Male Donryu Rats Research Articles

Abstract 358: The novel sentinel lymphnodes identification method using magnetic nanoparticle by MRI

Abstract [Introduction] Detection of sentinel lymph nodes (SN) has been used to predict regional lymph node (LN) metastasis in patients with various types of carcinoma. The technique used to detect SN has focused on using a vital blue dye, a radioactive tracer, or a combination of both. However there are several problems in the current method for SN identification, such as anaphylaxis shock, difficulties of detection, danger of radiation exposure, the limitation of use of radioisotopes, and short shelf life. The aim of this study was to develop new SN identification method using magnetic nanoparticles (MNPs) by MRI. [Methods] 5-week-old, Male Donryu rats were used for establishment of rat SN model and for optimization of MNPs size and amount. 4-week-old, male nude rats (F344/NJcl-rnu/rnu) were used for establishment of metastatic model. Three kinds of MNPs (4 nm (M4), 8 nm (M8), 20 nm (M20)) were synthesized. SN detectability was evaluated by T1-weighted gradient echo MR images after injection of synthesized MNPs or Resovist® in vivo. Signal change of LN induced by MNPs were evaluated T1-weighted MRI slice by two independent researchers. In addition, area (mm2) of susceptibility effect in LN was calculated using ROI tools of MRVision software. All MRI was examined for the receiver operating characteristic (ROC) curves by three individuals whether area of susceptibility was recognizable. ROC displaying sensitivity along with the false-positive rate (1αspecificity) for detecting MNPs by MRI, and the area under the curve with 95% confidence intervals was calculated. The amount of iron in the brachial lymph node (Br) and the axillary lymph node (Ax) was evaluated by inductively coupled plasma optical emission spectrometry (ICP-OES), and evaluated pathologically. MRI was performed weather Br and Ax were distinguishable. To evaluate toxicity of MNPs, exploratory single toxicity study was performed. Over all condition and weight status were observed. [Results] We established an original rat SN model and it revealed that Br is SN and Ax is a higher echelon nodes further downstream from SN. We also established metastatic rat model. M20 was sustained in Br selectively than M4, M8 and Resovist® and appropriate amount was 0.1mg. SN was distinguishable and detectable by MRI using M20 in normal and metastatic rat model. ROC curve analysis revealed that threshold of magnetite amount for MRI detection is 2.3μg/LN with 76.5% sensitivity and 25% specificity, and the area under receiver operating characteristic curve is 0.82 (95% CI, 0.64-1.0). Results of exploratory single toxicity study indicated that the fatal dose was equal to Resovist® and it was tolerable less than medium-low dose (1250 μmol/kg) injection. [Conclusion] We developed the novel SN identification method by MRI with our original 20nm MNPs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 358. doi:1538-7445.AM2012-358

Tumor blood flow interruption after radiotherapy strongly inhibits tumor regrowth

To clarify the therapeutic significance of interrupting tumor blood flow after irradiation, we investigated X-irradiation-induced changes in hemodynamic parameters (blood flow, extravasation and washout of fluorescein isothiocyanate-dextran, and interstitial fluid pressure) in a variant of Yoshida sarcoma, LY80. Tumors in anesthetized male Donryu rats received local irradiation (10 Gy). At 48 h after irradiation, tumor blood flow increased significantly; at 72-96 h after irradiation, a 2-2.5-fold increase was observed. All parameters then consistently showed improved tumor microcirculation, which probably contributed to regrowth of cancer because certain cells survived irradiation. Rats received an intravenous dose (10 mg/kg) of a combretastatin derivative, AC7700 (AVE8062), which interrupts tumor blood flow and disrupts tumor vessels. At all times evaluated after irradiation, AC7700 completely stopped tumor blood flow. Radiotherapy efficacy was significantly enhanced when combined with AC7700: AC7700 given 48 h after irradiation, when tumor blood flow increased significantly, remarkably suppressed tumor regrowth compared with AC7700 given 48 h before irradiation. Also, postirradiation AC7700 completely inhibited not only primary tumor regrowth but also regional lymph node metastases in half of tumor-bearing rats and led to a significant improvement in survival. These results strongly suggest that the combination effect was enhanced via interruption of increased tumor blood flow after irradiation. This therapeutic combination and timing may have important benefits, even in tumors with low sensitivity to either treatment alone, because the effect was considerably greater than additive. Our data thus show that destruction of tumor microcirculation after irradiation is quite effective for preventing cancer recurrence.

