Antiasthmatic effects of a leukotriene biosynthesis inhibitor (MK-0591) in allergic dogs

Peptidoleukotrienes may be important mediators of human bronchial asthma. Accordingly, the effects of a selective leukotriene (LT) biosynthesis inhibitor (MK-0591) were assessed in allergic dogs characterized by acute bronchoconstriction and subsequent airway hyperresponsiveness induced by inhaled ragweed allergen. Peak acute increases in airway resistance (Rrs) induced by ragweed were associated with increased bronchoalveolar lavage histamine concentration, and neither parameter was inhibited by MK-0591 (8 micrograms.kg-1.min-1 i.v.). However, the duration of the bronchoconstriction was significantly decreased by MK-0591, with a reduction in the area under the curve of 40% (P < 0.05). Associated with the acute bronchoconstriction in placebo-treated animals was a fivefold increase in urinary LTE4 excretion (as seen with allergic asthmatic patients), which was reduced to < 10% of basal values by MK-0591. Similarly, whole blood LTB4 biosynthesis was abolished in the MK-0591-treated animals. Bronchial hyperresponsiveness preallergen (measured as the percent concentration of acetylecholine required to increase Rrs by 5 cmH2O.l-1.s) tended to improve with MK-0591 (0.41 +/- 0.15 vs. 0.23 +/- 0.05%). Five hours after allergen inhalation, the percent concentration declined substantially in the placebo group (0.07 +/- 0.02%; P < 0.01), revealing an increased airway responsiveness that was significantly blunted by MK-0591 (0.26 +/- 0.07%; P < 0.001). These data suggest that selective inhibition of LT biosynthesis by novel compounds such as MK-0591 may modify the airway changes associated with bronchial hyperresponsiveness, as well as offer symptomatic relief in asthma.

Effect of nebulized ipratropium bromide on intraocular pressures in children

STUDY OBJECTIVE

To evaluate the effects of nebulized ipratropium bromide on intraocular pressures and pupillary responses in children with asthma.

DESIGN

A double-blind, randomized, crossover study.

SETTING

Children's Hospital of Winnipeg, University of Manitoba.

PATIENTS OR PARTICIPANTS

Age 6 to 17 years with asthma.

INTERVENTION

Nebulized ipratropium bromide added to albuterol sulfate, albuterol alone, or saline solution was given by face mask and nebulizer. Before and 0.5 h after nebulization, intraocular pressures (mm Hg), pupillary size (mm), and pupillary responses were measured. In a subsequent open study, patients who had been admitted to hospital with acute asthma who were treated with nebulized ipratropium bromide were recruited for measurement of intraocular pressures, pupillary size, and pupillary responses.

MEASUREMENTS AND RESULTS

Twenty patients completed the double-blind study, and 26 patients completed the open study. There were no changes in intraocular pressures, pupillary size, or pupillary response after any treatment on any study day in either the double-blind or the open studies.

CONCLUSION

In children with asthma, who have no pre-existing ocular abnormalities, the risk of an adverse reaction to nebulized ipratropium bromide delivered by face mask inadvertently absorbed in the eye is extremely small.

Binding properties of protein A and protein G for human IgE

We studied the binding of protein A and protein G to human monoclonal and polyclonal IgE. An ELISA was used to measure human IgE. Protein A-Sepharose did not bind to monoclonal IgE, but bound to 12-14% of serum polyclonal IgE and to -3% of the polyclonal IgE purified from the serum. No difference in binding to protein A was found between IgE from an allergic patient and that from a non-allergic subject. Protein G bound to neither polyclonal IgE nor monoclonal IgE. Thus, protein G is better than protein A with respect to separation of IgE from IgG.

Identification of glutamate-169 as the third zinc-binding residue in proteinase III, a member of the family of insulin-degrading enzymes

A novel active site has been identified in a family of zinc-dependent metalloendopeptidases that includes bacterial proteinase III, the human and Drosophila insulin-degrading enzymes, and the processing-enhancing protein subunit of the mitochondrial processing proteinase. None of these enzymes contains the conserved active site described in most other metalloendopeptidases, HEXXH; instead, all four contain an inversion of this motif, HXXEH. Prior mutagenesis studies of proteinase III indicate that the two histidines are essential for co-ordinating the zinc atom, while all three residues are required for enzyme activity. To identify the third zinc-binding residue in this protein family, three glutamates downstream from the active site were mutated to glutamine in proteinase III. The mutant proteins were expressed and their ability to degrade insulin was compared with the wild-type enzyme. The glutamate-204 mutant was as active as the wild-type protein, the glutamate-162 mutant retained 20% of the activity of the wild-type enzyme and the glutamate-169 mutant was completely devoid of insulin-degrading activity. The purified wild-type and glutamate-204 mutant enzymes were found to contain nearly stoichiometric levels of zinc by atomic absorption spectrophotometry, whereas the glutamate-162 mutant had a slight reduction in the level of zinc, and the glutamate-169 mutant retained less than 0.3 mol of zinc/mol of enzyme. These findings are consistent with glutamate-169 being the third zinc-binding residue in proteinase III.

