Induction of Extrahepatic Biliary Carcinoma by N-Nitrosobis(2-oxopropyl)amine in Hamsters Given Cholecystoduodenostomy with Dissection of the Common Duct

The methods we used to produce a carcinoma in the extrahepatic bile duct and gallbladder in hamsters are described along with the characteristics of the induced tumors. Female Syrian golden hamsters were first subjected to Cholecystoduodenostomy with dissection of the extrahepatic bile duct on the distal end of the common duct (CDDB) and were, 4 weeks later, treated with weekly subcutaneous injections of N-nitrosobis(2-oxopropyl)amine (BOP) at a dose of 10 mg/kg body weight for 9 weeks. The animals were killed at the 12th, 16th and 20th week after the initiation of BOP treatment. Extrahepatic bile duct carcinoma developed in 16%, 24% and 41% and gallbladder carcinoma occurred in 58%, 81% and 82% of the hamsters, respectively, at the corresponding times of killing. The incidences were significantly higher than those in sham-operated controls ( P <0.01). The induced extrahepatic bile duct carcinomas were predominantly of the polypoid type and gallbladder carcinomas were of the papillary type in growth form, being morphologically similar to early stage biliary carcinoma in humans. Immunohistochemical staining using bromodeoxynridine and anti-bromo-deoxyuridine monoclonal antibody demonstrated that the CDDB procedure greatly accelerated the cell kinetic activity of the biliary epithelium, and this was considered to be a major factor promoting the development of biliary carcinomas in this hamster model. In conclusion, this new model provides a high incidence of tumor development at the extrahepatic biliary tract and is expected to be useful for clarifying the characteristics of this highly malignant tumor.     

Modifying effects of 4-phenylbutyl isothiocyanate on N-nitrosobis(2-oxopropyl)amine-induced tumorigenesis in hamsters

The modifying effects of dietary 4-phenylbutyl isothiocyanate (PBITC), given during the initiation stage of carcinogenesis, were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1–3, each consisting of 30 hamsters, were given BOP by two subcutaneous injections, 1 week apart, at a dose of 20 mg/kg body weight, plus 0, 10 or 100 μmol/animal of PBITC in corn oil by gavage 2 h prior to each carcinogen treatment. Ten animals in group 4 served as a vehicle control, and animals in groups 5 and 6, each consisting of ten hamsters, were given 10 and 100 μmol of PBITC alone in corn oil. Sacrifice was 52 weeks after the first BOP injection. The PBITC treatments significantly (P<0.05) inhibited the development of pancreatic ductal dysplasias and adenocarcinomas. Also, lung tumors (adenomas and adenocarcinomas) were significantly (P<0.05) reduced in a dose-dependent manner. In contrast, both hepatocellular and cholangiocellular tumors (adenomas and carcinomas) tended to be or were significantly increased by PBITC. These results, taken together with our previous findings, indicate that the natural isothiocyanate, phenethyl isothiocyanate (PEITC), has a more potent chemopreventive action against BOP-induced tumorigenesis than synthetic isothiocyanates with longer alkyl chains, such as 3-phenylpropyl isothiocyanate (PPITC) and PBITC. Thus, their lipophilicity does not necessarily reflect the chemopreventive potential because the strength of lipophilicity is PEITC相似文献   

High Yields of Granulosa Cell Tumors/Luteomas in F344 Rat Ovaries after Transplacental Administration of N-Nitrosobis(2-oxopropyl)amine

Ovarian tumors were induced at very high incidence in the offspring of F344 rats receiving 3 subcutaneous injections of 10 mg/kg of N-nitrosobis(2-oxopropyl)amine on the 14th, 18th and 20th days of gestation. Histologically, all ovarian tumors were of the granulosa cell tumor and/or luteoma type. Many of them consisted of large, polygonal cells with abundant eosinophilic or vacuolated cytoplasm, arranged in sheets or in a pseudo-palisaded pattern separated by thin fibrovascular stroma, and they exhibited typical luteoma morphological character. The high yields, and the similarities in morphology as well as putative hormonal influence suggest that this experimental system may serve as a good animal model for granulosa cell tumor and/or luteoma development in women.     

