Atypical Acinar Cell Nodules Research Articles

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.

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.

Epidermal growth factor receptor expression in pancreatic lesions induced in the rat by azaserine

In the present study, the expression of the epidermal growth factor receptor (EGFR) was investigated in putative preneoplastic and neoplastic acinar cell lesions induced in the rat pancreas by azaserine, using Northern blotting, in situ hybridisation (ISH) and immunohistochemistry. EGFR protein levels were decreased in putative preneoplastic eosinophilic acinar cell lesions (atypical acinar cell nodules, AACN) in comparison with normal acinar cells of the pancreas. However, EGFR mRNA expression correlated positively with the volume of AACN in pancreatic homogenates and ISH showed equal or stronger EGFR mRNA expression in AACN than in the surrounding normal acinar cells. Neither EGFR protein nor EGFR mRNA was detected in more advanced lesions such as acinar adenocarcinomas (in situ). Moreover, EGFR protein expression showed an inverse relationship with the mitotic rate of the acinar cells. These findings suggest that down-regulation of EGFR at the protein level may abrogate negative constraints on cell growth, which may stimulate the development of putative preneoplastic AACN to more advanced lesions and, ultimately, acinar adenocarcinomas.

Dietary fish oil (MaxEPA) enhances pancreatic carcinogenesis in azaserine-treated rats

In the present study the putative chemopreventive effect of dietary fish oil (MaxEPA) on azaserine-induced pancreatic carcinogenesis in rats was investigated. Groups of rats were maintained on a semipurified low-fat (LF; 5 wt%) diet or on semipurified high-fat (HF; 25 wt%) diets containing 5 wt% linoleic acid (LA) and including 0.0, 1.2, 2.4, 4.7, 7.1 or 9.4 wt% MaxEPA. Animals fed a HF diet developed significantly higher mean numbers of atypical acinar cell nodules (AACNs), adenomas and carcinomas than animals fed a LF diet. Dietary MaxEPA caused a significant (P < 0.01) dose-related increase in mean number of AACNs (0.5 < phi < 3.0 mm). The mean number of adenomas and carcinomas remained similar among the groups. Cell proliferation was significantly lower in AACNs from animals fed HF containing 9.4% MaxEPA in comparison with HF without MaxEPA and with LF. LA levels had increased and arachidonic acid (AA) levels had decreased in blood plasma and pancreas with increasing dietary MaxEPA. Feeding MaxEPA resulted in significant decreases in 6-keto-prostaglandin (PG) F1 alpha (P < 0.05) and PGF2 alpha (P < 0.01) in non-tumorous pancreas, whereas PGE2, PGF2 alpha and thromboxane B2 (TXB2) levels were significantly (P < 0.001) higher in pancreatic tumour tissue than in non-tumorous pancreatic tissue. It is concluded that (i) dietary MaxEPA enhances dose-relatively growth of putative preneoplastic AACNs in the pancreas of azaserine-treated rats; (ii) dietary MaxEPA inhibits the conversion of LA to AA, as well as the conversion of AA to TXB2 or PGF2 alpha in non-tumorous pancreatic tissue; (iii) the high levels of PGE2, PGF2 alpha and TXB2 in pancreatic adenocarcinomas indicate a possible role for these eicosanoids in modulation of tumour growth.

Gut peptide receptors in pancreata of azaserine-treated and normal control rats.

Gut peptides are involved in the growth and carcinogenesis of the exocrine pancreas of rats after treatment with azaserine. However, little is known about the influence of azaserine on expression of gut peptide receptors in the pancreas of the rat. Cholecystokinin, bombesin, somatostatin, secretin, and vasoactive intestinal peptide receptors were therefore visualized and quantified by storage phosphor autoradiography in pancreata of either saline control or azaserine-treated rats. As expected, putative preneoplastic lesions were formed in the pancreata of the azaserine-treated but not in the control animals. The pancreata of control rats contained receptors for cholecystokinin, bombesin, somatostatin, secretin, and vasoactive intestinal peptide. Cholecystokinin receptors were of the A-type and showed, in contrast to the other receptors, a heterogeneous expression due to variability of the high-affinity receptors. In the pancreata of azaserine-treated animals a significantly increased binding capacity of high-affinity receptors fro cholecystokinin was found not only in atypical acinar cell nodules but also in non-nodular pancreas when compared to pancreas of control rats (P < 0.05). Neither atypical acinar cell nodules nor non-nodular pancreas of rats treated by azaserine were shown to possess receptors for the other four types of gut peptide receptors. The spectrum of peptide receptors in pancreas of control and azaserine-treated rats in this study may help to understand the mechanism whereby gut hormones may modulate pancreatic carcinogenesis.