Bronchoalveolar eosinophilic cells in a canine model of asthma: two distinctive populations

In a canine model of asthma, the identity and relationships of two types of cells with eosinophilic granules found in bronchoalveolar lavage (BAL) were investigated. Five female and three male newborn mongrel dogs were sensitized by intraperitoneal injection of 500 micrograms ragweed in 30 mg aluminum hydroxide repeated weekly for 8 weeks and then biweekly until 16 weeks of age. Three female and two male littermate controls received 30 mg aluminum hydroxide. From 4 months of age, dogs received six breaths of wet-nebulized ragweed solution through an endotracheal tube bimonthly. Bronchoalveolar lavage was performed 2 months or more after the last exposure to ragweed and was repeated 5 hours after ragweed inhalation. Dogs studied were 15 to 38 months of age. Eosinophilic cell populations were determined in BAL and peripheral blood; cells were examined by light and electron microscopy. Two eosinophilic cell types were in BAL: an eosinophil and an atypical cell with globule leukocyte characteristics. Specific microgranules, a constant feature of eosinophils, were prominent in the atypical cell and suggest a relationship to the eosinophil granulocyte series for the atypical cell and cells identified by others as globule leukocytes. In ragweed sensitized animals, there were more eosinophilic cells in BAL fluid and more eosinophils in peripheral blood. There was a proportional increase in BAL eosinophils 5 hours after ragweed inhalation and a corresponding decline in peripheral blood eosinophils. There was no increase in numbers of eosinophils in the sensitized animals; eosinophil and atypical cell numbers in littermate controls were unchanged.

Measurement of ragweed-specific IgE in canine serum by use of enzyme-linked immunosorbent assays, containing polyclonal and monoclonal antibodies

Using polyclonal rabbit and monoclonal mouse anti-dog IgE antibodies, we developed ELISA for measurement of ragweed-specific IgE in canine serum. In the ELISA, microtitration plates were coated with ragweed extract and sequentially incubated with canine serum, purified monoclonal or polyclonal anti-dog IgE, and conjugated goat antibody to mouse IgG or rabbit IgG. Serum ragweed-specific IgE values were measured by the 2 ELISA in serum samples from 60 ragweed-allergic dogs and in serum from 10 control dogs. Passive cutaneous anaphylaxis (PCA) tests were performed on these sera to compare results with those of the ELISA. Mean coefficient of variation between assays was 0.20 +/- 0.10 for the assay using the polyclonal antibody and was 0.17 +/- 0.10 for that using monoclonal antibody. Sensitivity was 0.6 U/ml for the ELISA, using polyclonal antibody, and 2.5 U/ml for the ELISA, using monoclonal antibody. Serum ragweed-specific IgE values measured by the 2 ELISA strongly correlated with PCA titers (P < 0.0000), but the ELISA using polyclonal antibody had higher correlation with PCA titer (r = 0.84) than the ELISA using monoclonal antibody (r = 0.59). The geometric mean ragweed-specific IgE value measured by the 2 ELISA and by PCA testing, was significantly higher (P < 0.0000). in allergic dogs than in control dogs. The 2 ELISA were specific, sensitive, and reproducible for measurement of ragweed-specific IgE in canine serum.

Binding of dog immunoglobulins G, A, M, and E to concanavalin A

The binding of dog immunoglobulins G, A, M and E to concanavalin A (Con A) has been investigated. A passive cutaneous anaphylaxis test was used for measurement of dog IgE, and enzyme-linked immunosorbent assay was used for measurement of dog IgG, IgA and IgM. After the dog serum fraction was applied to a Con A-Sepharose column, sequential elution with different buffers was performed; 100% of IgE and IgM, 60% of IgG and 58% of IgA bound to the Con A-Sepharose. IgE was eluted by mannose, methylglucose, and methylmannoside. IgG was eluted by glucose, mannose, methylglucose, and methylmannoside. IgA and IgM were eluted by methylmannoside only. This provides a useful technique in the purification of dog immunoglobulins, especially dog IgE.

