Pancreatic hypertrophy with acinar cell nodules after longterm fundectomy in the rat

Effect of hypergastrinemia on pancreatic carcinogenesis

BACKGROUND

Previous studies in our laboratory demonstrated that pancreatic carcinomas in rodents express receptors for the peptide hormone gastrin that are not present in normal adult pancreas. In view of an abundant literature suggesting that gastrin may promote growth of various gastrointestinal tissues and tumors, the effect of hypergastrinemia on the process of pancreatic carcinogenesis was evaluated.

METHODS

Rats received subcutaneous injections of the pancreatic carcinogen azaserine at 19 and 26 days of age. Starting at 12 months of age, animals were randomized to treatment with the proton pump inhibitor lansoprazole or vehicle by gavage for 6 months. At autopsy, pancreatic wet weight normalized to body weight was recorded, as well as the number of benign and malignant pancreatic lesions.

RESULTS

Serum gastrin levels were determined by radioimmunoassay and showed a greater than two-fold increase in lansoprazole-treated animals. Pancreatic wet weight in hypergastrinemic rats was increased compared to controls (p <0.05). Premalignant lesions such as acidophilic atypical acinar cell foci, adenomas, heterogeneous phenotypic populations of nodules within nodules, and carcinoma-in-situ were not increased in the hypergastrinemic group. Likewise, there was no difference in the incidence of invasive carcinoma in hypergastrinemic animals (10%) compared to controls (5.7%).

CONCLUSION

Hypergastrinemia stimulated an increase in pancreatic weight, but did not stimulate development of premalignant lesions or progression to cancer in the azaserine model of rat pancreatic acinar cell carcinoma.

The gastrin receptor promotes pancreatic growth in transgenic mice

INTRODUCTION

We demonstrated previously, in two different rodent models of pancreatic cancer, that the gastrin receptor is present on malignant pancreatic tumors in spite of the fact that the normal adult rat and mouse pancreas does not express gastrin receptors.

AIMS AND METHODOLOGY

To determine whether gastrin receptors mediate pancreatic growth or promote carcinogenesis or both, we created a transgenic mouse that constitutively expresses gastrin receptors in the exocrine pancreas. The transgene construct contained the full-length rat gastrin receptor cDNA sequence under the control of the rat elastase promoter.

RESULTS

Receptor presence and function on exocrine pancreatic tissue of transgenic but not control mice were confirmed by (125)I-gastrin-I binding studies and by gastrin stimulation of intracellular calcium release. Eighteen-month-old transgenic animals had larger pancreas-to-body weight ratios than their nontransgenic littermate controls (p < 0.001 for females; p < 0.01 for males); however, histopathologic examination revealed no neoplasms or other abnormalities.

CONCLUSION

In both female and male transgenic mice, the expression of the gastrin receptor in the exocrine pancreas is associated with a significant increase in pancreas weight, but it does not appear to promote the development of spontaneous pancreatic tumors.

Gastrin inhibits secretin-induced ductal secretion by interaction with specific receptors on rat cholangiocytes

We assessed the effect of gastrin on ductal secretion in normal and bile duct-ligated (BDL) rats. The effect of gastrin on ductal secretion was examined in the presence of proglumide, a specific antagonist for gastrin receptor (GR). We isolated pure cholangiocytes from normal and BDL rats and assessed gastrin effects on secretin receptor (SR) gene expression and intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels. We examined the presence of GR mRNA in cholangiocytes by reverse transcription polymerase chain reaction (RT-PCR). In normal or BDL rats, gastrin produced no changes in spontaneous bile secretion. Simultaneous infusion of gastrin inhibited secretin-induced choleresis and bicarbonate output in BDL rats. In the presence of proglumide gastrin did not inhibit secretin-induced choleresis in BDL rats. Gastrin decreased in cholangiocytes from BDL rats 1) SR gene expression and 2) secretin-induced cAMP levels. With the use of RT-PCR, GR mRNA was detected in cholangiocytes. Similar to what is shown for secretin and somatostatin, we propose that the opposing effects of secretin and gastrin on cholangiocyte secretory activity regulate ductal secretion in rats.

Effect of chronic endogenous hypergastrinaemia on pancreatic growth and carcinogenesis in the hamster

BACKGROUND

To examine the effect of gastrin on spontaneous and induced pancreatic carcinogenesis in the hamster.

METHODS AND RESULTS

Two sets of experiments were carried out, one involving long term hypergastrinaemia and one involving cancer induction during hypergastrinaemia. The effect of hypergastrinaemia accomplished by gastric fundectomy was studied for eight months. Neither fundectomised hamsters nor sham operated controls developed premalignant or malignant pancreatic lesions. In the fundectomy group, the mean pancreatic weight, total protein content, and DNA content was increased by 28%, 25%, and 25% respectively. No such increases were found in fundectomised animals receiving a cholecystokinin-B receptor antagonist during the last 24 days of the experiment. In the cancer induction study, the effect of fundectomy on N-nitrosobis(2-oxopropyl) amine induced pancreatic carcinogenesis was studied for three months. There were no significant differences in the incidence or [3H]-thymidine labelling index of focal pancreatic lesions between fundectomised and sham operated control animals.

