Morphologic changes in the lung during the lifespan of Fischer 344 rats

Cellular, biochemical and functional effects of ozone: new research and perspectives on ozone health effects

Ozone, a toxic component of photochemical oxidant air pollution, has been the focus of considerable research efforts for several decades. In spite of this large body of work, questions remain as to the potential risks to human health represented by chronic low-level exposure to ozone. Newer studies in animals have provided fundamental information on the range of biochemical, functional and morphologic responses to ozone exposure. While the response to ozone exposure is extremely complex, some generalities have emerged which may aid attempts to apply the results of these studies to decisions regarding the protection of human health.

Strain specific respiratory air space enlargement in aged rats

We studied lung structure and function in Fischer-344 and Sprague Dawley rats to compare the pathophysiologic features of the aged lung in animal strains. Both strains were maintained under identical conditions of minimal exposure to injurious environmental agents. We measured the number, size, and surface area of alveoli, pressure-volume characteristics and connective tissue content of lungs at midlife (12 or 14 months of age) and old age (24 months of age). Results showed differences in the older versus younger group of the Sprague Dawley strain as indicated by enlarged air spaces [154 +/- 21 (SEM) versus 118 +/- 13 micromicroliter] (p less than 0.05), increased collagen (hydroxyproline content 4.1 +/- 0.1 versus 3.0 +/- 0.1 mg/lung) (p less than 0.05), and a leftward shifted pressure-volume curve. There was no change in surface area or alveolar number. The structural lesions are consistent with air space enlargement with fibrosis and not emphysema. In contrast, no major changes were found in the lungs with age in Fischer-344 rats. We hypothesize that in the Sprague Dawley strain the aging process impairs the ability of the lung to maintain normal structure and function. Two strains of rats which differ pathologically in old age may be useful in the study of the effects of aging on the lung.

Neonatal pulmonary oxygen toxicity in the rat and lung changes with aging

The aims of this study were to determine if neonatal hyperoxia exposure causes permanent lung damage and to define the relationship between neonatal lung oxygen toxicity and aging. Sprague-Dawley newborn rats (n = 85) breathed 100% oxygen (O2) or room air (RA) during the first 8 days of life, and then RA. At 2 and 22 months of age we assessed right ventricular (RV) systolic pressure (RVSP), RV weight, saline and air pressure-volume curves, volume density of lung parenchyma and nonparenchyma, parenchymal air space (PAS), mean linear intercept (Lm), number of small arteries/mm2 and the extent of their medial muscularization. Aging in RA did not affect the RVSP, RV weight, the number of small arteries/mm2, or their muscularization. The maximal lung volume/g of dry lung and the elastic recoil pressure between 40 and 90% maximal lung volume decreased. The volume density of lung parenchyma increased but the fraction of the lung parenchyma that was PAS decreased and that of the alveolar septa and Lm increased. The O2-treated rats at 60 days of age had increased RVSP and RV weights with a decrease in the small arteries/mm2. The lung parenchymal volume density and PAS increased and the density of alveolar septa decreased. The Lm increased and the alveoli/mm2 and elastic recoil pressure decreased. The lung damage seen in the O2-treated rats at 60 days persisted and in addition underwent the changes seen in the aging controls. However, the extent of muscularization of the arteries decreased. We conclude that neonatal hyperoxia causes permanent functional and structural changes of the lung but these do not interact with aging; that is, the effects of O2 toxicity and aging are additive but not synergistic.

Type I cell-like morphology in tight alveolar epithelial monolayers

The pulmonary alveolar epithelium separates air spaces from a fluid-filled interstitium and might be expected to exhibit high resistance to fluid and solute movement. Previous studies of alveolar epithelial barrier properties have been limited due to the complex anatomy of adult mammalian lung. In this study, we characterized a model of isolated alveolar epithelium with respect to barrier transport properties and cell morphology. Alveolar epithelial cells were isolated from rat lungs and grown as monolayers on tissue culture-treated Nuclepore filters. On Days 2-6 in primary culture, monolayers were analyzed for transepithelial resistance (Rt) and processed for electron microscopy. Mean cell surface area and arithmetic mean thickness (AMT) were determined using morphometric techniques. By Day 5, alveolar epithelial cells in vitro exhibited morphologic characteristics of type I alveolar pneumocytes, with thin cytoplasmic extensions and protruding nuclei. Morphometric data demonstrated that alveolar pneumocytes in vitro develop increased surface area and decreased cytoplasmic AMT similar to young type I cells in vivo. Concurrent with the appearance of type I cell-like morphology, monolayers exhibited high Rt (greater than 1000 omega.cm2), consistent with the development of tight barrier properties. These monolayers of isolated alveolar epithelial cells may reflect the physiological and morphological properties of the alveolar epithelium in vivo.

