Role of cholecystokinin (CCK)-A receptor for pancreatic growth after weaning: a study in a new rat model without gene expression of the CCK-A receptor

This work extends a recent observation that Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which have been established as an animal model of non-insulin-dependent diabetes mellitus, show no expression of the cholecystokinin (CCK)-A receptor gene in the pancreas. The CCK-A receptor is known to be involved in regulating pancreatic exocrine function and growth. We examined the growth of the pancreas in terms of wet weight, enzyme compositions, and protein and DNA contents at 5-6 and 24-25 weeks of age in OLETF rats and control (Long-Evans Tokushima; LETO) rats. The pancreatic wet weight increased significantly with age in both OLETF and LETO rats but was significantly lower in OLETF rats than in LETO rats. The total DNA contents in the whole pancreas (cell numbers) were comparable for both strains and increased significantly with age. However, the ratio of protein content to DNA content (the cell size) significantly increased with age in LETO rats, with no increase in OLETF rats. The changes in chymotrypsin, amylase, and insulin with respect to age were in the same direction in both strains: a decrease or no change in total and/or cellular contents of chymotrypsin and insulin and increases in amylase. These results suggest that the CCK-A receptor plays some role in the increase in cell size associated with normal growth of the pancreas from 5 to 25 weeks of age (after weaning).

Pancreastatin-like immunoreactivity in globular dystrophic neurites of senile plaques in brains of patients with Alzheimer's disease

The immunohistochemical localization of pancreastatin (PST) was examined in brains of Alzheimer's disease (AD) and control cases using three different antisera to PST, and was compared with the staining for chromogranin A (CgA), the precursor of PST. In control brains, CgA-like immunoreactivity was observed in the cytoplasm and fibers of certain neuronal populations, which were not immunostained with any of the PST antisera. In AD brains, dystrophic neurites of globular shape located in senile plaques were immunostained with each of the PST antisera, as well as with the CgA antibody. PST-positive and CgA-positive dystrophic neurites showed similar profiles. The present study indicates that CgA is probably cleaved to produce PST in some globular dystrophic neurites in senile plaques.

[Cholecystokinin and cholecystokinin receptor]

Cholecystokinin (CCK) act as hormones and neuropeptides on central and peripheral CCK receptors. The application of modern molecular biological techniques has identified two CCK receptors, CCK-A receptor (CCKAR) and CCK-B/gastrin receptor (CCKBR). The genes of CCKAR and CCKBR consist of five exons interrupted by four introns. We have reported that OLETF rats, which have been established as an animal model of NIDDM, revealed no expression of CCKAR gene (a naturally occurring CCKAR gene knockout rat). Pancreatic exocrine functions in OLETF rats are regulated by all neural and peptidergic agents except CCK. Therefore, we have proposed that OLETF rats may be a useful experimental model for examining the biological functions of the CCKAR.

Regulation of pancreatic exocrine function in Otsuka Long-Evans Tokushima Fatty (OLETF) rats without gene expression of cholecystokinin-A receptor

This work extends a recent observation that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show a congenital defect of the cholecystokinin (CCK)-A receptor gene. Expression of CCK-A receptor mRNA in the pancreas, small intestine and brain were not detected in OLETF rats by the reverse transcriptase polymerase chain reaction. In vitro studies showed that the maximal effective concentrations of neuromedin C, acetylcholine and secretin for stimulation of amylase secretion were comparable in both strains, but that CCK-stimulated amylase secretion was observed only in Long-Evans Tokushima Otsuka (LETO) rats. Intracellular cytosolic Ca2+ movement stimulated by acetylcholine and neuromedin C was similar in both strains. In vivo studies showed that the pancreatic secretions in response to secretin and acetylcholine were not impaired in OLETF rats. However, protein responses to neuromedin C and 2-deoxy-D-glucose were impaired in OLETF rats. The findings suggest that pancreatic exocrine functions in OLETF rats are regulated by all neural and peptidergic agents except CCK.

