Effect of peripheral administration of cholecystokinin on food intake in apolipoprotein AIV knockout mice

Apolipoprotein AIV (apo AIV) and cholecystokinin (CCK) are satiation factors secreted by the small intestine in response to lipid meals. Apo AIV and CCK-8 has an additive effect to suppress food intake relative to apo AIV or CCK-8 alone. In this study, we determined whether CCK-8 (1, 3, or 5 μg/kg ip) reduces food intake in fasted apo AIV knockout (KO) mice as effectively as in fasted wild-type (WT) mice. Food intake was monitored by the DietMax food system. Apo AIV KO mice had significantly reduced 30-min food intake following all doses of CCK-8, whereas WT mice had reduced food intake only at doses of 3 μg/kg and above. Post hoc analysis revealed that the reduction of 10-min and 30-min food intake elicited by each dose of CCK-8 was significantly larger in the apo AIV KO mice than in the WT mice. Peripheral CCK 1 receptor (CCK1R) gene expression (mRNA) in the duodenum and gallbladder of the fasted apo AIV KO mice was comparable to that in WT mice. In contrast, CCK1R mRNA in nodose ganglia of the apo AIV KO mice was upregulated relative to WT animals. Similarly, upregulated CCK1R gene expression was found in the brain stem of apo AIV KO mice by in situ hybridization. Although it is possible that the increased satiating potency of CCK in apo AIV KO mice is mediated by upregulation of CCK 1R in the nodose ganglia and nucleus tractus solitarius, additional experiments are required to confirm such a mechanism.     

Gastroprotection and control of food intake by leptin. Comparison with cholecystokinin and prostaglandins.

Circulating peptide leptin which is the product of the ob gene is known to provide feedback information on the size of fat stores to central OB-receptors that control food intake. Recently, leptin messenger RNA and leptin protein have been detected in gastric epithelium and leptin was found to be released by CCK into circulation but the physiological role of this gastric leptin remains unknown. As CCK has been reported to protect gastric mucosa against various noxious agents, we designed the study to determine the influence of leptin and CCK on the gastroprotection and the control of food intake and to compare them with classic gastroprotective substance, prostaglandin E2, in rats with acute gastric mucosal lesions induced by topical application of 75% ethanol. Four series of Wistar rats (A, B, C and D) were used to determine; A) the effects of various doses of leptin (0.1-10 microg/kg) given intraperitoneally (i.p.) on ethanol-induced gastric lesions, gastric blood flow (GBF) and plasma levels of immunoreactive leptin; B) the effects of various doses of CCK-8 (0.1-10 microg/kg i.p.) on ethanol-induced gastric lesions, GBF and plasma levels of leptin; C) the effects of various doses of PGE2 (12.5--100 microg/kg) given intragastrically (i.g.) on ethanol-induced gastric lesions and GBF and D) the influence of leptin, CCK and PGE2 on the intake of liquid meal in rats. Rats were anesthetized with ether 1 h after i.g. administration of 75% ethanol to measure the GBF using H2-gas clearance technique and blood samples were withdrawn for the measurement of plasma leptin levels by radioimmunoassay (RIA). Food intake was assessed in separate group of rats fasted 18 h and then fed with liquid caloric meal. Leptin, CCK and PGE2 reduced dose-dependently gastric lesions induced by 75% ethanol, the dose reducing these lesions by 50% (ED50) being, respectively, 1 microg/kg, 5 microg/kg and 20 microg/kg. The protective effects of leptin, CCK-8 and PGE2 were accompanied by significant attenuation of the fall of the GBF caused by ethanol. Leptin and CCK reduced also dose-dependently the food intake while PGE2 was not effective. Leptin and CCK resulted a dose-dependent increment in the plasma leptin levels. We conclude that: 1) exogenous leptin and CCK, causing similar increments in plasma immunoreactive leptin levels, protect dose-dependently gastric mucosa against the damage provoked by 75% ethanol; 2) Leptin and CCK afford similar gastroprotective activity to that attained with PGE2 but unlike PGE2 were highly effective in the reduction in food intake and 3) the protective effects of leptin, CCK and PGE2 were accompanied by significant increase of GBF suggesting that the protection afforded by these substances are mediated, at least in part, by gastric hyperemia.     

