Effects Of CCK Research Articles

Effects of oral preload, CCK or bombesin administration on short term food intake of melanocortin 4-receptor knockout (MC4RKO) mice

We investigated whether either heterozygous (HET) or homozygous (knockout, KO) disruption of the melanocortin type 4 receptor (MC4R) gene alters post ingestive responsiveness of mice. Specifically, we tested the hypothesis that hyperphagia in MC4RKO mice might be due to a deficit in processes that sustain intermeal intervals (satiety) and/or processes that terminate ongoing episodes of eating (satiation). To test satiety, mice drank an oral preload and then we monitored intake of a subsequent liquid diet test meal. To test satiation, we examined the effect of exogenous administration of cholecystokinin (CCK) and bombesin (BN) on the size of a liquid diet meal. Experiment 1 was comprised of two studies. In the first, we determined that the intake of all three genotypes following fasts of either 6, 12, or 24 h were comparable, and so chose 12 h deprivation for the subsequent studies. In the second, 12 h fasted mice were allowed to consume a fixed preload, approximately 50% of their expected mean intake and, following delays of either 30 or 60 min, were allowed to consume to satiation. Compared with no preload, the preload significantly reduced meal size comparably in all three genotypes. The reduction in intake was greater when the test meal was presented 30 compared with 60 min after the preload, again with no genotype differences in this decay of satiety. In experiment 2, we administered either CCK or BN and examined suppression of meal size after a 12 h fast. Mice were tested repeatedly with CCK-8 (2, 6, or 18 μg/kg ip) or BN (2, 4 or 8 μg/kg ip) with vehicle injection days intervening. The 30 min intakes of HET and KO mice were suppressed more than those of WT following either CCK or BN. These experiments suggest that diminished responsiveness to nutrients or gut satiety hormones is not responsible for hyperphagia in MC4RKO mice.

Twenty years of non-peptide CCK1 receptor antagonists: all that glitters is not gold

During the last 20 years, pharmaceutical industry and academic efforts have led to several structurally unrelated classes of non-peptide cholecystokinin-1 receptor (CCK1-R) antagonists. Due to the lack of high resolution structure of CCK1-R and its peptide ligand, different strategies to design antagonists have been adopted. The rational design, based on conformational studies of the endogenous ligand, has provided the so-called ‘peptoid’ derivatives and conformationally restricted peptoids, whereas all of the other non-peptide antagonists derived by empirical and/or conventional approaches, including the chemical manipulation of natural products, disconnection strategies and the use of single key amino acids. All of these strategies include a final optimisation step of the obtained lead compound performed by chemical modifications. The CCK1-R antagonists, in addition to providing a better characterisation of the CCK1-R receptor subtype as pharmacological tools and improving the knowledge of the physiological and pathological role(s) of CCK, may possess therapeutic potential in humans. As the complex biological effects of CCK mediated by CCK1-R in the CNS are not yet completely established, the therapeutic potential of these antagonists at present is limited to the gastrointestinal system disorders. Up until now, loxiglumide and its R-enantiomer (dexloxiglumide) along with lintitript are the CCK1-R antagonists at the most advanced stage of clinical research in gastroenterology.

Constitutively active CCK2 receptor splice variant increases Src-dependent HIF-1α expression and tumor growth

Gastrointestinal (GI) cancers ectopically express multiple splice variants of the cholecystokinin-2 (CCK(2))/gastrin receptor; however, their relative contributions to the cancer phenotype are unknown. The aim of this study was to compare the effects of CCK(2) receptor (CCK(2)R) and CCK(2i4sv)R expression on cell growth both in vitro and in vivo using a human epithelial cell model, HEK239. In vitro, receptor variant expression did not affect cell proliferation either in the absence or presence of agonist. However, in vivo, the expression of CCK(2i4sv)R, but not CCK(2)R, increases HEK293 tumor growth in a constitutive, Src-dependent manner. Enhanced tumorigenicity of CCK(2i4sv)R is associated with an Src-dependent increase in the transcription factor, hypoxia-inducible factor-1alpha, its downstream target, vascular endothelial growth factor and tumor micro-vessel density, suggesting that CCK(2i4sv)R may contribute to the growth and spread of GI cancers through agonist-independent mechanisms that enhance tumor angiogenesis.

