Autoradiographic assessment of the sequence of cellular proliferation in postpneumonectomy lung growth

To determine the extent and sequence of proliferation of the various types of cells in postpneumonectomy lung growth, 4-wk-old male Sprague-Dawley rats were injected with tritiated thymidine prior to sacrifice on days 2, 4, 7, and 10 after left pneumonectomy. Autoradiography of sections from each lobe of the remaining lung was performed and compared to controls. All of the cell types studied, both parenchymal and nonparenchymal, participated in postpneumonectomy lung growth. Mesothelial cell labeling peaked on day 2 and declined thereafter. Labeling of alveolar endothelial cells, alveolar interstitial cells, types I and II pneumonocytes, bronchial epithelium, and nonparenchymal endothelium occurred in parallel, peaking on day 4. The different lobes had equal percentages of dividing cells, suggesting that a global stimulus such as an endocrine factor has a dominant role in postpneumonectomy lung growth.