Adrenergic airway vascular smooth muscle responsiveness in healthy and asthmatic subjects

The purpose of the present study was to determine the responsiveness of airway vascular smooth muscle (AVSM) as assessed by airway mucosal blood flow (Qaw) to inhaled methoxamine (α₁-agonist; 0.6-2.3 mg) and albuterol (β₂-agonist; 0.2-1.2 mg) in healthy [n = 11; forced expiratory volume in 1 s, 92 ± 4 (SE) % of predicted] and asthmatic (n = 11, mean forced expiratory volume in 1 s, 81 ± 5%) adults. Mean baseline values for Qaw were 43.8 ± 0.7 and 54.3 ± 0.8 μl·min^-1·ml^-1 of anatomic dead space in healthy and asthmatic subjects, respectively (P < 0.05). After methoxamine inhalation, the maximal mean change in Qaw was -13.5 ± 1.0 μl·min^-1·ml^-1 in asthmatic and -7.1 ± 2.1 μl·min^-1·ml^-1 in healthy subjects (P < 0.05). After albuterol, the mean maximal change in Qaw was 3.0 ± 0.8 μl·min^-1·ml^-1 in asthmatic and 14.0 ± 1.1 μl·min^-1·ml^-1 in healthy subjects (P < 0.05). These results demonstrate that the contractile response of AVSM to α₁-adrenoceptor activation is enhanced and the dilator response of AVSM to β₂-adrenoceptor activation is blunted in asthmatic subjects.