Alveolar enlargement in obesity-induced hyperplastic lung growth

Structural changes underlying obesity-induced pulmonary cellular hyperplasia were evaluated by lung morphometry and stereology in 8-wk-old male Long-Evans rats made obese by nursing in small litters with subsequent feeding of a high-fat diet. Control animals were raised in normal-sized litters and then fed standard rat chow. Compared with controls, obese rats had significant elevations in body weight (31%), fat pad weight (158%), fat pad weight-to-body weight ratio (97%), snout-to-anus length (8%), snout-to-tail length (7%), serum insulin concentration (64%), fixed lung volume (56%), and the ratios of lung volume to body weight (18%) and lung volume to body length3 (24%). Lungs of obese rats had enlarged alveoli, with significant increases in mean (182%) and total (71%) alveolar volume, mean chord length (28%), and mean (89%) and total (25%) alveolar surface area. Surface density (24%), surface-to-volume2/3 ratio (24%), and numerical density (43-53%) of alveoli in obese rats were significantly diminished compared with lungs of control rats. Unchanged were total alveolar number and alveolar volume density. Measurements of perihilar and subpleural alveoli within the obese and control groups were indistinguishable. These results indicate the presence of alveolar enlargement with relatively diminished respiratory surface area in lungs of young rats made obese by diet. This relative decrease in gas-exchanging area may contribute to physiological and functional alterations present in obesity.