AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 4 1309-R1313, Copyright © 1994 by American Physiological Society
Surfactant composition and function in lungs of air-breathing fishes
A. W. Smits, S. Orgeig and C. B. Daniels
Department of Biology, University of Texas at Arlington 76019.
Examination of lung washings from primitive air-breathing fishes (ropefish,
bichirs, and gar) revealed a lipid-based surfactant with an average
disaturated phospholipid-to-total phospholipid ratio five times lower than
in mammals. The lung lavage of fishes was exceptionally rich in
cholesterol, resulting in average cholesterol-to-phospholipid ratios three
times higher, and cholesterol-to-disaturated phospholipid ratios nearly 15
times higher, than those of mammals. Removal of lung surfactant doubled the
pressures necessary to initially open the anterior regions of collapsed
lungs in all three fish species but had little or no effect on pressures
required to fill the lung (i.e., compliance) after the initial opening. The
elevated cholesterol content found in pulmonary surfactant of these fishes
is consistent with such findings in other ectotherms, suggesting that the
proportional elevation of cholesterol may serve to stabilize the fluidity
of the lung surfactant over broader temperature ranges. The influence of
surfactant on lung opening pressures rather than on compliance contrasts
with that seen in mammals and supports an "antiglue" role of pulmonary
surfactant in the simpler open-design lungs of lower vertebrates.
