Proglumide fails to increase food intake after an ingested preload

Proglumide, a selective antagonist of exogenous cholecystokinin in vitro, also inhibits the reduction of food intake induced by the systemic administration of cholecystokinin octapeptide (CCK-8) in food deprived rats. On the basis of an increase in the size of a brief test meal which followed an oral preload and treatment with a single dose of proglumide, it was suggested that a role for endogenous cholecystokinin in satiety had been demonstrated. We attempted to replicate this finding and could not under very similar experimental conditions. Subsequently, we tested whether other proglumide doses would antagonize the satiating effect of a larger oral preload on test meal intake. When these results were also found to be negative, we confirmed that proglumide (at several doses) significantly antagonized the reduction in food intake induced by exogenous CCK-8 under our conditions. Since proglumide antagonized the satiating effect of exogenous CCK-8, but did not increase food intake after oral preloads that were presumed to release endogenous CCK, we conclude that a reliable satiating effect of endogenous CCK remains to be demonstrated.     

The effects of proglumide on cholecystokinin-, bombesin-, and glucagon-induced satiety in the rat

Intraperitoneal (IP) administration of the glutaramic acid derivative proglumide inhibited satiety induced by all IP doses of cholecystokinin octapeptide (CCK-OP) in 3-hour food-deprived intact rats. Proglumide did not influence satiety when administered alone and did not inhibit satiety induced by IP glucagon. While proglumide did not inhibit satiety induced by low doses of IP bombesin, it partially and significantly inhibited the satiety effects produced by high doses of this peptide. Since bombesin is a known secretagogue for CCK in several species, these results indicate that while bombesin and CCK act independently to induce satiety, the effect induced by high doses of bombesin is mediated, in part, by the release of endogenous CCK or a structurally related peptide. Furthermore, these results illustrate that proglumide is a specific antagonist of CCK-induced satiety and is, therefore, a potentially useful tool for investigating the physiologic role of this peptide in the control of food intake.     

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.     

Abdominal vagotomy does not block the satiety effect of bombesin in the rat

Bombesin (2-16 microgram-kg-1, intraperitoneally) inhibited food intake in rats after abdominal vagotomy. Since the same vagotomized rats did not respond to the octapeptide of cholecystokinin (1-8 micrograms-kg-1, intraperitoneally), these data are decisive evidence (1) that bombesin does not produce satiety by releasing endogenous cholecystokinin and (2) that vagal afferents are not necessary for the satiety effect of bombesin.     

Circulating GLP-1 and CCK-8 reduce food intake by capsaicin-insensitive, nonvagal mechanisms

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.     

Inhibition of satiety by a cholecystokinin antagonist is independent of gastric emptying

The ability of a cholecystokinin antagonist Proglumide to inhibit satiety induced by intraperitoneal injections of cholecystokinin octapeptide (CCK-OP) and bombesin was examined in rats equipped with chronic gastric cannulae. Both CCK-OP and bombesin significantly suppressed sham feeding. Proglumide administered alone did not alter sham feeding but it abolished the suppression of feeding induced by CCK-OP. In contrast, Proglumide did not inhibit the effect of a low dose of bombesin, but partially inhibited satiety induced by a high dose of bombesin, thus confirming our previous findings. These results indicate that the effect of Proglumide is independent of its recently described effects on gastric emptying in rat.     

The endogenous CCK mediation of electroacupuncture stimulation-induced satiety in rats

A major satiety hormone, cholecystokinin (CCK) is well known to be released by electroacupuncture (EA) stimulation at certain body sites which elicits profound psychophysiological responses. Previous clinical and animal studies have shown that EA stimulation reduces food intake and body weight in both normal and obese subjects. The aim of the present study was to elucidate the satiety effect of EA stimulation and its mechanism related to CCK in rats. Here we show that EA stimulation at "Zusanli" (ST36) acupoint significantly reduced 30-min and 60-min food intake in 48-h fasted Sprague-Dawley rats, and such effect was reversed by a lorglumide (CCK-1 receptor antagonist, 10mg/kg, i.p.) pretreatment. The ST36 EA stimulation-induced satiety was not observed in CCK-1 receptor knockout, Otsuka Long-Evans Tokushima Fatty rats, but in their controls, Long-Evans Tokushima Otsuka rats. Subdiaphragmatic vagotomy also blocked the satiety effect of ST36 EA stimulation in Sprague-Dawley rats. These results suggest that ST36 EA stimulation elicits satiety in rats and this is mediated by the endogenous CCK signaling pathway.     

