Timing of the quantitative recovery in the regenerating rat lung

Growing rats 23 days of age were subjected to the resection of the upper and middle lobes of the right lung (25% of total lung volume). On postoperative days 1, 4, 6, 9, 12, 18, and 30, the lungs of 5 animals were fixed by intratracheal instillation of glutaraldehyde, their volumes measured by water displacement, and the lung tissue processed for quantitative light (LM) and electron microscopic (EM) investigations. For each group, 3 age-matched sham-operated, and 4 normal rats served as controls. Sham operation consisted in entering the pleural space, and collapsing and ventilating the lungs. In all animals, the following parameters were measured by means of point and intersection counting stereology at either LM or EM-levels: volume densities of lung parenchyma and of its components (airspaces, tissue, capillary blood) and surface densities of airspaces and of capillaries. From these data absolute parameter values were calculated for each lung. The results showed that after bilobectomy the remaining lung re-expanded rapidly first by an overinflation of the airspaces and after Day 4 by an increase in tissue mass and capillary volume. On Days 9 and 12 the operated lungs did not differ quantitatively from control lungs. Later, however, further sequels of the bilobectomy were detected: On Day 18, lobectomy-lungs were smaller than controls, and on Day 30 lungs, the left lung was significantly different in structure from the right lung and from control lungs.(ABSTRACT TRUNCATED AT 250 WORDS)