G. Watt

Genetic analysis of allergic disease in twins

One hundred seven pairs of twins, sixty-one MZT and forty-six DZT, were investigated for allergic disease by a questionnaire, reaginic antibody levels, bronchial reactivity to inhaled methacholine, and skin test responses. Intrapair correlation coefficients (ri) of measured clinical markers of atopy were determined and a heritability analysis was performed. The intrapair correlation coefficient for serum IgE was 0.82 for MZT and 0.52 for DZT. The methacholine area demonstrated greater correlation in MZT with an ri of 0.67 compared to 0.34 for DZT. The total ISTS had an intrapair correlation coefficient of 0.82 in MZT and 0.46 in DZT. Our analysis demonstrates that methacholine sensitivity, total serum IgE levels, and total skin test scores to be heritable traits and suggests a genetic contribution to their expression.

Methacholine inhalation challenge studies

Methacholine sensitivity has become a valuable and widely used technique for studying the irritability of the airways. Asthmatics are lOOto l,OOO-fold more sensitive than normal subjects to various mediators such as methacholine (P-acetyl methacholine).‘-” This degree of sensitivity has been used to define asthma and also as a genetic marker.l The methacholine responsiveness may be determined by 1 of 2 methods: (1) by determining dose-response curves to increasing concentrations of methacholine while keeping the number of breaths and the volume of methacholine inhaled constant” and (2) by determining dose-response curves by keeping the concentration constant while increasing the number of inhalations of methacholine.” The first method is currently being used more widely and has been recommended by the American Academy of Allergy to provide a standard and uniform method. It is described in detail elsewhere.” The second method has been used since 1962 and has been the basis for a number of short-term and long-term studies. We have recently compared both of these methods to determine the short-term reliability of each method. The dose-response curves and thus the degree of bronchial sensitivity were determined in 19 subjects in a randomized 4-way crossover study. Each subject was challenged twice by each method at 1-wk intervals. The short-term reproducibility for both methods was good (r = 0.934 and 0.942). The correlation between methods was also significant (r =0.953). The various pulmonary function parameters that can be evaluated during an inhalation challenge are numerous and include the FVC, FEV,, SG,,,, FEF,,-,,, PEFR, flow volume loops, etc. The easiest and the most widely used currently is the FEV,, which is the minimum requirement for comparison of responses as recommended by the Standardization Committee, j

Segregation analysis of bronchial response to methacholine inhalation challenge in families with and without asthma

A segregation analysis was performed on the bronchial response to a standardized methacholine inhalation challenge obtained from members of 83 families that were part of a Natural History of Asthma study population. Each bronchial response was expressed as the area under the best fitting parabolic dose-response curve. Standard methods of statistical analysis demonstrated that age, sex, and recent respiratory infection had a significant effect on the bronchial response to methacholine inhalation. Segregation analysis indicated that, although a familial component exists in the transmission of bronchial response to methacholine, the bimodal distribution of the bronchial response is not due to segregation at a single autosomal locus.

Decreased mononuclear cell beta-adrenergic receptors in bronchial asthma: parallel studies of lymphocyte and granulocyte desensitization☆

To assess the interaction of bronchial asthma and beta-agonist drugs, beta-adrenergic receptors were measured in human mixed leukocyte, mononuclear cell, and polymorphonuclear leukocyte cell membranes simultaneously. The densities and affinities of beta-adrenergic receptors were determined, by Scatchard analysis, with a potent beta-antagonist 125I-hydroxybenzylpindolol (125I-HYP) and compared among 12 nonatopic controls (group I), 13 mild asthmatics not taking drugs (group II), and eight asthmatics receiving long-term beta-agonist therapy (group III). Our findings were as follows. (1) Asthmatics not taking drugs (group II) have significantly lower mean mononuclear leukocyte beta-adrenergic receptor density (p less than 0.05) but no significant difference in mean polymorphonuclear leukocyte beta-adrenergic receptor density than the control group. (2) Asthmatics receiving long-term beta-agonist treatment (group III) had significantly lower mean beta-adrenergic receptor density in all three cell fractions (p less than 0.05). (3) Group I and II females had a higher mean beta-adrenergic receptor density in mixed leukocyte and polymorphonuclear cell fractions than males (p less than 0.05). (4) Terbutaline sulfate clearly caused desensitization of beta-adrenergic receptors in human leukocyte membranes in vivo. These results show that beta-adrenergic receptor density is influenced by cell type, beta-adrenergic agonist administration, and sex; they also show that bronchial asthma itself is associated with lower lymphocyte beta-receptor density.

