Metabolic Activity of Developing Rat Lung

Abstract

The uptake and metabolism of <sup>3</sup>H-ρalmitate, <sup>14</sup>C-choline, <sup>14</sup>C-proline and <sup>3</sup>H-glucosamine were studied in lung slices prepared from rats aged 2–12 days. Palmitate incorporation increased from 18.2 ± 2.8 nmol/mg protein/h 2 days before birth to 40.0 ± 4.0 nmol/mg protein/h 3 days after birth, and decreased to 24.0 ± 2.3 nmol/mg protein/h at 12 days of age, it remained at the same level in the adult lung. At all ages tested, more than 75% of the palmitic acid taken up by the lung was in esterified form. Incorporation of palmitic acid into lecithin was highest 1 day after birth. Choline incorporation into lecithin increased eightfold between 2 days before and 1 day after birth (from 0.45 ± 0.12 to 3.75 ± 0.25 nmol/mg protein/h, respectively) and decreased 60% by 12 days of age. There was no difference between the incorporation rate at 12 days and that in the adult lung (1.52 ± 0.15 nmol/mg protein/h). Total lung phospholipid increased 220% between 2 days before birth and the day of birth, and changed little thereafter. Phosphatidyl choline made up 50–60% of lung phospholipids at all ages. Proline incorporation into lung protein was highest in the perinatal period (0.57–0.58 nmol/mg protein/h 2 days before and 1 day after birth) and decreased rapidly thereafter. Glucosamine incorporation was highest in the fetal lung (0.84 ± 0.05 nmol/mg protein/h) and decreased 67% 1 day after birth, the incorporation remained between 0.1 and 0.2 nmol/mg protein/h thereafter (from 3 days to adult age). The data presented show that in the rat lung the biosynthesis of structural components and of surfactant is highest during the immediate perinatal period.