Role of cholecystokinin in dietary fat-promoted azaserine-induced pancreatic carcinogenesis in rats

The role of cholecystokinin in dietary fat-promoted pancreatic carcinogenesis was investigated in azaserine-treated rats, using lorglumide, a highly specific cholecystokinin-receptor antagonist. The animals were killed 8 months after the start of treatment. Cholecystokinin, but not dietary unsaturated fat, increased pancreatic weight. Rats treated with cholecystokinin developed more acidophilic atypical acinar cell nodules, adenomas and adenocarcinomas than control animals. Rats maintained on the high-fat diet developed significantly more adenomas and adenocarcinomas than controls given a diet low in unsaturated fat. Lorglumide largely inhibited the enhancing effect of cholecystokinin, but not of dietary fat, on pancreatic carcinogenesis indicating that it is unlikely that the promoting effect of dietary unsaturated fat on pancreatic carcinogenesis is mediated via cholecystokinin.

Effects of sandostatin and castration on pancreatic carcinogenesis in rats and hamsters

The effects of treatment with the somatostatin analogue Sandostatin, separately and in combination with surgical castration, on the development of azaserine-induced lesions in rat pancreas and N-nitrosobis(2-oxopropyl)amine (BOP)-induced lesions in hamster pancreas were investigated. The animals were divided in 4 groups and treated as follows: (a) controls, injected s.c. with saline solution (0.9% NaCl); (b) orchiectomy directly after the last treatment with carcinogen; (c) Sandostatin (SMS 201-995) subcutaneously; (d) orchiectomy followed by treatment with Sandostatin. No significant suppressive effects on plasma EGF or IGF-I concentrations were noted after Sandostatin treatment, but plasma gastrin levels decreased slightly in the rats, not in the hamsters. In rats, Sandostatin treatment enhanced rather than inhibited growth of acidophilic atypical acinar cell nodules. In hamster pancreas, by contrast, Sandostatin inhibited the development of putative pre-neoplastic ductular lesions. There was no interaction between treatment with Sandostatin and surgical castration. It was concluded that Sandostatin, when administered prophylactically, has an inhibitory effect on the growth of putative pre-neoplastic ductular, but not acinar, lesions.

Effects of cholecystokinin and bombesin on development of azaserine-induced pancreatic tumours in rats: modulation by the cholecystokinin receptor antagonist lorglumide.

Cholecystokinin and bombesin have been shown to promote pancreatic growth and development of azaserine-induced acidophilic atypical acinar cell nodules in rat pancreas after treatment for 16 weeks. Lorglumide, a specific cholecystokinin receptor antagonist, inhibited the stimulating effect of cholecystokinin, but not of bombesin. The present study was carried out to determine effects of cholecystokinin and bombesin, alone and in combination with lorglumide, on pancreatic growth and carcinogenesis after chronic treatment. The animals were killed 8 months after the start of treatment. Growth of the pancreas and the development of acidophilic atypical acinar cell nodules in exocrine pancreas was enhanced significantly by both cholecystokinin and bombesin, but the number of carcinomas was increased only by bombesin. Lorglumide inhibited the effects of cholecystokinin on both pancreatic growth and on the development of acidophilic nodules. The effects of bombesin on pancreatic growth and development of pancreatic lesions, except for adenomas, were not inhibited by lorglumide.

