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).