Inhaled formoterol inhibits histamine-induced airflow obstruction and airway microvascular leakage

We studied the effects of inhaled formoterol (0.75 mg/ml, 60 breaths = 26 micrograms), a long-acting beta 2-adrenoceptor agonist, or of the more short-acting drug, salbutamol (25 mg/ml, 60 breaths = 875 micrograms), on acute airflow obstruction and airway microvascular leakage (MVL) induced by inhaled histamine in anesthetized guinea pigs. Lung resistance (RL) and its recovery following hyperinflation (recovery RL) were measured for 6 min after histamine (1 or 2 mg/ml, 30 breaths) in animals pretreated with either inhaled beta 2-adrenoceptor agonist or inhaled saline (0.9%, 60 breaths). MVL was measured by determining the amount of extravasated Evans blue dye at various airway levels. Histamine increased RL dose dependently with a mean peak RL (+/- S.E.M.) of 13.1 +/- 2.41 cmH2O/ml per s after 2 mg/ml of histamine. Both formoterol and salbutamol significantly inhibited both peak and recovery RL and MVL to a similar degree. There was a significant correlation between the degree of extravasated dye and both peak and recovery RL, suggesting that MVL partly contributes to histamine-induced airflow obstruction. Formoterol is approximately 35 times more potent than salbutamol to inhibit both MVL and airflow obstruction induced by histamine aerosol.