Endotoxin alters biochemical and morphological responses to pneumonectomy in adult rats

Adult rats treated with endotoxin, like untreated neonatal rats, are resistant to O2 toxicity and manifest very similar lung biochemical responses. We hypothesized that endotoxin might also alter the adult pneumonectomy response to resemble the accelerated response of younger animals. Adult and 19-day rats underwent pneumonectomy, followed in 24 h by endotoxin or saline injection. Pneumonectomized rats, shams, and controls were killed 72 h after surgery for lung biochemistry and morphometry. Compared with adult saline-pneumonectomized rats, adult endotoxin-pneumonectomized rats, adult endotoxin-pneumonectomized rats demonstrated a significantly greater growth response and a lung biochemical response pattern (increased RNA, markedly increased RNA/DNA) similar to 19-day rats. Morphologically, endotoxin-pneumonectomized rats showed a different pattern of lung regrowth (significantly larger air spaces). Saline pressure-volume curves were not different between the two groups. We conclude that endotoxin administration to pneumonectomized adult rats resulted in accelerated lung regrowth, a lung biochemical response pattern similar to 19-day rats, but a paradoxical morphological pattern resembling more closely that of the adult than the neonatal animal.