Trends in physician-diagnosed asthma prevalence in Manitoba between 1980 and 1990

We attempted to assess recent changes in the prevalence of physician-diagnosed asthma and the possible influence of diagnostic exchange on these trends. The routinely collected data of the provincial Health Insurance Plan (physicians' claims) were used to determine the annual prevalence of physician-diagnosed asthma in Manitoba. Results indicate that the prevalence of physician-diagnosed asthma increased for all age groups in both male and female subjects between 1980 and 1990. The average increases were the highest in the age group 5 to 14 years for both sexes. The average increases varied with age and there were significant differences between the two sexes. There was evidence of increasing diagnostic exchange, that is, a tendency to label patients with asthma instead of alternative diagnoses. This was particularly prominent in those younger than 35 years of age. However, the increased prevalence of physician-diagnosed asthma, even for the younger population, cannot be fully explained by diagnostic exchange.

Treatment of allergic rhinitis with intranasal corticosteroids in patients with mild asthma: effect on lower airway responsiveness

The effect of treatment of allergic rhinitis with intranasal corticosteroids on lower airway responsiveness was assessed in a randomized, double-blind, placebo-controlled, crossover study. Twenty-one young patients with perennial allergic rhinitis and asthma, with documented lower airway hyperresponsiveness (PC20 methacholine < 8 mg/ml), were treated with intranasal aqueous beclomethasone dipropionate and placebo, each given for 4 weeks. Patients recorded rhinitis and asthma symptom scores and monitored peak expiratory flow rates every morning and evening. Patients recorded global assessment of rhinitis and global asthma symptom scores at the beginning and end of each treatment. PC20 methacholine was performed at baseline and at the end of each treatment period. Intranasal beclomethasone dipropionate significantly reduced global rhinitis symptom scores (p = 0.05) after 4 weeks of treatment. Global asthma scores did not change significantly (p = 0.2). Geometric mean PC20 methacholine improved significantly after 4 weeks of intranasal beclomethasone, but not after placebo (p = 0.04). Daily morning and evening rhinitis symptom scores were lower in patients treated with intranasal corticosteroids over the first 4 weeks of treatment, but carryover effect of steroids precluded comparative analysis of the second 4-week block (morning p = 0.06, evening p = 0.03). Morning asthma scores tended to decrease (p = 0.07). Evening asthma scores were significantly decreased at weeks 2 and 3 (p = 0.001, p = 0.02, respectively). No change in peak expiratory flow rate was seen. This study confirms that treatment of inflammation in the upper airways indirectly improves asthma symptoms and decreases bronchial hyperreactivity. Ignoring inflammation in the upper airway may lead to suboptimal results in asthma treatment.

Purification and identification of polyclonal IgE antibodies from ragweed-sensitized dog sera

We have purified and characterized polyclonal dog IgE. Serum IgE was precipitated by (NH4)2SO4 and then purified by two different procedures. Ion exchange on DEAE-Sephacel, followed by HPLC using Tonen hydroxylapatite and then Protein G-Sepharose, produced a highly purified IgE fraction (No. 1) free of IgG, IgA and IgM as measured by ELISA, but recovery of IgE as measured by passive cutaneous anaphylaxis was low. Gel filtration on Sephacryl S-300, Con A-Sepharose and Protein G-Sepharose recovered 18% of initial IgE, 0.02% IgG, 0.4% IgM and 0.3% IgA. This IgE fraction (No. 2) was used to induce antibody production in rabbits. Western blot analysis was then performed for dog IgE fractions No. 1 and 2. Using the rabbit anti-dog IgE, a prominent IgE band with an apparent molecular mass of 226 kD was identified in fractions No. 1 and 2 subjected to nonreducing SDS-PAGE. This band also reacted with anti-human IgE, but not with anti-dog IgG or anti-dog IgA. Under reducing conditions the approximate molecular mass for the IgE & chain, estimated by Western blot using rabbit anti-dog IgE, was 73 kD, providing a molecular mass of 196 kD for dog IgE.

Bronchodilator and bronchoprotective effects of salmeterol in young patients with asthma

BACKGROUND

In adults with asthma, the selective beta 2-adrenergic agonist salmeterol has a prolonged bronchodilator and bronchoprotective effect. To date, there are few published studies of salmeterol in children.

