Morphologic evidence that large inflations of the lung stimulate secretion of surfactant.

We ventilated rats at normal tidal volume without periodic deep breaths, or with a 4-times tidal volume inflation every 5 min for 1 h. The volume density of lamellar bodies in alveolar type 2 cells was about one-third lower after 60 min of ventilation in sighed than in unsighed rats, and this effect of sighs was not blocked by bilateral cervical vagotomy. These morphologic data support previously reported biochemical studies indicating that large inflations are potent stimuli of surfactant secretion.