Distribution of methacholine inhalation challenge responses in a selected adult population

To determine bronchial reactivity patterns in adults, 211 subjects, 22 to 86 years of age, underwent a methacholine challenge in a Natural History of Asthma study. The diagnosis of asthma or nonasthmatic allergic diseases was based on a standardized respiratory questionnaire. Subjects were nonsmokers and had not had an infection for 1 month. Intradermal skin tests were done to a battery of common antigens. The methacholine challenge response was expressed as the area under the dose-response curve integrated to a 35% fall in the FEV1 or 800 breath units. Thirty-three subjects with asthma, 47 normal subjects from normal families (NF), 59 normal subjects from families with asthma (AF), 31 allergic subjects without asthma, 23 subjects with questionable asthma, and 18 subjects with prior asthma were studied. Overall, 50% of the subjects without asthma had a negative response to methacholine. There was a difference (p less than 0.02) in the distribution of log10 methacholine area under the dose-response curve integrated to a 35% fall in the FEV1 or 800 breath units responses in normal subjects from NFs compared to normal subjects from AFs. The allergic subjects from AF had a greater degree of bronchial reactivity compared to normal individuals from NF. The age of the normal subjects had an influence on the degree of bronchial reactivity. Methacholine challenge studies in adult patients need to be interpreted with age and family history in mind.

Protective effect of lodoxamide tromethamine on allergen inhalation challenge

Lodoxamide tromethamine (U-42,585E) is a new drug intended for prophylaxis of mast cell-mediated allergic disease. It is a water-soluble, cromolyn-like agent with demonstrated activity in rat peritoneal mast cell assay, rat percutaneous anaphylaxis (rat PCA) and sensitized rhesus monkey airway system. Ten allergen-sensitive asthmatics were pretreated with lodoxamide (0.01, 0.1, or 1.0 mg) or placebo, then challenged with serial dilutions of allergen extract. Analysis of allergen dose-response curve parameters shows that pretreatment with lodoxamide offers significant protection against experimental allergen-induced bronchoconstriction. At 0.01 mg, lodoxamide was effective in over half the subjects tested. Administration of lodoxamide by inhalation at doses of 0.1 and 1.0 mg uniformly allowed subjects to tolerate significantly larger doses of inhaled allergen. Side effects observed at these doses were minimal.

Lymphocyte glucocorticoid receptors in asthmatic and control subjects

Glucocorticoid hormones, which are widely used in the treatment of asthma, have been shown to potentiate physiological and biochemical beta‐adrenergic responsiveness in asthmatics. These effects are presumably mediated through glucocorticoid receptors. In order to better understand glucocorticoid pharmacology in asthmatics, we assayed glucocorticoid receptors by directly binding a radioactively labelled glucocorticoid hormone, dexamethasone, to intact lymphocytes prepared from the peripheral blood of asthmatics and control subjects. Binding studies were performed with dexamethasone at 100 nm and 5 nm concentrations. At 100 nm dexamethasone, the mean number of lymphocyte glucocorticoid receptors (per cell) in control subjects (7191 ± 385. n= 9) was not significantly different from that in asthmatic subjects (7772 ± 437, n = 9). At 5 nm dexamethasone, the mean number of glucocorticoid receptors in control subjects (1177 ± 194, n= 5) was not significantly different from that in asthmatic subjects (1215 ± 108. n= 8). At 100 nm dexamethasone, males had significantly more receptors (7939 ± 360. n= 11) than females (6764 ± 72, n= 7). Our results suggest that the number of lymphocyte glucocorticoid receptors and the apparent affinity of dexamethasone for receptors are not related to the presence or severity of asthma; however, a significant sex effect exists which should be corrected for in future studies of lymphocyte glucocorticoid receptors.

Protection by ipratropium bromide and metaproterenol against methacholine and histamine bronchoconstriction.

To establish relative protection against methacholine and histamine, 40 μg of ipratropium bromide, an anticholinergic compound, 1.3 mg of metaproterenol or placebo aerosols were administered by metered‐dose inhaler prior lo inhalation challenge with methacholine or histamine in nine asthmatic subjects. Double‐blind, randomized challenges were performed. Subjects required a mean methacholine dose of l.72 ± 0.73 and 2.46 ± 0.72 (Ln inhalation units), and mean histamine dose of 2.l6 ± 0.65 and 2.68 ± 0.49, to cause a drop of 20% and 35% respectively in the FEV1 following the placebo. In the methacholine challenges, both ipratropium bromide and metaproterenol had significant protection as compared to placebo (P<0.001). There was no statistical difference in the degree of protection against methacholine between ipratropium bromide and metaproterenol. In histamine challenges, metaproterenol had significant protection as compared to the placebo, while ipratropium bromide did not protect against histamine.