Alterations in the composition and function of pulmonary surfactant
associated with torpor in a heterothermic mammal (sminthopsis
crassicaudata).
Langman, Carly, Sandra Orgeig, and Christopher B. Daniels.
Department of Physiology, The University of Adelaide, Adelaide,
South Australia 5005
APStracts 3:0067R, 1996.
Cold profoundly influences lung compliance in homeothermic mammals.
Much of this effect has traditionally been attributed to the
inactivation of the surfactant system. However, many mammals undergo
large fluctuations in body temperature (heterothermic). Here, the
surfactant lipid composition and lung compliance of warm-active
dunnarts (Sminthopsis crassicaudata) and the homeothermic mouse (Mus
musculus) (body temperature, TB =35-37 degrees C) were compared with
those of dunnarts killed after 1, 4 or 8 hours of torpor (TB<20
degrees C). Lung compliance was measured before and after the removal
of surfactant and tissue compliance was determined by inflating the
lung with saline. Relative to total phospholipid (PL), mouse
surfactant contained proportionately less phosphatidylinositol (PI)
but more cholesterol (CHOL) and phosphatidylglycerol (PG) than that
of the dunnart. Lung compliance was lower in dunnarts than in mice,
consistent with an allometric effect. Surfactant levels, including
total PL, CHOL and disaturated phospholipid (DSP) increased during
torpor. The relative proportions of CHOL and DSP increased after 4
and 8 hours, respectively. In marked contrast to previous studies on
the behaviour of isolated lungs from homeothermic mammals, the lung
compliance of dunnarts remained unchanged throughout torpor. Tissue
compliance decreased at 1 and 4 hours of torpor but was abolished by
8 hours. It appears that the surfactant of the dunnarts counteracted
the negative effect of tissue compliance at 1 and 4 hours, an effect
not present in homeothermic mammals. However, as lung compliance was
maintained at 1 hour of torpor in the absence of a compositional
change in surfactant lipids, the changes in lipid composition
observed at 4 and 8 hours of torpor are thought to relate to
functions of surfactant other than that of maintaining lung
compliance.
Received 15 November 1995; accepted in final form 19 February
1996.
APS Manuscript Number R714-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96