Therapy with antibody-coated immune and hyperimmune peritoneal cells in a murine lymphoma system.

Goat-antimouse (DBA/2) SL2 lymphoma immunoglobulin was specifically cytotoxic to DBA/2-derived sl2 lymphoma cells. This anti-SL2 immunoglobulin, or a part of it, was cytophylic for peritoneal macrophages as shown by target cells adhering to macrophages incubated in vitro with the immunoglobulin. The target cells became free in the medium after incubation with 0.1% trypsin for 1 hour. In in vivo experiments, the incubation of immune or hyperimmune peritoneal cells with immunoglobulin from normal goat serum or from goat-anti-SL2 serum before use in immunotherapy decreased the number of DBA/2 mice surviving for more than 35 days an intraperitoneal injection with SL2 cells compared to the number of survivors inoculated with immune or hyperimmune cells only. These results show that, in immunotherapy with immune cells, we must consider the possibility that specific antitumor antibodies and antibodies not directed against the tumor cloud the therapeutic potnecy of the immune cells.

Effects of dietary linoleic acid on pancreatic carcinogenesis in rats and hamsters.

It has been suggested that linoleic acid (LA) is responsible for the promoting effect of dietary polyunsaturated fat on pancreatic carcinogenesis via an accelerated prostaglandin synthesis, caused by metabolism of LA-derived arachidonic acid in (pre)neoplastic tissue. The purpose of the present study was to investigate whether dietary LA is the cause of pancreatic tumor promotion by a high fat diet. Five groups of 30 azaserine-treated rats and 5 groups of 30 N-nitrosobis(2-oxopropyl)amine-treated hamsters were maintained for 6 months (rats) and 12 months (hamsters) on high fat (25 weight %) AIN diets containing 2, 4, 6, 10, or 15 weight % LA. The results indicated that the strongest enhancing effect on the growth of pancreatic (pre)neoplastic lesions in rats and hamsters was obtained with 4 and 2 weight % of dietary LA, respectively. At higher LA levels the tumor response seemed to decrease rather than increase. In both rats and hamsters the fatty acid profiles of blood plasma and pancreas showed an accurate reflection of the dietary fatty acid profiles: a proportional increase in LA levels was observed in plasma and pancreas with increasing dietary LA. In both species plasma and pancreatic AA levels remained constant, except for arachidonic acid levels in rat plasma, which significantly increased with increasing dietary LA levels. Fatty acid profiles in hamster pancreatic tumors did not differ from fatty acid profiles in nontumorous pancreatic tissue from hamsters fed the same diet. Prostaglandin (PG) E2, 6-keto-PGF1 alpha, PGF2 alpha, and thromboxane B2-concentrations in nontumorous pancreatic tissue were similar among the diet groups. Ductular adenocarcinomas from hamster pancreas showed significantly higher levels of 6-keto-PGF1 alpha, PGF2 alpha, and thromboxane B2, but not of PGE2 in comparison with nontumorous pancreas. It is concluded that the strongest pancreatic tumor promotion by dietary LA is 4 weight % in rats and 2 weight % or less in hamsters, and that PGs may be involved in the development of ductular adenocarcinomas induced in hamster pancreas by N-nitrosobis(2-oxopropyl)amine.

Modulation by CR-1409 (lorglumide), a cholecystokinin receptor antagonist, of trypsin inhibitor-enhanced growth of azaserine-induced putative preneoplastic lesions in rat pancreas.

Feeding of raw soya flour or other trypsin inhibitors such as camostate is a well-established method for promoting growth of (pre)neoplastic foci induced in the exocrine pancreas of rats by azaserine. The effect of trypsin inhibitors is thought to be mediated through an increased release of cholecystokinin. Using the specific cholecystokinin receptor antagonist lorglumide (CR-1409), we performed a 16-wk study to investigate the potential of this drug in inhibiting growth of putative preneoplastic foci and to determine whether and to what extent cholecystokinin is responsible for the effect of trypsin inhibitors on pancreatic growth. After initiation with 30 mg/kg of azaserine at 19 days of age, six groups of 15 rats each received one of the following treatments: camostate, cholecystokinin-8, or gelatin control, either or not in combination with CR-1409, once daily, 3 days wk for 16 wk. Plasma cholecystokinin levels, measured 30 min after the stimulus, were similar after camostate and cholecystokinin octapeptide administration. After 16 wk the pancreata were removed, weighted, and quantitatively analyzed for the number and size of putative preneoplastic foci by light microscopy. Both camostate and cholecystokinin octapeptide stimulated pancreatic growth and development of acidophilic putative preneoplastic foci, whereas growth of basophilic putative preneoplastic foci was inhibited by camostate but stimulated by cholecystokinin. CR-1409 almost completely abolished the effect of cholecystokinin and was found to cause a significant decrease in the effects of camostate. It is concluded that (a) cholecystokinin plays a significant role in camostate-stimulated growth of acidophilic putative preneoplastic foci in rat pancreas and (b) CR-1409 inhibits growth of putative preneoplastic foci induced in rat pancreas by azaserine and hence may be of potential value for the treatment of pancreatic cancer in humans.

