Contrasting natures of lung growth after transplantation and lobectomy1

Objective: We hypothesized that posttransplantation lung growth in an immature recipient and postlobectomy compensatory lung growth are two distinct processes. Methods: Mature swine underwent left upper lobectomy, and growth of the left lower lobe was studied after 2 weeks and after 3 months. Left lower lobes from another set of mature pigs were transplanted into immature animals, and growth of the transplanted lobe was then studied after 2 weeks and after 3 months. Left lower lobes from mature animals that did not undergo operation were used as normal control lobes. The lobes were weighed on removal and fixed intrabronchially. Sections stained with hematoxylin and eosin were used to determine alveolar surface density and percentage volume of respiratory region. Immunostaining for 5-bromo-2′-deoxyuridine was used to determine alveolar cell proliferation index, and epidermal growth factor receptor expression was detected by Western blot. Results: Postlobectomy lung growth (increase in lobe weight) reached statistical significance at 2 weeks, with a concomitant rise in cell proliferation index. The transplanted lobe, in contrast, exhibited a gradual growth response, with a statistically significant increase in cell proliferation index at 3 months. Volume of respiratory region was noted to increase only in the transplanted lobe at 3 months. Epidermal growth factor receptor expression was upwardly regulated relative to that in normal control lobes in the 2-week postlobectomy and 3-month posttransplantation lobes. Conclusions: Postlobectomy lung growth appears to be regulated by a different mechanism than is posttransplantation lung growth and is a more rapid and restorative process. The growth peaks in both processes correlate with upward regulation of cell proliferation index and epidermal growth factor receptor expression.