Morphogenesis of esophageal carcinoma induced by N-methyl-N'-nitro-N-nitrosoguanidine in the house musk shrew, Suncus murinus (Insectivora)

Mechanisms of adrenal damage induced by 7,12-dimethylbenz (alpha) anthrancene in female Sprague--Dawley rats

The mechanisms of adrenal damage induced by 7,12-dimethylbenz (alpha) anthrancene (DMBA) in 50-day-old female Sprague--Dawley rats were investigated. A single dose of DMBA, either fed (30 mg) per os or injected (6 mg) in a caudal vein, caused inner cortical cell death (cells of the zonae fasciculata and reticularis) by an apoptotic mechanism. Apoptotic cells were identified by cell morphology, and terminal dUTP nick end labeling (TUNEL)-positive cells were seen at 12 hrs post-DMBA, reached a maximum at 36 h, and were accompanied by blood congestion followed by massive hemorrhage leading to post-apoptotic necrosis at 48 and 72 h. The apoptotic cascade involved the up-regulation of Bax, the down-regulation of Bcl-2, and the activation of caspase-3. At 72 h, regeneration as evidenced by the appearance of 5-bromo-2'-deoxyuridine-positive cells began to occur in the damaged inner cortical zones, with the cells proliferating toward the medulla thereafter. Regenerative cells expressed cytochrome P450 11 beta hydroxylase. The damage was repaired but calcification appeared at 2 weeks post-DMBA, leaving bow-shaped lesions in some adrenals.

Colon carcinogenesis in shrews by intrarectal infusion of N-methyl-N-nitrosourea

Intrarectal infusion of a 0.15 ml solution containing 1.5 mg or 0.5 mg of N-methyl-N-nitrosourea (MNU) was given to female shrews from 6 weeks of age. Fifteen shrews were given 16 doses of 1.5 mg MNU administered biweekly (group 1), 15 shrews were given 24 doses of 0.5 mg MNU weekly (group 2), and four untreated shrews served as controls (group 3). Moribund shrews were killed during the course of the experiment and all remaining animals were killed at 37 weeks of age and terminated the experiment. The mean age when killed was 30.8 weeks in group 1 and 36.2 weeks in group 2. All autopsied shrews in group 1 and group 2, 13 shrews each, had colon cancers, and there were a few small intestinal cancers and uterine squamous cell carcinomas, while no tumors were seen in the untreated shrews. The colonic lesions were of both exophytic and endophytic type with a variety of histologies and depths of invasion. Mesenteric lymph node metastasis was seen in 31% (4/13) of group 1 and 23% (3/13) of group 2. Thus, MNU, a colonotrophic carcinogen in rodents, also induced colon cancer in shrews in the present study.

Effect of ethanol on esophageal cell proliferation and the development of N-methyl-N'-nitro-N-nitrosoguanidine induced-esophageal carcinoma in shrews

The effect of ethanol (EtOH) on esophageal cell proliferation and the development of esophageal cancers induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in shrews were investigated. Sequential histological examination was done, and cell proliferation was assessed by BrdU labeling. At 5 weeks of age, animals were given tap water, 2% EtOH, 50 ppm MNNG, or 50 ppm MNNG plus 2%, 5% or 10% EtOH in the drinking water. Administration of 10% and 5% EtOH simultaneously with MNNG caused death in 40% (10/25) within 4 days and in 20% (6/30) within 7 days respectively, whereas other treatment were well tolerated with no sudden deaths. Administration of 2% EtOH for 30 weeks caused a 2-fold increase, and that of MNNG caused a 4.5-fold increase in the proliferation index of the basal cells of the esophagus compared with control shrews, and MNNG plus 2% EtOH caused a 5.5-fold increase. In MNNG-treated shrews, with or without 2% EtOH administration, sequential histological examination of esophageal tissue revealed a similar change; dysplasia appeared at 30 weeks of age, squamous cell carcinoma occurred at 35 weeks of age, and the depth of invasion extended to adventitia at 45 weeks of age. These finding indicate that treatment with 2% EtOH promoted the proliferation of esophageal basal cells but did not alter the tumor induction period and did not have tumor-promoting activity. EtOH per se was not carcinogenic; no tumors were seen in shrews not administered MNNG.