Michael J. Evans

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.

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.

Effects of NO2 on the lungs of aging rats: I. Morphology

Abstract This research was undertaken to study the early effects of NO 2 on the lungs of aging rats. Male rats 1, 3, 11, 19, and 25 months old were exposed to NO 2 for up to 15 days. At various intervals during exposure, rats were sacrificed and studied by light and electron microscopy. Older rats had a higher mortality rate than young rats during the first day of exposure. Death in these rats was due to pulmonary edema. Morphologically, rats of all ages had injury to ciliated cells in the terminal bronchioles and Type 1 cells in the alveoli. In the older rats, the amount of tissue so damaged was much greater than that in young rats. After injury, rats of all ages began repair of the epithelium; however, the onset was slower in the older rats than in young rats. These two factors probably accounted for the larger accumulation of edema in alveoli of older rats, resulting in their increased mortality.

Alveolar type 1 cell response to exposure to 0.5 PPM O3 for short periods

Abstract Young male rats were exposed for 2 to 6hr to 0.5 ppm O 3 and sacrificed. Precise handling of the tissue permitted a critical evaluation of the alveolar lining epithelium immediately beyond the cuboidal epithelium of the terminal bronchiole. The Type 2 cells and endothelium in this region were very resistant to damage by O 3 , whereas Type 1 cells were severely injured. The first recognizable change was a mild swelling in the attenuated peripheral cytoplasm of the Type 1 cells. This process continued to increase in severity until it was quite pronounced. Mitochondria, both in the attenuated portions of the cell as well as those around the nucleus, became progressively swollen until they were scarcely recognizable. This was followed either by a sloughing away of the entire cell from the basement lamina or by rupture of the plasma membrane and disintegration of the cell, leaving the basement lamina devoid of an epithelial covering. The endothelium on the opposite side of the basement membrane usually remained normal in appearance.

Dust Exposure in the Chrysotile Asbestos Mines and Mills of Quebec

Past and present features of the Quebec chrysotile mining and milling environment and methods used to establish indices of exposure for epidemiological studies are described. Environmental dust concentrations used for calcuation of dust exposure indices were derived mainly from systematic midget-impinger samples taken since 1948, and from field surveys made in 1968, using impinger and a variety of other techniques. Though dust levels within the industry fluctuated widely, there was a steady fall from an average of approximately 75 million particles per cubic foot (MPCF) in 1948 to less than 10 MPCF in 1968. Considerable variation in the fiber content of airborne dust in this industry suggests that any safety standard should probably take account of fibrous and nonfibrous components.

Morphological basis of tolerance to ozone

The purpose of this research was to study Type 1 epithelial cells in the ozone (O3)-tolerant lung epithelium. Rats were made tolerant by exposure to 0.5 ppm O3 for 2 days and allowed to recover in air. Reexposure to a lethal concentration of O3 (6 ppm) at 3, 7, and 15 days of recovery revealed that tolerance was present at 3 days but almost absent at 7 and 15 days of recovery. Using Type 2 cell proliferation as a means of quantitating Type 1 cell injury, it was observed that when the preexposed rats were reexposed to 0.5 ppm at 3, 7, and 15 days, very little Type 1 cell injury occurred at 3 days. However, at 7 and 15 days the amount of Type 1 cell injury was the same as that associated with the original exposure. To determine whether there was any change in the alveolar epithelial cell populations between the periods of tolerance (3 days) and its decline (7 and 15 days), the percentage of tritiated thymidine [( 3H]TdR-labeled Type 1 and 2 cells at these times were determined. There was a significant decrease in [3H]TdR-labeled Type 1 and 2 cells between the third and fifteenth days of recovery as excess cells were sloughed off and the tissue returned to normal. Using electron microscopic morphometry, Type 1 and 2 cells were then studied during the decline of tolerance. No change was found in the morphology of Type 2 cells; however, the morphology of Type 1 cells revealed a 58% decrease in surface area and a 25% increase in the arithmetic mean thickness when tolerance was present at 3 days. As tolerance declined (7 and 15 days), Type 1 cell morphology returned to normal. It was concluded that tolerance exists when the surface area of a cell exposed to a particular concentration of ozone is small enough so that the existing antioxidant mechanism contained within that cell volume can protect it from damage.