Expression profiling of colon cancer cell lines and colon biopsies: towards a screening system for potential cancer-preventive compounds.

Interest in mechanisms of colon cancer prevention by food compounds is strong and research in this area is often performed with cultured colon cancer cells. In order to assess utility for screening of potential cancer-preventive (food) compounds, expression profiles of 14 human cell lines derived from colonic tissue were measured using cDNA microarrays with 4000 genes and compared with expression profiles in biopsies of human colon tumours and normal tissue. Differences and similarities in the gene expression profiles of the cell lines were analysed by clustering and principal component analysis (PCA). Cytoskeleton genes and immune response genes are two functional classes of genes that contributed to the differences between the cell lines. A subset of 72 colon cancer-specific genes was identified by comparing expression profiles in human colon biopsies of tumour tissue and normal tissue. A separation of the cell lines based on the tumour stage of the original adenocarcinoma was observed after PCA of expression data of the subset of colon cancer-specific genes in the cell lines. The results of this study may be useful in the ongoing research into mechanisms of cancer prevention by dietary components.

Effects of dietary fish oil (MaxEPA) on N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic carcinogenesis in hamsters.

In the present study the chemopreventive potential of 25% fat (HF) diets containing 2 wt% linoleic acid (LA) and including 0.0, 1.2, 2.4, 4.7, 7.1 or 9.4 wt% dietary fish oil (MaxEPA) has been investigated using the N-nitrosobis(2-oxopropyl)amine (BOP)-hamster model for pancreatic cancer. The number of pancreatic borderline lesions (BLL) was significantly higher (P < 0.05) in the HF groups containing 1.2, 2.4 or 9.4 wt% MaxEPA in comparison with the HF group without MaxEPA. MaxEPA inhibited the metabolism of LA to arachidonic acid (AA) and of AA to prostaglandins (PGs) in both blood plasma and pancreatic microsomes. The pancreatic levels of PGE2 (P < 0.05), 6-keto-PGF1 alpha (P < 0.01) and PGF2 alpha (P < 0.05) decreased significantly with increasing dietary MaxEPA. The levels of PGE2 (P < 0.001), 6-keto-PGF1 alpha (P < 0.05), PGF2 alpha (P < 0.001) and thromboxane (TX) B2 (P < 0.001) in pancreatic adenocarcinomas were higher than in non-tumorous pancreas. The MaxEPA had no significant effect on the BrdU labeling index (LI) in acinar, ductular or centroacinar cells, nor on the LI in BOP-induced pancreatic lesions. It is concluded that (i) dietary fish oil has a slight enhancing effect on BOP-induced pancreatic carcinogenesis in hamsters and (ii) dietary fish oil dose-dependently inhibits the conversion of LA to AA and of AA to certain PGs and (iii) dietary fish oil does not influence the cell proliferation in hamster pancreas.

Effects of long term feeding of raw soya bean flour on virus-induced pancreatic carcinogenesis in guinea fowl.

The effects of a diet enriched with 25% raw soya bean flour (RSF) on the pancreas and on the avian retrovirus Pts 56-induced pancreatic carcinogenesis in guinea fowl were studied. It has been shown that prolonged RSF feeding of new-hatched virus-infected and uninfected guinea fowl-poults induced enlargement of the pancreas, which was less pronounced when administration of the RSF supplemented diet started at the age of 75 days. Time-dependent multifocal inter- and intralobular hyperplasia of pleomorphic ducts lined by mucin-producing epithelium in the exocrine pancreas of virus-infected guinea fowls fed a RSF supplemented diet was regularly observed. Enlargement of virus-induced ductular neoplasms has been shown only after simultaneous RSF and virus administration.