Central and peripheral proglumide administration and cholecystokinin-induced satiety

Peripheral (50 mg/ml) or central (50 micrograms/microliter) injections of proglumide were made into Sprague-Dawley rats which displayed satiety-like responses after the peripheral (100 micrograms/kg) or central (50 ng in 1 microliter) administration of cholecystokinin (CCK). The satiety produced by CCK injection into the lateral hypothalamus, area postraema and ventromedial hypothalamus was significantly reversed by proglumide injections into these areas during a 4 h food intake test. Peripheral injection of proglumide after central or peripheral CCK injection did not modify this type of CCK-induced satiety. Central proglumide injection produced a reliable decrease in water intake and this is compatible with previous findings which describe the stimulation of water intake after central gastrin administration. These results suggest that various central and peripheral mechanisms which are involved in the regulation of appetite may function independently as a 'failsafe' system.     

Gut peptides and food in the gut produce similar satiety effects

We compared the satiety effects and mechanisms of action of food stimuli delivered to anatomically restricted areas of the gut with the satiety effects and mechanisms of action of the gut peptides cholecystokinin (CCK) and bombesin (BBS). When food is limited to contact with the pregastric and gastric gut surfaces at a test meal, rats stop eating and display the fixed sequence of postprandial behaviors which characterizes normal satiety. This “gastric satiety” effect is unaffected by total abdominal vagotomy. Intraperitoneal administration of BBS produces a large, specific, and dose-related inhibition of food intake at a test meal; this action, like the gastric satiety effect of food, is unaffected by total abdominal vagotomy. Since a BBS-like peptide is present in high concentration in the stomach, these parallels between gastric satiety and BBS-induced satiety suggest that an endogenous BBS-like peptide plays a role in gastric satiety. When small amounts of food are infused directly into the small intestine of sham feeding rats, they stop eating and display the behavioral satiety sequence. This “intestinal satiety” effect requires the synergistic input of oropharyngeal food stimulation in close temporal association. Intraperitoneal administration of CCK alone to sham feeding rats stops eating and elicits the behavioral satiety sequence; this action, like the intestinal satiety effect of food, requires the synergistic input of oropharyngeal food stimulation in close temporal association. Since CCK is present in high concentration in the upper small intestine, and is released into the circulation by food at this site, the parallels between intestinal satiety and CCK-induced satiety suggest that endogenous CCK plays a role in intestinal satiety.     

The effect of vagotomy on the satiety effects of neuropeptides and naloxone

As abdominal vagotomy blocks the satiety effect of cholecystokinin-octapeptide, we felt it would be worthwhile to examine whether the satiety effect of any of the other putative satiety neuropeptides was mediated through the vagus. We confirmed that the satiety effect of peripherally administered cholecystokinin (10 micrograms/kg) was mediated through the vagus. In addition, the satiety effect of peripherally administered TRH (8 mg/kg) also was not present in vagotomized animals. Vagotomy had no effect on the satiety effects of peripherally administered bombesin, calcitonin and naloxone. Nor did vagotomy alter the satiety effect produced by central administration of bombesin, TRH, calcitonin nor naloxone.     

Ceruletide acts in the abdomen, not in the brain, to produce satiety

Ceruletide (caerulein), a decapeptide extracted from the skin of the frog, Hyla caerulea, is very similar in structure to the C-terminal octapeptide of cholecystokinin (CCK-8). Although ceruletide and CCK-8 act through similar or identical receptors to produce the same visceral effects, previous studies in the rat suggested that peripherally administered ceruletide acted directly on the ventromedial hypothalamic (VMH) area to decrease food intake, but peripherally administered CCK-8 acted at a vagally innervated abdominal site to decrease food intake. Since it is unprecedented for these two peptides to produce the same effect by acting at different sites, we investigated the site of action of ceruletide's satiety effect in the rat and compared it to the site of action of CCK-8. The major results were: (1) intraperitoneal administration of ceruletide and CCK-8 inhibited food intake, but intraventricular administration did not; (2) the satiety effect of ceruletide and CCK-8 was not changed by bilateral lesions of the VMH; and (3) the satiety effect of ceruletide and CCK-8 was abolished or markedly reduced by bilateral abdominal vagotomy. We conclude that ceruletide acts at the same vagally innervated abdominal site to produce satiety as CCK-8 does and that neither peptide acts directly on the VMH area.     

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     

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.     

Peptidergic regulation of feeding in the dog (Canis familiaris)

Although the incidence of obesity in the domesticated dog is high, few studies have investigated the regulation of food intake in this species. In the present study we investigated the response of the dog to a number of putative satiety agents including cholecystokinin (CCK), bombesin, calcitonin and naloxone. CCK significantly suppressed food intake during a scheduled fifteen minute meal in intact dogs and in dogs receiving total subdiaphragmatic vagotomies. Emesis occurred following injection of higher doses of CCK in most dogs. Bombesin and calcitonin reduced intake in both normal and vagotomized dogs, although higher doses of calcitonin were needed to significantly suppress feeding in vagotomized dogs compared with intact animals. Naloxone reduced feeding by as much as 60% in intact and vagotomized animals. Glucagon suppressed feeding in intact dogs, but not in vagotomized animals. Somatostatin and pancreatic polypeptide did not alter food intake. Thus the domesticated dog responds somewhat differently to some neuropeptides compared with the laboratory rat stressing the importance of examining the regulation of food intake across species.     

