Morphogenetic and proliferative changes in the regenerating lung of the rat

Unilateral extirpation of the lung in rats is followed by increased mitotic activity in alveolar cells of the contralateral lung, reaching a maximum six to seven days after operation. The response is delayed if the cavity created by the operation is packed with plastic sponge. Unilateral collapse of the lung without removal of tissue also leads to a contralateral mitotic response. Changes in the rate of cell proliferation evidently are not directly dependent on changes in tissue mass and it is suggested that compensatory growth in the lung may be controlled by chemical factors whose local concentration depends on variations in the rate of blood flow. Other changes which follow partial extirpation, observed particularly in the residual tissue of resected lungs, include high rates of proliferation in pleural cells, sub‐pleural tissue and bronchial epithelium. It appears that in the regenerating lung new tissue may be formed partly by the proliferation of cells in the main mass of residual tissue and partly by more localized changes in specific tissues.