Greater airway narrowing in immature than in mature rabbits during methacholine challenge

Shen, X., V. Bhargava, G. R. Wodicka, C. M. Doerschuk, S. J. Gunst, and R. S. Tepper. Greater airway narrowing in immature thanin mature rabbits during methacholine challenge. J. Appl. Physiol. 81(6): 2637-2643, 1996.It hasbeen demonstrated that methacholine (MCh) challenge produces a greaterincrease in lung resistance in immature than in mature rabbits (R. S. Tepper, X. Shen, E. Bakan, and S. J. Gunst.J. Appl. Physiol. 79: 1190-1198, 1995). To determine whether this maturational difference in the response to MCh was primarily related to changes in airway resistance (Raw) or changes in tissue resistance, we assessed airway narrowing in1-, 2-, and 6-mo-old rabbits during intravenous MCh challenge (0.01-5.0 mg/kg). Airway narrowing was determined frommeasurements of Raw in vivo and from morphometric measurements on lungsections obtained after rapidly freezing the lung after the MChchallenge. The fold increase in Raw was significantly greater for 1- and 2-mo-old animals than for 6-mo-old animals. Similarly, the degree of airway narrowing assessed morphometrically was significantly greaterfor 1- and 2-mo-old animals than for 6-mo-old animals. The foldincrease in Raw was highly correlated with the degree of airwaynarrowing assessed morphometrically(r² = 0.82, P < 0.001). We conclude that thematurational difference in the effect of MCh on lung resistance isprimarily caused by greater airway narrowing in the immature rabbits.