Variability of airway responses in mice

We examined the effect of animal strain, type of spasmogen, and mode of spa smogen administration on the pattern of lung mechanical responses in intuba ted and mechanically ventilated mice. We determined the response in inspira tory respiratory system resistance (R-rs) and inspiratory static respirator y system compliance (C-rs) to increasing doses of inhaled or intravenous ca rbachol or serotonin in Balb/C and C57BL/6 mice. R-rs responsiveness was qu antitated by calculating, by interpolation, the inhaled spasmogen concentra tion (PC150) and intravenous spasmogen dose (PD150) causing an increase in R-rs to 150% of baseline. C-rs responsiveness was calculated similarly for a decrease in C-rs to 85% of baseline (PC85 for inhaled and PD85 for intrav enous spasmogen). Baseline R-rs and C-rs were similar in all groups. R-rs r esponsiveness to inhaled and intravenous carbachol and serotonin tended to plateau and was not different in the two strains. In contrast, C-rs respons es were variable and had a greater mean PC85 for inhaled serotonin than car bachol in both strains and a greater fall in mean C-rs at PC150 for carbach ol in Balb/C mice; no interstrain and interdrug differences in PD85 were no ted for intravenous spasmogens. Intravenous atropine attenuated the R-rs re sponse to high-dose inhaled and intravenous serotonin, suggesting the invol vement of a vagal reflex. In contrast, atropine attenuated C-rs responses o nly for intravenous serotonin in Balb/C mice. These results suggest that an imal strain, spasmogen, and mode of administration determine the extent to which induced airflow resistance is accompanied by increases in elastic rec oil.