Subcellular distribution of disaturated phosphatidylcholine in developing rabbit lung

Abstract

To determine the subcellular distribution of disaturated phosphatidylcholine (DSPC) in lung tissue during perinatal development, fetal rabbits at 24, 26, 28 and 31 (term) days gestation and newborns were studied. Following alveolar lavage, fractions enriched in nuclei-cellular debris, mitochondria, microsomes, surfactant (lamellar bodies) and cytosol were prepared from the residual tissue homogenate, and their DSPC content was determined. The DSPC content of the unfractionated residual lung tissue homogenate progressively and significantly increased during fetal development, rising from 9.09 +/- 0.91 to 17.45 +/- 2.88 mg/g dry lung between 24 days gestation, and term. Between 24 and 26 days gestation the overall increase in tissue DSPC was due to a two-fold increase in the mitochondrial, microsomal and cytosolic pools. Lamellar bodies were first isolable at 26 days gestation. The DSPC content of this fraction increased six-fold (from 0.10 +/- 0.02 to 0.67 +/- 0.15 mg/g dry lung) between 26 and 28 days gestation and a further seven-fold (to 4.63 +/- 1.06 mg/g dry lung) by term, accounting for the overall increase in the tissue homogenate value during this time period. By the first postnatal day, microsomal and cytosolic DSPC increased another two-fold, but no significant change occurred in the other subcellular fractions. Alveolar lavage DSPC progressively increased over the time period studied. While there was no change in the lamellar body DSPC/total PC ratio during fetal development, each of the mitochondrial, microsomal and cytosolic ratios decreased between days 26 and 28 of gestation and then increased at term.(ABSTRACT TRUNCATED AT 250 WORDS)

Alveolar metabolism of natural vs. synthetic surfactants in preterm newborn rabbits

“…We have previously reported that the surfactant preparation isolated by this procedure consists entirely of characteristic lamellar body (LB)-like structures, as evidenced by electron microscopic analysis (22), and is virtually free from contamination by other nonsurfactant membrane components, as determined by marker enzyme assays (22). Also, as previously reported (21,22), this preparation has the chemical composition characteristic of surfactants isolated from a wide variety of mammalian species, is highly surface active, as determined in vitro by the pulsating bubble surfactometer (22), and is biologically active, as assessed in vivo in the preterm rabbit model (16,24). We also found that surfactants isolated separately from the extraand intracellular pools were identical in these properties (Oulton, unpublished observations).…”

“…The natural surfactants were isolated from adult and fetal rabbit lungs using differential and density gradient procedures, which have been described in detail in previous reports (21,22,23). We have previously reported that the surfactant preparation isolated by this procedure consists entirely of characteristic lamellar body (LB)-like structures, as evidenced by electron microscopic analysis (22), and is virtually free from contamination by other nonsurfactant membrane components, as determined by marker enzyme assays (22).…”

“…The washed surfactant pellets were suspended in sterile 0.85% NaCl, and an aliquot was removed for phosphorus analysis. The natural surfactants, ARS and FRS, contain high levels of disaturated phosphatidylcholine (PC) [ϳ60% of the total lipid phosphorus (21)] and all of the surfactantassociated proteins. However, term fetal surfactant contains proportionately less phosphatidylglycerol (PG) and more phosphatidylinositol (PI) than the adult surfactant preparation (22), and SP-A from term fetal surfactant reportedly has properties different from those in the adult form (1,32).…”

“…The postlavaged lung tissue was removed, weighed, and homogenized, and the intracellularly stored surfactant (LB fraction) was isolated using the differential and density gradient procedure referred to above for preparations of the natural surfactants (21)(22)(23).…”

“…Preterm rabbits at 27 days of gestation (term ϭ 31 days) have almost no alveolar surfactant, as evaluated by alveolar lavage, and very little intracellularly stored surfactant (21,22); therefore, they are widely used for studying several aspects of lung development (4, 9, 18, 19, 26-28, 30, 31). We recently used this model to examine the effects of the intratracheal administration of different surfactant preparations on lung water clearance (16,24) in preterm rabbits ventilated for periods of up to 6 h. A surfactant preparation obtained from term fetal rabbits (FRS) was associated with longer survival and improved lung water clearance compared with an adult rabbit surfactant preparation (ARS) and two commercially available preparations, Exosurf and Survanta.…”