Recovery of polyclonal hematopoiesis in patients with myelodysplastic syndromes following successful chemotherapy

We performed X-linked restriction fragment length polymorphism (RFLP)-methylation analysis to study the clonality of hematopoiesis in five patients with myelodysplastic syndromes (MDS), who had responded to chemotherapy. Two patients had MDS in blast crisis, two had refractory anemia with an excess of blasts in transformation (RAEB-T), and one had acute myelogenous leukemia with trilineage myelodysplasia (AML-TMDS). Following the administration of low-dose cytarabine therapy or of conventional intensive chemotherapy, we observed a reversion to polyclonal hematopoiesis in three patients who achieved a complete remission (CR). Polyclonal hematopoiesis persisted in one patient in CR, and monoclonal hematopoiesis persisted in another patient of minor response. These results indicate that polyclonal hematopoiesis can be restored in some MDS patients who achieved CR. We are encouraged, therefore, to administer intensive consolidation chemotherapy to prolong the duration of remission.

[Flare response on bone scintigraphy in metastatic prostate cancer]

Seventy-seven cases of prostate cancer were treated for 5 years at our department and all cases were followed by bone scintigraphy and tumor markers. Of these cases on case of flare response on bone scintigraphy was recognized. A 51-year-old man was hospitalized with chief complaint of lumbago. Serum PAP and gamma-Sm levels were 320 ng/ml and 15 ng/ml, respectively. Prostate biopsy revealed moderately differentiated adenocarcinoma. Bone scintigraphy and CT scan demonstrated multiple bone metastases and lymph nodes involvements. Treatment was started with diethylstilbestrol diphosphate (DES). At one month after the initiation of treatment tumor markers fell down to the normal level and lumbago was diminished, but only serum alkaline phosphatase was elevated and bone scintigraphy showed apparent progression of individual lesions (flare response). The treatment was not altered. At the times after 2, 8, 12 and 36 months successful treatment the bone imaging improved with reduced tracer uptake and no new lesions. The flare response is a healing reaction and is followed apparent improvement. In general, serial bone scintigrams accurately depict the activity of bone metastases in the patients of prostate cancer, but between 1 and 3 months after starting treatment the paradoxical "flare phenomenon" should be taken care.

The alpha subunit of GTP-binding protein G0 in neuroblastoma: correlation with advanced disease stage

Tissue levels of the alpha subunit of G protein G0 (G0 alpha) were measured in solid tumors from pediatric patients by immunoassay. G0 alpha concentrations were determined in the supernatant obtained by centrifugation of tissue homogenates prepared in the presence (total G0 alpha) or absence of 2% sodium cholate (soluble G0 alpha). Mean G0 alpha concentrations (total G0 alpha and soluble G0 alpha) in neuroblastomas (7 ganglioneuromas, 13 ganglioneuroblastomas, and 50 neuroblastomas) were over 50-fold higher than those in other solid tumors from pediatric patients (n = 13). Mean total G0 alpha and soluble G0 alpha concentrations were 207.0 +/- 166.0 (SD) ng/mg of cholate-extractable protein and 58.6 +/- 47.0 ng/mg of soluble protein, respectively, in the neuroblastoma group (n = 70). Total G0 alpha concentration decreased with disease stage and was strongly correlated with outcome in patients with neuroblastoma. The mean total G0 alpha concentration in tumors from younger patients (< 1 year old) was 297.0 +/- 137.0 ng/mg of cholate-extractable protein, significantly higher than in tumors from older patients (140.0 +/- 155.0 ng/mg cholate-extractable protein, P < 0.0001). These results suggest that total G0 alpha levels in neuroblastoma may indicate the degree of malignancy.

