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Deposition of inhaled particulates onto the respiratory mucosa is relatively great in that portion of the nasal cavity unprotected by ciliated, goblet, or keratinized superficial cells. The cytochrome P-450 system is an important enzyme system involved in the biotransformation of xenobiotics into metabolites that are more readily absorbed. To examine the transitional region caudal to the nasal vestibule, nasal tissues of hamster and rat were prepared for immunocytochemistry. Blocks of tissue representing four levels along the long axis of the nasal cavity were examined. Paraffin sections were processed through the avidin-biotin peroxidase procedure, with diaminobenzidine tetrahydrochloride as the chromagen. Enzyme localization was accomplished through the use of antibodies for three rabbit cytochrome P-450 isozymes; 2, 5, and 6 (subfamilies IIB, IVB, and IA, respectively); and for rabbit NADPH-cytochrome P-450 reductase. Enzyme distribution was similar in both hamster and rat nasal tissues except in cells of striated and intercalated ducts of nasal glands and in cells of the nasolacrimal duct where immunoreactivity was greater in the hamster. Immunoreactivity for reductase and isozyme 2 was intense in nonciliated cells lining the nonolfactory epithelium, in sustentacular cells of the olfactory epithelium, and in acinar cells of olfactory glands. Distribution of reaction products to isozyme 5 and 6 were similar to but not so intense as those of reductase and isozyme 2. Reaction products for reductase and isozyme 2 occurred generally in the same cellular and intracellular regions with the following exceptions: isozyme 2 was more concentrated in cells of striated ducts and of the nasolacrimal duct, and reductase was more abundant in intercalated ducts of nasal glands.(ABSTRACT TRUNCATED AT 250 WORDS)

The epithelium of the respiratory bronchiole in the adult rhesus monkey consists of two populations: a pseudostratified epithelium with basal, mucous goblet, and ciliated cells located near the pulmonary artery (PA); and a simple cuboidal epithelium composed only of nonciliated bronchiolar epithelial (or Clara) cells in areas away from the PA. This study describes the pattern of differentiation of these two epithelial populations, and their relationship to the PA and to the time of appearance of alveoli in the respiratory bronchiole of the rhesus monkey during the period of 90-125 days gestational age (DGA). These events were related to changes in the adjacent parenchyma. Dissected airways of infusion-fixed, critical-point-dried lungs were evaluated by scanning microscopy followed by light microscopy of the same airways. At 54% of gestation (90 DGA), the distal airway was lined by a mixture of ciliated and nonciliated cells. By 67% of gestation (110 DGA), the ciliated cells were confined to the epithelium over the PA. The underlying connective tissue initially was cellular containing few fibers but was fibrous by 76% of gestation (125 DGA). Alveolarization began near the most distal cartilage at 57% of gestation (95 DGA), the same period at which secondary septation occurred in the distal acinus. Thus, alveolarization occurred simultaneously in two centers: 1) the proximal centriacinar region in the vicinity of the most distal cartilage and 2) the distal lung parenchyma. The duration of centriacinar alveolarization was short, approximately 5 days.

To estimate the numbers and volumes of bronchiolar epithelial cells during lung maturation, we examined rabbits at three time points, 30 days gestation and 4 and 17 weeks postnatal age. Morphometric measures (mean caliper diameter, surface area, and volume) of nonciliated and ciliated bronchiolar cell nuclei, using computer modeling from serial sections, showed a significant decrease in nuclear size for both cell types and a significant increase in cell volume for the nonciliated bronchiolar cell during lung maturation. A shape coefficient (beta) proved to be the most efficient estimator of the number of cells per unit volume when it was used with estimates of the number of nuclei per unit area and the volumetric density of nuclei. Two-dimensional estimates of bronchiolar epithelial cell abundance (the number of nuclei per unit length or area) significantly underestimated the percentage of nonciliated bronchiolar cells as compared to three-dimensional estimates for rabbits 17 weeks of age. We have shown an inverse relationship between nonciliated and ciliated bronchiolar cell abundance during lung maturation. Nonciliated cells decreased while ciliated cells increased. We have confirmed that cytodifferentiation of the nonciliated bronchiolar cell occurs within the first 4 weeks of postnatal development. The volume of the nonciliated bronchiolar cell increased about twofold during development. Because of the concomitant decrease in nuclear volume, the cytoplasm of the cell showed an even greater increase in volume. Within the cytoplasm of the nonciliated bronchiolar cell, glycogen significantly decreased, and agranular endoplasmic reticulum (AER) and mitochondria significantly increased in volume during development. The biosynthesis of AER closely correlated with pharmacological studies of xenobiotic metabolism during rabbit lung maturation.