Application of the disector method in the light microscopic quantification of type II pneumocytes in control and ozone-exposed rats

Alveolar type II cells in control and ozone-exposed rat lungs were counted at the light microscopical level with the 'disector method'. The type II cells were unequivocally marked by histochemical staining for alkaline phosphatase activity in 2 microns plastic sections. By this counting method, the mean number of type II cells per lung in control rats was of the same magnitude as those reported in the literature, using point counting methods. After exposure of rats to 1.6 mg ozone/m3 for 7 days, a 50% increase in the mean number of type II cells was observed. The use of the disector method at the light microscopical level offers some advantages above a quantification at the electron microscopical level. The procedure is less time-consuming, larger areas can be screened, two parallel countings can be performed in one set of sections and there is no need for an exact knowledge about the diameter of the measured particle.

Interspecies comparisons of lung responses to inhaled particles and gases

Two important challenges for inhalation toxicologists involve the elucidation of mechanisms of lung toxicity caused by inhalation of chemicals or particulate materials, as well as the extrapolation of animal data to humans. Because risk estimates of toxicity generally are dependent upon experimental data for which a variety of species are utilized, a fundamental knowledge of species similarities and differences in lung anatomy, physiology, biochemistry, cell biology, and corresponding disease processes is essential. In the present review, the known mechanisms of particle deposition and clearance among various species have been highlighted and related to structure/function relationships and pathogenetic responses to some selected inhaled toxicants. In the aggregate, there is remarkable homogeneity in form and function among the species. Morphologic aspects of the respiratory tract and lung defense mechanisms are qualitatively similar among species. On the other hand, quantitative differences between humans and experimental animals are known to exist with respect to deposition and mucociliary clearance of inhaled particulates, and these factors are likely to influence the dose that is delivered to specific target sites in the lung. It is interesting to consider that pathologic cellular events following asbestos, ozone, and nitrogen dioxide exposure are likely to occur at similar sites in humans, nonhuman primates, and rodents. In this respect, it has been demonstrated that the early lesions of asbestos-induced lung disease in both rats and humans are initiated at similar anatomical sites, i.e., the junctions of terminal airways and alveolar regions. PMs and complement-mediated mechanisms have been implicated in the development of asbestosis in rats; however, it remains to be determined whether complement activation plays an important role in human asbestosis, although pulmonary and interstitial macrophages clearly are associated with the fibrogenic process associated with this restrictive lung disease. The toxic pulmonary effects following ozone exposure have been well studied in rodents and nonhuman primates. It has been established that distal airway and alveolar epithelial cells are principal targets of oxidant pollutants, and this is well supported by dosimetry considerations, morphologic observations, and morphometric analyses. Chronic ozone exposure in rats and monkeys causes epithelial injury at the level of the terminal bronchiole and proximal alveolar regions of the lung.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural study of the alveolar-capillary membrane and the tubular endoplasmic reticulum in alveolar type I cells of the caprine lung

The ultrastructural features of alveolar type I cells of the goat lung were studied by using vascular perfusion and direct airway instillation of fixatives. The morphological features of smooth endoplasmic reticulum (SER) were characterized by measuring the diameter of individual SER tubules which conformed in size and appearance to the tubular endoplasmic reticulum (TER) already described in various types of epithelium. The TER appeared as large tubular aggregates in a palisade arrangement; these aggregates ramified into various areas of the extended cytoplasm of alveolar type I cells. The TER also existed as a mixture of short cisternae and vesicles, and glycogen alpha particles were present in the non-perikaryonic portion of the cell. The different forms of TER had varying relationships to the plasmalemma. The interchangable configurations seen in the structure of TER indicated the functional modalities of the cells and were comparable to similar structural modifications in electrolyte-secreting cells. The role of TER, microtubules, and large populations of endocytic vesicles in the alveolar type I cells in the goat lung is examined in the context of physiological eructation of rumenal gases and the absorption of electrolyte-rich fluids which escape into the lung at each eructation in ruminants.

