Ultrastructure of free nerve endings in respiratory and squamous epithelium on the rat nasal septum.

The distribution of nerve fibres in the mucosa of the nasal septum of the rat was investigated by means of transmission electron microscopy on transverse and tangential ultrathin sections. Near the basement membrane of respiratory and squamous epithelium, a rather dense network of unmyelinated nerve fibres occurs. Some fibres in the respiratory epithelium ascend between the epithelial cells to reach up to the tight junctions. These fibres appeared in transverse sections to end as hooks or boutons, sometimes with branches. These shapes resemble the free nerve endings that are considered to act as nociceptors. The small intraepithelial fibres, with diameters of about 0.5-1 microns, contain both dense granules and clear vesicles comparable to synaptic vesicles. Substance P was found in dense granules in basal fibres; vasoactive intestinal peptide was absent throughout the epithelium. Acetylcholinesterase activity was observed closely associated with the basal fibres; the apical fibres showed little if any activity. Membrane specializations pointing to an efferent function as well as structures usually associated with mechanoreceptive functions were lacking in both respiratory and squamous epithelium.

The role of nasopharyngeal lymphoid tissue.

Nasal-associated lymphoid tissue (NALT), which comprises paired lymphoid organs in the nasopharynx of rodents, is the principal mucosal lymphoid tissue of the respiratory tract. As described in this review, NALT bears certain similarities to the Peyer's patches of the intestine but the two differ remarkably in morphology, lymphoid migration patterns and the binding properties of their high endothelial venules (HEV).

Characterization of adenocarcinomas of the dorsolateral prostate induced in Wistar rats by N-methyl-N-nitrosourea, 7,12-dimethylbenz(a)anthracene, and 3,2'-dimethyl-4-aminobiphenyl, following sequential treatment with cyproterone acetate and testosterone propionate.

Carcinomas of the rat prostate induced by a single injection of N-methyl-N-nitrosourea, 7,12-dimethylbenz(a)anthracene, and 3,2'-dimethyl-4-aminobiphenyl, after sequential treatment with cyproterone acetate and testosterone propionate, were evaluated as potential animal models for prostatic cancer. All ten carcinomas examined were located in the dorsolateral prostate region and did not involve the distal parts of the seminal vesicles and coagulating glands. The incidence of urinary obstruction leading to the animals' death was 6 of 10 rats, and metastases in the lung, abdominal lymph nodes, and/or liver also occurred in 6 of 10 rats. The tumors were invasive adenocarcinomas, showing frequent perineural invasion and a variable degree of differentiation. There were ultrastructural similarities with human prostatic carcinomas, such as intracellular lumina. Plasma acid phosphatase was increased. Enzyme histochemical analysis revealed similarities with the Dunning R3327H and -HI prostatic carcinomas but was not helpful in determining the site of origin of the tumors. The gross and microscopic appearance of the tumors and the observation of preneoplastic lesions exclusively located in the dorsolateral prostate suggest this lobe as site of origin of the carcinomas. Preneoplastic lesions (n = 9) included atypical hyperplasias (n = 5) and lesions with all histological characteristics of carcinoma except for local invasion and metastases, which were classified as carcinoma in situ (n = 4). Although androgen sensitivity could not be assessed, the observed characteristics of the tumors [their long latency time (46-80 weeks), the presence of preneoplastic lesions, and the short duration of the treatment, leaving the animals intact] all indicate that the present approach is a valid animal model for the study of prostatic carcinogenesis.

Nasal lymphoid tissue in the rat.

The structure and organization of paired lymphoid tissue in the nasal mucosa, situated in the transitional zone on both sides of the septal opening of the pharyngeal duct, of conventionally-housed rats was examined by light microscopy and scanning and transmission electron microscopy. Each lymphoid structure consisted of follicles containing T- and B-cell areas, and was covered with specialized epithelium. This epithelium consisted of cuboidal ciliated cells with oval nuclei parallel to the basal lamina. Goblet cells were sparse. Occasionally, islands of microvilli-bearing cells (so called membraneous or M cells) covered the lymphoid structures. M Cells were also found as single cells among the ciliated cells. The morphological characteristics and the particular localization justify the conclusion that the nasal lymphoid tissue described belongs to the mucosa-associated lymphoid tissue. It is therefore suggested that this nasal structure be designated nasal lymphoid tissue.

Cytotoxic and adaptive effects in rat nasal epithelium after 3-day and 13-week exposure to low concentrations of formaldehyde vapour.

