Am. J. Respir. Crit. Care Med., Vol 150, No. 3, Sep 1994, 853-856.
Neutral endopeptidase inhibitor thiorphan increases airway narrowing to inhaled sodium metabisulfite in normal subjects
S Bellofiore, F Caltagirone, A Pennisi, N Ciancio, A Mistretta and GU Di Maria
Istituto di Malattie Respiratorie, Universita di Catania, Italy.
Possible mechanisms involved in inhaled sodium metabisulfite (MBS)- induced
bronchoconstriction include cholinergic reflex and release of tachykinins
from sensory nerve endings. Tachykinins are potent bronchoconstrictors
cleaved and inactivated by neutral endopeptidase (NEP) in the airways. To
investigate the role of tachykinins in airway response to MBS, we assessed
the effect of NEP-inhibitor thiorphan on airway response to MBS in nine
nonatopic, nonasthmatic subjects. Two inhalational challenges with doubling
doses of MBS (0.03 to 16 mumol) were performed 3 d apart. Ten minutes
before MBS challenge, subjects randomly inhaled either thiorphan (1.25 mg)
or placebo according to a double-blind cross-over design. Airflow at 30% of
vital capacity (V30p) from partial expiratory flow-volume curves was
measured at baseline, 10 min after thiorphan or placebo, and 2 min after
each MBS dose. The dose of MBS causing 40% fall in V30p (PD40V30p) was
calculated. Neither thiorphan nor placebo affected baseline airway caliber.
Thiorphan caused a leftward shift of the dose-response curve to MBS. After
placebo a measurable PD40V30p was obtained in four of nine subjects. In
these subjects PD40V30p fell significantly after thiorphan inhalation. Four
of five subjects who did not exhibit PD40V30p after placebo showed
measurable PD40V30p after thiorphan. Percent fall in V30p caused by highest
dose of MBS was significantly greater after thiorphan compared with placebo
(55.9 +/- 4.6% versus 30.8 +/- 5.6%; mean +/- SE; p < 0.001). Results of
this study demonstrate that the NEP-inhibitor thiorphan increases
MBS-induced bronchoconstriction in normal subjects, suggesting that
tachykinins are involved in airway responses to inhaled MBS.