Pravastatin sodium, a competitive inhibitor of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase, decreases the cholesterol content of newly secreted very-low-density lipoprotein in Watanabe heritable hyperlipidemic rabbits

We examined the secretion of very-low-density lipoprotein (VLDL) when hepatic 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme of cholesterol biosynthesis, was inhibited. To inhibit HMG-CoA reductase in liver, pravastatin sodium, a competitive inhibitor of HMG-CoA reductase, was administered to homozygous Watanabe heritable hyperlipidemic (WHHL) rabbits, a low-density lipoprotein receptor-deficient animal model, at a dosage of 50 mg/kg per day for 5 weeks. Although triglyceride levels were not changed, total cholesterol levels of sera and each atherogenic lipoprotein were decreased by approximately 30%. As a result, the percentage of cholesterol concentration in newly secreted VLDL was significantly decreased by 24%. The VLDL secretion rate was determined by intravenous injection of Triton WR-1339. The VLDL secretion rate was significantly decreased by 23% using cholesterol as an index, but it did not change using triglyceride, phospholipid, or protein as an index. It is concluded that one of the mechanisms of serum total cholesterol decrease due to reduction of the putative cholesterol pool of the liver in homozygous WHHL rabbits is caused by a decrease of cholesterol content in newly secreted VLDL particles.

Benefits of rate-responsive pacing in patients with sick sinus syndrome

The effect of changing a rate-responsive pacemaker program (which reacts to evoked QT interval) to fixed-rate ventricular pacing was studied in 10 patients with sick sinus syndrome (SSS). After the patients had been in the rate-responsive mode (VVIR) for at least one year, the exercise capacity (maximal oxygen consumption [peak VO2], anaerobic threshold [AT], and cardiac output [CO] at these points) was examined. Three hours later on the same day, the pacemaker was reprogrammed to the fixed-rate pacing (VVI) and the exercise capacity was examined again (VVI-S). One month later, a similar exercise test was also done in the VVI mode (VVI-L). There was no significant difference in peak VO2 and AT between VVIR and VVI-S, but both peak VO2 and AT were significantly lower in VVI-L than in VVIR. However, there were no significant differences in the CO at peak VO2 or AT between any of the pacing modes. These findings indicate that a VVIR pacemaker should not be reprogrammed to the VVI mode in SSS patients, because the change can cause the exercise capacity to deteriorate.

Roles of transcription and repair in alkylation mutagenesis

Mutations occurring in Escherichia coli cells exposed to alkylating agents have been analyzed using an assay for forward mutations in the E. coli rpsL gene cloned on a high copy number plasmid. N-Methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced mutations were recovered from wild-type and O6-methylguanine methyltransferase-deficient mutant (ada- ogt-) cells and their sequence alterations determined. We found that the mutations recovered from the wild-type strain were predominantly G:C to A:T transitions located at several hot spots in the rpsL sequence. A vast majority of the mutations were found at guanine residues preceded by thymine on the transcribed strand of the target gene. Although the methyltransferase mutant showed hypersensitivity to the alkylating reagent in terms of mutagenic effect and cell killing effects, the class and site distributions of the rpsL- mutations recovered from MNNG-treated ada- ogt- cells were similar to those observed with MNNG-treated wild-type cells. Therefore, the site preference of MNNG-induced rpsL- mutations seems to be due not to the specificity of methyl-transferring repair enzymes but probably to the distribution of the mutagenic lesions (O6-methylguanine) in the target sequence. Mutations induced by methyl methanesulfonate, an SN2 alkylating agent, showed similar class and site distributions in the rpsL system. The site preference of MNNG-induced mutations was significantly changed when the level of transcription of the rpsL gene was decreased to 120-fold lower than that promoted by the authentic rpsL promoter. Under these conditions, 78% of mutations were induced at the central guanine of 5'-GG(A or C)-3' and 2/3 of them were on the non-transcribed strand of the rpsL gene. These results suggested that the site preference of MNNG-induced mutations is determined by at least three factors: (i) a flanking-base effect on the chemical reactivity of a guanine residue, (ii) transcribed strand-specific repair, probably by the UvrABC system, and (iii) the effects of transcription of the target gene on the alkylation of DNA and the strand-specific repair.

Cyclophosphamide-induced tolerance in fully allogeneic heart transplantation in mice

We have established a long-lasting heart allograft tolerance in H-2-incompatible combinations by intravenous injection of 10(8) allogeneic spleen cells followed by the administration of 200 mg/kg of cyclophosphamide (CP). When C57BL/10 mice (B10, H-2b) were primed iv with 1 x 10(8) viable spleen cells from naive BALB/c mice (H-2d) and treated ip with 200 mg/kg CP 2 days later, BALB/c heart allografts were lasting in the recipients for as long as 8 weeks. On the other hand, B10 mice receiving either allogeneic spleen cells or CP rejected the heart allograft within 10 days after transplantation. A direct approach assessing the donor-reactive T cells for frequency and reactivity showed that the donor-reactive T cells were partially deleted and the rest were rendered unresponsive. CP-induced tolerance may be applied for the induction of antigen-specific tolerance to allogeneic heart transplantation.

