Gustave Freeman

Transformation of alveolar Type 2 cells to Type 1 cells following exposure to NO2

Abstract This research was undertaken to study the fate of Type 2 cells after they have divided. To accomplish this, male rats were exposed to NO 2 to increase the number of dividing Type 2 cells. Dividing cells were labeled with 3 H-TdR and studied with autoradiographic techniques in the electron microscope for up to 14 days after labeling. The results show that initially most of the 3 H-TdR labeled cells were Type 2. However, by 2 days there was a decrease in frequency of labeled Type 2 cells and a large increase in labeled Type 1 cells. The new frequencies of labeled alveolar epithelial cells were stable from 2 through 14 days. This evidence supports the interpretation that Type 2 cells may transform into Type 1 cells. In addition, it was shown that under the conditions of this experiment: (1) the time for transformation was about 2 days, and (2) during this process an intermediate cell type was present.

Early response of lungs to low levels of nitrogen dioxide. Light and electron microscopy.

Significant changes in the lungs of rats exposed to nitrogen dioxide occur during the first 72 hours in animals exposed to 17 ppm. These changes appear in focal areas at the level of the terminal bronchiole: loss of cilia; thickening of tissue; injury to the epithelium lining the adveoli adjacent to the terminal bronchioles, when whole type 1 cells slough away leaving the basement membrane exposed to the air; between 24 and 48 hours of continuous exposure, these areas are repaired with a low cuboidal cell type that tolerates NO2 and thickens the air-blood barrier; and eventual formation of crystalloids and interruption of ciliogenesis. Changes at 2 ppm include loss of cilia, hypertrophy and focal hyperplasia in the epithelium of the terminal bronchiole, and “apparent” return to normal after 21 days of continuous exposure.

Cell Renewal in the Lungs of Rats Exposed to Low Levels of NO2

Effects of continuous exposure to low concentrations of NO2 on cell proliferation in bronchiolar and alveolar tissues were determined. Young rats were exposed continuously for as long as 360 days, removed at intervals, and killed. Dividing cells were labeled with tritiated thymidine. Animals exposed to 17 ppm NO2 showed an Increased labeling index in terminal bronchioles and alveoli after two to three days of exposure; the index returned to control levels by five days. Similar results were found in animals exposed to 2 ppm NO2, but the increase was not as great. This resulted in epithelial hyperplasia of terminal bronchioles and increased cellularity of alveoli associated with the distal ends of the terminal bronchioles. In peripheral alveoli, there was an increase in turnover rate of type 2 alveolar cells. All of these changes occurred within three days of continuous exposure. After this time, the areas of cellularity did not increase In size and the labeling indexes returned to normal for the remainder ...

Pathology of Pulmonary Disease From Exposure to Interdependent Ambient Gases (Nitrogen Dioxide and Ozone)

Nitrogen dioxide (NO2) and ozone (O3) are capable individually of inducing emphysema in rats exposed to high subacute concentrations. Mixtures of NO2 and O3 at levels reached in severe smog were used to estimate the degree of injury sustained by rats exposed to these ambient, interdependent, photochemically produced gases. Histologically, the major site of injury was at the level of the junction of the respiratory bronchiole and the alveolar duct, somewhat more peripherally than the lesion caused by NO2 alone. Ozone, the more toxic component, was largely responsible for the injury at the selected concentrations and for the characteristic fibroblastic activity in that region. The observations suggest that potential injury from ambient smog would result mainly from O3, whereas injury from tobacco smoke would be due largely to its relatively high concentration of NO2. The indications are that smoking and residing in smoggy areas would be additively injurious.

Cell renewal in the lungs of rats exposed to low levels of ozone

Abstract This research was undertaken to study the early effects of low levels of ozone on cell renewal in the lungs of rats. To accomplish this, male rats were exposed to ozone for up to 8 days. Dividing cells were labeled with tritiated thymidine ([3H]TdR) and studied with autoradiographic techniques in the light microscope. The results showed that all labeled cells increased and then decreased to near control levels within 4 days. Type 2 cells showed the largest change in labeling index. Since the labeling indexes decreased by the fourth day despite continuous exposure and no further injury occurred, it was assumed the tissue had become tolerant to that concentration of O3. To test the degree of tolerance, groups of animals adapted to O3 were exposed to higher concentrations of O3, and the labeling indexes of Type 2 cells were studied. These studies showed that tolerance to the initial concentration of O3 did not ensure total protection to rats against reexposure to higher concentrations of O3.