METHODS

We compared the bronchodilator and bronchoprotective effects of salmeterol, 25 and 50 micrograms, with salbutamol, 200 micrograms, and with placebo, administered via metered-dose inhaler, in a randomized, double-blind, within-patient, four-way crossover, single-dose study in 20 children.

RESULTS

Mean baseline forced expiratory volume in 1 second (FEV1) and PC20 methacholine were not significantly different (p > 0.05) on the 4 study days, and did not change significantly after placebo. FEV1 increased significantly from 5 to 30 minutes after salbutamol, and from 5 minutes to 12 hours after 25 micrograms or 50 micrograms salmeterol, compared with placebo. After 25 micrograms or 50 micrograms salmeterol, FEV1 was significantly lower than after salbutamol at 5 and 10 minutes, did not differ from salbutamol at 30 minutes, and was significantly greater than after salbutamol from 3 to 12 hours. No significant difference occurred between the effect of 25 micrograms salmeterol and the effect of 50 micrograms salmeterol on FEV1. After salbutamol, there was a significant increase in PC20 only at 30 minutes. After 25 micrograms or 50 micrograms salmeterol, PC20 increased significantly from 30 minutes to 12 hours. Salmeterol, 25 micrograms and 50 micrograms provided significantly greater bronchoprotection than salbutamol from 3 to 12 hours and from 30 minutes to 12 hours, respectively. Salmeterol, 50 micrograms, provided significantly better bronchoprotection than 25 micrograms salmeterol from 30 minutes to 12 hours. The amount of change in PC20 accounted for by change in FEV1 varied from 14% to 28%, indicating that protection against bronchoconstriction was not entirely dependent on bronchodilation.

CONCLUSIONS

Salmeterol is a potent, long-acting bronchodilator, with a slower onset of bronchodilation than salbutamol. It provides significantly greater and longer-lasting protection against bronchoconstriction than salbutamol.

Biochemical and ultrastructural studies suggest that the effects of thapsigargin on human platelets are mediated by changes in intracellular calcium but not by intracellular histamine

The involvement of intracellular histamine in thapsigargin (Tg)-induced platelet aggregation was studied. Platelet aggregation induced by 0.25 and 0.5 microM Tg was not accompanied by a rise in intracellular histamine but a significant (p < 0.01) increase in the level of intracellular histamine was observed at 1 microM Tg. Preincubation of platelets with inhibitors of histamine metabolizing enzymes had little effect on intracellular histamine levels in platelets stimulated by 0.5 microM Tg. In addition, the inhibitors of histidine decarboxylase (HDC), alpha-methyl histidine (alpha-MH) and alpha-fluoromethyl histidine (alpha-FMH) failed to inhibit Tg-induced aggregation. The intracellular histamine receptor antagonist, N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine. HCl (DPPE), inhibited Tg-induced aggregation but with IC50 values dependent on the concentration of agonist used. The inhibitory effects of DPPE on Tg-induced aggregation were not reversed by the addition of histamine to saponin-permeabilized platelets suggesting non-histamine mediated effects of DPPE on Tg-induced aggregation. Tg stimulated an increase in the cytosolic free calcium concentration which was unaffected by DPPE indicating that the effects of DPPE are also not due to the inhibition of mobilization of cytosolic calcium. The ultrastructural studies suggest that the major Tg-induced changes (pseudopod formation and granule centralization) are consistent with a primary role for Tg to mobilize calcium; DPPE had very little effect on these ultrastructural changes. The results indicate that the effects of Tg on human platelets are mediated by an increase in cytosolic calcium but not by intracellular histamine.

Christmas candy maker's asthma. IgG4-mediated pectin allergy

We evaluated a 29-year-old candy maker with no history of asthma who developed asthma after exposure to pectin, a compound manufactured from fruits and fruit rinds. Following eight years of employment during which he added pectin to a recipe for Christmas candies, the candymaker developed acute respiratory symptoms. Challenge testing with the pectin mixture caused a 40 percent decrease in FEV1. Skin prick testing was positive to the pectin extract. Total IgE was normal and pectin-specific IgE antibodies were not detected. A strongly positive pectin-specific IgG4 antibody response was present that was not detected in a control serum and could be inhibited by the addition of pectin. Antigen-specific IgG4 should be sought in IgE negative cases of occupational asthma.