To study in detail possible effects of low concentrations of formaldehyde on the nasal epithelium, Wistar rats were exposed to 0, 0.3, 1 and 3 ppm formaldehyde vapour for 6 h/day, 5 days/week during 3 days or 13 weeks, using in vivo [3H]thymidine labeling for cell proliferation studies, and light and electron microscopy for detecting morphological effects. Compound related histopathological nasal changes varying from epithelial disarrangement to epithelial hyperplasia and squamous metaplasia were found in the 3 ppm group, and were restricted to a small area of the anterior part of the nose which is normally covered with respiratory epithelium. These changes were confirmed by electron microscopy and were not observed in the other groups. Increased cell turnover in the same anterior location confirmed high mitotic activity in the 3 ppm group after 3 days and 13 weeks of exposure. At a slightly more posterior level in the nose a transient response in cell turnover was observed. After 3 days of exposure a nearly log-linear relationship was found between cell turnover and exposure concentration reaching a 10-fold increase in the 3 ppm group, and suggesting challenge of the mucociliary and/or regenerative defence systems not only at 3 ppm but also at 0.3 and 1 ppm. After 13 weeks of exposure mean turnover rates in all exposed groups were markedly lower than after 3 days, and the mean rates of the formaldehyde-exposed groups tended to be below that of the controls. The variation in turnover rate after 13 weeks had increased in a concentration related way, suggesting individual variation in adaptation. The most likely adaptive mechanism at this more posterior level of the nose seemed to be the mucociliary defence apparatus.

Influence of retinoids on the mutagenicity of cigarette-smoke condensate in Salmonella typhimurium TA98.

The effects of 3 different retinoids (all-trans-retinol, all-trans-retinoic acid, and all-trans-retinyl acetate) on the mutagenic activity of cigarette-smoke condensate were investigated in Salmonella typhimurium TA98. Neither an enhancing nor an inhibitory effect of the retinoids on the mutagnicity of cigarette-smoke condensate was observed.

Pulmonary response of hamsters to fibrous glass. Clearance and morphology after a single intratracheal instillation.

In a one-year serial sacrifice study 10 mg glass fibres (length, 95% alpha 20 microns, 89% alpha 12 microns, 58% alpha 5 microns and 25% alpha 2 microns; diameter, 88% alpha 1.0 micron, 60% alpha 0.5 micron and 31% alpha 0.25 micron) suspended in 0.2 ml saline solution were administered to Syrian golden hamsters by a single intratracheal instillation to determine the clearance of the glass fibres from the lungs and to examine their effects on the lungs using light and electron microscopy. The clearance was rather efficient with a half-time of about 3 months. Coating and corrosion of glass fibres were sporadic findings. A violent focal acute pneumonitis was evoked by the glass fibres and was followed by excessive accumulations of alveolar macrophages often loaded with glass fibres. Thereafter, "silicotic granulomas" developed which were seen as clusters of tightly packed iron-positive macrophages containing glass fibres. These granulomas were surrounded by a layer of alveolar epithelium, and were by the end of the study the predominant lesion in otherwise normal lungs.

Pulmonary response of hamsters to fibrous glass: chronic effects of repeated intratracheal instillation with or without benzo[a]pyrene.

Syrian golden hamsters were given intratracheal instillations of glass fibres with or without benzo[a]pyrene suspended in saline, once a fortnight for 52 weeks. The experiment was terminated at week 85. 'Silicotic granulomas' consisting of tightly packed, iron-positive macrophages filled with glass fibres and surrounded by a layer of alveolar epithelial cells were the predominant pulmonary lesion. No mesotheliomas or other tumours of the respiratory tract were observed in hamsters treated with glass fibres alone. There was no indication that glass fibres enhanced the development of respiratory tract tumours induced by benzo[a]pyrene. In hamsters similarly exposed to crocidolite fibres with or without benzo[a]pyrene no mesotheliomas or other respiratory tract tumours were observed either. An explanation for the absence of pulmonary tumours might be that repeated administration of fibres over a period of 52 weeks entails an acute pulmonary reaction after each administration with the implication that the fibres cannot settle down well enough to be able to induce tumours. Another possible explanation is the relatively short duration of the experimental period.

On the mechanism of dialkyltin-induced thymus involution.

