Effects of acetylsalicylic acid on rats: An in vivo experimental study in azaserine-rat model.

AIM: The effect of acetylsalicylic acid (ASA) on thiol levels was studied in a rat model of azaserine carcinogenesis. MATERIALS AND METHODS: ASA and azaserine were applied to the animals to research changes in cellular sulfhydryl (-SH) content and variations in free and protein-bound molecules containing the -SH group. Such effects in rats injected with azaserine were investigated at low (200 ppm) and high (400 ppm) concentrations of ASA over a relatively short (6 months) and a relatively long (12 months) period. RESULTS: Changes in the hepatic, pancreatic, and renal -SH contents were also determined. CONCLUSION: Compared to the other tissues studied, the liver contained the highest levels of both free and protein-bound -SH.

Assessing eco-toxicological effects of industrial 2,4-D acid iso-octylester herbicide on rat pancreas and liver.

We studied the eco-toxic and carcinogenic effects of a commonly used 2,4-D acid iso-octylester herbicide on rat liver and pancreas. The rats in Group 1 were fed a standard feed and the rats in Group 2 were fed with standard feed to which was added 200 mg/kg/day 2,4-D acid iso-octylester for 16 weeks. Azaserine, 30 mg/kg/body weight, was injected into rats of Groups 3 and 4 to investigate the effects of 2,4-D acid iso-octylester on the development of neoplasms. After feeding the rats with neoplasms in Group 4 with food including 200 mg/kg/day 2,4-D acid iso-octylester for 16 weeks, an autopsy was carried out on all animals. We found that 2,4-D acid iso-octylester caused the formation of atypical cell foci (ACF) in the pancreata and livers of rats. ACF that were formed experimentally by exposure to azaserine had increased diameter, volume and number of atypical cell foci/mm(2) and mm(3) after exposure to 2,4-D acid iso-octylester. Our observations indicated that this herbicide potentially is a cancer initiator.

Inhibitory effects of acetylsalicylic acid on exocrine pancreatic carcinogenesis.

We investigated short (6 months) and long (12 months) term inhibitory effects of low (200 ppm) and high (400 ppm) dosages of acetylsalicylic acid (aspirin) on exocrine pancreatic carcinogenesis. It is known that exocrine pancreatic carcinogenesis can be detected by the presence of atypical acinar cell foci (AACF) in pancreas. We investigated possible inhibitory effects of acetylsalicylic acid in an azaserine-treated rat model. AACF were produced in rats by injection with azaserine according to previous studies. Our findings showed that the number, volume and diameter of pancreatic AACF were reduced after acetylsalicylic acid application. These observations suggest that acetylsalicylic acid may exert a protective effect against neoplastic development of pancreatic acinar cells in azaserine injected rats. Our findings corroborate reports in the literature concerning the effects of aspirin in reducing neoplastic development.

Expression of cholecystokinin-2/gastrin receptor in the murine pancreas modulates cell adhesion and cell differentiation in vivo.

The presence of gastrin and cholecystokinin-2 (CCK2) receptors in human preneoplastic and neoplastic gastrointestinal lesions suggests a role in cancer development. In addition to the growth-promoting action of gastrin, recently a role of the cholecystokinin-2/gastrin receptor (CCK2-R) modulating cellular morphology in cultured epithelial cells has been shown. Here, we have investigated in transgenic (ElasCCK2) mice whether ectopic expression of human CCK2-R in the exocrine pancreas affected epithelial differentiation. Cellular localization of cell adhesion molecules, differentiation markers, and transcription factors was determined using immunofluorescence techniques. Before tumor formation, expression and subcellular localization of proteins of the adherens junction complex, differentiation markers, and transcription factors were altered in ElasCCK2 exocrine pancreas, indicating an evolution from an acinar to a ductal phenotype. Loss of cell polarity, defective secretion, and loss of intercellular adhesion in acini of ElasCCK2 mice was confirmed by ultrastructural analysis. Finally, expression of the transgene in mice treated with the carcinogen azaserine resulted in enhanced size of preneoplastic lesions as well as an increased degree of acinar-ductal transdifferentiation. Thus, these data represent the first evidence for the CCK2-R modulating intercellular adhesion and cell fate in vivo and show that these alterations may contribute to enhanced sensitivity of ElasCCK2 pancreas to chemical carcinogens.

Characterisation of the progression of azaserine-induced rat pancreatic adenocarcinoma by proliferative cell nuclear antigen, basement membrane laminin and trypsinogen immunohistochemistry.