Long-term inhibition of NO synthesis promotes atherosclerosis in the hypercholesterolemic rabbit thoracic aorta. PGH2 does not contribute to impaired endothelium-dependent relaxation

We examined whether prostaglandin (PG) H2, as an endothelium-dependent contracting factor, or the disturbed production of endothelium-derived relaxing factor, impairs endothelium-dependent relaxation and whether long-term inhibition of nitric oxide (NO) synthesis aggravates atherosclerosis in hypercholesterolemic rabbits. Male New Zealand White rabbits were fed one of the following diets: (1) standard chow; (2) 2% cholesterol-supplemented chow; (3) standard chow with 80 micrograms/mL N omega-nitro-L-arginine methylester (L-NAME), an NO synthetase inhibitor, in their drinking water; or (4) 2% cholesterol-supplemented chow with 80 or 160 micrograms/mL L-NAME in their drinking water. The rabbits were fed these diets for 8 or 12 weeks. Then aortic rings were obtained, and changes in isometric tension were recorded. Intimal atherosclerotic areas of the thoracic aortas were subsequently measured by planimetry. The cholesterol-supplemented diet significantly impaired endothelium-dependent aortic relaxation to acetylcholine. Pretreatment with the thromboxane A2/PGH2 receptor antagonist ONO-3708 did not reverse this impaired response. Vessels from both normocholesterolemic and hypercholesterolemic rabbits given L-NAME showed more impaired endothelium-dependent relaxation than those from their dietary counterparts not given L-NAME. Morphometric analysis revealed marked enlargement of intimal atherosclerotic areas in aortas from L-NAME-treated hypercholesterolemic rabbits compared with those from untreated hypercholesterolemic rabbits. These findings suggest that PGH2 does not contribute to impaired endothelium-dependent relaxation and that long-term administration of L-NAME promotes atherosclerosis by inhibition of NO synthesis in the hypercholesterolemic rabbit thoracic aorta.

The rejection mechanism of rat pancreaticoduodenal allografts with a class I MHC disparity

The present study has demonstrated for the first time that PVG.R1 (RT1.AaBcDcCc) pancreatic grafts are rejected by so-called "low"-responder PVG (RT1.AcBcDcCc) recipients with an isolated class I MHC disparity (mean survival time; MST: 21.4 +/- 1.8 days, n = 5), whereas PVG.R1 heart grafts are able to survive indefinitely (MST: > 100 days, n = 5). Splenic CD4+ T cells but not CD8+ T cells from the PVG recipients of PVG.R1 pancreatic grafts show a remarkable proliferative response against donor class I RT1.Aa alloantigens, while only a minimal proliferation is observed in the PVG recipients of PVG.R1 heart grafts or naive PVG rats. Naive PVG rats display an extremely low frequency of IL-2-producing helper T cell precursors (fThp) of 1/40,609 +/- 15,441 against class I RT1.Aa alloantigen. The PVG recipients of PVG.R1 heart grafts have a slightly greater fThp of 1/17,326 +/- 6822. On the other hand, the PVG recipients that rejected PVG.R1 pancreatic grafts show a significantly increased fThp of 1/5030 +/- 3396 compared with those of PVG.R1 heart grafts (P < 0.05) or naive PVG rats (P < 0.01). The frequency of cytotoxic T cell precursors (fTcp) increases slightly in the PVG recipients of PVG.R1 pancreatic grafts (1/1848 +/- 330) compared with those of PVG.R1 heart grafts (1/2215 +/- 2131) or naive PVG rats (1/2476 +/- 585). The size of cytotoxic T cell clones alone does not adequately account for a proliferation sufficient to complete the rejection of pancreatic grafts. The PVG recipients of PVG.R1 pancreatic grafts, but not heart grafts, demonstrate a strong cytotoxic alloantibody response to donor class I RT1.Aa alloantigens. In the study of alloantibodies, IgM is detected mainly in the early phase and IgG in the late phase during the course of pancreatic rejection. It is determined that in blocking studies by FACS analysis these antibodies target class I MHC antigens. These results suggest that cytotoxic T cells do not appear to be responsible for the rejection of PVG.R1 pancreatic grafts in PVG recipients. Rather, the rejection is mediated by CD4+ T cells and complement-fixing antibodies directed at class I MHC antigens.

