A quantitative study of the development of interalveolar pores in the postnatal mouse.

Quantitative analysis of regional interalveolar pore development in the lungs of C3Hf/He mice was performed using scanning electron microscopy. Lungs of male mice ages 7, 10, 14, 21, 28, and 56 days were studied following intratracheal fixation. Interalveolar pores were counted in subpleural, midzonal, and peribronchiolar regions. Interalveolar pores were rarely observed in mice ages 7, 10, and 14 days but appeared abruptly at age 21 days throughout the lung. The number of interalveolar pores increased 2-3 fold from ages 21 to 56 days. By age 28 days and thereafter interalveolar pores were more numerous in subpleural alveoli than in midzonal or peribronchiolar alveoli. We conclude that interalveolar pores appear diffusely in the lungs of mice during the third postnatal week and that regional differences in the number of interalveolar pores are established by age 28 days.