FETAL LUNG LAMELLAR BODIES IN HUMAN AMNIOTIC-FLUID

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Abstract
Amniotic fluid from women near term contains lamellar bodies resembling those of the pulmonary alveolar type II cell. A lamellar body-rich fraction was prepared by differential centrifugation of amniotic fluid at 9200 g for 10 min. Although this fraction contained only a small amount (1-2%) of the total protein present in amniotic fluid, it contained a large proportion of the phospholipid (46-50%). EM examination of this fraction revealed the presence of lamellar bodies (1-5 .mu.m in diameter) consisting of numerous membranes arranged concentrically about an electron-lucent focal region. Many of the membranes appeared contiguous with a peripherally located amorphous region. Tubular myelin figures were also present. Most of the phospholipid phosphorus (72.3 and 76.1%) in the lamellar body-rich fractions from 2 cases chromatographed as lecithins; smaller amounts of phosphatidylethanolamine and/or phosphatidylglycerol (11.9 and 13.0%), lysolecithin (2.4 and 3.8%), sphingomyelin (1.1 and 2.3%) and phosphatidylserine and/or phosphatidylinositol (7.3 and 9.7%) were also identified. Lecithin-rich lamellar bodies, synthesized and secreted by the type II cell, were transferred from alveolar space into the amniotic fluid. Surface-active phospholipid reached the amniotic fluid, at least in part, in an insoluble form.