DISTRIBUTION OF ALVEOLAR TYPE-II CELLS IN NEONATAL AND ADULT-RAT LUNGREVEALED BY RT-PCR IN-SITU

Type II pneumocytes in newborn lungs are more uniformly distributed, w hereas in adult lungs they are located at alveolar corners. We used mo rphometry and reverse transcription-polymerase chain reaction in situ hybridization of surfactant protein C mRNA to determine the patterns o f type II cell distribution in random lung sections from Sprague-Dawle y rats at various neonatal st;ages and adults. There was a progressive increase in the percentage of type II cells at alveolar corners from 30% at 1 day to 51, 62, 78, and 81% at 3, 5, and 7 days old and adult rats, respectively. There were statically significant differences (P < 0.001) in the localization of type II cells from the nearest alveolar corner in the 1-day-old compared with 7-day-old and adult rat lungs. These results show that rat type II cells localize to the alveolar cor ners within the first 7 days postnatally and provide a system for stud y of factors that regulate alveolar epithelial cell distribution.