Inhibitory Effects of 1'-Acetoxychavicol Acetate on N-Nitrosobis(2-oxopropyl)-amine-induced Initiation of Cholangiocarcinogenesis in Syrian Hamsters

The influence of 1'-acetoxychavicol acetate (ACA) during the initiation stage was investigated in the N -nitrosobis(2-oxopropyl)amine (BOP)-initiated hamster tumorigenesis model. Ninety male 5-week-old hamsters were divided into three groups, each consisting of 30 animals, and s.c. injected with 20 mg/kg of BOP twice with a one-week interval. Groups 1 through 3 were fed diet supplemented with ACA at concentrations of 500, 100 and 0 ppm, respectively, for 3 weeks starting one week before the first carcinogen application. At the termination of experimental week 54, the total incidence and multiplicity of cholangiocellular adenomas and carcinomas in group 1 (17.9% and 0.3±0.9) were significantly ( P < 0.05 and P < 0.01) decreased as compared to the group 3 values (50.0% and 0.7±0.8). The ACA treatments also showed a tendency to reduce the development of preneoplastic lesions in the pancreas, a main target organ of BOP, although this was not statistically significant. Our results thus indicate that ACA exerts an inhibitory effect on BOP-induced cholangiocarcinogenesis in hamsters. Taken together with previous findings of inhibited colon, oral and skin carcinogenesis in rats and mice, they suggest that ACA is a candidate chemopreventive agent with a wide spectrum of activity.     

Modifying effects of 4-phenylbutyl isothiocyanate on N-nitrosobis(2-oxopropyl)amine-induced tumorigenesis in hamsters

The modifying effects of dietary 4-phenylbutyl isothiocyanate (PBITC), given during the initiation stage of carcinogenesis, were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). A total of 120 female 5-week-old hamsters were divided into six groups. Animals in groups 1–3, each consisting of 30 hamsters, were given BOP by two subcutaneous injections, 1 week apart, at a dose of 20 mg/kg body weight, plus 0, 10 or 100 μmol/animal of PBITC in corn oil by gavage 2 h prior to each carcinogen treatment. Ten animals in group 4 served as a vehicle control, and animals in groups 5 and 6, each consisting of ten hamsters, were given 10 and 100 μmol of PBITC alone in corn oil. Sacrifice was 52 weeks after the first BOP injection. The PBITC treatments significantly (P<0.05) inhibited the development of pancreatic ductal dysplasias and adenocarcinomas. Also, lung tumors (adenomas and adenocarcinomas) were significantly (P<0.05) reduced in a dose-dependent manner. In contrast, both hepatocellular and cholangiocellular tumors (adenomas and carcinomas) tended to be or were significantly increased by PBITC. These results, taken together with our previous findings, indicate that the natural isothiocyanate, phenethyl isothiocyanate (PEITC), has a more potent chemopreventive action against BOP-induced tumorigenesis than synthetic isothiocyanates with longer alkyl chains, such as 3-phenylpropyl isothiocyanate (PPITC) and PBITC. Thus, their lipophilicity does not necessarily reflect the chemopreventive potential because the strength of lipophilicity is PEITC<PPITC<PBITC.     

Ki-ras Activation in Pancreatic Carcinomas of Syrian Hamsters Induced by N-Nitrosobis(2-hydroxypropyl)amine

Five pancreatic carcinomas induced by N -nitrosobis(2-hydroxypropyl)amine in Syrian golden hamsters were analyzed for activation of Ki- ras at codons 12 and 13, using the polymerase chain reaction and direct sequencing. The Ki- ras gene was shown to be activated in four of the five carcinomas, and the results were further confirmed by subcloning and sequencing. All the mutations involved a G-to-A transition at the second position of codon 12, which resulted in a change at the amino acid level from glycine to aspartic acid. This mutation is identical with that reported for pancreatic tumors of Syrian hamsters induced by N -nitrosobis(2-oxopropyl)amine.     

The formation of N-nitrosomethyl(2-oxopropyl)amine from N-nitrosobis(2-oxopropyl)amine in vivo

After injection of N-nitrosobis(2-oxopropyl)amine (BOP) (10mg/kg) to male Syrian golden hamsters there were higher concentrationsof BOP and many of its metabolites in the hamster pancreas comparedwith the liver and salivary gland. Also, a potential methylatingmetabolite of BOP, N-nitrosomethyl(2-oxopropyl)amine, was foundin both tissues.     