Inhibition of dietary fat promoted development of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters by supplemental selenium and beta-carotene.

The modulating effects of selenium and beta-carotene on the development of putative preneoplastic foci in exocrine pancreas were investigated in rats and hamsters, treated with azaserine and N-nitrosobis(2-oxopropyl)amine (BOP), respectively. The animals were fed a semipurified diet high in saturated fat (20% lard) either supplemented or not with beta-carotene or selenium. A separate group maintained on a diet low in saturated fat (5% lard) was incorporated as an extra control group. The animals were given their diets 12 days after the last treatment with carcinogen. Four months postinitiation, the pancreata were quantitatively examined for the number and size of putative (pre)neoplastic lesions. Rats as well as hamsters maintained on a low-fat diet had significantly less putative preneoplastic pancreatic lesions as compared to animals fed a diet containing 20% lard. Selenium and beta-carotene both inhibited the growth of basophilic foci in rat pancreas. In hamster pancreas, beta-carotene and selenium caused a significant decrease in the number of early ductal complexes. The number of carcinomas was decreased in the beta-carotene group and increased in the group fed a diet high in selenium.

Inhibition of dietary fat-promoted development of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters by supplemental vitamins A, C and E.

The effects of vitamins A, C and E on the development of putative preneoplastic foci in exocrine pancreas were investigated in azaserine-treated rats and N-nitrosobis(2-oxoproypy)amine-treated hamsters. The animals were fed a semipurified diet high in saturated fat (20% lard) either or not supplemented with vitamin A, vitamin C or vitamin E. A separate group maintained on a diet low in saturated fat (5% lard) was incorporated as extra controls. The animals were given their diets 12 days after the last treatment with carcinogen. At 4 months postinitiation, the pancreata were quantitatively examined for both the number and size of early, putative preneoplastic lesions and the presence of neoplastic lesions. Rats as well as hamsters maintained on 5% lard exhibited a significantly lower number of putative preneoplastic pancreatic lesions than animals fed a diet containing 20% lard. Growth of acidophilic but not of basophilic foci was inhibited in rats of the high vitamin A and C group, whereas vitamin E exerted an inhibitory effect on growth of basophilic but not of acidophilic foci. In hamsters maintained on a diet high in vitamins A or C, the number of early ductular lesions was significantly decreased, whereas the number of (micro)carcinomas was increased. Vitamin E did not have any modulating effect on development of ductal lesions in hamster pancreas.

Lack of inhibitory effects of beta-carotene, vitamin C, vitamin E and selenium on development of ductular adenocarcinomas in exocrine pancreas of hamsters.

The effects of vitamins E and E, beta-carotene and selenium on development of N-nitrosobis(2-oxopropyl)amine (BOP)-induced pancreatic tumours in hamsters were investigated. Dietary supplementation of vitamin C, alone as well as in combination with beta-carotene resulted in consistently lower numbers of advanced ductular lesions. The differences with the controls, however, did not reach the level of statistical significance. Beta-Carotene alone demonstrated no inhibitory effect on the development of (pre)neoplastic lesions in the pancreas. Vitamin E or Se, either alone or in combination, had no effect on the development of advanced ductular lesions in BOP-treated hamsters.

Azaserine-induced pancreatic carcinogenesis in rats: promotion by a diet rich in saturated fat and inhibition by a standard laboratory chow.

Dietary fat has been shown to enhance pancreatic carcinogenesis. Uncertainty still exists whether the amount of linoleic acid or the amount of fat is the main determining factor. In the present study the effects of a high lard, a low lard, a linoleic acid supplemented low lard and a laboratory chow diet were investigated on the development of (pre)neoplastic pancreatic lesions in rats treated with azaserine. The rats were killed 15 months after carcinogen treatment and the pancreata were examined for the number and size of putative preneoplastic lesions and for the occurrence of neoplasms. The linoleic acid supplemented low lard group showed a significantly increased number of basophilic foci as compared to the low lard group. Rats maintained on the linoleic acid supplemented diet or the laboratory chow developed significantly less atypical acinar cell nodules larger than 1.0 mm in diameter and adenocarcinomas as compared to the high lard group. Animals maintained on the low lard diet developed significantly less adenocarcinomas than rats on the high lard diet did. Overall, the number of benign and malignant pancreatic tumours was consistently higher in the high lard group and consistently lower in the linoleic acid supplemented low lard group than the number of these types of tumours in the low lard group, with the exception of the number of carcinomas in situ, which was lower in the high lard group. The laboratory chow group showed a significant lower number of atypical acinar cell nodules with a diameter over 1.0 mm and a lower number of adenocarcinomas as compared to both the high lard and the low lard group. It is concluded that a diet high in saturated fat has a promoting and that laboratory chow has an inhibitory effect on pancreatic carcinogenesis in azaserine-treated rats.

