Development of angiotensin converting enzyme in fetal lung and placenta of the rat and human.

Angiotensin converting enzyme (ACE) activity in fetal lung and placenta was determined by the method of Cushman and Cheung (1971) during the second trimester of human pregnancy and throughout the rat gestation. The enzyme activity in the neonatal rat lung was also determined during the first 19 days of life. The enzyme activity in both tissues of both species increased with gestation. The activity in human fetal lung at the end of the second trimester was already 70% of that present in the adult human lung while rat fetal lung enzyme activity at term was only 15% of the adult value. The activity in the term placenta of the human and rat was respectively 13% and 5% that of the adult lung value. Developmental increases in enzyme activity continued in the neonatal rat lung till adult value at about 19 days postpartum. The pattern of fetal lung enzyme development in the rat resembled that of the rabbit fetal lung as determined by other investigators using different techniques but was different from that of the human. The findings support the suggestion that ACE in the lung and placenta play important roles in the maintenance of circulatory homeostasis during the latter part of gestation, at birth and early postpartum, albeit at a different extent in different species.