Bowman's Glands Research Articles

Toxicity of divinylbenzene-55 for B6C3F1 mice in a two-week inhalation study.

Divinylbenzene (DVB) is a crosslinking monomer used primarily for copolymerization with styrene to produce ion-exchange resins. The toxicity of inhaled DVB was investigated because of the potential for worker exposure and the structural similarity of DVB to styrene, a potential carcinogen. Male and female B6C3F1 mice were exposed to 0, 25, 50, or 75 ppm DVB for 6 hr/day, 5 days/week for up to 2 weeks. Six mice/sex/dose group were killed after 3, 5, and 10 exposures and six mice/sex in the 75 ppm group were killed 7 days after 10 exposures. The most severe effects occurred in the nasal cavity and liver, with less severe effects occurring in the kidneys. In the nasal cavity olfactory epithelium acute necrosis and inflammation were present at early time points followed by regeneration, architectural reorganization, and focal respiratory metaplasia by 7 days after the last exposure. Olfactory epithelial changes were concentration-dependent with extensive involvement at 75 ppm and peripheral sparing at 25 ppm. There was also necrosis and regeneration of olfactory-associated Bowman's glands as well as the lateral nasal (Steno's) glands. Hepatocellular centrilobular (CL) necrosis was observed only in the 75 ppm dose group and was similar to that caused by styrene. A time-dependent progression was observed, characterized by CL degeneration after 1 exposure, necrosis after 3 and 5 exposures, and chronic inflammation with CL karyomegaly after 10 exposures and 7 days after the 10th exposure. Hepatic GSH levels were decreased in a dose-dependent manner. In the kidneys, transient tubular damage was observed in some male mice exposed to 75 ppm, and appeared to be a response to DVB-induced tubular epithelial injury.

Mitogenic responses of rat nasal epithelium to hexamethylphosphoramide inhalation exposure

Hexamethylphosphoramide (HMPA) is a rat nasal carcinogen that induces squamous cell carcinomas in the anterior portions of the nasal cavity following chronic inhalation exposures as low as 50 ppb. These tumors may arise as a result of P-450-mediated release of formaldehyde (HCHO), a known rat nasal carcinogen. The goal of this research was to investigate early responses of the nasal epithelium to inhaled HMPA. Rats were exposed nose-only to approximately 3 ppm HMPA for 6 h, and killed 18, 48, 96 or 144 h post-exposure. In a separate study, rats were exposed nose-only for 6 h for 1, 2, 3, or 5 consecutive days and killed 18 or 96 h post-exposure. With both single and repeated doses of HMPA, there was no evidence of cytotoxicity in the anterior nose. Olfactory degeneration and necrosis of the dorsal meatus, Bowman's glands and tips of the ethmoid turbinates increased in severity with repeated exposures to HMPA. Cell proliferation was assessed in levels of nasal tissue that included regions of squamous, respiratory, transitional and olfactory epithelium. Regional induction of cell proliferation was measured by BrdU incorporation, and reported as the number of labeled cells/mm basement membrane. At 18 h after a single exposure, there was an increase in cell proliferation in squamous epithelium, which returned to control levels within 48 h. A transitory increase in cell proliferation was observed regions of respiratory and transitional epithelium, although the response of each tissue, in terms of magnitude and peak time of response post-exposure, also differed. Along the dorsal meatus in Level 9, olfactory labeling initially decreased, returned to control levels by 96 h, but again declined at 144 h post-exposure. In repeat dose studies, the squamous epithelium response was variable 18 h post-exposure. For respiratory and transitional epithelium, increased cell proliferation 18 h post-exposure was correlated with increased dose (exposure) of HMPA. Cell proliferation responses following two or more exposures returned to near control levels within 96 h post-exposure. In conclusion, HMPA induced cell proliferation, but not cytotoxicity, in the anterior nose at approximately 3 ppm. These data suggest that HMPA induces proliferative, perhaps mitogenic, responses in the nasal epithelium, and this response may facilitate the fixation of low level genetic damage induced by liberated HCHO.

Monoclonal antibody marker for olfactory sustentacular cell microvilli.