The progression of azaserine-induced rat pancreatic adenocarcinoma (AC) was characterised using quantitative and semiquantitative immunohistochemistry for proliferating cell nuclear antigen (PCNA), basement membrane laminin (BML) and trypsinogen (TG). Samples were taken 5-20 months after initiation. High PCNA-labelling indices (PCNA LIs) were measured 5 months after the induction of atypical acinar cell nodules (AACNs), which decreased later and stagnated until a further decline in the month 10 adenomas. Then a second premalignant proliferative wave was observed (month 13) within the adenoma stage. Later, in month 20 differentiated ACs PCNA LIs fell to the host tissue level but were found highest in the month 20 anaplastic ACs indicating a switch to malignant proliferation. Month 20 invasive ACs showed a number of separate proliferative foci. In early AACNs, BML decreased and remained low till the local maximum in the month 13 adenoma. Invasive ACs did not express BML. Month 5 AACN and differentiated AC were TG deficient but anaplastic AC regained its TG expression. However invasive AC was again TG negative. These results are discussed in combination with our previous data on progressional changes of autophagic capacity and microvessel densities.

Ubiquitin cytochemical changes during azaserine-initiated pancreatic carcinogenesis.

The ubiquitin (Ub)-proteasome proteolytic system is highly selective, and the specific proteins involved in cell division, growth, activation, signaling and transcription are degraded at different rate depending on the physio-pathological state of the cell. Ubiquitination serves first of all as a signal for protein degradation of short-lived and abnormal proteins under several stressful conditions. The immunocytochemical localization of Ub in some malignant tumours has recently been presented and differences in Ub expression has been observed during malignant transformation. Change in the level of Ub and Ub-conjugated proteins might reflect a higher metabolic-catabolic ratio in neoplastic cells. Most studies have been focused on the malignant stage of tumour progression, and only a few papers have dealt with the change in Ub and Ub-protein conjugates level during the whole progression. To address this problem, we applied an azaserine-induced pancreatic carcinogenesis model, in which premalignant and malignant stages were investigated throughout the progression. The level of Ub immunoreactivity was measured in nucleus and cytoplasm by electron microscopic immunocytochemical and morphometrical methods. We found a significant increase of Ub level in the nucleus and the cytoplasmic area in premalignant atypical acinar cell nodule (AACN) cells and in malignant adenocarcinoma in situ (CIS) cells at month 20 after initiation.

Changes in cellular autophagic capacity during azaserine-initiated pancreatic carcinogenesis.

Growth regulation is a crucial event in tumour progression. Surprisingly, relatively few papers have dealt with the catabolic side of regulation, and there are practically no data regarding the autophagic process during tumour development. We approach this problem by morphometrical investigation into the possible changes of autophagic activity during the progression of rat pancreatic adenocarcinoma induced by azaserine. In the present study, autophagic capacity of the azaserine-induced premalignant and malignant cells were characterised and compared to the respective host tissue cells of the rat pancreas and to the acinar cells in other stages of tumour development. Using vinblastine (VBL) as an enhancer, and cycloheximide (CHI) as an inhibitor of autophagic segregation we observed that autophagic capacity of premalignant cells (month 6 and 10 after initiation) is much higher than in the host tissue cells. We found a sharp decrease in self-digesting capacity in adenocarcinoma cells (month 20) where VBL induced a minimal accumulation of autophagic vacuoles which was, surprisingly, not inhibited by CHI, i.e. the CHI-sensitive regulatory step was lost. The changes in autophagic capacity are probably associated to specific steps of tumour progression in our system.

Quantitative microvascular changes during azaserine-initiated pancreatic carcinogenesis.

Although angiogenesis is considered to be indispensable for continuous tumour growth, only very few studies have been published performing microvessel quantification during tumour progression. We measured the tumour vascularity in different stages of rat pancreatic carcinogenesis induced by azaserine and promoted by raw soya flour-containing pancreatotrophic diet. Besides the tumour samples taken at 6 (atypical acinar cell nodules), 15 (adenomas) and 20 (localised adenocarcinomas) months after carcinogen initiation, we also investigated 3 control groups: tumour-bearing host tissue of azaserine-treated rats and normal tissue of untreated rats kept on standard or pancreatotrophic diet. In contrast with the usual microvessel counting on hot spots, we determined microvascular surface density (Sv) and volume density (Vv) by electron microscopic morphometry. There was no significant difference in these respect between the control groups. At month 6 after the azaserine induction Sv and Vv showed slight, nonsignificant decrease as compared to the host control. Both values remained unchanged until the 15th month and increased significantly by the 20th month. These results may indicate comparable growth rate of tumour and new microvessels in the premalignant stages of carcinogenesis while a more intense angiogenesis than tumour growth afterwards.