Early indicators of exocrine pancreas carcinogenesis produced by non-genotoxic agents

In the past 40 years the incidence of pancreatic cancer in many Western countries has increased. Since no single factor responsible for the development of pancreatic cancer has been identified, it is believed that non-genotoxic factors may play an important role in the pathogenesis of this highly fatal form of cancer. Focal abnormalities of acinar cells, referred to as atypical acinar cell foci or nodules, occur spontaneously in rats and some of other species. Their incidence increases with age from zerom at birth to about 75% in 2-year-old rats. These spontaneous lesions have a phenotype that cannot be distinguished from the putative, atypical preneoplastic, acinar cell foci induced in rat pancreas by the carcinogen azaserine. Unsaturated fat (corn oil) has been foun to increase the incidence of atypical acinar cell nodules and adenomas in the pancreas of non-carcinogen-treated rats without influencing the weight of the pancreas. Furthermore, unsaturated fat has a specific promoting effect on the growth potential of atypical acinar cell foci and nodules induced in rat pancreas by azaserine, resulting in an increase in the number and size of these lesions. Rats fed raw soya flour or trypsin inhibitors developed an enlarged pancreas as a result of hypertrophy and hyperplasia. They also develop acidophilic atypical acinar cell foci and nodules, adenomas and adenocarcinomas after being fed full-fat raw soya flour for 2 years. It may be concluded from the observations in rat pancreas that non-genotoxic compounds or condions that enhance pancreatic growth may be classified as non-genotoxic pancreatic tumour promoters. The oservations with corn oil, however, indicate that there may be non-genotoxic compounds that specifically enhance growth of spontaneous initiated atypical cell foci without causing hyperplasia of the pancreas. The possible mechanisms whereby unsaturated fat and trypsin exert their effects on exocrine pancreatic carcinogenesis are discussed.

Glutathione S-transferase (μ class) as an early marker of azaserine-induced foci in the rat pancreas

The alpha, mu and pi classes of glutathione S-transferase (GST) were evaluated as early immunocytochemical markers for the development of atypical foci within the pancreases of azaserine treated rats. Changes detected with haematoxylin and eosin (H&E) were compared with those detected by immunocytochemistry using antibodies raised against each class of GST. All foci detected with H&E staining were classified as acidophilic atypical acinar cell nodules (AACN), which have previously been reported in this model. All of these AACN overexpressed GST mu. However, 64% of foci detected with GST mu staining had not been identified as AACN during a prior examination with H&E. Re-evaluation of the H&E sections revealed that some of these foci showed subtle morphological changes which are indicative of AACN. In many cases, however, no morphological difference could be seen with H&E staining. We conclude that immunocytochemical staining for GST mu is a more reliable and sensitive method than H&E for detecting the early stages of azaserine-induced foci. Furthermore, we suggest that studies on the incidence and growth of these foci can be shortened considerably if GST mu staining is used in conjunction with H&E.

Inhibitory effects of micronutrients on pancreatic carcinogenesis in azaserine-treated rats

A study was made on the effects of long-term dietary administration of beta-carotene, vitamin C, vitamin E and selenium, either alone or in combination, on azaserine-induced pancreatic carcinogenesis in rats. Male Wistar rats were given two i.p. injections of 30 mg azaserine per kg body weight at 19 and 26 days of age. The rats were allocated to eight groups of 40 animals each and were fed an AIN-76 diet rich in saturated fat (20% lard), either as such or after supplementation with beta-carotene, vitamin C, beta-carotene + vitamin C, vitamin E, selenium, vitamin E + selenium, or the combination of all micronutrients investigated. Fifteen months after the last treatment with azaserine the survivors were killed. The pancreata were examined for the number and size of advanced putative preneoplastic lesions and the number of neoplasms as well. Rats maintained on a diet high in either beta-carotene, vitamin C or selenium developed significantly less atypical acinar cells nodules, adenomas and carcinomas as compared to controls. The number of tumour-bearing animals was significantly lower in the groups fed the diet high in beta-carotene or selenium. In animals of the group given a diet high in all micronutrients investigated, both the number and incidence of pancreatic tumours was lower than in all other groups. It was concluded that selenium, beta-carotene and vitamin C, alone as well as in combination, have an inhibitory effect on pancreatic carcinogenesis induced in rats by azaserine.

