Effects of kappa opiate agonists, cholecystokinin and bombesin on intake of diets varying in carbohydrate-to-fat ratio in rats

Lipid profile dysregulation in opium users based on Fasa PERSIAN cohort study results

One of the main health problems in many societies is the increased opium abuse, which was found to be correlated with many problems like cardiovascular disease. This study aimed to evaluate the correlation of opium use with blood lipoproteins as the risk factor of CVD. This was a cross-sectional study conducted on participants of the first phase of the PERSIAN Cohort study who were aged between 35 and 70 years old. Demographic characteristics; history of smoking, alcohol, and opium consumption; medical history; and medications were asked and the related checklists were filled out. The levels of physical activity and fat intake were also registered. As well, lipoprotein profiles were investigated by blood sampling. The linear and logistic regression was used to analyze the relationship between opium and lipid profile and the statistical significant level was considered as < 0.05. Among 9300 participants with a mean age of 48.06 ± 9.44 years old, 49.6% of them were men. About 24.1% of the participants used opium. In the linear regression models, unlike TG (β = 2.2, p = 0.36), total cholesterol (β = − 2.5, p = 0.02), LDL (β = − 2.0, p = 0.04), and HDL (β = − 1.0, p = 0.04) were significantly lower in people who used opium compared to the others. In the logistic regression models, abnormal level of LDL (OR = 0.78, p = 0.003) and total cholesterol (OR = 0.82, p = 0.008) were less in people who used opium compared to the others. This study showed that there is a correlation between opium usage and lower levels of total cholesterol and LDL; however, the lower level of HDL in normal range was seen in opium users. Considering the current evidences, most of them showed the increased risks of ischemic heart disease, heart attack, hypertension, cerebrovascular disease, and cancer in opium users. Therefore, Healthcare providers and patients should be noticed about the deleterious effects of opium consumption on various vascular events. In addition, it is necessary for managers and policy makers of the health care system to take the necessary measures to raise the level of awareness and health literacy of the general public about the high-risk side effects of opium use and to take necessary and effective strategies to prevent and reduce its use.

Sweet/Fat Preference Taste in Subjects Who are Lean, Obese and Very Obese

Purpose

This study assessed the perception of sweetness, creaminess, and pleasantness from a sweet/fat preference test in subjects who are lean (BMI: 19–25), obese (BMI: 30–33) or very obese (BMI: 34–40) using categorical modeling.

Methods

Subjects tasted 16 dairy solutions consisting of 0%, 3.5%, 11.3% and 37.5% fat and each containing 0%, 5%, 10%, or 20% sugar and rated them for sweetness, creaminess and pleasantness.

Results

A proportional odds model described the perception of sweetness using an Emax for the effect of sugar and a linear effect for fat. Perception of creaminess was dependent on the fat and sugar content and was described with proportional odds model with linear effects of sugar and fat. Perception of pleasantness increased with sugar and fat but decreased in solutions containing 37.5% fat. A differential odds model using an Emax model for fat and sugar with a negative interaction between them allowed the sugar content to be less than proportional and the fat content to be greater than proportional for pleasantness.

Conclusions

Application of modeling provided understanding of these complex interactions of sugar and fat on the perception of sweetness, creaminess, and pleasantness and provides a tool to investigate obesity and pharmacological intervention.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11095-020-02968-9.

Cardiovascular complications and related risk factors underlying opium consumption

Opium is considered as the second most abused addictive compound in worldwide. It seems that one of the causes for common consumption of opium in many countries is a traditional belief, even among medical personnel, through which opium might have advantageous influences on cardiovascular events and be beneficial in controlling hypertension, dyslipidemia, and diabetes. According to several investigations, it is thought that opium not only has no beneficial effects on cardiovascular events, but it might have deleterious influences on these settings. As a result, people need to be trained with regard to the adverse effects of opium on cardiovascular events. In this review, we try to go through the understanding of the effects of opium cardiovascular disorders and related complications such as blood pressure, blood sugar, lipid circumstances, and finally atherosclerosis.

Effects of in utero conditions on adult feeding preferences

The fetal or early origins of adult disease hypothesis states that environmental factors, particularly nutrition, act in early life to program the risks for chronic diseases in adult life. As eating habits can be linked to the development of several diseases including obesity, diabetes and cardiovascular disease, it could be proposed that persistent food preferences across the life-span in people who were exposed to an adverse fetal environment may partially explain their increased risk to develop metabolic disease later in life. In this paper, we grouped the clinical and experimental evidence demonstrating that the fetal environment may impact the individual's food preferences. In addition, we review the feeding preferences development and regulation (homeostatic and hedonic pathways, the role of taste/olfaction and the reward/pleasure), as well as propose mechanisms linking early life conditions to food preferences later in life. We review the evidence suggesting that in utero conditions are associated with the development of specific food preferences, which may be involved in the risk for later disease. This may have implications in terms of public health and primary prevention during early ages.

Effects of opium consumption on cardiometabolic diseases

Opium is the second-most-commonly abused substance (after tobacco) in developing countries of the Middle East region, and in many Asian nations. One of the reasons for the high prevalence of opium abuse in these countries is a traditional belief among Eastern people, even including some medical staff, that opium might have beneficial effects on cardiovascular health and in the control of diabetes mellitus, hypertension, and dyslipidaemia. In this Perspectives article, we summarize the current understanding of the pharmacotoxicology of opium and its specific effects on glycaemic control, blood pressure, lipid profile, and atherosclerosis. On the basis of the available evidence, we believe not only that opium has no ameliorating effect on cardiovascular diseases, but also that the use of this drug might have adverse effects on these conditions. Therefore, people should be educated about the hazardous effects of opium consumption on cardiometabolic diseases.