Modulation of vagal afferent excitation and reduction of food intake by leptin and cholecystokinin

The gut-peptide, cholecystokinin (CCK), reduces food intake by acting at CCK-1 receptors on vagal afferent neurons, whereas the feeding effects of the adipokine hormone, leptin, are associated primarily with its action on receptors (ObRb) in the hypothalamus. Recently, however, ObRb mRNA has been reported in vagal afferent neurons, some of which also express CCK-1 receptor, suggesting that leptin, alone or in cooperation with CCK, might activate vagal afferent neurons, and influence food intake via a vagal route. To evaluate these possibilities we have been examining the cellular and behavioral effects of leptin and CCK on vagal afferent neurons. In cultured vagal afferent neurons leptin and CCK evoked short latency, transient depolarizations, often leading to action potentials, and increases in cytosolic calcium. There was a much higher prevalence of CCK and leptin sensitivity amongst cultured vagal afferent neurons that innervate stomach or duodenum than there was in the overall vagal afferent population. Furthermore, almost all leptin-responsive gastric and duodenal vagal afferents also were sensitive to CCK. Leptin, infused into the upper GI tract arterial supply, reduced meal size, and enhanced satiation evoked by CCK. These results indicate that vagal afferent neurons are activated by leptin, and that this activation is likely to participate in meal termination, perhaps by enhancing vagal sensitivity to CCK. Our findings are consistent with the view that leptin and CCK exert their influence on food intake by accessing multiple neural systems (viscerosensory, motivational, affective and motor) at multiple points along the neuroaxis.

Effects of CCK-8 on independent ingestion and central c-Fos-like immunoreactivity in rats on postnatal days 10 and 11

Controls of the independent ingestion of food in the preweanling rat emerge in the second postnatal week. We investigated the effects of CCK-8 (0, 1, 5, or 10 μg/kg IP) on intake and c-Fos-like immunoreactive (CFLI) cells in hindbrain and forebrain on postnatal days 10 and 11. Five micrograms per kilogram decreased intake and increased the number of CFLI cells in four subnuclei of the nucleus tractus solitarius (NTS), in arcuate nucleus (ARC), and in central nucleus of the amygdala (CeA). Ten micrograms per kilogram decreased intake and increased CFLI in three NTS subnuclei as much as 5 μg/kg did, but was more potent than 5 μg/kg in the medial NTS subnucleus. Ten micrograms per kilogram increased CFLI in paraventricular (PVN) and supraoptic (SON) nuclei, but 5 μg/kg did not. Thus, reduction of intake by CCK-8 on days 10 and 11 is associated with increased hindbrain and forebrain CFLI.

Involvement of endogenous cholecystokinin in tolerance to morphine antinociception in the nucleus accumbens of rats

Cholecystokinin (CCK) is an endogenous anti-opioid peptide in the central nervous system. The present study investigated the effects of endogenous CCK on tolerance to morphine antinociception in the nucleus accumbens (NAc) of rats. Chronic administration of morphine to NAc induced marked tolerance to antinociception. Intra-NAc administration of the CCK2 receptor antagonist LY225910 inhibited not only the development but also the expression of chronic morphine-induced antinociceptive tolerance. However, intra-NAc injection of LY225910 did not influence the antinociception induced by intra-NAc administration of morphine in the intact rats. The results indicate that endogenous CCK plays an important role in morphine-induced antinociceptive tolerance in the NAc of rats.