Pancreatic endocrine dysfunction in rats not expressing the cholecystokinin-A receptor

Cholecystokinin (CCK) has been suggested to modulate insulin output. We have shown that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show little or no expression of the CCK-A receptor gene in the pancreas. We examined whether the CCK-A and CCK-B receptor genes are expressed in the islets and the role of CCK-A receptor in insulin secretion. Gene expressions of CCK receptors were determined by the reverse-transcriptase polymerase chain reaction (RT-PCR) followed by Southern blot hybridization and Northern transfer analysis using LETO rats as controls. Pancreatic endocrine function was examined in perfusion (exogenous CCK stimulation) and meal ingestion (endogenous CCK stimulation) studies. CCK-A receptor mRNA was detected in the islets of LETO rats but not OLETF rats. Expression of the CCK-B receptor gene was detected in both strains by RT-PCR. Insulin secretion was impaired in OLETF rats, but the insulin contents of OLETF and LETO rats were not different. No abnormalities were detected histologically in either strain. These results suggest that the occurrence of pancreatic endocrine dysfunction in OLETF rats may be due to a defect in expression of the CCK-A receptor gene, not to insulin deficiency.

Neurohormonal regulation of pancreatic exocrine function in rats without gene expression of the cholecystokinin-A receptor

Otsuka Long-Evans Tokushima Fatty (OLETF) rats revealed no or reduced expression of the cholecystokinin (CCK)-A receptor gene in the pancreas and that the pancreas of this strain of rats did not respond to CCK stimulation. We examined whether the pancreatic responses to hormonal and neural stimulation except for CCK in OLETF rats were maintained. The pancreatic responses of conscious OLETF rats to various stimuli were examined in vivo and compared with those of control (Long-Evans Tokushima; LETO) rats. Moreover, the levels of expression of CCK-A and -B receptor genes in the small intestine were examined. Pancreatic responses to intravenous injection of secretin and acetylcholine and to intracerebroventricular administration of thyrotropin-releasing hormone were comparable in OLETF and LETO rats. However, responses to intravenous injection of neuromedin C, to intraduodenal injection of capsaicin, and to intragastric injection of a liquid meal were impaired in OLETF rats. CCK-A receptor mRNA was not expressed in the small intestine of OLETF rats but was in LETO rats. The pancreatic responses to various stimuli in OLETF rats were well conserved except for the involvement of CCK-A receptor function. OLETF rats are confirmed as a new experimental model deficient in CCK-A receptor gene expression and represent a useful tool for studying the physiological role of these in vivo.

Analysis of Ki-ras codon 12 mutations in the duodenal juice of patients with pancreatic cancer

BACKGROUND & AIMS

Point mutations of the Ki-ras gene at codon 12 have been frequently identified in pure pancreatic juice of patients with pancreatic cancer in studies examining pancreatic cancer tissues. The aim of this study was to examine mutations of the Ki-ras codon 12 in the duodenal juice collected from patients with various pancreatic disorders.

METHODS

The duodenal juice was collected through a Dreiling tube installed in the duodenum during a secretin test. Analysis of the Ki-ras mutations was performed using the enriched polymerase chain reaction--single-strand conformation polymorphism technique.

RESULTS

Point mutations were detected in 12 of 19 patients with pancreatic cancer; of the 12 patients, 10 had ductal tubular adenocarcinoma and 2 intraductal papillary adenocarcinoma. Mutational patterns included GAT (n = 4), GTT (n = 3), CGT (n = 1), and double mutations of GTT and GAT (n = 3) and GAT and CGT (n = 1). In 41 patients with benign pancreatic disorders, a point mutation was detected in only 1 patient with chronic pancreatitis.

CONCLUSIONS

Analysis of the Ki-ras codon 12 mutations in the duodenal juice is useful in the diagnosis of pancreatic cancer.

Somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic nerves in conscious rats

Somatostatin is known to be a potent inhibitor of pancreatic exocrine secretion, but the mechanism of its effect is not fully understood. The mechanism of the inhibition by centrally administered somatostatin was examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately, and with a duodenal cannula, an extrajugular vein cannula and a cerebroventricular cannula. Somatostatin was injected into the left lateral ventricle, and the inhibitory mechanism was examined using vagotomized rats and various drugs that affect sympathetic neurons. Intracerebroventricular administration of somatostatin significantly inhibited pancreatic exocrine secretion stimulated by bile-pancreatic juice diversion. The inhibitory effect was not abolished by vagotomy, pretreatment with propranolol, but was abolished by pretreatment with hexamethonium or phentolamine. The plasma level of somatostatin after its intracerebroventricular administration increased 3-fold, but its intravenous infusion at a rate giving a similar plasma somatostatin level to that produced by its intracerebroventricular injection, had no significant effect on pancreatic secretion. These results suggest that somatostatin inhibits pancreatic exocrine secretion centrally via sympathetic efferent nerves and that alpha-adrenergic receptors have an important role in its inhibitory action.