Preference or fat? Revisiting opioid effects on food intake

It is well established that opioid signaling in the central nervous system constitutes a powerful stimulus for food intake. The role of opioids in determining food preference, however, is less well defined. Opioids have been proposed to promote intake of preferred foods, or, alternatively, to preferentially increase consumption of fat. In the present manuscript, I comprehensively review results from previous studies investigating this issue. Data from these studies suggests a mechanism for opioid action that may reconcile the previously proposed hypotheses: opioid effects on food intake do appear to be largely specific for fat consumption, but individual animals' sensitivity to this effect may be dependent on baseline food preferences. In addition, I highlight the possibility that the selectivity of endogenous opioid effects may importantly differ from that of exogenous agonists in the degree to which baseline preferences, rather than macronutrient intake, are altered. The paper represents an invited review by a symposium, award winner or keynote speaker at the Society for the Study of Ingestive Behavior [SSIB] Annual Meeting in Portland, July 2009.

Baclofen, raclopride, and naltrexone differentially affect intake of fat and sucrose under limited access conditions

Gamma-aminobutyric acid (GABA), dopamine, and opioids are implicated in impulse control, addiction and binge eating. Recent evidence suggests that sucrose alters the effects of GABAergic, dopaminergic, and opioid receptor ligands on consumption of a fatty food in a rat limited-access binge protocol. This study determined the independent effects of fat and sucrose on the efficacy of these ligands under limited-access conditions. Nonfood-deprived male Sprague-Dawley rats had 1 h access to fat (vegetable shortening) or sucrose (3.2, 10, or 32% w/v). Half had intermittent access (Monday, Wednesday, Friday) and half had daily access. Effects of baclofen (GABAB agonist), SCH 23390 (D1 antagonist), raclopride (D2 antagonist), and naltrexone (opioid antagonist) were assessed. Baclofen and naltrexone reduced fat intake regardless of the access schedule. Baclofen had no effect on sucrose intake; naltrexone reduced sucrose intake at higher doses than were required to reduce fat intake. Raclopride stimulated fat intake in intermittent-access rats and had no effect in daily-access rats; raclopride reduced sucrose intake in all groups. SCH 23390 reduced intake in a nonspecific manner. The results indicate the involvement of GABAB receptors in fat but not sucrose intake, and of D2 receptor dysfunction in rats with a history of bingeing on fat.

Effects of sucrose, glucose and fructose on peripheral and central appetite signals

In the Western world, consumption of soft drinks has increased the last three decades and is partly responsible for the epidemic-like increase in obesity. Soft drinks, originally sweetened by sucrose, are now sweetened by other caloric sweeteners, such as fructose. In this study, we investigated the short-term effect of sucrose, glucose or fructose solutions on food intake and body weight in rats, and on peripheral and central appetite signals. Rats received water containing either of the sugars and standard rat chow for two weeks. Rats receiving water alone and standard chow were controls. All rats offered the sugar solutions increased their total caloric intake. The increased caloric intake occurred despite the fact that the rats offered either of the sugar solutions consumed less chow. As a consequence of the increased caloric intake, the sugar-drinking rats had elevated serum levels of free fatty acids, triglycerides and cholesterol. In addition, consuming sugar solutions resulted in increased serum leptin, decreased serum PYY and down-regulated hypothalamic NPY mRNA. Serum ghrelin was increased in rats receiving fructose solution. Moreover, consumption of sucrose or fructose solution resulted in up-regulated hypothalamic CB1 mRNA. Hypothalamic POMC mRNA was down-regulated in rats receiving glucose or fructose. In conclusion, consumption of glucose, sucrose or fructose solution results in caloric overconsumption and body weight gain through activation of hunger signals and depression of satiety signals as well as activation of reward components. The weight-promoting effect of these sugar solutions may possibly be ameliorated by the down-regulation of NPY mRNA and increased serum leptin.

Central opioids and consumption of sweet tastants: when reward outweighs homeostasis

Numerous reports have described opioids as peptides involved in the regulation of food intake. The role of these endogenous substances appears to be linked with reward-dependent feeding, since injection of opioid receptor ligands alters consumption of palatable foods and solutions more readily than of non-palatable ones, and intake of such tastants affects the activity of the opioid system within the brain. Among a variety of available foods, those rich in sucrose and other sweet tastants, are extremely appealing to humans and laboratory animals. In the current review, we focus on the rewarding aspects of consummator behavior driven by opioids. We attempt to delineate opioid-dependent central mechanisms responsible for overconsumption of "rewarding" palatable diets, especially foods high in sugar that can potentially jeopardize homeostasis.

Endogenous opioids and feeding behavior: a 30-year historical perspective

This invited review, based on the receipt of the Third Gayle A. Olson and Richard D. Olson Prize for the publication of the outstanding behavioral article published in the journal Peptides in 2002, examines the 30-year historical perspective of the role of the endogenous opioid system in feeding behavior. The review focuses on the advances that this field has made over the past 30 years as a result of the timely discoveries that were made concerning this important neuropeptide system, and how these discoveries were quickly applied to the analysis of feeding behavior and attendant homeostatic processes. The discoveries of the opioid receptors and opioid peptides, and the establishment of their relevance to feeding behavior were pivotal in studies performed in the 1970s. The 1980s were characterized by the establishment of opioid receptor subtype agonists and antagonists and their relevance to the modulation of feeding behavior as well as by the use of general opioid antagonists in demonstrating the wide array of ingestive situations and paradigms involving the endogenous opioid system. The more recent work from the 1990s to the present, utilizes the advantages created by the cloning of the opioid receptor genes, the development of knockout and knockdown techniques, the systematic utilization of a systems neuroscience approach, and establishment of the reciprocity of how manipulations of opioid peptides and receptors affect feeding behavior with how feeding states affect levels of opioid peptides and receptors. The role of G-protein effector systems in opioid-mediated feeding responses, which was the subject of the prize-winning article, is then reviewed.

