NORMAL LUNG GROWTH AND RESPONSE AFTER PNEUMONECTOMY IN RATS AT VARIOUS AGES

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Abstract
Lung growth was accompanied by alveolar multiplication in rats 4-10 wk of age; the multiplication then ceased until 14 wk of age, and in this latter interval the alveolar walls appeared to lengthen. The relationship between size of surface alveoli and size of internal alveoli of the lower lobe changed with age, and the relationship was not altered by pneumonectomy. The surface alveoli were smaller than internal alveoli at 4 wk of age, the same size at 6 and 10 wk of age and larger at 14 wk of age. Four week old rats responded to pneumonectomy with an increase in size of the contralateral lung and an increase in the number of alveoli. Direct alveolar counts did not show a significant increase in number of alveoli after pneumonectomy in 8 and 12 wk old rats. The alveolar surface area increased almost directly with the increase in gas-exhanging lung volume in 8 wk old rats, suggesting that alveolar multiplication might have occurred. In 12 wk old rats the alveolar surface increased to the 0.71 power of the increase in gas-exchanging lung volume, suggesting that alveolar enlargement, rather than alveolar multiplication, had occurred. Apparently compensatory alveolar multiplication is part of the adaptive response to pneumonectomy when this operation is performed at a time at which alveolar multiplication normally occurs. When pneumonectomy is performed after alveolar multiplication has ceased, the adaptive response is primarily one of air-space enlargement. Lung volume, weight, surface area and protein responses to pneumonectomy were smaller at 12 wk of age than at 4 and 8 wk of age.