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Cholecystokinin (CCK) is a peptide that has been implicated in pain modulation. Acid sensitive ion channels (ASICs) also play an important role in pain associated with tissue acidification. However, it is still unclear whether there is an interaction between CCK signaling and ASICs during pain process. Herein, we report that a functional link between them in rat dorsal root ganglion (DRG) neurons. Pretreatment with CCK-8 concentration-dependently increased acid-evoked ASIC currents. CCK-8 increased the maximum response of ASICs to acid, but did not changed their acid sensitivity. Enhancement of ASIC currents by CCK-8 was mediated by the stimulation of CCK2 receptor (CCK2R), rather than CCK1R. The enhancement of ASIC currents by CCK-8 was prevented by application of either G-protein inhibitor GDP-β-S or protein kinase C (PKC) inhibitor GF109203×, but not by protein kinase A (PKA) inhibitor H-89 or JNK inhibitor SP600125. Moreover, CCK-8 increased the number of action potentials triggered by acid stimuli by activating CCK2R. Finally, CCK-8 dose-dependently exacerbated acid-induced nociceptive behavior in rats through local CCK2R. Together, these results indicated that CCK-8/CCK2R activation enhanced ASIC-mediated electrophysiological activity in DRG neurons and nociception in rats. The enhancement effect depended on G-proteins and intracellular PKC signaling rather than PKA and JNK signaling pathway. These findings provided that CCK-8/CCK2R is an important therapeutic target for ASIC-mediated pain., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

In a fasting gastrointestinal tract, a characteristic cyclical rhythmic migrating motor complex (MMC) occur that comprises of three phases: I, II, and III. Among these, phase III contractions propagate from the stomach to the lower intestine in mammals, including humans, dogs, and Suncus murinus (suncus). Apart from the phase III of MMC propagating from the stomach, during the gastric phase II, small intestine-originated strong contractions propagate to the lower small intestine; however, the mechanism of contractions originating in the small intestine has not been clarified. In this study, we aimed to elucidate the role of cholecystokinin (CCK) in small intestinal motility. Administration of sulfated CCK-8 in phase I induced phase II-like contractions in the small intestine, which lasted for approximately 10-20 min and then returned to the baseline, while no change was observed in the stomach. Contractions of small intestine induced by CCK-8 were abolished by lorglumide, a CCK1 receptor antagonist. Gastrin, a ligand for the CCK2 receptor, evoked strong contractions in the stomach, but did not induce contractions in the small intestine. To examine the effect of endogenous CCK on contractions of small intestinal origin, lorglumide was administered during phase II. However, there was no change in the duodenal motility pattern, and strong contractions of small intestinal origin were not abolished by treatment with lorglumide. These results suggest that exogenous CCK stimulates contractions of small intestine via CCK1 receptors, whereas endogenous CCK is not involved in the strong contractions of small intestinal origin., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Background: The treatment of chronic myeloid leukemia (CML) is facing the dilemma of tyrosine kinase inhibitors (TKIs) resistance and disease recurrence. The dysfunctional DNA damage repair mechanism plays an essential role not only in the initiation and progression of hematological malignancies but also links to the development of TKI resistance. Deciphering the abnormally regulated DNA damage repair and proteins involved brings new insights into the therapy of leukemias. As a G2/M phase checkpoint kinase and a DNA damage repair checkpoint kinase engaged in the DNA damage response (DDR), along with an oncogenic driver present in various cancers, the particular involvement of Wee1 in DNA damage is far from clear. Deciphering its function and targeting it via modulating DNA repair pathways is important for improving our understanding of cancer treatment., Methods: Wee1 expression was assessed in cell lines using RT-qPCR and western blot, and Wee1 knockdown efficacy was validated using RT-qPCR, western blot, and immunofluorescence. Wee1 function was investigated by CCK-8, colony formation, and flow cytometry assay in vitro. Wee1 role in DNA repair and its interactions with other proteins were then studied using western blot, immunofluorescence, and double plasmid-repair studies. Finally, the CCK-8 and flow cytometry assay was utilized to investigate Wee1 and imatinib's synergistic effect, and a CML mouse model was constructed to study Wee1's role in carcinogenesis in vivo., Results: Wee1 was reported to respond quickly to DDR in an ATM-γH2AX-MDC1-dependent way upon DNA double-strand breaks (DSBs) occurrence, and it regulated homologous recombination by stimulating the recruitment of critical proteins RAD51/BRCA1 upon DSB sites. Wee1 was also revealed to be abnormally upregulated in CML cells. Further suppression of Wee1 not only causes cell cycle arrest and inhibits the proliferation of cancer cells but also enhances CML cell sensitivity to Imatinib in vitro and in vivo, possibly through an excessive accumulation of overall DSBs., Conclusion: Wee1 is extensively involved in the DRR signaling and DSB repair pathway. Inhibiting abnormally elevated Wee1 benefits CML therapy in both IM-resistant and IM-sensitive cells. Our data demonstrated that Wee1 participated in promoting cell proliferation and imatinib resistance in chronic myeloid leukemia via regulating DNA damage repair dependent on ATM-γH2AX-MDC1. In the fight against CML, Wee1's dysregulation in the DNA damage repair mechanism of CML pathogenesis makes it a viable therapeutic target in clinical applications., (© 2022. The Author(s).)

Objective: Activation of PI3K pathway has been reported to promote survival, tumorigenicity and metastasis in the esophageal cancer (EC), and the PI3Kp110β (one of PI3K family) contributed to tumorigenesis in types of cancers. However, it is still unclear whether PI3Kp110β effects the progression of EC., Methods: RT-qPCR and western blot were used to detect the expression of PI3Kp110β in the patients with EC and ECA-109 cells transfected with si-PI3Kp110β. CCK-8 and clonogenic assays were performed to analyze the proliferation of ECA-109 cells. Flow cytometry was used to investigate cell cycle and apoptosis of ECA-109 cells., Results: The expression of PI3Kp110β was up-regulated in the patients with EC by online RNA Sep data and RT-qPCR assay. Compared with the ECA-109 cells with si-control, the proliferation was suppressed in the ECA-109 cells with si-PI3Kp110β. The G1 phase of the cells with si-PI3Kp110β was significantly higher than that of cells with si-control. The apoptosis of cells with si-PI3Kp110β was accelerated, compared with that of cells with si-control. The expression of cyclinD1 and Bcl-2 was decreased, while the expression of Bax was increased in the ECA-109 cells with si-PI3Kp110β., Conclusion: Inhibition of si-PI3Kp110β attenuates cell viability and enhances apoptosis in esophageal cancer., (© 2022 by the Association of Clinical Scientists, Inc.)

Introduction: Increasing evidence indicated that miR-2682-5p acted as a tumor suppressor in various cancers. The current study aimed to investigate the biological function of exosomal miR-2682-5p in non-small cell lung cancer (NSCLC)., Methods: The expression of miR-2682-5p in NSCLC tissues and adjacent non-tumor tissues, NSCLC cell lines and human embryonic lung fibroblast, as well as serum and serum exosomes of NSCLC patients and healthy donors was detected by RT-qPCR. The effects of miR-2682-5p on the viability, migration, and apoptosis of NSCLC cells were detected by CCK-8, Transwell, and flow cytometry assays. Dual-luciferase reporter gene and RNA immunoprecipitation assays were used to evalutate the relationship between miR-2682-5p and HDAC1., Results: Low expressed miR-2682-5p was found in tumor tissues, cell lines, serum, and serum exosomes of NSCLC patients. MiR-2682-5p overexpression suppressed NSCLC cell viability and migration and promoted apoptosis, while miR-2682-5p knockdown showed the opposite results. Furthermore, exosomes from healthy donor serum inhibited NSCLC cell viability and migration and promoted apoptosis. Dual-luciferase reporter gene and RNA immunoprecipitation assays verified that HDAC1 was a target of miR-2682-5p. HDAC1 overexpression abolished the effects of miR-2682-5p mimic on NSCLC cell viability, migration, and apoptosis. Chromatin immunoprecipitation assay indicated that HDAC1 bound to the promoter region of ADH1A. Upregulation of ADH1A counteracted the effects of HDAC1 overexpression on NSCLC cell viability, migration, and apoptosis., Conclusion: Taken together, exosomal miR-2682-5p inhibited NSCLC cell viability and migration and promoted apoptosis by the HDAC1/ADH1A axis, and this result might provide a novel therapeutic target for NSCLC.

