Architecture, elastic fiber, and collagen in the distal air portion of the lung of the 18-month-old rat.

BACKGROUND: The increase in the distal air spaces which takes place with age is the only sufficiently documented datum for differentiation between the senile and the adult lung. There are other pulmonary components which may be modified as the lung enters the phase of old age, but they have not as yet been sufficiently studied. The purpose of this study is to make a morphometric comparison between the wall thickness of the distal air spaces, elastic fiber, and collagen in lungs of rats of between 5 and 18 months of age. METHODS: The left lung of each rat was histologically processed for light microscopy. The sections were contrasted using methylene blue, resorcinfuchsin and Sirius red. Systematic randomized sampling was used for the selection of the histological fields studied. Morphometric variables were studied, and were systematized into three groups, namely: variables related with the alveolar architecture, variables which quantify elastic fiber, and those which quantify collagen. RESULTS: The old animals exhibited significant differences (p < 0.05) in the following variables: 1. In relation with the alveolar architecture, mean linear intercept, alveolar chord and wall thickness increased, whereas internal alveolar perimeter and tissue density decreased. 2. The relation elastic fiber density/lung tissue density increased. None of the variables which quantify collagen displayed significant differences. CONCLUSION: Our data lead us to consider that the lungs of the old animals displayed, not only an enlargement of the distal air spaces, but also a thickening of the alveolar wall and an increase in elastic fiber in relation to the rest of the lung tissue.

Methodological contributions for the morphometric study of the lung: approximation to the ideal sample size and quantification of collagen fiber.

BACKGROUND: A morphometric study of the rat lung was done to determine the importance, within the precision of a morphometric study, of the sample size in relation to the quality of the image and to propose a method for the quantification of lung collagen fiber. METHODS: Sixty Wistar rats, divided into two age groups consisting of adult and old rats, were used. The left lungs were studied and processed for light microscopy. Methylene blue, resorcin-fuchsin, and Sirius red stainings were performed. The variables were quantified automatically. In the sections stained with methylene blue, the variables alveolar chord, wall thickness, mean linear intercept index, tissue density, and internal alveolar perimeter were quantified, in two series, one with x40 magnification (panoramic image) and the other with x100 magnification. In the sections stained with resorcin-fuchsin, elastic fiber was quantified and the result related with that obtained for the variable tissue density. The results were compared statistically, and those obtained with different magnifications for single variables were related by using the correlation test; the misclassification indices were also calculated. In the sections stained with Sirius red, the surface that was birefringent to polarized light was quantified and related to the collagen fiber; the results were compared statistically. RESULTS: Concerning results obtained for single variables with different magnifications good, correlation indices were obtained (r > or = 0.62) for all but the wall thickness (r = 0.3). The results obtained for the panoramic images were the highest. The misclassification index was lower for the panoramic images. Significant differences (P < 0.5) were not found when comparing the mean birefringent surface in the two groups of animals. CONCLUSIONS: The results obtained lead us to consider that, despite the fact that the quality of the panoramic images is poorer, the results for these images are more accurate, possibly because a greater number of structures was analyzed. The measurement of the birefringent surfaces of the sections stained with Sirius red may be used in the study of lung collagen fiber.