Very low levels of cholecystokinin octapeptide activate Na-pump in the cerebral cortex of CCK2 receptor-deficient mice

This study provides the first evidence that CCK-8 (0.01pM to 0.1mM) stimulates Na,K-ATPase in the cortical membranes of wild-type and CCK2 receptor-deficient mice. In each genotype, the maximal stimulation was about 40%. Homozygous mice revealed substantially lower EC50 (4pM) than heterozygous (37pM) or wild-type animals (682pM). In homozygous CCK2 receptor-deficient mice, the expression of CCK1 receptor gene was 5-fold higher than in wild-type animals. CCK1 receptor antagonist devazepide counteracted effect of CCK-8 in all three genotypes, whereas CCK2 receptor antagonist L-365, 260 showed significant antagonism in wild-type and heterozygous mice. The cooperativity of Na,K-ATPase for Na+, but not for K+, was lost in homozygous mice. Altogether, very low concentrations of CCK-8 via CCK1 and CCK2 receptors stimulate Na,K-ATPase in the cerebral cortex. CCK2 receptor-deficiency leads to the altered functionality of Na,K-ATPase that might be compensated by CCK1 receptor mediated influence of CCK (and its agonists) on the enzyme.

The sympathoinhibitory effects of systemic cholecystokinin are dependent on neurons in the caudal ventrolateral medulla in the rat

The gastrointestinal hormone CCK inhibits a subset of presympathetic neurons in the rostroventrolateral medulla (RVLM) that may be responsible for driving the sympathetic vasomotor outflow to the gastrointestinal circulation. We tested the hypothesis that the central neurocircuitry of this novel sympathoinhibitory reflex involves a relay in the caudal ventrolateral medullary (CVLM) depressor area. Blood pressure and greater splanchnic sympathetic nerve discharge (SSND) or lumbar sympathetic nerve discharge (LSND) were monitored in anesthetised, paralyzed male Sprague-Dawley rats. The effects of phenylephrine (PE, 10 microg/kg iv; baroreflex activation), phenylbiguanide (PBG, 10 microg/kg iv; von Bezold-Jarisch reflex) and CCK (4 or 8 microg/kg iv) on SSND or LSND, were tested before and after bilateral injection of 50-100 nl of the GABAA agonist muscimol (1.75 mM; n=6, SSND; n=7, LSND) or the excitatory amino acid antagonist kynurenate (55 mM; n=7, SSND) into the CVLM. PE and PBG elicited splanchnic and lumbar sympathoinhibitory responses that were abolished by bilateral muscimol or kynurenate injection into the CVLM. Similarly, the inhibitory effect of CCK on SSND was abolished after neuronal inhibition within the CVLM. In contrast, CCK-evoked lumbar sympathoexcitation was accentuated following bilateral CVLM inhibition. In control experiments (n=7), these agents were injected outside the CVLM and had no effect on splanchnic sympathoinhibitory responses to PE, PBG, and CCK. In conclusion, neurons in the CVLM are necessary for the splanchnic but not lumbar sympathetic vasomotor reflex response to CCK. This strengthens the view that subpopulations of RVLM neurons supply sympathetic vasomotor outflow to specific vascular territories.

Hunger and satiety: one brain for two?

understanding the physiological controls of eating and developing effective pharmacological tools to reduce eating has never been more important. The modern world faces an unprecedented obesity epidemic, and the current treatment strategies are rather unsuccessful. One possible solution may be a

Cellular action of cholecystokinin-8S-mediated excitatory effects in the rat periaqueductal gray

The peptide cholecystokinin (CCK) is one of the major neurotransmitters modulating satiety, nociception, and anxiety behavior. Although many behavioral studies showing anti-analgesic and anxiogenic actions of CCK have been reported, less is known about its cellular action in the central nervous system (CNS). Therefore, we examined the action of CCK in rat dorsolateral periaqueductal gray (PAG) neurons using slice preparations and whole-cell patch–clamp recordings. Application of CCK-8S produced an inward current accompanied by increased spontaneous synaptic activities. The CCK-8S-induced inward current ( I CCK) was recovered after washout and reproduced by multiple exposures. Current–voltage plots revealed that I CCK reversed near the equilibrium potential for K + ions with a decreased membrane conductance. When several K + channel blockers were used, application of CdCl 2, TEA, or apamin significantly reduced I CCK. I CCK was also significantly reduced by the CCK 2 receptor antagonist, L-365,260, while it was not affected by the CCK 1 receptor antagonist, L-364,718. Furthermore, we examined the effects of CCK-8S on miniature excitatory postsynaptic currents (mEPSCs) in order to determine the mechanism of CCK-mediated increase on synaptic activities. We found that CCK-8S increased the frequency of mEPSCs, but had no effect on mEPSC amplitude. This presynaptic effect persisted in the presence of CdCl 2 or Ca 2+-free bath solution, but was completely abolished by pre-treatment with BAPTA-AM, thapsigargin or L-365,260. Taken together, our results indicate that CCK can excite PAG neurons at both pre- and postsynaptic loci via the activation of CCK 2 receptors. These effects may be important for the effects of CCK on behavior and autonomic function that are mediated via PAG neurons.