The olfactory epithelial sustentacular cells may support the survival and function of olfactory receptor neurons, but few reagents are available to mark and manipulate such cells. Novel nasal cell-specific monoclonal antibodies were generated using whole cultured rat olfactory mucosal cells as the antigenic stimuli. They were characterized by immunostaining at the light level in rat tissues and newborn rat olfactory cell cultures, and at the electron microscopic level in adult tissues using freeze-substitution, post-embedding staining. An IgMkappa monoclonal antibody designated 1F4 selectively labeled apical surfaces of the rat olfactory and respiratory epithelia in tissue sections and what appeared to be sustentacular cells in olfactory cell cultures. Using electron microscopy, 1F4 bound selectively to the microvilli of sustentacular cells and ductal cells of Bowman's glands in the olfactory epithelium, and to the microvilli and cilia of ciliated but not secretory cells in the respiratory epithelium. No staining was detected in olfactory receptor neurons, basal cells, or two types of microvilli-bearing cells that differed from sustentacular cells. A contrasting antibody, 2H4, bound to granules of secretory respiratory cells. Developmental expression of 1F4 binding began at E17 and increased at and after E18/E19. Bulbectomy did not alter 1F4 immunoreactivity. Cell culture studies found that the 1F4 epitope was external and insensitive to trypsin treatment, and that both 1F4 and 2H4 positive cells required contact with aggregated cells for survival up to fifteen days in vitro. The antibody 1F4 is a useful marker and potential manipulation reagent specific for sustentacular cells and their microvilli.

Differential distribution of mRNAs encoding phosphatidylinositol transfer proteins alpha and beta in the central nervous system of the rat.

The expression of the alpha and beta isoforms of phosphatidylinositol transfer protein (PI-TP alpha and PI-TP beta) in the adult rat brain was examined by in situ hybridization analysis with isoform-specific RNA probes. PI-TP alpha mRNA was detected in rather restricted regions of the brain whereas PI-TP beta mRNA was widely distributed in the brain. PI-TP alpha mRNA signals were remarkable in neocortex layers II/III and V/VI, Purkinje cell layer, deep cerebellar nuclei of the cerebellum, red nucleus and most part of brain stem. Low levels of PI-TP alpha transcript were present in CA3 of the hippocampus, ventral and dorsal thalamic nuclei, and motoneurons of spinal cord. No hybridization signals was obtained in the olfactory bulb, basal ganglia, amygdala, hypothalamus, and pituitary gland. In contrast, strong signals of PI-TP beta mRNA were detected in the dentate gyrus. The beta isoform mRNA was moderately expressed in olfactory bulb, layers II/III of the neocortex, striatum, CA1-CA4 regions of the hippocampus, medial habenula, cerebellum, amygdala, hypothalamus, spinal cord, and pituitary gland. Thalamus and brain stem contained relatively low, but significant levels of PI-TP beta transcript. The distinct distribution of PI-TP alpha and PI-TP beta mRNAs suggests different functional roles for each of the gene products in the mature nervous system.

Nasal and Pharyngeal Abnormalities Caused by the Mouse Goosecoid Gene Mutation

TheGoosecoid(gsc) gene is a homeobox-containing gene expressed first in the gastrula, and later during organogenesis in development. The gsc gene transcript is found in the first and second branchial arches, frontonasal mass in its late phase of expression. We have previously shown that targeted mutation of the mouse gsc gene leads to neonatal death and craniofacial defects. In this study, we performed histological studies on craniofacial phenotypes in order to elucidate the processes underlying the neonatal death of gsc mutant mice. We found that gsc mutant mice have aplastic nasal cavities and lack the Sinus Paranasalis. We also showed that secretory olfactory glands in the basal layers are aplastic. This is suggested to be essential defects for olfaction. gsc mutant mice also show several pharyngeal phenotypes, including defects in the pharyngeal muscles and the pharyngeal mucosa. It is therefore suggested that mutant mice develop lethal gastro-intestinal phenotypes caused by defects in breathing and sucking of milk as a consequence of these craniofacial disorders. These results should help elucidating the molecular genetic programs essential to the neonatal development of mammals.

Effects of dichlobenil on ultrastructural morphology and cell replication in the mouse olfactory mucosa.