Enhanced radiation response of a solid tumor with the artificial oxygen carrier ‘albumin‐heme’

Tumor-cell hypoxia is one of the main factors inducing radioresistance. Enhanced tumor oxygenation has previously been achieved in an animal model using the synthetic heme-based oxygen carrier 'albumin-heme' (recombinant human serum albumin-Fe cyclohexanoil heme; rHSA-FeP). The present study was done to determine whether rHSA-FeP enhances the radiation response in an experimental tumor model. Male Donryu rats and LY80, a variant of the syngenic liver ascites tumor, were used. A total of 1 x 10(6) cells were injected into the subfascial tissue of the right thigh. The rats were divided randomly into five groups: sham (tumor implantation and sham operation); rHSA-FeP; irradiation; rHSA + irradiation; and rHSA-FeP + irradiation. Six days after, under general anesthesia, intra-arterial administration of 10 mL/kg of either 5% rHSA solution or oxygenated rHSA-FeP solution at 2.5 mL/min was done and a dose of 20 Gy was given. There were significant differences in tumor growth between the sham and irradiation groups, and between the sham and rHSA-FeP + irradiation groups. Tumor growth delay was observed and differences were significant between the sham and irradiation groups, and between the irradiation and rHSA-FeP + irradiation groups. In the present study, rHSA-FeP itself had a slight effect on tumor growth without irradiation. Enhancing the effect of rHSA-FeP on the radiation response is responsible in part for the oxygen-carrying property of rHSA-FeP. In conclusion, rHSA-FeP is a candidate radiation-enhancing drug. Arterial infusion of rHSA-FeP may serve as a local oxygenation method that enhances the radiation effect.

Superficial contact cryoablation attenuates experimentally created lung air leakage

Previously, we, and others found that cryoablation on normal lung produced localized pulmonary hemorrhage and edema, causing obliteration of air space. Therefore, we hypothesized that lung air leakage may be diminished by this procedure. In the present study, we examined if cryoablation can attenuate experimentally created lung air leakage. Male domestic pigs ( n = 4) underwent a thoracotomy. The lung was resected approximately 5 mm in diameter and 1 mm in depth to create air leakage lesions. An argon gas cryoprobe with a copper plate attached to its tip was used to cryoablate the lesions superficially. After cryoablation, the positive airway pressure that produced macroscopic bubbles from each lesion site was compared between cryoablated and untreated lesions. Also, cryoablation of the lung surface was carried out in male Donryu rats ( n = 20) which were sequentially sacrificed to observe the histological changes over a time course. In the pigs, the air leakage pressure was significantly increased with cryoablation (40 cmH 2O <) compared to no treatment (19 ± 5 cmH 2O) ( p = 0.021, Mann–Whitney U test). Histologically, cryoablation produced acute pulmonary hemorrhage and edema. In the rats, the region with extensive hemorrhage progressed to fibrosis in 1 month, and the areas with edema recovered. This study provides supportive evidence that cryoablation has the potential to stop air leakage from surface pulmonary injury. This procedure may provide a useful adjunct to surgical resection for spontaneous pneumothorax, and the control of air leakage from dissected raw lung surfaces during lung resection.

Omega-3 fatty acids in colorectal cancer prevention.

Omega-3 fatty acids in colorectal cancer prevention.

The effects of an additive small amount of a low residual diet against total parenteral nutrition–induced gut mucosal barrier

Background Total parenteral nutrition (TPN) negatively influences the gut mucosal barrier. It has been suggested that enteral nutrition is effective against the harmful influence. Methods Forty-eight male Donryu rats underwent placement of a central venous catheter and tube gastrostomy. They were divided into six groups, receiving isocaloric nutrients in various proportions of PN and a low residual diet (LRD) for 7 days. Intestinal permeability, villous height and crypt depth, and number of secretory IgA-positive cells in the villus were measured. Results Intestinal permeability was significantly reduced in rats receiving an LRD corresponding to more than 15% of total caloric intake. Gut morphological structure was maintained in rats receiving an LRD corresponding to more than 10%. A higher number of IgA-positive cells was observed in rats receiving an LRD corresponding to more than 15%. Conclusions A small amount of LRD could prevent decreases in gut mucosal integrity. There was a stepwise defense mechanism in the gut mucosal barrier.