In relation to the thymolytic activity of dialkyltin compounds, the effects of di-n-butyltin (DBTC) and di-n-octyltin dichloride (DOTC) on the ultrastructure of the rat thymus, the proliferation of bone marrow stem cells and their interference with growth hormone production are analyzed. Ultrastructurally, depletion of small lymphocytes in the thymic cortex, without signs of lymphocyte destruction or macrophage activation, was the most prominent feature of DOTC treatment. The thymus cortex was maximally depleted 96 h after a single i.p. injection of 1 mg DOTC/kg body weight. 120 h after DOTC treatment a repopulation of the cortex with small lymphocytes was noted together with the presence of many pale large nuclei of large lymphocytes, suggestive of active blast transformation. These thymus effects are probably not caused by a diminished input of bone marrow stem cells into the thymus, since neither the spontaneous blastogenesis nor the colony formation of bone marrow cells isolated from DBTC-treated animals were affected. An indirect mechanism of thymus involution induced by interference with the hormonal system is also very unlikely. A stress-related increase of glucocorticosteroids by dialkyltins has already been excluded (Seinen and Willems, 1976). An interference of dialkyltins with growth hormone production, as indicated in this study, did not occur. Application of growth hormone in amounts that reversed the hypophysectomy-induced thymus atrophy did not modify the thymus involution induced by DOTC treatment of rats. However, an interference with the production of thymic humoral factors cannot be excluded yet, although it is not supported by morphological changes in thymic reticular cells. Only an increased vacuolization of reticular epithelial cells is seen when the thymus is markedly involuted, but this is considered to be a consequence rather than a cause of thymus atrophy. Most probably the dialkyltin-induced thymus involution is caused by an antiproliferative activity, which is strongly supported by an inhibition of thymidine incorporation of thymocytes isolated from DBTC-treated rats.

Effects of feeding stannous chloride on different parts of the gastrointestinal tract of the rat.

The effects of feeding inorganic tin on the gastrointestinal tract were examined in rats. Three groups of male weanling Wistar rats were fed a diet to which 0, 250, or 500 ppm Sn2+ had been added as SnCl2. A fourth group was subjected to feed restriction by pair feeding with the 500-ppm group. Comparison of the data from the tin-fed groups with both the control and the reduced diet groups allowed discrimination between effects of reduced feed intake and Sn2+ effects. Independent of the reduced feed intake, Sn2+ affected hemoglobin concentration in the blood and several small intestine parameters. Total length of the small intestine, as well as absolute and relative weights, was increased. An increase was also observed in the migration of epithelial cells along the villus, as revealed by [3H]thymidine incorporation and autoradiography in rats fed 900 ppm Sn2+ for 4 weeks. Stereo-light microscopy and scanning electron microscopy revealed the formation of ridge-like villi due to Sn2+ feeding and a decreased number of villi per unit surface. These data suggest that an increase in cell turnover in the small intestine, due to Sn2+, was responsible for these changes.

Glass fibers and vapor phase components of cigarette smoke as cofactors in experimental respiratory tract carcinogenesis.

Syrian golden hamsters were given intratracheal instillations of glass fibers with or without BP suspended in saline, once a fortnight for 52 weeks; the experiment was terminated at week 85. No tumors of the respiratory tract were observed in hamsters treated with glass fibers alone. There was no indication that glass fibers enhanced the development of respiratory tract tumors induced by BP. In another study Syrian golden hamsters were exposed to fresh air or to a mixture of 4 major vapor phase components of cigarette smoke, viz. isoprene (800----700 ppm), methyl chloride (1000----900 ppm), methyl nitrite (200----190 ppm) and acetaldehyde (1400----1200 ppm) for a period of at most 23 months. Some of the animals were also given repeated intratracheal instillations of BP or norharman in saline. Laryngeal tumors were found in 7/31 male and 6/32 female hamsters exposed only to the vapor mixture, whereas no laryngeal tumors occurred in controls. The tumor response of the larynx most probably has to be ascribed entirely to the action of acetaldehyde. Simultaneous treatment with norharman or BP did not affect the tumor response of the larynx. Acetaldehyde may occur in the vapor phase of cigarette smoke at levels up to 2000 ppm. Chronic inhalation exposure of rats to acetaldehyde at levels of 0 (controls), 750, 1500 or 3000----1000 ppm resulted in a high incidence of nasal carcinomas, both squamous cell carcinomas of the respiratory epithelium and adenocarcinomas of the olfactory epithelium. It was discussed that acetaldehyde may significantly contribute to the induction of bronchogenic cancer by cigarette smoke in man. No evidence was obtained for a role of isoprene, methyl chloride or methyl nitrite in the induction of lung cancer by cigarette smoke.

Restoration of the hamster tracheal wall following injury by electrocoagulation.