Carcinogenicity testing of complete human diets in rats.

So far, in most animal experimental studies isolated food components have been tested. However, as components may interact with each other at different mechanistic levels, testing complex food mixtures more representative for human consumption patterns may better predict the ultimate carcinogenic risk. Studies were performed in Wistar rats using human and rat control diets to assess the effect of relevant food factors such as heat processing and the presence of non-nutrients in vegetables and fruit. The complete human diets, containing meat, bread and eggs, with or without vegetables and fruit, were composed according to mean consumption figures, balanced for macro- and micronutrients. Experiments were performed with spontaneous as well as with chemical-induced tumor models. Heat processing had no effect on tumor induction, while vegetables and fruit only exerted a protective effect on chemically induced tumors in rats fed low-fat animal diets. Data suggest interaction between major food factors in the human diet on colon carcinogenesis.

Nasal tumours in rats after short-term exposure to a cytotoxic concentration of formaldehyde.

Male Wistar rats were exposed to 0, 10 or 20 ppm formaldehyde vapour for 4, 8 or 13 weeks (6 h/day; 5 days/week), and were then observed for periods up to 126 weeks. Transient growth retardation occurred in both test groups. Death rate was not noticeably affected by formaldehyde. Despite recovery periods of at most 126 weeks, the nasal respiratory and olfactory epithelium of many rats of the 20 ppm group exhibited non-neoplastic histopathological changes. Similar but much less severe changes of the respiratory epithelium were seen in a small number of rats of the 10 ppm group; the olfactory epithelium was not visibly affected in rats of this group. Nasal tumours considered to be induced by formaldehyde were seen only in the 20 ppm group and mainly in rats that had been exposed for 13 weeks, the incidence being 4.5% (6/132). These tumours comprised 3 squamous cell carcinomas, 1 carcinoma in situ and 2 polypoid adenomas, all originating from respiratory epithelium. It was concluded that rat nasal respiratory epithelium severely damaged by formaldehyde vapour often does not regenerate and in some cases develops tumours.

Effects of bombesin on the development of N-nitrosobis(2-oxopropyl)amine-induced pancreatic lesions in hamsters.

Bombesin (BBS) has been shown to promote pancreatic growth as well as the development of pancreatic (pre)neoplasia in rats. The present study was carried out to determine the effects of bombesin on pancreatic growth and on the development of pancreatic (pre)neoplastic lesions in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Bombesin caused an increase in growth of the pancreas accompanied by a decrease in the number of (pre)neoplastic ductular pancreatic lesions. Lorglumide (CR-1409) did not influence these effects of bombesin. It is concluded that in BOP-treated hamsters the effect of bombesin on the pancreas is not mediated by cholecystokinin (CCK). These data support the existence of species difference between rats and hamsters with regard to the effect of bombesin on pancreatic carcinogenesis.

Effects of the synthetic trypsin inhibitor camostate on the development of N-nitrosobis(2-oxopropyl)amine-induced pancreatic lesions in hamsters.

Trypsin inhibitors have been shown to promote pancreatic growth as well as the development of pancreatic tumours in rats. The present study was carried out to examine the effects of the synthetic trypsin inhibitor camostate on the growth of the pancreas and on the development of pancreatic preneoplastic and neoplastic lesions in hamsters treated with N-nitrosobis(2-oxopropyl)amine. A specific cholecystokinin-receptor antagonist was administered to determine the role of cholecystokinin in camostate action. The animals were killed 19 weeks after the first injection with N-nitrosobis(2-oxopropyl)amine. Camostate caused an increase in growth of the pancreas and a decrease in the number of (pre)neoplastic ductular pancreatic lesions. Lorglumide (CR-1409) did not influence these effects of camostate. It was concluded that rats and hamsters behave differently with regard to the effect of camostate on pancreatic growth and carcinogenesis.