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was −0.19 ± 0.02 and −0.14 ± 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 ± 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 ± 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.

Survival curve modified through dietary restriction (DR) in male Donryu rats

It is well known that dietary restriction (DR) can prolong the life of certain inbred strains of laboratory rodents. This prolongation can be usually shown in a survival curve in parallel to that of non-DR groups. On an outbred strain, Donryu, however, DR resulted in a unique pattern of survival curve. In DR group, the first three quarters of male rats survived longer in a form parallel to non-DR, while the last quarter of them survived far longer in a quite different shape from controlled group. DR may select animals that are capable of longer survival within Donryu. The selection of a quarter animal indicates the parameter for selection may be regulated by a single recessive locus.

Glutamine supplementation in cancer patients

OBJECTIVES: Three series of studies investigated whether 1) glutamine deficiency occurs in tumor-bearing rats, 2) glutamine supplementation improves protein metabolism during chemotherapy in tumor-bearing rats, and 3) oral glutamine supplement improves systemic immune and gut-barrier function in patients with esophageal cancer receiving radiochemotherapy.METHODS: In the animal studies, AH109A hepatoma cells or Yoshida sarcoma cells were inoculated into male Donryu rats to induce tumors. Glutamine production was measured by U-14C-glutamine infusion and the conversion of arginine to glutamine was measured by infusion of U-14C-arginine. The effect of glutamine on protein metabolism was investigated by 1-14C-leucine infusion. In the clinical study, 13 patients with esophageal cancer were randomized into two groups, control and glutamine supplemented (30 g/d), for 4 wk.RESULTS: Glutamine levels in plasma and skeletal muscle were decreased in tumor-bearing rats, although glutamine production and the conversion of arginine to glutamine were increased. Glutamine-supplemented total parenteral nutrition reduced whole-body protein breakdown rate during chemotherapy in tumor-bearing rats. Oral supplementation of glutamine to the patients with esophageal cancer enhanced lymphocyte mitogenic function and reduced permeability of the gut during radiochemotherapy.CONCLUSIONS: Glutamine depletion in host tissues occurs in tumor-bearing rats. Glutamine supplementation can attenuate loss of protein in the muscle in tumor-bearing animals and protect immune and gut-barrier function during radiochemotherapy in patients with advanced cancer.

Effect of Dietary Conjugated Linoleic Acid on the In Vivo Growth of Rat Hepatoma dRLh-84

We examined the effect of dietary conjugated linoleic acid (CLA) on the growth of injected hepatoma dRLh-84 in Donryu rats. After experimental diets containing 0% or 2% CLA were given to male Donryu rats for 3 wk, dRLh-84 cells were injected into the left lobe of the hepatic capsule, and the experimental diet was continued. The cells formed a solid tumor ≥1 wk after the injection, and thereafter the tumor grew with feeding duration. In a morphological study, this tumor appeared to be a low-differentiated hepatoma, and there was no remarkable difference in the morphology of the tumor between 0% and 2% CLA groups. Tumor weight was significantly higher in the 2% CLA group than in the 0% CLA group throughout the feeding period after the injection. Serum glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase activities were significantly higher in 2% CLA-injected rats than in 0% CLA-injected rats at 3 wk after the injection. CLA upregulated acyl-CoA oxidase activity, especially 1 wk after the injection. However, dietary CLA did not activate carnitine palmitoyl transferase II, which is a rate-limiting enzyme in the mitochondrial β-oxidation pathway. Natural killer cell activity in the spleen tended to be higher in injected rats, but a significant effect of dietary CLA was not recognized. Serum interferon-γ and tumor necrosis factor-a levels were higher in injected than in sham rats. Moreover, these levels were higher in 2% CLA groups than in the respective 0% CLA groups.