Sugars: hedonic aspects, neuroregulation, and energy balance

The prevalence of obesity has increased dramatically in recent years in the United States, with similar patterns seen in several other countries. Although there are several potential explanations for this dramatic increase in obesity, dietary influences are a contributing factor. An inverse correlation between dietary sugar intake and body mass index has been reported, suggesting beneficial effects of carbohydrate intake on body mass index. In this review we discuss how sugars interact with regulatory neurochemicals in the brain to affect both energy intake and energy expenditure. These neurochemicals appear to be involved in dietary selection, and sugars and palatable substances affect neurochemical changes in the brain. For example, rats that drink sucrose solutions for 3 wk have major changes in neuronal activity in the limbic area of the brain, a region involved in pleasure and other emotions. We also investigate the relations between sucrose (and other sweet substances), drugs of abuse, and the mesolimbic dopaminergic system. The presence of sucrose in an animal's cage can affect the animals desire to self-administer drugs of abuse. Also, an animal's level of sucrose preference can predict its desire to self-administer cocaine. Such data suggest a relation between sweet taste and drug reward, although the relevance to humans is unclear. Finally, we address the influence of sugar on body weight control. For example, sucrose feeding for 2 wk decreases the efficiency of energy utilization and increases gene expression of uncoupling protein 3 in muscle, suggesting that sucrose may influence uncoupling protein 3 activity and contribute to changes in metabolic efficiency and thus regulation of body weight.

Dietary fat dose dependently increases spontaneous caloric intake in rat

OBJECTIVE

To characterize the dose-response relationship between dietary fat to carbohydrate ratio and spontaneous caloric intake.

RESEARCH METHODS AND PROCEDURES

Male Long-Evans rats consumed milk-based liquid diets that differed in fat content (17% to 60% of kilocalories) but had equivalent protein content and energy density. In Experiment 1, rats consumed one of the diets (n = 9/diet group) as the sole source of nutrition for 16 days. In Experiment 2, diets were offered as an option to nutritionally complete chow for 4 days followed by a 3-day chow-only washout in a randomized within-subjects design (n = 30). In Experiment 3, nine rats received isocaloric intragastric infusions of diet overnight, with chow available ad libitum. At least two no-infusion days separated the different diet infusions, which were given in random order. Food intake was measured daily

RESULTS

Dietary fat dose dependently increased total daily kilocalories in each of the three paradigms.

DISCUSSION

These data imply that the postingestive effects of carbohydrate and fat differentially engage the physiological substrates that regulate daily caloric intake. These findings reiterate the importance of investigating macronutrient-specific controls of feeding, rather than prematurely concluding that dietary attributes that covary with fat content (e.g., caloric density and palatability) drive the overeating associated with a high-fat diet.

Sugars and fats: the neurobiology of preference

The appetite for specific foods and nutrients may be under neuroregulatory control. In animal studies, fat intake is increased by both opioids and galanin and reduced by enterostatin, whereas carbohydrate intake is increased by neuropeptide Y (NPY). However, what may be affected is the consumption of preferred foods rather than macronutrients. Fat and sugars are highly preferred whether consumed separately or as mixtures in foods. Studies suggest that sustained consumption of sugars and fats may have additional metabolic consequences; among these are neurochemical changes in brain sites involved in feeding and reward, some of which are also affected by drugs of abuse. Furthermore, the consumption of fats and sugars alters tissue expression of uncoupling proteins, which are also influenced by neuroregulatory peptides and may be markers of energy expenditure. These data suggest that these palatable nutrients may influence energy expenditure through changes in central neuropeptide activity. Fats and sugars could affect central reward systems, thereby increasing food intake, and might have an additional effect on energy expenditure. Such palatable substances may contribute to the observed increase in the body weight of populations from affluent societies during the past few decades.

Effect of morphine on caloric intake and macronutrient selection in male and female Lou/c/jall rats during ageing

Previous studies have showed a shift of preferences from carbohydrate to fat in the Lou/c/jall rat with advancing age when they are submitted to a self-selection procedure. Protein intake also decreased according to the age, earlier for males (after 16 months) than for females (29 months). The present study aimed at investigating the mechanism underlying these modifications. We analysed the effect of the reference mu agonist, morphine (5 mg/kg subcutaneous), on the caloric intake, body weight and macronutrient intake of 30 male and 30 female rats divided in four age groups: young adults (10), mature (17), old (24) and senescent rats (29 months). During the experiment, animals had the choice between separate sources of the three pure macronutrients. Morphine injection reduced total daily caloric intake and induced a decrease in body weight. The weight loss was age- and sex-related (males and old rats were more affected by the drugs). The injection of morphine evoked a triphasic influence on the chronology of the intake. A brief (1 h) hypophagia was followed by an hyperphagia (3 h) and a persistent hypophagia (8 h). No modification in the diet composition was observed. These results did not support a clear involvement of the opioid system concerning the modifications in macronutrient rates in diet previously observed across ageing.

Opioidergic contribution to conditioned place preference induced by corn oil in mice

We previously reported that voluntary intake of corn oil in the light box showed place preference in the conditioned place preference (CPP) test in mice. In the present study, we investigated the contribution of opioidergic systems to the corn oil-induced CPP in mice. Acquisition of the place preference by corn oil intake was blocked by i.p. injections of an opioid mu antagonist, naloxone (0.1 and 0.3 mg/kg), and delta antagonists, 7-benzylidenenaltrexone (0.5 mg/kg) and naltriben (0.5 mg/kg) 15 min before conditioning. The opioid kappa agonist U-50488H (1 and 3 mg/kg i.p.) also blocked corn oil-induced CPP. Naloxone (1 mg/kg, i.p.) and naltriben (0.5 mg/kg, i.p.) did not affect corn oil intake in the home cage. However, 7-benzylidenenaltrexone (0.5 mg/kg, i.p.) and U-50488H (1 mg/kg i.p.) decreased and increased the corn oil intake, respectively. These results suggested that the rewarding effects of corn oil in the CPP test are at least partially mediated via opioidergic systems through mu and delta receptors. Further, we showed that an opioid kappa agonist reduced the rewarding effects of corn oil in the CPP test in mice, although it increased corn oil intake.