Upper respiratory tract tumors in Cpb:WU (Wistar random) rats.

A survey is given of upper respiratory tract tumors in Cpb:WU (Wistar random) rats. Data were collected from ten 24- to 30-month toxicity/carcinogenicity studies and from one 12-month study. Nasal tumors may lead to dyspnea, mouth breathing, and nasal discharge. These clinical signs mainly occurred in rats bearing squamous cell carcinomas. The large nasal tumors were often osteolytic, they invaded the subcutis over the premaxilla, resulting in swellings on the back of the nose, and extended into the brain. The incidence of nasal tumors in untreated male controls was 1.1% (7/661), the tumors invariably being squamous cell carcinomas. There were no nasal tumors found in untreated female controls. The type of compound-induced nasal tumor most frequently observed was adenocarcinoma (of the olfactory epithelium) followed, in order of decreasing incidence, by squamous cell carcinoma, carcinoma in situ, polypoid adenoma, Schwannoma, and carcinosarcoma. It was proposed that adenocarcinomas of the olfactory epithelium should be classified as neuroepitheliomas. It was also suggested that squamous cell carcinomas, seen in association with necrotizing inflammation of an incisor tooth, should be considered as part of the malocclusion syndrome. No spontaneous tracheal tumors were observed, and only one out of 422 untreated female controls (0.2%) was seen to have a laryngeal tumor, an adenoma. Induced laryngeal tumors included carcinoma in situ, squamous cell carcinoma, and adenocarcinoma. Squamous cell carcinoma was the only type of treatment-related tracheal tumor found. The incidences of induced laryngeal and tracheal tumors were very low, and in no case were these tumors statistically significantly different from the respective incidences in controls.

Long-term persistence of DNA alkylation in hamster tissues after N-nitrosobis(2-oxopropyl)amine.

The persistence of 7- and O6-alkylation of guanine in DNA of cell nuclei of male Syrian hamster pancreas, liver, kidneys, lungs [target tissues of N-nitrosobis(2-oxopropyl)amine (BOP)] and salivary glands (nontarget tissue) was studied immunocytochemically 6 h, 1, 3, 7, 14, 28, and 56 days after a single s.c. injection of 20 mg BOP/kg. Conventional antisera raised against O6-methylguanine and imidazole-ring-opened 7-methyl-guanine were used. Persistent alkyl-specific staining was observed for up to 7 days (7-alkylguanine) or 56 days (O6-alkylguanine) in inter- and intralobular duct cells and centro-acinar cells of the pancreas, periportal hepatocytes and bile duct cells of the liver, cells of the proximal convoluted tubules of the renal cortex, and bronchiolar Clara and alveolar cells in the lungs. Both adducts disappeared from centrilobular liver cells within 1 day, from pancreatic acinar cells within 3 days, and from ducts and acini of the submandibular salivary glands within 14 days after BOP treatment. A high level of persistent O6-alkylation of guanine was related with a high tumor incidence only in case of the ductal/ductular system of the pancreas, the main target tissue of BOP-induced carcinogenesis. The relatively weak carcinogenicity of BOP in other tissues with long-term persistence of O6-alkylguanine in DNA indicates that the formation and persistence of DNA alkylation are not sufficient to account for the carcinogenic organotropism of BOP. Additional factors, such as cell proliferation, appropriate promoting stimuli and the (onco)genes critically involved, may be as important as the modification of DNA.

Cholecystokinin and gastrointestinal cancer.

The gut hormone cholecystokinin exerts various actions on the gastrointestinal tract, including the regulation of growth. The hormone has been reported to induce hypertrophy and hyperplasia of the pancreas and to enhance chemically-induced pancreatic carcinogenesis in animals. Stimulation of endogenous cholecystokinin secretion through the induction of deficiency of intraintestinal proteases and bile salts by trypsin-inhibiting nutrients, bile salt-binding drugs or surgical intervention is also capable of stimulating growth and tumour development in the rat. In man, factors suggested to increase the risk of pancreatic cancer, such as a high-fat and high-protein diet or gastrectomy, are known to stimulate plasma cholecystokinin secretion. Receptors for cholecystokinin have been demonstrated on human pancreatic adenocarcinomas, and cholecystokinin has been demonstrated to enhance the growth of xenografted pancreatic cancer and to inhibit growth of gastric and bile duct cancer. The recently developed cholecystokinin-receptor antagonists inhibit not only pancreatic growth but also pancreatic carcinogenesis in animals. These new drugs may be valuable new tools for inhibiting pancreatic cancer growth in humans.

