Despite the controversy of airway responsiveness to beta2-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 beta2-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.