Retrospective evaluation of serum ornithine carbamyltransferase activity as an index of hepatotoxicity in toxicological studies with rats.

The sensitivity of elevated serum ornithine carbamyltransferase (OCT) as an index of hepatotoxicity in rats was assessed in different studies conducted over a number of years and originally designed to examine the toxicity or carcinogenicity of a variety of test chemicals and diets. Changes in serum OCT activities were compared with the more widely used clinical endpoints, alanine aminotranserase (ALT) and aspartate aminotransferase (AST). In the first study, rats received a single oral dose of the hepatotoxic and hepatocarcinogenic fungal toxin aflatoxin B(1) (AFB(1)). The increase in enzyme levels between control and AFB(1)-treated rats was greater for serum OCT than for ALT or AST. This response was similar to the changes in serum enzyme levels in studies where rats ingested a hepatotoxic and hepatocarcinogenic choline deficient (CD) diet. When rats were exposed to the hepatotoxic and nephrotoxic fungal toxin fumonisin B(1) (FB(1)) by intraperitoneal injection for 6 days, serum AST and ALT were significantly elevated above control levels while OCT was unaffected. The peroxisome proliferator ciprofibrate caused elevated ALT and AST but not OCT at week 52 of dietary exposure, after the development of liver nodules and tumours. Of the two liver-specific enzymes examined in all of the studies, ALT was more consistently predictive of hepatotoxicity than OCT.

Cellular autophagic capacity is highly increased in azaserine-induced premalignant atypical acinar nodule cells.

Although cellular autophagy is recognized as a major pathway of macromolecular catabolism, little data are available regarding its activity or regulation in tumor cells. We approach this problem by morphometrical investigation into the possible changes in autophagic activity during progression of rat pancreatic adenocarcinoma induced by azaserine and promoted by a raw soya flour-containing pancreatotrophic diet. In the present study, the autophagic capacity of the carcinogen-induced premalignant atypical acinar nodule cells was characterized and compared with controls (normal tissue of rats kept on standard laboratory or pancreatotrophic diet and host tissue of the premalignant nodules of the azaserine-treated rats). Given for 90 min, vinblastine, an enhancer of autophagic segregation (i.e. formation of autophagic vacuoles), caused a one to two orders of magnitude larger expansion of the autophagic compartment in atypical nodule cells than in the controls. Then a 20 min blockade of segregation by cycloheximide led to regression of the autophagic compartment, which was barely measurable or moderate in the controls but exceeded 50% in the premalignant cells. At the same time, the cytoplasmic volume fraction of early autophagic vacuoles regressed to a near zero value in each cell type. Expansion and regression rates of these nascent vacuoles showed that both segregation and degradation were 6-20 times faster in the nodule than in normal tissue cells. These results show that the autophagic capacity of the premalignant cells in our system is greatly increased, possibly making these cells unusually sensitive to up-regulation of their self-digesting activity in response to different extracellular signals or drugs.

The cytotoxicity of DNA carboxymethylation and methylation by the model carboxymethylating agent azaserine in human cells.

Carboxymethylating agents are potential sources of endogenous DNA damage that have been proposed as possible contributors to gastrointestinal carcinogenesis. The cytotoxicity of the model DNA carboxymethylating agent azaserine was investigated in human cells. Expression of the DNA repair enzyme O(6)-methylguanine-DNA methyltransferase (MGMT) did not affect sensitivity to the drug in two related Raji Burkitt's lymphoma cell lines. DNA mismatch repair-defective variants of Raji cells which display increased tolerance to DNA methylation damage were not selectively resistant to azaserine. Complementary results were obtained with a second carboxymethylating agent, potassium diazoacetate. In contrast, lymphoblastoid cell lines representative of each of the xeroderma pigmentosum complementation groups, including the variant, were all significantly more sensitive to azaserine than nucleotide excision repair-proficient cells. The hypersensitivity of XP cells was not due to systematic differences in the concentrations of intracellular thiol compounds or related thiol metabolizing enzymes. The data indicate that of the two types of potentially lethal DNA damage which azaserine introduces, carboxymethylated bases and O(6)-methylguanine, the former are repaired by nucleotide excision repair and are a more significant contributor to azaserine lethality in human cells.