Effects of 3-Aminobenzamide on Induction of Multiorgan Carcinogenesis by N-Nitrosobis(2-hydroxypropyl)amine in Hamsters

The effects of an inhibitor of poly(ADP-ribose)polymerase, 3-aminobenzamide (ABA), on N-nitrosobis(2-hydroxypropyl)amine (BHP)-induced pancreas, liver, gallbladder and lung carcinogenesis in Syrian golden hamsters were investigated. Animals were given either BHP alone, by subcutaneous injection at a dose of 500 mg/kg body weight, or in combination with an intraperitoneal injection of ABA 30 min after the BHP at a dose of 300 or 600 mgAg body weight once a week for 5 weeks, and then killed 35 weeks after the commencement of the experiment. ABA exerted inhibitory effects on pancreas and lung carcinogenesis induced by BHP, with mean numbers of lesions (including hyperplasias and carcinomas) being significantly decreased compared with the BHP-alone group values, while no significant effect was observed on liver or gallbladder carcinogenesis. These results suggest that the effects of ABA on carcinogenesis depend on the target organ as well as the chemical carcinogen examined.     

DNA alkylation by nitrosobis-(2-oxopropyl)amine in rats of different ages

We have examined the methylation of liver DNA (O6- and N7-methylguanine) by nitrosobis-(2-oxopropyl)amine (BOP) in male and female rats at various ages, following treatment with 2.5 mg of BOP; this dose given twice weekly for 30 weeks induces tumors in all animals. Except in young rats there was more methylation in female rat liver than in male rat liver, when adjusted for different sizes of the animals. There were differences in the extent of methylation between young (4 weeks) and older rats, but not between young adult (20 weeks) and old adult (65 weeks) males; the latter developed liver tumors when treated with BOP, and the former did not. There was no obvious relation between increased susceptibility to liver tumor induction by BOP and the extent of alkylation of liver DNA. Methylation of DNA was lower in the kidney than in the liver and, here, there was little difference between the sexes. In the testis there was N7-methylation of guanine in DNA, but no O6-methylguanine was detected.     

A cyclooxygenase-2 inhibitor,nimesulide, inhibits postinitiation phase of N-nitrosobis(2-oxopropyl)amine-induced pancreatic carcinogenesis in hamsters

The modification effects of nimesulide, a cyclooxygenase (COX)-2 inhibitor, administration during the postinitiation phase of pancreatic carcinogenesis were investigated in hamsters treated with N-nitrosobis(2-oxopropyl)amine (BOP). Male Syrian hamsters were given 4 weekly s.c. injections of BOP at a dose of 10 mg/kg and thereafter administered 0, 100 or 400 ppm nimesulide in the diet for 36 weeks. Additional groups of hamsters were fed 400 ppm nimesulide without prior BOP initiation or nontreated. At week 40, all surviving animals were killed and development of neoplastic and preneoplastic lesions was assessed histopathologically. The incidence of pancreatic adenocarcinomas was significantly (p < 0.05) decreased in the BOP/400 ppm nimesulide group compared to the BOP alone group. The multiplicity of total lesions of pancreatic adenocarcinoma plus atypical hyperplasia was also significantly (p < 0.05) lowered. Immunohistochemically, COX-2 was clearly expressed in pancreatic and lung tumor cells, whereas expression was not remarkably affected by the 400 ppm nimesulide treatment. Proliferating cell nuclear antigen labeling indices of pancreatic ducts were significantly (p < 0.01) reduced by nimesulide. The incidence and multiplicity of neoplastic lesions in other organs did not significantly differ among the BOP-treated groups, though only the multiplicity of lung tumors showed a tendency to decrease. No neoplastic lesions were detected in animals receiving nimesulide alone. Our results clearly indicate that nimesulide protects against BOP-induced pancreatic tumors in hamsters.     

Induction of pancreatic DNA damage and nodules in rats treated with N-nitrosobis(2-oxopropyl)amine and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine

DNA damage was demonstrated by alkaline elution analysis inpancreas of rats treated with 100 mg/kg N-nitrosobis(2-oxopropyl)amine(BOP) and 20 mg/kg N-nitroso(2-hydroxy-propyl)2-oxopropyl)amine(HPOP). Young rats were treated with a single dose of BOP orHPOP and autopsied 4 months later. Histologically the pancreasescontained multiple foci and nodules of atypical acinar cellswhich were not seen in controls.     

