Response of the gastric vagal afferent activity to cholecystokinin in rats lacking type A cholecystokinin receptors

A systemic administration of cholecystokinin (CCK) increases gastric vagal afferent activity via type A CCK receptors (CCKAR). In the present study, the response of gastric vagal afferent activity to an intravenous administration of CCK was investigated in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which lack CCKAR, and compared with its control strain, Long-Evans Tokushima Otsuka (LETO) rats. The intravenous administration of 300 pmol kg(-1) and 3 nmol kg(-1) of CCK elicited dose-dependent increases in the gastric vagal afferent activity in LETO rats. The responses were not influenced by the pretreatment with L-365,260, a type B CCK receptor (CCKBR) antagonist, while they were significantly diminished by pretreatment with MK-329, a CCKAR antagonist. After pretreatment with MK-329, 3 nmol kg(-1) (but not 300 pmol kg(-1)) of CCK still elicited a small but significant increase in the activity. In the OLETF rats, both 300 pmol kg(-1) and 3 nmol kg(-1) of CCK produced small increases in the vagal afferent activity, and the responses were not influenced by pretreatment with either L-365,260 or MK-329. In addition, the systemic administration of CCK did not change gastric motility in the OLETF rats, indicating that the response of the vagal afferent activity in OLETF rats was independent of the gastric motility change. These results demonstrate that neither CCKAR nor CCKBR contributes to the response of the afferent activity of the gastric vagal nerve to a systemic administration of CCK in OLETF rats, suggesting an involvement of novel (non-A, non-B) CCK receptors.

Atropine-resistant secretion of a putative luminal CCK-releasing peptide in conscious rats

The changes in levels of the newly discovered luminal CCK-releasing factor (LCRF) in the small intestinal lumen before and after bile-pancreatic juice diversion in conscious rats were examined by a specific RIA. Moreover, we also examined whether LCRF secretion was under cholinergic control. Anti-LCRF antiserum was raised in rabbits, and a sensitive RIA was established. The localization of LCRF was examined by immunohistochemistry. The luminal content of LCRF was significantly increased by bile-pancreatic juice diversion, during which luminal trypsin activity was eliminated. The increase in luminal LCRF content was not inhibited by intravenous infusion of atropine. The changes in plasma levels of CCK and pancreatic secretion were similar to those in luminal LCRF contents. LCRF immunostaining was observed in villus tip enterocytes of the small intestine and was most prominent in the duodenal portion. These results support our original hypothesis that LCRF may be released spontaneously into the small intestinal lumen from the villus tip enterocytes and its intraluminal degradation by proteases regulates CCK release. Furthermore, LCRF release was not subject to cholinergic regulation.

Central somatostatin diminished inhibitory action of central CGRP on pancreatic basal secretion in conscious rats

We examined whether central somatostatin prevents an inhibitory effect of central calcitonin-gene related peptide (CGRP) on pancreatic secretion in conscious male Wistar rats (330-330 g). Rats were prepared with separate cannulas for draining bile and pancreatic juice and with a duodenal cannula and an extrajugular vein cannula. In addition, another cannula was stereotactically implanted into the left lateral cerebral ventricle. Rats were placed in restraint cages and experiments were conducted 4 days after the operation without anesthesia. An injection of CGRP (0.1, 1.0 nmol/10 microl) into the left lateral cerebral ventricle (i.c.v.) inhibited pancreatic secretion dose-dependently. To confirm the inhibitory effect of CGRP (i.c.v.) was mediated via sympathetic nerves, phentolamine was injected intravenously (i.v.) bolus (0.5 mg kg(-1)) 0.5-h before CGRP (i.c.v.), followed by continuous infusion of 0.2 mg kg(-1) h(-1). Phentolamine (i.v.) reversed the inhibition produced by CGRP (i.c.v.). An injection of 4 nmol/10 microl somatostatin (i.c.v.) 5 min prior to CGRP injection diminished the inhibitory effect of CGRP (i.c.v.). It is concluded that centrally administered somatostatin diminished the inhibitory action of CGRP (i.c.v.) on pancreatic secretion, probably via inhibiting autonomic (sympathetic) nerve excitation at the central site.