The herbicide dichlobenil (2,6-dichlorobenzonitrile) is a tissue-specific inducing necrosis in the olfactory mucosa. Transmission electron microscopy showed vacuolations (1 hr) and necrosis (4 hr) in the Bowman's glands following intraperitoneal injection of dichlobenil (25 mg/kg) in C57B1 mice, whereas no lesions were noted in the olfactory neuroepithelium at these timepoints. Twenty-four hr following injection (25 mg/kg), most of the propria and the olfactory epithelium were severely damaged; the basal lamina, nerves, and blood vessels in the lamina propria, however, remained intact. Following a lower dose (12 mg/kg), the lesions were not as pronounced. The effects of dichlobenil (6, 12, and 25 mg/kg) on cell replication in the olfactory mucosa, as determined by incorporation of 3H-thymidine 3 days later, were more pronounced in the lamina propria than in the neuroepithelium and occurred at a lower dose in the lamina propria than in the neuroepithelium. Together these studies support the previous proposal that dichlobenil induces a primary damage in the Bowman's glands.

Metallothioneins 1 and 2 Are Expressed in the Olfactory Mucosa of Mice in Untreated Animals and during the Regeneration of the Epithelial Layer

We have examined the expression of the MT1 and MT2 isoforms of metallothionein in the mouse olfactory mucosa. In untreated mice, metallothionein was strongly expressed in supporting cells, acinar cells of the Bowman's glands, and olfactory neurons. Expression was however restricted to a subset of cells within each type, and to zones within the olfactory system. Irrigation with ZnSO4solution caused exfoliation of the olfactory epithelium and during the resultant regeneration, metallothionein immunoreactivity was associated with the proliferating basal cells. The ability to express MTs 1 and 2 did not appear to be obligatory for the early stages of regeneration since mice which do not express these isoforms responded similarly to wild type mice. Strong nuclear expression of metallothionein was noted in the untreated olfactory chamber following unilateral irrigation.

Chronic inhalation toxicity and oncogenicity of methyl methacrylate in rats and hamsters

Male and female Fischer 344 rats were exposed to methyl methacrylate (MMA) monomer vapours at 0, 25, 100 and 400 ppm, 6 hr/day, 5 days/wk for 24 months and male and female Golden hamsters were exposed to similar vapour concentrations of MMA for 18 months. Parameters monitored throughout the study included clinical signs, individual body weights, haematology, clinical chemistry (rats only) and urinalyses (rats only). 10 rats per sex per exposure group were killed after 13 and 52 wk of exposure and all surviving rats were killed during wk 104–106. All surviving hamsters were killed at wk 78. Mortality and haematological, clinical chemistry and urinalyses parameters were not affected by MMA exposure. Body weights of male rats were not affected by exposure to MMA while body weights of female rats exposed to 400 ppm were lower than control values after wk 52. Male and female hamsters exposed to 400 ppm had body weight decreases ranging from 9 to 12% after wk 48. The nasal cavity was identified as the target organ for chronic toxicity in male and female rats exposed to 100 or 400 ppm. The microscopic nasal cavity changes occurred primarily in olfactory epithelium lining the dorsal meatus and consisted of degeneration of neuroepithelium, basal cell hyperplasia and atrophy of Bowman's glands. Hamsters did not have demonstrable nasal cavity microscopic changes. Chronic exposure to MMA vapour did not cause tumours in either rats or hamsters.

Parathyroid hormone‐related protein in tissues of the emerging frog (Rana temporaria): immunohistochemistry and in situ hybridisation

Using antiserum to human parathyroid hormone-related protein (1-16) [PTHrP(1-16)] we have examined tissues of the common frog (Rana temporaria) for the presence of immunoreactive PTHrP (irPTHrP) at the stage of emergence from water to land. irPTHrP was detected in dorsal and ventral stratum granulosum of the skin, in the developing ovary, striated muscle and the choroid plexus epithelium of the brain as well as in the olfactory gland epithelium and olfactory lobe neurons of the brain. In the pituitary and hypothalamus irPTHrP protein could be demonstrated in the median eminence, infundibular stem and principally in the neural lobe and pars distalis of the pituitary with weak reaction in the pars intermedia. In situ hybridisation of the same tissues with an oligonucleotide probe to chicken PTHrP 55-65 clearly showed the presence of mRNA for PTHrP-like molecule in all the tissues containing irPTHrP. There was a major inconsistency in the pituitary in that the highest level of gene expression, assessed by in situ hybridisation, was found in the pars intermedia with only very low expression in the pars distalis and neural lobe and undetectable levels in the infundibular stem and median eminence. These observations suggest that tissues of the frog synthesise a PTHrP-like molecule but that in the pituitary the pars intermedia cells may export the protein to cells in other regions of the pituitary and hypothalamus.