Background/aims: Myocardial infarction (MI) increases myocardial fibrosis (MF) and subsequent cardiac remodeling. Cholecystokinin octapeptide (CCK-8) is expressed in cardiomyocytes and plays an important role in cardiovascular regulation. In this study, we intend to use a rat model of myocardial infarction to evaluate the effects of CCK-8 on myocardial fibrosis and cardiac remodeling., Methods: Male Sprague-Dawley rats were separated into 3 groups: sham operation, MI + NaCl, and MI + CCK-8. All rats were subjected to left coronary artery ligation to induce MI or sham operation and then treated with CCK-8 or saline for 28 days. After 4 weeks, echocardiography was performed to assess cardiac function and myocardial fibrosis was evaluated using H&E and Masson's Trichrome-stained sections. The levels of BNP, CCK-8 in the plasma of all rats were detected by ELISA; RNA sequencing (RNA-seq) analysis was also adapted to detect differentially expressed genes in myocardial tissues of each group. Myocardial expression of fibrosis markers was analyzed by western blotting, immunohistochemistry and qRT-PCR., Results: CCK-8 was demonstrated to improve left ventricular function and results of H&E staining, Masson's trichrome staining, immunohistochemistry and western blotting showed that CCK-8 attenuated MF. Gene expression profiles of the left ventricles were analysed by RNA-seq and validated by qRT-PCR. Cardiac fibrosis genes were downregulated by CCK-8 in the left ventricle., Significance: CCK-8 can alleviate fibrosis in the noninfarcted regions and delay the left ventricular remodeling and the progress of heart failure in a MI rat model., Competing Interests: Declaration of Competing Interest The authors declared that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Cholecystokinin octapeptide with sulfate (CCK-8s) regulates feeding behavior and psychomotor activity. In rodents and goldfish, intracerebroventricular (ICV) injection of CCK-8s decreases food intake and also induces anxiety-like behavior. The zebrafish has several merits for investigating the psychophysiological roles of neuropeptides. However, little is known about the brain localization of CCK and the behavioral action of CCK-8s in this species. Here we investigated the brain localization of CCK-like immunoreactivity and found that it was distributed throughout the brain. As CCK-like immunoreactivity was particularly evident in the ventral habenular nucleus, the interpeduncular nucleus and superior raphe, we subsequently examined the effect of zebrafish (zf) CCK-8s on psychomotor control. Since the zebrafish possesses two molecular forms of zfCCK-8s (zfCCKA-8s and zfCCKB-8s), two synthetic peptides were administered intracerebroventricularly at 1, 5 and 10 pmol g -1 body weight (BW). As the zebrafish shows a greater preference for the lower area of a tank than for to the upper area, we used this preference for assessment of anxiety-like behavior. ICV administration of zfCCKA-8 s or zfCCKB-8s at 10 pmol g -1 BW significantly shortened the time spent in the upper area. The actions of these peptides mimicked that of the central-type benzodiazepine receptor inverse agonist FG-7142 (an anxiogenic agent) at 10 pmol g -1 BW. The anxiogenic-like action of the two peptides was attenuated by treatment with the CCK receptor antagonist proglumide at 200 pmol g -1 BW. These results indicate that zfCCKA-8s and zfCCKB-8s potently induce anxiety-like behavior via the CCK receptor-signaling pathway in the zebrafish brain., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflicts of interest., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objective: To determine if use of the oral cholecystagogue, Ensure Plus (EP), in hepatobiliary scintigraphy (HBS) leads to a similar distribution of normal and abnormal gallbladder ejection fractions (GBEFs) versus other historical secondary findings of chronic biliary disease in a similar patient population compared with the conventional cholecystokinin analog, sincalide. The HBS findings analyzed included the GBEF, small bowel transit time, gallbladder fill time, and reversal of the normal gallbladder versus small bowel transit. The secondary objectives were to determine whether patient outcomes were significantly different for EP and sincalide HBS study patients following cholecystectomy, namely, the surgical pathology and patient-reported biliary-type pain., Methods: We reviewed all HBS examinations over a retrospective 34-month period. Data from 446 patients who underwent sincalide or EP HBS with GBEF determination for evaluation of chronic symptoms concerning for biliary etiology met the inclusion criteria. The aforementioned HBS findings and postsurgical patient outcomes were obtained for each patient group., Results: Comparing HBS examinations performed with sincalide or EP, no significant differences were noted in the major HBS findings of similar patient populations. Outcomes for the sincalide and EP groups status post cholecystectomy were assessed to determine their sensitivity, specificity, positive predictive value, and negative predictive value. The outcomes assessed were the histopathology and patient-reported amelioration of biliary-type pain. No significant differences were noted., Conclusions: The sincalide and EP cholecystagogues did not lead to significantly different HBS findings for similar patient populations or postcholecystectomy outcomes.

Objective: Vagus Nerve Stimulation (VNS) has shown great promise as a potential therapy for a number of conditions, such as epilepsy, depression and for Neurometabolic Therapies, especially for treating obesity. The objective of this study was to characterize the left ventral subdiaphragmatic gastric trunk of vagus nerve (SubDiaGVN) and to analyze the influence of intravenous injection of gut hormone cholecystokinin octapeptide (CCK-8) on compound nerve action potential (CNAP) observed on the same branch, with the aim of understanding the impact of hormones on VNS and incorporating the methods and results into closed loop implant design., Methods: The cervical region of the left vagus nerve (CerVN) of male Wistar rats was stimulated with electric current and the elicited CNAPs were recorded on the SubDiaGVN under four different conditions: Control (no injection), Saline, CCK1 (100[Formula: see text]pmol/kg) and CCK2 (1000[Formula: see text]pmol/kg) injections., Results: We identified the presence of A[Formula: see text], B, C1, C2, C3 and C4 fibers with their respective velocity ranges. Intravenous administration of CCK in vivo results in selective, statistically significant reduction of CNAP components originating from A and B fibers, but with no discernible effect on the C fibers in [Formula: see text] animals. The affected CNAP components exhibit statistically significant ([Formula: see text] and [Formula: see text]) higher normalized stimulation thresholds., Conclusion: This approach of characterizing the vagus nerve can be used in closed loop systems to determine when to initiate VNS and also to tune the stimulation dose, which is patient-specific and changes over time.

Activation of the cholecystokinin type B receptor (CCKBR) by cholecystokinin octapeptide (CCK-8) inhibits opioid analgesia. Chronic opiate treatment leads to an increase in the CCK-8 concentration and thus enhances the antagonism of CCK-8 against opioid analgesia; the underlying molecular mechanisms remain of great interest. In the present study, we validated the colocalization of the μ-opioid receptor (MOR) and CCKBR in pain signal transmission-related spinal cord dorsal horn and dorsal root ganglion neurons of rats. Co-immunoprecipitation (Co-IP) and fluorescence lifetime-imaging-microscopy-based fluorescence resonance energy transfer (FLIM-FRET) assays showed that MOR heteromerized with CCKBR directly in transfected HEK293 cells. Combined with MOR mutant construction, the third transmembrane domain of MOR (TM3 MOR ) was demonstrated to participate in heteromerization with CCKBR. Receptor ligand binding, ERK phosphorylation and cAMP assays showed that MOR heteromerization with CCKBR weakened the activity of MOR. A cell-penetrating interfering peptide consisting of TM3 MOR and TAT (a transactivator of HIV-1) sequences from the N terminal to the C terminal disrupted the MOR-CCKBR interaction and restored the activity of MOR in transfected HEK293 cells. Furthermore, intrathecal application of the TM3 MOR -TAT peptide alleviated CCK-8-injection-induced antagonism to morphine analgesia in rats. These results suggest a new molecular mechanism for CCK-8 antagonism to opioid analgesia in terms of G-protein-coupled receptor (GPCR) interaction through direct heteromerization. Our study may provide a potential strategy for pain management with opioid analgesics.

Objectives: Our previous studies demonstrated that pretreatment with cholecystokinin octapeptide (CCK-8) could alleviate endothelial cell injury and reverse abnormal vascular reactivity as well as reduce LPS-induced inflammation cascades, which suggested that CCK-8 plays a potential role in anti-endotoxic shock. The present study aimed to determine the therapeutic effects of CCK-8 on rat liver and kidney microcirculatory perfusion disorder under endotoxic shock (ES) conditions., Materials and Methods: Sprague-Dawley rats were induced to lethal endotoxic shock by an injection of LPS. CCK-8 was administered 30 min after LPS injection. Either a specific CCK-1R antagonist or CCK-2R antagonist was injected before CCK-8 treatment. The mean arterial pressure (MAP), liver and kidney microcirculatory perfusion, and heart rate (HR) were recorded with a multi-channel data acquisition system. The serum concentrations of alanine aminotransferase (ALT) and creatinine (Cr) were measured, and the histopathological changes in the liver and kidney were also observed., Results: Administration of CCK-8 significantly delayed the LPS-induced decreases in not only the liver and kidney microcirculation perfusion but also the HR. The pathology changes induced by LPS in the liver and kidney tissues were significantly mitigated in the LPS + CCK-8 group. The levels of ALT and Cr in the serum of the LPS + CCK-8 group were obviously lower than those in the LPS group. In addition, the specific antagonist at the CCK-2 receptor (CCK-2R) abrogated the action of CCK-8 significantly., Conclusions: These results indicated that CCK-8 has potential therapeutic effects on microcirculation failure in an ES rat model via the CCK-2 receptor.