Disappearance of diurnal rhythm of energy expenditure in genetically diabetic obese rats

The daily profile of energy expenditures was examined in the new animal model of genetically diabetic obese rats. The diurnal rhythm was observed at 8 weeks of age, with highest and lowest values for energy consumption per hour observed in the dark and light periods, respectively. However, at 24 weeks of age after the manifestation of noninsulin-dependent diabetes mellitus, the rhythm completely disappeared, but it did not in the control rats.

Jun and MAP kinases are activated by cholecystokinin in the pancreatic carcinoma cell line KP-1N

Growth of the human pancreatic carcinoma cell line KP-1N was stimulated with cholecystokinin (CCK)-8. A 40% increase in cell numbers was observed in the presence of 10(-10) MCCK-8 and this increase was inhibited by the addition of 25 microM CCK-A receptor antagonist (CR1505). The binding affinity of CCK-8 to KP-1N cells was 21-fold higher than that of gastrin 17-I. No significant increase in intracellular Ca2+ concentration was found upon stimulation with CCK-8. Components of signal transduction pathways that were activated in KP-1N cells after stimulation with CCK-8 were studied. CCK-8 stimulated tyrosine phosphorylation of a mitogen-activated protein kinase (MAPK) of approximately 42 kDa (p42map). c-Jun amino-terminal kinases (JNKs) of 46 kDa (p46jnk) and 55 kDa (p55jnk) were also activated by CCK-8 and increased the phosphorylation of c-Jun. CCK-8 at 10(-7) M induced 1.5-fold increases in the phosphorylation of MAPK and of c-Jun by JNKs, respectively. These results suggest that cell proliferation stimulated with CCK-8 in KP-1N cells may be mediated by signal transduction cascades leading to activation of JNKs and MAPKs.

Clinical assessment of pancreatic diabetes caused by chronic pancreatitis

Despite the high prevalence of diabetes mellitus in patients with chronic pancreatitis, few studies of pancreatic diabetes have been reported. We investigated 154 patients with chronic pancreatitis, of whom 50% were diabetics, with special reference to the features and clinical course of pancreatic diabetes. We arrived to clarify the features of pancreatic diabetes by comparing pancreatic exocrine function in 112 patients with primary diabetes with findings in a separate group of 80 patients with chronic pancreatitis. Pancreatic diabetes is proposed as a type of diabetes in which exocrine pancreatic function is markedly decreased. Progressive and fatal angiopathies were found in patients with pancreatic diabetes after a long duration of diabetes. The present investigation suggests that treatment of malnutrition is necessary in patients with pancreatic diabetes and that control of blood glucose is often difficult in these patients because of the high incidence of insulin-induced hypoglycemic episodes.

Luminal feedback regulation, monitor peptide, CCK-releasing peptide, and CCK receptors

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 cholecystokinin (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.

Role of cholecystokinin-A (CCK-A) receptor in pancreatic regeneration after pancreatic duct occlusion: a study in rats lacking CCK-A receptor gene expression

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 1, 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.

A disrupted cholecystokinin A receptor gene induces diabetes in obese rats synergistically with ODB1 gene

Otsuka Long-Evans Tokushima fatty (OLETF) rats develop hyperglycemia, hyperinsulinemia, and mild obesity, which are characteristic of human non-insulin-dependent diabetes mellitus. We have shown that two recessive genes, ODB1 mapped on the X chromosome and ODB2 mapped on chromosome 14, are involved in the induction of the diabetes in OLETF rats. Recently we found that OLETF rats are the naturally occurring cholecystokinin type A receptor (CCKAR) gene knockout rats. In this study, we focused on the genotype of CCKAR gene and the ODB1 gene in regulation of glucose homeostasis in the F2 cross of the OLETF rats. Relatively high plasma glucose levels were observed in the F2 offspring with the homozygously disrupted CCKAR gene. A synergistic effect for increasing plasma glucose levels in F2 rats between disrupted CCKAR gene and the ODB1 gene was shown. The CCKAR gene was found to map very close to ODB2 by a linkage analysis using microsatellite markers. These results suggest that CCKAR gene maintains normoglycemia in rats.

