Development of the fetal lung

Area of Science:

• Developmental biology
• Respiratory physiology
• Endocrinology

Background:

• Fetal lung development is uniquely sensitive to external stimuli, unlike other organs.
• Limited space or diaphragm paralysis impairs lung growth, suggesting a role for lung volume and distension.
• Fetal breathing movements may generate distending forces essential for lung growth.

Purpose of the Study:

• To investigate the role of mechanical forces (lung distension) and hormonal factors in fetal lung development and maturation.
• To understand the relationship between fetal breathing, lung volume, and lung growth.
• To identify key hormones regulating fetal lung maturation.

Main Methods:

• Studies involved experimental procedures affecting fetal breathing movements and lung space in animal models.
• Lung distensibility and stability were assessed in relation to plasma hormone concentrations.
• Hormonal manipulation through hypophysectomy and infusions of adrenocorticotropin and cortisol were performed in fetal sheep.

Main Results:

• Lung growth is impaired when space is limited or diaphragm movement is restricted, indicating dependence on distension.
• Experimental inhibition of fetal breathing leads to lung hypoplasia, supporting the role of breathing-generated forces.
• Lung distensibility and stability mature rapidly postnatally, correlating with plasma cortisol levels.
• Hypophysectomy in fetal sheep delays maturation, which can be reversed by adrenocorticotropin but not cortisol infusion.

Conclusions:

• Fetal lung growth is significantly influenced by mechanical factors, primarily lung distension generated by fetal breathing.
• Lung maturation is primarily regulated by the hormonal environment, with cortisol, iodothyronines, and catecholamines playing key roles.
• While cortisol is critical for maturation, the precise interplay of various hormones requires further investigation.