Food intake occurs in bouts or meals, and numerous meal-generated signals have been identified that act to limit the size of ongoing meals. Hormones such as cholecystokinin (CCK) are secreted from the intestine as ingested food is being processed, and in addition to aiding the digestive process, they provide a signal to the brain that contributes to satiation, limiting the size of the meal. The potency of CCK to elicit satiation is enhanced by elevated levels of adiposity signals such as insulin. In the present experiments we asked whether CCK and insulin interact at the level of the blood-brain barrier (BBB). We first isolated rat brain capillary endothelial cells that comprise the BBB and found that they express the mRNA for both the CCK1R and the insulin receptor, providing a basis for a possible interaction. We then administered insulin intraperitoneally to another group of rats and 15min later administered CCK-8 intraperitoneally to half of those rats. After another 15min, CSF and blood samples were obtained and assayed for immunoreactive insulin. Plasma insulin was comparably elevated above baseline in both the CCK-8 and control groups, indicating that the CCK had no effect on circulating insulin levels given these parameters. In contrast, rats administered CCK had CSF-insulin levels that were more than twice as high as those of control rats. We conclude that circulating CCK greatly facilitates the transport of insulin into the brain, likely by acting directly at the BBB. These findings imply that in circumstances in which the plasma levels of both CCK and insulin are elevated, such as during and soon after meals, satiation is likely to be due, in part, to this newly-discovered synergy between CCK and insulin., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Peripheral administration of cholecystokinin (CCK)-8 or secretin activates oxytocin (OXT)-secreting neurons in the hypothalamus. Although OXT is involved in the regulation of feeding behavior, detailed mechanism remains unclear. In the present study, we examined the central OXTergic pathways after intraperitoneally (i.p.) administration of CCK-8 and secretin using male OXT-monomeric red fluorescent protein 1 (mRFP1) transgenic rats and male Wistar rats. I.p. administration of CCK-8 (50μg/kg) and secretin (100μg/kg) decreased food intake in these rats. While i.p. administration of CCK-8 decreased water intake, i.p. administration of secretin increased water intake. Immunohistochemical study revealed that Fos-Like-Immunoreactive cells were observed abundantly in the brainstem and in the OXT neurons in the dorsal division of the parvocellular paraventricular nucleus (dpPVN). We could observe marked increase of mRFP1 fluorescence, as an indicator for OXT, in the dpPVN and mRFP1-positive granules in axon terminals of the dpPVN OXT neurons in the nucleus tractus solitarius (NTS) after i.p. administration of CCK-8 and secretin. These results provide us the evidence that, at least in part, i.p. administration of CCK-8 or secretin might be involved in the regulation of feeding/drinking via a OXTergic pathway from the dpPVN to the NTS., (Copyright © 2016 Elsevier Ireland Ltd and Japan Neuroscience Society. All rights reserved.)

In an effort to mimic in part the redundancy of satiety peptides involved in energy homeostasis, the combined benefits of the well-established satiety peptide CCK8 and an apparently anorectic peptide obestatin were studied in Swiss albino mice. The optimal dose of obestatin that was required to give the most pronounced effect with CCK8 was worked out by varying the concentration of obestatin while keeping CCK8 concentration constant at 200 nmol/KgBW. Mice administered 160 nmol obestatin and 200 nmol CCK8 per kilogram body weight showed the most drastic reduction in food intake. Gain in body weight was arrested after day four during the eight day experiment. These studies reemphasize the beneficial effects imparted by co-administration of obestatin and CCK8 and their potential use towards countering obesity., (Copyright © 2016 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM). All rights reserved.)

Glucagon-like peptide-1 (GLP-1) and cholecystokinin (CCK) exert important complementary beneficial metabolic effects. This study assessed the biological actions and therapeutic utility of a novel (pGlu-Gln)-CCK-8/exendin-4 hybrid peptide compared with the stable GLP-1 and CCK mimetics exendin-4 and (pGlu-Gln)-CCK-8, respectively. All peptides significantly enhanced in vitro insulin secretion. Administration of the peptides, except (pGlu-Gln)-CCK-8 alone, in combination with glucose significantly lowered plasma glucose and increased plasma insulin in mice. All treatments elicited appetite-suppressive effects. Twice-daily administration of the novel (pGlu-Gln)-CCK-8/exendin-4 hybrid, (pGlu-Gln)-CCK-8 alone, or (pGlu-Gln)-CCK-8 in combination with exendin-4 for 21 days to high-fat-fed mice significantly decreased energy intake, body weight, and circulating plasma glucose. HbA1c was reduced in the (pGlu-Gln)-CCK-8/exendin-4 hybrid and combined parent peptide treatment groups. Glucose tolerance and insulin sensitivity also were improved by all treatment modalities. Interestingly, locomotor activity was decreased in the hybrid peptide group, and these mice also exhibited reductions in circulating triglyceride and cholesterol levels. Pancreatic islet number and area, as well β-cell area and insulinotropic responsiveness, were dramatically improved by all treatments. These studies highlight the clear potential of dual activation of GLP-1 and CCK1 receptors for the treatment of type 2 diabetes., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Cholecystokinin octapeptide (CCK-8), a brain-gut peptide, plays an important role in several opioid addictive behaviors. We previously reported that CCK-8 attenuated the expression and reinstatement of morphine-induced conditioned place preference. The possible effects of CCK-8 on the negative affective components of drug abstinence are not clear. There are no studies evaluating the effect of CCK-8 on emotional symptoms, such as anxiety, in morphine-withdrawal animals. We investigated the effects of CCK-8 on the anxiety-like behavior in morphine-withdrawal rats using an elevated plus-maze. Morphine withdrawal elicited time-dependent anxiety-like behaviors with peak effects on day 10 (5 days after induction of morphine dependence). Treatment with CCK-8 (0.1 and 1 μg, i.c.v.) blocked this anxiety in a dose-dependent fashion. A CCK1 receptor antagonist (L-364,718, 10 μg, i.c.v.) blocked the effect of CCK-8. Mu-opioid receptor antagonism with CTAP (10 μg, i.c.v.) decreased the 'anxiolytic' effect. CCK-8 inhibited anxiety-like behaviors in morphine-withdrawal rats by up-regulating endogenous opioids via the CCK1 receptor in rats. This study clearly identifies a distinct function of CCK-8 and a potential medication target of central CCK1 receptors for drugs aimed at ameliorating drug addiction., (Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.)

Cholecystokinin octapeptide (CCK-8), an immunomodulatory peptide, can promote or suppress the development or function of specific CD4(+) T cell subsets by regulating antigen-presenting cell functions. In the current study, we investigated whether CCK-8 exerts a direct effect on T cells through influencing differentiation and cytokine production of distinct CD4(+) T cell subsets in vitro. Our results showed that CCK-8 differentially affects the development and function of CD4(+) T cell populations, with a negative influence on Th1 and Th17 cells and positive regulatory effect on inducible T regulatory cells (iTreg). Notably, CCK-8 suppressed Th1 while slightly enhancing Th2 development and cytokine production. Similarly, CCK-8 inhibited the differentiation of Th17 cells and promoted Foxp3 expression. L-364,718 and LY-288,513, selective antagonists of CCK1R and CCK2R, respectively, suppressed the effects of CCK-8 on CD4(+) T cell subset-specific transcription factors. Our findings strongly indicate that CCK-8 exerts a direct effect on T cells, which is dependent on CCKRs, particularly CCK2R. The collective results aid in further clarifying the mechanism underlying the anti-inflammatory and immunoregulatory effects of CCK-8., (Copyright © 2014 Elsevier B.V. All rights reserved.)

It has been accepted for decades that "all forms of cholecystokinin (CCK) have equal bioactivity," despite accumulating evidence to the contrary. To challenge this concept, we compared two feeding responses, meal size (MS, 10% sucrose) and intermeal interval (IMI), in response to CCK-58, which is the major endocrine form of CCK, and CCK-8, which is the most abundantly utilized form. Doses (0, 0.1, 0.5, 0.75, 1, 3 and 5 nmol/kg) were administered intraperitoneally over a 210-min test to Sprague Dawley rats that had been food-deprived overnight. We found that (1) all doses of CCK-58, except the lowest dose, and all doses of CCK-8, except the lowest two doses, reduced food intake more than vehicle did; (2) at two doses, 0.75 and 3 nmol/kg, CCK-58 increased the IMI, while CCK-8 failed to alter this feeding response; and (3) CCK-58, at all but the lowest two doses, increased the satiety ratio (IMI between first and second meals (min) divided by first MS (ml)) relative to vehicle, while CCK-8 did not affect this value. These findings demonstrate that the only circulating form of CCK in rats, CCK-58, prolongs the IMI more than CCK-8, the peptide generally utilized in feeding studies. Taken together, these results add to a growing list of functions where CCK-8 and CCK-58 express qualitatively different bioactivities. In conclusion, the hypothesis that "all forms of cholecystokinin (CCK) have equal bioactivity" is not supported., (Published by Elsevier Inc.)

In the present work, we have evaluated the effect of an acute addition of melatonin on cholecystokinin octapeptide (CCK-8)-evoked Ca(2+) signals and amylase secretion in mouse pancreatic acinar cells. For this purpose, freshly isolated mouse pancreatic acinar cells were loaded with fura-2 to study intracellular free Ca(2+) concentration ([Ca(2+)](c)). Amylase release and cell viability were studied employing colorimetric methods. Our results show that CCK-8 evoked a biphasic effect on amylase secretion, finding a maximum at a concentration of 0.1 nM and a reduction of secretion at higher concentrations. Pre-incubation of cells with melatonin (1 μM-1 mM) significantly attenuated enzyme secretion in response to high concentrations of CCK-8. Stimulation of cells with 1 nM CCK-8 led to a transient increase in [Ca(2+)](c), followed by a decrease towards a constant level. In the presence of 1 mM melatonin, stimulation of cells with CCK-8 resulted in a smaller [Ca(2+)](c) peak response, a faster rate of decay of [Ca(2+)](c) and lower values for the steady state of [Ca(2+)](c), compared with the effect of CCK-8 alone. Melatonin also reduced the oscillatory pattern of Ca(2+) mobilization evoked by a physiological concentration of CCK-8 (20 pM), and completely inhibited Ca(2+) mobilization induced by 10 pM CCK-8. On the other hand, Ca(2+) entry from the extracellular space was not affected in the presence of melatonin. Finally, melatonin alone did not change cell viability. We conclude that melatonin, at concentrations higher than those found in blood, might regulate exocrine pancreatic function via modulation of Ca(2+) signals.

