Development of fetal rat lung during prolonged gestation

Area of Science:

• Perinatology
• Developmental Biology
• Respiratory Physiology

Background:

• Progesterone plays a crucial role in maintaining pregnancy.
• Understanding the effects of prolonged gestation on fetal lung maturation is vital for perinatal care.

Purpose of the Study:

• To investigate the impact of progesterone-induced prolonged gestation on fetal lung development in rats.
• To identify potential factors contributing to respiratory distress in postmature neonates.

Main Methods:

• Daily subcutaneous progesterone injections were administered to pregnant rats from day 20 to 24 of gestation (term = 22 days).
• Fetal rats were harvested via cesarean section on gestation days 21 through 25.
• Fetal body weight, placental weight, lung weights (wet and dry), lung cell numbers, lung glycogen, and disaturated phosphatidylcholine were analyzed.
• Lung surface tension, histological features (lamellar bodies, terminal sacs), and atelectasis were assessed.

Main Results:

• Prolonged gestation resulted in increased fetal body weight despite reduced placental weight.
• Lung wet and dry weights decreased relative to body weight.
• Post-term fetuses (GD 25) exhibited a 10% reduction in lung cell numbers and a 90% reduction in lung glycogen compared to term fetuses.
• Disaturated phosphatidylcholine levels initially increased then decreased by GD 25.
• Increased surface tension, decreased lamellar bodies, reduced terminal sac size, and atelectasis were observed in post-term lungs.
• Pulmonary fluid loss and reduced surface activity were noted.

Conclusions:

• Progesterone-induced prolonged gestation in rats impairs fetal lung maturation.
• Key factors contributing to respiratory distress in postmaturity include lung hypocellularity, glycogen depletion, reduced phospholipids, atelectasis, and decreased pulmonary fluid surface activity.