Airway Responsiveness to Beta‐Adrenergic Agonist (Salbutamol) in Asthma

Abstract

Despite the controversy of airway responsiveness to β₂‐agonist drugs in asthma, in a previous study we showed increased responsiveness of asthmatic airways to isoprenaline. Therefore, in the present study of airway sensitivity to other β₂‐agonists, salbutamol and its relationship to histamine responsiveness was reexamined. The threshold bronchodilator concentrations of inhaled salbutamol required for a 20% increase in forced expiratory flow in 1 sec (FEV₁), (PC₂₀) was measured in 20 normal and 19 asthmatic adults. Airway responsiveness to histamine, as the concentration that caused a 20% decrease in FEV₁, was also measured in 11 normal and 12 asthmatic subjects; and the correlation between PC₂₀ salbutamol and PC₂₀ histamine was evaluated. Sensitivity to salbutamol was greater in asthmatics (PC₂₀ = 7.24 mg/L) than in non‐asthmatics (PC₂₀ = 124.25 mg/L, p < 0.001). Airway responsiveness to histamine in asthmatics (PC₂₀ = 0.18 g/L) was also significantly greater than in normal subjects (PC₂₀ = 19.46 g/L, p < 0.001). There was a significant correlation between PC₂₀ salbutamol and histamine (Rs = 0.6052, p < 0.005). Maximum response to both salbutamol and histamine and slope of concentration‐response curves of both agents were significantly greater in patients with asthma than in normal subjects (p < 0.001 and p < 0.005 for maximum response and slope, respectively). The increased sensitivity of asthmatics to inhaled salbutamol suggests that they also may be more sensitive to their endogenous adrenaline, which may thus dilate and stabilize their airways.

• Adrenoceptor
• Asthma
• Airway responsiveness
• Salbutamol
• Histamine