Age-related changes in vasoactive intestinal polypeptide levels and distribution in the rat lung

Vasoactive intestinal polypeptide (VIP) levels and distribution were studied in the lung of young-adult (3-month-old) and aged (28-month-old) male Wistar rats by radioimmunoassay and immunofluorescence. VIP concentrations were reduced approximately by 60% as the animal ages. The density of VIP-immunoreactive nerve fibres was remarkably reduced within bronchial smooth muscle and bronchial glands. Moreover, the number of VIP-immunoreactive nerve cell bodies located in intraparenchymal ganglia was decreased in old rats. The density of VIP-containing perivascular plexuses was slightly reduced in senescence. The present data are indicative that VIP neuronal system is impaired in the lung of old rats. In view of the significant age-dependent loss of VIP-immunoreactive nerve fibres that supply the bronchial tree and bronchial glands it cannot be excluded that the relaxant action exerted by peptide on airway smooth muscle and the control of bronchial secretion exerted by VIP are impaired in old age.

Age-related morphometric differences in responses of rat lungs to ozone

The influence of age on morphologic changes in lungs of rats exposed to ozone was studied in female Sprague-Dawley rats, aged 60 and 444 days. Rats of both age groups were exposed continuously for 72 hr to either 0.35 or 0.80 ppm ozone, or to filtered air. Tissues were evaluated using light microscopic morphometry and scanning electron microscopy. The lungs from ozone-exposed 60-day-old rats had larger volume fractions of centriacinar lesions than lungs from exposed 444-day-old rats. Within each age group there was an observed dose response, with rats exposed to 0.80 ppm ozone having larger volume fractions of lesions than those exposed to 0.35 ppm. Only the 444-day-old rats lost body weight during the exposure period. They also had smaller fixed lung volumes than same-aged controls. All 60-day-old rats gained weight during the exposure period, although rats exposed to 0.80 ppm ozone gained less than filtered air controls. Lesions observed in both age groups of female rats were qualitatively similar to those previously described in young adult male rats. We conclude that there are age-related differences in the morphometric responses of rats to ozone exposure. Younger rats had larger proportions of centriacinar lesions and macrophages while older rats had greater body weight and lung volume changes.

Effects of ozone on lung and somatic growth. Pair fed rats after ozone exposure and recovery periods

Minor differences in lung growth and development during childhood have been considered as a potential cause of rapid decline in pulmonary function in adulthood. Inhalation of ozone commonly causes changes in both body weight and lung volumes, which complicates interpretation of any changes in lung growth. The effects of ozone on lung growth were studied in rats which were pair fed. This technique permitted comparison of ozone-exposed and filtered-air control rats of the same body weight and body size as well as age and sex. Exposure was to filtered air or to 0.64 or 0.96 ppm ozone (UV standard) 8 h/night for 42 nights. A second control group was fed ad libitum and exposed to only filtered air. Half the rats were studied at the end of the 42-night exposures, the rest after a 42-day post-exposure period during which all rats were fed ab libitum and breathed filtered air. Rats examined at the end of the exposure period had larger saline and fixed lung volumes. These larger lungs had greater volumes of parenchyma, alveoli and respiratory bronchioles. Some of these changes persisted throughout a 42-day post-exposure period. Ozone inhalation by young rats alters lung growth and development in ways likely to be detrimental and those changes persist after ozone inhalation stops.

Asbestos-induced changes in rat lung parenchyma

Fischer 344 rats have been exposed to UICC crocidolite by whole-body inhalation procedures for periods of 1 d to 12 mo. Material was obtained from the same location in the left lung, and the numbers of cells in the parenchyma were identified and determined by transmission electron microscopy. An immediate increase (1 d of exposure) was evident in the number of type II cells, suggesting a direct action of the dust on these cells. The number of interstitial and alveolar macrophages showed a significant increase after 3 mo of exposure. The number of alveolar macrophages containing dust particles after a 1-d exposure was 49%, and the corresponding value after 12 mo of exposure was 92%. The longer periods of exposure were associated with an increase in the number of particles per macrophage. Polymorphs appeared in the interstitium at airway bifurcations, prior to their appearance in the alveolar space. These bifurcations were also the initial sites where evidence of cell damage and collagen deposition was seen. In this experiment crocidolite appears to be weakly fibrogenic, and other factors may be needed to produce the marked lesions seen in human asbestosis.