Interaction of serotonin and cholecystokinin in the lateral parabrachial nucleus to control sodium intake

Serotonin [5-hydroxytryptamine (5-HT)] and CCK injected into the lateral parabrachial nucleus (LPBN) inhibit NaCl and water intake. In this study, we investigated interactions between 5-HT and CCK into the LPBN to control water and NaCl intake. Male Holtzman rats with cannulas implanted bilaterally in the LPBN were treated with furosemide + captopril to induce water and NaCl intake. Bilateral LPBN injections of high doses of the 5-HT antagonist methysergide (4 microg) or the CCK antagonist proglumide (50 microg), alone or combined, produced similar increases in water and 1.8% NaCl intake. Low doses of methysergide (0.5 microg) + proglumide (20 microg) produced greater increases in NaCl intake than when they were injected alone. The 5-HT(2a/2c) agonist 2,5-dimetoxy-4-iodoamphetamine hydrobromide (DOI; 5 microg) into the LPBN reduced water and NaCl intake. After proglumide (50 microg) + DOI treatment, the intake was not different from vehicle treatment. CCK-8 (1 microg) alone produced no effect. CCK-8 combined with methysergide (4 microg) reduced the effect of methysergide on NaCl intake. The data suggest that functional interactions between 5-HT and CCK in the LPBN may be important for exerting inhibitory control of NaCl intake.     

The role of cholecystokinin octapeptide in the central control of food intake in the dog

Cholecystokinin octapeptide (CCK-8, 1, 190 pmol/5 min) decreased food intake and water consumption in two models of ingestive behavior, i.e., food deprivation-induced feeding and insulin-induced feeding, when administered into the third (3V) and lateral (LV) cerebral ventricles. In fasted dogs, the suppression of food intake was more prominent after 3V CCK-8, whereas intravenously administered CCK-8 was without effect. Neuropeptide Y (NPY, 1, 190 pmol) had no significant stimulatory effect on food intake and water consumption in fasted as well as satiated dogs, and actually reduced both food and water intake in insulin-treated dogs. There was a slight but significant decrease in food and water intake after 275 nmol naloxone administration in both feeding models, and some of the dogs vomited. In insulin-treated animals, CCK-8 reversed, but NPY potentiated the hypothermic phase of temperature response observed after saline administration, whereas naloxone failed to alter rectal temperature. These results suggest that the effect of CCK-8 on feeding seems to involve central mechanisms in the dog, and that the mechanisms by which CCK-8, NPY and naloxone affect feeding behavior are different.     

Effect of cholecystokinin receptor antagonists on voluntary food intake in chickens

The effect of two cholecystokinin (CCK) receptor antagonists (L-364718 and L-365260) and of diazepam on voluntary food intake in chicken was studied. L-365260 significantly increased cumulative food intake at 30 and 60 min, whereas L-364718 had no effect. Diazepam also increased food intake at 30 minutes. It was therefore concluded that anxiolytic effects could account for an increase in food intake in the conditions under which the study was carried out. Consequently, the effect of L-365260 could either be due to its anxiolytic properties or to its direct effects on food intake control.     

The cholecystokinin antagonist,proglumide, increases food intake in the rat

Cholecystokinin, secreted in response to ingested food entering the duodenum, may play a role in limiting food intake. Inhibition of cholecystokinin should therefore induce an increase in food intake. Proglumide, a specific antagonist of cholecystokinin was used to block the satiety effect of a food preload in rats. A significant increase in food intake was obtained following proglumide injection, thus supporting the hypothesis that cholecystokinin, released by food in the duodenum, acts as a short-term satiety factor.     

