Involvement of gene expressions of cholecystokinin and secretin in luminal feedback regulation in conscious rats

Pancreatic exocrine secretion in conscious rats in regulated by bile and pancreatic juice in the proximal intestinal lumen; exclusion of bile and pancreatic juice produces release of cholecystokinin (CCK) and pancreatic hypersecretion (luminal feedback regulation). In the present study, we examined the changes of gene expressions of CCK and secretin, another representative gastrointestinal hormone in the intestine, and found that exclusion of bile and pancreatic juice significantly enhanced gene expressions of both CCK and secretin. These results suggested involvement of both CCK and secretin in luminal feedback regulation.

Effect of a cholecystokinin (CCK) antagonist (CR 1505) on gene expressions of CCK and secretin in rat intestine

The effects of intragastric administration of cholecystokinin (CCK) antagonist (CR 1505; 60-300 mg/kg/day) to rats for 3 days on the gene expressions of CCK and secretin, the plasma CCK immunoreactivity, and the CCK content in the intestinal mucosa were examined. CR 1505 increased the level of CCK mRNA in the intestine dose dependently to up to 1.6 times the level in control rats but did not affect the level of secretin mRNA. It also significantly increased the plasma CCK immunoreactivity and the amount of CCK extracted from intestine with acid dose dependently. CR 1505 tended to decrease the trypsin activity in the intestine. These results suggest that ingested CR 1505 increased the CCK mRNA level in the intestine.

Acetylcholine regulates glucagon secretion from human glucagonoma cells

Human glucagonoma cells were isolated and maintained in vitro. Incubation experiments showed that carbachol (Cch) induced the simultaneous release of glucagon, VIP (vasoactive intestinal polypeptide), and pancreatic polypeptide (PP) at levels significantly higher than basal levels. Atropine abolished the stimulatory effect of Cch on glucagon, VIP, and PP release. An immunohistological study of the tumor tissues revealed that the cells contained glucagon, VIP, and PP. These findings demonstrate, for the first time, the in vitro release of glucagon from glucagonoma cells by Cch stimulation.

Lack of satiety effect of cholecystokinin (CCK) in a new rat model not expressing the CCK-A receptor gene

This work expands recent observations that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show little or no pancreatic expression of the cholecystokinin (CCK)-A receptor gene. We examined whether the CCK-A and -B receptor genes were expressed in the brain (hypothalamus) of OLETF rats in comparison with control (Long-Evans Tokushima Otsuka = LETO) rats. CCK-A receptor mRNA was detected in the hypothalamus of LETO rats but not OLETF rats. The CCK-B receptor gene was expressed in the hypothalamus in both strains. Cerebroventricular administration of CCK-8 sulfate inhibited daily food intake in LETO rats, but not in OLETF rats. These results show that in OLETF rats the absence of CCK-A receptor gene expression in the hypothalamus results in hyperphagia because of lack of satiety.

Mechanisms of stimulatory effect of neuromedin C on pancreatic exocrine secretion in conscious rats

The mechanisms of the stimulatory effect of the bombesin-like peptide neuromedin C on pancreatic exocrine secretion were examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately. Intravenous infusion of 0.35 nmol/kg/h of neuromedin C significantly increased the secretions of pancreatic bicarbonate and protein, and transiently increased the plasma cholecystokinin (CCK) concentration. The increase in pancreatic secretion persisted for 90 min, whereas the increase in plasma CCK was observed only after 15 and 30 min from the beginning of neuromedin C infusion. Intravenous infusion of CR-1409, a specific CCK-receptor antagonist, inhibited, but did not abolish, the protein secretion stimulated by neuromedin C. Intraduodenal infusion of a potent proton pump inhibitor, omeprazole, suppressed, but did not abolish, protein secretion induced by neuromedin C. Omeprazole abolished the increase in bicarbonate secretion produced by neuromedin C. These results indicate that neuromedin C induces release of CCK and that its induction of pancreatic hypersecretion is due to both its direct effect and CCK. The results also suggest that gastric hypersecretion may have a role in the bicarbonate hypersecretion induced by neuromedin C.

