ABSTRACT
I. Introduction 18
A. Pulmonary Surfactant 18
B. Surfactant Composition 18
C. Alveolar Type II Cells 19
D. The Surfactant Cycle 19
E. Temperature 22
II. Temperature and the Biophysical Properties of Surfactant 22
A. Comparative Biology of Surfactant Function 22
B. Function of Surfactant as an Antiadhesive in
Ectothermic Animals 23
C. Surface Activity Measurements 26
Homeothermic Mammals 27
Heterothermic Mammals 29
III. Temperature and Surfactant Composition 32
A. Lipid Composition 32
Ectothermic Animals 37
Heterothermic Mammals 37
Homeothermic Mammals 39
B. Protein Composition 40
IV. Temperature and Control of Surfactant Secretion 41
A. Basal Secretion 41
B. Ventilation (Mechanical Stimulation) 43
Homeothermic Mammals 43
Ecothermic Animals 43
Heterothermic Mammals 43
C. Adrenergic Agonists 44
Homeothermic Mammals 44
Ectothermic Animals 44
Heterothermic Mammals 45
D. Cholinergic Agonists 46
Homeothermic Mammals 46
Ecothermic Animals 46
Heterothermic Mammals 47
E. Other Factors 48
V. Summary and Future Directions 49
References 49
I. Introduction
A. Pulmonary Surfactant
A surface tension is created at any air-liquid interface because the forces of
attraction between water molecules are stronger than the forces between water
and air. In the lungs, such a surface tension would promote lung collapse and
increase the work required to inflate the lung (1). Surface tension is usually
defined as the force required to stretch a rectangular surface fluid by a known
length (usually 1 cm) and is expressed either as dyn/cm or mN/m (where 1 dyn/cm ¼ 1025 N/cm or 1 mN/m). Pure water has a surface tension of 70 dyn/cm (or 70 mN/m) at 378C. Pulmonary surfactant interferes with the interaction of the surface water molecules and varies the surface tension at the
air-liquid interface. This behavior is termed “surface activity” (2). Pulmonary
surfactant can reduce surface tension in the lung to ,5 mN/m in mammals (3).