Subchronic toxicity study of dietary N-acetylglucosamine in F344 rats.

A subchronic toxicity study of N-acetylglucosamine (GlcNAc), a monomeric form of chitin, was conducted in groups of 10 male and 10 female F344 rats fed pelleted diets containing 0, 0.625, 1.25, 2.5 or 5% concentrations for 13 weeks. All animals survived until the end of the experiment. Slight, non-significant increase in body weights was observed in males receiving 0.625, 1.25 or 2.5% from week 4 until the end of the experiment, when significant elevation was found for the males receiving 0.625, 1.25 or 2.5% at the terminal sacrifice to result in decreased relative weights of many organs in these cases. However, there were no obvious indications of toxicity in any group receiving GlcNAc in terms of clinical signs, food intake, hematology, serum biochemistry, and histopathological findings. Thus, it was concluded that orally administered GlcNAc exerts no obvious toxicity to F344 rats at concentrations up to 5% in the diet for 13 weeks. Based on the present toxicity data, > or =5% was determined to be a no-observed-adverse-effect level, translated into 2476 and 2834 mg/kg/day for male and female rats, respectively.     

Subchronic toxicity study of water pepper extract in F344 rats.

A subchronic toxicity study of water pepper extract (WPE) from Polygonum hydropiper L. was conducted in groups of 10 male and 10 female F344 rats fed powdered diets containing 0, 62.5, 250, 1000 or 4000 ppm concentrations for 13 weeks. Suppression of body weight gain due to decreased food consumption was observed in both sexes at 4000 ppm, and at autopsy, increase of relative weights was observed for the brain, liver, spleen, kidneys, and testes in these animals, suggestive of the reflection of the reduced body weights. At this dose, slight increases of blood urea nitrogen in both sexes and serum alanine aminotransferase, Na and Cl in females, were observed, suggestive of weak hepatic and renal toxicity, at least in females. The same females also exhibited slight decrease of red blood cells and haematocrit, slight increase of mean corpuscular volume and mean corpuscular haemoglobin, and minimal increase of splenic haemosiderin deposition, providing evidence of slight haemolytic anemia. On the other hand, enhanced accumulation of mast cells was observed in the mesenteric lymph nodes at 4000 ppm in males and 1000 and 4000 ppm in females. Considering the anti-anaphylactic properties of polygodial, a major constituent of WPE, the mast cell accumulation was concluded to be an adaptive change in response to the subchronic oral administration of WPE. Based on the present toxicity data, 1000 ppm was determined to be the no-observed-adverse-effect level, translating into 57.4 and 62.9 mg/kg/day for male and female rats, respectively.     

Subchronic toxicity study of gallic acid by oral administration in F344 rats.

Subchronic toxicity of gallic acid (GA) was investigated in F344 rats by feeding diet containing 0, 0.2, 0.6, 1.7 and 5% GA for 13 weeks. Each group consisted of 10 rats of each sex. Toxicological parameters included clinical signs, body weight, food consumption, hematology, blood biochemistry, organ weights and histopathological assessment. Body weight gain in the 5% GA-treated animals of both sexes from week 1 to the end of the experiment was significantly lower than that of the untreated controls. Toxic effects following administration of 0.6% or more in males and 5% in females included reduction of hemoglobin concentration, hematocrit and red blood cell counts and increase in reticulocytes. Histopathologically, extramedullary hematopoiesis, hemosiderin deposition and congestion appeared in the spleens of 5% GA-treated animals, suggesting development of hemolytic anemia. In addition, centrilobular liver cell hypertrophy, reflected in increase in liver weight, was observed in animals of both sexes from 1.7%. In the kidney, Berlin blue-negative brown pigment deposition in the proximal tubular epithelium was observed at 5% GA. However, the severity of these pathological changes was weak. Based on the present toxicology data, 0.2% was determined to be a no-observed-adverse-effect level (NOAEL) in rats. This level was translated into 119 and 128 mg/kg/day, respectively for male and female rats.     