EMPHYSEMA AFTER LOW-LEVEL EXPOSURE TO NO2.

Rats were exposed to various levels of NO/sub 2/ for their life-span. At a concentration of 100 ppM they began to die within 24 h from acute pulmonary edema. At 50 ppM, 6 of 9 rats died within 48 to 68 days, 2 were removed to control environment. At 25 ppM, rats sacrificed after 40 days appeared normal in weight but some had histopathologic lung changes (e.g., hyperplasia, hypertrophy). Ten of 15 died within 121 to 180 days, 1 died of other causes in 7 days, 1 was allowed to recover, 3 were sacrificed. Low body weight was noted. At 12.5 ppM, 8 of 9 rats survived. One died with above pathology at 213 days. Body weights were 20% less than normal. Increased respiratory rate of 60 per min as opposed to 40 for control was noted. Emphysema occurred in terms of voluminous lungs but with no inflammation. Hyperplasia, accumulation of mucus and macrophages may obstruct terminal bronchioles.

Lesion of the Lung in Rats Continuously Exposed to Two Parts Per Million of Nitrogen Dioxide

Rats exposed continuously to 2 ppm ot nitrogen dioxide in air survived their ordinary lifetimes with persistent tachypnoea and usually died of nonpulmonary diseases. Resistance to airflow and dynamic compliance were not different from those in controls. Terminal and respiratory bronchiolar epithelium was affected mainly by a loss of exfoliative activity, reduced blebbing of cytoplasm into the airways, reduction in or loss of cilia, and the appearance of rod-shaped intracytoplasmic crystalloid inclusions. Morphologic evidence suggests that rats exposed to 2 ppm would have reduced cleansing function of the periphery of the lung. Pulmonary tissue was embedded in plastic and sections were cut at 1μ for light microscopy and thinner sections for electron microscopy.

Electron Microscopic Study of Cadmium Nephrotoxicity in the Rat

In rats given drinking water containing cadmium chloride, renal changes evidenced by electron microscopy were confined to the cells of proximal tubules, consisting of two distinct histologic features, increase of lysosomes and swelling of mitochondria. The size and number of lysosomes inereased in proportion to the amount of ingestion of cadmium. The usual elongated, rod-shaped mitochondria of the proximal tubular cells became oval or rounded and increased in volume. The cristae were vesicular, shortened, and marginal. There were some other changes, such as increase of microbodies, focal proliferation of the smooth endoplasmics reticulam, and appearance of intranuclear inclusions. It is considered that these alterations in the proximal tubular cells of cadmium-intoxicated rats indicate an activation of detoxifying process and impairment of energy metabolism.

Ultrastructural changes in the terminal bronchiole of the rat during continuous, low-level exposure to nitrogen dioxide.

Abstract The epithelial cells of the terminal bronchioles of rats continuously exposed to NO2 show several conspicuous ultrastructural changes. In this study tissue from animals exposed to 2 ppm for up to 2 years was compared with that from animals exposed to 17 ppm for up to 43 days. In addition, tissue from animals repeatedly exposed to 17 ppm NO2 with intervening recovery phases in clean air were compared with the tissue mentioned above. The ultrastructural changes observed were common to all groups of animals strongly suggesting a concentration-time response of the tissue to NO2. Among the changes reported are (1) loss of cilia, (2) failure of new cilia to develop although centriolar replication is not interrupted, (3) disorientation of basal bodies, (4) formation of intracytoplasmic ciliated vacuoles, and (5) formation of intracytoplasmic crystalloid inclusions.

Changes in Dogs’ Lungs After Long-Term Exposure to Ozone

Dogs were exposed to 1 to 3 ppm of ozone (O3) 8 to 24 hours daily for 18 months. Macrophages appeared and increased with “dosage.” Fibrous elements were deposited rarely at the lowest dosage but increased with the concentration of O3. Additional features were thickening of the terminal and respiratory bronchiolar walls at the higher concentrations and their infiltration by lymphocytes, plasma cells, and “fibroblasts” that formed peribronchiolar collars. Connective tissue obstructed alveolar openings into bronchioles and ducts and extended into alveolar walls. Thick bronchiolar walls reduced the caliber of small airways. Bronchiolar epithelial changes included an increase in the proportion of mucus-forming cells and squamous metaplasia of columnar and cuboidal cells with occasional islands of hyperplasia. Metabolic effects were reflected in ultrastructural alteration of preexisting, intracytoplasmic bodies. Together with nitrogen dioxide, O3 may contribute to pulmonary disease in a susceptible population.