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

Medium-chain triglycerides inhibit long-chain triglyceride-induced GIP secretion through GPR120-dependent inhibition of CCK

Long-chain triglycerides (LCTs) intake strongly stimulates GIP secretion from enteroendocrine K cells and induces obesity and insulin resistance partly due to GIP hypersecretion. In this study, we found that medium-chain triglycerides (MCTs) inhibit GIP secretion after single LCT ingestion and clarified the mechanism underlying MCT-induced inhibition of GIP secretion. MCTs reduced the CCK effect after single LCT ingestion in wild-type (WT) mice, and a CCK agonist completely reversed MCT-induced inhibition of GIP secretion. In vitro studies showed that medium-chain fatty acids (MCFAs) inhibit long-chain fatty acid (LCFA)-stimulated CCK secretion and increase in intracellular Ca²⁺ concentrations through inhibition of GPR120 signaling. Long-term administration of MCTs reduced obesity and insulin resistance in high-LCT diet-fed WT mice, but not in high-LCT diet-fed GIP-knockout mice. Thus, MCT-induced inhibition of GIP hypersecretion reduces obesity and insulin resistance under high-LCT diet feeding condition.

The rôle of the gastrointestinal tract in the control of voluntary food intake

The short-term regulation of intake is thought to be achieved at least in part by signals from the gastrointestinal tract. Infusions of glucose, protein hydrolysate or emulsified fat into the stomach, and of glucose or protein hydrolysate into the duodenum, jejunum or ileum caused pigs to reduce their intake to compensate approximately for the energy infused, probably through the regulation of gastric emptying. Protein or protein hydrolysate infusions also caused a long-term inhibition of intake for 30 h by up to three times the energy infused. During feeding gastric emptying occurred at a constant rate of calories, the rate increasing linearly with body weight; duodenal infusion of glucose slowed gastric emptying to compensate for the infused energy and satiety occurred at a reduced food intake but at the same stomach volume. Duodenal infusion of emulsified fat caused a greater than caloric inhibition of intake, which was blocked by the cholecystokinin (CCK) antagonist L-364,718 and appeared to be mediated through a mono-glyceride-induced CCK release. Emulsified fat infused into the duodenum slowed gastric emptying by more than the energy infused and the gastric volume at satiety was decreased suggesting that the effects of fats on intake are possibly independent of gastric emptying. Since L-364,718 did not increase intake on a normal diet (186 g protein, 20 g fat per kg), CCK may only contribute to satiety in pigs eating high-fat diets.

Postprandial Cholecystokinin Secretion in Elderly with Protein-Energy Undernutrition

OBJECTIVE

Malnutrition is currently observed in aged people, and cholecystokinin is an important peripheral satiety signal. The aim of this study was to examine the effect of aging and protein-energy malnutrition on postprandial cholecystokinin (CCK) release.

DESIGN

Non-randomized, cross-sectional comparison by age group.

SETTING

Gastroenterology section of a teaching hospital.

PARTICIPANTS

Twenty-one human volunteers divided into three groups: young healthy subjects (Group 1: mean 29 years, n = 7), aged healthy subjects (Group 2, mean 80 years, n = 7), and aged subjects with an important degree of malnutrition (Group 3, mean 84.6 years, n = 7).

INTERVENTION

Each subject ingested a standardized liquid meal after an overnight fast.

MAIN OUTCOME MEASURES

Plasma cholecystokinin was measured using a sensitive bioassay before and after the ingestion of the liquid meal.

RESULTS

Basal cholecystokinin levels were similar (0.9 to 1 pM equivalent CCK-8) in the three groups. Postprandial levels were significantly increased over basal (P less than 0.05). The maximal cholecystokinin value was lower in Group 1 (3.5 +/- 0.8 pM equivalent CCK-8) and Group 2 (3.3 +/- 0.77 pM equivalent CCK-8) than in Group 3 (8.3 +/- 2 pM equivalent CCK-8) (P less than 0.05). Integrated plasma cholecystokinin was also similar in Group 1 (171 +/- 38 pM.60 min), (P less than 0.05).

CONCLUSION

The increase of postprandial maximal levels of cholecystokinin is more related to malnutrition than to aging.