Effects of cholecystokinin octapeptide on a pancreatic acinar carcinoma in the rat.

PURPOSE: To investigate the effects of increasing concentrations of cholecystokinin octapeptide (CCK-8) on a pancreatic acinar adenocarcinoma. METHODS: Growth of the tumour was estimated in vivo on rats bearing a subcutaneous pancreatic carcinoma, and in vitro on primary cultured tumour cells. CCK receptors were characterized by binding assays. RESULTS: CCK-8, administered for 12 successive days, exerted a biphasic action on tumour growth: a dose-dependent stimulation with low doses (0.1 and 0.5 microg/kg) and inhibition with high doses (2 and 4 microg/ kg) as shown by respective increases and decreases in tumor volume, protein, RNA and amylase contents. In cell cultures, [3H]thymidine incorporation was dose-dependently increased with 10-(10) to 10(-8) M CCK-8 and inhibited with 10(-7) M. Both effects were completely suppressed by the CCK-receptor antagonists CR 1409 and L 364,718 (10(-4) M). Binding studies showed the overexpression of two classes of CCK-A receptors of low and high affinity when compared to the normal pancreas which was less sensitive to CCK-8. CONCLUSIONS: CCK-8 exerts a biphasic growth response on the acinar pancreatic carcinoma, mediated by two classes of CCK-A receptors overexpressed in the tumour.

Inhibition by amiloride of experimental carcinogenesis induced by azaserine in rat pancreas.

The effects of prolonged administration of the diuretic amiloride on pancreatic carcinogenesis induced by azaserine and on the labeling index of carcinogen-induced pancreatic lesions were investigated in Wistar rats. Rats were given 25 weekly injections of 10 mg/kg body weight azaserine and also 5 mg/kg body weight amiloride every other day until the end of the experiment at week 62. Carcinogen-induced pancreatic lesions were examined by histochemical techniques and were classified as ATPase-positive or ATPase-negative. In week 62, quantitative histologic analysis showed that prolonged administration of amiloride significantly reduced the number and size (as percent of parenchyma) of ATPase-positive pancreatic lesions, which are closely correlated with the subsequent development of pancreatic cancer. Amiloride also significantly decreased the labeling index of carcinogen-induced pancreatic lesions, but not of the surrounding acinar cells. In contrast, amiloride has no significant influence on the number and size of ATPase-negative pancreatic lesions. These findings indicate that amiloride inhibits pancreatic carcinogenesis, and that this effect may be related to the reduction of ATPase-positive lesions and to amiloride's inhibition of cell proliferation in neoplastic lesions of the pancreas.

Effects of dietary beta-carotene and selenium on initiation and promotion of pancreatic carcinogenesis in azaserine-treated rats.

In the present study the effects of 0.1 or 1.0 g beta-carotene/kg diet (L beta C or H beta C) and 1.0 mg or 2.5 mg selenium/kg diet (LSel or HSel), as well as combinations of the respective low and high concentrations of beta-carotene and selenium (LMix or HMix) on the initiation/early promotion phase or on the late promotion phase of pancreatic carcinogenesis in azaserine-treated rats, were investigated using cell proliferation and volumetric data of atypical acinar cell foci (AACF) as parameters. The present results indicate chemopreventive effects of dietary selenium, dietary beta-carotene and of their combination on the development of acinar pancreatic lesions induced in rats by azaserine. The inhibitory effect was most pronounced when beta-carotene and/or selenium were added to the diets during the late promotion phase of the carcinogenic process, although inhibition was also observed with these compounds when they were added to the diets during the first 5 weeks of the study only (initiation/early promotion phase). Neither in the initiation/early promotion phase nor in the late promotion phase was a dose-related trend observed. The multiplicities of AACF with a diameter over 1.0 mm and of carcinomas in situ (CIS), as well as the incidence of CIS were not significantly different among the groups. However, in the late promotion experiment a dose-related decline in multiplicity could be observed in the selenium supplemented groups and in the groups receiving combinations of beta-carotene and selenium. Cell proliferation in azaserine-induced AACF, as estimated by the bromodeoxyuridine (BrdU) labeling index, was significantly higher in H beta C, HSel, LMix and HMix groups (initiation/early promotion phase) as well as in H beta C, LSel, HSel, LMix and HMix groups (late promotion phase) than in high fat controls. From the present results it can be concluded that: (i) beta-carotene and selenium have inhibitory effects on pancreatic carcinogenesis induced in rats by azaserine; (ii) the most clear effects were observed when selenium was given as such, or in combination with beta-carotene during the late promotion phase; and (iii) beta-carotene and selenium stimulate cell proliferation in AACF.