Bidirectional modulation of GABAergic transmission by cholecystokinin in hippocampal dentate gyrus granule cells of juvenile rats

Cholecystokinin (CCK) interacts with two types of G protein-coupled receptors in the brain: CCK-A and CCK-B receptors. Both CCK and CCK-B receptors are widely distributed in the hippocampal formation, but the functions of CCK there have been poorly understood. In the present study, we initially examined the effects of CCK on GABA(A) receptor-mediated synaptic transmission in the hippocampal formation and then explored the underlying cellular mechanisms by focusing on the dentate gyrus region, where the highest levels of CCK-binding sites have been detected. Our results indicate that activation of CCK-B receptors initially and transiently increased spontaneous IPSC (sIPSC) frequency, followed by a persistent reduction. The effects of CCK were more evident in juvenile rats, suggesting that they are developmentally regulated. Cholecystokinin failed to modulate the miniature IPSCs recorded in the presence of TTX and the amplitude of the evoked IPSCs, but produced a transient increase followed by a reduction in action potential firing frequency recorded from GABAergic interneurons, suggesting that CCK acts by modulating the excitability of the interneurons to regulate GABA release. Cholecystokinin reduced the amplitude of the after-hyperpolarization of the action potentials, and application of paxilline or charybdotoxin considerably reduced CCK-mediated modulation of sIPSC frequency, suggesting that the effects of CCK are related to the inhibition of Ca(2+)-activated K(+) currents (I(K(Ca))). The effects of CCK were independent of the functions of phospholipase C, intracellular Ca(2+) release, protein kinase C or phospholipase A(2), suggesting a direct coupling between the G proteins of CCK-B receptors and I(K(Ca)). Our results provide a novel mechanism underlying CCK-mediated modulation of GABA release.

The Src family kinase, Lyn, is activated in pancreatic acinar cells by gastrointestinal hormones/neurotransmitters and growth factors which stimulate its association with numerous other signaling molecules

Src family kinases (SFK) play a central signaling role for growth factors, cytokines, G-protein-coupled receptors and other stimuli. SFKs play important roles in pancreatic acinar cell secretion, endocytosis, growth, cytoskeletal integrity and apoptosis, although little is known of the specific SFKs involved. In this study we demonstrate the SFK, Lyn, is present in rat pancreatic acini and investigate its activation/signaling. Ca 2+-mobilizing agents, cAMP-mobilizing agents and pancreatic growth factors activated Lyn. CCK, a physiological regulator of pancreatic function, rapidly activated Lyn. The specific SFK inhibitor, PP2, decreased Lyn activation; however, the inactive analogue, PP3, had no effect. Inhibition of CCK-stimulated changes in [Ca 2+] i decreased Lyn activation by 55%; GFX, a PKC inhibitor by 36%; and the combination by 95%. CCK activation of Lyn required stimulation of high and low affinity CCK A receptor states. CCK stimulated an association of Lyn with PKC-δ, Shc, p125 FAK and PYK2 as well as with their autophosphorylated forms, but not with Cbl, p85, p130 CAS or ERK 1/2. These results show Lyn is activated by diverse pancreatic stimulants. CCK's activation of Lyn is likely an important mediator of its ability to cause tyrosine phosphorylation of numerous important cellular mediators such as p125 FAK, PYK2, PKC-δ and Shc, which play central roles in CCK's effects on acinar cell function.

