Developmental changes of sheep surfactant: in vivo function and in vitro subtype conversion

Area of Science:

• Pulmonary physiology and developmental biology
• Respiratory medicine
• Biochemistry of lung surfactant

Background:

• Pulmonary surfactant is crucial for lung function, reducing surface tension and preventing alveolar collapse.
• The intrinsic properties and developmental changes of surfactant, particularly heavy-subtype surfactant, are not well understood.
• Surfactant composition and function can be altered in premature infants, contributing to respiratory distress.

Purpose of the Study:

• To evaluate developmental differences in the intrinsic characteristics and function of heavy-subtype surfactant.
• To compare surfactant from preterm lambs, newborn lambs, and adult sheep.
• To assess the functional impact of developmental surfactant changes on lung mechanics in preterm rabbits.

Main Methods:

• Recovery of heavy-subtype surfactant from alveolar washes of preterm lambs (132-, 139-, 148-day), newborn lambs (2-3 days), and adult sheep.
• Analysis of surfactant density and surfactant protein-A to saturated phosphatidylcholine ratios.
• Assessment of the conversion rate from heavy to light surfactant forms.
• Functional testing of heavy-subtype surfactant in ventilated preterm rabbits (27-day gestational age).

Main Results:

• Heavy-subtype surfactant density and surfactant protein-A to saturated phosphatidylcholine ratios increased significantly with developmental age.
• Preterm animals exhibited a more rapid conversion from heavy to light surfactant forms compared to mature or adult animals.
• Surfactant from the most immature preterm animals was less effective in improving lung compliance and maintaining lung volumes during deflation in preterm rabbits.

Conclusions:

• Significant intrinsic and functional differences exist in surfactant between developing and mature sheep, correlating with surfactant protein-A content.
• The observed surfactant abnormalities in preterm animals suggest a potential disadvantage for lung development and function.
• These findings highlight the importance of developmental stage on surfactant properties and its implications for respiratory health in preterm neonates.