Impaired release of cholecystokinin (CCK) from synaptosomes in old rats

Cholecystokinin (CCK) is an abundant neurotransmitter peptide in the brain. CCK release from synaptosomes obtained from the cerebral cortex, the level of CCK mRNA and the tissue concentration of CCK were examined in young and old rats. CCK release stimulated by KCl was attenuated in old rats but that stimulated by calcium ionophore was comparable in animals at both ages. The CCK mRNA level in the cerebral cortex was decreased significantly in old rats despite the significant increase in CCK content. These results suggested that aging impaired CCK release, resulting in tissue accumulation and a decrease in the synthesis of CCK (the level of CCK mRNA).

Effects of intraduodenal administration of a low dose of cholecystokinin (CCK) antagonist (CR-1505) on plasma CCK concentration, intestinal CCK content, and levels of CCK mRNA

The effects of the intraduodenal administration of a low dose of CR-1505 for 3-7 days on the gene expression of cholecystokinin (CCK), plasma CCK concentration, and CCK content in the intestinal mucosa were examined in rats. The simultaneous changes of protein and enzyme content in the pancreas were also determined. CR-1505 was infused continuously into the duodenum at a dose of 3 mg/kg per day, calculated to correspond to a dose of 150-200 mg/day in humans. Seven days after the administration of CR-1505, a liquid meal (4.5 kcal/3 ml) was introduced into the stomach and changes in the intestinal CCK content and plasma CCK concentration were examined. The level of CCK mRNA in the intestine was significantly higher in rats treated with CR-1505 than in control rats. The plasma CCK concentration, the CCK content of the intestinal mucosa, and the composition of pancreatic enzymes did not significantly differ in rats treated with CR-1505 and the untreated controls. In control rats, the administration of the liquid meal increased the plasma CCK concentration and significantly decreased the intestinal CCK content in water extracts, but did not affect the amount extracts in acid whereas the ingestion of the meal did not cause any significant changes in rats treated with CR-1505. These findings indicate that a low dose of CR-1505 stimulates the gene expression of CCK without enhancing CCK release or exerting an effect on the pancreas.

Changes in gene expression of cholecystokinin-A receptor after induction of pancreatitis by pancreatic duct occlusion in rats

Serial changes in the levels of cholecystokinin (CCK)-A receptor mRNA in the pancreas after pancreatic duct occlusion were examined in rats. CCK-A receptor mRNA level was determined by Northern blot analysis with a rat CCK-A-receptor cDNA probe. The level of CCK-A receptor mRNA first decreased, reaching the lowest level 7 days after occlusion, and then began to increase. On day 14, it had completely recovered to the control level and it remained at that level until 28 days after occlusion.

Regulation of gene expression of pancreatic secretory trypsin inhibitor-61 and -56 by bile and pancreatic juice in rats

The rat possesses two pancreatic secretory trypsin inhibitors (PSTI-61 and -56). PSTI-61 has been known to stimulate cholecystokinin (CCK) release, whereas PSTI-56 did not. Both PSTIs are synthesized in the pancreatic acinar cells. CCK has a trophic effect on pancreatic acinar cells, and the exclusion of bile-pancreatic juice from the intestine has been known to be a most potent stimulator of CCK release. In the present study, we examined whether the mRNA levels of PSTI-61 and -56 produced by bile-pancreatic juice diversion were different from each other and compared the changes in CCK mRNA levels in the small intestinal mucosa and the plasma and intestinal CCK concentrations. Male Wistar rats were prepared with internal fistula and bile-pancreatic juice was excluded from the proximal intestine, being introduced into the distal ileum. Rats were sacrificed 1, 3, and 7 days after the operation. The concentrations of plasma and intestinal CCK and the levels of mRNA of CCK in the intestinal mucosa and PSTIs in the pancreas were significantly increased by bile-pancreatic juice diversion. The increase in the mRNA level of PSTI-61 was significantly higher than that of PSTI-56. Administration of CCK antagonist inhibited these changes but administration of CCK agonist could not fully reproduce these changes. These studies suggest that bile-pancreatic juice regulates gene expression of CCK and PSTIs and that the regulatory mechanisms of gene expression of PSTI-61 and -56 may be different.

