The production of DNA adducts, O⁶-methyldeoxyguanosine (O⁶-medG) and N7-methyldeoxyguanosine (N7-medG), was examined in various organs of rats administrated N-methyl-N-nitrosourea (MNU) using an immunohistochemical approach. Fisher 344 rats divided into 4 groups were treated with alkylating agents. Animals in groups I and 2 were administered MNU (20mg/kg) intragastrically and intraperitoneally, respectively. Animals in group 3 were administered dimethylnitrosamine (DMN) (60mg/kg, i.p.) as a positive control and group 4 was maintained as a negative control group. At 10 hours after the carcinogen administration, rats were killed under ether anesthesia and the liver, stomach, and esophagus were removed from each. In the animals treated with MNU i.g., N7-medG positive nuclei were found in forestomach, glandular stomach, liver, and esophagus while only the liver and forestomach were positive after the i.p. treatment. O⁶-medG positive cells were not detected in any organs of animals receiving MNU (i.g. or i.p.). In the livers of animals treated with DMN, nuclei of hepatocytes were strongly stained with antibodies to both 06-and N7-modG. In the control group no O⁶-or N7-medG positive cells were detected in any of the organs.

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X-ray induction of tumors were examined in five-week-old male CD(SD) : Crj rats, treated with two 10 Gy doses to the gastric region with a 3-day interval (total 20 Gy). After irradiation, the rats received a 1% NaCI supplement in the diet and survivors were killed 22 months after the first X-irradiation. The total tumor incidence was 59% (48 of 82 effected rats), the first animal demonstrating a sarcoma at day 273. Islet tumors of the pancreas appeared from the 455 day time point. Pancreatic and kidney tumors developed in 15 rats (18%) each, and apocrine tumors at the irradiated site and sarcomas in 9 rats (11%) and 5 (6%), respectively. Gastric tumors were found in 3 rats (4%). Immunohistochemistry revealed the islet tumor cells to be generally positive for insulin, although some cells contained somatostatin or glucagon, but not gastrin. The present results thus showed that the insulinomas and tumors other than gastric lesions are induced by X-irradiation of the upper peritoneal region.

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L-cysteine monohydrochloride (LCM) was added to the drinking water of groups of 50 male and 50 female F344/DuCrj rats at levels of 0.5 and 0.25% for 108 weeks. There were no statistically significant differences between treated and control rats in the results of the urine and serum analyses or hematological determinations or in the incidences of tumors, apart from mammary, pituitary and peritoneal lesions. The mammary gland in the females and the pituitary adenoma in males showed some increase in tumor development over the concurrent controls but these values did not differ significantly from the reported spontaneous incidences in this strain. Mesotheliomas were found in 3 of 41 male rats treated with 0.5% LCM but this was again in line with historical control data. It was concluded that LCM does not induce any neoplasms when given orally to F344/DuCrj for 108 weeks.
With regard to non-neoplastic lesions, necrosis of renal papillae was seen in six of 38 females rats in the 0.5% group and 2 of 43 in the 0.25% group. Pelvic hyperplasia was also evident in single female of the two treatment groups. These results suggest that development of papillary necrosis of the urinary tract may occur due to a direct or indirect-action of LCM.

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In order to investigate the effects of vitamin A (VA) supplementation on thyroid proliferative lesions associated with goitrogens other than thiourea, F344 rats were given VA in the diet at 0.1% and drinking water containing sulfadimethox-ine, propylthiouracil, potassium thiocyanate or phenobarbital for 19 weeks after initiation with N-bis (2-hydroxypropyl) nitrosamine. At the end of the treatment period, serum T3, T4, and TSH levels, T4-uridinedi phosphate glucuronosyltransferase (UDP-GT) activity in the liver, and thyroid weights were determined. In addition, thyroid proliferative lesions were histologically examined and evaluated for their PCNA labeling indices. Although serum T4 levels were lowered by VA in all goitrogen-treatment cases, serum levels of TSH, which is responsible for control of proliferation of thyroid follicular cells, were not elevated by the VA supplementation. There were also no enhancing effects of VA in terms of the other parameters, suggesting that the enhancement observed ealier with thiourea is a special case.

