Atypical bile ducts induced by 0.1% ethionine in choline deficient diet (ECD) were biologically and histologically examined in rat liver. At 1 week after administration, enlargement of nucleolus and central lobular fatty change were observed in hepatic cells. At 2 weeks, there were diffuse and tubular proliferation of oval cells in periportal and along sinusoidal regions. The fatty droplets were large in size and expanded throughout the lobules. At 4 weeks oval cells became more conspicuous, occasionally formed duct structures (bile duct proliferation), and atypical bile ducts were observed with obvious border and secretion of mucin. The neoplastic nodules were first recognized at this time. At 8 weeks the oval cells increased more prominently, and there were many atypical bile ducts with fibrosis. At 12 weeks (group 50% ECD), atypical bile ducts and neoplastic nodules were more conspicuous. In the recovery period, the number of oval cells was much less than during administration, and neoplastic nodules were hardly seen. The atypical bile ducts, however, showed large nodular expansions in the periportal region, being much more conspicuous than those during administration. Macroscopically, the bile duct lesions could be seen as transparent small and whity nodules and could be readily distinguished from neoplastic nodules which were milky white in color. The cell proliferation activity of the bile duct lesions showed a higher value in recuperating rats than in administered ones.
From the above findings it was confirmed that the atypical bile ducts are induced in association with oval cell proliferation, and that the cell proliferation activity and covering area did not show reduction by removal of the exciting agent, and that the lesion has the ability of autonomous development.

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T-2 toxin (0, 2 and 4mg/kg/day) was orally administered to mice for up to 56 consecutive days to examine the effect of T-2 toxin on hepatocyte proliferation under physiological condition and to clarify the characteristics of subacute hepatotoxicity of T-2 toxin. Immunohistochemical staining for BrdU revealed that the number of BrdU-positive hepatocytes was lower in the T-2 toxin-treated groups than in the control, and this indicates that T-2 toxin depressed hepatocyte proliferation under physiological condition. Biochemical and electron microscopical examinations revealed that the subacute hepatotoxicity of T-2 toxin was characterized by depression of protein synthesis and its related changes such as lipid accumulation in hepatocytes.

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Hepatocyte-like cells were observed in the pancreas of two male and one female B6C3F, mic and one male BDF₁ mouse. These cells appeared in the areas composed of atrophic pancreatic acinar cells and showed no specificity for appearance near the pancreatic islets as reported in rats and Syrian hamsters. This result suggested that there may be no influence of the islet cells in pathological development of pancreatic hepatocytes in mice. Since no relationship between the appearance of pancreatic hepatocytes and administration of chemicals was shown in these mice, spontaneous occurrence of these cells, probably by metaplasia of the regenerating cells after atrophy of the acinar cells in the exocrine pancreas, has been suggested.

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The frequency and mutational profile of c-H-ras gene activation were determined in spontaneous hepatocellular tumors in aged B6C3F1 mice.
After DNA isolation from formalin-fixed paraffin-embedded tissue sections and amplification by a polymerase chain reaction (PCR), a non-isotopic method using chemiluminescence for dot blot hybridi-zation was applied to detect c-H-ras mutations.
DNA sequence analysis of the c-H-ras gene from 59 hepatocellular tumors (39 carcinomas and 20 adenomas) revealed that 49 (83%) contained a point mutation at codon 61. Of 34 hepatocellular carcinomas with mutations, 15 tumors (44%) had a CAA to AAA transversion at the first base of the codon, and 11 (32%) and 8 (24%) had a CAA to CTA transversion and CAA to CGA transition, respectively, at the second base. Of 15 hepatocellular adenomas with mutations, 5 (33%) had CAA to AAA, 6 (40%) CAA to CTA, and 4 (27%) CAA to CGA mutations. There was no association between the morphological features of the spontaneous mouse liver tumors and the presence or pattern of codon 61 mutations.
These results show that spontaneous mouse liver tumors contain at least three different codon 61 mutations of the c-H-ras gene and that the non-isotopic method employed is useful in conventional laboratories to examine oncogene mutations.