Stimulatory effect of synthetic luminal cholecystokinin releasing factor (LCRF) fragment (1-35) on pancreatic exocrine secretion in conscious rats

The effects of a synthetic putative luminal cholecystokinin (CCK) releasing factor (LCRF) fragment (1-35) on pancreatic exocrine secretion were examined in conscious Wistar rats and a mutant strain of rats lacking the CCK-A receptor. Intraduodenal injection of graded doses of the LCRF fragment induced biphasic responses in Wistar rats. The injection of 0.1 microgram of the LCRF fragment produced a maximal response, while 1 microgram produced a lower response. No significant effect was observed in rats lacking the CCK-A receptor. The synthetic LCRF fragment stimulated pancreatic secretion via CCK-A receptors in conscious rats.

Disrupted cholecystokinin type-A receptor (CCKAR) gene in OLETF rats

OLETF rats develop hyperglycemia, hyperinsulinemia and mild obesity, which is characteristic of human non-insulin-dependent diabetes mellitus (NIDDM). We cloned and sequenced the cholecystokinin type-A receptor (CCKAR) gene in the rats. Comparing the DNA sequences of the OLETF CCKAR gene and LETO CCKAR gene, normal gene, we found a deletion in the OLETF gene, 6847 bases in length, which was flanked by two 3-base-pair direct repeats (5'-TGT-3') at positions -2407/-2405 and 4441/4443, numbered according to the LETO gene sequence, one of which was lost. The promoter region, the first and second exons were missing in the mutant. The region upstream and downstream of the deletion, including exons 3, 4 and 5, was conserved between the two strains, and did not contain any base changes. We found that the gene mapped to chromosome 14 in rats. OLETF rats are the naturally occurring knockout animals with the homozygously disrupted CCKAR gene.

Interleukin-1beta sensitizes the response of the gastric vagal afferent to cholecystokinin in rat

Interleukin-1beta (IL-1beta) and cholecystokinin (CCK) are important mediators in the development of anorexic response during disease. The role of IL-1beta and CCK in the peripheral mechanisms of anorexia was studied by recording the mass afferent activity of the gastric vagal nerve in anesthetized rats. The i.v. administration of CCK (1 nmol) increased the activity of the vagal nerve, and this response was raised by 55-72% 2 h after i.v. injection of IL-1beta. It is proposed that IL-1beta-induced anorexia is mediated via the sensitization of type A CCK receptors in the periphery.

Decreased level of light-induced Fos expression in the suprachiasmatic nucleus of diabetic rats

We assessed light-induced Fos-immunoreactive cells in the suprachiasmatic nucleus of diabetic rats. The number of Fos-immunoreactive cells significantly decreased in diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats as compared with control Long-Evans Tokushima Otsuka (LETO) rats. In contrast there was no decrease in the number of Fos-immunoreactive cells in young OLETF rats which have not yet developed diabetes. Two months after the administration of streptozotocin (STZ) to Wistar rats, the number of Fos-immunoreactive cells significantly decreased, although 1 week after the administration of STZ, the number had not yet changed in these STZ-induced diabetic rats. These results suggest that chronic diabetic (hyperglycemic) conditions may affect the light entraining responses in the suprachiasmatic nucleus (SCN).