Characterization of the feeding inhibition and neural activation produced by dorsomedial hypothalamic cholecystokinin administration

Within the dorsomedial hypothalamus (DMH), cholecystokinin (CCK) has been proposed to modulate neuropeptide Y (NPY) signaling to affect food intake. However, the neural circuitry underlying the actions of this CCK-NPY signaling system in the controls of food intake has yet to be determined. We sought to characterize the feeding inhibition and brain neural activation produced by CCK administration into the DMH of rats. We determined the time course of feeding inhibitory effects of exogenous DMH CCK, assessed NPY gene expression in the DMH in response to DMH CCK administration, and characterized c-Fos activation in the entire brain induced by CCK injection into the DMH using c-Fos like immunohistochemistry. We found that parenchymal injection of CCK into the DMH decreased food intake during the entire 22 h observation period, with a primary effect in the first 4 h, and down-regulated NPY gene expression in the DMH. c-Fos immunohistochemistry revealed that DMH CCK increased the number of c-Fos positive cells in the paraventricular nucleus (PVN), arcuate nucleus, suprachiasmatic nucleus and retrochiasmatic area as well as in the contralateral DMH. This pattern of activity is different from that produced by peripherally administered CCK which is short acting and primarily activates neurons in the nucleus of the solitary tract and area postrema, as well as the PVN and DMH. Together, these data suggest that DMH CCK plays an important role in the control of food intake, and does so by activating different pathways from those activated by peripheral CCK.

Independent ingestion and microstructure of feeding patterns in infant rats lacking CCK-1 receptors

Otsuka Long-Evans Tokushima fatty (OLETF) rats are a strain of Long-Evans Tokushima Otsuka (LETO) rats that do not express CCK-1 receptors, developing in adulthood, hyperphagia, obesity, and non-insulin-dependent diabetes mellitus (NIDDM). We examined weight gain and meal patterns during a 30-min independent ingestion test on postnatal days 2-4 and again on days 9-11 in OLETF and LETO rat pups. OLETF pups were significantly heavier compared with their LETO controls at both ages, and they consumed significantly more of the sweet milk diet. The difference in intake can be attributed to a significant increase in meal size and duration. Number of clusters and bursts of licking within a meal were greater in OLETF rat pups, with no difference between strains in burst and cluster size. Interlick interval (ILI) was not significantly different between OLETF and LETO pups. This measure decreased on days 9-11 compared with days 2-4 in both strains. Latency to start feeding was significantly shorter on days 2-4 in OLETF vs. LETO pups, but this difference disappeared at the second test at the older age. Two- to four-day-old OLETF pups consumed a larger volume of milk during the first minute of feeding, and their initial lick rate and decay of lick rate were significantly larger compared with their LETO controls. Lack of CCK-1 receptors, or other OLETF-related abnormalities, therefore, resulted in a satiation deficit, leading to increased meal size, hyperphagia, and increased weight gain as early as 2-4 postnatal days.

Gut peptides in the control of food intake: 30 years of ideas

The demonstration of the ability of exogenous cholecystokinin (CCK) to inhibit food intake began a series of investigations into whether and how gut and brain peptides affected ingestive behavior. In that original demonstration, Gerry Smith and colleagues both established criteria for evaluating roles for gut peptides in food intake and shifted the focus of feeding controls to factors that contribute to limiting meal size. Although new gut peptides with novel mechanisms and durations of action have been identified in the past few years, Smith's criteria and his distinction between direct and indirect controls of meal size continue to provide a framework for understanding how such peptides may contribute to overall feeding control.

Differential roles for cholecystokinin a receptors in energy balance in rats and mice

