Control of pulmonary surfactant secretion: an evolutionary perspective

Area of Science:

• Comparative physiology
• Pulmonary research
• Vertebrate biology

Background:

• Pulmonary surfactant, composed of phospholipids and proteins, is crucial for lung function.
• Secretion by type II cells is vital for lung compliance.
• Control mechanisms in nonmammalian vertebrates remain largely unknown.

Purpose of the Study:

• To investigate the autonomic regulation of pulmonary surfactant secretion in diverse vertebrate species.
• To compare the effects of acetylcholine (ACh) and epinephrine (Epi) on surfactant secretion.
• To understand the evolutionary basis of surfactant secretion control.

Main Methods:

• Primary type II cell cultures were established from Australian lungfish, North American bullfrogs, and fat-tailed dunnarts.
• Cells were treated with ACh and Epi to measure phospholipid and cholesterol secretion.
• Secreted phospholipids, including disaturated phospholipids (DSP), were quantified.

Main Results:

• ACh stimulated total and DSP secretion in lungfish, while Epi had no effect.
• Both ACh and Epi stimulated total and DSP secretion in bullfrogs and dunnarts.
• Cholesterol secretion was unaffected by ACh or Epi in bullfrogs and dunnarts.

Conclusions:

• Pulmonary surfactant secretion is primarily controlled by the autonomic nervous system in nonmammalian vertebrates.
• The parasympathetic nervous system may play a dominant role at lower temperatures.
• Adrenergic influences and ventilatory control likely evolved later in tetrapod and mammalian lineages, respectively.