Distribution of alveolar type II cells in neonatal and adult rat lung revealed by RT-PCR in situ.

Type II pneumocytes in newborn lungs are more uniformly distributed, whereas in adult lungs they are located at alveolar corners. We used morphometry and reverse transcription-polymerase chain reaction in situ hybridization of surfactant protein C mRNA to determine the patterns of type II cell distribution in random lung sections from Sprague-Dawley rats at various neonatal stages 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 statistically 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 corners within the first 7 days postnatally and provide a system for study of factors that regulate alveolar epithelial cell distribution.