Although cholecystokinin A (CCK-A) receptors (CCK-AR) mediate the feeding inhibitory actions of CCK in both rats and mice, the absence of CCK-AR results in species-specific phenotypes. The lack of CCK-AR in Otsuka Long-Evans Tokushima fatty (OLETF) rats results in hyperphagia and obesity. We have suggested that demonstrated increases in meal size and elevated levels of dorsomedial hypothalamic (DMH) neuropeptide Y (NPY) gene expression may contribute to this phenotype. In contrast to OLETF rats, CCK-AR(-/-) mice have normal total daily food intake and do not develop obesity. To assess the basis underlying the different phenotypes in rats and mice lacking CCK-AR, we characterized meal patterns in CCK-AR(-/-) mice and determined whether CCK-AR(-/-) mice exhibited an alteration in DMH NPY gene expression. We demonstrate that although CCK-AR(-/-) mice show a similar dysregulation in meal size as OLETF rats, they do not have an elevation in DMH NPY mRNA expression levels. In fact, intact mice have no CCK-AR in the DMH. Furthermore, in intact rats, NPY and CCK-AR are colocalized in DMH neurons, and parenchymal injection of CCK into the DMH reduces food intake and down-regulates DMH NPY mRNA expression. These results suggest that although CCK-AR plays a role in the mediation of CCK actions in the control of meal size in both rats and mice, CCK-AR seems to contribute to modulating DMH NPY levels only in rats. The deficit in CCK's action in the control of DMH NPY gene expression may play a major role in the obese phenotype in OLETF rats.

Effects of duodenal fat, protein or mixed-nutrient infusions on epigastric sensations during sustained gastric distension in healthy humans

Duodenal fat modulates sensory and motor responses to gastric distension and raises plasma cholecystokinin compared with glucose. The effects of protein (also releasing cholecystokinin), or mixed nutrients (with a balanced macronutrient composition), on gastrointestinal sensations in relation to gastric relaxation and plasma cholecystokinin concentrations are not known. The aim of this study was therefore to compare the effects of duodenal infusion of fat, protein or mixed nutrients during sustained gastric distension (mimicking the intragastric presence of food) on these parameters. In 10 healthy subjects, gastric distension to fullness was maintained for 90 min, while gastric volume, sensations and plasma cholecystokinin were monitored during duodenal infusion of isotonic saline or nutrients (2 kcal min-1). During saline infusion, all parameters remained unchanged for 90 min. Initially, only lipid increased plasma cholecystokinin, gastric volume and scores for sensations. Cholecystokinin and gastric volume responses to protein and mixed nutrients were delayed and not associated with significant changes in sensations. In conclusion, the intensity of gastrointestinal sensations is related to, but not entirely explained by, the magnitude in intragastric volume and plasma cholecystokinin changes. Our results offer new insights into the role of dietary nutrient composition in gastrointestinal sensations, and may have implications for the dietary management of digestive symptoms.

Food for thought: a critique on the hypothesis that endogenous cholecystokinin acts as a physiological satiety factor

This review evaluates the various lines of evidence supporting the hypothesis that cholecystokinin (CCK) released from the small intestine during feeding plays a physiological satiety. Issues considered include, the effects of systemic injection of CCK on consummatory and operant feeding, the role of the vagus nerve, the effects of CCKB receptor antagonists, and the neuroendocrine responses to exogenous CCK. A critical appraisal of this research indicates that while it is clearly demonstratable that exogenous peripheral CCK can alter food intake by acting on CCKA receptors, the mechanism involved may be more closely related to the induction if aversion and nausea, rather than satiety. With regard to peripheral endogenous CCK, the available evidence also does not seem to support a role for the hormone in satiety. In particular, it is doubtful whether plasma concentrations of CCK following a meal are sufficiently high to inhibit feeding. Moreover, CCKA receptor antagonist which do not cross the blood brain barrier fail to increase meal size, as would be expected if peripheral CCK was an effective satiety factor. In addition, the recent literature concerned with the possibility that CCK may have a direct action within the brain in the control of food intake has been reviewed. These studies show that CCK administered intracerebroventicularly, or by micoinjection into discrete brain regions, also inhibits feeding via a CCKA receptor mechanism. However, the physiological relevance of these findings have yet to be determined.

Age-dependent effects of CCK and devazepide in male and female rats

Peripheral administration of the brain/gut peptide cholecystokinin (CCK) has been demonstrated to inhibit food intake in a variety of species, and administration of the specific type A CCK receptor antagonist devazepide increases food intake in a variety of experimental paradigms. The potency of CCK to inhibit intake depends upon a variety of factors, but CCK is generally less potent under conditions of elevated food intake. At different developmental stages, rats' intake requirements differ as growth rates change. To determine whether CCK plays a variable role in the control of intake in rats of different ages, we examined the feeding-inhibitory effect of various doses of CCK and the feeding-enhancing potential of various doses of devazepide on glucose consumption (0.5 kcal/ml) in male and female rats at 45-70 and 110-130 days of age. CCK was more potent in older male and female rats than in younger rats, and inhibited intake in a dose-related fashion. In younger rats, the efficacy of CCK was attenuated and the inhibition was not dose related. Administration of devazepide had no effect on intake in younger rats of either sex, but significantly increased glucose consumption in the older rats. These data suggest that during a period of rapid growth and high levels of food intake relative to body weight, adolescent rats are relatively insensitive to exogenous CCK and endogenous CCK does not appear to play a significant role in controlling their intake.

