Effect of lung collapse on compensatory lung growth.

The effect of unilateral lung collapse on compensatory lung growth was studied in 3-wk-old (young) and 10-wk-old (adult) male Long-Evans rats. Under light halothane anesthesia, left lung collapse was produced by injection of dental plastic through a thracheostomy cannula. The rats were killed either 5 days or 4 wk later. At 5 days postcollapse, the 3-wk-old rats had an increase in DNA over sham controls (21%) (P less than 0.05), with no significant change in the protein/DNA ratio. At 4 wk postcollapse, increases in DNA over shamoperated controls were observed in both the 3-wk-old (58%) and the 10-wk-old (28%) rats, whereas the protein/DNA ratio at both ages was significantly less than that of sham controls (P less than 0.05). Thus, unilateral lung collapse stimulates growth of the contralateral lung by cellular hyperplasia, not hypertrophy, both in the young and adult rat. The hyperplasia begins within 5 days after collapse and is greater by 4 wk. The extent of hyperplasia is greater in the young than in the adult rat.