Role of ornithine decarboxylase and polyamines in early postnatal lung growth.

We assessed the importance of ornithine decarboxylase (ODC) and polyamines in early postnatal lung growth. Lung-ODC activity in newborn rats rose rapidly after birth and was highest at 4-6 days of age. Lung putrescine and spermidine specific contents also peaked during this period, but spermine specific content remained relatively unchanged. The temporal pattern of these changes differed markedly from that in the heart, brain, and kidney where ODC activity is highest at birth then rapidly declines. The period of peak lung-ODC activity and polyamine specific content correlated with rapid increases in lung DNA content, protein content, and weight. The specific irreversible ODC inhibitor, alpha-difluoromethylornithine, significantly reduced lung-ODC activity and putrescine and spermidine specific content; it also caused significant early reductions in lung DNA and protein content without simultaneously affecting body weight and appearance. Morphometrically, the lungs of alpha-difluoromethylornithine-treated rats had significantly fewer type 2 epithelial cells, interstitial cells, and capillary endothelial cells than the lungs of controls. We conclude that ODC and polyamines play an important role in postnatal lung growth and that alpha-difluoromethylornithine can be used as a probe to disrupt lung growth.

Zonal distribution of alveolar macrophages, type II pneumonocytes, and alveolar septal connective tissue gaps in adult human lungs.

The distribution of alveolar macrophages, Type II cells, and alveolar septal connective tissue discontinuities or gaps in two neighboring alveoli from a human lung obtained at surgery, and preserved by vascular perfusion-fixation, was studied by electron microscopy. Discontinuities or gaps are defined as complete interruptions of all the connective tissue elements of the alveolar septum, including the basement membranes. Serial-sectioning of the alveoli, and the creation of montages of the entire circumference of each alveolus at intervals of every twentieth section (approximately 1.6 micron) at a magnification of X 2,160 permitted precise identification of cells and connective tissue gaps and allowed the reconstruction, by computer techniques, of the alveolar walls in 3 dimensions. These studies showed that all of the 48 alveolar macrophages identified, and over two thirds of all Type II cells and alveolar septal gaps, were located or bordered on alveolar septal junctional zones (within 10 microns of septal junctions). The profiles of 739 alveoli examined by light microscopy from 6 lungs similarly preserved by vascular perfusion-fixation, in which the alveolar surface lining was well fixed, also showed alveolar macrophages preferentially distributed in alveolar junctional zones. These were compared with 242 alveolar profiles from 3 other vascularly-fixed lungs and 971 alveolar profiles from 9 lungs fixed by way of the airways, in which the alveolar surface lining was lost. In these lungs, most of the alveolar macrophages were in the alveolar air spaces.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential changes in lung morphology during the repair of acute oxygen-induced lung injury in adult rats.

We studied changes in lung ultrastructure and collagen content during the repair of acute lung injury in adult rats exposed to 100% O2 for 60 h and recovering in ambient air. In the interstitium, during the first 3 days of repair, the number of neutrophils decreased 16-fold, and monocytes and lymphocytes increased to 7-fold and 4-fold the respective control values. Myofibroblasts increased about 5-fold and the volume of the interstitial matrix remained high. By 7 days, the differential count of inflammatory cells was normal although the number of total interstitial cells and myofibroblasts decreased more slowly. In the capillary endothelium, after 3 days of repair, the cells were hypertrophied and had organelle-rich cytoplasm, and total cell number had increased back to control values; endothelial cell number increased an additional 63% between 3 and 7 days of repair. In the epithelium, type 2 cells increased 150% during the first 3 days of repair before decreasing; type 1 cell number did not change. After 28 days of repair, the lungs appeared qualitatively almost normal; however, interstitial cell number and collagen content were still increased. We conclude that the repair of oxygen-induced lung injury involves a complex pattern of morphologic changes that has important similarities to those occurring during repair on other tissues such as the skin.

Anatomical relationships between type II pneumonocytes and alveolar septal gaps in the human lung.