Retardation of pancreatic regeneration after partial pancreatectomy in a strain of rats without CCK-A receptor gene expression

This study extends a recent observation that Otsuka Long-Evans Tokushima Fatty (OLETF) rats show no expression of the cholecystokinin (CCK)-A receptor gene in the pancreas because of a genetic abnormality. We compared the changes in pancreatic regeneration in terms of wet weight and protein and DNA contents after partial pancreatectomy (30% resection) in OLETF and control (Long-Evans Tokushima Otsuka: LETO) rats and examined whether the CCK-B receptor has a role in pancreatic regeneration after pancreatectomy. The pancreatic wet weight increased significantly with age in both OLETF and LETO rats regardless of surgical procedure, but the increase with respect to time was significantly less in OLETF than in LETO rats. The protein and DNA concentrations in the pancreas (mg/g wet tissue) were comparable for both strains after sham operation. However, they were significantly lower than pancreatectomy in OLETF rats compared to those after sham operation, whereas they were comparable in LETO rats regardless of surgical procedure. The ratio of protein content/DNA content (cell size) was significantly lower in OLETF than LETO rats under all conditions. CCK-B receptor gene expression was not enhanced after pancreatectomy. In conclusion, the CCK-A receptor is not an absolute requirement for pancreatic normal growth but is important for pancreatic regeneration.

Involvement of cholinergic processes in cholecystokinin (CCK) release [corrected] by luminal oleic acid

Cholecystokinin (CCK) is an important bioactive peptide that stimulates pancreatic enzyme secretion. Circulating CCK is secreted from endocrine cells in the upper small intestine in response to various luminal stimuli and to vascular administration of gastrin releasing peptides. However, the mechanism of its release has not been fully elucidated. In the present study, the vascularly perfused duodenojejunum was isolated from male Wistar rats. The effects of luminal infusion of sodium oleate (2 or 0.4%) or intra-arterial infusion of neuromedin C(10(-7) M) with or without atropine and with a recently synthesized specific bombesin antagonist (EABI) were examined. The CCK release produced by intra-arterial infusion of neuromedin C was inhibited by EABI in a dose-dependent manner. The CCK release produced by luminal sodium oleate was inhibited by atropine, but not affected by EABI. The CCK release stimulated by luminal sodium oleate is mediated, at least in part, by a cholinergic mechanism, but neuromedin C directly stimulates CCK release via its receptor on CCK-producing cells.

Mouse cholecystokinin type-A receptor gene and its structural analysis

The mouse cholecystokinin type-A receptor (CCK(A)R) gene was cloned and sequenced, and the exon/intron boundaries were determined by cDNA cloning. The gene, approximately 10 kb in length, contains the entire coding region, and consists of five exons. The deduced amino acid sequence was homologous with that of other species, with the exception of an additional DNA sequence encoding 7 amino acids in exon 5. A region of the 5' end of exon 2 appeared to be alternatively spliced, and generated an isoform shorter by 52 bases. The shorter isoform may encode an 48 amino acid open reading frame due to frameshift of translation. These two mRNA isoforms were expressed equally in the mouse gallbladders.

Apoptosis in the pancreas of genetically diabetic rats with a disrupted cholecystokinin (CCK-A) receptor gene

In a previous study, we reported that the pancreatic wet weight in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, cholecystokinin-A (CCK-A) receptor-defective because of a congenital gene abnormality, was significantly lower than in control rats (Long-Evans Tokushima Otsuka; LETO) from 3 weeks of age. In this study we examined apoptosis of pancreatic acinar cells in OLETF rats at 5 to 6 weeks of age in comparison with that in LETO rats. We present here direct morphologic evidence of apoptosis in OLETF rats, using a 3'-OH nick end-labeling method for detecting cells with DNA strand breaks and electron microscopy. Nick end-labeling revealed a small number of positively labeled acinar cells in OLETF rats. On electron microscopic examination, small numbers of apoptotic cells were seen in the lobules in OLETF rats but not in LETO rats. These results suggest that apoptosis plays an important role in the destruction of acinar cells of OLETF rats and induces atrophy of the pancreas.

