We hypothesized that compensatory lung growth after lobectomy is characterized by a combination of cellular hyperplasia and hypertrophy and that up-regulation of epidermal growth factor receptor (EGFR) is involved in these processes.

Age-matched mature pigs were divided into four groups. The control group (group C) did not have operation. Two groups underwent left upper lobectomy and were studied 2 weeks (group L2) or 3 months (group L3) later. The last group underwent a sham left thoracotomy, and the left lower lobe was harvested 2 weeks later for EGFR analysis. Left lower lobes were studied using wet weight, cell proliferation index through immunostaining for 5-bromo-2′-deoxyuridine, morphometry, and Western blot analysis for EGFR. Content of protein and DNA (deoxyribonucleic acid) in the lung tissue was also determined.

Left lower lobe weights were elevated in both groups L2 and L3 compared with group C. We noted a significant rise in the proliferation index, with a concomitant increase in EGFR expression, in group L2 compared with group C. In group L3, there was an increase in the protein to DNA ratio compared with group C.

We conclude that compensatory lung growth after lobectomy comprises an early increase in the cell proliferation index (ie, cellular hyperplasia) and a late increase in the protein to DNA ratio (ie, cellular hypertrophy). The early proliferative phase is associated with EGFR up-regulation.