An unusual active site identified in a family of zinc metalloendopeptidases

An unusual active site has been identified in a family of zinc metalloendopeptidases that includes bacterial protease III and the human and Drosophila insulin-degrading enzymes. All of these enzymes have been characterized as metalloendopeptidases and purified protease III has been shown to contain stoichiometric levels of zinc. However, all three proteases lack the consensus sequence (HEXXH) described in the active site of other zinc metalloendopeptidases. Instead, these proteases contain an inversion of this motif, HXXEH. To determine whether this region could represent the active site in these proteins, the two histidines in protease III were individually mutated to arginine and the glutamate was mutated to glutamine. All three mutants were devoid of proteolytic activity toward an exogenous substrate, insulin, as compared to the wild-type protease. Three lines of evidence indicate that this loss of activity in the mutants is not due to distortion of the three-dimensional structure of the protein: (i) the mutants are secreted into the periplasmic space and chromatograph normally; (ii) all three mutants are expressed at levels nearly identical to wild-type protein and do not appear to have an increased susceptibility to proteolysis in the bacteria; and (iii) the mutants compete equally with wild-type protein in a radioimmunoassay. The purified wild-type and glutamate mutants were found to contain stoichiometric amounts of zinc by atomic absorption spectrophotometry, whereas both histidine mutants had negligible zinc signals. These findings are consistent with this region being the active site in this protein, with the histidine residues coordinating the essential zinc atom and the glutamate involved in catalysis.

Comparison of the enzymatic and biochemical properties of human insulin-degrading enzyme and Escherichia coli protease III

The enzymatic and biochemical properties of human insulin-degrading enzyme and Escherichia coli protease III have been compared. Both enzymes were found to degrade insulin in such a way that its receptor binding activity was rapidly lost but its precipitability in trichloracetic acid was only slightly decreased. Both enzymes were also found to be inhibited by chelating agents. The bacterial enzyme, which could be purified in large amounts, was found to contain 0.6 mol of zinc per mol of enzyme but no detectable manganese. The mammalian enzyme but not the bacterial one was inhibited by a sulfhydryl alkylating agent. The two enzymes also differed in substrate specificity. The mammalian enzyme degraded insulin much better than insulin-like growth factor II, whereas the bacterial enzyme degraded them equally. The mammalian enzyme could be labeled by cross-linking to insulin = bombyxin II much greater than insulin-like growth factor I and II much greater than relaxin, while the bacterial enzyme was labeled by insulin-like growth factor II greater than insulin = insulin-like growth factor I much greater than relaxin much greater than bombyxin. Finally, sucrose gradient centrifugation and cross-linking studies both in vitro and in vivo indicated that active human enzyme partially existed as a homo- or heterodimer, whereas the bacterial enzyme was active as a monomer.

Differential binding properties of protein A and protein G for dog immunoglobulins

We studied the binding of dog immunoglobulins G, A, M and E to protein A and protein G. Passive cutaneous anaphylaxis (PCA) testing was used for the measurement of dog IgE and enzyme-linked immunosorbent assays (ELISA) were used for the measurements of dog IgG, IgA and IgM. Protein A from lyophilized cells of Staphylococcus aureus bound 97% of IgE, 98% of IgG, 81% of IgA, and 97% of IgM. Protein A-Sepharose CL-4B bound 87% of IgE, 100% of IgG and IgA, and 98% of IgM. In a stepwise elution with varying pH, a small amount of IgE was eluted at pH 5 and pH 6 and all the remaining Igs were eluted at pH 3 from the protein A column. In contrast to protein A, dog IgE was not bound to Protein G-Sepharose, while 100% of IgG, 95% of IgA, and 44% of IgM were bound to Protein G-Sepharose.

An inwardly rectifying chloride channel in ragweed-sensitized canine tracheal epithelial cells

The single channel inside-out patch clamp technique was used to characterize ion channels in the apical membranes of ragweed-sensitized and control canine tracheal epithelial cells maintained in primary culture. Patches were obtained from single isolated cells or from cells at the edges of confluent sheets. A new type of chloride channel was seen in sensitized cells but not in control cells. The channel showed inward rectification in symmetric chloride solutions with conductance varying from 95 pS to 52 pS over the range of -60 mV to 60 mV membrane potential. Channel gating was voltage dependent with maximal opening at about -30 mV. Kinetic analysis showed that distributions of closed and open times could both be well fitted by the sums of three exponential components. Rate constants for transitions between the states of a linear kinetic model were calculated, with only one rate being significantly voltage dependent. The possible significance of this channel is discussed.

