Am. J. Respir. Crit. Care Med., Vol 149, No. 1, Jan 1994, 76-80.
Effect of pilocarpine on propranolol-induced bronchoconstriction in asthma
M Okayama, T Shen, J Midorikawa, JT Lin, H Inoue, T Takishima and K Shirato
First Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
To investigate whether increased release of acetylcholine may be involved
in propranolol-induced bronchoconstriction (PIB), the inhibitory effect of
pilocarpine (Pilo), an agonist of M2-muscarinic receptors that in 11 stable
asthmatic subjects. The bronchial responsiveness to Pilo was also measured
in terms of Dmin, defined as the cumulative dose at the point where
respiratory resistance (Rrs) began to increase. In PIB, the maximum
increase in Rrs (Rrs max) after stopping inhalation for 1 min was measured.
Atropine reversed PIB. After pilocarpine pretreatment at a dose equal to
Dmin, Rrs max divided by baseline Rrs decreased significantly from 206.6
+/- 61.1 to 163.0 +/- 42.6% (mean +/- SD) (p = 0.001). The ratio of PIB
(Rrs max/baseline Rrs) with Pilo to PIB without Pilo correlated inversely
according to the pretreatment dose (Dmin) of Pilo (p < 0.05). These
results suggest increased release of acetylcholine in PIB and that
M2-muscarinic receptors are at least in part functioning in stable
asthmatic airways.