Compartmental origin of pulmonary macrophages harvested from mechanically disrupted lung tissue

Alveolar macrophages (AM) have been extensively studied, but whether these lavageable cells are representative of the lung's interstitial macrophage population is unknown. Previous investigators have compared AM with macrophages obtained from mechanically disrupted whole lung tissue and have found both populations to be morphologically and functionally similar. In such studies, neither the anatomical origin of the macrophages harvested from lung tissue postlavage nor the quantitative removal of AM by bronchoalveolar lavage (BAL) was demonstrated. Accordingly, the extent to which unlavaged AM contributed to the macrophage population obtained from mechanically disrupted lung tissue remains obscure. The present study was undertaken to determine whether macrophages harvested by mechanical disruption of lung tissue following exhaustive BAL are in fact primarily of interstitial origin. We addressed this problem by labeling rat AM with opsonized sheep red blood cells (SRBC-IgG) in situ, exhaustively lavaging the lungs to remove AM, and then mincing the residual lung tissue to liberate unlavaged macrophages for subsequent in vitro analyses. We recovered 24.5 +/- 1.3 X 10(6) AM with 18 lavages, 79.5 +/- 2.5% of which had phagocytized SRBC-IgG. Mincing the lavaged tissue resulted in the further release of 2.7 +/- 0.4 X 10(6) viable cells, approximately 85% of which morphologically appeared to be macrophages. The percentage of these cells that were prelabeled with SRBC-IgG and the numerical distribution of the SRBC-IgG among them were virtually identical to those among AM. The percentage of SRBC-IgG-containing macrophages was increased only slightly (11.4 +/- 1.9%) by further incubating macrophages harvested from minced lung with the SRBC-IgG in vitro, and most of this increase could be accounted for by unlavaged AM that did not phagocytize the test particles in situ. Moreover, multiparameter flow cytometric analyses of macrophages obtained by BAL and from minced lung tissue demonstrated that these populations were identical in terms of size, light scatter properties, and laser-excited blue and green-yellow autofluorescence characteristics. We conclude that (1) exhaustive lavage fails to retrieve a significant number of AM, and (2) macrophages obtained by mechanically disrupting lung tissue are derived primarily from the alveolar space compartment and not the interstitial compartment, as some investigators contend.

Deposition and phagocytosis of inhaled particles in the gas exchange region of the duck, Anas platyrhynchos

Little is known about the fate of inhaled aerosol particles in birds; even the anatomical location of phagocytic cells within the lungs has yet to be clearly demonstrated. We exposed 2 anesthetized, spontaneously breathing ducks to a non-toxic iron oxide aerosol (aerodynamic mass mean diameter = 0.18 micron; 460 mg/m3) for 1.75 h and 2 awake, resting ducks to less concentrated aerosol (38 mg/m3) for 6 h on two consecutive days. All 4 ducks were sacrificed 24 h after the end of the last exposure. Their lungs, as well as the lungs from a control duck not exposed to the aerosol, were fixed in situ by insufflation of osmium tetroxide vapor or by intravascular perfusion. Then samples of the gas exchange region were examined with a transmission electron microscope. We found iron oxide particles: trapped within the trilaminar substance that is unique to avian lungs and coats the atria and infundibula; within epithelial cells of the atria and initial portions of the infundibula; and within interstitial macrophages. Only occasionally, small amounts of particles were found in the air capillaries. We conclude that both epithelial cells and interstitial macrophages can phagocytize particles in avian lungs, and that there is some convective transport of aerosol to the atria and the initial portions of the infundibula.