A NEWLY DRUG DELIVERY SYSTEM IN CANCER CHEMOTHERAPY, USING DIRECT ELECTRIC CURRENT (2nd Report)

Purpose: A new drug delivery system for ionized agents, using the direct electric current was invented and reported in the last ASAIO meeting. To know more precise principles of pharmaco-dynamic changes with this new method for Adriamycin(ADR), electrically charged as cation in blood, another animal experiment was done. Methods: In 6 male Donryu rats, platinum electrodes, cathode and anode were placed into right kidney and muscles of abdominal wall, respectively. DC group was received electric therapy with continuous direct current of 50 μA, 3.5 Volt, and one-shot of ADR (5mg / kg) was given intravenously during the electric therapy, while the control group was inserted the same electrodes and was given ADR injection but no current. ADR concentrations in urine, plasma, and tissues of liver, kidney, lung, heart were determined for 60 minutes, by high performance liquid chromatography. Results & Conclusion: Urinary excretion of ADR was higher in the DC group than in the controls (p<0.05). Both plasma and renal ADR clearance were higher in the DC group (p<0.005, p<0.001, respectively). ADR concentrations in tissues of liver and lung were lower in the treated group (both p<0.05). The electric therapy might potentially induce pharmacokinetic modification of ADR by iontophoresis, and that the therapy might effectively change ADR concentration systemically.

Microvasculature of small liver metastases in rats.

Neovascularization is important in the development of liver metastasis. We sought to define the origin and fine structure of the blood supply of small experimental liver metastases in rats using an injection replica method. Liver metastases were produced by intraportal inoculation of ascitic fluid containing AH60C hepatoma cells in male Donryu rats (n = 40). Intrahepatic microvasculature was studied by scanning electron microscopy and by stereomicroscopy of microvascular casts produced by perfusion via the abdominal aorta or portal vein 7 days following tumor inoculation. Intrahepatic microvasculature in rats without liver metastases (n = 10) also was studied by scanning electron microscopy. In the normal liver, branches of the hepatic artery typically terminated in the peribiliary plexus and less frequently led to sinusoids and terminal portal veins. In 69 metastatic tumors ranging from 269 to 1875 microm in diameter, arterially perfused metastatic tumors larger than 300 microm showed newly developed neovascularization. Portally perfusion of metastatic tumors did not visualize neovascularization irrespective of tumor size. At the periphery of metastases, tumor vessels disclosed by arterial perfusion most often communicated with the peribiliary plexus and less frequently with terminal arterioles. Metastatic liver tumors as small as 300 microm in diameter receive their main blood supply from the hepatic artery but not from the portal vein, and tumor vessels more often are derived from the arterially filled peribiliary plexus rather than from terminal arterioles.

The influence of dietary restriction on the process of age-related disorders in male Donryu rats

Life span, which is mainly influenced by pathologic lesions, was compared between specific pathogen-free male Donryu rats fed ad libitum (AL group) and those with dietary restriction (DR group, restricted to 60% of the ad libitum intake). The major age-related lesions observed were pituitary tumor, chronic nephropathy, cardiomyopathy, and myopathy (anterior tibial and masseter muscle). Dietary restriction was effective in slowing the progression of pituitary tumor, chronic nephropathy and myopathy in anterior tibial muscle. Although cardiomyopathy worsened with age, no difference was seen between the AL and DR group. In conclusion, 1) dietary restriction acts to suppress or delay the development of pathologic lesions that occur with age, 2) the onset phase of a pathologic lesion differs with the lesion and organ involved, 3) inhibiting the development of pituitary adenoma and chronic nephropathy can help prolong the life span of rats, 4) for muscle lesions, depending on their anatomical location, the physiological condition of exercise, as well as the relationship with other organs can be involved.

Small amount of low-residue diet with parenteral nutrition can prevent decreases in intestinal mucosal integrity.

To investigate the suitable combination ratio of low-residue diet (LRD) and parenteral nutrition (PN) for nutritional support of surgical patients. Bacterial translocation (BT) is a severe complication of total parenteral nutrition (TPN). However, it is sometimes impossible to supply sufficient amounts of nutrients to surgical patients by the enteral route. The authors reported previously that concomitant use of LRD with PN provided preferable nutritional support for patients undergoing surgery for colorectal cancer. Ninety male Donryu rats were used for three experiments. In experiment 1, rats were divided into two groups to receive TPN or total enteral nutrition with LRD. In experiment 2, rats were divided into six groups, receiving variable amounts of LRD. In experiment 3, rats were divided into five groups to receive isocaloric nutritional support with variable proportions of PN and LRD. Intestinal permeability was assessed by monitoring urinary excretion of phenolsulfonphthalein. BT was assessed in tissue cultures of mesenteric lymph nodes and spleen. In experiment 1, increases in intestinal permeability and BT were observed in rats maintained on 7-day TPN, but not in those maintained on total enteral nutrition for up to 14 days. In experiment 2, the changes in body weight of rats were correlated with the dose of LRD. However, the intestinal permeability was increased only in rats receiving LRD at 15 kcal/kg per day. In experiment 3, additive LRD corresponding to 15% of total caloric intake prevented increases in intestinal permeability and BT. Combined nutritional therapy consisting of PN and small amounts of LRD can provide better nutritional support than TPN for surgical patients.