Transforming growth factor-alpha and epidermal growth factor expression in the exocrine pancreas of azaserine-treated rats: modulation by cholecystokinin or a low fat, high fiber (caloric restricted) diet.

Expression of transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) was studied in normal pancreatic tissue and in (pre)neoplastic pancreatic lesions of azaserine-treated rats. They were given either a low fat, high fiber (low caloric) diet, to inhibit carcinogenesis, or a low fat diet combined with injections of the cholecystokinin analog caerulein to enhance carcinogenesis. The control groups, maintained on a low fat diet, were injected with azaserine or were not treated at all. Autopsy was performed at 6 and 15 months after the last azaserine injection. After both 6 and 15 months immunohistochemistry revealed a weak expression of EGF and TGF-alpha peptides in the acinar cells, and a stronger expression in the ductular and centroacinar cells. TGF-alpha peptide expression was reduced in both putative preneoplastic and neoplastic acinar cell lesions, but no differences in EGF peptide expression were observed between the various stages of exocrine pancreatic carcinogenesis. After 16 months an increase in TGF-alpha mRNA due to treatment with azaserine was detected by semi-quantitative PCR in total pancreatic homogenates, whereas EGF mRNA expression had decreased. TGF-alpha mRNA levels in macroscopically isolated tumors were significantly lower, but EGF mRNA levels were significantly higher, than in total pancreatic homogenates from azaserine-treated rats. Furthermore, EGF and TGF-alpha mRNA levels in isolated tumors did not differ significantly from mRNA levels in non-carcinogen-treated rats. Neither with immunohistochemistry nor with PCR were differences in EGF or TGF-alpha expression observed due to either inhibition or stimulation of carcinogenesis. It is concluded that putative preneoplastic acinar cell lesions induced in rat pancreas by azaserine may develop into acinar adenocarcinomas independently of TGF-alpha and EGF. The results suggest involvement of these growth factors at the early stage of the carcinogenic process, during the initiation of normal acinar cells into putative preneoplastic cells. However, modulation of azaserine-induced pancreatic carcinogenesis by cholecystokinin or a low fat, high fiber (caloric restricted) diet appeared not to be regulated by EGF or TGF-alpha.

Mutagenicity of O-diazoacetyl-L-serine (azaserine) and 6-diazo-5-oxo-L- norleucine (DON) in a soybean test system.

The mutagenicity of O-diazoacetyl-L-serine (azaserine) and 6-diazo-5-oxo-L-norleucine (DON), glutamine analogues, were assayed in heterozygous soybean plants (Y11y11), according to the appearance of mutational spots (yellow, dark green and twin) on the leaves. The mutagenicity of azaserine was detected at 0.1 mg/ml, and that of DON, at 0.05 mg/ml. DON was strongly cytotoxic at doses exceeding 0.1 mg/ml. After azaserine and DON treatment, large spots which occupied more than half the leaflet were found in the first and second compound leaves. The glutamine analogues increased the frequency of yellow spots much more than dark green spots or twin spots. Light green spots were observed on y11y11 plants. Azaserine and DON induce somatic crossing over, point mutation and segmental loss as major effects.

Dissimilar effect of the carcinogenic agent azaserine on pancreatic and hepatic polyamine metabolism in rats.

The present study was designed to investigate the effects of the carcinogenic agent azaserine on the induction of pancreatic and hepatic polyamine metabolism in rats. One single injection of 30 mg azaserine/kg body weight i.p. is known to induce adenoma and subsequently carcinoma, predominantly in the pancreas, after several months. Male Lewis rats were treated with either azaserine (30 mg/kg body weight i.p.) or saline and 5-10 animals per group were sacrificed 2, 6, 9, 12, 18, 24, and 48 h later. Furthermore, animals were simultaneously treated with the ornithine decarboxylase (ODC) inhibitor alpha-difluoromethylornithine (DFMO) or the polyamine oxidase inhibitor MDL 72527 and killed 6 and 12 h after azaserine injection. The azaserine-induced significant increase in pancreatic putrescine concentrations was accompanied by an increase in spermidine/spermine N1-acetyltransferase but unchanged ODC and was significantly inhibited by N, N'-bis(2,3-butadienyl)putrescine (MDL 72527) but not by DFMO. S-Adenosylmethionine decarboxylase (SAM-DC) activity was significantly decreased in the pancreata of azaserine-treated animals compared to controls. In contrast, the azaserine-induced significant increase in hepatic putrescine was lower and transient, was accompanied by an increase in ODC and SAM-DC, and was completely inhibited by simultaneous DFMO treatment but not by MDL 72527. These data show completely different patterns of activation of polyamine metabolism in the pancreas and in the liver: Azaserine treatment forms putrescine in the liver by de novo synthesis via ODC only, while azaserine-induced pancreatic putrescine is exclusively produced by the interconversion pathway via oxidation of N1-acetylspermidine.

