Lung Lecithin Biosynthesis in the Nonhuman Primate Fetus: Determination of the Primary Pathway in vivo

Abstract

The two pathways for denovo lecithin (phosphatidylcholine) biosynthesis, choline incorporation (I) and phosphatidylethanolamine methylation (II), were examined simultaneously in lung and other tissues of Rhesus monkey fetuses. Cannulation of inter-placental fetal vessels permitted studies on the intrauterine fetus without disruption of fetal-placental-maternal-amniotic fluid anatomic integrity. In contrast to observations with indirect techniques in the same species, direct measurement of the incorporation of isotopic precursors (³H-choline and ¹⁴C-ethanolamine) into lecithin indicated that pathway I predominates by 100-fold over PE methylation in pulmonary lecithin synthesis. Fetal liver, brain, and kidney also showed 10–70-fold, greater choline incorporation than methylation activity. Measurement of lung phosphatidylcholine production via the two pathways in acidemic fetuses (umbilical venous pH < 7.20) demonstrated marked inhibition of pathway I, but not II. It is concluded that the choline pathway is the major mechanism of lung lecithin synthesis in fetal primates and that this pathway is pH sensitive in vivo.