Laminar distribution of pheromone-receptive neurons in rat vomeronasal epithelium.

1. Responses of vomeronasal sensory neurons to urine excreted from rats, mice and hamsters were studied by the on-cell patch clamp method in slices of sensory epithelium from female Wistar rats. 2. The urine excreted from male and female Wistar rats, male Donryu rats and male C57BL/6 mice induced relatively large responses, while urine from male Sprague-Dawley rats and male Syrian hamsters induced small responses. 3. Of the 62 neurons responding to urine, 57 responded to only one of the urine preparations. 4. The sensory neurons that responded to the male Wistar urine were localized in the apical position of the epithelium where one type of GTP-binding protein, Gi2alpha, is selectively expressed. The neurons in the basal position of the epithelium, which express Goalpha, responded to urine from the other animals. 5. This study demonstrates that sensory neurons responsive to different urinary pheromones are localized in a segregated layer in the rat vomeronasal sensory epithelium.

Changes of liver-enriched nuclear transcription factors for albumin gene in starvation in rats.

The regulatory mechanism of albumin gene transcription was examined using male Donryu rats (7 wk old) starved for 1 or 3 d. At the designated times, the rats were sacrificed to harvest the liver and to measure the serum albumin level. Neither the serum albumin nor the albumin messenger RNA (mRNA) level showed a significant change for these starvation periods. Among nuclear factors binding to the D site of albumin gene promoter, the CCAAT/enhancer binding protein alpha (C/EBP alpha) mRNA level showed a decrease and the D site binding protein (DBP) mRNA level tended to decrease after 3 d of starvation. In contrast, the C/EBP beta mRNA level showed a significant increase at day 1. As a B site binding nuclear factor, the hepatocyte nuclear factor 1 (HNF-1) mRNA level significantly increased at day 1. Gel mobility-shift analysis combined with Western immunoblotting confirmed the presence of D site binding proteins composed of DBP and C/EBP alpha and beta in both groups subjected to oral feeding and to 3-d starvation, though quantitative analysis could not be done. In conclusion, the nuclear transcription factors binding to the albumin gene promoter undergo regulatory changes during 3 d of starvation, whereas there is no significant decrease in the albumin mRNA level.

Role of Thromboxane A2 in Healing of Gastric Ulcers in Rats

We investigated the role of thromboxane (TX) A2 in gastric ulcer healing in rats. Acetic acid ulcers were produced in male Donryu rats. TXA2 synthesis in the stomachs with ulcers was significantly elevated in ulcerated tissue, but not in intact tissue, compared with that in the gastric mucosa of normal rats. Indomethacin inhibited both TXA2 and prostaglandin E2 (PGE2) synthesis in ulcerated tissue, while NS-398 (selective cyclooxygenase-2 inhibitor) reduced only PGE2 synthesis. OKY-046 (TXA2 synthase inhibitor) dose-relatedly inhibited only TXA2 synthesis. The maximal effect of OKY-046 (80% inhibition) was found at more than 30 mg/kg. When OKY-046 was administered for 14 days, the drug at more than 30 mg/kg significantly accelerated ulcer healing without affecting acid secretion. The maximal reduction of ulcerated area by OKY-046 was about 30%, compared with the area in the control. Histological studies revealed that regeneration of the mucosa was significantly promoted by OKY-046, but neither maturation of the ulcer base nor angiogenesis in the base were affected. OKY-046 and TXB2 had no effect on proliferation of cultured rat gastric epithelial cells, but U-46619 (TXA2 mimetic) dose-relatedly prevented the proliferation without reducing cell viability. These results indicate that the increased TXA2, probably derived from cyclooxygenase-1 in ulcerated tissue, exerts a weak inhibitory effect on ulcer healing in rats. The effect of TXA2 might be due partly to prevention of gastric epithelial cell proliferation at the ulcer margin.

