Morphometric analysis of adult rat lung after bilobectomy.

Female rats (mean body weight, 245 g) were subjected to resection of the upper and middle lobes of the right lung (25% of the total lung volume). Forty-five days after the surgery, the animals were killed and their lungs were fixed and processed for quantitative light and electron microscopic investigation. Two groups of animals, sham-operated and normal rats with the same body weight, served as controls. At death the resected animals had the same body weight and lung volumes as the control animals. The remaining tissue of the right lung had increased in volume by 40%, the left lung by 26%. In light microscopic morphometry, volume densities of parenchyma, air spaces, and septums were all close to control values. Nonparenchymal structures, bronchi, and larger blood vessels also contributed to the normalization; they were not significantly different from control values. Electron microscopic quantitation performed on the lung parenchyma revealed the volume densities of capillaries and tissue as well as the surface densities of air spaces and capillaries to be in the range of control data, both in the right and left lung. For total lung the absolute volumes of air spaces, capillaries, and tissue, the alveolar and capillary surface areas, and the arithmetic and harmonic mean thicknesses of the air-blood barrier were practically identical in resected and control animals. The morphometrically calculated DLO2 was restored to normal values. This adaptive response resembled closely that obtained in growing rats, despite the comparatively limited growth potential of the animals in this study.