Influence of fasting on the lung.

We examined the following in fed rats and in rats fasted for 72 h: 1) the dipalmitoyl lecithin (DPL) content of lung lavage fluid and of the remaining lung tissue, 2) descending air and saline pressure-volume curves of excised lungs, and 3) the volume density of granular pneumocyte lamellar bodies. Lung tissue DPL was decreased by 27% and lavage DPL was decreased by 40% in lungs of fasted rats. The decreased lung DPL content was associated with a 20% decrease in the volume density of lamellar bodies of granular pneumocytes. In spite of the decrease in lavage DPL content, air pressure-volume curves of excised lungs were the same as curves of lungs of fed rats. Saline pressure-volume curves of excised lungs were also the same in fed and fasted rats. The amount of lavage DPL obtained from both fed (1.1 +/- 0.1 mg, n=6) and fasted (0.7 +/- 0.1 mg, n=7) rats exceeded the theoretical minimum amount of DPL (0.5 mg) required for a monomolecular film to cover the alveolar surface of the rat at functional residual capacity. If we assume that lavage DPL represents mainly DPL lining the alveolus (surface film and hypophase) the data suggest that there is an alveolar reserve of DPL above that amount needed to maintain normal alveolar stability.