheal muscle. Following antigen challenge, vascular responses remained unchanged; however endotracheal relaxations to histamine were reversed (i.e. contractions). Allergenic 'challenge' impairs H2-receptors (airway relaxation), thus diminishing a compensatory mechanism which may relate to hyperresponsiveness characteristic of asthma.

Cigarette smoking in asthma

A survey was performed of smoking habits and respiratory symptoms of 106 asthmatic patients attending a hospital out-patient clinic. A quarter of the patients were currently smokers and a further quarter were ex-smokers. Less than a third of the smokers complained of symptoms of wheeze or dyspnoea after smoking. Asthmatic smokers had a much higher prevalence of chronic cough but their lung function appeared no lower than non-smokers. Ten asthmatic smokers were selected to contrast their acute bronchial response to smoking a currently marketed cigarette with that of ten asymptomatic smokers. Only four of ten asthmatic patients and two of ten asymptomatic smokers developed acute airway narrowing after smoking despite changes in venous blood nicotine levels which confirmed cigarette smoke inhalation. Many more asthmatic patients smoke than might be expected from the known instability of their airways. Our failure to show frequent and substantial airway reactivity to cigarette smoke in these patients suggests either that cigarette smoke may not be as acutely irritant as might be anticipated or that some asthmatic patients acquire tolerance to it. The effects of chronic cigarette consumption could be demonstrated even in this small sample which suggests that asthmatic patients should be advised to stop smoking, especially as many clinicians expect asthma and smoking to be a rare coincidence.

Multiple exercise and histamine challenge in asthmatic patients

We studied the effects of repeated exercise and histamine challenge in asthmatic patients to determine the frequency and degree to which a state of refractoriness was induced by these stimuli. Twenty-nine patients performed three exercise tests, and on a separate day 16 of these patients had three histamine inhalational challenge tests. Forty minutes separated each challenge. Changes in airways resistance were measured using the peak expiratory flow rate (PEFR). The fall in PEFR (expressed as a percentage of the pre-challenge value) was used to quantify the response to challenge. Significant “protection” was defined as a fall in PEFR after a repeated challenge less than 50% of the fall observed on the first challenge. All patients had a fall in PEFR greater than 22% on the first challenge of the day. With repeated exercise 28 out of 29 patients had a fall in PEFR less than that observed on the first test and 12 had significant “protection”. The fall in PEFR after the third exercise challenge was not significantly different to the second challenge and a “plateau” effect was observed. There was no significant difference in the fall in PEFR after the first and second histamine challenge although two of the 16 patients were significantly protected. After the third histamine challenge five of the 16 patients were significantly protected from the effects of the same dose of histamine. The degree to which repeated exercise challenge induces a diminished response is variable. With repeated challenge the response to histamine remains relatively constant in most patients though 30% may be expected to be refractory after a third challenge.

Protective effect of inhaled salbutamol powder in children assessed by histamine challenge

A double-blind placebo-controlled trial of 100, 400, and 800 micrograms inhaled salbutamol powder was conducted on 12 children. The protective effect at 10 minutes, two hours, and four hours was assessed by histamine challenge. At 10 minutes there was good protection with all doses, but by four hours there was significant protection only with 800 micrograms (p less than 0.01). Salbutamol powder may need to be taken at least every four hours for complete protection. There was a dose-related effect with a single dose of up to 800 micrograms; increasing the dose increased the effect and duration of action. Currently advertised dose regimens of salbutamol powder for children (200 micrograms three or four times a day) are apparently submaximal. Histamine challenge is a satisfactory method of assessing the proective effect of a drug in asthmatic children.

Pharmacological study of chicken airway smooth muscle

Isolated chicken bronchus contracts to carbachol, PGF2alpha, histamine, 5-HT, bradykinin and phenylephrine. The bronchial strips from the horse plasma sensitized domestic fowl contracted to specific sensitizing antigen in vitro (Schultz-Dale anaphylactic reaction) and were 5 to 10 fold more reactive to PGF2alpha, histamine and 5-HT compared with the bronchi from normal chickens. Second antigen challenge was inactive or produced a weak response (desensitization). Allowing the bronchi to rest for 1 h resulted in partial recovery of anaphylactic response. Bronchi which had partially contracted submaximally to carbachol, antigen or PGF2alpha, relaxed to isoprenaline, adrenaline and PGE1 and E2.