Endogenous cholecystokinin is not a major regulator of food intake in the chicken

This study investigated whether or not endogenous cholecystokinin exerts satiety effects in chickens. After several doses (0, 1, 2 and 4 g·kg body weight^-1) of intravenous injection of caerulein, the bile flow was increased in a dose-dependent fashion. However, the pharmacological level of caerulein failed to suppress the food intake of chickens. Two potent stimulators of endogenous cholecystokinin, i.e., soybean trypsin inhibitor and phenylalanine were administered to chickens before feeding and food intake was determined over 2 h. The soybean trypsin inhibitor and phenylalanine did not alter food intake. Devazepide, a cholecystokinin-A receptor antagonist, significantly decreased amylase release from the dispersed chicken pancreatic acini stimulated by caerulein. However, devazepide did not improve food intake of the chicken. The results obtained suggest that endogenous cholecystokinin may not act as a satiety signal in chickens.Abbreviations BSA bovine serum albumin - BW body weight - CCK cholecystokinin - DVZ devazepide - Hepes N-2-Hydroxyethylpiperazine-N-2-ethanesulfonic acid - i.p. intraperitoneal - i.v. intravenous - Phe phenylalanine - SBTI soybean trypsin inhibitor - SEM standard errors of means     

Comparative effects of amylin and cholecystokinin on food intake and gastric emptying in rats

CCK is a physiological inhibitor of gastric emptying and food intake. The pancreatic peptide amylin exerts similar actions, yet its physiological importance is uncertain. Objectives were to compare the dose-dependent effects of intravenous infusion of amylin and CCK-8 on gastric emptying and food intake in rats, and to assess whether physiological doses of amylin are effective. Amylin and CCK-8 inhibited gastric emptying with mean effective doses (ED(50)s) of 3 and 35 pmol x kg(-1) x min(-1) and maximal inhibitions of 60 and 65%, respectively. Amylin and CCK-8 inhibited food intake with ED(50)s of 8 and 14 pmol x kg(-1) x min(-1) and maximal inhibitions of 78 and 69%, respectively. The minimal effective amylin dose for each effect was 1 pmol x kg(-1) x min(-1). Our previous work suggests that this dose increases plasma amylin by an amount comparable to that produced by a meal. These results support the hypothesis that amylin acts as a hormonal signal to the brain to inhibit gastric emptying and food intake and that amylin produces satiety in part through inhibition of gastric emptying.     

The inhibition of tail-pinch-induced food intake by cholecystokinin octapeptides and their fragments

The effects of intraperitoneally (ip.) and intracerebroventricularly (icv.) administered sulfated and nonsulfated cholecystokinin octapeptide (CCK-8-SE and CCK-8-NS) and their N- and C-terminal fragments on the tail-pinch-induced feeding behavior of rats were investigated. After ip. administration, only CCK-8-SE inhibited tail-pinch-induced food intake. After icv. administration, both CCK-8-SE and CCK-8-NS, in doses of 800 pmole/rat, reduced the amount of food eaten. Of the CCK fragments tested icv., the sulfated N-terminal fragments, the middle portion of the CCK-8-sequence (the CCK-3-6 fragment), and the C-terminal tetrapeptide depressed the food intake of rats during tail-pinch, whereas the C-terminal tripeptide significantly increased it. The results suggest that CCK peptides inhibit tail-pinch-induced feeding by separate mechanisms, depending on the route of administration.     

The hormonal control of food intake

Numerous circulating peptides and steroids produced in the body influence appetite through their actions on the hypothalamus, the brain stem, and the autonomic nervous system. These hormones come from three major sites-fat cells, the gastrointestinal tract, and the pancreas. In this Review we provide a synthesis of recent evidence concerning the actions of these hormones on food intake.     

The effect of vagotomy on the increase in food intake induced by the cholecystokinin antagonist, proglumide

Cholecystokinin, secreted when ingested food enters the duodenum, may act as a satiety factor. Injection of proglumide, a specific antagonist of cholecystokinin, induced an increase in food intake. The satiety effect of administered cholecystokinin is abolished by bilateral subdiaphragmatic vagotomy. If endogenous and exogenous cholecystokinin act via the same mechanism, then vagotomy should abolish the proglumide-induced increase in food intake. Proglumide was used to block the satiety effect of a food preload in sham-operated and vagotomized rats. Proglumide induced an increase in food intake in sham-operated rats confirming earlier results. No change in meal size was observed in vagotomized rats following proglumide injection. These results suggest that vagotomy abolishes the effect of endogenous cholecystokinin on food intake. However, evidence of dumping in vagotomized rats prevents the interpretation of the data as a direct vagal involvement in endogenous CCK-induced satiety.     