Effects of subchronic inhalation of low concentrations of nitrogen dioxide. I. The proximal alveolar region of juvenile and adult rats

Inhalation of nitrogen dioxide (NO2) produces injury to the epithelium of terminal airways and the alveoli proximal to the airways. Techniques were devised to isolate alveolar tissue from this region for morphometric studies to define the extent of alveolar septal injury caused by NO2. One-day-old and six-week-old rats were exposed to either room air or 0.5 ppm NO2 for 23 hr per day 7 days per week for 6 weeks. An additional group of 6-week-old rats were exposed to 2.0 ppm NO2 for the same duration. Two daily hour spikes to three times the background concentrations (0.5 to 1.5 ppm and 2.0 to 6.0 ppm) were applied Monday through Friday. At the end of the exposure, rat lungs were fixed by intratracheally infusing buffered 2% glutaraldehyde. Pieces of lung tissue were embedded in large plastic blocks which were softened with heat and thin (0.3 mm) sliced. Terminal bronchioles and their corresponding proximal alveolar regions were identified from the thin plastic slices, removed, and glued to cylindrical EM blocks for thin sectioning. Morphometric analysis revealed that epithelial injury occurred in all exposed animals. The juvenile rats which had been exposed to 0.5 ppm NO2 since 1 day of age exhibited changes in the characteristics of type II epithelial cells. These cells spread to cover more alveolar surface and became thinner. Adult animals exposed to 0.5 and 2.0 ppm NO2 showed changes in alveolar macrophages and in the alveolar interstitium in addition to changes in the epithelium. Animals exposed to 0.5 ppm NO2 showed spreading and hypertrophy of type II epithelial cells. Those animals exposed to the higher concentration of NO2 had similar changes in type II epithelial cells and in addition showed an increase in type I cell number. The type I epithelial cells were smaller and covered less alveolar surface area than normal type I cells, suggesting a regenerating population of type I cells. These results suggest that prolonged exposure to low concentrations of NO2 can cause injury to the alveolar epithelium indicated initially by spreading and hypertrophy of type II cells followed by differentiation into type I cells to compensate and repair the injury. Adult rats were as sensitive or more sensitive to NO2 injury than were juvenile rats.

Isolation of viable type II alveolar epithelial cells by flow cytometry

We developed a new method for isolating viable type II cells from fractionated and unfractionated lung cell suspensions by flow cytometry using acridine orange (AO). Fischer-344 rat lungs were dispersed into single-cell suspensions by a technique that yields a high number of cells (4-5 X 10(8) cells/lung, congruent to 85% viable), congruent to 11% of which are type II cells. Elutriated fractions from the lung cell preparation and parent, unfractionated cell suspensions were incubated with 1.0-0.02 micrograms/ml AO and analyzed by flow cytometry. Parameters analyzed included axial light loss (ALL) and red fluorescence (RF). Based on their unique RF, attributable to AO staining of type II cell lamellar bodies, and their ALL characteristics, type II pneumocytes were sorted from elutriated fractions to greater than 95% purity. Using the same approach, type II pneumocytes were sorted from unfractionated lung cell suspensions at greater than or equal to 85% purity. The viabilities of the type II alveolar epithelial cells isolated by this method range from 85% to 95%, and the ultrastructural features of the sorted cells were unaltered by AO labeling or sorting.

Protein synthesis in the growing rat lung

Developmental control of protein synthesis in the postnatal growth of the lung has not been systematically studied. In male Fischer 344 rats, lung growth continues linearly as a function of body weight (from 75 to 450 g body weight). To study total protein synthesis in lungs of growing rats, we used the technique of constant intravenous infusion of tritiated leucine, an essential amino acid. Lungs of sacrificed animals were used to determine the leucine incorporation rate into newly synthesized protein. The specific radioactivity of the leucine associated with tRNA extracted from the same lungs served as an absolute index of the precursor leucine pool used for lung protein synthesis. On the basis of these measurements, we were able to calculate the fractional synthesis rate (the proportion of total protein destroyed and replaced each day) of pulmonary proteins for each rat. Under the conditions of isotope infusion, leucyl-tRNA very rapidly equilibrates with free leucine of the plasma and of the extracellular space of the lung. Infusions lasting 30 minutes or less yielded linear rates of protein synthesis without evidence of contamination of lung proteins by newly labeled intravascular albumin. The fractional synthesis rate is considerably higher in juvenile animals (55% per day) than in adult rats (20% per day). After approximately 12 weeks of age, the fractional synthesis rate remains extremely constant in spite of continued slow growth of the lung. It is apparent from these data that in both young and adult rats the bulk of total protein synthesis is devoted to rapidly turning over proteins and that less than 4 percent of newly made protein is committed to tissue growth.