Significant Increase of 8-Hydroxydeoxyguanosine in Liver DNA of Rats Following Short-term Exposure to the Peroxisome Proliferators Di(2-ethylhexyl)phthalate and Di(2-ethylhexyl)adipate

8-Hydroxydeoxyguanosine (8-OH-dG) levels were examined in liver and kidney DNA after di(2-ethylhexyl)phthalate (DEHP), di(2-ethylhexyl)adipate (DEHA) and phthalic anhydride administration to male 6-week-old F-344 rats in the diet at concentrations of 1.2, 2.5 and 1.5%, respectively. Significant increases in 8-OH-dG levels were observed only in the liver (target organ of DEHP and DEHA carcinogenesis) DNA after 1 and 2 weeks of treatment with DEHP and DEHA, respectively. The results suggest the involvement of oxidative DNA damage in hepatocarcinogenesis by peroxisome proliferators.     

Alkylation of rodent tissue DNA induced by N-nitrosobis(2-hydroxypropyl)amine.

Levels of methyl and hydroxypropyl adducts induced by single s.c. injections of various doses of tritium-labeled N-nitrosobis(2-hydroxypropyl)amine ([1-3H]BHP) were determined in the liver, pancreas, kidney and lung of hamsters and rats. At doses of BHP used in carcinogenesis studies (100-500 mg/kg), methylation of DNA was more extensive than its hydroxypropylation; however, it did not increase proportionally with the dose and gradually became secondary to hydroxypropylation at higher doses of the carcinogen. Ratios of hydroxypropyl versus methyl adducts also varied significantly depending on the tissue and species. In both species ratios of N7-hydroxypropylguanine (N7-HpG) versus N7-methylguanine (N7-MeG) were greater in kidney and pancreas than in liver or lung. Due to apparent differences in the repair of O6-methylguanine (O6-MeG) and O6-hydroxypropylguanine (O6-HpG), and the propensity of 2-hydroxypropylating as compared to methylating agents to yield a greater percentage of oxygen adducts, ratios of O6-HpG versus O6-MeG were markedly greater than those of N7-HpG versus N7-MeG. Levels of O6-HpG were greater than those of O6-MeG in rat liver, pancreas and kidney and also in hamster kidney, while such levels were similar in rat lung and also in hamster liver, pancreas and lung. Like N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-hydroxypropyl) (2-oxopropyl)amine (HPOP), BHP was activated primarily in the liver and induced substantially greater DNA damage in this than in any other tissue examined. However, unlike BOP and HPOP, which induced similar levels of hepatic DNA damage in the above two species, BHP methylated and hydroxypropylated hamster liver DNA more extensively than that of the rat. Differences between BOP and BHP were also observed regarding levels and distribution of DNA adducts in extrahepatic tissues. In rats, BHP induced greater levels of methylation and hydroxypropylation in lung than in kidney, while the reverse was observed with BOP. Apparently reduction of the beta-carbon of pancreas-specific nitrosamine carcinogens results in a shift of alkylation from kidney to the lung. Excretion of HPOP in the urine of BHP-treated animals and the observed saturation of DNA methylation at high doses of BHP, supported the hypothesis that the BHP-induced methylation of DNA proceeded via the intermediate formation of HPOP. This was further supported by the observation that both excretion of HPOP and levels of methyl adducts were greater in hamsters than in rats.(ABSTRACT TRUNCATED AT 400 WORDS)     

Cholecystokinin inhibits DNA alkylation induced by N-nitrosobis (2-oxopropyl)amine (BOP) in hamster pancreas.

Cholecystokinin (CCK) inhibits pancreatic cancer but not hepatic tumor induction by N-nitrosobis (2-oxopropyl) amine (BOP) in hamsters when administered with or shortly before BOP. In this study, we evaluated the capability of sulfated CCK-8 to inhibit DNA alkylation in the hamster pancreas. We examined the pattern of O6-methylguanine (G6-Me) and N7-methylguanine (G7-Me) in pancreatic ductal, acinar and liver tissues from Syrian hamsters treated with a single dose of BOP (20 mg/kg s.c.) and with five s.c. injections of CCK-8 (200 pM/kg, 30 min apart). The first CCK injection was given either 90 min before, or together, or 3 h after POP administration. The amount of G6-Me in liver DNA did not differ significantly. We observed a decrease of G7-Me in the liver of the group treated with CCK together with POP as compared to POP alone (P less than 0.005). Lower amounts of G6-Me were found in ductal preparations (P less than 0.01) of the animals treated with CCK before POP as compared to POP alone. CCK also modified the pattern of alkylation in the acinar tissue, but without a clear relationship with the timing of administration. The results suggest that the inhibitory effect of CCK-8 on pancreatic carcinogenicity of BOP could be related to its capability to modify DNA alkylation by yet unknown mechanisms.     

