Role of CCK-A receptor in the regulation of pancreatic bicarbonate secretion in conscious rats: a study in naturally occurring CCK-A receptor gene knockout rats

Gastrin, cholecystokinin and gastrointestinal tract functions in mammals

The aim of the present review is to synthesise and summarise our recent knowledge on the involvement of cholecystokinin (CCK) and gastrin peptides and their receptors in the control of digestive functions and more generally their role in the field of nutrition in mammals. First, we examined the release of these peptides from the gut, focusing on their molecular forms, the factors regulating their release and the signalling pathways mediating their effects. Second, general physiological effects of CCK and gastrin peptides are described with regard to their specific receptors and the role of CCK on vagal mucosal afferent nerve activities. Local effects of CCK and gastrin in the gut are also reported, including gut development, gastrointestinal motility and control of pancreatic functions through vagal afferent pathways, including NO. Third, some examples of the intervention of the CCK and gastrin peptides are exposed in diseases, taking into account intervention of the classical receptor subtypes (CCK1 and CCK2 receptors) and their heterodimerisation as well as CCK-C receptor subtype. Finally, applications and future challenges are suggested in the nutritional field (performances) and in therapy with regards to the molecular forms or in relation with the type of receptor as well as new techniques to be utilised in detection or in therapy of disease. In conclusion, the present review underlines recent developments in this field: CCK and gastrin peptides and their receptors are the key factor of nutritional aspects; a better understanding of the mechanisms involved may increase the efficiency of the nutritional functions and the treatment of abnormalities under pathological conditions.

Role of CCK-A receptor for pancreatic function in mice: a study in CCK-A receptor knockout mice

INTRODUCTION

The cholecystokinin (CCK) family of peptides and receptors is present throughout the brain and gastrointestinal tract. The CCK receptors can be pharmacologically subdivided into two subtypes: CCK-A and CCK-B. CCK-A receptor is enriched in the pancreas of mice.

AIMS

To determine pancreatic functions in a CCK-A receptor deficient mouse mutant generated by gene targeting in embryonic stem cells. The targeting vector contained lacZ and neo insertions in exon 2.

METHODOLOGY

To examine exocrine functions, amylase release from the dispersed acini in vitro was examined. In the in vivo study, the mixture of bile-pancreatic juice was collected, and amylase, bicarbonate, and bile acid outputs were determined after the administration of various stimulants. The cystic duct of the gallbladder and the pylorus were ligated to exclude the involvement of gallbladder contraction and gastric acid. Pancreatic enzyme content was measured, and histologic examinations by HE and lacZ staining were conducted. To examine endocrine functions, oral glucose tolerance test (2 g/kg) was determined.

RESULTS

The body weight, pancreatic wet weight, and enzyme content in the pancreas were similar among the three genotypes. Amylase release in vivo and in vitro and bicarbonate secretion in vivo were not stimulated by CCK-8 in CCK-AR (-/-) mice, whereas the responses to other stimulants were substantial in (-/-) mice. Administration of secretin did not increase bicarbonate secretion regardless of genotype. A normal glucose tolerance was observed in (-/-) mice. Acinar cells, islets, and duct cells were stained by lacZ, and HE staining revealed no pathologic findings.

CONCLUSION

The CCK-A receptor is important for pancreatic exocrine secretion, but not essential for maintaining glucose concentration and pancreatic growth in mice.

Oral administration of a synthetic trypsin inhibitor increases pancreatic duct function in CCK-A receptor-deficient rats

The effects of oral administration of a synthetic trypsin inhibitor on bicarbonate secretion were examined in cholecystokinin A (CCK-A) receptor-deficient (OLETF) rats and compared with Wistar rats. Rats were fed chow containing 0.1% trypsin inhibitor for 7 days. Rats were prepared with cannulae draining bile and pancreatic juice separately and with duodenal and extrajugular vein cannulae after 3-day trypsin inhibitor ingestion. Then the animals were maintained in Bollman cages, and the experiments were conducted 4 days after surgery. After 1.5 h of basal secretion with bile-pancreatic juice return, bile-pancreatic juice was diverted for 2 h. The responses of bicarbonate secretion to bile-pancreatic juice diversion were significantly enhanced in rats treated with trypsin inhibitor compared with those given a control diet, whereas responses of fluid and protein secretion were not affected in OLETF rats. The response of protein secretion, but not those of fluid or bicarbonate secretion, was enhanced in Wistar rats by treatment with trypsin inhibitor. Carbonic anhydrase II gene expression was increased by 7-day treatment with trypsin inhibitor only in OLETF rats, and not in Wistar rats.

Different effects of trypsin inhibitors on intestinal gene expression of secretin and on pancreatic bicarbonate secretion in CCK-A-receptor-deficient rats

The effects of oral administration of two synthetic trypsin inhibitors (camostate and ONO-3403) and soybean trypsin inhibitor (SBTI) on cholecystokinin (CCK), secretin gene expression and pancreatic secretion were examined in CCK-A-receptor-deficient (OLETF) rats. The rats were fed chow containing 0.1% trypsin inhibitors for 7 days. To examine pancreatic secretion, the rats were prepared with cannulae to drain the bile and pancreatic juice separately, a duodenal cannula and an external jugular vein cannula. The animals were maintained in Bollman cages and the experiments were conducted 4 days after surgery. The levels of CCK mRNA were significantly increased by each treatment. The levels of secretin mRNA were significantly increased by camostate and SBTI, but not by ONO-3403. Bicarbonate secretion was significantly increased in rats treated with camostate and ONO-3403, but not SBTI, while protein secretion was not affected by any treatment. These observations suggest that increased bicarbonate secretion produced by synthetic trypsin inhibitors in CCK-A-receptor-deficient rats may not be due to secretin but due to ONO-3403 in the circulation.