The neuropeptide cholecystokinin octapeptide (CCK) is involved in a variety of brain functions. In the hippocampus, most CCK is released from CCK-positive (CCK+) neurons, but the effects of CCK on CCK+ neurons are poorly understood. We employed primary hippocampal cultures to explore the modulatory effect of CCK on CCK+ neurons. CCK-8S (0.2 μM) was added to the culture medium from day in vitro 2 (DIV-2) to DIV-11. An adenovirus integrated with the CCK promoter was used to label CCK+ neurons. Whole-cell patch clamp recording was carried on to record the electrophysiology properties. The results show that: (1) CCK-8S significantly decreased membrane capacity but increased the membrane resistance (Rm) of CCK+ neurons, (2) CCK-8S increased action potential (AP) firing frequency of CCK+ neurons but did not affect the firing pattern, (3) CCK-8S facilitated CCK+ neuron excitatory synaptic transmission but attenuated inhibitory synaptic transmission, and (4) the expression of postsynaptic density-95 (PSD-95) in cultured hippocampal neurons was elevated by CCK-8S treatment. Our results demonstrate that CCK-8S significantly alters the membrane electrophysiological characteristics and synaptic activity of cultured hippocampal CCK+ neurons. These findings may enhance our understanding of the modulatory effect of CCK in the brain., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

The contractile effects of neurotensin (NT) and cholecystokinin octapeptide (CCK-8) on isolated circular smooth muscle strips of chicken gallbladder were investigated. The NT (0.25-300 nM) produced concentration-dependent contractions on smooth muscle with an EC50 of 8.5 nM (95% confidence limits = 5.3-13.6 nM). In comparison, CCK-8 produced concentration-dependent contractions with an EC50 of 13 nM (95% confidence limits of 9-20 nM). There were no statistical differences in contractile responses when comparing NT and CCK-8 at equimolar concentrations. The NT appears to act directly on smooth muscle tissue in the chicken; the contractile responses were not blocked by 10 µM atropine or tetrodotoxin. A portion of the activity is mediated by extracellular calcium as 100 nM nifedipine inhibited 30% of peptide-induced muscle tension. The NT receptor (NTR) type 1 antagonist SR 48692 (0.1 µM) did not significantly reduce NT potency. The contractile effects of CCK-8 remained unaltered in tissues pretreated with atropine, TTX, or nifedipine. The CCK-A antagonist lorglumide, at a concentration of 1 µM, reduced the contractile potency of CCK-8 by one-half. Avian receptors for NT and CCK may differ pharmacologically from their mammalian counterparts, but their contractile actions on the gallbladder resulting in increased biliary output by flow are further evidence of their role in the postprandial regulation of lipid digestion in chickens.

Aim: The incretin hormones, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) and cholecystokinin (CCK) are gastrointestinal peptides with important physiological effects. However, rapid enzymatic degradation results in short-lived biological actions., Methods: This study has examined metabolic actions of exendin-4, GIP[mPEG] and a novel CCK-8 analogue, (pGlu-Gln)-CCK-8 as enzymatically stable forms of GLP-1, GIP and CCK, respectively., Results: All peptides significantly (p < 0.01-p < 0.001) stimulated insulin secretion from BRIN BD11 cells, and acute in vivo experiments confirmed prominent antihyperglycaemic and insulinotropic responses to GLP-1 or GIP receptor activation in normal mice. Twice daily injection of (pGlu-Gln)-CCK-8 alone and in combination with exendin-4 or GIP[mPEG] in high fat-fed mice significantly decreased accumulated food intake (p < 0.05-p < 0.01), body weight gain (p < 0.05-p < 0.01) and improved (p < 0.05) insulin sensitivity in high fat-fed mice. However, there was no evidence for superior effects compared to (pGlu-Gln)-CCK-8 alone. Combined treatment of (pGlu-Gln)-CCK-8 and exendin-4 resulted in significantly (p < 0.05) lowered circulating glucose levels and improved (p < 0.05) intraperitoneal glucose tolerance. These effects were superior to either treatment regime alone but not associated with altered insulin concentrations. A single injection of (pGlu-Gln)-CCK-8, or combined with exendin-4, significantly (p < 0.05) lowered blood glucose levels 24 h post injection in untreated high fat-fed mice., Conclusion: This study highlights the potential of (pGlu-Gln)-CCK-8 alone and in combination with incretin hormones for the treatment of type 2 diabetes., (© 2013 Blackwell Publishing Ltd.)

Cholecystokinin octapeptide (CCK-8), a neuropeptide, plays an important role in morphine dependence and several addictive behaviors. We have previously reported that CCK-8 attenuates the acquisition of morphine-induced conditioned place preference (CPP), but the possible functions of CCK-8 on drug relapse remain unclear. Here we evaluated the effects of CCK-8 on the reinstatement of extinguished morphine-induced CPP and behavioral sensitization. A single injection of 0.1 and 1μg CCK-8 (i.c.v.) significantly attenuated both drug- (morphine) and stress- (foot shock) primed reinstatement of CPP and reduced the escalated locomotor activity in reinstatement tests. Additionally, CCK-8 blocked the expression of morphine-induced behavioral sensitization. However, administration of CCK-8 (0.01, 0.1 and 1μg) alone to morphine-pretreated rats could not trigger reinstatement of CPP and had no significant effect on threshold sensitivity to foot shock. In conclusion, our study identifies a distinct inhibitory effect of CCK-8 on the reinstatement of drug-seeking behavior and provides a potential application to the medication of drug relapse., (Copyright © 2013 IBRO. Published by Elsevier Ltd. All rights reserved.)

Cholecystokinin (CCK) is an important regulator of food digestion but its influence on small intestinal secretion has received little attention. We characterized effects of CCK-8, ghrelin and some related peptides on duodenal HCO3(-) secretion in vivo and demonstrated CCK-induced calcium signaling in acutely isolated enterocytes. A segment of proximal duodenum with intact blood supply was cannulated in situ in anaesthetized rats. Mucosal HCO3(-) secretion was continuously recorded (pH-stat). Peptides were administrated to the duodenum by close intra-arterial infusion. Clusters of duodenal enterocytes were attached to the bottom of a perfusion chamber. The intracellular calcium concentration ([Ca(2+)]i) was examined by dual-wavelength imaging. CCK-8 (3.0, 15 and 60 pmol/kg,h) caused dose-dependent increases (p<0.01) in duodenal alkaline secretion in both overnight fasted and continuously fed animals. The CCK1R-antagonist devazepide but neither the CCK2R-antagonist YMM022 nor the melatonin MT2-selective antagonist luzindole inhibited the rise in secretion. Atropine decreased sensitivity to CCK-8. The appetite-related peptide ghrelin was without effect on the duodenal secretion in fasted as well as fed animals. Superfusion with CCK-8 (1.0-50 nM) induced [Ca(2+)]i signaling in acutely isolated duodenal enterocytes. After an initial peak response, [Ca(2+)]i returned to near basal values within 3-5min. Devazepide but not YMM022 inhibited this [Ca(2+)]i response. Low doses of CCK-8 stimulate duodenal alkaline secretion and induce enterocyte [Ca(2+)]i signaling by an action at CCK1 receptors. The results point to importance of CCK in the rapid postprandial rise in mucosa-protective duodenal secretion., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Cholecystokinin (CCK) is a hormone that has important physiological effects on energy balance. This study has used a stable CCK(1) receptor agonist, (pGlu-Gln)-CCK-8, to evaluate the metabolic effects of prolonged administration in normal mice. Twice-daily injection of (pGlu-Gln)-CCK-8 for 28 days resulted in significantly lowered body weights (P<0.05) on days 24 and 28, which was associated with decreased accumulated calorie intake (P<0.01) from day 12 onward. Nonfasting plasma glucose was significantly reduced (P<0.05) on day 28, while plasma insulin concentrations were increased (P<0.05). After 28 days, glucose tolerance and glucose-mediated insulin secretion were not significantly different in (pGlu-Gln)-CCK-8-treated mice. However, following a 15-min refeeding period in 18-h fasted mice, glucose levels were significantly (P<0.05) decreased by (pGlu-Gln)-CCK-8 despite similar food intake and nutrient-induced insulin levels. Insulin sensitivity in (pGlu-Gln)-CCK-8-treated mice was significantly (P<0.01) improved compared with controls. Accumulation of triacylglycerol in liver was reduced (P<0.01) but there were no differences in circulating cholesterol and triacylglycerol concentrations, as well as triacylglycerol content of pancreatic, muscle, and adipose tissue in (pGlu-Gln)-CCK-8 mice. These data highlight the beneficial metabolic effects of prolonged (pGlu-Gln)-CCK-8 administration and confirm a lack of detrimental effects.