Effects of the CCK receptor antagonist MK-329 on food intake in broiler chickens

The cholecystokinin (CCK) receptor antagonist MK-329 (previously L-364,718) was administered intraperitoneally to free-feeding broiler chickens and tested for conditioning effects using the colored food paradigm. The 8.0, 16.0, and 32.0 micrograms/kg doses of MK-329 did not exert any effect on food intake and failed to condition a color preference or aversion. When higher doses were used (90, 180, and 360 micrograms/kg) MK-329 caused a significant increase in food intake during the 2-h test period. Intravenously injected MK-329 (70, 140, and 280 micrograms/kg) produced an increase in food intake, with maximum increases occurring at a dose of 70 micrograms/kg. CCK (14 micrograms/kg) caused a reduction in feeding, and this effect was not blocked by pretreatment with intraperitoneal injection of MK-329 (32, 90, 180, and 360 micrograms/kg). The results question the role of endogenous CCK in satiety in chickens.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Voluntary intake and gastric emptying in pigs: effects of fat and a CCK inhibitor

The influence of the cholecystokinin (CCK) antagonist MK-329 (0.1 mg/kg) on short-term control of voluntary food intake and gastric emptying was studied in five pigs. Arterial injection of MK-329 abolished the inhibition of intake resulting from duodenal infusion of emulsified fat (Intralipid, 24 g/h). However, MK-329 only reduced the inhibition of dry matter (DM) and liquid emptying, and hence increased stomach volume at satiety. Intralipid infusion decreased the rise in gastric pressure during feeding. All these changes are consistent with endogenous CCK, released by Intralipid, inhibiting intake independent of the concomitant slowing of gastric emptying. MK-329 alone significantly increased intake using two different diets, but had no effect on gastric emptying so that gastric volume at satiety was significantly increased. These results suggest that endogenous CCK may be part of short-term satiety control in the pig.

Cholecystokinin antagonist and lipid intake as a function of caloric density and familiarity

The effect of treatment with the cholecystokinin antagonist L364,718 on intake of different dilutions of corn oil emulsion was tested under two levels of familiarity with the oil emulsion. No increase in intake was observed. To see if the CCK antagonist was effective under our conditions, exogenous CCK was administered under the same conditions. A complete suppression of the large reduction produced by CCK on intake was found.

Increased food intake after type A but not type B cholecystokinin receptor blockade

To assess the role of cholecystokinin (CCK) receptors in mediating the satiating effect of an oral preload, overnight food-deprived rats (n = 7) were given access to a high-carbohydrate liquid diet for 40 min. At the end of 40 min, food was removed and rats were injected subcutaneously (SC) with devazepide (DVZ; 1 ng/kg-1 mg/kg), an antagonist selective for the CCK-A receptor, or its vehicle, 0.5% carboxymethylcellulose (CMC). Thirty min after injection, rats were given access to the same liquid food for 60 min. DVZ increased food intake significantly. Furthermore, the effectiveness of a very low dose of DVZ (10 ng/kg) is strong evidence that the effect of DVZ was specific for CCK-A receptors. Three of the rats that increased food intake after DVZ were also tested with L-365,260, an antagonist selective for the CCK-B receptor (10 ng/kg-100 micrograms/kg). L365,260 did not increase food intake significantly. These results confirm and extend previous reports that CCK-A receptor blockade increases food intake after an oral preload. They do not, however, demonstrate a role for the CCK-B receptor in mediating the satiating effect of ingested food under the same experimental conditions.

