Bronchial cholinergic tone and sensitivity in normal and asthmatic subjects

In nine patients with asthma and 11 normal subjects, by means of specific airway conductance (Gaw/VL) and flow volume loops, we measured: resting airway caliber, bronchodilation after 0.75 and 1.50 mg of quantitatively inhaled atropine (A0.75 and A1.50), provocation dose-40 of acetylcholine (ACH) (PD40-ACH), dose ratio of ACH (DR-ACH) after saline solution, A0.75 and A1.50, and the slope of log-dose response curves to ACH (SLDRC-ACH). Normal and asthmatic subjects showed different PD40-ACH (1.26 +/- 1.37 mg and 0.34 +/- 0.32 mg) but similar resting Gaw/VL, delta Gaw/VL after A0.75 or A1.50, DR-ACH after A0.75, and SLDRC-ACH. There was no correlation between atropine-induced bronchodilatation PD40-ACH or any of the above-mentioned tests. We conclude that in normal subjects and in those with asthma, extramuscarinic or postmuscarinic receptor mechanisms may account for the presence of comparable atropine-induced bronchodilatation and resting Gaw/VL in spite of widely different PD40-ACH. The regulatory site responsible for PD40-ACH, the only test separating asthmatics from normal subjects, seemingly is located downstream from the regulatory site of other nondiscriminative tests.