Kompensatorisches Lungenwachstum nach unilateraler Pneumonektomie bei der Maus - Methodenvergleich zur Bestimmung der Alveolenzahl

In our study we investigated compensatory lung growth after left-sided pneumectonomy in 12-14 week old C57BL/6 mice. The question was if the complete restauration of the gas exchange surface is caused by the formation of new alveoli or by enlarging of existing alveoli. The aim was to determine the number of alveoli, which were counted by using a new design-based, stereological method at the CAST-Grid-System. Therefore we cut consecutive pairs of sections from lungs slices and compared corresponding areas directly (disector-method). First we had to prove what kind of method would be preferable for histological evaluation: directly by using the fractionator-principle or indirectly by calculating with volume density of alveoli and reference volume. At the same time we investigatetd the influence of different embedding methods on the estimation of alveoli: paraffin versus plastics. By comparing control mice with both methods there were large differences in the number of alveoli with a mean of 1,2 x 106 ± 1,4x105 by using the direct method and 5,4 x 106 ± 5,9x105 alveoli of lungs by using the indirect method, independent of the thickness of the slices. A reason for the overestimation of alveoli in lungs by using the direct method may be tissue deformation like shrinkage or swelling. The fractionator-method is independent of it. Another problem are arteficial fractures of alveolar septae which often appear and often cannot be distinguished from alveolar openings. Therefore, the directly method is preferable when the number of alveoli has to be investigated. To investigate compensatory lung growth after left-sided PNX we compared mices on day 6 (n=6) and 20 (n=5) after PNX with control mices (n=10). The lungs of left sided pneumectonomised mice already showed an increase in lung volume as well as an increase of 26 % in number of alveoli of the remaining right lungs on day 6 after PNX which increases more (33 %) until day 20 after PNX (p<0,05) and reaches nearly the total number of alveoli of control mices. By estimating the number of alveoli we concluded that the compensation after left-sided PNX which includes the complete restauration of gas exchange surface may be the result of both an inrease in number as well as an increase in volume of alveoli.