Subchronic toxicity of trinitrotoluene in Fischer 344 rats rats

This study was conducted to evaluate the toxicity of trinitrotoluene (TNT) in Fischer 344 rats when administered in the diet for 13 weeks. Groups of 10 rats per sex received TNT at doses of 1, 5, 25, 125 or 300 mg/kg/day. Thirty rats per sex served as untreated controls. Toxicologic endpoints included clinical signs, body weight, food consumption, hematology, clinical biochemistry, organ weights and gross/histopathology. Toxic effects following 125 mg/kg/day or greater included decreased food intake and body weight gain, elevated serum cholesterol levels, and anemia (reduced hemoglobin, hematocrit and RBC counts). Splenomegaly, hepatomegaly/hepatocytomegaly and testicular atrophy with degeneration of the seminiferous tubular epithelium were also seen at 125 and 300 mg/kg/day. Hemosiderin-laden macrophages, congestion of the splenic red pulp, methemoglobin production indicative of the oxidizing activity of TNT and/or its metabolites, and the lack of bone marrow toxicity suggested hemolysis as the mechanism of anemia.     

Toxicity and carcinogenicity studies of Caramel Colour IV in F344 rats and B6C3F1 mice.

Caramel Colour IV, a type of caramel colour used in the manufacture of cola soft drinks, was evaluated for subchronic and chronic toxicity in rats, and carcinogenicity in Fischer-344 (F344) rats and B6C3F1 mice. In each of the studies, Caramel Colour IV was mixed with demineralized water and the solutions given to the animals ad lib. in the drinking fluid. The concentrations of Caramel Colour IV in the drinking fluid were adjusted periodically to achieve the desired caramel colour intake per kg body weight. In the range-finding studies, groups of 30 rats/sex were given Caramel Colour IV at levels of 0, 15, 20, 25 or 30 g/kg for 13 wk, and groups of 10 male rats were given levels of 0, 2.5, 5, 10 or 15 g/kg for 6 wk followed, for some dose groups, by a 2-wk withdrawal period, and then re-initiation of dosing for another 2 wk. In the rat chronic toxicity study, levels of Caramel Colour IV of 0, 2.5, 5, 7.5 or 10 g/kg were given to groups of 25 rats/sex for 12 months. The test groups in the rat and mouse carcinogenicity studies were composed of 50 animals/sex and each species was given the caramel colour at levels of 0, 0, 2.5, 5 or 10 g/kg for 24 months. In each of the studies, treated animals tended to have dose-related lower water consumption than controls. This was attributed to poor palatability of the drinking fluid, and was generally associated with decreased food consumption and body weights. Rats given caramel colour often had soft or liquid malodorous faeces although there were no treatment-related ante-mortem observations in mice. Blood biochemical changes in the rat (i.e. reduced blood urea nitrogen, alkaline phosphatase and total serum protein) appeared to be related to dietary influences and were not considered toxicologically significant. There were no treatment-related alterations in haematological variables or treatment-related differences in survival or in the incidence of benign or malignant tumours among treated and control groups and no toxicologically important pathological findings. On the basis of these studies, Caramel Colour IV was not toxic or carcinogenic in F344 rats or B6C3F1 mice. The highest dose level tested in the long-term studies (10 g/kg) was considered to be the no-observed-adverse-effect level (NOAEL).     

Toxicity studies of Caramel Colour III and 2-acetyl-4(5)-tetrahydroxybutylimidazole in F344 rats.

Caramel Colour III is used as a colour additive in beers and a variety of foods. Beer is the most important single source of Caramel Colour III in the diet although consumption of dark beers has been decreasing in recent years. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has established an acceptable daily intake of 200 mg/kg/day for Caramel Colour III. The safety of Caramel Colour III has been questioned during recent years following feeding studies in the rat that were associated with reduced white cell and lymphocyte counts. These effects have been attributed to the presence of 2-acetyl-4(5)-tetrahydroxybutylimidazole (THI) in this class of caramel colour. Short-term oral toxicity studies were conducted on low-THI and high-THI samples of Caramel Colour III (13 wk) and on a sample of THI (28 days). In both studies, the test materials were mixed with demineralized water and the solutions were given to the animals ad lib. in the drinking fluid. In the 13-wk subchronic toxicity study of Caramel Colour III, groups of 20 rats/sex were given concentrations of caramel colour equivalent to intakes of 0, 10, 15 or 20 g low-THI caramel colour/kg body weight/day or 20 g/kg of a high-THI caramel colour. In the 4-wk toxicity study with THI, groups of 20 rats/sex were given 0, 8 or 64 ppm THI (equivalent to approx. 0, 0.9 or 7.2 mg/kg/day) and 10 rats/sex were given 1, 2, 4, 16 or 32 ppm THI (equivalent to approx. 0.1, 0.2, 0.5, 1.9 or 3.7 mg/kg/day) for 4 wk followed by a 2-wk recovery phase for 10 rats/sex in the 0, 8 and 64 ppm groups. Rats given Caramel Colour III had soft faeces; there were no other treatment-related clinical observations and no treatment-related deaths occurred. All treated groups given Caramel Colour III had lower food and fluid consumption than controls. Males given 15 or 20 g low-THI caramel colour/kg or 20 g high-THI caramel colour/kg and females given 20 g/kg of either type had lower body weights than controls. In the 4-wk toxicity study with THI, there were no treatment-related ante-mortem observations, and no effects on body weights or food consumption. Fluid consumption by males and females treated with 64 ppm THI was lower than that of controls.(ABSTRACT TRUNCATED AT 400 WORDS)     