Of the eight categories of epithelial cells identified in pulmonary conducting airways, four are found in the trachea of adult primates: basal, mucous goblet, intermediate, and ciliated cells. While their ultrastructure is well characterized, little is understood about their origin or differentiation. This study describes the pattern of differentiation of the tracheal luminal epithelium in a species of nonhuman primate, the rhesus monkey, Macaca mulatta. Tracheas of 57 fetal and postnatal rhesus were fixed with glutaraldehyde/paraformaldehyde: ten at 29-54 days gestational age (GA), ten at 59-80 days GA (pseudoglandular stage), sixteen at 82-130 days GA (canalicular stage), ten at 141-168 days GA (saccular stage), eight at 1-134 days postnatal, and three adults (2 yr 11 months to 11 yr 11 months). Slices taken proximal to the carina were processed for electron microscopy by a selective embedding procedure. In the youngest fetuses, essentially one population of cells lined the tracheal epithelial surface. These cells were columnar in shape with a central nucleus, few organelles, and large amounts of cytoplasmic glycogen. At 46 days GA, ciliated cells were observed on the membranous side of the trachea. Some nonciliated cells had concentrations of organelles in the most apical portion of their cytoplasm. At 59 days GA, membrane-bound cored granules were intermixed with organelles in the apices of some glycogen-filled cells. They were observed first on the cartilaginous side. Between 59 and 100 days GA, a large number of cell forms which appeared to be transitional between ciliated, secretory, basal, and undifferentiated cells were present. These included ciliated cells with electron-lucent inclusions resembling mucous granules. Mucous secretory cells were more numerous and had more granules and less glycogen in older fetuses. By 105 days GA, few of the secretory cells had significant amounts of glycogen and the cytoplasm was condensed. Secretory granules were very abundant in some cells and minimal in others. The Golgi apparatus was prominent. In animals 120 days GA and older, small mucous granule cells and basal cells resembling these cells in adults were present. By 134 days postnatal age, the epithelium resembled that in adults. We conclude that most of the differentiation of tracheal epithelium in the rhesus monkey occurs prior to birth; the cells differentiate in the following sequences: ciliated, mucous goblet, small mucous granule, basal; and basal and small mucous granule cells do not play a role in ciliated and mucous cell formation in the fetus.

The nonciliated bronchiolar epithelial (Clara) cell of adult lung is commonly defined by two cellular components: abundant agranular endoplasmic reticulum (AER) and electron-dense ovoid secretory granules. These reflect the Clara cell's proposed functions as the source of bronchiolar surface secretions and the site of xenobiotic metabolism via the cytochrome P-450 monooxygenase system. Since previous studies have indicated that Clara cells may not attain a fully functional state until some weeks after birth, the present study was undertaken to characterize systematically the differentiation of this cell type during lung maturation. Lungs were fixed by airway infusion with glutaraldehyde/paraformaldehyde (550 mOsm, pH 7.4) from at least three male rabbits at each of the following ages: 24, 27, and 30 days fetal, and 0-1 day, 3-4 days, 1, 2, 3, 4, 5, 8, 12, 15, 17, and 25 weeks postnatal; and pieces were processed for transmission electron microscopy by a selective embedding procedure. Quantitation was performed on electron micrographs (at 15,750 X) of cell profiles, which included the base, apex, and nucleus. Volume fractions of constituents of a minimum of 30 cells per animal (8 weeks and younger) and 10 per animal in older groups, were estimated by point counting with a Weibel 168-point test grid. Cell and nuclear size were estimated with a computerized digitizer (Zeiss Videoplan). Nonciliated cells of prenatal animals had large amounts of cytoplasmic glycogen (over 60% of the cell cytoplasm), few mitochondria (less than 15%), little granular endoplasmic reticulum (GER) (20%), minimal AER (less than 5%), and no granules. Postnatal animals 2 weeks of age and younger were similar, except for the presence of secretory granules and slightly more abundant AER (5 to 20%). By 4 weeks postnatal age, nonciliated cells resembled that of older animals with abundant apical AER (over 40%), secretory granules, little glycogen (11%), and GER (10%). We concluded that (1) the Clara cell is immature at birth; (2) differentiation occurs primarily during weeks 3 and 4 of postnatal life; (3) vast amounts of cytoplasmic glycogen are characteristic of the undifferentiated cell; and (4) four cellular constituents, AER, glycogen, mitochondria, and GER, undergo significant shifts in abundance during differentiation. These shifts appear to be in the sequence expected of a cell type undergoing the initiation of biosynthesis of secretory products and biogenesis of agranular endoplasmic reticulum.