Effects of abdominal vagotomy on serum LH concentrations in female rats

Vagotomy on the morning of pro-oestrus did not prevent the pro-oestrous LH surge and rats became oestrous on the following day. However, vagotomized rats then exhibited a period of acyclicity which lasted for 20.4 +/- 1.3 (s.e.m.) days. Food intake and body weight also declined after vagotomy. During the first week after vagotomy, afternoon LH surges generally did not occur, a pattern which was similar in animals pair fed with vagotomized rats. However, pair-fed rats showed oestrous cycles while vagotomized rats were acyclic. At 7 days after vagotomy, LH surges were induced by oestradiol benzoate and progesterone treatment of ovariectomized rats. Vagotomy suppressed the post-ovariectomy increase in serum LH at 7 and 21 days after surgery. These results, combined with those of other studies, suggest impairment of LH release in vagotomized rats.     

Intraportal administration of DPP-IV inhibitor regulates insulin secretion and food intake mediated by the hepatic vagal afferent nerve in rats

Glucagon-like peptide-1 (GLP-1) stimulates insulin secretion and suppresses food intake. Recent studies indicate that the hepatic vagal afferent nerve is involved in this response. Dipeptidyl peptidase-IV (DPP-IV) inhibitor extends the half-life of endogenous GLP-1 by preventing its degradation. This study aimed to determine whether DPP-IV inhibitor-induced elevation of portal GLP-1 levels affect insulin secretion and feeding behavior via the vagal afferent nerve and hypothalamus. The effect of DPP-IV inhibitor infusion into the portal vein or peritoneum on portal and peripheral GLP-1 levels, food intake, and plasma insulin and glucose was examined in sham-operated and vagotomized male Sprague-Dawley rats. Analyses of neuronal histamine turnover and immunohistochemistry were used to identify the CNS pathway that mediated the response. Intraportal administration of the DPP-IV inhibitor significantly increased portal (but not peripheral) GLP-1 levels, increased insulin levels, and decreased glucose levels. The DPP-IV inhibitor suppressed 1- and 12- but not 24-h cumulative food intake. Intraportal infusion of the DPP-IV inhibitor increased hypothalamic neuronal histamine turnover and increased c-fos expression in several areas of the brain. These responses were blocked by vagotomy. Our results indicate that DPP-IV inhibitor-induced changes in portal but not systemic GLP-1 levels affect insulin secretion and food intake. Furthermore, our findings suggest that a neuronal pathway that includes the hepatic vagal afferent nerve and hypothalamic neuronal histamine plays an important role in the pharmacological actions of DPP-IV inhibitor.     

Loxiglumide, a CCK-A receptor antagonist, stimulates calorie intake and hunger feelings in humans

Exogenous cholecystokinin (CCK) induces early satiety when infused into humans. Whether alimentary CCK (CCK-A) receptor blockade stimulates food intake in humans is, however, uncertain. The aim of the present investigation was, therefore, to establish the effect of CCK-A receptor blockade on satiety and eating behavior in healthy volunteers. To further explore the role of endogenous CCK, the effects of the specific CCK-A receptor antagonist loxiglumide (Lox; 22 micromol. kg(-1). h(-1)) on satiety and eating behavior were investigated in healthy men and compared with saline infusions (as placebo) in a series of randomized, double-blind, placebo-controlled, crossover studies. Lox produced a slight (7%), but not significant (P = 0.104), increase in food intake that was accompanied by a modest (10%), but significant (P < 0.004), increase in calorie intake. Fluid ingestion was not affected by Lox. Subjects experienced more hunger and delayed fullness during Lox infusion than during saline infusion (P < 0.05). This study provides further evidence that CCK is an endogenous physiological satiety signal acting through CCK-A receptor-mediated mechanisms. Repeated-dose studies comparing hunger and satiety responses after CCK-A receptor blockade in healthy subjects and patients with eating disorders may help clarify the possible involvement of endogenous CCK in these conditions.     