Expression of the alpha 2-macroglobulin-encoding gene in rat brain and cultured astrocytes

The alpha 2-macroglobulin (alpha 2M), a protease inhibitor, is a major acute-phase protein in rats, and is produced in the liver during acute inflammation. Recently, it has been demonstrated that alpha 2M is also produced by cultured astrocytes from newborn rat brain and has neurite-promoting activity. Here, we found that the expression of the alpha 2M gene was significantly enhanced in the brain following intraperitoneal injection of the neurotoxicant, kainic acid (KA), suggesting that alpha 2M acts as an acute-phase protein in the brain, as in the case of the liver, and may be involved in neural repair processes. Expression of alpha 2M in cultured astrocytes was shown to be stimulated by interleukin-6 (IL-6) and/or leukemia inhibitory factor (LIF) in the presence of glucocorticoid. The amount of mRNAs for IL-6 and LIF increased in the brain of KA-injected rats prior to alpha 2M induction. These results strongly suggested that IL-6 and LIF are involved in alpha 2M induction in the brain, as in the case of the liver. Analysis of the cis-acting element(s) and the trans-acting factor(s) suggested that the regulatory mechanism for alpha 2M expression in astrocytes was similar to that in inflamed liver.

Increased expression of c-met messenger RNA following acute gastric injury in rats

The aim of the present study was to evaluate messenger RNA expression of c-met, a hepatocyte growth factor receptor gene, after gastric mucosal injury in rats. Male Sprague-Dawley rats were fasted for 24 hours, received 0.6 N hydrochloric acid (HCl), and served for polyadenylated RNA extraction from the oxyntic gastric mucosa. The transcripts of rat c-met gene were analyzed by reverse-transcript polymerase chain reaction and Northern blotting. Although it was detected even before the HCl administration, the c-met expression increased 6, 24 and 48 hours after the HCl administration. Thereafter, gastric mucosal injury diminished and the c-met expression declined. Hepatocyte growth factor reportedly plays an important role in gastric cell proliferation. The increased c-met expression indicates that this gene may participate in the healing process of gastric mucosa after injury.

Identification of protein receptor for Clostridium botulinum type B neurotoxin in rat brain synaptosomes

The protein receptor for Clostridium botulinum type B neurotoxin was purified 340-fold from rat synaptosomes by successive chromatography on DEAE-Sepharose, phenyl-Toyopearl, and heparin-Toyopearl columns. 125I-Labeled neurotoxin bound to lipid vesicles containing the protein receptor and ganglioside GT1b or GD1a. The reconstituted receptor showed the same affinities as the native receptor on synaptosomes. Chemical cross-linking of 125I-toxin to the receptor in the presence of gangliosides resulted in formation of a cross-linked product of 161 kDa under reducing conditions. Cross-linking was specific, as it was inhibited by the presence of excess unlabeled toxin. A monoclonal antibody against the purified 58-kDa receptor protein and a monoclonal antibody against the heavy chain (103 kDa) of the neurotoxin reacted with the cross-linked product of 161 kDa in immunoblotting experiments. We determined partial amino acid sequences of the 58-kDa protein, which were identical to synaptotagmin, a synaptic vesicle membrane protein. In addition, the monoclonal antibody against the 58-kDa receptor protein recognized recombinant rat synaptotagmin. These results suggest that synaptotagmin in association with ganglioside GT1b or GD1a may be a natural receptor for C. botulinum type B neurotoxin at the nerve terminals.

Prostaglandin H2 as an endothelium-derived contracting factor modulates endothelin-1-induced contraction

OBJECTIVE

To investigate the possible involvement of prostaglandin H2, an endothelium-derived contracting factor in the rat aorta, in the development of the contraction induced by endothelin-1.

METHODS

The aortic rings from spontaneously hypertensive rats (SHR) were prepared, and the changes of isometric tension of these rings developed by endothelin-1 were recorded with or without the treatment of several inhibitors or an antagonist. The concentrations of prostaglandins and thromboxane B2 in the bath solution with the rings contracted by endothelin-1 were measured by radioimmunoassay. The effects of a thromboxane A2/prostaglandin H2 receptor antagonist (ONO-3708) on endothelin-1-induced contraction were compared in SHR and Wistar-Kyoto (WKY) rats.