Is there a limit on in situ, genomic replication in Drosophila?

The number of genomic replications of four separate tissues was determined in Drosophila melanogaster by summing the total number of nuclei and the maximum amount of DNA per nucleus in each tissue. It was found that for a given tissue the total number of nuclei was generally inversely proportional to the maximum amount of DNA per nucleus. In addition the sum of the number of divisions giving rise to the nuclei and the number of DNA replications occurring in the nucleus in each tissue never exceeded 20.

Lung and pleural "free-cell responses" to the intrapulmonary deposition of particles in the rat

Deposition of a high lung burden of particulate carbon or latex in the mouse elicits a biphasic macrophagic response, with the early increase in the size of the population of the alveolar macrophages (AM) being mainly due to an influx of mononuclear phagocytes from the blood compartment and the later phase being due to the egression of interstitial macrophages (IM). In the present study, we investigated the lung's free-cell response in the rat to the intrapulmonary instillation of microspheres and determined the contributions of newly arrived blood monocytes to the macrophagic response over a 30-d period. As of 24 h after deposition, the lavageable population size increased approximately fivefold. Most of the increase in the free cell population was due to a recruitment of polymorphonucleated leukocytes (PMN), although the size of the AM population nearly doubled. Only about 13% of the AM on d 1 were positive for myeloperoxidase activity, suggesting that recruitment of mononuclear phagocytes from the blood compartment plays a limited role in the early expansion of the AM pool in the rat. As of 14 and 30 d after particle deposition, lavaged AM numbers continued to be elevated; the enlarged sizes of the AM populations at these times could be explained, in part, by a continuing influx of blood monocytes. In a parallel component of the study, we also investigated how the pleural cell population might be affected during the lung's free-cell response to the particulate burden. No acute influx of PMN into the pleural space (PS) accompanied the early free-cell response; the chemotactic factors initially involved in recruitment of the PMN into the lung apparently did not reach the PS in significant or biologically active concentrations, or they were inoperable in the pleural compartment. On the other hand, the numbers of macrophages in the PS were significantly elevated on d 1 and 14 after particle deposition in the lung. The macrophagic response in the PS subsided by d 30, but at this latter sacrifice time, pleural mast-cell and lymphocyte numbers were significantly increased and decreased, respectively. These results indicate that the deposition of particles into the lung can lead to numerical alterations in the cell types composing pleural cell populations.

Pulmonary macrophages: alveolar and interstitial populations

The sizes of the alveolar macrophage (AM) and interstitial macrophage (IM) populations in the lungs of adult Fischer-344 rats were determined during steady state. AM labeled with opsonized erythrocytes during an in situ phagocytic assay were lavaged from excised lungs. The lungs were then dispersed into single-cell suspensions with collagenase and mechanical agitation, and the remaining mononuclear phagocytes were identified following a second labeling step. The size of the AM population was 1.3 X 10(7) cells, or approximately equal to 3% of the total lung cell population. The AM were negative for cytoplasmic myeloperoxidase granules. The size of the IM population was 8 X 10(6) cells, or approximately equal to 2% of the total lung cell population. IM were also negative for myeloperoxidase and, like AM, demonstrated marked Fc gamma R-mediated phagocytic activity. The high cell yields (approximately equal to 4 X 10(8) cells/lung; viability, greater than 85%) and the percentages of type II cells (11%) and ciliated epithelial cells (less than 0.5%) indicated the enzymatic dispersion method resulted in a highly efficient and representative sampling of the lung parenchyma. The collagenase method used in this study to disperse the lung cells into single-cell suspensions, in conjunction with additional cell separation techniques, may be of potential use for isolating enriched populations of IM, as well as other lung cell types, for in vitro study.

Application of morphometric methods to study diffuse and focal injury in the lung caused by toxic agents

Morphometric techniques are now being widely applied to a variety of toxicologic problems in order to obtain reproducible and quantitative data about changes in lung structure caused by environmental pollutants. Many environmental pollutants cause lung injury which is concentrated in specific regions of the lung, such as, in small airways and in the proximal portions of alveolar ducts. Morphometric techniques to obtain unbiased estimates of tissue changes occurring in these specific regions are reviewed and contrasted to well-established techniques for morphometric analysis of the distal alveolar regions of the lung. Specific applications of morphometric studies in different toxicologic problems are illustrated and include quantification of the changes in lung tissue and in lung cellular population pattern in response to exposure of small animals to hyperoxic atmospheres and to ozone. Pulmonary oxygen toxicity is an example of a diffuse lesion throughout the distal portion of the acinus whereas ozone exposure is an example of an environmental pollutant causing a greater degree of lung injury in the proximal alveolar region and in the small airways.