Nasal Cytochrome P450 2A: Identification, Regional Localization, and Metabolic Activity toward Hexamethylphosphoramide, a Known Nasal Carcinogen

Two members of the cytochrome P450 2A subfamily, CYP2A10 and 2A11, are abundant nasal enzymes previously characterized in rabbit olfactory microsomes. Rabbit CYP2A is active toward a number of nasal toxicants, including the rat nasal procarcinogen hexamethylphosphoramide (HMPA). While P450s immunochemically related to the rabbit CYP2As have been detected in rat and human nasal mucosa, confirmation of these enzymes as members of the CYP2A subfamily and efforts to characterize their ability to bioactivate toxicants have been limited. In the present study, the regional distribution and cell-specific expression of CYP2A in the rat nasal cavity were examined using an antibody to rabbit CYP2A10/11. In sections of the anterior nose, immunoreactive CYP2A was present in ciliated cells of the nasal respiratory epithelium and cuboidal epithelial cells of the nasal transitional epithelium, but was absent in squamous epithelial cells. The most intense immunostaining was observed in the posterior nose. Olfactory sustentacular cells and Bowman's gland cells in sections posterior to the nasal papilla stained most intensely. Western blot analysis revealed that anti-CYP2A10/11 recognized a sharp band of approximately 50 kDa in nasal respiratory and olfactory microsomes, supporting the premise that the antibody is reacting with a cytochrome P450 enzyme. The nasal expression of CYP2A6 mRNA—a member of the human CYP2A subfamily having a high degree of homology to rabbit 2A10 and 2A11—was examined in human surgical patients. Middle turbinectomy tissues—largely composed of nasal respiratory epithelia—from 11 patients were analyzed for the presence of CYP2A6 using reverse transcription–polymerase chain reaction (RT–PCR). Identification of CYP2A6 was confirmed by DNA sequencing of RT–PCR products. CYP2A6 mRNA was detected in all of the human samples analyzed. In additional experiments, human CYP2A6 metabolized HMPA to formaldehyde, suggesting that this compound might cause nasal toxicity in humans. The identification of CYP2A cytochromes in rat and human nasal tissues may have important implications for risk assessment of inhaled xenobiotics.

Antibodies to the sulphated, high molecular mass mouse tectorin stain hair bundles and the olfactory mucus layer

Polyclonal antibodies were raised in chickens to the glycosylated forms of the high (H), medium (M) and low (L) molecular mass (MM) mouse tectorins. In the mouse cochlea, all three antibodies stained the tectorial membrane. Antibodies raised to HMM tectorin also stained the hair bundles of both inner and outer hair cells. A number of other mouse tissues were screened with the anti-tectorin antibodies to look for similar or antigenically related molecules. Staining was not observed in any other tissue type with the antibodies directed against the MMM and LMM tectorins. In the nose, the anti-HMM tectorin antibodies stained Bowman's glands and the mucus layer overlying the olfactory epithelium. The surface of the adjacent respiratory epithelium was not stained by these antibodies. HMM tectorin can be specifically radiolabelled by injecting neonatal mice with 35SO4 and undergoes a shift in electrophoretic mobility following treatment with keratanase, an endo-β-galactosidase from Pseudomonas. However, when centrifuged on shallow CsCl gradients HMM tectorin has a buoyant density similar to that of glycoproteins and does not behave as a typical cartilage type proteoglycan. HMM tectorin does not react with mab 5D4, a monoclonal antibody that recognises keratan sulphate glycosaminoglycan from corneal and skeletal muscle proteoglycan. Unlike antibodies to HMM tectorin, mab 5D4 selectively stains the upper surface of the tectorial membrane, Hensen's stripe and the mucus layer overlying the respiratory epithelium. These studies indicate that the MMM and LMM tectorins may be unique to the cochlea, and that HMM may be a ‘light’ keratan sulphate proteoglycan that is antigenically related to either the mucins or a more specific component of the olfactory mucus layer.