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FK506 (Tacrolimus) is a potent immunosuppressive agent and its ointment formulation was shown to be effective on atopic dermatitis in a clinical study. As atrophy of the skin is one of the adverse effects of dermal application of such drugs as glucocorticoid ointment, the aim of the present study was to investigate whether FK506 ointment induces skin atrophy in rats.
0.3% FK506 ointment treatment did not induce skin atrophy at the application site when applied daily for 3 weeks to rats. In contrast, glucocorticoid ointments such as 0.05% clobetasol 17-propionate (CP: Dermovate^®), 0.12% betamethasone 17-valerate (BV; Rinderon^®-V), 0.05% clobetasone 17-butyrate (CB; Kindavate^®), and 0.5% prednisolone (Pr: Prednisolone) elicited skin atrophy, and histopathologically decreased subcutaneous adipose tissue, and caused thinning of the epidermis and dermis. Furthermore, staining by proliferating cell nuclear antigen (PCNA) showed that these glucocorticoid ointments led to suppression of epidermal cell proliferation, and their potency in descending manner was CP>Pr>CB>BV.
In conclusion, it was clearly established that FK506 does not induce skin atrophy, which is one of the characteristic dermal toxicities of glucocorticoid ointments. The drug is therefore expected to be well tolerated for long term application in skin deseases.

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Promotion effects of sodium L-ascorbate (Na-AsA) on two-stage urinary bladder carcinogenesis were examined in male NCI-Black-Reiter (NBR) rats, which lack a2u-globulin-synthesizing ability, and F344 rats for comparison of the action. The animals were initiated with exposure to 0.05% N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) via the drinking water for 4 weeks, and then treated with a basal diet containing a 5% supplement of Na-AsA or no added chemical for 32 weeks. The urinary pH and Na ion concentration in both strains of rats treated with BBN followed by Na-AsA (BBN→Na-AsA) were significantly higher than those in the matched controls (BBN alone). Microscopically, significantly increased incidences of papillary or nodular hyperplasia, papillomas, and transitional cell carcinomas were observed in F344 rats treated with BBN →Na-AsA, whereas the incidences of these lesions in NBR rats were comparable in the BBN→Na-AsA and BBN alone cases. These data indicate NBR rats to be resistant to Na-AsA-induced promotion of two-stage urinary bladder carcinogenesis. Since the elevation of urinary parameters generally associated with tumor promotion by Na-AsA was a feature with both strains, another factor such as a2u-globulin, may also be active for enhancement of lesion development.

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A renal tumor was found in a I-year-old Shi-Tzu dog. Histopathological observation revealed that the tumor consisted of nephroblastic neoplastic cells, some of which formed tubular and primitive glomerular structures, and mesenchymal tissues showing differentiation into smooth muscle, bone, and neuronal components. The tumor was a rare case of canine nephroblastoma with unusual neuronal components.

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A case of spontaneous trichoepithelioma having a partial granular cell appearance, which was found in a 109-week-old male F344Du/Crj rat, is described. Grossly, a white soft subcutaneous nodule approximately 16×13mm in diameter was found at the right axilla of the animal. Histologically, the tumor showed two structural patterns, one composed of eosinophilic granular cell nests and the other resembling trichoepithelioma composed of basal cells in ribbon or solid pattern nests occasionally with horny cysts or whorls. The cytoplasm of the granular cells was positively stained with PAS and was diastase-resistant. Trichoepithelioma components were strongly immunostained for keratin, but granular cells were weakly stained for keratin. None of the tumor cells were stained for S-100 protein, desmin, and vimentin. Ultrastructurally, the granular cell cytoplasm was filled with lysosome-like structures containing numerous electron-dense bodies. Many of the tumor cells had a prominant desmosome with attached tonofilament. These findings appeared to be essentially similar to those of the granular cell basal cell tumor in dogs and humans. However, the most appropriate diagnosis of this case may be “trichoepithelioma with granular cell appearance or trichoepithelioma, granular cell type”, based on its characteristic his-tological features showing a differentiation to hair follicles.

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We examined rats treated with a high dosage of recombinant human granulocyte colony-stimulating factor (rhG-CSF) in order to investigate the relation between marrow hematopoietic activity and development of bone changes. Recombinant human G-CSF (1, 000, μg/kg/day) was daily given intravenously to 14-week-old rats for 28 days, and the hindlimb bones were examined histopathologically. In all types of bones, the bone marrow cellularity in the rhG-CSF-treated group was higher than that in the control group. In the rhG-CSF-treated rats, granulocytic hypercellularity was observed in the bone marrow, and the marrow cavities of several bones were fully occupied by hematopoietic cells. Bone changes characterized by accelerated osteoclastic bone resorption and osteogenesis due to intramembranous ossification were observed in the rhG-CSF-treatd rats, and these changes were found only in the bones with active hematopoietic marrow. These results suggest that the development of bone lesions induced by rhG-CSF may be closely related to the bone marrow hematopoietic activity and that the changes may take place in the bone with active hematopoietic marrow.

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