Reduction of food intake by cholecystokinin requires activation of hindbrain NMDA-type glutamate receptors

Intraperitoneal injection of CCK reduces food intake and triggers a behavioral pattern similar to natural satiation. Reduction of food intake by CCK is mediated by vagal afferents that innervate the stomach and small intestine. These afferents synapse in the hindbrain nucleus of the solitary tract (NTS) where gastrointestinal satiation signals are processed. Previously, we demonstrated that intraperitoneal (IP) administration of either competitive or noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonists attenuates reduction of food intake by CCK. However, because vagal afferents themselves express NMDA receptors at both central and peripheral endings, our results did not speak to the question of whether NMDA receptors in the brain play an essential role in reduction of feeding by CCK. We hypothesized that activation of NMDA receptors in the NTS is necessary for reduction of food intake by CCK. To test this hypothesis, we measured food intake following IP CCK, subsequent to NMDA receptor antagonist injections into the fourth ventricle, directly into the NTS or subcutaneously. We found that either fourth-ventricle or NTS injection of the noncompetitive NMDA receptor antagonist MK-801 was sufficient to inhibit CCK-induced reduction of feeding, while the same antagonist doses injected subcutaneously did not. Similarly fourth ventricle injection of d-3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphoric acid (d-CPPene), a competitive NMDA receptor antagonist, also blocked reduction of food intake following IP CCK. Finally, d-CPPene injected into the fourth ventricle attenuated CCK-induced expression of nuclear c-Fos immunoreactivity in the dorsal vagal complex. We conclude that activation of NMDA receptors in the hindbrain is necessary for the reduction of food intake by CCK. Hindbrain NMDA receptors could comprise a critical avenue for control and modulation of satiation signals to influence food intake and energy balance.     

Comparative activity of two cholecystokinin analogues with partial agonist activity: effects on food intake and brain monoamines

Two analogues of the C-terminal heptapeptide of cholecystokinin have been synthesized, in which the C-terminal phenylalanine residue has been replaced by a phenylethylester (JMV 180) or a phenylethylamide (JMV 170) group. They have been shown to present partial agonist CCK activity on pancreatic amylase release. In this study, the effects of the two peptides were investigated on food intake and brain monoamine metabolism after intraperitoneal (IP) and intracerebroventricular (ICV) administration. Neither peptide was active on feeding after IP administration but both decreased food intake after ICV injection, with a slightly higher potency for JMV 170. JMV 180 induced no change in monoamine metabolism whatever the route of administration. JMV 170 IP decreased cortical levels of dopamine and its metabolites. This effect was stronger after ICV injection and was accompanied by changes in serotonergic metabolism in the hypothalamus and cortex. Contrary to CCK8 S, which is more active on feeding after peripheral injection, the feeding effects of the analogues obtained by modification of the C-terminal phenylalanine residue appear to involve a central site of action. Furthermore, phenylethylamide substitution (JMV 170) gives rise to greater potency on monoaminergic variations than replacement with a phenylethylester (JMV 180) and the effect is enhanced following central administration.     

Effects of selective cholecystokinin antagonists L364,718 and L365,260 on food intake in rats

The selective type A and B cholecystokinin (CCK) receptor antagonists L364,718 and L365,260 were used to identify the receptor subtype that mediates the satiety effect of endogenous CCK. Male rats (n = 12–13/group), fed ground rat chow ad lib, received L364,718 (0, 1, 10, 100, or 1000 μg/kg IP) or L365,260 (0, 0.1, 1, 10, 100, 1000, or 10,000 μg/kg IP) 2 h after lights off, and food intake was measured 1.5, 3.5, and 5.5 h later. L364,718 significantly stimulated 1.5-h food intake by more than 40% at 10 μg/kg and higher doses; cumulative intake at 3.5 and 5.5 h remained elevated by about 20% at 1000 and 100 μg/kg of L364,718, respectively. In contrast, L365,260 had no significant stimulatory effect on feeding at any dose. The potency of L365,260 for antagonizing gastrin-stimulated gastric acid secretion was examined in unanesthetized rats. Male rats (n = 14), prepared with gastric and jugular vein cannulas, received doubling doses of gastrin (G-17I) (0.16–5 nmol/kg/h IV), each dose for 30 min, and gastric juice was collected for each 30-min period. G-17I stimulated gastric acid output dose dependently; the minimal effective dose was 0.16 nmol/kg/h, while maximal output (5-fold above basal) occurred at 5 nmol/kg/h. L365,260 (0, 1, 10, 100, 1000, or 10,000 μg/kg IV), administered 30 min before continuous infusion of G-17I (1.25 or 5 nmol/kg/h), significantly inhibited acid output only at 10,000 μg/kg; cumulative 60-min output was decreased by 60%. These results suggest that CCK acts at CCK-A receptors to produce satiety during the dark period in ad lib-feeding rats.     