Role of lipid type on morphine-stimulated diet selection in rats

Administration of morphine is said to increase fat consumption among rats allowed to self-select nutrients. However, fats represent a diverse group of molecules, differing in metabolic and sensory properties. Despite this, lipid has yet to be manipulated as a variable in drug-stimulated nutrient selection studies. To determine whether lipid source can impact daily and morphine-stimulated (1, 3, and 10 mg/kg) diet intake, rats were provided with a choice between a high-fat and high-carbohydrate diet in three regimens in which the source of fat was varied between vegetable shortening, lard, or corn oil. Daily and morphine-stimulated diet selections were determined under all conditions. Under daily feeding conditions, rats ate more of the high-lipid diet compared with the high-carbohydrate diet when vegetable shortening or lard was the main lipid alternative, but lipid and carbohydrate intake did not differ when corn oil was the main lipid alternative. When rats were stimulated with morphine, the percentage of lipid increased relative to baseline intake only when the lipid diets were the preferred alternatives (i.e., vegetable shortening or lard). When preference between lipid and carbohydrate diets was neutral (i.e., corn oil condition), morphine did not enhance lipid consumption. These results indicate that morphine increases consumption of total energy or preferred diets and not lipid per se.

Differential response to kappa-opioidergic agents in dietary fat selection between Osborne-Mendel and S5B/P1 rats

We have investigated the central effect of a kappa-opioid agonist and an antagonist on the macronutrient preference in two strains of rat, the Osborne Mendel (OM) and S5B/P1 rats, that have different susceptibility to obesity and differential preference for dietary fat intake. OM rats prefer diets high in fat and are sensitive to diet-induced obesity, whereas S5B/P1 prefer a low fat diet and are resistant to high-fat diet-induced obesity. Rats adapted to a two-choice high fat (HF)/low fat (LF) diet were food deprived (20 h) and then infused into the third cerebroventricle with 10 micrograms nor-binaltorphimine (nor-BNI), a selective kappa-antagonist. Nor-BNI preferentially suppressed HF intake, but not LF intake in OM rats, whereas it affected neither diet in S5B rats. Infusion of U50488, a selective kappa-agonist (33 nmol), into the third cerebroventricle in sated rats, potently stimulated the intake of HF only in the OM rats, whereas it induced a significant but moderate stimulation of intake of both HF and LF diets in the S5B/P1 rats. Total energy intake following U50488 was not significantly different between the two strains. These findings suggest that the enhanced sensitivity of the OM rats to kappa-opioid stimulation for dietary fat may contribute to their preference for dietary fat and possibly their increased susceptibility for obesity.

Rats maintained on high-fat diets exhibit reduced satiety in response to CCK and bombesin

Rats maintained on high-fat diets often exhibit increased food intake and weight gain. We hypothesized that high-fat diets might result in reduced sensitivity to hormonal signals responsible for terminating food intake--satiety signals. The intestinal hormone cholecystokinin (CCK) and the gastrointestinal neuropeptide, bombesin (BBS) both have been proposed as satiety signals. To determine whether maintenance on high-fat diets alters sensitivity to satiating effects of CCK and bombesin (BBS), rats were maintained on a low fat diet (LF), a high-fat diet that was isocaloric with the low-fat diet (HF), or one of two hypercaloric high-fat diets (HF-1, HF-2) that differed from HF and LF in fat, fiber, and total caloric content. CCK and bombesin reduced food intake significantly less in rats maintained on high-fat diets, compared to those on the low fat diet. Neither high caloric intake, which was associated with increased body weight gain on the two hypercaloric diets, nor fiber content of the diet accounted for the reduced response of HF rats to CCK. Rather, reduced sensitivity to CCK was related only to the high proportion of calories taken as fat. We also determined whether reduced CCK sensitivity was due to the maintenance on a particular diet or to the diet eaten during a CCK test. After CCK, rats maintained on LF reduced food intake more (49%) than rats maintained on HF (22%), regardless of whether they ate HF or LF during the CCK test itself. These findings indicate that maintenance of rats on high-fat diets reduces sensitivity to some peptide satiety signals. Reduced sensitivity to satiety signals might contribute to overeating and obesity often observed when rats are maintained on high-fat diets.

Beta-casomorphins stimulate and enterostatin inhibits the intake of dietary fat in rats

The effects of beta-casomorphins 1-7, 1-5 and 1-4 on food intake of rats adapted to either a high fat (HF) or high carbohydrate (HC) diet have been studied and compared to the effects of enterostatin. Intracerebroventricular (icv) beta-casomorphin1-7 (beta-CM1-7) stimulated intake of HF diet in overnight fasted rats, but beta-CM1-5 and beta-CM1-4 were ineffective. Peripheral injection of beta-CM1-7 also increased the intake of a high fat diet, but reduced the intake of HC diet in satiated rats. Intracerebroventricular (ICV) beta-CM1-7 caused a dose-dependent increase in the intake of HF diet, but a dose-dependent inhibition of HC ingestion in satiated rats. Enterostatin (ICV) inhibited the beta-CM1-7 stimulation of HF intake, as did the general opioid antagonist naloxone. Ligand binding studies with [3H-pro] enterostatin identified on low affinity binding site (Kd 100nM) on a crude brain membrane preparation. This binding was displaced by beta-CM1-7, beta-CM1-5 and beta-CM1-4. These data suggest that at high doses enterostatin and beta-CM1-7 may interact with the same low affinity receptor to modulate intake of dietary fat.