This report describes a relationship between type II pneumonocytes and breaks in continuity in the alveolar septum of the human lung. Breaks in continuity of the septum are defined as gaps in the connective tissue matrix of the alveolar septum, with or without discontinuity of the accompanying alveolar epithelium. Septal connective tissue gaps accompanied by epithelial discontinuity are recognized as interalveolar pores of Kohn. When the discontinuity is confined to the connective tissue matrix, epithelial continuity may be maintained by either a single or a double layer of type I epithelium, by a type II cell, or by both type I and type II epithelial cells. Alveolar septal gaps were studied by electron microscopy on random sections in 26 adult human lung specimens and by serially sectioning and montaging the entire circumference of one alveolus to a depth of 103 microns (approximately one-half a normal alveolus) from one of the specimens. Fixation was by way of the airways in most specimens, but by vascular perfusion in the serially sectioned specimen and in seven others. In lungs studied by random sections, we found that the incidence of septal connective tissue gaps with epithelial continuity per specimen correlated with the incidence of pores (r = .468, P less than .016), and also with the incidence of type II cells (r = .422, P less than .025) in the specimen. Five percent of all type II cells observed in the random sections in the 26 specimens (103/1,955) occupied septal gaps, and 2.5% (49/1,955) were located at the rim of a pore. In contrast, in the single serially sectioned montaged alveolus, 69% of all type II cells occupied some type of septal gap, with 24% of all type II cells forming part of the rim of a pore. Over half of all pores in this alveolus were associated with a type II cell. We concluded that a relationship between the incidence of type II cells and gaps in the alveolar septum could be demonstrated on random sections in normal human lungs, which was much more obvious in a single serially sectioned hemialveolus. Serial section techniques of whole alveoli may be necessary to establish relationships that may not be apparent on random sections and that require the study of whole cells in continuity with their environment in order to be identified. The findings may be significant in suggesting a possible role of the type II cell in alveolar septal repair.

Repair of oxygen-induced lung injury in adult rats. The role of ornithine decarboxylase and polyamines.

We studied the repair of lung injury in adult rats exposed to 100% oxygen for 60 h, then placed in ambient air. Lung ornithine decarboxylase (ODC) activity and polyamine (putrescine, spermidine, and spermine) content during repair were correlated with changes in lung ultrastructure. The effect of difluoromethylornithine (DFMO), a selective Irreversible ODC inhibitor, was also studied; ODC activity increased to 25-fold baseline 2 days after injury and returned to normal by 7 days. Polyamine content increased to 3-fold baseline during the first 3 days. During the same period, the number of capillary endothelial cells and the capillary surface area almost doubled, and the number of type 2 epithelial cells increased 2.5-fold. The DFMO treatment lowered ODC activities below baseline, reduced the increase in polyamine content, and also reduced the morphometric parameters described above to only 60 to 70% of the values during normal repair. It also caused a significant decrease in the number of type 1 epithelial cells during repair, suggesting that deficient replacement by differentiating type 2 epithelial cells occurred. We conclude that marked changes in lung ODC activity and polyamine content occur during the repair of oxygen-induced injury to the lung and that selective inhibition of these changes adversely affects repair.

Early ultrastructural changes in papain-induced experimental emphysema.

These studies show that very soon after exposure of canine lungs to crude papain mixed with a marker (India ink), the alveolar surface-active lining was both morphologically and functionally altered, and alveolar macrophages were destroyed in significant numbers. These changes occurred before other identifiable major alterations. The morphologic changes were characterized by replacement of the normal alveolar surface lining by an amorphous material adhering to the alveolar surfaces and penetrating the pores of Kohn, which were significantly enlarged. Type II epithelial cells and alveolar macrophages were increased in number, with a significant proportion of the latter observed to be disintegrating. Polymorphonuclear leukocytes were also noted in increased numbers, but this was also observed in control lungs (instilled only with saline plus India ink). Functionally the alveolar surface lining as studied in lung extracts showed an abnormal stability index after either in vivo or in vitro exposure to crude papain. These findings suggest that the early effects of this exogenous protease on the lung are interrelated, alveolar surface lining injury appearing to set the stage for accelerated macrophage lysis, with the probable release of phagocytosed exogenous protease as well as intracellular endogenous proteases. These events may represent early steps in the pathogenesis of experimental papain-induced pulmonary emphysema.

Ultrastructural studies of canine interalveolar pores (of Kohn).

Normal canine lungs were prepared for ultrastructural studies using two different routes for fixation: the airways route and the vascular route. Using the airways route, under conditions of controlled pressure, scanning and transmission electron microscopic studies of alveolar surfaces allowed identification of an average of 19 alveolar pores per exposed alveolar surface, each pore averaging approximately 3 micron. in diameter. The alveolar surface was honeycombed in appearance, with the walls of multiple capillaries bulging into the alveolar space. Using the other route, vascular perfusion of the lungs with the fixative and controlling pressures in both the vascular and airway compartments, scanning electron microscopic studies showed that most exposed alveoli exhibited a smooth or slightly wrinkled surface, essentially devoid of pores and averaging only three pores per alveolus. By transmission electron microscopy, alveolar surfaces were found to be covered with an extracellular material suggestive of lung surfactant; alveolar pores, averaging approximately 1 micron. in diameter, were filled with the same material. It is concluded that most alveolar pores of normal dogs are bridged by and filled with lung surfactant. These findings can be demonstrated most reliably by using vascular perfusion of the lungs for introducing the fixative.