A model of inducible expansion of the gas exchange area in adult mice would be ideal for the investigation of molecular determinants of airspace regeneration in vivo. Therefore, the post-pneumonectomy (post-PNX) compensatory lung growth in adult C57BL/6 mice was characterised in this study.Mice underwent left-sided PNX. Right lung volume was assessed on days 1, 3, 5, 7, 10 and 21 after PNX, and total DNA and cellular proliferation of the right lung were determined. Lung histology was studied using immunohistochemistry and quantitatively characterised by detailed stereological investigations. Pulmonary function was assessed using a mouse body-plethysmograph.Following PNX, right-lung volume rapidly restored the initial volume of left and right lung. Total DNA increased significantly over 21 days and equalled the total DNA amount of both lungs in the control mice. Septal cell proliferation significantly increased after PNX, and included endothelial cells, epithelial cells, smooth muscle cells and fibroblasts. Stereological investigations of left and right control lungs versus right lungs 21 days after PNX indicated complete restoration of body mass-specific alveolar surface area. Pulmonary function testing showed marked alteration at 3 days and normalisation at 21 days post-PNX.In conclusion, well reproducible reconstitution of alveolar gas-exchange surface based on septal tissue expansion may be provoked by pneumonectomy in adult mice. Eur Respir J 2004; 24: 524-532. Several pulmonary diseases originate from or are deteriorated by the loss of alveolar septae or, alternatively, remodelling processes of the septal walls, which result in severely compromised gas exchange within the alveoli. The principal ability of mammals to completely restore lung function after major losses of lung tissue by compensatory development of additional gas-exchange surface areas provides a rationale for identifying intrinsic regenerative programmes of the lung that may be employed for therapeutic purposes.The molecular basis of alveolar generation and alveolar remodelling is presently not well understood [1]. Furthermore, the cellular components which contribute to repair and remodelling of pulmonary tissue still await ultimate elucidation. Solutions to the problems concerning repair and regeneration of lung tissue for restoration of functional alveoli are at the cutting edge of identifying novel therapeutic options for lung diseases like chronic obstructive pulmonary disease (COPD) and fibrosis.It has been previously reported that partial resection of the lung results in a rapid compensatory growth process of the remaining lung tissue, restoring normal lung volume, cell mass and organ function, in a variety of mammalian species [2][3][4][5][6]. Compensatory lung growth following unilateral pneumonectomy (PNX) has been documented for dogs, rabbits, ferrets, rats and mice. However, it has been most extensively studied in rats, and the time course, volumetric and morphological changes are well characterised in this species [7,8]...

Ischemia and reperfusion (I/R) result in surfactant dysfunction. Whether the impairment of surfactant is a consequence or a cause of intraalveolar edema formation is still unknown. The cumulative effects of lung perfusion, ischemic storage, and subsequent reperfusion on surfactant ultrastructure and pulmonary function were studied in a rat isolated perfused lung model. The left lungs were fixed for electron microscopy by vascular perfusion either immediately after excision (control; n = 5) or after perfusion with modified Euro-Collins solution (EC), storage for 2 h at 4 degrees C in EC, and reperfusion for 40 min (n = 5). A stereological approach was chosen to discriminate between intraalveolar surfactant subtypes of edematous regions and regions free of edema. Intraalveolar edema seen after I/R in the EC group occupied 36 +/- 6% (mean +/- SEM) of the gas exchange region as compared with control lungs (1 +/- 1%; p = 0.008). Relative intraalveolar surfactant composition showed a decrease in surface active tubular myelin (3 +/- 1 versus 12 +/- 0%; p = 0.008) and an increase in inactive unilamellar forms (83 +/- 2 versus 64 +/- 5%; p = 0.008) in the EC group. These changes occurred both in edematous (tubular myelin, 3 +/- 1%; unilamellar forms, 88 +/- 6%) and in nonedematous regions (tubular myelin, 4 +/- 3%; unilamellar forms, 77 +/- 5%). The ultrastructural changes in surfactant were associated with an increase in peak inspiratory pressure during reperfusion. In conclusion, surfactant alterations seen after I/R are not directly related to the presence of edema fluid in the alveoli. Disturbances in intraalveolar surfactant after I/R are not merely the result of inactivation due to plasma protein leakage but may instead be responsible for an increased permeability of the blood-air barrier, resulting in a vicious cycle of intraalveolar edema formation and progressing surfactant impairment.

These data indicate that our model of chronic aerosol allergen challenges leads to a phenotype of experimental asthma with participation of distal airways and persistence of inflammation thereby resembling many morphological and physiological aspects of human bronchial asthma.

Regeneration of the gas exchange area by induction of neoalveolarisation would greatly improve therapeutic options in destructive pulmonary diseases. Unilateral pneumonectomy is an established model to remove defined portions of gas exchange area and study mechanisms of compensatory lung growth. The question of whether new alveoli are added to the residual lung after pneumonectomy in mice was addressed.Left-sided pneumonectomy was performed in 11 adult C57BL/6 mice. Alveolar numbers were analysed in lungs fixed at days 6 and 20 after pneumonectomy and in 10 age-matched controls using design-based stereology based on a physical fractionator. Post-fixation lung volume was determined by fluid displacement.Complete restoration of lung volume was observed 20 days after pneumonectomy. Alveolar numbers were significantly increased by 33% in residual right lungs at day 20 in comparison with control right lungs. In control left lungs, an average of 471¡162610 3 alveoli was estimated, 49% of which were regenerated by residual lungs at day 20. Of the newly formed alveoli seen at day 20, 74% were already present at day 6. The present data demonstrate that, in addition to growth in size of existing alveoli, neoalveolarisation contributes to restoration of the gas exchange area in adult mice and is induced early after pneumonectomy.