Localization of 11/β-Hydroxysteroid Dehydrogenase: Specific Protector of the Mineralocorticoid Receptor in Mammalian Olfactory Mucosa

The enzyme 11/β-hydroxysteroid dehydrogenase (11β HSD) plays a major role in the protection of the mineralocorticoid (type 1) receptor. The cellular mechanism of aldosterone selectivity relies on the coexpression of mineralocorticoid receptors and 11β HSD in the same cells. In the current study, 11β HSD activity was localized in the mammalian olfactory mucosa by a histochemical technique which links steroid metabolism with the deposition of formazan. The histochemical reaction results from oxidation of the synthetic substrate β-hydroxyandrostenedione and is dependent on nicotine-adenine dinucleotide (NAD). This demonstrates the presence of a dehydrogenase activity separate from the nicotineamide-adenine dinucleotide phosphate (NADP)-dependent 11βHSD. In the olfactory mucosa, the presence of NAD-dependent 11βHSD activity is localized to the sustentacular cells and acinar cells of Bowman's glands. No definite NAD-dependent activity was demonstrated in the olfactory receptor neurons. These data suggest that mineralocorticoid receptors present in acinar cells and sustentacular cells are aldosterone selective.

Manganese and Copper-Zinc Superoxide Dismutases in the Human Olfactory Mucosa: Increased Immunoreactivity in Alzheimer's Disease

Superoxide dismutases are the cell's major enzymatic defenses against cytotoxic reactive oxygen species and oxidative stress. Reactive oxygen species, which induce the expression of these enzymes, have been implicated in the neurodegeneration associated with Alzheimer's disease (AD), and individuals with AD exhibit early, severe deficits in olfactory ability. We used immunohistochemistry to examine the cellular localization of manganese and copper-zinc superoxide dismutases in the olfactory mucosae of nondemented young/middle-aged and old subjects as well as age- and postmortem-interval matched nondemented elderly individuals and those with AD. Tissues were obtained at autopsy from individuals ranging in age from 19 to 98 years old. Immunoreactivity for both enzymes was localized in olfactory receptor neurons, sustentacular and basal cells in the olfactory epithelium, and in olfactory and extrinsic nerves, Bowman's glands, and vascular endothelium in the lamina propria. Computer-assisted quantitative analysis demonstrated that very intense immunoreactivity for both manganese and copper-zinc superoxide dismutases occupied significantly more area, particularly near the surface and in the basal region, of the olfactory epithelium from subjects with AD than from the age- and postmortem interval-matched nondemented elderly subjects. The pronounced increase in superoxide dismutase immunoreactivity in the olfactory epithelium of AD subjects suggests that oxidative stress may be responsible, at least in part, for the olfactory deficits in subjects with AD.

Transforming growth factor‐α and other growth factors stimulate cell division in olfactory epithelium in vitro

The rate of cell division in olfactory epithelium (OE) is upregulated by ablation of the olfactory bulb (Carr and Farbman, 1992), or downregulated by occlusion of a naris. We used an organ culture assay of fetal rat olfactory mucosa to study regulation of the mitotic rate. Addition of any one of three members of the epidermal growth factor (EGF) family—EGF, transforming growth factor-α (TGF-α), or amphiregulin (AR)—to a serum-free culture medium resulted in a two- to threefold increase in the number of dividing OE cells. TGF-α elicited a maximal response in a dose of 100–200 pM culture medium and was 2 orders of magnitude more potent than the other EGF family members. Addition of TGF-β1, TGF-β2, insulinlike growth factor-1 or platelet-derived growth factor to the culture medium had slightly less effect than EGF or AR, in about the same molar dose range; addition of nerve growth factor had virtually no net effect on cell division. Immunohistochemistry on adult rat OE showed that basal cells, supporting cells, and acinar cells of Bowman's glands were immunoreactive with antibody to TGF-α but not with antibody to EGF. Most growth factors upregulated division of both olfactory neuron progenitors and supporting cells. The data suggest that several growth factors, most prominently TGF-α, may participate in the mitotic regulation of OE. © 1996 John Wiley & Sons, Inc.