Cytokinetic and morphological changes in the lungs and lung-associated lymph nodes of rats after inhalation of fly ash

Fischer-344 rats (male and female) were exposed to 36 mg/m3 of fluidized bed coal combustion fly ash or sham-exposed for 7 hr/day, 5 days/week for 4 weeks, and sacrificed after 2 or 4 weeks of exposure and at 2, 22, and 42 weeks after the end of exposure. Animals were injected with tritiated thymidine 2 hr before sacrifice and autoradiographs prepared from 1-micron sections of lung and lymph node tissue embedded in glycol methacrylate plastic. Differences in labeling indices of pulmonary epithelial cells, alveolar macrophages, airway epithelial cells, and cells of the lung-associated lymph nodes between the exposed and control animals were maximal after 2 and 4 weeks of exposure. Labeling indices for lung epithelial cells were about the same in control and exposed animals at 2, 22, and 42 weeks after the end of exposure. However, these values were elevated relative to earlier control levels. In contrast, morphological changes in the fly ash-exposed animals were most prominent after the end of the exposure. These changes included thickening of the alveolar walls, clusters of particle-filled macrophages in the alveolar region, and perivascular inflammation. Additionally, there were small granulomas in the alveolar region at 42 weeks after the end of exposure. Granulomas were also formed in the lung-associated lymph nodes and and bronchus-associated lymphoid tissue. We conclude that the inhalation of fly ash alone had little detrimental effect upon the rat lung. However, the increases in proliferation indicate the potential for fly ash combined with a carcinogen to enhance the carcinogen's effect.

The effect of age on lung structure in male BALB/cNNia inbred mice

Morphometric examination using light, scanning electron, and transmission electron microscopy was performed on the lungs from 32 inbred male BALB/ cNNia mice between 38 days and 28 months of age. Between 38 days and 9 months of age the changes were primarily those of growth. Alveolar multiplication and total elastic-fiber length appeared complete by 38 days of age. The major increase in the number of interalveolar pores occurred by 68 days, but there was a significant further increase from 68 days to 9 months of age. At 9 months, approximately 10% of the alveolar wall was formed by pores. Alveolar ducts, the cylindrical core of air central to alveolar mouths, increased more in diameter than length. Between 9 and 28 months the changes were attributed to aging and were different from those reported in humans and other species. Lung volume, alveolar surface area, and total volume of alveolar wall increased with age; there was no change in mean linear intercept and volume proportion of alveolar and alveolar duct air. Total area of pores increased with age, but their number and area fraction of the alveolar wall did not change. No transmission electron microscopic changes were seen in the alveolar walls. We speculate that the morphometric differences between our animals and those studied in other reports may reflect the fact that our animals were specific-pathogen-free animals and kept under protected circumstances.

The ultrastructure of rat type II pneumocytes: effects of age, sex, and strain

The morphology of type II pneumocytes was investigated in Fischer 344 and Sprague-Dawley rats to determine whether differences in age, sex, and/or genetic strain influence type II cell ultrastructure. In Fischer 344 rats the type II pneumocytes increased in size with age due to an increase in the cytoplasmic component of the cell. Although mitochondrial volume density increased with age no significant changes in lamellar body volume density or lamellar body size were detected. No ultrastructural differences were observed between the type II cells in 6-week-old male and female Fischer 344 rats. However, substantial ultrastructural differences were found to exist among type II cells from the Fischer and Sprague-Dawley strains. Lamellar body volume density was 60% greater, P less than 0.001, in the Fischer rats due to the larger size of individual lamellar bodies. While mitochondrial volume density was also 22% greater in the Fischer rats, P less than 0.01, type II cell size was similar in the two strains. These results indicate that the ultrastructure of type II cells can differ within a genetically inbred strain as a function of age as well as between genetically different strains of the same species.