Low-dose carbon monoxide reduces airway hyperresponsiveness in mice

expired gas has been shown to be elevated with asthma; however, its function is not known, and there is some poten-tial that it may serve a bronchoprotective role to decrease airway hyperresponsiveness (AHR). Thus the ability of CO to reverse methacholine (MCh)-induced bronchoconstriction was evaluated in C57BL/6 (C57) and A/J mice with and without airway inflammation produced by ovalbumin (OVA). Acutely administered CO (1 % in air, 10 min) reduced MCh-driven increases in lung resistance in OVA-challenged C57 mice by an average of 50 % (from 14.5 to 7.1 cmH2O ml1 s1), whereas no effect was observed in naı̈ve C57 mice or OVA-challenged C57 mice inhaling air alone. Acutely inhaled CO (500 ppm 0.05%, for 10 min) reduced MCh-induced airway reactivity (AR) by 20–60 % in airway hyperresponsive naı̈ve A/J mice, whereas repeated 10-min administrations of 500 ppm C