Food intake and food choice: the role of the endogenous opioid peptides in the marsupial Sminthopsis crassicaudata

Endogenous opioid peptides activate food seeking behaviour and influence macronutrient choice in a number of animal species and previous studies have suggested that the palatability of food is strongly modulated by the opioid feeding system. The effect of opioid peptides on appetite and food choice in marsupials has not been evaluated. The aim of these studies was to determine the effect of mu, delta and K opioid receptors on food intake and food choice in the marsupial Sminthopsis crassicaudata. When offered a choice of mealworms or laboratory diet after 24 h food deprivation, S. crassicaudata ate predominantly mealworms. After a 24 h fast, adult male S. crassicaudata were injected peripherally with opioid receptor antagonists or saline. Animals were re-fed with either their laboratory diet alone, or a choice of laboratory diet and mealworms. In animals re-fed with laboratory diet alone, naloxone at doses of 15 and 10 mg/kg produced a 31% (P < 0.05) and 38% (P < 0.05) respectively reduction in food intake in the first 30 min after laboratory diet was re-introduced, but lower doses had no effect. The selective delta antagonist naltrindole at 20 mg/kg resulted in a 65% (P < 0.01) reduction in food intake compared to controls between 30 and 60 min. The selective kappa opioid antagonist nor-binaltorphimine had no effect on the intake of laboratory diet. In animals offered a choice of laboratory diet and mealworms, naloxone doses of 1, 5, 10, 15 and 20 mg/kg significantly decreased intake in the first 0.5 h after re-feeding, due to a preferential suppression of the intake of mealworms. Naltrindole and nor-binaltorphimine had no effect on food choice. These studies demonstrate that endogenous opioid peptides influence both food intake and choice in S. crassicaudata and that the role of the opioid feeding system is in part modulated by food palatability. In S. crassicaudata these effects appear to occur predominantly by a mu opioid receptor mechanism.

Effect of enterostatin and kappa-opioids on macronutrient selection and consumption

Enterostatin, the activation peptide of pancreatic procolipase, suppresses consumption of high-fat diets and selectively suppresses fat consumption over carbohydrate consumption. Kappa-opioid subtype agonists stimulate feeding whereas antagonists suppress feeding. We investigated the effects of enterostatin, the kappa-opioid agonist U50488, and the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) on macronutrient selection and food consumption in rats adapted to choose between a high-fat (HF) diet or a low-fat-high-carbohydrate (LF) diet. In fasted rats, lateral cerebro-ventricular injection (LV) of enterostatin selectively suppressed consumption of the HF diet, with no effect on LF diet consumption. Nor-BNI also selectively suppressed consumption of the HF diet without affecting LF diet consumption. Additionally, U50488 prevented the suppression of consumption of the HF diet in response to enterostatin. In food-sated rates, U50488 preferentially increased consumption of the HF diet and had no effect on consumption of the LF diet. Combined infusions of subthreshold doses of enterostatin and nor-BNI also inhibited consumption of the HF but not the LF diet, whereas combined infusions of maximal doses of enterostatin and nor-BNI had no additive effects. Collectively, these data suggest that a kappa-opioid pathway modulates selection and consumption of diets high in fat and that enterostatin modulates consumption of dietary fat by interacting with this pathway.

Control of food intake. A physiologically complex, motivated behavioral system

This article has examined the control of food intake as a physiologically complex, motivated behavioral system. During the past four decades, considerable progress has been made in understanding putative signals for hunger, satiation, and satiety, although hunger signals have proven to be more difficult to identify. The putative physiologic controls of food intake include positive and negative sensory feedback; gastric and intestinal distension; the effects of nutrients, nutrient reserves, and metabolism in producing signals to the liver or brain; and peptides and hormones released in the gastrointestinal tract or the brain. However, food intake is not influenced solely by physiologic signals for hunger, satiation, and satiety. To comprehend feeding behavior more thoroughly, current physiologic models must be extended to include modulating factors such as feeding-associated responses adapted through learning processes and the influence of circadian rhythms, which can be dominating over hunger, satiation, and satiety signals.

The physiology and brain mechanisms of feeding

This article is designed as an introduction to the major theoretical models in the field of regulation of eating behavior, and a selective review of relevant neurobiological data. We first critically consider the paradigm of homeostasis as it relates to body energy content, and argue that additional theoretical constructs will be needed to account for the complexity of eating behavior in both nonhumans and humans. We then summarize some of the methods available to the neuroscientist in this area, and address some of their limitations. We review treatments and potential mechanisms that increase food intake, including deprivation, antimetabolites, norepinephrine, and several peptides including neuropeptide Y. We next review treatments that decrease food intake, including a variety of humoral, gastrointestinal, and pancreatic factors, as well as examine central pathways of satiety. This includes a discussion of leptin and other potential anorectic agents. We conclude with a discussion of human obesity and anorexias, and prospects for pharmacotherapy of eating disorders. We emphasize throughout that most regions of the human brain probably make some contribution to feeding behavior, and so a focus on any one area of transmitter/hormone is an unrealistic approach both in basic and applied areas.

Palatability-induced hyperphagia increases hypothalamic Dynorphin peptide and mRNA levels