The prevention of postoperative intraperitoneal adhesions by tranilast: N-(3',4'-dimethoxycinnamoyl)anthranilic acid.

The development of postoperative intraperitoneal adhesions continues to be a major concern for surgeons. The purpose of this study was to establish a postoperative adhesion model in rats, and to assess the effectiveness of tranilast (N-(3',4'-dimethoxycinnamoyl)anthranilic acid) in preventing postoperative adhesion formation. The adhesion model was established in 12 male Donryu rats. This involved two essential factors, drying and bleeding. Another 22 male Donryu rats were used to study the prevention of intraperitoneal adhesions. Tranilast was administered orally pre- and postoperatively. Adhesion strength was evaluated by grading, and basic fibroblast growth factor (bFGF) and transforming growth factor-beta-1 (TGF-beta1) concentration were measured. Postoperative intraperitoneal adhesions were seen in all rats, but the adhesions in the tranilast group were significantly less severe than those in the control group. Serum bFGF and TGF-beta1 levels in the tranilast group were lower at the time of surgery than those in the control group, and bFGF levels were lower at the endpoint of this study in the tranilast group than in the control group. The TGF-beta1 levels at the end-point did not differ between the two groups. These findings demonstrated that tranilast significantly reduced postoperative intraperitoneal adhesion formation.

Different responses other than the formation of DNA-adducts between the livers of carcinogen-resistant rats (DRH) and carcinogen-sensitive rats (Donryu) to 3'-methyl-4-dimethylaminoazobenzene administration.

Carcinogen‐resistant inbred DRH rats developed from the Donryu strain showed a remarkably low incidence of liver tumors when they were fed diets containing hepatocarcinogens such as 3′‐methyl‐4‐dimethylaminoazobenzene (3′‐Me‐DAB). In this work, we examined various characteristics of male DRH and Donryu rats during 3′‐Me‐DAB administration for 8 weeks. 32P‐Postlabeling analysis showed that essentially similar levels of DNA‐adducts were generated by the metabolites of 3′‐Me‐DAB in the livers of these two strains of rats at several time points. However, both GADD45 (growth arrest and DNA damage‐inducible) and O6‐methylguanine methyltransferase (putatively DNA damage‐inducible) mRNA levels were increased significantly in Donryu rat livers, but were increased to a lesser extent in DRH rats. [3H]Thymidine incorporation into hepatic DNA began to increase around 10 to 20 days after the start of 3′‐Me‐DAB administration in Donryu rats probably due to DNA repair, while no significant change occurred in DRH rats under the same conditions. Furthermore, inductions of heme oxygenase (due to degradation of heme‐proteins) and hepatocyte growth factor (HGF; cell death and regeneration of hepatocytes) mRNAs were greater in Donryu rat livers than those of DRH, suggesting that the former were more sensitive to cytotoxic effects of 3′‐Me‐DAB than the latter. Another remarkable difference observed between these two strains was the significant induction of cytochrome P‐450 2E1 mRNA in Donryu rat livers; this may contribute to the generation of reactive oxygen intermediates. Finally, increases of glutathione S‐transferase (P‐form) and γ‐glutamyltranspeptidase mRNAs as marker enzymes of preneoplastic changes of hepatocytes were clearly seen only in Donryu rat livers at 6 to 8 weeks after the start of 3′‐Me‐DAB administration. These results indicate that the different susceptibility to hepatocarcinogenesis between these two strains of rats may arise from events other than the DNA adduct formation.

Effects of azoxymethane on X-ray induced intestinal metaplasia in Donryu rats.

The present study was undertaken to determine the effect of azoxymethane (AOM) administration on intestinal metaplasia induced by X-irradiation in male Donryu rats. Five-week-old animals were X-irradiated with two doses of 10 Gy each at a 3-day interval or three X-ray doses of 10 Gy at a 2-day interval and then received AOM injections i.m. at a dose of 15 mg/kg body weight once weekly for 3 weeks, 6 months after irradiation. Alkaline phosphatase positive foci were decreased after AOM treatments, but aberrant crypt like-foci appeared within areas of intestinal metaplasia. In contrast no induction was observed in normal-appearing gastric mucosa.