Involvement of cholecystokinin in peripheral nociceptive sensitization during diabetes in rats as revealed by the formalin response

The possible pronociceptive role of peripheral cholecystokinin (CCK-8) as well as CCK A and CCK B receptors in diabetic rats was assessed. Subcutaneous injection of 0.5% formalin induced a greater nociceptive behavior in diabetic than in non-diabetic rats. Moreover, local peripheral injection of CCK-8 (0.1–100 μg) significantly increased 0.5% formalin-induced nociceptive activity in diabetic, but not in non-diabetic, rats. This effect was restricted to the formalin-injected paw as administration of CCK-8 into the contralateral paw was ineffective. Local peripheral administration of CCK-8, in the absence of formalin injection, produced a low level of, but significant increase in, flinching behavior in diabetic compared to non-diabetic rats. In addition, local peripheral administration of the non-selective CCK receptor antagonist proglumide (1–100 μg), CCK A receptor antagonist lorglumide (0.1–100 μg) or CCK B receptor antagonist CR-2945 (0.1–100 μg), but not vehicle or contralateral administration of CCK receptor antagonists, significantly reduced 0.5% formalin-induced flinching in diabetic rats. CR-2945 was the most effective drug in this condition. These effects were not observed in non-diabetic rats. The local peripheral pronociceptive effect of CCK-8 (100 μg) was significantly reduced by proglumide (100 μg), lorglumide (100 μg), and CR-2945 (100 μg). Results suggest that diabetes-induced peripheral sensitization could be due to a local peripheral release of CCK-8, which in turn would act on CCK B, mainly but also in CCK A, receptors located on the primary afferent neurons.

Intracellular Activation of Trypsinogen in Rat Pancreatic Acini After Supramaximal Secretagogue Stimulation

The aim of the study was to explore the mechanism by which trypsinogen becomes activated during acute pancreatitis. Given the ability of cholecystokinin (CCK) to induce pancreatitis in vivo, the effects of high-dose CCK on preparations of isolated pancreatic acini were examined using immunofluorescence techniques for the detection of trypsinogen activation. Acini were pretreated with weak base or serine or cysteine protease inhibitors before CCK hyperstimulation. CCK was found to stimulate the generation of trypsinogen activation peptide (TAP), a marker for trypsinogen processing. The generation of TAP was inhibited by pretreatment with a weak base, chloroquine (40 micromol/L). TAP generation was also inhibited by pretreatment with serine protease inhibitor FUT-175 (1 micromol/L) but not cysteine protease inhibitor E64 (0.1 mmol/L) or E64-d (0.1 mmol/L). Although treatment with a high dose of E64-d (1 mmol/L) reduced activation, it also caused cell injury. High-dose CCK stimulated the intracellular activation of trypsinogen within isolated pancreatic acini. This event appears to require an acidic subcellular compartment and serine protease activity. The role for thiol proteases in this model remains unclear.

Neurons in the caudal ventrolateral medulla mediate the sympathoinhibitory effects of CCK

The gastrointestinal hormone cholecystokinin (CCK) inhibits a subset of presympathetic neurons in the rostroventrolateral medulla (RVLM) that may be responsible for driving the sympathetic vasomotor outflow to the gastrointestinal circulation. We tested the hypothesis that the central neurocircuitry of this novel reflex is similar to that of other sympathoinhibitory reflexes that utilise a relay in the caudal ventrolateral medulla (CVLM). Blood pressure, heart rate and splanchnic sympathetic nerve discharge (SSND) were monitored in anesthetised (1.5% halothane in 100% O2), paralysed male Sprague-Dawley rats. After electrophysiological localisation of a barosensitive RVLM neuron, a pressure microinjector was inserted into the medulla 1.6mm caudal and 0.4 mm dorsal to this site. The effects of phenylephrine (PE, 10 μg/kg i.v.; baroreflex activation), phenylbiguanide (PBG, 10 μg/kg i.v.; von Bezold-Jarisch reflex) and CCK (4 μg/kg, i.v.) on SSND, were tested before and after bilateral injection of 50-100 nl of muscimol (1.75 mM; n=6) or kynurenate (55 mM; n=6) into the CVLM. In control experiments (n=8), these agents were injected outside the CVLM. CVLM injections abolished the sympathoinhibitory responses to PE, PBG and CCK whereas control injections had no effect. These results implicate CVLM neurons in the gastrointestinal reflex responsible for the sympathoinhibitory responses to CCK.