Development of the Bowman's and Jacobson's Glands in the Japanese Reddish Frog, Rana japonica.

The olfactory organs are equipped with their own associated glands, Bowman's glands (BG) of the olfactory epithelium (OE), and Jacobson's glands (JG) of the vomeronasal organ (VNO). Histology and ultrastructure of these glands in the adult were investigated in the Japanese reddish frog, Rana japonica, along with their development from hatching to the end of metamorphosis. In the adult, BG cells contained large, electron-opaque secretory granules, intensely PAS-positive by light microscopy, while JG cells contained middle-sized secretory granules with moderate electron density, only faintly PAS-positive. Embryologically, BG appeared within the OE at 44 days after hatch, increased in number and were situated in the lamina propria under the OE at 52 days after hatch. BG cells contained large, electron-opaque granules, and well-developed rER at this time. While, JG appeared much earlier than BG. The VNO appeared as a concave of the ventral part of the OE at 4 days after hatch, and JG appeared under the VNO at 10 days after hatch. JG cells contained well-developed rER at 12 days after hatch. Secretory granules appeared in a small number in JG at 24 days after hatch, and increased thereafter. These findings suggest that JG may take part in secretion earlier than BG in ontogeny.

Toxicity and cell proliferation in the liver, kidneys and nasal passages of female F-344 rats, induced by chloroform administered by gavage

Dose-response relationships were determined for the induction of cytolethality and regenerative cell proliferation in the established target organs (liver, kidneys, and nasal passages) of female F-344 rats given chloroform daily by gavage. Rats were administered chloroform dissolved in corn oil at doses of 0, 34, 100, 200 or 400 mg/kg/day for 4 consecutive days or for 5 days/wk for 3 wk. Bromodeoxyuridine (BrdU) was administered through an implanted osmotic pump 3.5 days prior to autopsy to label cells in S-phase. Cells in S-phase were visualized immunohistochemically in tissue sections and the labelling index (LI) calculated as the percentage of cells in S-phase. Mild degenerative centrilobular changes and dose-dependent increases in the hepatocyte LI were observed after administration of 100 mg or more chloroform/kg/day. Rats given 200 or 400 mg/kg/day for 4 days or 3 wk had degeneration and necrosis of the proximal tubules of the renal cortex. Regenerating epithelium lining proximal tubules was seen histologically and as an increase in LI. Dose-dependent increases in LI were observed in the kidneys at doses of 100 mg or more cholorform/kg/day at both 4 days and 3 wk. Two distinct treatment-induced responses were observed in specific regions of the olfactory mucosa lining the ethmoid region of the nose. A peripheral lesion was seen at all doses used and included new bone formation, periosteal hypercellularity and increased cell replication. A central lesion was seen at doses of 100 mg or more chloroform/kg/day and was characterized by degeneration of the olfactory epithelium and superficial Bowman's glands. These observations define the dose-response relationships for the liver, kidneys and nasal passages as target organs for chloroform administered by gavage in the female F-344 rat.

Dichlobenil in the fetal and neonatal mouse olfactory mucosa

The irreversible binding and toxicity of the olfactory toxicant dichlobenil in the mouse perinatal olfactory mucosa were examined by autoradiography and histopathology. In the olfactory mucosa of adult mice the irreversible binding of [ 14C]dichlobenil-derived radioactivity is confined to the Bowman's glands. The results in this study showed a low irreversible binding of [ 14C]dichlobenil-derived radioactivity in the fetal olfactory mucosa from day 17 of gestation and a markedly increased binding after birth in accord with the development of the Bowman's glands. No morphologicalchanges were observed in the olfactory mucosa of 1- or 4-day-old neonates given s.c. injections with dichlobenil 12 mg/kg but in 8- or 11-day-old mice given 12 or 25 mg/kg, scattered necrotic Bowman's glands occurred in the dorsomedial olfactory region 24 h after administration. In adult male mice dosed i.p. with dichlobenil a more extensive toxicity in the Bowman's glands was observed. The low toxicity of dichlobenil in the postnatal olfactory mucosa, despite a high irreversible binding at this site, may possibly be related to the cell proliferation in the developing olfactory mucosa leading to replacement of damaged cells.

