LTD4-induced bronchoconstriction in patients with asthma: lack of a vagal reflex.

The mechanism by which leukotriene D4 (LTD4) induces bronchoconstriction in man is unclear. We have investigated this mechanism by examining the effect of nedocromil sodium and ipratropium bromide on LTD4-induced bronchoconstriction in six mild asthmatic patients. The bronchoconstrictor response to increasing concentrations of inhaled LTD4 (0.08 to 100 nmol) was assessed by measuring changes in respiratory resistance (Rrs) at 6 Hz by the forced oscillation method. Results were expressed as the provocative dose causing 100% increase in Rrs (PD100). Neither nedocromil (4 mg) nor ipratropium (0.8 mg) showed significant effect on LTD4-induced bronchoconstriction in asthmatic subjects. These results suggest that in asthmatics LTD4-induced bronchoconstriction is unlikely to involve vagal reflexes.