The qualitative evaluation of airway responses to immunologic and pharmacologic stimuli in rhesus monkeys

This report describes the current status of a colony of rhesus monkeys composed of a group of animals with consistent asthmatic responses to Ascaris antigen challenge, a variable group and a negative group. The cumulative experience with the consistent group of 5 animals totals 144 months of observation with 86 positive respiratory responses to 86 aerosol challenges. Further studies compare rhesus airway responses to Ascaris antigen, anti-IgE, histamine, prostaglandin (PG)F2alpha, carbocholine, and physostigmine. We report that two abnormalities of pulmonary function which occur as a result of aerosol challenge, an increase in breathing frequency (f) and pulmonary resistance (PR), differ in degree of abnormality and time of onset following challenge with different agonists. These results indicate that the f and PR changes in response to these agonists are controlled by different physiologic mechanisms in rhesus monkeys. We suggest that the f changes may occur as a result of reflex afferent vagal stimulation and PR changes as a result of direct effect on smooth muscle receptors. The effect of histamine and PGF2alpha on the airway of rhesus monkeys more closely simulates the airway response to immunologic stimuli than does the effect of cholinergic type agonists.

Autacoid and anaphylactic reactivity of pulmonary and hepatic smooth musculature of the cat

Histamine, 2-methylhistamine (2-MeH: a relatively specific H1 receptor agonist), 5-HT, carbachol, bradykinin (BK) and PGF2alpha contract isolated cat pulmonary vein, artery and hepatic vein. PGE1, PGF2alpha and 4-methylhistamine (4-MeH: a relatively specific H2-receptor agonist) contract pulmonary arterial strips but further increase in the dose of PGE1 produces relaxation. Isoproterenol relaxes partially contracted blood vessels at low doses, but contracts at high doses. Cat trachea contracts to 5-HT, acetylcholine and carbachol but is insensitive to histamine, its analogues, BK and PGF2alpha. However, partially contracted trachea relaxes to histamine, 4-MeH, 2-MeH, isoprenaline, BK, PGE1, E2 and F2alpha. PGF2alpha and SRS-A contract cat bronchus. Isoprenaline, PGE1 and E2 relax cat bronchus contracted to carbachol, 5-HT, PGF2alpha, SRS-A and antigen. The in vitro anaphylactic contraction (Schultz-Dale reaction) of isolated pulmonary and hepatic veins, bronchus and trachea from horse plasma sensitized cat suggested the involvement of lung and liver in anaphylaxis of the cat.

Canine airway responses to acetylcholine, prostaglandin F2alpha, histamine, and serotonin after chronic antigen exposure

Dose-response curves were obtained for aerosols of acetylcholine (ACh), prostaglandin F2alpha (PGF2alpha), histamine (H), and 5-hydroxytryptamine (5-HT) on pulmonary resistance (Rp) and dynamic lung compliance (Cdyn) in Ascaris-hypersensitive dogs. Previously, these animals had been subjected to chronic biweekly "allergic asthmatic" episodes by aerosol administration of Ascaris antigen. When examined either one week before or after antigen provocation the airways were not hyperreactive to ACh, H, or 5-HT but did demonstrate a modest hyperreactivity to PGF2alpha. When aerosol dose-response curves were obtained for these agonists immediately following an "allergic asthmatic" episode, the airways were hyporeactive to PGF2alpha, H, and 5-HT, but not to ACh. Studies with atropine indicated that the hyporeactivity was the result of decreased airway responsiveness to both direct and indirect effect of PGF2alpha and H. It is concluded that, in dogs, chronic antigen challenge is not accompanied by a general increase in airway reactivity to pharmacologic agents.