The purpose of the present study was to characterize ultrastructurally the nonolfactory nasal epithelium of a nonhuman primate, the bonnet monkey. Nasal cavities from eight subadult bonnet monkeys were processed for light microscopy, and scanning and transmission electron microscopy. Nonolfactory epithelium covered the majority of the nasal cavity and consisted of squamous (SE), transitional (TE), and respiratory epithelium (RE). Stratified SE covered septal and lateral walls of the nasal vestibule, while ciliated pseudostratified RE covered most of the remaining nasal cavity. Stratified, nonciliated TE was present between SE and RE in the anterior nasal cavity. This epithelium was distinct from the other epithelial populations in abundance and types of cells present. TE was composed of lumenal nonciliated cuboidal cells, goblet cells, small mucous granule (SMG) cells, and basal cells, while RE contained ciliated cells, goblet cells, SMG cells, basal cells, and cells with intracytoplasmic lumina lined by cilia and microvilli. TE and RE contained similar numbers of total epithelial cells and basal cells per millimeter of basal lamina. TE was composed of more SMG cells but fewer goblet cells compared to RE. We conclude that nonolfactory nasal epithelium in the bonnet monkey is complex with distinct regional epithelial populations which must be recognized before pathologic changes within this tissue can be assessed adequately.

Since there are major differences between the airway epithelium of man and that of common laboratory species, the tracheobronchial epithelium of the bonnet macaque was characterized to evaluate its usefulness as a model for study of human conducting airways. This study compared the light microscopic, scanning electron microscopic, and ultrastructural appearance of epithelium from the posterior membranous and anterior cartilaginous trachea and mainstem bronchus. Population densities, epithelial volumetric densities, and frequency distributions of cross-sectional areas of nuclei were determined for cell types present on electron micrographs. Four epithelial cell types were distinguished by ultrastructural criteria. Basal cells were 31% of the population and were similar to those described in other species. Ciliated cells were also similar to those of other species and composed 41% of the population; their nuclei were larger than those of other cell types. Mucous goblet cells had large numbers of secretory granules with electron-dense cores and a lucent periphery. They were only 8% of the population by nuclear count but composed 20% of the epithelial volume. The fourth cell type had multiple small vesicles containing small amounts of granular material and was termed a "small mucous granule cell." Small mucous granule cells (16% of the population) were present in greater numbers than mucous goblet cells but were a smaller proportion of the epithelial volume (8%). While population densities of cell types determined from transmission electron micrographs did not vary between sample sites, scanning electron microscopy demonstrated longitudinal streaks of secretory cells in the posterior trachea suggesting that regional differences in epithelial organization exist. We conclude that the macaque extrapulmonary airway epithelium differs from published descriptions of laboratory rodents in both cell types present and relative abundance of those cell types. Although detailed quantitative studies of human extrapulmonary airways are not available, the primate airways resemble those of man in both the types of cells present and the complexity of pseudostratification.