Surfactant treatment effects on alveolar type II cell morphology in rabbit lungs

The effects of exogenous surfactant administration on alveolar type II cells and the lung parenchyma were examined in adult rabbits. Natural surfactant was instilled into the left lobe of New Zealand White rabbits while the right lobe served as the control. Four hours post-instillation, the lungs were fixed by vascular perfusion. Surfactant instillation did not change alveolar type II cell size but was associated with a significant reduction in the volume fraction of lamellar bodies in type II cells (20.4% in control lobes compared with 11.9% in surfactant-treated lobes). The size distribution of lamellar body profiles was different in surfactant-treated lobes compared with control lobes, with a significant decrease in lamellar bodies > 0.8 microns in diameter and a twofold increase in lamellar bodies 0.2-0.4 microns in diameter. Composite body profile number was also increased by 87% (P < 0.05) after instillation of surfactant compared with control. Saline instillation decreased lamellar body volume fraction in type II cells but three times less than surfactant instillation. These observations are consistent with a strong stimulus for secretion of endogenous surfactant 4 h after surfactant instillation in normal adult rabbit lungs, whereas the increase in composite bodies is consistent with new lamellar body formation, probably from both de novo synthesized and exogenous natural rabbit surfactant. These observations confirm that the secretory and synthetic processes of alveolar type II cells are significantly affected by exogenous surfactant instillation.