Regional bronchoconstriction in asthma. 133Xenon washout scans following parenteral methacholine

To determine the influence of bronchoconstriction on the distribution of ventilation during an asthma attack, pulmonary clearance of 133xenon was evaluated in four normal and eight asthmatic subjects within three to five minutes after intramuscular injection of methacholine. In asthmatics, administration of 4-10 mg methacholine resulted in a decrease of forced vital capacity of 28.5 +/- 5.1 (SE) percent and a decrease in expiratory flow at 60 percent vital capacity of 44.2 +/- 6.9 percent (P less than 0.001). The cumulative ventilation required to reach 50 percent of the pre-washout radioactivity increased from 3.6 +/- 0.8 to 9.9 +/- 1.6 L after administration of the drug (P less than 0.05). The normal subjects showed no ventilatory effects after receiving 10 mg methacholine. Comparison of clearance of 133xenon from ten areas of lung (each representing approximately 6 percent of the surface area of one lung) showed that all areas were affected to approximately the same extent during drug-induced asthma. These findings suggest that parenteral methacholine is an effective way to demonstrate airway hyperreactivity and that the airway response to methacholine in asthmatics is relatively generalized throughout the lung.

Oral aspirin challenges in asthmatic patients: a study of plasma histamine

Under carefully controlled conditions, seven aspirin-intolerant asthmatic patients were challenged with oral aspirin and experienced respiratory tract reactions with a decline in forced expiratory volume in 1 sec (FEV1) ranging from 26 to 64%. Venous blood samples, which were collected during the challenges, showed a rise in plasma histamine in all seven patients. The increase in plasma histamine occurred at the onset of their respiratory reactions and those patients with the most severe asthmatic responses were found to have the highest and most prolonged levels of plasma histamine. The aspirin-intolerant asthmatic patients were able to ingest Maalox or sodium salicylate without untoward effects, decline in FEV1 values or changes in plasma histamine levels. Ten non-asthmatic individuals and eight out of ten asthmatic control patients were able to ingest aspirin without any reactions or changes in their plasma histamine levels. However, two asthmatic control individuals, with severe asthma requiring treatment with moderate dosages of corticosteroids, were found to have elevated pre-challenge plasma histamine levels which increased during their ASA challenges despite the absence of respiratory reactions or changes in FEV1 values. It is possible that these two individuals were unsuspected aspirin-intolerant asthmatics. These studies demonstrate that asthmatic reactions to acetylsalicylates are associated with release of histamine into plasma in the subgroup of asthmatic patients with the aspirin-intolerance syndrome. Such a finding suggests that histamine may be one of the mediators of bronchospasm in aspirin-induced asthma.

Reagin-mediated asthma in rhesus monkeys and relation to bronchial cell histamine release and airway reactivity to carbocholine

Rhesus monkeys with persistent immediate-type cutaneous and respiratory responses (RR) to ascaris antigen (AA) were compared with rhesus monkeys with skin reactivity and no respiratory responses, and animals with no skin reactivity and no respiratory responses to inhaled antigen (NR). The RR group could not be distinguished from the nonresponding (NR) group by the cutaneous skin test titers, serum, or respiratory secretion IgE concentration. Leukocyte histamine (H) release due to anti-IgE was similar with peripheral blood leukocytes and bronchial lumen mast cells (MC) from RR and NR animals. The RR group of animals could be distinguished from the NR group by their degree of sensitivity to inhaled carbocholine and H release from respiratory MC exposed to AA. The RR group demonstrates consistent, persistent respiratory responses suitable for immunologic, pharmacologic, and physiologic studies. Finally, it was found that the IgE concentration in respiratory secretions of rhesus monkeys was comparatively higher than in serum, evidence for IgE as a secretory Ig in the respiratory tract of this species.

Bronchial sensitivity to methacholine in current and former asthmatic and allergic rhinitis patients and control subjects