The current study has determined the ability of (pGlu-Gln)-CCK-8 to counter the development of diet-induced obesity-diabetes and examined persistence of beneficial metabolic effects in high fat and ob/ob mice, respectively. Twice daily injection of (pGlu-Gln)-CCK-8 in normal mice transferred to a high fat diet reduced energy intake (p < 0.001), body weight (p < 0.01), circulating insulin and LDL-cholesterol (p < 0.001) and improved insulin sensitivity (p < 0.001) as well as oral and intraperitoneal (p < 0.001) glucose tolerance. Energy intake, body weight, circulating insulin and glucose tolerance of (pGlu-Gln)-CCK-8 mice were similar to lean controls. In addition, (pGlu-Gln)-CCK-8 prevented the effect of high fat feeding on triacylglycerol accumulation in liver and muscle. Interestingly, (pGlu-Gln)-CCK-8 significantly (p < 0.001) elevated pancreatic glucagon content. Histological examination of the pancreata of (pGlu-Gln)-CCK-8 mice revealed no changes in islet number or size, but there was increased turnover of beta-cells with significantly (p < 0.001) increased numbers of peripherally located alpha-cells, co-expressing both glucagon and GLP-1. Beneficial metabolic effects were observed similarly in ob/ob mice treated twice daily with (pGlu-Gln)-CCK-8 for 18 days, including significantly reduced energy intake (p < 0.05), body weight (p < 0.05 to p < 0.01), circulating glucose (p < 0.05 to p < 0.01) and insulin (p < 0.05 to p < 0.001) and improved glucose tolerance (p < 0.05) and insulin sensitivity (p < 0.001). Notably, these beneficial effects were still evident 18 days following cessation of treatment. These studies emphasize the potential of (pGlu-Gln)-CCK-8 for the treatment of obesity-diabetes., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Cholecystokinin, a neuroactive peptide functioning as a neurotransmitter and neuromodulator in the central nervous system, mediates a number of processes and is implicated in neurological and psychiatric disorders such as Parkinson's disease, anxiety and schizophrenia. Striatum is one of the brain structures with the highest concentrations of CCK in the brain, rich in CCK receptors as well. The physiological effect of CCK on cholinergic interneurons, which are the major interneurons in striatum and the modulatory interactions which exist between dopamine, acetylcholine and cholecystokinin in this brain structure are still unclear. We studied the effect of cholecystokinin octapeptide (CCK-8) on the release of acetylcholine (ACh) from striatal slices of the rat brain. CCK-8 (0.01-0.1μM) showed no statistically significant effect on the basal but enhanced dose-dependently the electrically (2Hz)-evoked release of [(3)H]ACh. When slices were preperfused with 100μM sulpiride, a selective dopamine D(2) receptor antagonist, the CCK-8 (0.01μM) effect on electrically stimulated ACh release was increased nearly 2-fold. A similar increase was observed after depletion of endogenous dopamine (DA) from nigro-striatal dopaminergic neurons with 6-hydroxydopamine (6-OHDA) (2× 250μg/animal, i.c.v.). Furthermore in the presence of dopamine (100μM) or apomorphine (10μM), the prototypical DA receptor agonist, CCK-8 (0.01μM) failed to enhance the stimulation-evoked release of [(3)H]ACh. The D(2) receptor agonist quinpirol (1μM) abolished the CCK-8 effect on electrically stimulated ACh release as well. The increase in electrically induced [(3)H]ACh release produced by 0.01μM CCK-8 was antagonized by d,l loxiglumide (CR 1505), 10μM, a non-peptide CCK-A receptor antagonist and by Suc-Tyr-(OSO3)-Met-Gly-Trp-Met-Asp-β-phenethyl-amide (GE-410), 1μM, a peptide CCK-A receptor antagonist. The antagonistic effect of GE-410 on the CCK-8-potentiated, electrically induced release of [(3)H]ACh was studied in striatum for the first time. CAM 1028 (10μM), a CCK-B receptor antagonist, also prevented the potentiating effect of CCK-8 (0.01μM) on electrically stimulated release of [(3)H]ACh. The presented results indicate that (i) CCK-8 is capable of increasing ACh elicited by field electrical stimulation in striatum; (ii) CCK-8 is more effective in its ACh-stimulating effect when dopaminergic activity in striatum is blocked i.e. CCK-8-facilitated release of electrically induced ACh from cholinergic interneurons in the striatum is under the inhibitory control of the tonic activity of dopamine from the nigrostriatal pathway; (iii) the enhancing effect of CCK-8 on electrically evoked ACh release is mediated through both CCK-A and CCK-B cholecystokinin receptors located most likely on the cell bodies of cholinergic interneurons in striatum., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Vagal CCK-A receptors (CCKARs) and leptin receptors (LRbs) interact synergistically to mediate short-term satiety. Cocaine- and amphetamine-regulated transcript (CART) peptide is expressed by vagal afferent neurons. We sought to demonstrate that this neurotransmitter regulates CCK and leptin actions on short-term satiety. We also examined the signal transduction pathways responsible for mediating the CART release from the nodose ganglia (NG). ELISA studies coupled with gene silencing of NG neurons by RNA interference elucidated intracellular signaling pathways responsible for CCK/leptin-stimulated CART release. Feeding studies followed by gene silencing of CART in NG established the role of CART in mediating short-term satiety. Immunohistochemistry was performed on rat NG neurons to confirm colocalization of CCKARs and LRbs; 63% of these neurons contained CART. Coadministration of CCK-8 and leptin caused a 2.2-fold increase in CART release that was inhibited by CCK-OPE, a low-affinity CCKAR antagonist. Transfection of cultured NG neurons with steroid receptor coactivator (SRC) or phosphatidylinositol 3-kinase (PI3K) small-interfering RNA (siRNA) or STAT3 lentiviral short hairpin RNA inhibited CCK/leptin-stimulated CART release. Silencing the expression of the EGR-1 gene inhibited the CCK/leptin-stimulated CART release but had no effect on CCK/leptin-stimulated neuronal firing. Electroporation of NG with CART siRNA inhibited CCK/leptin stimulated c-Fos expression in rat hypothalamus. Feeding studies following electroporation of the NG with CART or STAT3 siRNA abolished the effects of CCK/leptin on short-term satiety. We conclude that the synergistic interaction of low-affinity vagal CCKARs and LRbs mediates CART release from the NG, and CART is the principal neurotransmitter mediating short-term satiety. CART release from the NG involves interaction between CCK/SRC/PI3K cascades and leptin/JAK2/PI3K/STAT3 signaling pathways.

Aims/hypothesis: Cholecystokinin (CCK) is a rapidly degraded gastrointestinal peptide that stimulates satiety and insulin secretion. We aimed to investigate the beneficial weight-lowering and metabolic effects of the novel N-terminally modified CCK analogue, (pGlu-Gln)-CCK-8., Methods: The biological actions of (pGlu-Gln)-CCK-8 were comprehensively evaluated in pancreatic clonal BRIN BD11 cells and in vivo in high-fat-fed and ob/ob mice., Results: (pGlu-Gln)-CCK-8 was completely resistant to enzymatic degradation and its satiating effects were significantly (p < 0.05 to p < 0.001) more potent than CCK-8. In BRIN-BD11 cells, (pGlu-Gln)-CCK-8 exhibited enhanced (p < 0.01 to p < 0.001) insulinotropic actions compared with CCK-8. When administered acutely to high-fat-fed or ob/ob mice, (pGlu-Gln)-CCK-8 improved glucose homeostasis. Sub-chronic twice daily injections of (pGlu-Gln)-CCK-8 in high-fat-fed mice for 28 days significantly decreased body weight (p < 0.05 to p < 0.001), accumulated food intake (p < 0.05 to p < 0.001), non-fasting glucose (p < 0.05) and triacylglycerol deposition in pancreatic (p < 0.01), adipose (p < 0.05) and liver (p < 0.001) tissue, and improved oral (p < 0.05) and i.p. (p < 0.05) glucose tolerance and insulin sensitivity (p < 0.001). Similar observations were noted in ob/ob mice given twice daily injections of (pGlu-Gln)-CCK-8. In addition, these beneficial effects were not reproduced by simple dietary restriction and were not associated with changes in energy expenditure. There was no evidence for development of tolerance to (pGlu-Gln)-CCK-8, and analysis of histology or blood-borne markers for pancreatic, liver and renal function in mice treated with (pGlu-Gln)-CCK-8 suggested little abnormal pathology., Conclusions/interpretation: These studies emphasise the potential of (pGlu-Gln)-CCK-8 for the alleviation of obesity and insulin resistance.

Background: Pain contains both sensory and affective dimensions. Using a rodent visceral pain assay that combines the colorectal distension (CRD) model with the conditioned place avoidance (CPA) paradigms, we measured a learned behavior that directly reflects the affective component of visceral pain, and showed that perigenual anterior cingulate cortex (pACC) activation is critical for memory processing involved in long-term visceral affective state and prediction of aversive stimuli by contextual cue. Progress has been made and suggested that activation of vagal afferents plays a role in the behavioral control nociception and memory storage processes.In human patients, electrical vagus nerve stimulation enhanced retention of verbal learning performance. Cholecystokinin-octapeptide (CCK), which is a gastrointestinal hormone released during feeding, has been shown to enhance memory retention. Mice access to food immediately after training session enhanced memory retention. It has been well demonstrated that CCK acting on vagal afferent fibers mediates various physiological functions. We hypothesize that CCK activation of vagal afferent enhances visceral pain-related affective memory., Results: In the presented study, infusion of CCK-8 at physiological concentration combining with conditional training significantly increased the CRD-induced CPA scores, and enhanced the pain affective memory retention. In contrast, CCK had no effect on CPA induced by non-nociceptive aversive stimulus (U69,593). The physiological implications were further strengthened by the similar effects observed in the rats with duodenal infusion of 5% peptone, which has been shown to induce increases in plasma CCK levels. CCK-8 receptor antagonist CR-1409 or perivagal application of capsaicin abolished the effect of CCK on aversive visceral pain memory, which was consistent with the notion that vagal afferent modulates affective aspects of visceral pain. CCK does not change the nociceptive response (visceral pain sensitivity) and anterior cingulate cortex neuronal responses to CRD., Conclusion: CCK activating vagal afferent C fibers enhances memory consolidation and retention involved in long-term visceral negative affective state. Thus, in a number of gastrointestinal disorders, such as irritable bowel syndrome, nutrient content may contribute to painful visceral perception by enhancing visceral aversive memory via acts on vagal afferent pathway.