A chronic toxicity study of josamycin in F344 rats.

The chronic toxicity of josamycin was examined in Fischer 344 (F344) rats. Groups of 10 males and 10 females were given the test compound in the diet at concentrations of 0 (control), 0.02, 0.1, 0.5 or 2.5% for 52 weeks. Daily intake of josamycin was 0, 10, 50, 260 and 1310 mg/kg body weight in males and 0, 10, 60, 290 and 1460 mg/kg body weight in females, respectively. Body weight gain was significantly (P<0.05) reduced in the male 2.5% group but no noticeable changes were found in food intake. In hematological examination, the platelet count was significantly (P<0.01) lower in the male groups given 0.02% or more of josamycin and in the 2.5% female group as compared with the control group values in a dose-dependent manner. In serum biochemical examination, blood urea nitrogen was significantly (P<0.05 and P<0.01, respectively) higher in males given 0.5 and 2.5% and total bilirubin was significantly (P<0.05) higher in females receiving 2.5% as compared with those of the control group. No death occurred at any dose levels during the dosing period. At necropsy, with the exception of cecal enlargement in the groups given more than 0.1% josamysin and a significant (P<0.01) increase in the relative liver weight of females in the 2.5% group, no particular findings related to the administration were observed. Histopathologically, the incidence and severity of liver bile duct proliferation in female 2.5% group were significantly (P<0.01) greater than those of the control group. Other histological changes found in the treated and control groups were similar to the spontaneous lesions in this strain of rats in terms of the incidence and severity. Interestingly, the josamycin treatment reduced the development of altered liver cell foci in females in a dose-dependent manner. Thus, it is concluded that, under the present experimental conditions, josamycin induces bile duct proliferation in female F344 rats at a high dose of 1460 mg/kg body weight. Based on the decrease of platelet count found in males given 10 mg/kg body weight or more, the no-observed-adverse-effect level (NOAEL) was estimated to be less than 10 mg/kg body weight.     

A subchronic toxicity study of dunaliella carotene in F344 rats.

Dunaliella carotene, extracted from dunaliella alga (Dunaliella bardawil or Dunaliella salina), for use as a food-coloring agent, has beta-carotene as its mainly constituent. As there have been no reports of toxicological evaluation, a 90-day subchronic toxicity study was here performed in F344 rats at dose levels of 0 (control), 0.63%, 1.25%, 2.5% and 5% in powdered basal diet. The average daily intakes of dunaliella carotene were 352, 696, 1420 and 2750 mg/kg/day, respectively, for males, and 370, 748, 1444 and 2879 mg/kg/day for females. No mortality or treatment-related clinical signs were observed throughout the experimental period in any of the groups. Body weight gain was slightly but significantly (p < 0.05) reduced from week 5 to the end of the experiment in 2.5% and 5% males. Increased PLT were observed in 1.25% and 5% males, and 2.5% and 5% females. Significant elevations or tendencies for increase in serum T. Cho and Ca were observed in all treated males and females, with clear dose-dependence in males. Organ weight measurement and histopathological observation revealed no toxicological changes. Based on growth suppression, no-observed-adverse-effect-levels (NOAELs) were estimated to be 1.25% (696 mg/kg/day) for males and 5% (2879 mg/kg/day) for females. As increases in serum Ca were observed in the lowest group in both sexes, a no-observed-effect level (NOEL) could not be determined in this study.     

Subchronic inhalation study of 1-hexene in Fischer 344 rats.