Disturbed cholecystokinin secretion in patients with eating disorders

It has been shown that the gastrointestinal hormone cholecystokinin (CCK) induces satiety and reduces food intake in laboratory animals and humans. In the light of this evidence we studied CCK release in patients suffering from eating disorders. The secretion of CCK into the general circulation was measured in 10 anorectic, in 7 bulimic patients, and in 8 healthy controls before and after a high-caloric liquid testmeal. Baseline CCK values were similar in controls (0.6 +/- 0.2 pmol/l) and bulimics (0.6 +/- 0.1 pmol/l) and were significantly increased in the anorectic group (1.8 +/- 0.4 pmol/l) (p less than or equal to 0.005). After eating peak plasma levels increased to 6.1 +/- 0.9 pmol/l in the anorectic, to 3.8 +/- 0.5 pmol/l in the bulimic and to 2.7 +/- 0.6 pmol/l in the control group. All postprandial CCK values were significantly higher in the anorectic group. The secretion of CCK-8-S, an important peptide in the CCK family, was significantly elevated, too. This disturbed CCK secretion in patients suffering from anorexia nervosa, even if it is a secondary, diet-induced defect, may perpetuate this disorder.

Multiple cholecystokinin (CCK) receptors and CCK-monoamine interactions are instrumental in the control of feeding

Almost two decades ago, exogenous cholecystokinin (CCK) was shown to suppress food consumption in rats. Since then, CCK has been detected not only in peripheral tissue but extensively throughout the central nervous system. Furthermore, specific CCK receptors have been described, and a distinction drawn between CCK-A and CCK-B receptors. Recently, potent, orally active CCK antagonists, which show a high degree of selectivity for either CCK-A or CCK-B receptors, have been introduced. The present report reviews recent evidence obtained in studies using devazepide (a selective CCK-A receptor antagonist) and L-365,260 (a selective CCK-B/gastrin receptor antagonist). Both compounds increased food consumption and postponed the onset of satiety in well-satiated rats. L-365,260 was more potent, suggesting that central CCK-B type receptors may mediate the satiety effects of endogenously released CCK. Only devazepide was effective in blocking the feeding-suppressant effect of exogenous CCK, indicating that CCK-A type receptors mediate this effect. In a second series of studies, devazepide but not L-365,260 antagonized the anorectic effect of either d-fenfluramine or systemically administered 5-HT. Hence, CCK-A type receptors appear to be involved in the anorectic effects of these serotonergic drugs. We propose that CCK and 5-HT mechanisms involved in mediating satiety are mutually interdependent. Possible interactions between CCK and catecholaminergic mechanisms are also briefly considered.

Effects of cholecystokinin (CCK-8) on two classes of gastroduodenal vagal afferent fibre

In order to investigate the vagal afferent pathway responsible for the previously reported effects of cholecystokinin (CCK) on gastric emptying and food intake, single afferent fibres were recorded from the cervical vagus of urethane-anaesthetized ferrets. Sixty tension receptor afferents with receptive fields in the corpus, antrum, duodenum, jejunum and ileum all showed a resting level of discharge which was augmented powerfully by distension of the segment containing the ending. Close intraarterial injection of CCK-8 (100-200 pmol) caused relaxation in proximal regions, but enhanced contractile activity in more distal regions. Mechanoreceptor discharge closely followed intraluminal pressure at all times, indicating a sensitivity primarily to tension and no direct sensitivity to CCK. Only duodenal tension receptors were significantly excited by CCK (due to increased contractile activity), whereas those in the stomach showed a net decrease. Thirty-seven mucosal receptors from the corpus, antrum, duodenum and jejunum showed responses to luminal stimuli: predominantly light stroking, acidity and hypertonicity as has been previously described. No responses to glucose or amino-acid infusions could be evoked. However, mucosal fibres showed a strong sensitivity to close-intraarterially injected CCK-8 (3-200 pmol) in 19/26 fibres tested. These responses were unaffected by cholinergic blockade when tested. The data strongly suggest that in the ferret only vagal mucosal receptors are directly sensitive to CCK-8. These fibres are therefore likely candidates for mediating some of the reflex and behavioural effects of CCK when it is released from the gastrointestinal tract and acts directly on vagal sensory endings.

