IMPLICATIONS OF NEWBORN LUNG LECITHIN METABOLISM

Abstract

Premature and term newborn and adult rabbit lungs were pulse labeled in vivo with lecithin precursors choline, palmitic acid, and phosphate. Lecithin was isolated from parenchyma, alveolar wash, lamellar bodies and microsomes from the lungs of each group of animals. Time of appearance and biological half-life of lecithin in each fraction was monitored by changes in lecithin specific activity with time. All animals rapidly incorporated isotopic precursors into microsomal lecithin. Radioactive lecithin appeared after a 3 hour delay in premature and term newborn lamellar bodies; no delay was noted in appearance of labeled lecithin in lamellar bodies isolated from adult lung. Maximal specific activity in alveolar lecithin was reached by 6 hours in adult rabbits and in about 20 hours in premature and term newborns. Biological half-life values for lecithin in the lung fractions of premature and term newborn rabbits were greater than 3 times longer than comparable half-life values determined for the adult. The long delay (3 hours) before de novo synthesized lecithin begins to reach the alveolar space suggests that synthesis does not contribute to alveolar stability until many hours after birth. Significant lecithin synthesized de novo is not present at the alveolar space of the newborn for at least 20 hours. Premature and term newborn rabbits must rely on lecithin stored in anticipation of birth to maintain alveolar stability at birth. The prolonged half-life argues against lecithin degradation contributing to RDS.