Ultrastructure and cell proliferative activities of karyomegalic alveolar epithelial cells in early pulmonary inflammatory lesions of Syrian golden hamsters induced by N-methyl-N-nitrosourethane

To clarify the biological behavior of karyomegalic alveolar epithelial cells induced by N-methyl-N-nitrosourethane (MNUR) and whether these cells progress to lung tumors, female Syrian golden hamsters, 6 weeks old, were given five subcutaneous injections of 0.6 mg/animal of MNUR at two week intervals and their lungs were examined at weeks 1, 4, 8 and 12 after the termination of treatment. At week 1, in severely affected areas where marked multifocal thickening of alveolar walls due to interstitial edema and cellular infiltration was observed, some regenerative alveolar epithelial cells had abundant eosinophilic cytoplasm and gigantic bizarre nuclei. The cells were confirmed ultrastructurally to be derived from alveolar type II cells. The number of these karyomegalic epithelial cells became significantly decreased thereafter, together with the reduction of inflammatory changes. On AgNOR staining, normal alveolar epithelial cells had 1.8 +/- 0.03 black dots within their nuclei while the karyomegalic epithelial cells had 4 black dots or more, from 1 week. The PCNA labeling index of the karyomegalic epithelial cells at week 1 was 14.6 +/- 2.4, and was significantly decreased from 4 week. This epithelial cell population also displayed a wider range of DNA contents (2.1-5.5C) than normal epithelial cells (1.6-2.3C). These results suggest that karyomegalic alveolar epithelial cells may be mutant cells which occur after initiation with MNUR, but the possibility that they can act as progenitors of alveolar epithelial cell tumors was considered to be extremely low.

Experimental acute alveolar injury in the dog. Morphologic--mechanical correlations

In 26 dogs, a single subcutaneous injection of N-nitroso-N-methylurethane produced acute lung injury characterized by tachypnea cyanosis, increased static lung recoil, and decreased lung compliance. During the first few days, light microscopic examination revealed widespread interstitial and perivascular edema and alveolar collapse. At the same time, electron microscopy showed the major alteration to be widespread necrosis of both types of alveolar epithelial cells without significant injury to the vascular endothelium. During recovery, new epithelial cells appeared which probably were derived from granular pneumocytes. These cells developed into mature granular pneumocytes through a phase in which they resembled fetal granular pneumocytes. The late stage was characterized by a picture resembling diffuse interstitial fibrosis but which was due to irreversible closure of clusters of small airspaces with no apparent increase in collagen. Elastic recoil of the lungs, as reflected by peak inspiratory airway pressure, increased during the acute phase and showed a return toward normal that was coincident with the appearance of mature granular pneumocytes in the regenerating epithelium. Lung compliance decreased during the acute phase and in most animals returned toward normal during the recovery phase. These observations strongly suggest that the alteration in lung mechanics is related to epithelial necrosis and that recovery is related to epithelial regeneration.

Pre- and postnatal toxicity induced in guinea pigs by N-nitrosomethylurea

Oral administration of N-nitrosomethylurea at maximally tolerated doses to guinea pigs on alternate days from days 34-58 of pregnancy induced prenatal toxicity, as evidenced by a high frequency of stillbirths and intrauterine growth retardation, and postnatal toxicity, as evidenced by stunting and progressive mortality. Similar administration of N-nitrosomethylurethane at maximally tolerated doses did not induce such toxic effects.

Chemical carcinogenesis and the pancreas

Although carcinoma of the pancreas is an increasingly prevalent form of human cancer, there has been relatively little experimental work on the etiology of this tumor until recently, probably because of the lack of adequate experimental models. However, at least two good experimental systems are now available. Several epidemiologic investigations suggest that chemical carcinogens may induce cancer of the pancreas in humans. If this is so, chemicals must reach the pancreas either through the blood supply or by reflux into the pancreatic duct from bile or duodenal contents. The route of exposure may vary according to the chemical and physical characteristics of different chemical carcinogens. Additional work is needed to determine the ability of different classes of chemicals to reach the pancreatic duct by these routes and the presence of enzymes required for activation of carcinogens in the pancreas. Levels of such enzymes as well as the response of cells of the pancreatic duct to carcinogens may be affected by the physiologic state of the pancreas or pathologic conditions within it. Research is needed to investigate these possibilities.