Beta-oxidized N-nitrosoalkylcarbamates as models for DNA alkylation by N-nitrosobis(2-oxopropyl)amine in Syrian hamsters

A single dose of N-nitrosobis(2-oxopropyl)amine (NDOPA) can selectively induce pancreatic-duct adenocarcinomas in Syrian hamsters. Multiple doses or a higher single dose can induce tumours of the liver and other organs. Our earlier studies employing NDOPA systematically labelled with 14C in the three-carbon chain showed that hamster pancreatic DNA is almost exclusively methylated and that the sole source of the methyl group is the alpha carbon of NDOPA. Hamster liver DNA was equally methylated and alkylated by a three-carbon chain. Current studies using generally labelled tritiated NDOPA with a very high specific activity have shown that the three-carbon alkylation is 2-hydroxypropylation. We have identified two adducts isolated from hamster liver DNA, N7-(2-hydroxypropyl)-guanine and O6-(2-hydroxypropyl)guanine, which contain this group, and we have also isolated and identified N7-methylguanine and O6-methylguanine in DNA from hamster liver and pancreas. beta-Oxidized N-nitrosocarbamates, ethyl N-nitroso-2-oxopropylcarbamate (NOPC) and ethyl N-nitroso-2-hydroxypropylcarbamate (NHPC), are useful models for predicting the DNA adducts observed in vivo following NDOPA treatment. Base-catalysed decomposition of NOPC in the presence of exogenous DNA yields five methylated purines (N3-, N7- and O6-methylguanines and N1- and N3-methyladenines). NHPC, a model for N-nitrosamines containing the 2-hydroxypropyl group, reacts with guanosine to yield N7- and O6-(2-hydroxypropyl)guanines.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nicotinamide and selenium stimulate the repair of DNA damage produced by N-nitrosobis (2-oxopropyl) amine

The effects of nicotinamide (NIC) and selenium (SE), given alone or together, on N-nitrosobis (2-oxopropyl) amine (BOP)-induced DNA damage were measured in rat liver and colon. SE stimulated DNA repair in both tissues, whereas NIC was without effect. The failure of NIC to stimulate the repair of BOP-induced DNA damage in rat liver, where BOP is a methylating and hydroxypropylating agent, suggested that the nature of the DNA damaging agent could be important. NIC stimulated the repair of DNA damage induced by BOP (methylating agent in the pancreas) and N-nitrosodiethylamine (ethylating agent) but not by azaserine (carboxymethylating agent) or N-nitroso-5,6-dihydrouracil (carboxyethylating agent).     

Induction of benign and malignant lip tumors in Syrian hamsters by topical application of N-nitrosobis(2-oxopropyl)amine and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine

Weekly topical application of equitoxic doses of N-nitrosobis(2-oxopropyl)amine (BOP) or N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) to lip and/or vagina of female Syrian hamsters led to the development of papillomas and carcinomas of the lip, papillomas of the vagina, and tumors of internal organs. The relative incidence of the tumor types is affected by the dose of BOP or HPOP administered. BOP is excreted unchanged and as HPOP in the saliva of Syrian hamsters injected subcutaneously with BOP and pilocarpin. This result may help to explain preliminary observations that subcutaneously injected BOP and pilocarpin also lead to lip tumors.     

