Effects of pancreaticobiliary diversion and gastric fundectomy on azaserine-induced pancreatic carcinogenesis in the rat

Cholecystokinin expression in tumors: biogenetic and diagnostic implications

Cholecystokinin (CCK) is a classic gut hormone. CCK is also a complex system of peptides expressed in several molecular forms in enteroendocrine I cells, in cerebral and peripheral neurons, in cardiac myocytes and spermatozoa. CCK gene expression has now been found at protein or peptide level in different neuroendocrine tumors; cerebral gliomas and astrocytomas and specific pediatric tumors. Tumor hypersecretion of CCK was recently reported in a patient with a metastatic islet cell tumor and hypercholecystokininemia resulting in a novel tumor syndrome, the cholecystokininoma syndrome. This review presents an overview of the cell-specific biogenesis of CCK peptides, and a description of the CCK expression in tumors and of the cholecystokininoma syndrome. Finally, assays for the diagnosis of CCK-producing tumors are reviewed.

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.

Closing the gastrin loop in pancreatic carcinoma: coexpression of gastrin and its receptor in solid human pancreatic adenocarcinoma

BACKGROUND

Alpha-amidated gastrin promotes the growth of nontransfected pancreatic cell lines expressing the gastrin/cholecystokinin (CCK)-B receptor. Gastrin/CCK-B and CCK-A receptors recently were demonstrated in human pancreatic adenocarcinomas, but to the authors' knowledge expression of their ligands to date have not been adequately investigated. As a prerequisite for making suggestions regarding local growth stimulation, the authors examined whether gastrin and the homologous CCK peptides as well as their specific receptors were expressed in consecutively collected solid human pancreatic adenocarcinomas.

METHODS

Using a library of radioimmunoassays specific for different epitopes on proCCK, progastrin, their processing intermediates, and bioactive end products, CCK and gastrin gene expression was measured in extracts of solid human pancreatic adenocarcinomas (n = 19), resection margins (n = 15), and normal pancreatic tissue (n = 8). Moreover, CCK, CCK-A receptor, and gastrin/CCK-B receptor mRNA were measured by reverse transcriptase-polymerase chain reaction.

RESULTS

Amidated gastrins were synthetized in 14 of 19 carcinomas (median, 0.4 pmol/g; range, < 0.1-84.0 pmol/g) and in 12 of 15 resection margin samples (median, 0.3 pmol/g; range, < 0.1-6.1 pmol/g). In contrast, normal human pancreatic tissue expressed only traces of poorly processed progastrin. Gastrin/CCK-B receptor mRNA was present in all carcinomas, resection margins, and normal pancreatic tissue. CCK-A receptor mRNA was detected in most tumors, but neither the mature ligands (alpha-amidated and O-sulfated CCK peptides) nor their precursors were expressed in carcinoma and normal pancreatic tissue.

CONCLUSIONS

The results of the current study demonstrate that alpha-amidated gastrin peptides and their receptor invariably are coexpressed in pancreatic adenocarcinoma. Therefore these findings support the contention of a role for local gastrin regulatory mechanisms, but no CCK mechanisms, in pancreatic carcinoma.

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.