Reversal of the anorectic effect of (+)-fenfluramine in the rat by the selective cholecystokinin receptor antagonist MK-329

1. Experiments were conducted to determine whether or not the effect of (+)-fenfluramine (3.0 mg kg-1, i.p.) on food intake can be antagonized by the selective cholecystokinin receptor antagonist MK-239 (formerly L364,718; (3S(-)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1-H-1,4-benzodiazepin++ +-3-yl)-1H- indole-2-carboxamide). Two feeding paradigms were employed. In the first, non-deprived rats were familiarized with eating a highly palatable, sweetened mash in a 30 min test. In the second, freely-feeding rats were trained to consume powdered chow in their home-cages, and their intake was monitored over the first 6 h of the night-period. 2. In doses of 30.0 and 100.0 micrograms kg-1, s.c., MK-329 almost completely blocked the anorectic effect of (+)-fenfluramine in the palatable food intake test. These doses of MK-329 have previously been reported to antagonize the anorectic effect produced by exogenous cholecystokinin-octapeptide (CCK8) in rats. Both doses of MK-329 were also effective in significantly attenuating the anorectic effect of (+)-fenfluramine in nocturnal free-feeding animals over a 6 h-period. 3. MK-329 (10.0-100.0 micrograms kg-1, s.c.) failed to antagonize the anorectic effect of either the specific dopamine D2-receptor agonist quinpirole (0.3 mg kg-1, s.c.) or the beta-carboline FG 7142 (10.0 mg kg-1, i.p.) in the palatable food intake test. 4. MK-329 (10.0-300.Opgkg-1, s.c.) had no effect, when administered alone, on the level of palatable food intake in non-deprived rats, even when substantial satiation was produced by a pre-feeding procedure. Furthermore, MK-329 had no effect, when administered alone, on nocturnal food intake in freelyfeeding rats. 5. In conclusion, not only was MK-329 a potent antagonist of the effect of CCK8 on food intake, it also blocked the effect of (+)-fenfluramine to a significant degree. The effect of MK-329 was selective in that the anorectic effects of either quinpirole or FG 7142 remained unaffected. Administered alone, MK-329 did not affect food intake, indicating that its reversal of (+ -fenfluramine-induced anorexia was not secondary to an intrinsic hyperphagic effect. The results provide some evidence that the depressant effect of (+ )-fenfluramine on food intake depends on the activity of endogenous CCK.

Effects of the CCK receptor antagonist MK-329 on food intake in pigs

The cholecystokinin (CCK) receptor antagonist MK-329 (previously L364,718) was administered intravenously (IV) (17.5-140 micrograms/kg) to pigs trained to make operant responses for food reinforcements after 4 hr of food deprivation. MK-329 produced a dose-related increase in food intake during the 2-hr test period, with maximum increases occurring at a dose of 70 micrograms/kg. CCK (1 micrograms/kg IV) produced a short-term reduction in feeding and this effect was completely abolished by pretreating the animals with MK-329 (70 micrograms/kg). The present results lend support to the hypothesis that endogenous CCK is involved in satiety.

Postponement of satiety by blockade of brain cholecystokinin (CCK-B) receptors

Exogenous cholecystokinin (CCK) decreases food intake and causes satiety in animals and man. However, it has not been established that endogenous CCK causes satiety or whether the response is mediated by peripheral-type (CCK-A) or brain-type (CCK-B) receptors. The development of potent and selective antagonists for CCK-A (MK-329) and CCK-B (L-365,260) receptors now allows these issues to be addressed. The CCK-A antagonist MK-329 and the CCK-B antagonist L-365,260 increased food intake in partially satiated rats and postponed the onset of satiety; however, L-365,260 was 100 times more potent than MK-329 in increasing feeding and preventing satiety. These results suggest that endogenous CCK causes satiety by an agonist action on CCK-B receptors in the brain.

Duodenal infusion of fat, cholecystokinin secretion and satiety in the pig

The influence of the cholecystokinin (CCK) antagonist L-364,718 (0.1 mg/kg) on short-term control of food intake was studied in 6 pigs. Arterial injection of L-364,718 abolished the inhibition of intake to CCK octapeptide infusion (4 micrograms/kg/hr; from 42% p less than 0.001, to 97% of control intake), but did not alter control intake (99%). Injection of L-364,718 also abolished the inhibition of intake to duodenal infusion of emulsified fat (12 g/hr; from 76% p less than 0.001 to 105%) and of monoglyceride (24 g/hr; from 64% p less than 0.001 to 101%), but did not alter the inhibition to oleic acid (60 g/hr; 48% p less than 0.01 and 61% p less than 0.02), to glycerol (127 g/hr; 84% p less than 0.05 and 89%) or to glucose (144 g/hr; 78% p less than 0.02 and 69% p less than 0.001). These results suggest that monoglyceride-induced CCK secretion is mainly responsible for the satiety to duodenal fat in the pig, but that there is also a CCK-independent effect via the fatty acid. The results further indicate that intake of a normal barley-based diet (2% fat) is controlled via CCK-independent mechanisms.

