Distal airspace enlargement in the fawn-hooded rat: Influences of aging and alveolar wall destruction

Background: A recent study has revealed that the peripheral airspace in the lungs of the fawn-hooded rat (FHR) is enlarged. However, morphological and functional factors of the FHR lung have not been fully investigated. Objec tive: The purpose of our study was to examine the structural and functional changes in the FHR lung and to investigate the influence of aging on this process. Furthermore, morphological and functional measurements of the lung s of FHRs (4-48 weeks of age) were performed and the results compared with those of age-matched Wistar control rats (WCRs). Methods: All animals were studied under controlled conditions, and morphological and functional chang es of the lungs were examined. Measurements of body and lung weights were r ecorded, and the lungs were subjected to morphological evaluation. Morpholo gical measurements: mean linear intercept (MLI) and destructive index were determined. Functional evaluation of the lungs: total lung capacity, pressu re-volume curve, and exponential constant (K) which describes the shape of the curve were analyzed. In addition, right ventricular hypertrophy measure ments were performed to assess the severity of pulmonary hypertension. Stat istical analysis was performed using the unpaired t test, analysis of varia nce, and the Fisher post hoc test (p < 0.05). Results: Morphological analys is revealed a significant increase in airspace size (MLI) in all FHRs as co mpared with the WCRs which was evident from an early age (4 weeks). The inc rease in MLI did not progress age dependently in the FHR, whereas a tendenc y for an age-dependent increase in MLI was observed in the WCR. The destruc tive index measurements revealed that the increase in MLI of FHR was not ac companied by alveolar wall destruction. Concerning the functional examinati on, a leftward and upward shift of the pressure-volume curve was observed i n the FHRs as compared with the WCRs at all ages. As compared with the WCRs , a higher K value was observed in all FHRs which was evident from an early age (4 weeks). Age-dependent changes similar to those in MLI were observed in the K in both rat strains. Conclusions: The results of our study sugges t that FHRs manifest characteristics of distal airspace enlargement accompa nied by increased lung distensibility without alveolar wall destruction at an early age and that the changes do not progress age dependently. Neither an accelerated aging process nor destruction of the alveolar walls appears to be the mechanism responsible for the enlarged airspace in this rat strai n. Copyright(C)2001 S. Karger AG,Basel.