Binding of radioactivity after transplacental administration of tritiated N-nitrosodiethylamine to Syrian golden hamsters

Urethane and N-nitrosodiethylamine are mutagenic for the Syrian hamster fetus

Urethane and N-nitrosodiethylamine are soluble environmental carcinogens that initiate tumors transplacentally, but have a mixed history of effectiveness in mutagenesis assays in vitro or in vivo with adult rodents. To test for their transplacental mutagenicity, Syrian hamster fetuses at 12 days in gestation were exposed transplacentally to urethane or N-nitrosodiethylamine at 0.5 or 1.0 mM/kg. The fetal cells were isolated on day 13 of gestation and tested for diphtheria toxin resistance as a mutation marker. Both compounds were significantly mutagenic, at both doses, causing 6- to 20-fold increases in mutations compared with controls. Compared with N-nitrosodiethylamine, urethane was somewhat more effective as a mutagen with a more marked dose-response. These results are consistent with mutagenesis as part of the mechanism of transplacental carcinogenicity of urethane and N-nitrosodiethylamine.

The immunocytochemical detection of cytochrome P-450 monooxygenase in the lungs of fetal, neonatal, and adult hamsters

Antibodies against rabbit cytochrome P-450 reductase (reductase), cytochrome P-450 isozyme 2 (P-450 IIB), and cytochrome P-450 isozyme 5 (P-450 IVB) were used to detect homologous enzymes in the developing lung of the Syrian golden hamster. No immunocytochemical labeling was observed on gestational days 11, 12, and 13. On gestational day 14, light immunoperoxidase labeling for reductase and P-450 IIB was observed over cells lining the trachea and cranial portions of lobar bronchi. On gestational day 15, these enzymes were detected in conducting airways at all anatomic levels, and in the media of the pulmonary vein and its branches. Light labeling for P-450 IVB was first observed over cells lining the trachea and lobar bronchi on gestational day 15, but the smallest bronchioles and the media and endothelium of the pulmonary vein did not label for this enzyme until gestational day 16 (neonatal day 1). Type II pneumocytes and the pleural mesothelium first labeled for each of the three enzymes on neonatal day 1. Although the mesothelium no longer labeled for reductase or P-450 IIB in hamsters 3.5 wk old, the other labeling sites persisted in adult hamsters. Because cytochrome P-450 enzymes are associated with the endoplasmic reticulum, an ultrastructural examination of differentiating secretory cells was made to detect its appearance. At each conducting airway level, smooth endoplasmic reticulum was present in the cells 2 d before cytochrome P-450 enzymes could be detected immunocytochemically. The appearance of these enzymes paralleled the development of the hamster lung; they were first present in the trachea and lobar bronchi, then in the bronchioles, and finally in the alveoli.

Development of hamster tracheal epithelium: IV. Cell proliferation and cytodifferentiation in the neonate

The development of the tracheal epithelium was studied in neonatal hamsters beginning on the day of birth (day 1) and ending on day 8. Morphological changes were characterized and the proportions of cells (basal, secretory, ciliated) and mitotic indices were quantified along dorsal and ventral epithelial surfaces. Cellular proportions were stable throughout the week but the makeup of the dorsal and ventral epithelia was different. The ventral epithelium was composed of about 59% secretory cells, 39% basal cells, and 2% ciliated cells, whereas the dorsal epithelium was composed of about 52% secretory cells, 32% basal cells, and 16% ciliated cells. Mitotic indices were generally less than 1% and mitotic activity in secretory cells predominated proportionate to the ratios of secretory cells and basal cells in dorsal and ventral epithelia. During the first postnatal week changes occurred that were related to the maturation of basal cells and secretory cells. Glycogen was rapidly lost from both cell types during the first part of the week and the lateral cell membranes became increasingly complex. Apical microvilli had formed in the secretory cells by day 2 and hemidesmosomes were well developed in the basal cells. Rough and smooth endoplasmic reticulum membranes developed rapidly in the secretory cells, and mucous granules were abundant in some cells on days 4-8, especially in the ventral epithelium between the cartilage rings. The study shows that shifts in the proportions of basal, secretory, and ciliated cells do not occur in dorsal or ventral tracheal epithelium during the first postnatal week but the basal cells and secretory cells undergo rapid cytodifferentiation and functional maturation at this time.