Lack of effect of cholecystokinin receptor antagonist (CR1505) on recovery of experimental pancreatitis after pancreatic duct occlusion in rats

The effect of long term administration of a synthetic cholecystokinin (CCK) receptor antagonist CR1505 (loxiglumide) on pancreatitis was examined in rats after pancreatic duct ligation (PL) with an internal bile fistula. All rats were given both 6 mg/day of CR1505 continuously infused intraduodenally with an osmotic pump and 32 mg/day introduced into the stomach with an orogastric tube. Rats were killed 7, 14, and 28 days after PL, and changes of body weight, pancreatic wet weight, daily food intake, pancreatic protein content, and histology, plasma amylase concentration, and both plasma and duodenal CCK concentrations were examined. Administration of CR1505 for 7 days from immediately after PL, resulted in decrease of body weight, increase of daily food intake, and significant increases of intestinal CCK concentration and the level of CCK mRNA. However, its administration from day 7 to day 14 or 28 did not improve any of the parameters examined except inflammatory infiltration of the pancreas on the 14th postoperative day. These results suggest that CR1505 may have a beneficial effect on recovery from pancreatitis when administered during the early stage, but not when administered during a later stage.

Pancreastatin-like immunoreactivity of cerebrospinal fluid in patients with Alzheimer type dementia: evidence of aberrant processing of pancreastatin in Alzheimer type dementia

The concentrations of pancreastatin-like immunoreactivity (PST-LI) of the cerebrospinal fluid (CSF) were measured in the patients with Alzheimer type dementia (ATD) and in age-matched normal subjects. The mean PST-LI concentration in the CSF of ATD patients was significantly lower than that of normal subjects. Gel chromatographic analysis revealed that the main PST-LI peak of ATD's CSF eluted at molecular weight (MW) 13.5 kDa. However, the age-related change of the molecular forms of PST-LI in CSF was observed in normal subjects as following; PST-LI in neonatal CSF showed one peak at MW 13.5 kDa, that of 16-64-year-old showed two peaks at MW 13.5 and 5.4 kDa, however, only one main peak was shown at MW 5.4 kDa in the CSFs of 72-85-year-old. These findings suggest that the production of PST-LI was decreased and the proteolytic cleavage, which should process big PST to PST (1-52) in normal subjects, was altered to that of neonatal type in the CNS of the patients with ATD.

Production and secretion of chromogranin A and pancreastatin by the human pancreatic carcinoma cell line QGP-1N on stimulation with carbachol

Chromogranin A (CGA) is thought to be a precursor of pancreastatin (PST). Carbachol (Cch) stimulated the secretion of CGA and PST from QGP-1N cells derived from a human pancreatic islet cell tumor. Atropine inhibited the secretion of both. Sodium fluoride, phorbol ester, and calcium ionophore also stimulated the secretion of both. Cch (10(-5) M) stimulated inositol 1,4,5-trisphosphate production in QGP-1N cells. Stimulation with Cch increased the total amount of PST in the cells and the medium 1.7-fold and decreased the amount of CGA in the cells and medium. QGP-1N cells were labelled with [35S]methionine, and then CGA and PST in the cells and medium were immunoprecipitated with specific antisera, and separated by electrophoresis in polyacrylamide gel. Stimulation with Cch resulted in an increase in the intensity of PST-immunoreactive bands and a decrease in those of CGA-immunoreactive bands. Cch did not increase the cellular level of CGA messenger RNA. These results suggested that (1) the secretion of CGA and PST from QGP-1N cells is regulated mainly through muscarinic receptors coupled with activation of polyphosphoinositide breakdown by a G protein, with intracellular calcium ion and protein kinase C playing a role in the stimulus-secretion coupling and that (2) Cch may induce the secretion of PST and CGA and processing from CGA to PST.

Glucagon-like peptide-1 (GLP-1) molecular forms in human pancreatic endocrine tumors resemble those in intestine rather than pancreas

Different glucagon-like peptide-1 (GLP-1) molecular forms are produced in the pancreas and the small intestine by differential processing of proglucagon. In this report, molecular forms of GLP-1 in two human pancreatic endocrine tumors were studied and compared with those in the pancreas and small intestine. A predominant GLP-1 immunoreactive form in the pancreas was eluted at the position of GLP-1(1-36) amide, whereas a predominant immunoreactive form in the ileal mucosa was eluted at the position of GLP-1(7-36) amide. In a glucagonoma, GLP-1 immunoreactive forms corresponding to GLP-1(7-36) amide and GLP-1(7-37) were predominant and immunoreactive forms at the position of GLP-1(1-36) amide and GLP-1(1-37) were minor. In another tumor, an insulinoma, immunoreactive forms were detected at the positions of GLP-1(7-36) amide, GLP-1(7-37), GLP-1(1-36) amide and GLP-1(1-37). Thus, the pattern of GLP-1 molecules in pancreatic tumors was not a pancreatic pattern and mimicked that found in the small intestine or consisted of both the patterns found in the small intestine and the pancreas. These data suggest that neoplastic transformation of the islet cells is associated with a switching in processing phenotype from islet (A) cells to intestinal (L) cells.