The cholecystokinin receptor antagonist L364,718 increases food intake in the rat by attenuation of the action of endogenous cholecystokinin

1. To determine the role of endogenous cholecystokinin (CCK) in the regulation of food intake, the effects of the potent CCK receptor antagonist L364,718 were investigated on the intake of a palatable diet in non-deprived rats. The effect of a single dose of proglumide was also investigated for comparative purposes. In addition, the ability of L364,718 to antagonize the reduction in food intake produced by exogenous cholecystokinin-octapeptide (CCK8) or bombesin in food-deprived rats was determined. 2. L364,718 (10-100 micrograms kg-1, i.p.) increased the intake of palatable diet during the 30 min test period. Proglumide (300 mg kg-1, i.p.) also increased the intake of palatable diet. Conversely, CCK8 (0.5-5 micrograms kg-1, i.p.) produced a reduction in the intake of the diet. 3. In fasted rats, L364,718 (100 micrograms kg-1, i.p.) antagonized the reduction in food intake produced by CCK8 (10 micrograms kg-1, i.p.) but not that produced by bombesin (50 micrograms kg-1, i.p.). L364,718 did not increase food intake in these animals when measured over a 6 h period. 4. It is concluded that L364,718 is a potent, selective antagonist of the effects of CCK8 on food intake. The observation that L364,718 and proglumide increase the intake of a palatable diet provides some evidence that endogenous CCK is involved in the control of food intake in this model.

Ineffectiveness of ceruletide to reduce food intake and body weight in obese women hospitalized for weight reduction and treated with a restricted diet. A double-blind study

Ceruletide is a synthetic decapeptide closely resembling the 8-carboxy-terminal peptide of cholecystokinin (CCK-8) with which it shares several biological properties. In a double-blind study versus placebo, we evaluated the effects of ceruletide on self-rated hunger and food intake at lunch time, as well as on body weight in 14 obese women hospitalized for weight reduction and on a restricted diet. During two 6-day courses of treatment with ceruletide or placebo, ceruletide 0.3 microgram/kg b.wt. or an equivalent volume of its diluent were injected IM at 11.30 a.m., i.e., 30 min before lunch. Feelings of hunger were quantitated, using a visual analogue self-rating scale, prior to the injection of ceruletide or placebo and 30 min thereafter, i.e., just prior to the start of meal ingestion, as well as 2 hr after the start of the meal. Duration and caloric content of food ingested at lunch, as well as morning body weight, were recorded daily. Ceruletide, compared to placebo, did not significantly influence any of the above variables. However, in the first three experimental days, the increase in self-rated hunger from values before the injection to 30 min thereafter was less marked, though not significantly so (0.05 less than p less than 0.1), with ceruletide than with placebo. Thus, it appears that ceruletide, under the experimental conditions of the present study, was not effective in enhancing the patients' motivation to lose weight and to further restrict their food intake at lunch time.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of synaptic transmission in the hippocampus by cholecystokinin (CCK) and its antagonism by a CCK analog (CCK27-33)

The actions of CCK-8 and putative CCK-8 antagonists were examined on synaptic transmission in the hippocampal slice preparation. CCK-8 (10(-7) M) caused a reversible depression of postsynaptic responses of the Schaffer collateral-CA1 synapse. CCK-mediated depression was unaffected by proglumide (10(-3) M) but was antagonized by a CCK analog (CCK27-33). The CCK analog alone had an excitatory effect on synaptic transmission. These results suggest that CCK has an inhibitory action on synaptic transmission.

