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Alcohol abuse causes pancreatic damage in humans. However, only 5% of alcoholic patients have a clinical manifestation of pancreatitis, and the genetic predisposition of alcohol-associated pancreatitis remains elusive. Nonoxidative metabolites of ethanol, fatty acid ethyl esters (FAEEs), might play an important role in pancreatic damage. Carboxylester lipase (CEL) has been known to catalyze FAEE synthesis from fatty acids and ethanol.

Although many studies have investigated the acute effect of ethanol on the rat pancreas, the effect of intravenous injection of ethanol on pancreatic secretion has been controversial. The purposes of this study were to examine whether intraduodenal and intravenous administration of ethanol stimulates pancreatic secretion in Wistar rats. To elucidate the mechanism, we examined whether ethanol influences pancreatic secretion in CCK-A receptor-deficient rats.

Pancreatic exocrine function and bile secretion were examined in cholecystokinin (CCK)-B receptor gene-targeted mice and compared among different genotypes [i.e., CCK-B receptor gene: (/), wild-type; (/−), heterozygous; and (−/−), homozygous deficient]. The histology and protein concentrations in the pancreas also were examined. Amylase release from the dispersed acini was examined in vitro by using the various doses of CCK-8, carbachol, and secretin. In vivo, the bile and pancreatic juice were collected, and the concentrations of amylase and bile acid were measured in anesthetized mice. The responses to CCK (100 pmol/kg) or acetyl-β-methylcholine (500 nmol/kg) were examined. In vitro studies showed that the maximal effective concentrations of CCK-8 (10−10M), carbachol (10−5M), and secretin (10−7M), were comparable for all genotypes. Fluid, amylase, and bile acid outputs in vivo also were comparable for all genotypes. Pancreatic wet weight and protein concentrations were not significantly different, and no abnormal findings were observed on histologic examination in any genotype. These results indicated that the CCK-B receptor has no role in pancreatic growth, exocrine secretion, or bile secretion in adult mice.

Whether cholecystokinin (CCK) has a direct action on duct cells and the role of CCK-A receptor in bicarbonate secretion were examined by comparing the results obtained from OLETF (CCK-A receptor-deficient rats) and control (LETO) rats. Rats were prepared with cannulae for draining bile and pancreatic juice separately, with two duodenal cannulae and an external jugular vein cannula. The experiments were conducted without anesthesia. The responses of bicarbonate secretion to intravenous infusion of CCK, acetyl-ß-methylcholine (Ach), and 2-deoxy-D-glucose (2DG), and to intraduodenal infusion of HCI and a liquid meal were examined. To examine the synergistic effect between CCK and secretin, the effect of CCK during a background secretin infusion was examined in LETO rats. CCK did not stimulate bicarbonate secretion in either strain, nor in LETO rats with secretin infusion. When gastric acid secretion was prevented by administration of omeprazole, Ach did not increase bicarbonate secretion, but 2DG did in both strains. Intraduodenal infusion of HCI and a liquid meal significantly increased bicarbonate secretion in both strains; however, the responses were much less in OLETF than LETO rats. In conclusion, intravenous injection of CCK did not stimulate bicarbonate secretion, and the lack of CCK-A receptor decreased bicarbonate secretion in response to luminal stimulants.

We summarize the discovery of luminal feedback regulation of pancreatic secretion in rats and its history. In rats, removal of proteolytic activity from the intestine produced a significant increase in pancreatic protein (enzyme) output. This increase was confirmed to be mediated by circulating chole-cystokinin (CCK). Subsequently, two CCK-releasing peptides, monitor peptide and luminal CCK-releasing factor (LCRF), were purified from the rat pancreatic juice and small intestine, respectively, to elicit CCK release in luminal feedback regulation. Furthermore, we emphasize the important physiologic roles of CCK and CCK receptors by the discovery of disrupted CCK-A-receptor gene in rats. These findings should help to determine the regulation of pancreatic secretion and CCK functions in humans.

We examined the role of the cholecystokinin-A (CCK-A) receptor in acute inflammatory and regenerative stages of experimental pancreatitis using a rat model lacking the CCK-A receptor [Otsuka Long-Evans Tokushima Fatty (OLETF) rats]. OLETF and control [Long-Evans Tokushima Otsuka (LETO)] rats were prepared with an internal bile fistula and with obstruction of pancreatic flow and were sacrificed 1-14 days later. Histological examination was performed, and changes in pancreatic wet weight, protein concentration, CCK-A and -B receptor mRNA levels, tyrosine kinase activities, and plasma amylase and CCK levels were determined. The plasma amylase level showed a transient increase on day I, the CCK level remained at high levels throughout, and tyrosine kinase activity was increased significantly on day 3 but declined thereafter. These parameters were comparable for both strains during the acute inflammatory stage. However, no regenerative findings were observed by histological examination and the protein concentration in the pancreas was significantly lower in OLETF rats on days 7-14, during which time regeneration was completed in LETO rats. These observations indicate that the absence of the CCK-A receptor did not modify the acute phase of pancreatitis but significantly retarded regeneration of the pancreatic tissue.

Changes in content and recovery of pancreatic enzymes after a protein-free diet were examined in young (8-month) and old (26-month) Fischer- 344female rats. In control rats fed a normal diet for 15 days, no significant difference between young and old rats was observed in pancreatic weight or in pancreatic content of protein, enzymes, and DNA. A 7-day protein-free diet significantly decreased pancreatic wet weight as well as content of protein, chymotrypsin, amylase, and DNA in both age groups, whereas body weight and amount of daily food intake did not differ from respective control values (in normal diet-fed rats) in either age group. In young rats, chymotrypsin and protein contents were significantly greater than control values during the recovery period in which rats were fed a normal diet following the 7-day protein-free treatment. In contrast, these values in old rats remained lower than corresponding control values throughout the entire recovery period. These results agree with our previous study suggesting that aging probably attenuates the reserve capacity of the pancreas for enzyme secretion, but not its basal functions.

Pancreatic duct occlusion is known to produce a sustained increase in the plasma cholecystokinin (CCK) concentration and to affect the tissue content of CCK in the rat. The tissue content of CCK is correlated with regenerative changes in the pancreas after pancreatic duct occlusion. In the present study, we examined the changes in mRNA levels of pancreatic secretory trypsin inhibitors (PSTIs), pancreatitis-associated protein (PAP), and amylase in the pancreas in comparison with changes in CCK and secretin mRNA levels in the intestine and the histological changes produced by pancreatic duct ligation. Rats with an internal bile fistula and with obstruction of pancreatic flow were prepared and were sacrificed 1, 3, 7, 10, 14, and 28 days later. Then mRNA levels of CCK, secretin, PSTIs, PAP, and amylase were determined by slot-blot analysis. The CCK mRNA level gradually increased to a peak on day 10, was slightly lower on day 14, and returned to the control level on day 28. The level of secretin mRNA did not change. The mRNA levels of PSTIs increased significantly on day 3 after occlusion. PAP mRNA was detectable on days 1 and 3, being maximal on day 1. The mRNA level of amylase was markedly decreased on days 1 and 3, then remained lower than the control level. Histological examination showed acute inflammatory changes in the pancreas on days 1 and 3 and regenerative changes from day 7. These results suggest that a change in gene expression of PAP reflects acute inflammatory changes in the pancreas most sensitively.