Cholecytokinin activates baro‐activated neurons in rat caudal ventrolateral medulla

Cholecystokinin (CCK) is a gastointestinal hormone that produces intestinal vasodilation, which appears to be mediated by reduced sympathetic nerve activity to the gut. Intravenous injection of CCK inhibits splanchnic nerve activity (SNA) and reduces the firing of a subset of pre-sympathetic neurons in the rostral ventrolateral medulla (RVLM) in chloralose-anesthetized rats. We determined whether the inhibition of RVLM neurons could be produced by the activation of GABAergic neurons in the caudal ventrolateral medulla (CVLM). In chloralose-anesthetized, artificially ventilated, paralyzed rats, we measured the effects of CCK (10 μg/kg, iv) on arterial pressure (AP), SNA, heart rate, and the firing of baro-activated, pulse-modulated CVLM neurons. CCK decreased SNA (49±10 %), heart rate (42±7 bpm), and AP (24±10 mmHg). The firing of 3 of 5 baro-activated CVLM neurons was increased by CCK (4 to 11 spikes/sec), but 2 of 5 did not change or were inhibited during the accompanying decrease in AP. In contrast, 8 of 10 neighboring baro-inhibited neurons were inhibited by CCK (3 to 0.4 spikes/sec). Four of these cells were silenced briefly. These data suggest a subset of baro-activated CVLM neurons are activated by CCK and may produce the inhibition observed in some pre-sympathetic RVLM neurons. Furthermore, these data suggest that baro-activated CVLM neurons may be subdivided into CCK-sensitive and CCK-insensitive neurons. Supported by NIH: RO1 HL075174.

Leptin and CCK selectively activate vagal afferent neurons innervating the stomach and duodenum

The hormone leptin and the gut peptide CCK synergistically interact to enhance the process of satiation. Although this interaction may occur at several levels of the neuroaxis, our previous results indicate that leptin can specifically enhance the satiation effect of CCK by acting on subdiaphragmatic vagal afferent neurons. Because of this localized action, we hypothesized that a high proportion of vagal afferent neurons innervating the stomach or duodenum would be responsive to leptin and/or CCK. To test this hypothesis, we measured changes in cytosolic calcium levels induced by leptin and CCK in cultured nodose ganglion neurons labeled with a retrograde neuronal tracer injected into either the stomach or the duodenum. In the neurons labeled from the stomach, CCK activated 74% (39 of 53) compared with only 35% (34 of 97) of nonlabeled cells. Of the CCK-responsive neurons 60% (18 of 30) were capsaicin-sensitive. Leptin activated 42% (22 of 53) of the stomach innervating neurons compared with 26% of nonlabeled neurons. All of the leptin-sensitive neurons labeled from the stomach also responded to CCK. In the neurons labeled from the duodenum, CCK activated 71% (20 of 28). Of these CCK-responsive neurons 80% (12 of 15) were capsaicin sensitive. Leptin activated 46% (13 of 28) of these duodenal innervating neurons, of which 89% (8 of 9) were capsaicin-sensitive. Among neurons labeled from the duodenum 43% (12 of 28) were responsive to both leptin and CCK, compared with only 15% (15 of 97) of unlabeled neurons. Our results support the hypothesis that vagal afferent sensitivity to CCK and leptin is concentrated in neurons that innervate the stomach and duodenum. These specific visceral afferent populations are likely to comprise a substrate through which acute leptin/CCK interactions enhance satiation.