Ischaemia/reperfusion (I/R) injury, a major problem in clinical lung transplantation, is associated with surfactant dysfunction. The present study aimed to test the hypothesis that preservation related improvements in post-ischaemic lung function are associated with improved ultrastructural preservation of pulmonary surfactant.Rat lungs were flush perfused with modified Euro-Collins solutions (ECS), stored for 2 h at 48C, and reperfused for 40 min. Lungs were preserved with conventional (ECS 115: 115 mmol . L -1 K + ), medium-K + (ECS 40: 40 mmol . L -1 K + ), or low-K + (ECS 10: 10 mmol . L -1 K + ) ECS. Functional parameters were monitored during reperfusion (n=10 per group). After reperfusion, left lungs were prepared for electron microscopical and stereological analysis of surfactant (n=5 per group).In all three experimental groups notable I/R injury developed which was lowest in ECS 40 as indicated by significantly less intraalveolar oedema, higher perfusate oxygenation, and lower peak inspiratory pressure. This was associated with a significantly superior preservation of the ultrastructure of the surface active surfactant subtype tubular myelin in ECS 40 compared with ECS 115 and ECS 10. Stereological analysis revealed that the relative amount of tubular myelin was highest in ECS 40 (mean SEM; 6.2 0.8%) compared with ECS 115 (3.0 1.0%) and ECS 10 (2.7 1.6%).Analysis of surfactant in its natural location within the organ showed that the severity of ischaemia/reperfusion injury correlates with differences in intraalveolar surfactant composition. Improved post-ischaemic respiratory function achieved by medium-K + Euro-Collins solution is associated with superior ultrastructural preservation of tubular myelin. It is concluded that the integrity of surface active tubular myelin represents an important criterion for the assessment of lung preservation quality. Eur Respir J 2000; 15: 526±531.

The aim of this study was to characterise pulmonary reimplantation injury in isolated, perfused rat lungs following 2 h of cold ischaemia, and 50 min. of in vitro reperfusion. The effects of 2 differently composed lung preservation solutions (low potassium Euro‐Collins and Celsior; each n=5) were examined in comparison with untreated, nonischaemic control lungs (n=3). After fixation by vascular perfusion and tissue collection by systematic random sampling, the volume weighted mean volume (v) of alveoli and acinar pathways was estimated by light microscopic stereology using the method of point sampled intercepts in plastic embedded, Azan‐stained material. Significantly higher v of alveoli and acinar paths was found in the Celsior group than in Euro‐Collins preserved lungs. However, in the controls the size of acinar pathways was similar to Celsior preserved lungs whereas alveolar size was comparable to preservation with Euro‐Collins. The between‐animal coefficient of variation of alveoli was very low in controls and Celsior preserved but higher in the Euro‐Collins group. Size distribution of alveoli and acinar paths in 15 size classes was largely homogeneous in all groups tested. In the Euro‐Collins group the fractions of both class 1‐alveoli and class 1‐acinar paths significantly exceeded those of the other groups. Widely expanded alveoli (size classes 13–15) only occurred after preservation with Celsior whereas wider acinar paths (size class 15) were found in the Celsior group and in the controls. It is concluded that lung preservation with low‐potassium Euro‐Collins and Celsior solutions may act differently on distinct spaces in the distal gas‐exchange regions of lungs. This may be due to selective effects on pulmonary surfactant activity and on elastic tissue elements in the alveolar ducts, respectively. Additionally, the method of point sampled intercepts is considered to be an efficient tool to evaluate the effects of different preservation solutions on lung parenchyma.

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Ischemia/reperfusion (I/R) injury results in the impairment of surfactant activity. The hypothesis that the differences in lung preservation quality obtained by EuroCollins (EC) and Celsior (CE) solutions were related to surfactant alterations was tested. To avoid extensive structural damage and edema formation, which can secondarily affect the surfactant system, lungs were stored for a short ischemic period (2 h at 10 degrees C) and reperfused (50 min) in an isolated perfused rat lung model after preservation with either potassium-reduced (40 mmol) EC40 or with CE. Using a modified stereological approach ultrastructure, total amount and distribution of phospholipid membranes composing tubular myelin (tm) and small (s) and large (l) unilameliar vesicles (ul) were investigated in the organ in lungs fixed by vascular perfusion either in situ (controls) or after I/R (n = 5 per group). The total amount of intraalveolar surfactant was increased after I/R. However, a significant amount (p = 0.008) of tm was displaced into the alveolar lumen and showed wider meshes of the tm lattices than did the controls (p = 0.023) where almost all tm was epithelial. In lungs preserved with EC40, epithelial tm was significantly reduced (p = 0.018), resulting in a higher ratio (p = 0.034) of surface-inactive small ul (0.05 to 0.3 microm) to surface-active epithelial tm. In the CE group approximately 50% of the total tm pool was epithelial. This was accompanied by higher parenchymal air space and improved functional parameters. Epithelial and endothelial cell-specific immunostaining did not reveal any gross damage of the blood-gas barrier. In summary, improved lung function during reperfusion was associated with beneficial effects of lung preservation on tm integrity after I/R. These observations suggest that preservation solutions ameliorate events leading to surfactant disturbance even before extensive lung injury is manifested.