RESULTS

Indomethacin (10(-5) mol/l) and ONO-3708 (10(-6) mol/l) significantly diminished endothelin-1 (3 x 10(-8) mol/l)-induced contractions in the aortic rings from SHR with but not without endothelium. The thromboxane A2 synthetase inhibitors OKY-046 (10(-5) mol/l) and RS-5186 (10(-5) mol/l) did not attenuate the contractions either with or without endothelium. Endothelin-1 significantly increased the release of 6-keto-prostaglandin F1 alpha, which is the metabolite of prostaglandin I2 and its precursor prostaglandin H2, from rings with endothelium of SHR, but the concentration of thromboxane B2 from aortic rings was unchanged. In the rings without endothelium the endothelin-1-induced release of 6-keto-prostaglandin F1 alpha was also observed. The half-maximal effective concentration of endothelin-1 for rings from SHR was shifted to the right by ONO-3708, but that of WKY rats was not changed, and significantly greater amounts of 6-keto-prostaglandin F1 alpha were released in the rings from SHR than in those from WKY rats by endothelin-1.

CONCLUSIONS

Endothelin-1 induced the release of prostaglandin H2 from endothelial cells in the rat aorta, the effect being greater in the hypertensive state. The released prostaglandin H2, an endothelium-derived contracting factor, modulated the vasoconstriction that is induced by endothelin-1, another endothelium-derived contracting factor, in addition to the direct vasoconstrictive action of endothelin-1 on vascular smooth muscle.

New neonatal extracorporeal membrane oxygenation circuit with a self-regulating blood pump

BACKGROUND

Because a roller pump used in a conventional extracorporeal membrane oxygenation (ECMO) circuit with a roller pump cannot change the output automatically according to the venous return, ECMO management requires considerable personnel to prevent serious mechanical complications. An automatic blood pump will make ECMO less laborious and safer.

METHODS

Takagi's self-regulating blood pump was modified for neonatal ECMO. The new ECMO circuit was tested in a simulation circuit, in puppies, and in two neonates clinically. Self-regulation of the pump was studied in response to various hemodynamic conditions.

RESULTS

The priming volume including a membrane lung and a heat exchanger was about 90 ml. The maximum flow was 700 ml/min in the simulation circuit, 101 ml/min/kg in puppies, and 113 and 135 ml/min/kg in two newborns, respectively. ECMO flow was self-regulating and stable in response to hemodynamic changes. The blood pumps remained functional for more than 400 hours in puppies and 67 and 149 hours in the two newborns, respectively.

CONCLUSIONS

The new automatic ECMO circuit is more reliable and requires less personnel than a conventional ECMO circuit.

[Unique association of p53 mutations with undifferentiated carcinoma of the thyroid]

In thyroid there is a wide variety of tumors varying from slowly growing differentiated adenocarcinomas to rapidly proliferating undifferentiated carcinomas. There has been some histopathological evidence that the undifferentiated thyroid carcinomas are derived from differentiated carcinomas. Moreover, it is suspected that some genetic events might be associated with such changes. To identify these genetic events that must be involved in thyroid tumor progression, we initially investigated p53 gene alterations in 10 papillary adenocarcinomas, 4 follicular adenocarcinomas, and 8 undifferentiated carcinomas. Base substitutional mutations in exons 5 to 8 and loss of heterozygosity (LOH) of the p53 gene were not detected in papillary or follicular adenocarcinomas. However, 7 of 8 undifferentiated carcinomasa were carrying base substitutional mutations, and LOH was detected in 3 of 5 informative cases. These results strongly suggest that the mutated p53 gene plays a crucial role in de-differentiation during the progression of thyroid tumors.

An extrapancreatic action of diazoxide to inhibit glucose transport activity on adipocytes

The effect of diazoxide on 3-O-methylglucose (3-O-MG) transport was studied in isolated rat adipocytes to elucidate its extrapancreatic action. Diazoxide (0.3-3 mmol/L) significantly inhibited 3-O-MG uptake into adipocytes in a basal state or an insulin-stimulated state. The inhibitory effect was mainly due to the inhibition of insulin responsiveness for 3-O-MG uptake. The insulin responsiveness is determined by the capacity in the process of insulin action and in the final glucose transport activity, and diazoxide mainly inhibited the 3-O-MG transport activity itself. Based on these findings, this extrapancreatic action of diazoxide is considered to contribute partially to raising the blood glucose level in children receiving the drug. Diazoxide, as a glucose transport inhibitor, may be a useful tool for studying the issues related to glucose transport or insulin action.