Opioid involvement in regulating the intake of highly palatable diets was studied by examining the effect of feeding either a cornstarch-based diet (CHO) or a high fat diet containing sucrose (Fat/Sucrose) on hypothalamic opioid levels. Rats received either CHO ad libitum, Fat/Sucrose ad libitum, Fat/Sucrose pair-fed to the caloric intake of CHO, or Fat/Sucrose at 60% of ad libitum Fat/Sucrose intake. Animals receiving Fat/Sucrose ad libitum consumed more calories and gained more weight than animals receiving CHO (P < 0.001). Relative to CHO, ad libitum intake of Fat/Sucrose elevated proDynorphin mRNA levels in the arcuate and Dynorphin A1-17 levels in the paraventricular nucleus (PVN) (P < 0.05), but did not affect arcuate mRNA levels of proEnkephalin or proOpiomelanocortin (POMC), or PVN levels of Met-Enkephalin or beta-Endorphin. Pair-feeding the Fat/Sucrose diet to the level of intake of the CHO diet resulted in levels of proDynorphin and Dynorphin A1-17 that were similar in the two diet groups. Pair-feeding Fat/Sucrose reduced mRNA levels of proDynorpin, proEnkephalin and POMC, and Dynorphin A1-17 levels, relative to ad libitum feeding of Fat/Sucrose. Met-Enkephalin and beta-Endorphin were not affected by dietary treatment. Feeding Fat/Sucrose at 60% of ad libitum intake resulted in mRNA levels of proDynorphin, proEnkephalin and POMC, and Dynorphin A1-17 levels that were similar to those observed in CHO group. Hypothalamic Dynorphin A1-17 and proDynorphin mRNA levels are stimulated by feeding a highly palatable diet rich in fat and sucrose. The increased synthesis may be due in part to a palatability-induced overconsumption of calories. Caloric restriction of the same diet decreases mRNA levels of proDynorphin, proEnkephalin and POMC, as well as levels of Dynorphin A1-17.

State-dependent changes of brain endogenous opioids in mammalian hibernation

Endogenous opioids belonging to three opioid families were measured in different states of the hibernation cycle in brain of the Columbian ground squirrels. Using high-performance liquid chromatography-EC detection, the hypothalamic and septal concentrations of met-enkephalin were found to be significantly higher (p < 0.05) in the hibernating state than that in the nonhibernating state. In contrast, met-enkephalin content in the medulla decreased significantly during hibernation. Leuenkephalin content was only increased in the hypothalamus of hibernating animals. Using radioimmunoassay, dynorphin A-like immunoreactivity was observed to increase in the claustrum and striatum, whereas beta-endorphin-like peptides showed a significant increase in the hypothalamus during hibernation. It is evident that the changes in endogenous opioids in brain during hibernation are state dependent, type specific and region specific. These specific alterations of various endogenous opioids may imply their different roles in hibernation.

Differential effects of enterostatin, galanin and opioids on high-fat diet consumption

Enterostatin, the activation peptide of pancreatic procolipase, suppresses high-fat diet consumption both centrally and peripherally. kappa-opioid agonists are also known to stimulate fat intake. These experiments were conducted to determine if an opioidergic central pathway might mediate the effects of enterostatin and galanin on fat intake. Male Sprague-Dawley rats were adapted to a high-fat diet (56% energy) and were implanted with cannulae aimed at the lateral cerebral ventricle (LV) or third cerebral ventricle (3V). Injection of enterostatin (1 nmol, LV) suppressed high-fat diet consumption in fasted (20 h) rats. This inhibition of high-fat intake by enterostatin was attenuated by central injection of the specific kappa-agonist U50488 (2.15, 21.5 and 215 nmol, LV) in a dose-dependent manner in fasted rats while only the highest dose of U50488 (215 nmol, LV) independently produced stimulation of high-fat diet consumption in sated rats. Galanin (0.1 nmol, 3V) induced consumption of high-fat diet in sated rats similar to that seen with U50488 and this stimulation was attenuated by peripheral injection of naloxone (1.0 mg/kg i.p.). We present a model which integrates the present data, as well as previous findings, in explaining a potential common opioid pathway modulating fat consumption.

Selective alterations in macronutrient intake of food-deprived or glucoprivic rats by centrally-administered opioid receptor subtype antagonists in rats

Two hypotheses have attempted to account for the abilities of opioid agonists and antagonists to respectively stimulate and inhibit food intake in rats. The first suggests that the opioid system selectively modulates fat intake, while the second suggest that the opioid system selectively alters intake of that macronutrient which the animal prefers. The present study evaluated these two hypotheses by examining total intake and individual macronutrient intake in either food-deprived (24 h) rats or rats made glucoprivic with 2-deoxy-D-glucose (2DG, 200 mg/kg, i.p.) following either vehicle treatment, systemic administration of naltrexone or intracerebroventricular administration of either naltrexone, the mu opioid antagonist, beta-funaltrexamine (B-FNA), the mu1 opioid antagonist, naloxonazine, the kappa opioid antagonist, nor-binaltorphamine (Nor-BNI), the delta opioid antagonist, naltrindole or the delta1 opioid antagonist, DALCE. Systemic administration of naltrexone (0.5-5 mg/kg significantly reduced carbohydrate, fat and total intake in deprived rats, and carbohydrate, fat, protein and total intake in glucoprivic rats. Central administration of naltrexone (5-50 micrograms) significantly reduced fat and total intake in both deprived and glucoprivic rats. B-FNA (5-20 micrograms) significantly reduced carbohydrate, fat and total intake in both deprived and glucoprivic rats Naloxonazine (10-100 micrograms) significantly reduced carbohydrate, fat and total intake in deprived rats, but failed to alter 2DC intake. Nor-BNI (5-20 micrograms) significantly reduced fat and total intake in glucoprivic rats, but failed to alter deprivation intake. Neither naltrindole (20 micrograms) nor DALCE (40 micrograms altered intake in deprived or glucoprivic rats. Carbohydrate or fat preference in deprived rats significantly increased the amount of explained variance in the inhibitory actions of central naltrexone, B-FNA and naloxonazine upon deprivation-induced intake. Carbohydrate or fat preference in glucoprivic rats significantly increased the amount of explained variance in the inhibitory action of systemic and central naltrexone, B-FNA, naloxonazine and Nor-BN upon 2-DG hyperphagia. These data are discussed in terms of the contentions that opioids either selectively alter fat intake pe se or selectively alter the preferred macronutrient.