Metabolism‐Dependent Toxicity of Methimazole in the Olfactory Nasal Mucosa

In mice given a single intraperitoneal injection of the antithyroid drug methimazole (0.44 mmol/kg; 50 mg/kg) detachment of the olfactory neuroepithelium and necrosis of the Bowman's glands in the lamina propria was observed 24 hr after administration. Three days after administration there was an atypical epithelium throughout the olfactory region and the Bowman's glands had disappeared. Pretreatment with the olfactory cytochrome P450 inhibitor metyrapone protected against the methimazole-induced changes at this site. In mice injected with the methimazole analogues 1-methylimidazole or 4-methylimidazole (0.44 mmol/kg; 36 mg/kg) or the antithyroid drug propylthiuracil (0.22 mmol/kg; 38 mg/kg) no morphological changes were observed in the olfactory mucosa. The results suggest that methimazole-induced toxicity in the olfactory mucosa is related to metabolism-dependent changes of the thiol group.

Distribution of microsomal epoxide hydrolase and glutathione S-transferase in the rat olfactory mucosa: relevance to distribution of lesions caused by systemically-administered olfactory toxicants.

This study represents part an of ongoing effort to understand the mechanism underlying the distribution of the olfactory mucosal lesion resulting from the systemic administration of compounds such as 2,6-dichlorobenzonitrile (dichlobenil) and beta,beta'-iminodipropionitrile (IDPN). Immunohistochemistry was performed to localize the microsomal form of epoxide hydrolase (mEH) and glutathione S-transferase (GST) isozymes alpha, mu and pi in the rodent olfactory mucosa. GST-pi was found in abundance in the Bowman's glands of the mucosa lining the dorsal medial meatus (DMM) of the nasal cavity and in the nuclei of basal and sustentacular cells of the dorsal and lateral nasal cavity. Liver and olfactory mucosal levels of mEH are equivalent by Western blot analysis. mEH appeared to be localized in the apical cytoplasm of sustentacular cells in all regions of the olfactory mucosa except for the epithelium lining the DMM. These observations, coupled with the known profile of metabolites for dichlobenil, suggest that systemically-administered compounds causing site-specific lesions in the epithelium lining the DMM of the nasal cavity may do so by the in situ production of reactive epoxide metabolites which are then poorly capable of being detoxified. Thus, the distribution of metabolic enzymes, rather than the absolute level of an enzyme in a tissue, may dictate lesion distribution in the case of toxicants which are bioactivated in target tissues.

窒素酸化物によるきゅう上皮障害の実験的研究

To investigate the effects of nitrogen dioxide (NO2), which is a major component of air pollution, on the olfactory epithelium, we exposed 38 8-week-old Wistar rats to 10 ppm NO2 for 14 days in an inhalation chamber at the National Institute for Environmental Studies. We performed histological examinations, including immunohistochemistry (microtubule-associated protein 5, MAP5), and behavioral olfactometry to examine the effect of NO2 on the olfactory epithelium. MAP5 is present in the cell bodies of neurons and all along their dendrites and is believed to be involved in the early stage of active axonal outgrowth.Irregular olfactory vesicles and olfactory cilia and increased numbers of Bowman's glands were observed immediately after NO2 exposure. Although the morphology of the olfactory epithelium was almost normal 14 days after exposure, behavioral olfactometry was still abnormal up to 30 days after the exposure. MAP5 was distributed diffusely in the dendrites of the olfactory epithelium in the control rats. In contract, MAP5 was dense in the upper regions of the olfactory epithelium from immediately until 30 days after the exposure. Thus, there was a discrepancy between the morphological changes and the behavioral olfactometry results, while immunoreactive test results with MAP5 were in accord with the behavioral olfactometry results. Our findings indicate that functional olfactory disturbances are not always in accord with morphological changes of the olfactory epithelium.