The objective of this study was to evaluate the toxicity of 1-hexene following repeated inhalation exposures in male and female Fischer 344 rats. Groups of 40 male and 40 female rats were exposed for 6 hours per day, 5 days per week, over a 13-week period. Treatment groups consisted of air-exposed control (0 ppm) and three test groups of 300, 1000, and 3000 ppm 1-hexene. During the treatment period, the rats were observed daily for clinical signs of toxicity; body weights and neuromuscular coordination [females only] were measured at 7-day intervals. After 7 weeks of exposure and at the end of the treatment period, the rats were subject to macroscopic and microscopic pathology, clinical chemistry, hematology, urinalysis, and sperm counts. No mortalities were observed during the course of the study. No clinical signs of toxicity attributable to 1-hexene exposure were observed. Female rats exposed to 3000 ppm had significantly lower body weights compared to control rats from exposure day 5 persisting throughout the treatment period. Male rats exposed to 3000 ppm had slightly but not statistically significant lower body weights in comparison to controls. Male rats exhibited slightly increased absolute and relative testicular weights, and female rats had slightly decreased absolute [but not relative] liver and kidney weights, at 3000 ppm. There were no gross or microscopic morphological findings attributed to treatment. Exposure to 1-hexene did not affect neuromuscular coordination in females as determined using the Rotarod, nor sperm counts in male rats. Several statistically significant effects in hematology, clinical chemistry, and urinalysis evaluations were observed, but were either of small magnitude or did not correlate with histopathological findings, and thus did not appear to be of biological significance. In summary, the no-adverse-effect-level for this study was determined to be 1000 ppm, based on decreased weight gain in female rats, and on slight organ weight changes in both sexes at 3000 ppm.     

Sub-acute toxicity of piperonyl butoxide in F344 rats.

Piperonyl butoxide, alpha-[2-(2-Butoxyethoxy)ethoxy]-4,5-methylenedioxy- 2-propyltoluene, is a pesticide synergist. F344 rats of both sex were maintained on diets containing 0, 0.6, 1.2 or 2.4% of piperonyl butoxide for 13 weeks. At the end of experimental period, they were necropsied. Selected organs were weighted and serum was analyzed by clinical chemistry. In male and female rats of the 2.4%-group, body weight gains were depressed, macroscopically, hepatomegaly was marked and liver weights were significantly higher than those of the control group. In male and female rats of all treated groups, relative kidney weights were significantly increased in a dose-dependent manner. Rats of the 2.4%-group had increased levels of albumin, cholesterol, urea nitrogen and gamma-glutamyl transpeptidase. Examination of livers of the male 2.4%-group by light microscopy showed enlarged hepatocytes with glassy cytoplasm and fatty deposition. On occasion, there was coagulative necrosis of a few hepatocytes in the periportal area and oval cell proliferation. The kidney of treated rats showed atrophy of epithelium in the proximal convoluted tubules. These results indicated that toxicity of piperonyl butoxide in rats was directed primarily to the liver and kidney.     

Subchronic toxicity study of peppermint oil in rats.

Peppermint oil was given p.o. to four groups of 28 rats at dosage levels of 0, 10, 40, and 100 mg/kg body wt. per day for 90 days. At the highest dose histopathological changes consisting of cyst-like spaces scattered in the white matter of cerebellum were seen. No other signs of encephalopathy were observed. Nephropathy was seen in the male rats in the highest dose group. A no-observed-adverse-effect level of 40 mg/kg body wt. per day was determined.     

A 13-week subchronic toxicity study of paprika color in F344 rats.

The fruit of the paprika (Capsicum annuum) has been widely used in various countries as a spice and food-coloring additive. As a part of the safety assessment of paprika color (Paprika oleoresin), a 13-week subchronic toxicity study was performed in F344 rats. To establish a no-observed-adverse-effect level (NOAEL) for application in subsequent long-term studies, rats were fed powder diet containing paprika color at dose levels of 0 (basal diet), 0.62, 1.25, 2.5 and 5% (maximum) for 13 weeks. During the experiment, there were no remarkable changes in general appearance and no deaths occurred in any experimental group. Although serum total cholesterol was dose-dependently increased in both sexes, no related histopathological changes were observed in the liver. Slight inflammatory cell infiltration in the myocardium and vacuolation of hepatocytes were noted in both control and paprika color-treated animals, but there were no clear differences between groups. In conclusion, paprika color even at 5% in the diet (0.67 g/rat/day or 2948.4 mg/kg bw/day for male rats and 0.43 g/rat/day or 3197.4 mg/kg bw/day for female rats) did not cause remarkable adverse effects in F344 rats. Thus, the NOAEL and the maximum dose level for carcinogenicity testing of paprika color were concluded to be 5% in the diet.     