Structural requirements for the biological activity of enterostatin

A series of enterostatin analogues were tested to investigate the minimal structure required for activity to suppress the intake of high-fat (HF) diets. The dose-response curve to intracerebroventricular (ICV) enterostatin was U-shaped (maximal inhibition at 1 nmol). Removal or modification of the N-terminal valine from enterostatin (Val-Pro-Asp-Pro-Arg) abolished activity, as did C-terminal amidation. The tripeptide (Pro-Asp-Pro) and the cyclo-diketopiperazine cyclo-Asp-Pro retained activity whereas the linear Asp-Pro dipeptide was inactive. In rats adapted to a three-choice macronutrient diet, cyclo-Asp-Pro specifically inhibited fat intake and had near maximal inhibition (50%) at the 0.03 nmol dose. The enterostatin inhibitory effect on fat intake may reside in the cyclo-diketopiperazine molecule, cyclo-Asp-Pro.

GRF-induced feeding: evidence for protein selectivity and opiate involvement

Growth hormone-releasing factor (GRF) is a hypothalamic peptide named for its ability to induce release of growth hormone from the anterior pituitary. GRF also acts as a neurotransmitter in the suprachiasmatic nucleus/medial preoptic area (SCN/MPOA) to stimulate food intake. The purpose of this series of experiments was to explore the nature of GRF-induced feeding, with a particular emphasis on macronutrient selectivity, and to examine the role of opiate activity in the paraventricular nucleus of the hypothalamus (PVN). Chow intake stimulated by GRF microinjection (1 pmol/0.5 microliters) into the SCN/MPOA was blocked by injection of methyl-naltrexone (3 micrograms/0.5 microliters) into the PVN. In animals habituated to macronutrient diets (Teklad, WI), GRF preferentially stimulated intake of protein at 2 and 4 h postinjection, whereas it had no effect on carbohydrate intake. Further, this effect was blocked by injection of naloxone (40 nmol/0.5 microliters) into the PVN. Microinjection of morphine (0, 1, 10, and 17 micrograms/0.5 microliter) into the PVN also specifically stimulated protein intake at 2 and 4 h postinjection. These results suggest that feeding derived from GRF actions in the SCN/MPOA is macronutrient selective, and is dependent on PVN opiate activity for expression.

Naloxone's anorectic effect is dependent upon the relative palatability of food

It has been suggested that opioids modify food intake by enhancing palatability. In the present series of studies we evaluated the effect of naloxone on food intake of a preferred food (chocolate chip cookies), normal rat chow, and an "aversive" food (high fiber chow). We found that naloxone decreased 18- and 48-h deprivation-induced intake of chocolate chip cookies much more potently than that of chow, when these foods were presented on separate occasions. When these foods were presented concurrently, this difference in naloxone's potency was no longer apparent. When rats were offered high fiber chow, only the 10 mg/kg dose of naloxone decreased intake. In these same rats naloxone significantly decreased normal chow intake at a dose of 0.1 mg/kg. Thus, naloxone's ability to decrease food intake appears to be dependent upon the palatability of the food.

The effects of continuous morphine infusion on diet selection and body weight

The administration of morphine causes a short-term increase in food intake, and repeated administration of morphine has been shown to cause progressively larger increases in intake and/or the relative intake of dietary fat. In this experiment, we measured the effects of continuous morphine infusions on diet choice and total intake. Male rats were given ad lib access to two diets: a high-carbohydrate diet (80% carbohydrate, 20% protein) and a high-fat diet (80% fat, 20% protein). Diet intakes were measured daily for 21 days. Via the implantation of osmotic minipumps, one group received continuous infusions of morphine sulfate (approx. 2.8 mg/kg/h) for days 1-7 and of saline for days 8-14. A second group was infused with saline for days 1-7 and with morphine for days 8-14. A third group received sham surgery but no minipumps. Total caloric intake was significantly decreased on the final 6 days of morphine infusions. The percentage of total caloric intake consumed from the high-fat diet was significantly increased for the first 2-3 days of morphine treatment; this effect was due to an initial reduction in carbohydrate intake and an increase in fat intake. Over the course of the infusion period, fat intake gradually decreased and carbohydrate intake increased. The effects of morphine when infused on days 1-7 were similar to those observed when the drug was infused during days 8-14.(ABSTRACT TRUNCATED AT 250 WORDS)

Central opioid receptor subtype antagonists differentially reduce intake of saccharin and maltose dextrin solutions in rats

Opioid modulation of ingestion includes general opioid antagonism of deprivation-induced water intake and intake of sucrose and saccharin solutions. Previous studies using selective subtype antagonists indicated that opioid effects upon deprivation-induced water intake occurred through the mu2 receptor and that opioid effects upon sucrose intake occurred through kappa and mu2 receptors. The present study compared the effects of intracerebroventricular administration of opioid receptor subtype antagonists upon intakes of a saccharin solution and a maltose dextrin (MD) solution to determine which receptor subtypes were involved in modulation of ingestion of different preferred tastants. Significant reductions in saccharin intake (1 h) occurred following naltrexone (20-50 micrograms: 66%) and naltrindole (delta, 20 micrograms: 75%), whereas [D-Ala2, Leu5, Cys6]-enkephalin (DALCE, delta 1, 40 micrograms: 45%) had transient (5 min) effects. Neither beta-funaltrexamine (B-FNA, mu), naloxonazine (mu1), nor nor-binaltorphamine (Nor-BNI, kappa) significantly altered saccharin intake. Significant reductions in MD intake (1 h) occurred following naltrexone (5-50 micrograms: 69%) and B-FNA (1-20 micrograms: 38%). MD intake was not reduced by naltrindole, DALCE, naloxonazine and Nor-BNI. Peak antagonist effects were delayed (20-25 min) to reflect interference with the maintenance, rather than the initiation of saccharin or MD intake. Comparisons of opioid antagonist effects across intake situations revealed that naltrexone had consistently low ID40 values for saccharin (29 nmol), MD (25 nmol), sucrose (6 nmol) and deprivation (38 nmol) intake. Despite its significant effects relative to naloxonazine, B-FNA had significantly higher ID40 values for saccharin (800 nmol), MD (763 nmol) and sucrose (508 nmol) relative to deprivation (99 nmol) intake, suggesting that mu2 receptors may be mediating maintenance of intake rather than taste effects. Nor-BNI had low ID40 values for intake of sucrose (4 nmol), but not for saccharin (168 nmol), MD (153 nmol) and deprivation (176 nmol), suggesting that kappa receptors may mediate ingestion of sweet-tasting stimuli. That delta (naltrindole: ID40 = 60 nmol), but not delta 1 (DALCE: ID40 = 288 nmol) antagonists consistently reduce saccharin intake suggests a role for the delta 2 receptor subtype in the modulation of hedonic orosensory signals.

