Gestational changes in pulmonary converting enzyme activity in the fetal rabbit.

Area of Science:

• Cardiovascular Physiology
• Pulmonary Medicine
• Developmental Biology

Background:

• Angiotensin-converting enzyme (ACE) plays a crucial role in cardiovascular regulation.
• Understanding ACE development in the fetal lung is essential for assessing pulmonary and cardiovascular maturation.
• Limited data exists on the ontogeny of pulmonary ACE activity in the developing fetus.

Purpose of the Study:

• To investigate the developmental changes in angiotensin-converting enzyme (ACE) activity in fetal rabbit lungs.
• To correlate ACE activity with lung and body weight growth and vascular bed development.
• To explore the potential contribution of the placenta to fetal ACE activity.

Main Methods:

• Isolated and perfused fetal rabbit lungs were used from 22 days gestation to 7 days postnatal.
• Bradykinin or angiotensin I infusion assessed enzyme activity, with residual peptide measured by radioimmunoassay.
• Morphological studies using immunofluorescence and electron microscopy examined enzyme localization and endothelial cell surface area.

Main Results:

• Pulmonary ACE activity increased significantly from early gestation (22 days) to neonatal life, with peptide clearance rising from one-third to over 80%.
• The most substantial increase in substrate clearance occurred earlier than the peak growth in lung and body weight.
• Morphological evidence showed ACE presence by 17 days gestation, with increasing endothelial surface area correlating with enhanced enzyme activity.

Conclusions:

• Pulmonary ACE activity develops progressively throughout fetal and neonatal life, with functional maturation preceding significant organ growth.
• The development of the pulmonary microvascular bed's surface area is a key factor in the increased ACE activity.
• The placenta may serve as a significant site for ACE activity in the fetus, particularly during the second half of gestation.