Gene expressions of cholecystokinin (CCK) and CCK receptors, and its satiety effect in young and old male rats

Cholecystokinin (CCK), one of the first discovered gastrointestinal hormones, which stimulates pancreatic enzyme secretion and induces gallbladder contraction, is one of the most abundant neurotransmitter peptides in the brain and is implicated in satiety via CCK-A receptors. We compared the suppressive effect of central administration of CCK on food intake in young and old rats. The suppressive effect on food intake was enhanced in old rats. To examine the mechanism of this enhanced suppression, we measured the mRNA levels of CCK, CCK-A and CCK-B receptors in the cerebral cortex and the hypothalamus of young and old male rats. The mRNA level of CCK-A receptors in the hypothalamus decreased with age, whereas the mRNA levels of CCK-B receptors in the hypothalamus and cerebral cortex did not. The mRNA level of CCK in the cerebral cortex decreased significantly in old rats, although the decrease in the hypothalamus was not significant. Therefore, the enhanced sensitivity to CCK of old rats could not be explained by changes in gene expressions of CCK and CCK receptors. Moreover, the effects of aging on the gene expressions of CCK-A and CCK-B receptors were different.

Sex difference in gene expressions of cholecystokinin (CCK) and CCK receptor in young and old rats

The gene expressions of cholecystokinin (CCK) in the proximal small intestinal mucosa and CCK-A receptor in the pancreas were examined in male and female young (4-8 months old) and old (26-29 months old) rats. Their concentrations of CCK in the intestine were also compared. In males, but not in females, the mRNA levels of CCK in the intestine and those of the CCK-A receptor in the pancreas were significantly lower in old than young rats. In females, but not in males, the tissue content of CCK in the proximal intestinal mucosa was significantly higher in old rats. The pancreatic wet weight and trypsin activity in the proximal lumen were similar in young and old rats of both sexes. Therefore, changes in the regulations of gene expressions of CCK and the CCK receptor with age differ in male and female rats.

The amelioration of hyperglycemia in streptozotocin-induced diabetic rats after the intraportal transplantation of an insufficient number of islets by nicotinamide treatment

The purpose of the present study was to determine whether or not hyperglycemia in streptozotocin (STZ)-induced diabetic rats after the intraportal transplantation of an insufficient number of isogenic islets can be ameliorated by nicotinamide treatment. WKA/Qdj (RT 1u) rats were used both as donors and recipients. Islets were isolated by the collagenase technique. A total of 350 islets was transplanted into the liver via the portal vein of the STZ-induced diabetic rats. Either nicotinamide (NA, 0.5 g/kg) or a vehicle (saline) was administered ip once a day for 60 days after transplantation. All the diabetic rats without islet transplantation remained hyperglycemic irrespective of the NA treatment. All the recipients (n = 12) bearing the islet grafts and treated with saline remained hyperglycemic (> 400 mg/dl) at 60 days after transplantation. In marked contrast, all the recipients (n = 18) with islet grafts and treated with NA became normoglycemic (< 200 mg/dl) at 16.2 +/- 7.1 days (mean +/- SD) after transplantation. Morphologically, islets were easily found in the liver of the recipients. Aldehyde-fuchsin stain revealed that the beta cells in the islet grafts of the NA treated recipients were well granulated, whereas those treated with saline were degranulated. The insulin content of the liver bearing the grafts treated with either NA or saline was 116.3 +/- 26.0 micrograms/liver (n = 4) or 5.7 +/- 2.2 micrograms (n = 4), respectively, while that of 350 donor islets was 29.4 +/- 2.5 micrograms (n = 5). The insulin content of the pancreas in the NA- or saline-treated recipients was 27.3 +/- 10.6 micrograms/pancreas (n = 4) or 2.7 +/- 1.2 micrograms (n = 4), respectively, while those of the pancreas from the diabetic rats without transplantation was 1.9 +/- 0.7 micrograms (n = 4) or 1.6 +/- 0.8 micrograms (n = 5), respectively. These findings clearly demonstrate that the hyperglycemia in the STZ-diabetic recipients after transplantation of an insufficient number of islets can be ameliorated while, in addition, the islet mass in the liver as well as the endogenous pancreas both increase in size with nicotinamide treatment.

Gene structure of rat cholecystokinin type-A receptor

Little is known about the gene structure and mRNA expression of cholecystokinin type-A(CCKA) receptor in animals or in human. By screening an EMBL phage library containing partially digested Long-Evans rat DNA, we isolated 7 genomic clones covering a continuous 27 kb region over which a rat CCKA receptor gene spanned. The gene is approximately 10 kb in length containing the entire coding region of the rat CCKA receptor cDNA and consists of five exons interrupted by four introns. The expected sizes of the transcripts from the initiation sites were consistent with the results of northern blot analyses.

Changes in gene expression of pancreatitis-associated protein and pancreatic secretory trypsin inhibitors in experimental pancreatitis produced by pancreatic duct occlusion in rats: comparison with gene expression of cholecystokinin and secretin

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.

