Strain and route differences in airway responsiveness to acetylcholine in mice.

The airway responsiveness to acetylcholine (ACh) was examined in C57BL/6 and DBA/2 mice, which are reported as hyporeactive and hyperreactive strains to ACh, respectively. The airway responsiveness of inhaled ACh was compared with that of i.v. injected ACh. No significant difference in baseline respiratory resistance (Rrs) was observed between strains. The Rrs increment induced by 30 mumoles/kg (i.v.) of ACh was significantly greater in DBA/2 than in C57BL/6 strain. However, the Rrs increments induced by inhalation of ACh were same levels between the two strains. These findings indicate that not only strain but also route differences participate in airway responsiveness to ACh in mice.