Different peripheral and central antagonistic activity of new glutaramic acid derivatives on satiety induced by cholecystokinin in rats

New glutaramic acid derivatives with cholecystokinin antagonistic activity were evaluated for their capacity to inhibit the satiety effect induced in the rat by intraperitoneal (i.p.) injection of cholecystokinin octapeptide (CCK-8). The most active compound, CR 1409, is about 4000 times more potent than proglumide when injected peripherally (i.p.). This compound competitively inhibits the action of CCK-8 at the receptor responsible for the satiety effect. In contrast, CR 1409, i.p. or intracerebroventricularly (i.c.v.) injected does not exhibit antagonistic effects when CCK-8 is administered i.c.v., confirming the existence of at least two different populations of CCK receptors.

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.

Intracerebroventricular injections of cholecystokinin octapeptide suppress feeding in rats--pharmacological characterization of this action

Cholecystokinin octapeptide (CCK-8), administered intracerebroventricularly (i.c.v.), will suppress feeding. The aim of the present study was to determine the pharmacological characteristics of this satiety inducing effect in rats. For this purpose, we employed a feeding bioassay model in 24 h fasted rats and examined the effects of CCK-8 and a variety of structurally related analogs on latency to feed after i.c.v. injection and on the amount of food and water consumed as measured after the initiation of feeding in sequential 20-min epochs for 1 h. CCK-8, given in doses of 0.1, 1 and 10 nmol, produced a dose-dependent increase in feeding latency and a reduction of food intake during the first 20 min after initiation of feeding. Food intake during the next 40 min and water consumption were not altered. Plasma levels of CCK-like immunoreactivity after an i.c.v. injection of a dose of CCK-8 which blocked feeding (10 nmol) rose insignificantly from 117 to 125 pg/ml. In contrast, at the minimally effective dose of CCK-8 after i.v. administration (10 nmol), which also produced an inhibition of feeding, the plasma level was 1430 pg/ml. This difference indicates that plasma levels of CCK after i.c.v. CCK-8 are not adequate to produce the observed feeding suppression and suggests that the effects of i.c.v. CCK-8 are not mediated by a peripheral redistribution. Systematic dose response studies revealed the following rank order of potencies: CCK-8 greater than or equal to G-17 II much greater than CCK-8 NS = G-17 I greater than or equal to CCK-4 = CCK 26-29 = 0. Only gastrin-17 II (sulfated) produced an effect comparably significant to CCK-8. I.c.v. proglumide at 2500 nmol failed to modify the effects of CCK-8 at 10 nmol after i.c.v. injection. These data demonstrate that the structural requirements for feeding suppressive activity in rat brain are the carboxyterminus with a sulfated tyrosine residue, located 6 to 7 residues from the carboxyterminus, as present in CCK-8 and gastrin-17 II.

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 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.

The satiety effect of cholecystokinin. Recent progress and current problems

Since the discovery of the satiety effect of CCK in 1973, progress has been made and problems have been encountered. The progress has included the accumulation of strong, indirect evidence that exogenous CCK acts in the abdomen to activate vagal afferent fibers and that exogenous CCK may be useful in the treatment of bulimia and obesity in humans. The most pressing problem is the current lack of evidence for the hypothesis that the satiety effect of exogenous CCK reveals a physiological function of endogenous CCK released by food entering the small intestine during a meal. Since clarification of this problem and exploitation of the current progress seem possible with current ideas and techniques, the satiety effect of CCK should continue to receive considerable experimental attention.

Internal signals cause large changes in food intake in one-way crossed intestines rats

Fifteen pairs of parabiotic rats had either a surgical operation in which a 15 or 30 cm segment of upper small intestine was disconnected from the digestive tract of one rat in the pair and reconnected to the transected duodenum of its partner or had control surgery. Food eaten by one rat in the pair went to the rat's own stomach, traveled through 5 cm of its upper duodenum and then crossed into the isolated segment of the partner's small intestine. After traversing the 15 or 30 cm isolated segment, the remaining unabsorbed food crossed back into the lower duodenum of the rat that fed. Food eaten by the partner went through its own digestive tract, but bypassed the isolated segment of its own upper small intestine. The operation produced a large and sustained change in food intake of both rats in a pair. For the rats with 30 cm crossed segments, the rat that lost intestinal chyme into its partner ate 3.6 times as much food as did its partner for a period of many months. At sacrifice, the rats that ate more, weighed less and had less body fat. These large changes in food intake may be caused by internal changes associated with changes in the amount of food absorbed into each rat or by differential stimulation of the lower digestive tracts. The results clearly show that there is a major internal control mechanism for the amount of food eaten.