Species specificity in the metabolism of N-nitrosobis(2-oxopropyl)amine and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine to mutagens by isolated rat and hamster hepatocytes

The metabolic activation of the carcinogens N-nitrosobis(2-oxopropyl)amine (BOP) and N-nitroso(2-hydroxypropyl)(2-oxopropyl)amine (HPOP) by Fischer rat and Syrian hamster hepatocytes was investigated in order to determine the existence of species differences in the induction of cell mutation. The conversion of BOP and HPOP into forms mutagenic to V79 cells was studied by using the hepatocyte-mediated mutagenicity assay. Mutations at the hypoxanthine:guanine phosphoribosyltransferase locus and the Na-K-ATPase locus were scored by the induction of 6-thioguanine resistance (TGr) or ouabain resistance (Ouar), respectively. Hepatocytes of both species were capable of converting BOP and HPOP to mutagens for V79 cells in a dose-dependent manner. Metabolism of BOP by rat hepatocytes resulted in higher mutation frequencies than that by hamster hepatocytes. At a BOP concentration of 240 microM, rat hepatocyte metabolism yielded 90.7 TGr mutants and 19.5 Ouar mutants per 10(5) V79 cells. At the same concentration, hamster hepatocyte metabolism of BOP yielded 54.1 TGr mutants and 13.0 Ouar mutants per 10(5) V79 cells. These results did not correlate with the known carcinogenic potency of BOP in the hamster as compared to the rat. Hamster hepatocytes carried out the catabolism of BOP to CO2 at faster rates than rat hepatocytes; therefore, the species difference in mutagenic activation was not due to a defect in BOP uptake or metabolism by hamster hepatocytes. In contrast, metabolism of HPOP by hamster hepatocytes resulted in significantly higher mutation frequencies than that by rat hepatocytes. At an HPOP concentration of 240 microM, hamster hepatocyte metabolism yielded 83.5 TGr mutants per 10(5) V79 cells; rat hepatocyte metabolism yielded only 19.8 TGr mutants per 10(5) V79 cells. This species difference in mutagenic activation correlated well with the known potency of HPOP as a carcinogen for the hamster as compared to the rat. Since hamster pancreatic cells and subcellular fractions are known to have very limited capacity to perform the metabolic activation of HPOP, the results of this study imply that liver metabolism plays an important role in the conversion of HPOP to an agent(s) which subsequently affects the hamster pancreas. The mutagenic potency of BOP versus HPOP was compared after metabolism by hepatocytes from both species. Following their metabolism by hamster hepatocytes, the two compounds were nearly equivalent in mutagenic potency. After metabolism by rat hepatocytes, BOP was significantly more potent mutagen than HPOP.(ABSTRACT TRUNCATED AT 400 WORDS)     

Carcinogenicity of N-nitrosobis(2-hydroxypropyl)amine and N-nitrosobis(2-oxopropyl)amine in MRC rats.

Weekly sc injections of equitoxic doses of N-nitrosobis(2-hydroxypropyl)amine (BHP) and N-nitrosobis(2-oxopropyl)amine (BOP) to Wister-derived MRC rats induced tumors. The incidence, latency, multiplicity, morphologic type, and distribution of these tumors varied according to the compound given. The esophagus was the main target organ for BHP (100%), followed by the respiratory tract (87%), pharynx (80%), colon and liver (each 73%), kidneys (20%), thyroid gland (20%), and urinary bladder and urethra (each 7%). BOP was ineffective in the esophagus and pharynx but induced a higher incidence of tumors in the kidneys (27%), thyroid gland (60%), urinary bladder (33%), and urethra (73%) and fewer neoplasms in the respiratory tract (20%), colon (67%), and liver (53%). In addition, BOP caused a few, apparently primary, prostate squamous cell carcinomas. The results are compared with results of BHP treatment in Sprague-Dawley rats and with results of BHP and BOP treatment in Syrian golden hamsters.     

DNA Modification by 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine in Rats

2-Amino-l-methyl-6-pheny]imidazo[4,5- b ]pyridine (PhIP) is the most abundant mutagenic heterocyclic amine by weight in cooked foods. This mutagen was found to produce DNA adducts in all ten tested organs of rats using the ³²P-postlabeling method. The level of DNA adducts in the pancreas, kidney and liver increased dose-dependently and feeding tinie-dependently up to four weeks. When diet containing 0.05% PhIP was given to rats for four weeks, levels of PhIP-DNA adducts were relatively high in the lung, pancreas and heart, being around 20 per 10⁷ nucleotides, and lowest in the liver, being 2.20 per 10⁷ nucleotides. Thus, PhIP showed a unique feature in the formation of DNA adducts compared to other mutagenic and carcinogenic heterocyclic amines, which produce the highest level of DNA adducts in the liver.