Changes in Schultz-Dale reaction in sensitized canine tracheal smooth muscle

Tracheal smooth muscles from adult dogs 17 to 20 months of age sensitized with ragweed pollen demonstrated a Schultz-Dale phenomenon in response to specific antigen challenge. Seventy percent of the sensitized tracheal smooth muscles developed a Schultz-Dale reaction that consisted only of a phasic response, and the remaining 30% developed a Schultz-Dale reaction that consisted of a phasic component followed by a discrete tonic component. All the Schultz-Dale reactions were mediated only by histamine. The triggering of presynaptic acetylcholine release by histamine during the Schultz-Dale reaction from tracheal smooth muscles of ragweed-pollen-sensitized puppies 6 to 8 months of age was not detected in sensitized adult dogs. Hyperresponsiveness to acetylcholine was detected in tissues from sensitized puppies but not from sensitized adult dogs. Maximal active tension obtained from the sensitized adult canine trachealis during the Schultz-Dale reaction was lower than that obtained from trachealis from sensitized puppies. Dose-response studies showed that sensitized tissues used in the present studies were hyperresponsive to histamine when compared with their nonsensitized control littermates. These results suggest that the nature of the Schultz-Dale response and the identity of the transmitters is age-dependent.

Synthesis of intracellular histamine in platelets is associated with activation of protein kinase C, but not with mobilization of Ca2+

In previous reports, we have provided evidence indicating that newly formed histamine is an intracellular messenger in human platelets. The involvement of protein kinase C (PKC) and intracellular calcium (Ca2+i) in the synthesis of histamine was investigated. Human platelets were stimulated by phorbol 12-myristate 13-acetate (PMA), collagen and the Ca2+ ionophore A23187, with or without the PKC inhibitor staurosporine. Aggregation, histamine synthesis and phosphorylation of pleckstrin (47 kDa; P47) and myosin light chain (20 kDa; P20) proteins were monitored. Staurosporine inhibited PMA- and collagen-induced aggregation, histamine synthesis and phosphorylation of 47 kDa and 20 kDa proteins in a dose-dependent manner. For PMA, median inhibitory concentrations (IC50 values) for staurosporine inhibition of aggregation, histamine synthesis and phosphorylation were similar, suggesting that histamine synthesis induced by this agonist may be a consequence of PKC activation. Conversely, collagen-stimulated histamine synthesis was inhibited by staurosporine at concentrations significantly higher than those required to inhibit aggregation (P less than 0.005) or pleckstrin phosphorylation (P less than 0.01), indicating the possible involvement of non-PKC mechanism(s) in the synthesis of histamine induced by this agonist. A23187 failed to induce the synthesis of intracellular histamine in platelets, whereas staurosporine blocked A23187-induced aggregation and phosphorylation of the 20 kDa protein at significantly higher concentrations than those needed to inhibit PKC. When platelets were stimulated with a combination of A23187 and PMA, the increase in platelet histamine was less than that with PMA alone. The results provide evidence that the synthesis of intracellular histamine in platelets occurs as a consequence of PKC activation and may be down-regulated under conditions where there is a substantial rise in [Ca2+]i.

Formoterol, a new long-acting selective beta 2-agonist, decreases airway responsiveness in children with asthma

We compared the protective effect and duration of action of inhaled formoterol with salbutamol and placebo in 16 asthmatic children in a double-blind, cross-over study. All had an FEV1 greater than or equal to 70% predicted normal and a provocative concentration of methacholine (MCh) required to decrease their FEV1 by 20% (PC20) less than or equal to 4 mg/ml. On each study day, FEV1 was within 10% and PC20 within one doubling-dose of the initial visit. Patients received either placebo, salbutamol 200 micrograms, formoterol 12 micrograms, or formoterol 24 micrograms by metered-dose inhaler. FEV1 and PC20 were measured repeatedly over 12 h. After salbutamol, peak FEV1 was 120% of baseline at 30 min and returned to baseline in 3 h. After formoterol (12 or 24 micrograms) peak FEV1 was 118% at 3 h and remained above baseline for at least 12 h. Protection from MCh by both doses of formoterol was significantly better than by salbutamol. Protection from formoterol 12 and 24 micrograms at 12 h was equivalent to that from salbutamol at 3 h. The PC20 of four children 48 h after formoterol 24 micrograms was more than twice their baseline PC20. Formoterol by inhalation is potent and long-acting and provides significantly better antiasthma protection than salbutamol.