Identification of a novel sugar, 4-amino-4,6-dideoxy-2-O-methylmannose in the lipopolysaccharide of Vibrio cholerae O1 serotype Ogawa

A novel sugar in the lipopolysaccharide of Vibrio cholerae O1 serotype Ogawa has been identified. The sugar was liberated from the lipopolysaccharide when hydrolyzed in 10 M HCl at 90 degrees C for 15 min. The sugar was purified and identified as 4-amino-4,6-dideoxy-2-O-methylmannose (2-O-methylperosamine). Since it was found only in the lipopolysaccharide of Vibrio cholerae O1 serotype Ogawa, it seems that the sugar is one of the specific constituents determining Ogawa serotype specificity.

Mutational analysis of disulfide bridges in the type C atrial natriuretic peptide receptor

The type C receptor (ANP-C or NPR-C) for the natriuretic peptides was demonstrated, by site-directed mutagenesis, to have an immunoglobulin-like disulfide bonding pattern that is very similar to that of the cytokine receptor superfamily. The mature form of ANP-C has a disulfide-linked homodimeric structure and contains 5 conserved cysteine residues per subunit, all in the extracellular domain. To identify the cysteine residue involved in the dimerization and further to determine the intramolecular disulfide bridges and their functional roles, cysteine to serine mutations of the 5 cysteine residues were constructed. An analysis of the mutant receptors expressed in COS-1 cells by 125I-ANP binding assay and by measuring difference in their electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gels indicated that 1) the first 4 cysteine residues are joined sequentially, forming the Cys104-Cys132 and Cys209-Cys257 loops of 29 and 49 residues, respectively; 2) the two disulfide-linked loops are essential for the ligand binding activity; 3) the 5th cysteine residue Cys469 is used in the formation of covalently linked dimers; and 4) the covalent association of the subunit through the disulfide bond involving Cys469 has no apparent influence on ligand-receptor interactions. The intramolecular disulfide bond Cys104-Cys132 was also confirmed by direct protein sequencing of tryptic fragments of purified ANP-C receptor. The secondary structural features revealed here will be useful in understanding the structure and function relationships of not only the dimeric ANP-C receptor, which has only a short cytoplasmic tail, but also the ANP-A (GC-A) and ANP-B (GC-B) receptor subtypes, which have a guanylate cyclase domain in their long cytoplasmic tail and have recently been shown to possess an oligomeric structure, since they have similarly spaced cysteine residues in their extracellular domains.

Airway epithelial cell changes in rats exposed to 0.25 ppm ozone for 20 months

The present study was designed to characterize and quantify morphologic changes occurring in rat intra-pulmonary airway epithelia after long-term exposure to a high ambient level of ozone. Fifteen rats were exposed to 0.25 ppm ozone for 20 months (5 hr/day, 7 days/week) and a control group of 15 rats were exposed to filtered room air. Many intra-cellular brown pigmented granules (presumed to be lipofuscin) were seen in both the control and exposed animals; however, more of these granules were observed in the bronchial and bronchiolar epithelia of the exposed animals. To detect DNA synthesis that occurred in airway epithelial cells during the repair process induced by ozone toxicity, bromodeoxyuridine (BrdU) was injected intraperitoneally one hour before animals were sacrificed; the BrdU-labeling index was evaluated immunohistochemically. There was no difference in the BrdU-labeling index between the groups, the airway epithelia of the ozone-exposed animals exhibiting tolerance to ozone toxicity. However, the epithelial populations in the airways were altered by ozone exposure, and regional differences were seen in the changes. In the exposed animals, mucous cells increased in the lobar bronchus. Calcitonin gene-related peptide-immunoreactive pulmonary endocrine cells and neuroepithelial bodies were more frequently observed in the terminal bronchioles of the exposed animals than in the controls, although there were no differences in the lobar bronchus. Moreover, one adenoma in the peripheral lung was found in the exposed animals, while no tumorous lesions were detected in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)