CONCLUSIONS

Fundectomy with chronic hypergastrinaemia induces pancreatic hypertrophy, but does not enhance N-nitrosobis (2-oxopropyl)amine induced pancreatic carcinogenesis in the hamster. The increases in growth were inhibited by a cholecystokinin-B receptor antagonist, indicating that the trophic effect of fundectomy is mediated by gastrin.

Gastrin does not stimulate growth of the rat pancreas

BACKGROUND

Gastrin is thought to stimulate growth of the pancreas via gastrin/cholecystokinin (CCK)-B-type receptors. The aim of the present study was to examine the trophic response of the pancreas to exogenous gastrin or to hypergastrinemia of endogenous origin and to hypogastrinemia with or without concomitant hyperCCKemia.

METHODS

Hypergastrinemia was induced in male Sprague-Dawley rats by continuous infusion of human Leu15-gastrin-17 (5 nmol/kg/h, subcutaneously), by removal of the acid-producing part of the stomach (fundectomy), or by treatment with omeprazole (400 mumol/ kg/day, orally). Hypogastrinemia was induced by antrectomy or by gastrectomy. HyperCCKemia was induced by pancreaticobiliary diversion (PBD). The rats were killed 10 days or 8 weeks after the operations or treatments. The concentrations of circulating gastrin and CCK were measured by radioimmunoassay. The pancreatic weight and DNA content were determined.

RESULTS

Gastrin infusion, omeprazole treatment, and fundectomy greatly increased the serum gastrin concentration. The resulting levels were very similar in the three groups and probably represent the maximum attainable physiologic serum gastrin concentration. Whereas gastrin infusion or omeprazole treatment (hypergastrinemia) and antrectomy (hypogastrinemia) were without effect on the weight and DNA content of the pancreas, gastrectomy (hypogastrinemia) and fundectomy (hypergastrinemia) increased the weight and DNA content. PBD (hyperCCKemia) greatly increased the weight and DNA content of the pancreas. PBD plus fundectomy, PBD plus gastrectomy, PBD plus antrectomy, and PBD plus omeprazole increased the weight and DNA content of the pancreas, as did PBD alone.

CONCLUSION

CCK is a physiologically important trophic stimulus for the rat pancreas, but gastrin is not. The increase in pancreatic weight and DNA content after fundectomy and gastrectomy cannot be explained by means of either gastrin or CCK.

Cholecystokinin-A and cholecystokinin-B/gastrin receptor mRNA expression in the gastrointestinal tract and pancreas of the rat and man. A polymerase chain reaction study

BACKGROUND

Gastrin and cholecystokinin (CCK) are thought to exert trophic effects on the gastrointestinal tract and pancreas. Two types of receptors have been cloned, CCK-A and CCK-B/ gastrin. We have examined the occurrence of CCK-A and CCK-B receptor mRNA in the brain, digestive tract, pancreas, and kidney of the rat and man by Northern blot and reverse transcribed polymerase chain reaction (RT-PCR).

METHODS

Total RNA was isolated from rat tissues and reverse transcribed into cDNA. cDNA from brain, kidney, and pancreas of the rat and man and from human whole stomach were commercially available. Northern blot and a PCR technique based on Taq polymerase-antibody interaction and using CCK-A and CCK-B receptor-specific primers, followed by Southern blot analysis, were the methods used.

RESULTS

By means of Northern blots, CCK-A receptor mRNA was detected in rat fundus mucosa and pancreas but not in the remaining GI tract or brain. By means of RT-PCR, CCK-A receptor mRNA was demonstrated in the brain and the mucosa of the fundus, antrum, duodenum, and colon, kidney, pancreas and pancreatic islets. CCK-B receptor mRNA was detected by Northern blot analysis in the brain and the fundus mucosa but not in the rest of the digestive tract and not in the pancreas, pancreatic islets, or kidney. By RT-PCR, expression of CCK-B receptor mRNA could also be detected in antrum mucosa. In man, CCK-A receptor mRNA was detected in the brain, stomach, pancreas, and kidney, whereas CCK-B receptor mRNA was found in the brain, stomach, and pancreas but not in the kidney. Cloning and DNA-sequence analysis of the PCR-amplified rat and human CCK-A and CCK-B receptor DNA fragments, which cover the protein-encoding regions of the intracellular loop C3, showed complete sequence homology as compared with published rat and human sequences.

CONCLUSIONS

It appears unlikely that CCK will have effects in the ileum, at least not effects mediated by CCK-A receptors. It also appears unlikely that physiologic concentrations of gastrin in the circulation will promote growth (or exert other effects) in the pancreas, duodenum, ileum, and colon, since CCK-B receptor mRNA is not expressed or is poorly expressed in these tissues.

The consequences of hypergastrinemia

The only gastrin-dependent gastric endocrine cells are the fundic ECL cells. Excessive hypergastrinemia stimulates ECL cell proliferation in animals and man. The growth of other gastric endocrine cells is regulated by the gastric pH. Hypergastrinemia in man results in diffuse and linear hyperplasia of the ECL cells, while micronodular hyperplasia is correlated to the grade of corpus gastritis. ECL cell dysplasia and gastric carcinoids in man have been observed only in patients with gastrinoma as part of the MEN I syndrome and with pernicious anemia. Gastrin dependence of GI adenocarcinoma has not been established. Experimental findings may be explained by the presence of gastrin receptors and the role of gastrin as an autocrine growth factor. Epidemiological data do not support gastrin dependence of carcinoma of the stomach, the pancreas and the colon.