A 13-week subchronic toxicity study of madder color in F344 rats.

A 13-week repeated oral dose toxicity study of madder color (MC), a natural food colorant extracted from the roots of Rubia tinctorum L., was performed using F344 rats. Five groups of animals, each consisting of 10 males and 10 females, were fed diet containing 0, 0.6, 1.2, 2.5 or 5.0% MC for 13 weeks. During the experiment, lower body weight was evident from the 2.5% dose. Hematologically, fluctuation in red blood cell (RBC) parameters suggestive of weak anemia (females), and slight increases of platelet counts (both sexes) and white blood cell (WBC) counts (males) were observed at higher doses. Serum biochemically, slight fluctuations were observed in many parameters, including increased total protein (TP), conjugated bilirubin, Ca, and inorganic phosphate, and decrease of the albumin/globulin (A/G) ratio in both sexes, with dose-dependence for TP and A/G from 0.6% in females. Histopathological changes were mainly observed in the renal proximal tubules, such as microvesicular vacuolar degeneration in the cortex and karyomegaly in the outer medulla involving both sexes, lesions being evident even with 0.6%. In the outer medulla, elevation of cell proliferation activity as assessed with proliferating cell nuclear antigen was observed in males from 2.5%. Severity of focal necrosis of hepatocytes was increased only in females at 5.0%, while the increased relative liver weight as with the increased conjugated bilirubin was evident in both sexes from 1.2%. The results thus suggest that MC exerts mild toxicity, targeting liver, kidneys, and possibly RBCs and WBCs, some renal changes being evident from 0.6% in diet, that is attributable to be the lowest-observed adverse effect level (305.8-309.2mg/kg body weight/day).     

Long-term toxicity/carcinogenicity study of calcium lactate in F344 rats

The long-term toxicity/carcinogenicity of calcium lactate, a food additive, was examined in F344 rats. Calcium lactate was given ad lib. in the drinking-water at levels of 0, 2.5 or 5% to groups of 50 male and 50 female rats for two years. No clear toxic lesion was specifically caused by long-term administration of calcium lactate. No significant dose-related increase was found in the incidences of tumours in any organ or tissue. The results indicated that calcium lactate had neither toxic nor carcinogenic activity in F344 rats.     

Subchronic oral toxicity study with cyadox in Wistar rats.

To investigate the potential subchronic toxicity of cyadox, groups of 15 male and 15 female Wistar rats were fed with diets containing cyadox (0, 50, 150 or 2500 mg/kg) or olaquindox (150 mg/kg), approximately equivalent to cyadox 5, 15, 250 or olaquindox 15 mg/kg b.w./day, for 13 weeks. Five rats/sex/group were sacrificed on days 30, 60 and 90. No test-material-related changes were seen in mortality, clinical signs, hematology, clinical chemistry, organ weight data and macroscopic examinations. Except that body weights of both sexes of the 2500 mg/kg cyadox group were significantly lower than controls beginning after the second week of treatment. Body weights of females of 150 mg/kg olaquindox group were significantly lower than those of the control group at weeks 3 and 4. Other groups were unaffected by treatments. Histopathological observations revealed that 2500 mg/kg cyadox or 150 mg/kg olaquindox induced swelling and fatty degeneration of the hepatocytes and proximal renal tubular epithelial cells. It was for the first time that changes were found in the liver and kidneys of rats fed 2500 mg/kg cyadox. The no-observed-adverse-effect level (NOAEL) of cyadox for rats was estimated to be 150 mg/kg dietary dose level.     

A 90-day ad libitum administration toxicity study of oligoglucosamine in F344 rats.