Peptide signals regulating food intake and energy homeostasis

The adiposity hormone leptin has been shown to decrease food intake and body weight by acting on neuropeptide circuits in the hypothalamus. However, it is not clear how this primary hypothalamic action of leptin is translated into a change in food intake. We hypothesize that the behavioral effect of leptin ultimately involves the integration of neuronal responses in the forebrain with those in the nucleus tractus solitarius in the caudal brainstem, where ingestive behavior signals are received from the gastrointestinal system and the blood. One example is the peptide cholecystokinin, which is released from the gut following ingestion of a meal and acts via vagal afferent nerve fibers to activate medial nucleus tractus solitarius neurons and thereby decrease meal size. While it is established that leptin acts in the arcuate nucleus in the hypothalamus to stimulate anorexigenic neurons that inhibit food intake while simulataneously inhibiting orexigenic neurons that increase food intake, the mechanisms linking these effects with regions of the caudal brainstem that integrate cues related to meal termination are unclear. Based on an increasing body of supportive data, we hypothesize that this integration involves a pathway comprising descending projections from neurons from the paraventricular nucleus to neurons within the nucleus tractus solitarius that are activated by meal-related satiety factors. Leptin's anorexic effect comprises primarily decreased meal size, and at subthreshold doses for eliciting an effect on food intake, leptin intensifies the satiety response to circulating cholecystokinin. The location of neurons subserving the effects of intracerebroventricular administration of leptin and intraperitoneal injection of cholecystokinin on food intake has been identified by analysis of Fos expression. These studies reveal a distribution that includes the paraventricular nucleus and regions within the caudal brainstem, with the medial nucleus tractus solitarius having the most pronounced Fos expression in response to leptin and cholecystokinin, and support the hypothesis that the long-term adiposity signal leptin and the short-term satiety signal cholecystokinin act in concert to maintain body weight homeostasis.     

Effects of amylin on feeding of goldfish: interactions with CCK

In mammals, amylin (AMY) is a peptide that is secreted from the pancreas in response to a meal. AMY inhibits food intake and may also contribute to the anorectic effects of the brain-gut peptide cholecystokinin (CCK). In this study, we assessed the role of AMY in the regulation of food intake in goldfish (Carassius auratus) and its interactions with CCK. Fish were injected intraperitoneally (i.p.) with mammalian AMY and intracerebroventricularly (i.c.v.) with mammalian AMY, alone or in combination with the sulfated octapeptide CCK-8S. We also assessed the effects of i.c.v. injections of AC187, an amylin receptor antagonist on the central actions of both AMY and CCK-8S, as well as the effects of i.c.v. injections of proglumide, a CCK receptor antagonist, on the central effects of AMY. AMY injected i.p. at 100 ng/g but not 25 or 50 ng/g or i.c.v. at 10 ng/g but not 1 ng/g significantly decreased food intake as compared to saline-treated fish. Fish co-treated i.c.v. with AMY at 1 ng/g and CCK-8S at 1 ng/g had a food intake lower than that of control fish and fish treated with either 1 ng/g CCK-8S or 1 ng/g AMY, suggesting a synergy between the two systems. Whereas low i.c.v. doses of AC187 (30 ng/g) had no effect, moderate doses (50 ng/g) induced an increase in food intake, indicating a role of endogenous AMY in satiety in goldfish. Blocking central amylin receptors with i.c.v. AC187 (30 ng/g) resulted in an inhibition of both i.c.v. AMY- and CCK-induced reduction in feeding. Blocking central CCK receptors with i.c.v. proglumide (25 ng/g) resulted in an inhibition of both i.c.v. CCK-induced and AMY-induced decrease in food intake. Our results show for the first time in fish that AMY is a potent anorexigenic factor and that its actions are interdependent with those of CCK.     

Abdominal vagal mediation of the satiety effects of CCK in rats

CCK type 1 (CCK1) receptor antagonists differing in blood-brain barrier permeability were used to test the hypothesis that satiety is mediated in part by CCK action at CCK1 receptors on vagal sensory nerves innervating the small intestine. Devazepide penetrates the blood-brain barrier; A-70104, the dicyclohexylammonium salt of N alpha-3-quinolinoyl-D-Glu-N,N-dipentylamide, does not. At dark onset, non-food-deprived control rats and rats with subdiaphragmatic vagotomies received a bolus injection of devazepide (2.5 micromol/kg i.v.) or a 3-h infusion of A-70104 (3 micromol.kg(-1).h(-1) i.v.) either alone or coadministered with a 2-h intragastric infusion of peptone (0.75 or 1 g/h). Food intake was determined from continuous computer recordings of changes in food bowl weight. In control rats both antagonists stimulated food intake and attenuated the anorexic response to intragastric infusion of peptone. In contrast, only devazepide was effective in stimulating food intake in vagotomized rats. Thus endogenous CCK appears to act both at CCK1 receptors beyond the blood-brain barrier and by a CCK1 receptor-mediated mechanism involving abdominal vagal nerves to inhibit food intake.