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Uracil and N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) were tested singly and in combination for their ability to influence urine composition, epithelial morphology, and DNA synthesis in the urinary bladder of male Syrian golden hamsters. Continuously for a period of 8 weeks groups consisting of 10-12 animals each, received BBN, administered in the drinking water at 0.05 %, uracil, included in the powdered diet at 3%, both or single or no treatment. After 4 weeks, half of the animals in each group were sacrificed and the remainder maintained until week 8. Except for a significant decrease in calcium ion content found in animals given BBN plus uracil at week 4, there were no significant changes in urinary pH, osmolarity and electrolytes in any of the groups at either time point. BBN plus uracil administration did not demonstrate any differences in terms of induction of urinary crystals or simple hyperplasia when compared with uracil or BBN treatments alone. No uracil-induced calculi were found. However, urinary bladder epithelial surface alterations observed by scanning electron microscopy (e.g., formation of short, uniform microvilli and ropy or leafy microridges) and DNA synthesis in the urothelium were greater in the BBN plus uracil treated animals than in the uracil, BBN and control groups. The results suggest a weak synergistic effect of uracil and BBN in inducing proliferation.

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The response of the urinary bladder epithelium in NCI-Black-Reiter (NBR) rats to administration of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), a potent carcinogen in rodents, was examined. Male NBR rats were exposed to 0.05% BBN in the drinking water for 8 weeks, or no added chemical. Microscopically, simple hyperplasia was observed in the urinary bladder epithelium of treated rats sacrificed at the end of week 4. Moreover, after 8 weeks administration of BBN, papillary or nodular (PN) hyperplasia and squamous metaplasia were produced. Levels of DNA synthesis, as indicated by incorporation of 5-bromo-2'-deoxyuridine, areas of simple and PN hyperplasia in rats treated by BBN were significantly increased than in non-treated ones at the end of week 8. These results indicate that the urinary bladder of NBR male rats is very responsive to BBN insult.

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The National Toxicology Program (NTP) has established a “qualitative” quality assurance (QA) pathology program in order to accurately generate pathology data in 90-day toxicity and 2-year carcinogenicity studies in rats and mice.
The NTP studies are conducted in several contract laboratory facilities in the United States. The study pathologist completes a histopathologic examination and submits a draft pathology report to the NTP. The pathology narrative and summary tables are evaluated to indentify target and semi-target organs and histopathologic lesions to be microscopically reviewed.
The NTP “qualitative” QA pathology procedures consist of three stages of reviews for histopathologic diagnoses, involving two independent pathologists and a panel of pathologists on a Pathology Working Group (PWG). First, the QA pathologist microscopically reviews the diagnoses for the following organs and lesions: (1) all tissues of target organs, (2) all of especially selected neoplastic or non-neoplastic lesions of semi-target organs, (3) all neoplasms diagnosed in the study, and (4) all tissues from 10% of animals in the control and high dose groups. In addition, the histotechnique quality, tissue accountability, slide identification, and untrimmed gross lesions are evaluated. Second, a chairperson of PWG slide review meeting also reexamines all of the aforementioned organs and lesions reviewed by the QA pathologist. Third, six to eight PWG pathologists primarily review the representative slides with compound-related lesions and histopathologic diagnostic discrepancies between the study and QA pathologists. When the PWG disagrees with the study pathologist, the PWG recommends the stud pathologist to reexamine the lesions in question. When the study pathologist agrees to the PWG's opinions, he corrects his original diagnoses and generates the final pathology report.

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The relationship between megakaryocytic emperipolesis in the bone marrow and lipopolysac-charide (LPS)-induced tumor necrosis factor (TNF) was investigated in adrenalectomized or dexameth-asone (Dex)-treated rats. Adrenalectomized rats were injected LPS intravenously at a single dose of 0.5μg/kg body weight 48 h after the operation, and Dex-treated rats were given LSP at a dose of 0.5mg/kg body weight 1 h after the Dex-treatment. Serum TNF activity markedly increased in the adrenalectomized rats (3279.3units/ml), but reduced in the Dex-treated rats (227.3units/ml) I h after LPS-treatment. Megakaryocytic emperipolesis was not influenced by these treatments 24 h after LPS-administration. Thus, LPS-induced serum TNF activity could not increase megakaryocytic emperipolesis.

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A 57-week-old male Wistar rat died one week before the end of a toxicity study. Necropsy revealed subcutaneous edema, hydrothorax, dilatation of all cardiac chambers, and congestion in several organs. Light and electron microscopic examinations revealed myocardial hypertrophy, degeneration, fibrosis, and disruption of myofibrils and variable sized mitochondria. The entity is concluded to be dilated cardiomyopathy.

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Anterior and posterior lens luxation were found in Sprague-Dawley rats. When the lens was luxated forward, the lens traversed the anterior chamber and reached a point of the corneal endothelium. The anterior pole was adhered with the corneal endothelium resulting in focal subcapsular cataract and regional corneal thickening. When the lens was luxated backward, it was completely embedded within the vitreous. This was associated with mature cataract and liquefaction. The iris became flattened as a result of the lack of posterior support from the lens.

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