Total parenteral nutrition (TPN) results in atrophy of the pancreas, while cholecystokinin (CCK) can significantly stimulate the exocrine pancreas in rodents. This study was designed to examine whether CCK may improve the atrophy of the pancreas in rats on TPN treatment. Forty-eight Sprague-Dawley rats were divided into orally fed and TPN groups and were infused with CCK at a dose of 5 μg/kg/h or the CCK-receptor antagonist devazepide at a dose of 200 μg/kg/h for 10 days. Infusion of CCK caused hypercholecystokininemia (hyperCCKemia) and decreased the atrophy of the pancreas resulting from TPN. The hyperplastic response to CCK in orally fed rats was decreased in the rats given TPN. Devazepide did not influence the pancreatic variables. This study further confirmed that CCK stimulates the exocrine pancreas and decreases the atrophy of the exocrine pancreas resulting from TPN. Our present findings suggest that the trophic effect of CCK on the exocrine pancreas declines in TPN., (© 2011 Blackwell Verlag GmbH.)

Cholecystokinin octapeptide (CCK-8) is the most potent endogenous anti-opioid peptide and regulates a variety of physiological processes. In our previous study, we found that exogenous CCK-8 attenuated naloxone-induced withdrawal symptoms, but the possible regulative effects of CCK-8 on the rewarding effects of morphine were not examined. In the present study, we aimed to determine the exact effects of exogenous CCK-8 at various doses on the rewarding action of morphine by utilizing the unbiased conditioned place preference (CPP) paradigm. We therefore examined the effects of CCK-8 on the acquisition, expression and extinction of morphine-induced CPP and on locomotor activity. The results showed that CCK-8 (0.01-1μg, i.c.v.), administered alone, induced neither CPP nor place aversion, but blocked the acquisition of CPP when administered with 10mg/kg morphine. The highest dose of CCK-8 (1μg) administered before CPP testing increased CPP and, along with lower doses (0.1μg), reduced its extinction. In addition, the highest dose (1μg) of CCK-8 suppressed locomotor activity. Our study provides the first behavioral evidence for the inhibitory effects of exogenous CCK-8 on rewarding activity and reveals significant effects of exogenous CCK-8 on various stages of place preference and the development of opioid dependence., (Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.)

We have shown that vagotomy (VGX) attenuates the reduction of meal size (MS) produced by cholecystokinin (CCK) -8 and -33 and that celiaco-mesenteric ganglionectomy (CMGX) attenuates the prolongation of the intermeal interval (IMI) produced by CCK-33. Here, we report the following novel data. First, by determining the distribution of CCK(1) receptor messenger RNA, which mediates reduction of MS and prolongation of IMI by CCK, in seven regions of the gastrointestinal tract in the adult rat we found that the duodenum contains the highest concentration of this receptor in the gut. Second, based on the previous finding we performed a unique surgical technique known as duodenal myotomy (MYO), which severs all the nerves of the gut wall in the duodenum including vagus, splanchnic and enteric nerves. Third, we determined MS and IMI in duodenal MYO rats in responses to endogenous CCK-58 released by the non-nutrient, trypsin inhibitor, camostat and CCK-8 to test the possibility that the duodenum is the site of action for reduction of MS and prolongation of IMI. We found that, similar to the previous work reported by using CCK-8 and MS, duodenal MYO also blocked reduction of MS by camostat. Forth, duodenal MYO blocked prolongation of IMI by camostat. As such, our current results suggest that the duodenum is the gut site that communicates both feeding signals of endogenous CCK, MS and IMI, with the brain through vagal and splanchnic afferents., (Published by Elsevier Inc.)

Previous reports suggest that glucagon-like peptide (GLP-1), a peptide secreted from the distal small intestine, is an endocrine satiation signal. Nevertheless, there are conflicting reports regarding the site where circulating GLP-1 acts to reduce food intake. To test the hypothesis that vagal afferents are necessary for reduction of food intake by circulating GLP-1, we measured intake of 15% sucrose during intravenous GLP-1 infusion in intact, vagotomized, and capsaicin-treated rats. We also measured sucrose intake during intravenous infusion of cholecystokinin, a peptide known to reduce food intake via abdominal vagal afferents. We found that reduction of intake by GLP-1 was not diminished by capsaicin treatment or vagotomy. In fact, reduction of sucrose intake by our highest GLP-1 dose was enhanced in vagotomized and capsaicin-treated rats. Intravenous GLP-1 induced comparable increases of hindbrain c-Fos immunoreactivity in intact, capsaicin-treated, and vagotomized rats. Plasma concentrations of active GLP-1 in capsaicin-treated rats did not differ from those of controls during the intravenous infusions. Finally, capsaicin treatment was not associated with altered GLP-1R mRNA in the brain, but nodose ganglia GLP-1R mRNA was significantly reduced in capsaicin-treated rats. Although reduction of food intake by intraperitoneal cholecystokinin was abolished in vagotomized and capsaicin-treated rats, reduction of intake by intravenous cholecystokinin was only partially attenuated. These results indicate that vagal or capsaicin-sensitive neurons are not necessary for reduction of food intake by circulating (endocrine) GLP-1, or cholecystokinin. Vagal participation in satiation by these peptides may be limited to paracrine effects exerted near the sites of their secretion.

Cholecystokinin octapeptide (CCK-8), a gut-brain peptide, regulates a variety of physiological behavioral processes. Previously, we reported that exogenous CCK-8 attenuated morphine-induced conditioned place preference, but the possible effects of CCK-8 on aversively motivated drug seeking remained unclear. To investigate the effects of endogenous and exogenous CCK on negative components of morphine withdrawal, we evaluated the effects of CCK receptor antagonists and CCK-8 on the naloxone-precipitated withdrawal-induced conditioned place aversion (CPA). The results showed that CCK2 receptor antagonist (LY-288,513, 10 µg, i.c.v.), but not CCK1 receptor antagonist (L-364,718, 10 µg, i.c.v.), inhibited the acquisition of CPA when given prior to naloxone (0.3 mg/kg) administration in morphine-dependent rats. Similarly, CCK-8 (0.1-1 µg, i.c.v.) significantly attenuated naloxone-precipitated withdrawal-induced CPA, and this inhibitory function was blocked by co-injection with L-364,718. Microinjection of L-364,718, LY-288,513 or CCK-8 to saline pretreated rats produced neither a conditioned preference nor aversion, and the induction of CPA by CCK-8 itself after morphine pretreatments was not significant. Our study identifies a different role of CCK1 and CCK2 receptors in negative affective components of morphine abstinence and an inhibitory effect of exogenous CCK-8 on naloxone-precipitated withdrawal-induced CPA via CCK1 receptor.

Background: Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. Little is known about the effects of cholecystokinin octapeptide (CCK-8) on HCN channels and excitability of murine interstitial cells of Cajal (ICCs)., Methods: In the present study, the effects and mechanisms of CCK-8 on HCN channels were investigated by measuring mechanical contraction of smooth muscle strips and ionic channels of ICCs in murine gastric antrum., Results: Sulfated CCK-8 (CCK-8S) was used, and we found that CCK-8S increased the contraction of smooth muscle strips in the gastric antrum, which could be suppressed by specific HCN channel blockers CsCl and ZD7288. Extracellular calcium could also intensify the contraction. Under the same conditions, when antral strips were exposed to calcium ion (Ca²⁺)-free solution, no significant changes could be recorded with CCK-8S or ZD7288. Isolated ICCs from the murine gastric antrum identified by specific c-Kit antibody primers were chosen for electrophysiological recordings. HCN current (I(h)) of cultured ICCs was studied by whole-cell patch clamp techniques. A spontaneous transient inward current was recorded in ICCs, which could be inhibited by addition of CsCl and ZD7288; the current proved to be I(h). CCK-8S-facilitated I(h) in cultured ICCs could be inhibited by CsCl and ZD7288. When cultured ICCs were exposed to Ca²⁺-free solution, no significant changes could be recorded by application of CCK-8S on I(h), which proved extracellular calcium might have an excitatory effect on HCN channels., Conclusion: We demonstrate that HCN channels are present in ICCs in the murine gastric antrum; they might be an important regulator of ICC excitability and pacemaker activity and are strongly affected by CCK-8S. Extracellular calcium might be a trigger in the activation of HCN channels caused by CCK-8S in cultured ICCs., (Copyright © 2012 S. Karger AG, Basel.)