Gene expression of erythropoietin in hepatocellular carcinoma

A 68-year-old man with hepatocellular carcinoma complicated by erythrocytosis showed an increased plasma level of immunoreactive erythropoietin (EPO). Northern blot analysis and RT-PCR (reverse transcriptase and polymerase chain reaction) of EPO mRNA extracted from a surgical specimen indicated high expression of EPO mRNA in the tumor tissue. Histological and immunocytochemical examination showed that the tumor was a hepatocellular carcinoma with predominant immunostaining for EPO. The erythrocytosis improved and the high serum EPO level decreased after resection of the tumor. This is the first demonstration of EPO mRNA expression in hepatocellular carcinoma tissue by RT-PCR.

Direct, concentration-dependent inhibition by taurocholate of pancreatic exocrine secretion and CCK release in conscious rats

In conscious rats, bile inhibits pancreatic secretion. The role of luminal taurocholate (TC), a major component of rat bile, in the regulation of pancreatic secretion was studied in conscious rats with external bile and pancreatic fistulae. On the fourth postoperative day, after the basal collection of bile and pancreatic juice (PJ) returned to the duodenum, graded doses of TC (0, 0.4, 4, 40 mM) containing 10 mM CaCl2 were infused into the duodenum instead of bile and PJ for 2 hr (1 ml/hr), with or without 1 mg/ml of porcine trypsin. Luminal trypsin activities were not affected by any dose of TC. The increases in pancreatic secretion in response to diversion of bile and PJ were progressively inhibited with increasing doses of infused TC from 0 mM to 4 mM both with and without trypsin infusion. The effects with 4 and 40 mM TC were not significantly different. Changes in plasma cholecystokinin concentrations roughly correlated with changes in protein output in rats without trypsin infusion. We concluded that TC directly inhibited pancreatic secretion independent of the luminal trypsin activity and that its inhibitory action was concentration dependent.

Effect of a new cholecystokinin antagonist (FK 480) on gene expression of cholecystokinin and secretin in rat intestine

The effects of a new cholecystokinin (CCK) antagonist (FK 480; 0.1 mg/kg per day given by intragastric administration to rats for 3 days) on the expression of the CCK and secretin genes, plasma CCK immunoreactivity, and CCK content in the intestinal mucosa were examined. FK 480 increased the level of CCK mRNA in the intestine to 1.7 times the level in control rats, but did not affect the level of secretin mRNA. It did not increase plasma CCK immunoreactivity or CCK content in the intestinal mucosa. These results suggest that the ingested FK 480 directly increased CCK mRNA level in the intestine and produced a dissociation between the synthesis and release of CCK.

In vitro release of vasoactive intestinal polypeptide and pancreatic polypeptide from human VIPoma cells and its inhibition by somatostatin analogue (SMS 201-995)

BACKGROUND

The purpose of the present study was to determine whether vasoactive intestinal polypeptide (VIP) is released from the tumor cells of VIPoma and if so then to attempt to show how its release is regulated by cultured human VIPoma cells.

METHODS

A resected specimen of a pancreatic tumor from a patient with watery diarrhea, hypokalemia, and achrohydria syndrome was examined. The dissociated cells were obtained by collagenase digestion of the tumor tissue and were cultured in vitro.

RESULTS

The extraction of tumor cells disclosed that the cells contained VIP and pancreatic polypeptide (PP). Neither insulin, glucagon, somatostatin nor pancreastatin was detected. Immunohistochemically, 40% to 60% of the cells in the tumor stained positively for VIP and 1% to 5% stained positively for PP. The dissociated cells became reaggregated in the culture (50 to 300 microns) and could be maintained in vitro. Incubation experiments revealed a simultaneous in vitro release of VIP and PP with a significant increase by either carbachol or phorbol myristate acetate but not by theophylline or caerulein. Atropine completely abolished the stimulatory effects of carbachol on VIP and PP release. Octreotide (somatostatin analogue [SMS 201-995]) significantly inhibited the carbachol and phorbol myristate acetate-stimulated VIP and PP release.

CONCLUSIONS

These findings show the in vitro release of VIP and PP from the VIPoma cells and also provide evidence for the direct inhibitory effect of somatostatin analogue on both the VIP and PP release from the tumor cells.