Ninety-eight subjects underwent methacholine (Mecholyl) aerosol challenge at a concentration of 5 mg/ml. All atopic groups differed significantly in their bronchial response to Mecholyl compared to nonatopic control subjects. Nineteen normal subjects had a mean decrease of 11.4% in forced expiratory volume in one second (FEV1) with 128 Mecholyl inhalations and 2 decreased by greater than 20%. Fifteen of 27 allergic rhinitis patients had a positive response to Mecholyl as defined by a decrease in FEV1 greater than 20%. Four of these responders developed greater diminution in FEV1 response with additional Mecholyl inhalations in a manner similar to that seen in the asthmatic patients. Eighteen current asthmatics showed the greatest bronchial sensitivity to Mecholyl with a mean 33% decrease in FEV1 at 4.5 inhalations. One hundred per cent of current asthmatics and 82% (28 of 34) of former asthmatics (free of asthma symptoms for 1 to 20 yr) showed positive response to Mecholyl. A 20% decrease in FEV1 with a total of 20 inhalations or less is consistent with a diagnosis of "current asthma," and even 20 of 34 former asthmatics responded in this manner. The Mecholyl aerosol test can be used to diagnose previous and current asthma and may be of value in predicting asthma in hay fever patients.

Bronchial hyperreactivity

Bronchial hyperreactivity is characterized by increased responsiveness of bronchial smooth muscle to non-specific constrictor stimuli. Tests used in assessing airway calibre are influenced by a number of factors and should be regarded as providing a qualitative rather than quantitative index of reactivity. One important determinant of bronchial reactivity is the resting state of the airways. An increase in resting bronchomotor tone either by the direct action of spasmogens or by the autonomic nervous system may potentiate a subsequent constrictor stimulus. Bronchial challenge may help in the diagnosis of asthma in patients with normal lung function at the time of testing.

Methacholine: a 7-day inhalation toxicity study with primates

The acute and sub-acute inhalation toxicity of methacholine to cynomolgus monkeys was assessed by exposure of animals to an aerosol of a 2% solution of the material in sterile saline. The acute response was characterized by a decrease in tidal volume, increase in respiratory rate, a fall in dynamic compliance and an increased pulmonary resistance. Onset of the acute response was rapid, reached a peak after 2-3 min of exposure and recovery appeared to be complete after 30 min following termination of an exposure. The sub-acute inhalation toxicity of methacholine was assessed by single daily aerosol exposure of primates to graded doses of the compound for 7 days. Pre- and post-exposure measurements of haematology and blood biochemistry, urinalysis, blood gas analysis and ECG showed no changes which could be attributed to exposure to methacholine. Nor were treatment-related histopathological changes observed in exposed animals. Distinct changes were seen in the mechanical characteristics of the lungs of exposed animals. Pulmonary resistances, measured on the day following final exposure, were increased in all animals exposed to the methacholine aerosol. During 9 weeks following the last of the daily exposures, increased pulmonary resistance values persisted in the animals retained for this period, although there was some indication of a gradual return to pre-exposure resistance values.

Acute systemic anaphylaxis in the horse

1. Histamine in small doses caused systemic depressor responses in horses, whereas greater doses caused biphasic effects. All doses of 5-hydroxytrypt-amine (5-HT) were pressor and all doses of bradykinin depressor. All three active substances raised pulmonary artery pressure and lowered central venous pressure. 5-HT reduced ventilation volume. Histamine caused brief apnoea followed by hyperpnoea only.2. Acute anaphylaxis in the horse was accompanied by a severe systemic arterial depressor response, a pressor response in the pulmonary artery and vena cava, and alternating phases of apnoea and dyspnoea.3. During anaphylaxis, profound haemoconcentration, leucopoenia, thrombocytopoenia and hyperkalaemia were in evidence. Early during anaphylactic shock (2 to 4 min) there were profound increases in plasma histamine (five to six-fold) and plasma kinin activity (four to five-fold). Plasma 5-HT concentrations were reduced initially but recovered. Later in anaphylaxis (10 to 20 min) whole blood histamine concentration fell significantly. This coincided with the most profound period of leucopoenia.4. No significant differences were observed in histamine concentration in any of five tissues between six ponies subjected to anaphylaxis and six controls. Mast cell numbers were not reduced but mast cells were more metachromatic (pink) and there was spilling of mast cell granules.5. Gross pathological changes were noted mainly in the lungs which were extensively oedematous and congested. Inflamed, congested and oedematous areas in the large colon and caecum were seen, and the kidneys, spleen and liver were engorged. Alveolar emphysema, peribroncheolar oedema (containing mononuclear cells and neutrophils) were recorded. Alveoli contained erythrocytes.