Study into the role of cholecystokinin in bombesin-stimulated pancreatic growth in rats and hamsters.

The effects of cholecystokinin and bombesin on growth of the exocrine pancreas have been studied extensively in rats but not in hamsters. Since hamsters are frequently used for studying pancreatic carcinogenesis it seems highly relevant to determine the effects of these peptides on growth of the hamster pancreas as well. In order to determine whether or not bombesin stimulates pancreatic growth in hamsters and to investigate the role of cholecystokinin in mediating this effect, we conducted a 2-week experiment in which cholecystokinin and bombesin were administered to both rats and hamsters, either with or without lorglumide (CR-1409; a specific cholecystokinin receptor antagonist). Rats were included in the study for comparison. Cholecystokinin and bombesin were found to stimulate pancreatic growth and DNA synthesis in both species. Lorglumide did not significantly influence the effect of bombesin on pancreatic weight but did significantly inhibit DNA synthesis in both species. The effect of cholecystokinin on pancreatic weight was greater in hamsters than in rats. This effect was significantly inhibited by lorglumide in hamsters but not in rats, whereas a significant decrease in DNA content was attained in both species. Thus, this study shows marked differences between rats and hamsters in the pancreatic growth response to cholecystokinin and bombesin.

Inhalation toxicity of acetaldehyde in rats. IV. Progression and regression of nasal lesions after discontinuation of exposure.

As part of a long-term inhalation toxicity study with acetaldehyde in rats, progression and regression of nasal lesions were studied in animals exposed to 0, 750, 1500 and 3000/1500 ppm of the test compound for 52 weeks and killed after recovery periods of 26 or 52 weeks. Major compound-related nasal lesions found at the end of the exposure period comprised: (a) thinning of the olfactory epithelium with loss of sensory and sustentacular cells at all concentrations; this condition was accompanied by focal basal cell hyperplasia in low- and mid-concentration animals; (b) hyper- and metaplasia of the respiratory epithelium frequently accompanied by keratinisation and occasionally by proliferations of atypical basal cells in the top-concentration group; and (c) rhinitis in several top-concentration rats. There was strong evidence on the one hand that the hyper- and metaplastic changes found in the respiratory epithelium and the basal cell hyperplasia seen in the olfactory epithelium after 52 weeks of exposure may progress to neoplasms despite discontinuation of the treatment. On the other hand these hyper- and metaplastic changes may regress during the recovery period. Regeneration of the olfactory epithelium was evident in several low- and mid-concentration animals, but not in top-concentration rats. The regenerated epithelium was seen as a layer of stratified undifferentiated epithelium containing small nerve bundles, tiny groups of sensory cells, and groups of epithelial cells resembling acinar cells of the glands of Bowman. Furthermore, replacement of olfactory epithelium by respiratory epithelium was a frequent finding. It was concluded that rat olfactory epithelium severely damaged by acetaldehyde may regenerate, most probably from basal cells, provided the olfactory epithelium has not been fully destroyed.

Inhalation toxicity of acetaldehyde in rats. I. Acute and subacute studies.

The 4-h LC50 of acetaldehyde in rats was determined and found to be 13,300 ppm (24.0 g/m3 air). In a 4-week study groups of 10 male and 10 female rats were exposed to 0, 400, 1000, 2200 or 5000 ppm acetaldehyde for 6 h/day, 5 days/week. Treatment-related changes observed at the 5000 ppm level included dyspnoea and excitation during the first 30 min of each exposure, yellow-brown fur, severe growth retardation, more neutrophils and less lymphocytes in the blood, a reduced production of urine with a high density, increased lung weights, and severe degenerative, hyperplastic and metaplastic changes of the nasal, laryngeal and tracheal epithelium. Major lesions seen at 1000 and 2200 ppm comprised growth retardation and an increased production of urine in males, slight to moderate degeneration with or without hyper- and metaplasia of the nasal epithelium, and only at 2200 ppm, minimal epithelial changes in the larynx and trachea. The only change observed at the 400 ppm level that could be attributed to acetaldehyde was slight degeneration of the nasal olfactory epithelium seen as loss of microvilli and thinning and disarrangement of the layer of epithelial cells.