Preneoplastic and Neoplastic Lesions in the Pancreas of Rats Fed Choline-Devoid or Choline-Supplemented Diets

Groups of male Fischer 344 rats were chronically fed semipurified choline-devoid or choline-supplemented diets, high in fat (15%), and containing or not containing 0.06% phenobarbital. Atypical acinar cell nodules were observed in the pancreas of the rats, irrespective of the diet fed, with incidences varying from 38% to 100% in the various groups. No consistent differential effects of the dietary treatments on the incidence and growth of the nodules were evident, even though the diameter of the nodules tended to be greater in some of the groups fed the basal choline-devoid diet. The vast majority of the nodules were of the acidophilic type. More advanced pancreatic acinar cell lesions were observed in a few of the rats. Since the rats were not exposed to a chemical carcinogen(s), development of the nodules and of the more advanced lesions, even in rats fed the control diets, was most likely due to evolution of endogenous (spontaneous) initiated pancreatic cells, promoted primarily by the feeding of semipurified diets with a high fat content.

Effects of castration, alone and in combination with aminoglutethimide, on growth of (pre)neoplastic lesions in exocrine pancreas of rats and hamsters

We studied the effects of hormonal manipulation by orchiectomy, alone or in combination with the aromatase inhibitor aminoglutethimide (AGT), and by luteinizing hormone-releasing hormone agonist (LH-RH-A) (goserelin) treatment on the development of early putative (pre)neoplastic lesions induced in the pancreas of rats and hamsters by azaserine and N-nitrosobis(2-oxopropyl)amine respectively. Treatment of the animals started 1 week after the last injection with carcinogen and continued for 4 months. Orchiectomy caused a significant inhibition of growth of acidophilic atypical acinar cell nodules in the rat model, whereas surgical castration did not show an effect in the hamster model. In rats, but not in hamsters, orchiectomy resulted in a significant decrease in body weight and in absolute, but not relative pancreatic weight. Treatment of the animals with AGT or goserelin did not cause a significant effect on the development of either putative preneoplastic acinar lesions in rat pancreas or early ductular lesions in hamster pancreas. Hamsters showed clearly higher plasma epidermal growth factor (EGF) and insulin-like growth factor 1 (IGF-1) concentrations than rats, while plasma testosterone levels were significantly lower. Plasma EGF and IGF-1 levels decreased with increasing age in both control and treatment groups. Compared to controls there were no clear unequivocal effects of treatment on EGF, IGF-1 and gastrin levels. Plasma testosterone levels decreased by orchiectomy and LH-RH-A treatment. In rats hormone-induced effects on food intake and altered nutritional status might be important with respect to the development of carcinogen-induced preneoplastic pancreatic lesions.

Azaserine-induced pancreatic carcinogenesis in rats: promotion by a diet rich in saturated fat and inhibition by a standard laboratory chow

Dietary fat has been shown to enhance pancreatic carcinogenesis. Uncertainty still exists whether the amount of linoleic acid or the amount of fat is the main determining factor. In the present study the effects of a high lard, a low lard, a linoleic acid supplemented low lard and a laboratory chow diet were investigated on the development of (pre) neoplastic pancreatic lesions in rats treated with azaserine. The rats were killed 15 months after carcinogen treatment and the pancreata were examined for the number and size of putative preneoplastic lesions and for the occurrence of neoplasms. The linoleic acid supplemented low lard group showed a significantly increased number of basophilic foci as compared to the low lard group. Rats maintained on the linoleic acid supplemented diet or the laboratory chow developed significantly less atypical acinar cell nodules larger than 1.0 mm in diameter and adenocarcinomas as compared to the high lard group. Animals maintained on the low lard diet developed significantly less adenocarcinomas than rats on the high lard diet did. Overall, the number of benign and malignant pancreatic tumours was consistently higher in the high lard group and consistently lower in the linoleic acid supplemented low lard group than the number of these types of tumours in the low lard group, with the exception of the number of carcinomas in situ, which was lower in the high lard group. The laboratory chow group showed a significant lower number of atypical acinar cell nodules with a diameter over 1.0 mm and a lower number of adenocarcinomas as compared to both the high lard and the low lard group. It is concluded that a diet high in saturated fat has a promoting and that laboratory chow has an inhibitory effect on pancreatic carcinogenesis in azaserine-treated rats.

