Fig. 2.

Parenchymal, arterial, and major airway elastase activity increase and decrease in parallel during the alveolar stage of lung development. A: to differentiate the elastase activity of different lung structures, we applied major artery (red) and major airway (blue) masks with parenchymal elastase activity defined as the unmasked signal. B: parenchymal lung elastase activity peaked at PND10 as did arterial elastase activity (C) and major airway elastase activity (D). Only differences by t-test are shown. Parenchymal (P < 0.001), arterial (P = 0.004), and major airway (P < 0.001) elastase activity were all significantly different by ANOVA.