The cholecystokinin test: An assessment

A cholecystokinin (CCK) test was performed on 13 female patients who were thought to be having attacks of gallbladder pain and in whom at least one cholecystogram had been normal. In 10 of these patients the CCK test was performed during the course of a repeat cholecystogram in order to assess the effect of CCK on gallbladder contraction. There was no constant relationship between a positive test and gallbladder contraction as measured radiographically. Cholecystectomy was undertaken in 9 patients and of these, 4 had been CCK positive, 4 had been CCK negative and 1 had reacted equivocally. None of the CCK positive patients had stones at operation, whereas 2 of the CCK negative patients had one or two small stones. In this small series cholecystectomy relieved both the CCK negative and CCK positive patients of pain with equal frequency. It is concluded that a negative CCK test by no means excludes the presence of symptomatic gallstones in patients with X-ray negative gallbladder pain.

Effect of cholecystokinin octapeptide on diacylglycerol-PKC signaling pathway in rat pulmonary interstitial macrophages stimulated by lipopolysaccharide1

To investigate the effect of cholecystokinin octapeptide (CCK-8) on the diacylglycerol-protein kinase C (DAG-PKC) signaling pathway in rat pulmonary interstitial macrophages (PIM) stimulated by lipopolysaccaride (LPS). The PIM from rat lung tissues were isolated using the collagenase digestion method combined with alveolar lavage and pulmonary vessel perfusion. DAG content and PKC activity were measured by radioenzymatic assay. The translocation of PKCzeta was determined by semi-quantitative immunoblot analysis. CCK-8, at high concentrations (1 x 10(-6) - 1 x 10(-5) mol/L), decreased DAG content and inhibited PKC activity and PKCzeta translocation compared with that in rat resting PIM of a control group (P< 0.01). LPS increased DAG content, and promoted PKC activity and PKCzeta translocation (P< 0.01). CCK-8 decreased LPS-induced DAG content and inhibited LPS-induced PKC activity and PKCzeta translocation significantly at 1 x 10(-8) - 1 x 10(-5) mol/L (P< 0.01). This inhibitory effect of CCK-8 could be abrogated partly by proglumide (non-selective CCK receptor antagonist), CR-1409 (selective CCK-A receptor antagonist), and CR-2945 (selective CCK-B receptor antagonist) in a concentration-dependent manner (P< 0.01). CCK-8 was a negative modulator of the DAG-PKC signaling pathway in rat resting PIM, which is very important for maintaining body homeostasis. It significantly inhibited LPS-induced DAG content, PKC activity and PKCzeta translocation in a concentration-dependent manner. The CCK receptor, especially the CCK-A receptor, might play a major role in this process.

Effect of intraperitoneal CCK-8 on food intake and brain orexin-A after 48 h of fasting in the rat

We investigated the interactions of the peripheral satiety peptide cholecystokinin and the brain orexin-A system in the control of food intake. The effect of an intraperitoneal (IP) injection of sulfated cholecystokinin octapeptide (in this article called CCK) (5 μg/kg, 4.4 nmol/kg) or of phosphate-buffered saline (PBS, vehicle control) on 48 h fasting-induced feeding and on orexin-A peptide content was analyzed in diverse brain regions innervated by orexin neurons and involved in the control of food intake. Administration of CCK after a 48 h fast reduced fasting-induced hyperphagia ( P < 0.05). IP CCK increased the orexin-A content in the posterior brainstem of 48 h fasted rats by 35% ( P < 0.05). Fed animals receiving CCK had 48% higher orexin-A levels in the posterior brainstem than fasted rats ( P < 0.05). In the lateral hypothalamus, fasting decreased orexin-A levels by 50% as compared to fed rats ( P < 0.05). In the septal nuclei, the combination of fasting and CCK administration reduced orexin-A contents compared to fed PBS and CCK animals by 13% and 17%, respectively ( P < 0.05). These results suggest a convergence of pathways activated by peripheral CCK and by fasting on the level of orexin-A released in the posterior brainstem and provide evidence for a novel interaction between peripheral satiety signaling and a brain orexigen in the control of food intake.