Immunohistochemical staining of Ha- ras oncogene product in normal, benign, and malignant human pancreatic tissues

We examined immunohistochemical staining with Ha- ras oncogene product in normal, benign, and malignant human pancreatic tissues. In cases of pancreatic cancer, its relation to histologic type was evaluated. Serous cystadenoma and atypical acinar cell nodules did not react with the Ha- ras oncogene product, and ductal cells and acinar cells in normal pancreas showed lower immunoreactivity than other benign or malignant lesions. However, the positive rate of islet cells in normal pancreas was almost the same in cases of pancreatic cancer. Strongest positivity was observed in cases of chronic pancreatitis, and islet cell tumors also showed high positive staining rates. In pancreatic cancer, the positive rate of well-differentiated adenocarcinomas was rather higher than that of poorly differentiated adenocarcinomas. Our study indicates that the Ha- ras oncogene p21 product does not correlate with neoplastic transformation in human pancreas, is not a useful marker for differentiating benign and malignant lesions, and cannot be used to determine the origin of differentiation in the pancreas.

L-Azaserine Induced Preneoplasia in the Rat Pancreas. A Morphometric Study of Dietary Manipulation (Lipotrope Deficiency) and Ultrastructural Differentiation

Putatively preneoplastic, pancreatic atypical acinar cell foci (AACF) and nodules (AACN), collectively termed atypical acinar cell lesions (AACL), were induced in male Lewis rats by L-azaserine (300 mg/kg body weight [bw] in divided doses). Rats given carcinogen and then fed a lipotrope deficient (LD) diet developed a significantly greater number of larger lesions than animals fed complete diet throughout the experiment. It is suggested that lipotrope deficiency plays a promoting role in this model of pancreatocarcinogenesis. Ultrastructural morphometric studies of AACF, when compared to control tissues, revealed the following significant results: 1) a decrease in surface area of cell cytoplasm with no change in nuclear area, and hence increased nucleus/cytoplasm (N/C) ratio; 2) a reduction in size and uniformity of zymogen granules; and 3) an increase in number of granules per microns 2 of cell. The results suggest that arrested development of the AACF cells is associated with reduced cytoplasm and zymogen production per cell. AACL may be eosinophilic due to an overall increased concentration of zymogen in these hyperplastic lesions and not because individual acinar cells in the AACL contain an increased amount of zymogen or are "zymogen-rich," as has been reported.

Effect of dietary omega-3 and omega-6 fatty acids on development of azaserine-induced preneoplastic lesions in rat pancreas.

We examined the effect of varying the ratio of dietary omega-3 (omega 3) to omega-6 (omega 6) on the development of pancreatic preneoplastic lesions in male Wistar rats given azaserine at 14 days of age. As the ratio of dietary omega 3 to omega 6 fatty acids increased in a diet totaling 20% by weight of fat, the development of preneoplastic atypical acinar cell nodules (AACNs) at 4 months after dosing with azaserine decreased significantly. In addition, serum levels of prostaglandin thromboxane B2, prostaglandin E2, and 6-keto-prostaglandin F1 alpha decreased significantly. The fatty acid composition of the rbc membrane was also significantly influenced by the ratio of dietary omega 3 to omega 6 fatty acids. In a second experiment, we examined the effect of dietary intervention with a different type of fat (corn oil or menhaden oil) 2 months into the 4-month postdosing period on AACN development at the end of the post-dosing period. Intervention of the omega 6 fatty acid-rich diet with the omega 3 fatty acid-rich diet significantly decreased focal development. The opposite was true when intervention involved substituting the omega 3 fatty acid-rich diet with the omega 6 fatty acid-rich diet.