A 90-day ad libitum administration toxicity study of oligoglucosamine (OG) was carried out using F344 rats of both sexes. The animals were divided into four groups of 20 animals each, 10 of each sex, and fed a diet containing 0, 0.04, 0.2 or 1.0 (w/w)% OG. During the administration period, no animals of either sex died or exhibited abnormal signs in the 0.04% OG and 0.2% OG groups. In the 1% OG group, in both sexes, erythema and swelling of the snout and forelimbs and loss of fur in the forelimbs were observed. On macroscopic observation, emaciation, swelling of the snout, auricles and forelimbs and alopecia of the forelimbs were also observed in 2-3 males of the 1% OG group. It was suggested that these topical abnormalities might be due to dermal responses to OG adhering to the skin and fur, which are easily soiled with saliva during grooming. In the animals of the 1% OG group, food consumption decreased, resulting in body weight gain being suppressed. This was found concomitantly with the abnormal findings mentioned above. Thus, feeding difficulties due to the topical lesions on the snout and forelimbs were thought to affect body weight. In hematology, platelet count, lymphocyte count and differential neutrophil count increased in males of the 1% OG group. These changes might be related to the dermal inflammation. Abnormalities in urinalysis and blood chemistry, as well as a small thymus, small spleen, dark spots or areas on the glandular stomach mucosa, pale Harderian glands and small testes in histopathology, were also observed in males in the 1% OG group. Whether or not all these changes were related only to the malnutrition remains to be elucidated. From these results, OG gave rise to no adverse effects in rats up to the dose level of 0.2 (w/w)%. Thus, the no observed adverse effect level was determined to be 0.2 (w/w)% for rats of either sex (124.0mg/kg/day in males, 142.0mg/kg/day in females).     

A 13-week subchronic toxicity study of dietary administered morin in F344 rats.

A subchronic toxicity study of a flavonoid morin was performed in both sexes of F344 rats with dietary administration at concentrations of 0%, 0.625%, 1.25%, 2.5% and 5% (w/w) for 13 weeks. No mortality or abnormal clinical signs were observed throughout the experimental period in any group. Although a slight tendency for increase in food intake was noted in both sexes of the 2.5% and 5.0% groups, slight non-significant body weight decrease was observed in 5.0% males. Significant increases in alanine transaminase (ALT; over 2.5%), alkali phosphatase (ALP; 1.25% and 5.0%) and relative liver weights (1.25% and 2.5%) in males and in gamma-glutamyl transpeptidase (gamma-GT), aspartate transaminase (AST), ALT, relative liver weights in the 2.5% and 5.0% females and ALP in 5.0% females were noted. Increased urea nitrogen and relative kidney weights at dose of 1.25% and above and creatinine at 5.0% were observed also in females. On histopathological observation, hepatocyte hypertrophy was detected in 3 of 10 5.0% females. Based on the above findings, the no-observed-adverse-effect level (NOAEL) for both sexes was estimated to be 0.625% (299 and 356 mg/kg b.w./day for males and females, respectively).     

Subchronic oral toxicity study of gamma-glycidoxypropyltrimethoxysilane in rats

The subchronic toxicity (28 days) of orally administered gamma-Glycidoxypropyltrimethoxysilane (GPTS) was studied in laboratory rats. The test material was administered daily for four weeks to groups of 10 male and 10 female Sprague-Dawley rats by gavage at dose levels of 0, 40, 400, and 1,000 mg/kg. Mortality, behavioral reactions, growth and food consumption were observed and measured along with hematology, blood biochemistry, absolute and relative organ weights. No overt signs of toxicity or behavioral abnormalities were observed in any of the test animals during the course of the study. There were no treatment related mortalities and no significant differences were observed in mean body weight, food consumption, absolute or relative organ weights of control and treated rats. Also, there were no meaningful differences in hematology, urinalysis or clinical blood chemistry values between control and treated animals. Gross and histopathologic examinations of organs or tissues from both control and GPTS treated animals did not reveal any treatment related changes. These results suggest that it is unlikely that serious injury would result from the ingestion of GPTS in amounts normally encountered incidental to its industrial use.     

Carcinogenicity study of gamma-oryzanol in F344 rats.

The carcinogenic potential of gamma-oryzanol, a drug mainly used for the treatment of hyperlipidaemia, was studied in F344 rats. Groups of 50 males and 50 females were fed a diet containing 0 (control), 200, 600 or 2000 mg gamma-oryzanol/kg body weight/day for 2 yr. Although females in the highest dose group (2000 mg/kg body weight) showed a slight decrease in body weight at 104 wk, there were no treatment-related changes in general condition, food consumption, mortality, organ weight or haematology. Histopathological examination showed various tumours in all groups, including the control group. In the control and 2000-mg/kg groups, high tumour incidences were observed in the testes, pituitary and thyroid of males, and in the pituitary, uterus and mammary gland of females; however, there was no significant increase in the incidence of any tumours between the control and the 2000-mg/kg groups. The findings indicate that under the experimental conditions described gamma-oryzanol was not carcinogenic in F344 rats.