Prostaglandins and regulation of the pulmonary circulation in the perinatal period.

Effects of indomethacin on pulmonary vasodilation caused by ventilation of the fetal lungs with air were evaluated in anesthetized, exteriorized fetal goats by means of an open-chest pump perfused lung preparation. When fetal lungs are ventilated with air, pulmonary vascular resistance decreases in two steps: 1) a rapid decrease in pulmonary vascular resistance during the first 30 seconds of ventilation, and 2) a slower decline which continues through the first 10-20 minutes of more of ventilation. Indomethacin has minimal effect upon the first component. The second component is absent following treatment with indomethacin. Effects observed with indomethacin were more pronounced in immature fetuses (less than 90% gestation), than in mature fetuses. Prostaglandin synthetase activity appears to have a role in the pulmonary vasodilation resulting from ventilation of the fetal lungs with air.