Cholecystokinin octapeptide (CCK-8) is a typical brain-gut peptide that exerts a variety of physiological actions in both the peripheral and central nervous systems. Our laboratory has previously reported that CCK-8 produces immunoregulatory action through activating CCK receptor (CCK1R/CCK2R) expression on immune cell surfaces. In the present study, we investigated the effect of CCK-8 on immunoglobulin G1 (IgG1) production in lipopolysaccharide (LPS)-activated B cells in vitro. CCK-8 inhibited the proliferation and IgG1 mRNA expression of LPS-activated B cells and therefore inhibited IgG1 production. The mechanism may be associated with the regulation of CCK-8 on transcription factors Blimp1, Pax5, Xbp1 and Bcl6. CCK-8 inhibited the expression of Blimp1, while the effect on Pax5, Xbp1 and Bcl6 varied with time, suggesting that CCK-8 acted as a complex regulator of LPS-activated B cells. The inhibitory action of CCK-8 was mainly mediated through the CCK2R pathway. These studies indicate that CCK-8 attenuates humoral immune responses and acts as endogenous immune deactivators in autoimmune diseases., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Total or selective branch vagotomy attenuates the reduction of cumulative food intake by cholecystokinin (CCK)-8 and CCK-33 respectively. However, the role of the sympathetic innervation of the gut and the role of the vagus nerve in feeding responses, which include meal size (MS) and intermeal interval (IMI), evoked by CCK-8 and CCK-33 have not been evaluated. Here, we tested the effects of total subdiaphragmatic vagotomy (VGX) and celiaco-mesenteric ganglionectomy (CMGX) on the previous feeding responses by CCK-8 and CCK-33 (0, 1, 3, and 5 nmol/kg given intraperitoneally). We found (1) that both peptides reduced meal size and CCK-8 (5 nmol) and CCK-33 (1 and 3 nmol) prolonged IMI, (2) that VGX attenuated the reduction of MS but failed to attenuate the prolongation of IMI by both peptides and (3) that CMGX attenuated the reduction of meal size by CCK-8 and the prolongation of IMI by both peptides. Therefore, the feeding responses evoked by CCK-8 require intact vagus and splanchnic nerves: the reduction of MS by CCK-33 requires an intact vagus nerve, and the prolongation of IMI requires the splanchnic nerve. These findings demonstrate the differential peripheral neuronal mediation of the feeding responses evoked by CCK-8 and CCK-33., (Published by Elsevier Inc.)

Camostat mesilate (or mesylate) releases endogenous cholecystokinin (CCK) or CCK-58, the only detectable endocrine form of CCK in the rat, and reduces cumulative food intake by activating CCK(1) receptor. However, the literature lacks meal pattern analysis and an appropriate dose-response curve for this peptide. Therefore, the current study determines meal size (MS), intermeal interval (IMI) and satiety ratio (SR) by orogastric gavage of camostat (0, 12.5, 25, 50, 100, 200, 300, 400, 800mg/kg) and compares them to those previously reported by a single dose of CCK-8 (1nmol/kg, i.p), the most utilized form of CCK. We found that camostat (200, 300, 400 and 800mg/kg) and CCK-8 reduced cumulative food intake and the size of the first meal, but only camostat prolonged IMI and increased SR. There was no change in the duration of the first two meals or in rated behaviors such as feeding, grooming, standing and resting in response to camostat and CCK-8, but there was more resting during the IMI in response to camostat. This study provides meal pattern analysis and an appropriate dose-response curve for camostat and CCK-8. Camostat reduces food intake by decreasing MS and prolonging IMI, whereas CCK-8 reduces food intake by reducing only meal size., (Published by Elsevier Inc.)

Research has shown that the synergistic interaction between vagal cholecystokinin-A receptors (CCKARs) and leptin receptors (LRbs) mediates short term satiety. We hypothesize that this synergistic interaction is mediated by cross-talk between signaling cascades used by CCKARs and LRbs, which, in turn, activates closure of K(+) channels, leading to membrane depolarization and neuronal firing. Whole cell patch clamp recordings were performed on isolated rat nodose ganglia neurons. Western immunoblots elucidated the intracellular signaling pathways that modulate leptin/CCK synergism. In addition, STAT3, PI3K, Src, and MAPK genes were silenced by lentiviral infection and transient Lipofectamine transfection of cultured rat nodose ganglia to determine the effect of these molecules on leptin/CCK synergism. Patch clamp studies showed that a combination of leptin and CCK-8 caused a significant increase in membrane input resistance compared with leptin or CCK-8 alone. Silencing the STAT3 gene abolished the synergistic action of leptin/CCK-8 on neuronal firing. Leptin/CCK-8 synergistically stimulated a 7.7-fold increase in phosphorylated STAT3 (pSTAT3), which was inhibited by AG490, C3 transferase, PP2, LY294002, and wortmannin, but not PD98059. Silencing the Src and PI3K genes resulted in a loss of leptin/CCK-stimulated pSTAT3. We conclude that the synergistic interaction between vagal CCKARs and LRbs is mediated by the phosphorylation of STAT3, which, in turn, activates closure of K(+) channels, leading to membrane depolarization and neuronal firing. This involves the interaction between CCK/Src/PI3K cascades and leptin/JAK2/PI3K/STAT3 signaling pathways. Malfunctioning of these signaling molecules may result in eating disorders.

Objective: To investigate the effects and mechanism of cholecystokinin octapeptide (CCK-8S) on the contractile activity of smooth muscles, L-type calcium current and membrane potentials of proximal colon myocytes in guinea pig., Methods: (1) Strips of proximal colon were obtained from adult guinea pigs. The contraction of these stripes was measured by a RM6240 multi-channel physiological signal system. (2) Suspension of single smooth muscle cells (SMCs) were obtained from proximal colon and isolated by enzymatic digestion. The effect of CCK-8S on intracellular calcium concentration ([Ca(2+)]i) of SMCs was examined by fura-2-loaded microfluorimetric measurement. (3) Resting potential (RP), action potential (AP) and L-type calcium current (I(Ca-L)) were recorded by patch-clamp technique., Results: (1) The contractile amplitude and frequency of muscle stripes enhanced by CCK-8S (10(-7) mol/L) were (149 ± 12)% and (132 ± 13)% respectively of those of control group (all P < 0.05). They were significantly attenuated by pretreating strips with CCK1 receptor antagonist devazepide (10(-7) mol/L), L-type calcium channel blocker nifedipine (10(-5) mol/L), Ca(2+)-ATPase inhibitor TG (thapsigargin) (10(-5) mol/L) and BA (boric acid) (10(-5) mol/L) respectively. (2) [Ca(2+)]i of SMCs intensified by CCK-8S was (738 ± 24)% of that of control group. And it was inhibited by pretreating SMCs with devazepide (all P < 0.05). (3) After the superfusion of CCK-8S, RP depolarized to (52 ± 9)%, the exogenously stimulated peak values of AP rose to (140 ± 4)% and fast repolarization time of AP decreased to (61 ± 13)% (all P < 0.05). They were significantly inhibited when these cells were pretreated with devazepide and/or nifedipine (n = 8, P < 0.05 for each group) whereas CI 988 had little effect. (4) The CCK-8S-evoked I(Ca-L) of SMCs at the voltage of + 10 mV was boosted to (138 ± 7)%. Such an effect was suppressed by a pretreatment with nifedipine, devazepide, TG and BA respectively. In the presence of an inhibitor of inositol 1,4,5-trisphosphate (IP3) receptors, heparin (10(-6) mol/L) and an protein kinase C (PKC) inhibitor, saurosporine (10(-6) mol/L), CCK-8S did not significantly intensify I(Ca-L) (all P > 0.05)., Conclusion: CCK-8S promotes proximal colon contraction by CCK1 receptors through the activation of IP3-mediated PKC pathway.

Cholecystokinin octapeptide (CCK8) can exert the immunoregulatory roles through activating immune cell surface receptors such as T lymphocytes, macrophages, dendritic cells, and so on. In this study, we discussed the effects of CCK8 on lipopolysaccharide (LPS)-activated B cells in terms of the expression of co-stimulatory molecules, and the capacity to activate CD4(+) T cells and cytokines production in vitro. The results revealed that B cells expressed two types of CCK receptors; CCK8 inhibited the expression of co-stimulatory molecules such as CD80 and CD86 on LPS-activated B cells, suppressed the proliferation of allogeneic T cells in a dose-dependent manner, and also reduced the secretion of Th1-type cytokine IFN-γ, whereas enhanced the secretion of Th2-type cytokine IL-4 by LPS-activated B cells. Both CCK1R and CCK2R participated in these effects. Taken together, CCK8 is capable of exerting immunomodulatory functions through B cells.

