Differences in airway structure in immature and mature rabbits

Our laboratory has previously demonstrated that maximal bronchoconstriction produces a greater degree of airway narrowing in immature than in mature r abbit lungs (33). To determine whether these maturational differences could be related to airway structure, we compared the fraction of the airway wal l occupied by airway smooth muscle (ASM) and cartilage, the proportion of w all area internal to ASM, and the number of alveolar attachments to the air ways, from mature and immature (6-mo- and 4-wk-old, respectively) rabbit lu ngs that were formalin fixed at total lung capacity. The results demonstrat e that the airway walls of immature rabbits had a greater percentage of smo oth muscle, a lower percentage of cartilage, and fewer alveolar attachments compared with mature rabbit airways; however, we did not find maturational differences in the airway wall thickness relative to airway size. We concl ude that structural differences in the airway wall may contribute to the gr eater airway narrowing observed in immature rabbits during bronchoconstrict ion.