Stimulation of the growth of azaserine-induced nodules in the rat pancreas by dietary camostate (FOY-305)

The effects of dietary camostate (FOY-305), a synthetic trypsin inhibitor, on the early stages of pancreatic carcinogenesis in the rat were studied because of earlier reports that feeding soy bean trypsin inhibitor stimulated growth and promoted carcinogenesis in the pancreas of rats. These effects are attributed to excess secretion of cholecystokinin, a trophic hormone for pancreatic acinar cells. Camostate has been shown to induce pancreatic enlargement in rats by the same mechanism. In preliminary experiments, pancreatic growth was studied in adult Fischer 344 (F344) and Lewis rats fed camostate mixed in the diet to define a level that induced pancreatic hypertrophy and hyperplasia. As little as 0.02% fed 3 days per week was effective. In a second experiment, F344 rats were injected with azaserine and thereafter were given camostate by gavage 5 days a week until autopsy 18 weeks later. In a third experiment, azaserine-treated Lewis rats were fed camostate in the diet 3 days a week for 8 or 16 weeks until autopsy. In the latter two experiments the number and size of atypical acinar cell foci and nodules (AACN) were measured in pancreas sections. Growth of acidophilic AACN was stimulated in camostate-fed groups; both the number and the size were increased in comparison with the control groups. The data suggest a promoting effect of dietary camostate on the growth of azaserine-induced preneoplastic lesions in the pancreas of both rat strains. The number of basophilic AACN was decreased in camostate-fed Lewis rats suggesting that the camostate diet also affected the phenotype of the carcinogen-induced AACN.

γ-Glutamyltransferase activity in atypical acinar cell nodules of rat pancreas

The biochemical and histochemical measurement of the enzyme γ-glutamyltransferase (GGT) was undertaken in normal rat pancreas and in rat pancreas containing azaserine-induced preneoplastic nodules. A steady decrease in pancreatic GGT activity was observed in the normal animals as they aged from 5 to 34 weeks. The azaserine-induced nodules contained a lower average GGT activity than the control pancreas although a 10-fold variation was noted in the GGT activity of individual nodules. A significant increase in concentrations of both reduced glutathione and oxidized glutathione was noted in pancreatic nodules from azaserine-treated rats compared to concentrations found in both control pancreas from untreated rats and internodular pancreas from azaserine-treated rats. A pancreatic acinar cell carcinoma contained low GGT activity-similar to that found in large nodules and about 10% of the level found in control pancreas. Pancreatic GGT levels were higher in 5- and 7-week-old rats fed chow than in rats fed a purified diet, but this effect of chow was not observed at 34 weeks of age. Feeding a purified diet supplemented with a retinoid, N-2-hydroxyethylretinamide (2-HER), for a period of 2 weeks did not influence the GGT activity level in either normal pancreas or in the azaserine-induced nodules. While decreased GGT activity does not serve as a marker for all atypical acinar cell nodules, deficient activity with concomitant increased glutathione levels appears to correlate generally with increased growth potential.

Effect of castration and hormone replacement on azaserine-induced pancreatic carcinogenesis in male and female Fischer rats.

Previous reports have shown that pancreatic cancer was induced preferentially in male versus female azaserine-treated rats. This study was designed to determine the importance of estrogen and testosterone in this phenomenon. Fischer (F344) rats received a single injection of azaserine (30 mg/kg) at 21 days of age. At 28 days of age, they were weaned and divided into 12 groups of 9-10 rats as shown below. Surgery (castration or sham operation) was performed at 4 weeks of age. All drugs (estradiol, the antiestrogen tamoxifen, testosterone propionate and/or the antiandrogen flutamide) were administered, starting at weaning, in 3-week timed-release pellets until autopsy. Rats were killed 4 months after the administration of azaserine. The pancreas was weighed and prepared for quantitative histologic analysis of atypical acinar cell nodules (AACNs) which are putative preneoplastic lesions. Both number and size of AACNs were analyzed. In intact female rats, AACN burden was smaller than in intact males (P less than 0.05). Ovariectomy increased the AACN burden (P less than 0.05), while estradiol or tamoxifen treatments to ovariectomized females resorted the burden to control levels (P less than 0.05). Testosterone with tamoxifen treatment to ovariectomized females led to a significant increase in AACN burden over control values. In intact male rats, orchiectomy decreased the AACN burden (P less than 0.05). In orchiectomized rats, testosterone treatment slightly increased the AACN burden, flutamide treatment alone increased this parameter (P less than 0.05) but flutamide with estradiol decreased the AACN burden (P less than 0.01). These data strongly support the hypothesis that sex steroids play a major role in the higher incidence of pancreatic cancer in male versus female rats.