Intravenous cholecystokinin octapeptide (CCK-8) elicits vago-vagal reflexes that inhibit phasic gastric contractions and reduce gastric tone in urethane-anaesthetized rats. A discrete proximal subdivision of the ventral gastric vagus nerve (pVGV) innervates the proximal stomach, but the fibre populations within it have not been characterized previously.We hypothesized that I.V. CCK-8 injection would excite inhibitory efferent outflow in the pVGV, in contrast to its inhibitory effect on excitatory efferent outflow in the distal subdivision (dVGV), which supplies the distal stomach. In each VGV subdivision, a dual-recording technique was used to record afferent and efferent activity simultaneously, while also monitoring intragastric pressure (IGP). CCK-8 dose dependently (100-1000 pmol kg(-1), I.V.) reduced gastric tone, gastric contractile activity and multi-unit dVGV efferent discharge, but increased pVGV efferent firing. Single-unit analysis revealed a minority of efferent fibres in each branch whose response differed in direction from the bulk response. Unexpectedly, efferent excitation in the pVGV was significantly shorter lived and had a significantly shorter decay half-time than did efferent inhibition in the dVGV, indicating that distinct pathways drive CCK-evoked outflow to the proximal vs. the distal stomach. Efferent inhibition in the dVGV began several seconds before, and persisted significantly longer than, simultaneously recorded dVGV afferent excitation.Thus, dVGV afferent excitation could not account for the pattern of dVGV efferent inhibition. However, the time course of dVGV afferent excitation paralleled that of pVGV efferent excitation. Similarly, the duration of CCK-8-evoked afferent responses recorded in the accessory celiac branch of the vagus (ACV) matched the duration of dVGV efferent responses. The observed temporal relationships suggest that postprandial effects on gastric complicance of CCK released from intestinal endocrine cells may require circulating concentrations to rise to levels capable of exciting distal gastric afferent fibres, in contrast to more immediate effects on distal gastric contractile activity mediated via vago-vagal reflexes initiated by paracrine excitation of intestinal afferents.

The serin/threonin-kinase, mammalian target of rapamycin (mTOR) was detected in the arcuate nucleus (ARC) and paraventricular nucleus of the hypothalamus (PVN) and suggested to play a role in the integration of satiety signals. Since cholecystokinin (CCK) plays a role in the short-term inhibition of food intake and induces c-Fos in PVN neurons, the aim was to determine whether intraperitoneally injected CCK-8S affects the neuronal activity in cells immunoreactive for phospho-mTOR in the PVN. Ad libitum fed male Sprague-Dawley rats received 6 or 10 μg/kg CCK-8S or 0.15M NaCl ip (n=4/group). The number of c-Fos-immunoreactive (ir) neurons was assessed in the PVN, ARC and in the nucleus of the solitary tract (NTS). CCK-8S increased the number of c-Fos-ir neurons in the PVN (6 μg: 103 ± 13 vs. 10 μg: 165 ± 14 neurons/section; p<0.05) compared to vehicle treated rats (4 ± 1, p<0.05), but not in the ARC. CCK-8S also dose-dependently increased the number of c-Fos neurons in the NTS. Staining for phospho-mTOR and c-Fos in the PVN showed a dose-dependent increase of activated phospho-mTOR neurons (17 ± 3 vs. 38 ± 2 neurons/section; p<0.05), while no activated phospho-mTOR neurons were observed in the vehicle group. Triple staining in the PVN showed activation of phospho-mTOR neurons co-localized with oxytocin, corresponding to 9.8 ± 3.6% and 19.5 ± 3.3% of oxytocin neurons respectively. Our observations indicate that peripheral CCK-8S activates phospho-mTOR neurons in the PVN and suggest that phospho-mTOR plays a role in the mediation of CCK-8S's anorexigenic effects., (Copyright © 2010 Elsevier Inc. All rights reserved.)

We have been extensively investigating the mechanisms by which neuropeptides regulate feeding behavior by using a goldfish (Carassius auratus) model. In this species, the anorexigenic action of melanocortin peptide is centrally mediated via the corticotropin-releasing hormone (CRH)/CRH receptor neuronal system, whereas sulfated cholecystokinin octapeptide (CCK-8s) is involved in the appetite regulation as a peripheral anorexigenic factor. The aim of the present study was to identify the mechanism of the anorexigenic effect of peripherally injected CCK-8s, which has not yet been identified in goldfish. Co-administration of capsaicin, a neurotoxin that destroys primary sensory afferents, at 100 nmol/g BW, blocked the anorexigenic action of intraperitoneally injected CCK-8s (100 pmol/g BW), whereas the anorexigenic action of intracerebroventricularly injected CCK-8s (5 pmol/g BW) was not blocked by co-administration of capsaicin. Pre-treatment with a specific CRH receptor antagonist, α-helical CRH((9-41)), attenuated the anorexigenic action of CCK-8s. The expression level of CRH mRNA in the diencephalic tissue of the CCK-8s-injected group was not changed, but the level of proopiomelanocortin mRNA was significantly increased at 1h after treatment. Therefore, we have identified for the first time that the reduction of appetite induced by peripherally injected CCK-8s in goldfish appears to be mediated by the vagal afferent and subsequently through the melanocortin- and corticotropin-releasing hormone-signaling pathways., (Copyright © 2010 Elsevier Inc. All rights reserved.)

In the cerebellum, there are numerous cholecystokinin (CCK-8)-containing fibers. Since systemic CCK-8 injection-induced anxiety (psychological stress) activates the locus coeruleus cells that send mossy fiber inputs to the cerebellum, we examined whether systemic CCK-8 injections activate the rat and mouse cerebellum. First, injections of CCK-8 were found to induce c-fos mRNA expression in a vague patchy pattern that is different from single methamphetamine-induced Zebrin band-like c-fos mRNA expression, suggesting that the CCK-8 activating mossy fibers induce gene expression differently from the dopamine-containing mossy fibers in the ventral tegmental area. Second, since CCK-8 facilitates neural activity of dopamine in the midbrain, we examined whether repeated methamphetamine administration that induced behavioral sensitization had similar effects on the cerebellar CCK system. Repeated administration of methamphetamine suppressed the CCK-8-induced c-fos mRNA expression in the rat cerebellum. Third, capsaicin injections (physical stress) into a hind limb of the rat increased junD mRNA expression with no effect on c-fos mRNA expression, and repeated methamphetamine injections had no effect on the capsaicin-induced expression of junD mRNA. Fourth, either single injection of methamphetamine or CCK-8 to mice increased c-fos mRNA expression in the locus coeruleus, and so noradrenalin, but not dopamine, might interact with CCK-8-activating system. However, we considered the possibility unlikely. Thus, we conclude that repeated methamphetamine administration though dopamine selectively inhibits the c-fos mRNA expression after CCK-8 injection in the cerebellum.

Cholecystokinin (CCK) plays a role in the short-term inhibition of food intake. Cocaine- and amphetamine-regulated transcript (CART) peptide has been observed in neurons of the paraventricular nucleus (PVN). It has been reported that intracerebroventricular injection of CART peptide inhibits food intake in rodents. The aim of the study was to determine whether intraperitoneally (ip) injected CCK-8S affects neuronal activity of PVN-CART neurons. Ad libitum fed male Sprague-Dawley rats received 6 or 10 microg/kg CCK-8S or 0.15M NaCl ip (n=4/group). The number of c-Fos-immunoreactive neurons was determined in the PVN, arcuate nucleus (ARC), and the nucleus of the solitary tract (NTS). CCK-8S dose-dependently increased the number of c-Fos-immunoreactive neurons in the PVN (mean+/-SEM: 102+/-6 vs. 150+/-5 neurons/section, p<0.05) and compared to vehicle treated rats (18+/-7, p<0.05 vs. 6 and 10 microg/kg CCK-8S). CCK-8S at both doses induced an increase in the number of c-Fos-immunoreactive neurons in the NTS (65+/-13, p<0.05, and 182+/-16, p<0.05). No effect on the number of c-Fos neurons was observed in the ARC. Immunostaining for CART and c-Fos revealed a dose-dependent increase of activated CART neurons (19+/-3 vs. 29+/-7; p<0.05), only few activated CART neuron were observed in the vehicle group (1+/-0). The present observation shows that CCK-8S injected ip induces an increase in neuronal activity in PVN-CART neurons and suggests that CART neurons in the PVN may play a role in the mediation of peripheral CCK-8S's anorexigenic effects., (Copyright 2010 Elsevier Inc. All rights reserved.)

We have studied the potential role of CCK as a regulator/modulator of the postprandial increase in gastrointestinal blood flow. Rainbow trout (Oncorhynchus mykiss) were instrumented with pulsed Doppler flow probes to measure the effects of CCK on cardiac output and gastrointestinal blood flow. Furthermore, vascular preparations were used to study the direct effects of CCK on the vessels. In addition, we used in situ perfused hearts to further study the effects of CCK on the cardiovascular system. When the sulfated form of CCK-8 was injected at a physiological concentration (0.19 pmol/kg) in vivo, there was a significant increase in the gastrointestinal blood flow (18 +/- 4%). This increase in gastrointestinal blood flow was followed by a subsequent increase in cardiac output (30 +/- 6%). When the dose was increased to 0.76 pmol/kg, there was only a 14 +/- 6% increase in gastrointestinal blood flow; possibly due to a dose-dependent increase in the gill vascular resistance as previously reported or a direct effect on the heart. Nevertheless, CCK did not affect the isolated vessel preparations, and thus, it seems unlikely that CCK has a direct effect on the blood vessels of the second or third order. CCK did, however, have profound effects on the dynamics of the heart, and without a change in cardiac output, there was a significant increase in the amplitude (59 +/- 4%) and rate (dQ/dt: 55 +/- 4%; -dQ/dt: 208 +/- 49%) of the phasic flow profile. If and how this might be coupled to a postprandial gastrointestinal hyperemia remains to be determined. We conclude that CCK has the potential as a regulator of the postprandial gastrointestinal blood flow in fish and most likely has its effect by inducing a gastrointestinal hyperemia. The mechanism by which CCK acts is at present unknown.