Dietary modulation of pancreatic carcinogenesis: calories and energy expenditure.

Physical activity (exercise) is a lifestyle factor that has received little attention with regard to its role in the etiology and/or prevention of cancer. These studies examined the effects of treadmill exercise on the early stages of pancreatic carcinogenesis initiated by azaserine in rats. Male Lewis rats were treated with azaserine at 2 weeks of age and weaned to experimental protocols at 3 weeks of age. Two experiments were undertaken; treadmill exercise began at 6 weeks of age (Experiment 1) or at 13 weeks of age (Experiment 2). Rats were exercised for 15-20 min/day and for 3-5 days/week. Treadmill speed and angle of incline were adjusted to afford a range of exercise intensities. The development of putative preneoplastic lesions of the pancreatic acinar cells (henceforth termed foci) was evaluated by quantitative stereological analysis using light microscopy. In Experiment 1, exercise resulted in a known paradoxical reduction in food intake by about 15% of the intake of the sedentary group fed ad libitum. The burden of azaserine-induced foci was decreased by approximately 37%, and this was attributed to the well known effects of reduced caloric intake in these young, rapidly growing rats. In Experiment 2, the higher intensity treadmill exercise group had an increased focal burden, compared to their sedentary pair-fed controls. Importantly, this enhancement occurred despite a reduction in food intake and body fat stores in this treadmill exercise group. These experiments demonstrate that exercise may suppress or promote carcinogenesis, depending upon the stage in the life cycle of the animal.

Effects of dietary linoleic acid on pancreatic carcinogenesis in rats and hamsters.

It has been suggested that linoleic acid (LA) is responsible for the promoting effect of dietary polyunsaturated fat on pancreatic carcinogenesis via an accelerated prostaglandin synthesis, caused by metabolism of LA-derived arachidonic acid in (pre)neoplastic tissue. The purpose of the present study was to investigate whether dietary LA is the cause of pancreatic tumor promotion by a high fat diet. Five groups of 30 azaserine-treated rats and 5 groups of 30 N-nitrosobis(2-oxopropyl)amine-treated hamsters were maintained for 6 months (rats) and 12 months (hamsters) on high fat (25 weight %) AIN diets containing 2, 4, 6, 10, or 15 weight % LA. The results indicated that the strongest enhancing effect on the growth of pancreatic (pre)neoplastic lesions in rats and hamsters was obtained with 4 and 2 weight % of dietary LA, respectively. At higher LA levels the tumor response seemed to decrease rather than increase. In both rats and hamsters the fatty acid profiles of blood plasma and pancreas showed an accurate reflection of the dietary fatty acid profiles: a proportional increase in LA levels was observed in plasma and pancreas with increasing dietary LA. In both species plasma and pancreatic AA levels remained constant, except for arachidonic acid levels in rat plasma, which significantly increased with increasing dietary LA levels. Fatty acid profiles in hamster pancreatic tumors did not differ from fatty acid profiles in nontumorous pancreatic tissue from hamsters fed the same diet. Prostaglandin (PG) E2, 6-keto-PGF1 alpha, PGF2 alpha, and thromboxane B2-concentrations in nontumorous pancreatic tissue were similar among the diet groups. Ductular adenocarcinomas from hamster pancreas showed significantly higher levels of 6-keto-PGF1 alpha, PGF2 alpha, and thromboxane B2, but not of PGE2 in comparison with nontumorous pancreas. It is concluded that the strongest pancreatic tumor promotion by dietary LA is 4 weight % in rats and 2 weight % or less in hamsters, and that PGs may be involved in the development of ductular adenocarcinomas induced in hamster pancreas by N-nitrosobis(2-oxopropyl)amine.