Expression of the cholecystokinin precursor gene in rat tissues

Cholecystokinin, a brain gut peptide that stimulates gall bladder contraction and pancreatic exocrine secretion, also acts as a neurotransmitter. In this study, we demonstrated that small amounts of cholecystokinin precursor mRNA were expressed in the heart, lung, and kidney, as well as in the brain and the small intestine. The nucleotide sequences of the coding regions of the cholecystokinin precursor mRNA in these tissues were identical to those of the small intestine, indicating that cholecystokinin precursor proteins produced in these tissues are identical to those in small intestine. This is the first report demonstrating that the cholecystokinin precursor gene is expressed in the heart, lung, and kidney, as well as in the gastrointestinal tract and brain.

Unique change of pancreastatin-like immunoreactivity in cerebrospinal fluid by aging

Using a specific antiserum for the C-terminal glycine amide region of human pancreastatin (PST), pancreastatin-like immunoreactivity (PST-LI) was measured in cerebrospinal fluid (CSF) from 447 subjects (368 +/- 10.8 pmol/l, mean +/- S.E.M.) free from endocrine diseases. The CSF contents of PST-LI showed a mountain-shape type change which peaked at 40 years of age. The highest concentration was found in the group of ages 40-49 years old (412 +/- 22.9 pmol/l) and the lowest concentration was found in the group of ages 80-89 years old (293.2 +/- 45.2 pmol/l) among various age groups. Gel chromatographic examination revealed the presence of two major forms (MW 13,500 and 5,400) of PST-LI in CSF. Because of the character of this antibody, the large molecular form is possibly an N-terminally elongated PST and the other may be PST-52. This may be the first report on the unique age-related change of PST concentration in CSF.

Little or no expression of the cholecystokinin-A receptor gene in the pancreas of diabetic rats (Otsuka Long-Evans Tokushima Fatty = OLETF rats)

Expression of the CCK-A receptor gene in the pancreas and pancreatic exocrine function was examined in diabetic model rats (OLETF) at 5 wks of age. Little or no CCK-A receptor was detected in the pancreas of OLETF rats. Pancreatic exocrine function in response to exogenous CCK and to bile-pancreatic juice diversion (endogenous CCK) was impaired in conscious OLETF rats. The pancreatic insulin and protein contents of OLETF (Otsuka Long-Evans Tokushima Fatty) and control LETO (Long-Evans Tokushima Otsuka) rats were not significantly different. No histological abnormalities or expression of pancreatitis associated protein (PAP) mRNA was detected in the pancreas in either group. These results suggest that OLETF rats are a new experimental model for congenital deficiency of CCK-A receptor in the pancreas.

Effectiveness of chemotherapy for advanced adenocarcinoma of the pancreas in combined modality therapy

Because it is difficult to diagnose at an early stage, pancreatic carcinoma is usually well advanced by the time it is diagnosed. The combined use of intraoperative radiotherapy, gastrointestinal and/or biliary tract bypass operation, celiac plexus nerve block, and chemotherapy is widely applied in treatment, with favorable results reported in some patients with advanced disease. To evaluate the efficacy of chemotherapy in such combinations, we compared the effect of 5-fluorouracil, its analogues, and mitomycin C on the survival of patients with advanced stage pancreatic cancer. We found no significant difference between the patients treated or not treated with these drugs. Clearly, there is a need for new agents having greater efficacy against pancreatic carcinoma.

[Effect of bilateral truncal vagotomy on cholecystokinin release and pancreatic exocrine secretion in conscious rats]

The effects of bilateral truncal vagotomy on cholecystokinin (CCK) release and pancreatic hypersecretion produced by bile and pancreatic juice (BPJ) diversion were examined in conscious rats. In addition, the effect of exogenous administration of CCK-8 (100 pmol/kg/h) on pancreatic secretion were compared in rats with and without vagotomy. Rats were prepared with external bile and pancreatic juice fistulae and the experiment was conducted on the 4th postoperative day. Basal pancreatic secretion was not affected by vagotomy. CCK release produced by bile and pancreatic juice diversion was enhanced, whereas protein secretion in response to high plasma CCK was inhibited by vagotomy. Pancreatic secretion stimulated by intravenous infusion of 100 pmol/kg/h of CCK-8 was also inhibited by vagotomy. These results proposed that vagal nerve is mandatory for the full response of pancreatic exocrine secretion to circulating CCK.

