Correlation of pulmonary ACE activity and capillary surface area during postnatal development

Area of Science:

• Pulmonary Physiology
• Vascular Biology
• Neonatal Development

Background:

• Pulmonary arterial circulation remodeling and growth are well-documented.
• Postnatal development of the pulmonary microcirculation remains less understood.
• Angiotensin-converting enzyme (ACE) activity is crucial in cardiovascular regulation.

Purpose of the Study:

• To investigate the relationship between pulmonary ACE activity and lung microcirculation development in lambs.
• To determine if maximal velocity (Vmax) of ACE activity reflects capillary endothelial surface area.
• To assess postnatal lung growth using functional and structural parameters.

Main Methods:

• Measured apparent kinetics of pulmonary ACE activity using a synthetic substrate (3H-labeled benzoyl-phenylalanyl-alanyl-proline) in lambs aged 2-171 days.
• Simultaneously determined in vivo carbon monoxide diffusing capacity (DLCO).
• Conducted postmortem structural assessment of alveolar septal dimensions using stereology and electron microscopy.

Main Results:

• A progressive increase in Vmax of ACE activity and DLCO was observed with age.
• Vmax and DLCO showed a strong positive correlation with capillary endothelial cell surface area.
• Neither Vmax nor DLCO was significantly affected by increased left atrial pressure, suggesting minimal vessel recruitment.

Conclusions:

• Maximal velocity of pulmonary ACE activity serves as a functional indicator of lung capillary endothelial surface area in developing lambs.
• Age-dependent increases in Vmax and DLCO reflect postnatal growth of the pulmonary microcirculation.
• Data suggest selective, differential postnatal development of the alveolar septum endothelium in lambs.