The trachea of Syrian golden hamsters was injured by electrocoagulation. The lesions induced as well as the repair process were studied by light and scanning electron microscopy. The changes observed were considered to create the proper conditions for studying the significance of severe focal damage to the respiratory tract for the formation of tumors at the site of injury. Electrocoagulation caused deep crater-like injuries measuring 2 to 3 mm in diameter. Not only the mucosa, but also the submucosal tissues and cartilage rings were damaged. The repair process of the epithelium followed the pattern of covering the defect by squamous epithelium, hyperplasia, and stratified squamous metaplasia and finally differentiation into normal tracheal epithelium. The recovery of the epithelium was strikingly slow; even after a recovery period of 10 weeks regeneration of the epithelium was still incomplete in some animals. This relatively slow process of repair was ascribed to the depth and severity of the injuries involving a large mass of damaged tissues other than epithelium. Regeneration of the cartilage rings comprised three processes, viz removal of necrotic cartilage, growth of fibroblasts into the necrotic cartilage, and deposition of new cartilage along the necrotic rings.

Induction of lipid droplets in fibroblasts of the hamster lung by a diet high in vitamin A.

To investigate the effect of vitamin A on the occurrence of lipid droplets in alveolar fibroblasts, light and electron microscopic studies were carried out on the lungs of Syrian golden hamsters fed on diets with a low, normal, or high vitamin A content for a period of 17 weeks. The feeding of the high vitamin A diet resulted in a considerable increase in size and number of lipid droplets in alveolar fibroblasts. These droplets also occurred in fibroblasts of the visceral pleura, and in fibroblasts of connective tissue around bronchioli and larger blood vessels. Most of the lipid-laden fibroblasts could be recognized as myofibroblasts. The significance of the droplets for the deposition of interstitial materials or for the synthesis of prostaglandins is discussed.

Tissue damage and nutritional factors in experimental respiratory tract (Co-)carcinogenesis.

Cofactors involved in respiratory tract carcinogenesis were studied in Syrian golden hamsters or in rats using benzo(a)pyrene as the carcinogenic agent. These factors included severe tissue damage induced by electro-coagulation, glass fibers administered by intratracheal instillation, acetaldehyde as irritant vapor, food restriction, and nutrients such as vitamin A and saturated and unsaturated fats. In addition, the effects of a combined exposure to four different major gaseous cigarette smoke components--methyl nitrate, isoprene, methyl chloride and acetaldehyde--and to one solid cigarette smoke component--norharman--were examined in short- and long-term inhalation studies. An interesting finding was the carcinogenicity of acetaldehyde, of which the possible mechanism is briefly discussed. Another conspicuous observation was the substantial increase in number and size of lipid droplets in alveolar fibroblasts of hamsters fed a high vitamin A diet.

Staging, growth properties and metastatic behaviour of a transplantable murine T-cell lymphoma.

Cell surface markers, enzymatic patterns, proliferation characteristics and metastatic behaviour of the DSA/2 derived SL2 lymphoma were determined. SL2 cells are sensitive to a heterologous antiserum to murine T-cells and to allo-antisera for Thy 1.2 and TL 1.2.3. They show acid-phosphatase, betaglucuronidase, acid-alpha-naphthytesterase and non-specific esterase staining. The reactions for ATP-ase, and 5'nucleotidase were negative. The SL2 tumour cells can be transplanted in vivo, growing rapidly both as an ascites or a solid tumour, and can be grown in vitro as a suspension culture (doubling time about 18 hours). One hundred cells kill an animal after i.p. transplantation, while 1,000 cells kill an animal after s.c. transplantation. Histopathological examination combined with TEM shows that SL2 metastasizes rapidly, especially after i.p. injection. The metastasizing cells reach the blood vessels in the lung septa and extravascular positions in the liver.

Ultrastructural changes in the kidneys of rabbits treated with lead acetate.

Electron microscopical studies were carried out on the kidneys of rabbits given s.c. injections of 0 (control), 0.25 or 0.50 mg lead acetate/kg b.w. 3 times a week during 14 weeks. At the end of the experimental period the animals had lead blood levels of 60, 500 and 600 micrograms/l whole blood respectively. Treatment-related renal changes were found in the proximal tubules; they consisted of a dose-related increase in the amount of lysosomes in epithelial cells of the convoluted part, and of severely damaged cells and loss of brush border in the straight part. There was also an increase in lysosomal tubular inclusions, which are considered characteristic of lysosomes of the proximal tubular cells of the rabbit kidney. The significance of these findings for assessing the risk of occupational exposure to lead is briefly discussed.