Involvement of 5-hydroxytryptamine (5-HT)3 receptor mechanisms in regulation of basal pancreatic secretion in conscious rats

The effects of 5-hydroxytryptamine (5-HT)3 receptor antagonists (azasetron and granisetron) on basal pancreatic exocrine secretion were examined in conscious rats. Rats were prepared with cannulae draining bile and pancreatic juice separately. Intravenous injection of azasetron significantly increased pancreatic fluid and protein outputs in a dose-dependent manner. These increases were completely abolished by treatment with atropine, but not affected by bilateral truncal vagotomy. Intravenous injection of granisetron also increased pancreatic secretion, significantly. Intragastric injection of azasetron increased pancreatic secretion, although a double dose was required to elicit the stimulatory effect compared with intravenous injection. It is concluded that 5-HT3 receptor activity is involved in regulation of basal pancreatic secretion in conscious rats.

Aging impairs release of central and peripheral cholecystokinin (CCK) in male but not in female rats

BACKGROUND

Cholecystokinin (CCK) is an important bioactive peptide which stimulates pancreatic enzyme secretion and is also a neuromodulator in the central nervous system. We examined whether CCK release from the central and peripheral tissues was decreased in old animals, and whether there were sex-related differences.

METHODS

Young (5-10-month-old) and old (25-29-month-old) male and female Wistar rats were used. Synaptosomes were prepared from the cerebral cortex, and the vascularly perfused duodenojejunum was isolated to examine central and peripheral CCK release, respectively. In some young female rats, 21 days after bilateral ovariectomy, the peripheral CCK release and the changes in CCK mRNA levels were examined.

RESULTS

The central CCK release was impaired in response to the higher concentration of KCl, and the peripheral CCK response to the highest dose of neuromedin C was impaired in old male rats. However, no aging effect was observed in female rats, and ovariectomy did not affect CCK release or CCK mRNA level.

CONCLUSIONS

CCK release from both central and peripheral tissues was decreased in old male rats, but not in old female rats.

Regulation of cholecystokinin release and transcription in a rat without gene expression of cholecystokinin-A receptor

An Otsuka Long-Evans Tokushima Fatty (OLETF) rat does not possess cholecystokinin (CKK)-A receptor gene expression because of a genetic abnormality. We examined the CCK release and its transcription in OLETF rats in comparison with control (Long-Evans-Tokushima-LETO) rats. Animals at 5-6 and 24-25 weeks of age were used. The level of CCK mRNA and CCK concentration in the small intestinal mucosa, and the level of CCK-A receptor mRNA in the pancreas were examined. To examine CCK release, rats were prepared with external bile and pancreatic fistulae. The basal plasma levels of CCK and those at 2 h after bile-pancreatic juice diversion were measured by radioimmunoassay. The levels of CCK mRNA, and tissue CCK concentration increased significantly with age in both strains, but the values in OLETF rats were significantly lower than those in LETO rats. The CCK-A receptor mRNA level also increased with age in LETO rats. The plasma CCK concentration was significantly increased by bile-pancreatic juice diversion regardless of age and strain; however, the level of plasma CCK in OLETF rats at 24-25 weeks of age was significantly lower than that of LETO rats. It is suggested that the long-term defect of CCK-A receptor may decrease CCK release and transcription.

Decrease in exploratory behavior in naturally occurring cholecystokinin (CCK)-A receptor gene knockout rats

We recently found a specific strain of rats (Otsuka Long Evans Tokushima Fatty; OLETF rats) lacking cholecystokinin (CCK)-A receptor because of a genetic abnormality. Since CCK is an abundant neurotransmitter peptide in the brain, we examined whether these animals exhibit any behavioral abnormalities by conducting open-field tests. OLETF rats showed hypolocomotor activity and a decrease in the incidence of rearing in open-field tests. CCK release from the synaptosomes, and levels of CCK and CCK-B receptor mRNAs were the same as those observed in normal rats. It is suggested that the decreased exploration in OLETF rats may be due to the lack of CCK-A receptor.