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, R. S. Tepper. Departments of Pediatrics and Physiology and Biophysics, Indiana University School of Medicine, Indianapolis, Indiana, 46223 and School of Electrical and Computer Engineering, Purdue University2, West Lafayette, Indiana
APStracts 3:0406A, 1996.
We have previously demonstrated that methacholine(MCh) challenge produces a greater increase in lung resistance(RL) in immature than in mature rabbits(JAP.79:1190,1995). In order 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 in 1, 2, and 6 month old rabbits during intravenous MCh challenge (0.01-5.0 mg/kg). Airway narrowing was determined from measurements of Raw in vivo, and from morphometric measurements on lung sections obtained after rapidly freezing the lung following the MCh challenge. The fold increase in Raw was significantly greater for 1 and 2 month than for 6 month animals. Similarly, the degree of airway narrowing assessed morphometrically was significantly greater for 1 and 2 month than for 6 month animals. The fold increase in Raw was highly correlated with the degree of airway narrowing assessed morphometrically (r2=0.82, p&LT0.001). We conclude that the maturational difference in the effect of MCh on lung resistance is primarily caused by greater airway narrowing in the immature rabbits. 

Received 17 April 1996; accepted in final form 6 August 1996.
APS Manuscript Number A368-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996