Effect of long-term exercise under restricted-feeding on intestinal content of cholecystokinin and on the pancreas in aging rats

The effects of exercise (5000 m/day running from 100 to 600 days of age) on the cholecystokinin (CCK) content in the proximal intestine, and the enzyme and insulin contents of the pancreas were examined in food-restricted rats. Food restriction decreased the body weight and the wet weights of the pancreas and proximal intestine but not the wet weight of the stomach. Food restriction also decreased the chymotrypsin content of the pancreas but not its amylase content. The contents of enzymes in the pancreas were not affected by exercise. The insulin content of the pancreas was lower in lean rats produced by food restriction and/or exercise than in controls. Exercise increased the wet weight of the proximal intestine and the CCK content of the intestine. The increase in the CCK content may be due to compensational change in the efficiency of digestion of luminal nutrients induced by exercise.

Secretory capacity of pancreatic protein during luminal feedback regulation in conscious rats

Pancreatic exocrine secretion in conscious rats is regulated by bile and pancreatic juice in the proximal intestine (luminal feedback regulation), and bile-pancreatic juice diversion from the intestine results in cholecystokinin (CCK) release and pancreatic hypersecretion. Pancreatic protein secretion increases to a maximum 60-90 min after bile-pancreatic juice diversion, and then decreases slightly to a steady level of two times the basal level. Change in plasma CCK concentration parallels protein secretion. In this study, the mechanism of the decreases of protein secretion and CCK concentration was examined by stimulation with various species of peptides having different stimulatory mechanisms. Cannulae for draining bile and pancreatic juice separately and a duodenal cannula and extrajugular vein cannula were inserted into male Wistar rats. Four days later, basal levels in a 90-min period were determined, bile and pancreatic juice were diverted for 90 min, and then either secretin (1.2 nmol/kg/h), CCK-8 (25 and 100 pmol/kg/h), neuromedin C (350 pmol/kg/h and 3.5 nmol/kg/h), or CCK-JMV-180 (200 nmol/kg/h) was infused intravenously for 60 min. Infusion of secretin significantly increased protein secretion and prevented its decrease after its maximum induced by bile-pancreatic juice diversion. The plasma CCK concentrations were not increased further by neuromedin C. In conclusion, pancreatic exocrine secretion and CCK release in conscious rats are maximally stimulated by luminal feedback regulation that the decrease after maximal protein output may be due to limitation of secretory capacity and/or desensitization of acinar cells.

Pancreastatin molecular forms in normal human plasma

Circulating molecular forms with pancreastatin (PST)-like immunoreactivity in plasma from normal subjects were examined. An immunoreactive form corresponding to a human PST-like sequence [human chromogranin-A-(250-301)] (hPST-52) and a larger form (mol wt 15-21 kDa) were detected by gel filtration of plasma from normal subjects. On high performance liquid chromatography, predominant immunoreactive forms coeluted with the three larger forms which were purified from the xenograft of human pancreatic islet cell carcinoma cell line QGP-1N cells and with synthetic hPST-52. The fraction containing larger forms purified from xenograft of QGP-1N cells had biological activity equivalent to that of hPST-52 on the inhibition of pancreatic exocrine secretion. These results suggest that the larger molecular forms as well as hPST-52 may be physiologically important circulating forms of PST in human.

Time course of recovery from pancreatic hypertrophy during partial exclusion of bile-pancreatic juice in rats

The time course of recovery from hypertrophied pancreas to the normal size was examined and compared with the time course of normal size pancreas getting hypertrophied in rats. The bile-pancreatic duct was cannulated and bile-pancreatic juice was partly bypassed the proximal intestine. Trypsin and bile salts disappeared from the lumen of proximal quarter of intestine during the first 7 postoperative days; however, these appeared again after the 14th postoperative day and luminal trypsin activity reached 3 to 4 times the control level during the postoperative days 14-56. Conversely, the plasma cholecystokinin (CCK) concentration significantly increased on day 7, then declined thereafter, and the mRNA level of CCK in the proximal intestinal mucosa increased and reached the maximal level on day 7. Pancreatic wet weight, as an index of size, was significantly increased and remained high on postoperative days 7-28, then returned to the control size on day 56. Therefore, it took 7 d for the pancreas to become hypertrophied by high circulating CCK, however the pancreatic size recovered to the normal size on the 56th postoperative day although the plasma CCK level decreased with the appearance of luminal bile salt and trypsin during postoperative days 14-56. In conclusion, it took longer for the hypertrophied pancreas to return to the normal size (14 or more d) than for the normal size pancreas to become hypertrophied (7d).