Comparison of chromogranin A and pancreastatin levels in plasma of patients with pancreatic islet cell tumor

The plasma levels of chromogranin A (CGA) in patients with islet cell tumor and plasma CGA responses to administration of a somatostatin analogue (Octreotide) in two of these patients were examined in comparison with plasma pancreastatin (PST) levels. There was a significant correlation between the fasting plasma levels of CGA and PST (r = 0.6, P < 0.001). Administration of the somatostatin analogue reduced the plasma concentrations of PST and CGA within 1 h, but the responses of CGA and PST to the analogue were not parallel in either patient. Thus, the suppressive effects of the analogue on the secretions of PST and CGA may be different. The results suggest the value of the PST and CGA assays used in this study.

An animal model of congenital defect of gene expression of cholecystokinin (CCK)-A receptor

Expressions of the CCK-A and B receptor genes in fetal and adult pancreas of OLETF rats were examined by the reverse transcriptase polymerase chain reaction followed by Southern blot hybridization. The pancreatic responses to various stimulants were examined in vitro and results were compared with those of control (LETO) rats. CCK-A receptor mRNA was not expressed in the fetal pancreas of either strain or in the adult pancreas of OLETF rats, but was expressed in the adult pancreas of LETO rats. CCK-B receptor mRNA was expressed in fetal and adult pancreas in both strains. Southern blot hybridization indicated a difference in gene structure in the two strains. The maximal effective concentrations of neuromedin C, carbachol, and secretin for amylase secretion and intracellular Ca2+ movement stimulated by carbachol and neuromedin C were similar in the two strains. CCK-8 and the non-sulfated form stimulated amylase secretion only in LETO rats. These results suggest that OLETF rats are a new model of a congenital defect of the CCK-A receptor gene and should be useful for determining CCK receptor function.

Cholinergic stimulatory effect of intragastric administration of a prostaglandin E2 analogue on pancreatic exocrine secretion in conscious rats

The effect of a long-acting, potent synthetic analogue of prostaglandin E2, enprostil, on pancreatic exocrine secretion was examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately. Pancreatic exocrine secretion was increased by intragastric administration of enprostil but inhibited by its intravenous administration. The pancreatic response to intragastric administration of enprostil was not inhibited by the administration of cholecystokinin antagonist or secretin antibody, or by bilateral vagotomy, but was completely abolished by atropine. Therefore, intragastric administration of enprostil seemed to stimulate pancreatic exocrine secretion via a peripheral gastro-(entero)-pancreatic reflex.

The human pancreatitis-associated protein (PAP)-encoding gene generates multiple transcripts through alternative use of 5' exons

The nucleotide (nt) sequence of the human cDNA encoding PAP, a pancreatic secretory protein induced during acute pancreatitis, was found to be identical with that of a gene activated in human primary hepatocellular cancer, designated HIP. To obtain insight into the expression of PAP/HIP, we characterized the gene organization, especially focusing on the 5'-flanking region, and found that it spans about 3 kb and is composed of six exon. Exon 1 encodes the 5'-noncoding sequence and exon 2 consists of three miniexons, 2a, 2b and 2c; the common exon 2c encodes the sequence including the start codon. Analysis by RT-PCR revealed the presence of at least three different types 5'-ends of human PAP/HIP transcripts which were derived from alternative use of 5'-exons. Although all three types of transcripts were expressed in both normal small intestine and pancreas, their gene expression was increased ectopically in gastric cancer, hepatocellular cancer and pancreatic acinar cell carcinoma. Furthermore, significant differences among the transcript types were detected between normal and tumor tissues, and especially between gastric and hepatocellular cancers, suggesting that PAP/HIP expression may vary with differences in 5'-alternative splicing.

Stimulatory effect of ursodeoxycholate on pancreatic exocrine secretion in an in vitro study

Ursodeoxycholate (UDCA; 300 microM) significantly stimulates amylase secretion from isolated rat pancreatic acini but not Ca2+ mobilization. Removal of extracellular Ca2+ completely abolished the UDCA-stimulated secretory response. Ca ionophore (A23187) potentiated the response. However, staurosporine, a protein kinase C inhibitor, did not affect the UDCA-stimulated amylase secretion. These results indicated that UDCA directly acted on the pancreatic acini and stimulated amylase secretion by the mechanism of stimulation of influx of extracellular Ca2+, but not through inositol [1,4,5] triphosphate and diacylglycerol formation or Ca2+ mobilization.