Strain specific respiratory air space enlargement in aged rats

We studied lung structure and function in Fischer-344 and Sprague Dawley rats to compare the pathophysiologic features of the aged lung in animal strains. Both strains were maintained under identical conditions of minimal exposure to injurious environmental agents. We measured the number, size, and surface area of alveoli, pressure-volume characteristics and connective tissue content of lungs at midlife (12 or 14 months of age) and old age (24 months of age). Results showed differences in the older versus younger group of the Sprague Dawley strain as indicated by enlarged air spaces [154 +/- 21 (SEM) versus 118 +/- 13 micromicroliter] (p less than 0.05), increased collagen (hydroxyproline content 4.1 +/- 0.1 versus 3.0 +/- 0.1 mg/lung) (p less than 0.05), and a leftward shifted pressure-volume curve. There was no change in surface area or alveolar number. The structural lesions are consistent with air space enlargement with fibrosis and not emphysema. In contrast, no major changes were found in the lungs with age in Fischer-344 rats. We hypothesize that in the Sprague Dawley strain the aging process impairs the ability of the lung to maintain normal structure and function. Two strains of rats which differ pathologically in old age may be useful in the study of the effects of aging on the lung.