The composition and function of reptilian pulmonary surfactant

Area of Science:

• Comparative Physiology
• Respiratory Biology
• Biochemistry

Background:

• Mammalian pulmonary surfactant, rich in dipalmitoylphosphatidylcholine (DPPC), reduces lung surface tension.
• Reptilian preferred body temperatures (20-30°C) are lower than DPPC's effective range (41°C).
• This study investigates reptilian surfactant composition and function in relation to environmental factors.

Purpose of the Study:

• To review the presence and composition of pulmonary surfactant in reptiles.
• To correlate surfactant composition with reptilian lung structure, function, phylogeny, and environmental pressures like body temperature.
• To discuss the function and turnover of reptilian surfactant.

Main Methods:

• Review of existing literature on reptilian pulmonary surfactant.
• Analysis of surfactant composition (lipids, proteins, phospholipids, fatty acids) across reptile species.
• Correlation of compositional data with environmental factors and lung physiology.

Main Results:

• Pulmonary surfactant is abundant in all examined reptiles.
• Warmer reptiles have more surfactant, enriched in disaturated phospholipids (DSP).
• Cold lizards show elevated cholesterol; phosphatidylglycerol (PG) is largely absent, unlike in mammals.
• Palmitic acid (16:0) is the dominant acyl group, with ~20% polyunsaturates.
• Surfactant functions primarily as an antiglue, lowering opening pressure and reducing breathing work, but less so influencing lung compliance compared to mammals.

Conclusions:

• Reptilian surfactant composition is adapted to their thermal physiology and environmental conditions.
• Key differences exist in phospholipid profiles (e.g., absence of PG) compared to mammals.
• The primary role of reptilian surfactant appears to be facilitating lung mechanics rather than solely surface tension reduction as in mammals.