The effect of cholecystokinin in controlling appetite and food intake in humans.

The present review of the satiating effect of cholecystokinin in humans has revealed that cholecystokinin is a physiological satiety factor in humans. The results demonstrate the efficacy of the satiating actions of exogenous and endogenous CCK in humans. The therapeutic potential of CCK analogues cannot be estimated until further studies are performed that demonstrate the efficacy of CCK analogues for decreasing body weight, and the safety of CCK when administered repetitively for prolonged periods.     

Regulation of the human apolipoprotein AIV gene expression in transgenic mice

The apolipoprotein (Apo) AI-CIII-AIV gene cluster has a complex pattern of gene expression that is modulated by both gene- and cluster-specific cis-acting elements. In particular the regulation of Apo AIV expression has been previously studied in vivo and in vitro including several transgenic mouse lines but a complete, consistent picture of the tissue-specific controls is still missing. We have analysed the role of the Apo AIV 3' flanking sequences in the regulation of gene expression using both in vitro and in vivo systems including three lines of transgenic mice. The transgene consisted of a human fragment containing 7 kb of the 5' flanking region, the Apo AIV gene itself and 6 kb of the 3' flanking region (-7+6 Apo AIV). Accurate analysis of the Apo AIV mRNA levels using quantitative PCR and Northern blots showed that the 7+6 kb Apo AIV fragment confers liver-specific regulation in that the human Apo AIV transgene is expressed at approximately the same level as the endogenous mouse Apo AIV gene. In contrast, the intestinal regulation of the transgene did not follow, the pattern observed with the endogenous gene although it produced a much higher intestinal expression following the accepted human pattern. Therefore, this animal model provides an excellent substrate to design therapeutic protocols for those metabolic derangements that may benefit from variations in Apo AIV levels and its anti-atherogenic effect.     

Mechanism of actions of cholecystokinin octapeptide on food intake and insulin and pancreatic polypeptide release in the dog

We investigated the mechanism by which CCK-8 injected into the third cerebral ventricle (ITV administration) inhibits food intake and stimulates insulin and pancreatic polypeptide (PP) secretion in the dog. ITV administration of CCK-8 (4.08 micrograms/5 min) resulted in a significant elevation of plasma insulin and PP concentrations. This effect was abolished by truncal vagotomy and promptly inhibited by ITV administration of atropine (20 micrograms) and proglumide (10 mg). CCK-8 was less effective in increasing insulin and PP concentrations than in reducing feeding. Thus, 1.36 micrograms of ITV CCK-8 markedly reduced food intake to 14, 15, 29 and 31% of control values at 10, 30, 60 and 120 min, respectively. Atropine and naloxone (50 micrograms) had no blocking effect on CCK-8-induced satiety, whereas proglumide antagonized it. These results indicate that ITV CCK-8 effects the endocrine pancreas and food intake through atropine-sensitive and atropine-insensitive mechanisms, respectively, both of which are likely to be mediated by CNS CCK receptors. Intravenous CCK-8 also stimulated PP and insulin release, through mechanisms that were atropine-sensitive and atropine-insensitive, respectively. However, its mode of action, especially on insulin secretion, was quite different from that of ITV CCK-8. Therefore, exogenous CCK appears to act in the brain and the periphery in concert with and independently from cholinergic systems.