The nutrient balance hypothesis: peptides, sympathetic activity, and food intake

Food intake can be increased or decreased after either central or peripheral administration of peptides. Galanin, neuropeptide Y, opioid peptides, growth hormone releasing hormone and desacetyl-MSH increase food intake whereas insulin, glucagon, cholecystokinin, anorectin, corticotropin releasing hormone, neurotensin, bombesin, enterostatin, cyclo-his-pro and thyrotropin-releasing hormone reduce food intake. A number of these peptides also affect the activity of the sympathetic nervous system. The peptides which have been tested have a reciprocal effect on food intake and sympathetic activity. Opioids, NPY and GHRH, which increase food intake, decrease sympathetic activity. Conversely, peptides which reduce food intake, increase sympathetic activity, with glucagon, cholecystokinin, corticotropin releasing hormone, calcitonin, neurotensin and bombesin being examples, Several of these peptides also affect the intake of specific nutrients. Insulin reduces food intake in animals fed a high carbohydrate diet, but not when fed a high fat diet. Neuropeptide Y increases carbohydrate intake. Galanin and opioid peptides increase fat intake. Enterostatin and cyclo-His-Pro, on the other hand reduce fat intake. Glucagon decreases protein intake. The effect of peptides on the intake of specific nutrients suggests that peptides may work in part by modulating basic feeding mechanisms to lead to the selection of specific nutrients from the diet. This hypothesis might be called a nutrient specific model of peptide-induced food intake.

Gastrointestinal disturbances with obesity

Steatosis and steatohepatitis are associated with obesity. Despite florid histological changes, patients with non-alcoholic steatohepatitis generally remain asymptomatic, and it usually runs a relatively benign course. An elevated insulin level may be important in the pathogenesis. There is a marked regression of fatty changes after weight reduction. In obese subjects the risk of developing gallstones is increased due to an increased saturation of gallbladder bile with cholesterol and possible gallbladder stasis. During weight reduction with very low calorie diets the incidence in gallstones increases probably because of an increased saturation of bile during the loss of weight. Ursodeoxycholic acid appears to be a promising prophylactic agent. Chenodeoxycholic acid is not useful for these subjects. There is controversy over whether obesity contributes to gastroesophageal reflux and gastric emptying disturbances. There are changes in gastrointestinal peptide plasma levels in obesity but it is not clear if this contributes to its development. The risk for high-risk colorectal adenomas and carcinomas is reported to be increased in obese males. Vertical banded gastroplasty and gastric bypass procedures are nowadays the surgical options for the treatment of obesity. Nutritional deficiencies, particularly of vitamin B12, folate and iron are common after gastric bypass and must be sought and treated. Dumping is another potential complication of this operation. If stenosis and gastric outlet obstruction develop endoscopic dilatation is a good therapeutic option.

Role of dietary fat in calorie intake and weight gain

This paper reviews the literature on the role of dietary fat in calorie intake and body weight gain in humans and laboratory animals. An overview of 40 animal studies which compared growth on high-fat (HF) and high-carbohydrate (HC) solid/powdered diets indicated that the HF diet elicited greater weight gain in 33 out of 40 studies. Enhanced growth on the HF diet was often, but not exclusively, attributable to greater caloric intake. Additional evidence for the growth-enhancing effect of HF diets emerges from "diet option" and "supermarket" feeding studies in rats, and experimental and epidemiological studies in humans. Three principal factors that contribute to the different responses to HF and HC diets are (a) caloric density, (b) sensory properties and palatability, and (c) postabsorptive processing. It is concluded that both calorie intake and metabolic energy expenditure are biased towards weight gain when a HF diet is consumed, and that the high caloric density of high-fat diets plays a primary role in weight gain. Humans may be biologically predisposed to gain weight when a HF diet is consumed.

[The regulation of feed intake and selection with special reference to poultry]

Feed intake is regulated in a dialogue between the animal and the feed, which is influenced by numerous factors. The hypothalamus has a central integrative function. Furthermore, caudal brain areas (medulla oblongata, pons) are of importance because these areas are relays of peripheral signals and gustatory afferents. All peripheral informations are integrated by various neurotransmitters and neurohormones. The function of this neuronal system is not exactly known yet. Sensorial informations, mechano-, chemo- and osmoreceptors of the gastrointestinal tract and gastrointestinal hormones are discussed as influences of the periphery. The physiological satiety function of cholecystokinin is questionable in poultry. Hepatic chemoreceptors, which are activated by various metabolites, influence the amount of feed ingested. The feed choice appears to be regulated by the same mechanisms. Our knowledge about the translation of peripheral signals into choice behaviour by changes of neurotransmitter systems is limited.

The effects of morphine on diet selection are dependent upon baseline diet preferences

It has been reported that morphine causes a selective increase in the intake of dietary fat. Because we have noted considerable variability among rats in their preferences for carbohydrate and fat, we reasoned that the effect of morphine on diet selection may differ in fat-preferring vs. carbohydrate-preferring rats. Male Sprague-Dawley rats were given ad lib access to separate sources of carbohydrate, fat and protein (Experiment 1), or to a carbohydrate/protein and a fat/protein diet (Experiment 2). After daily baseline intakes of the diets were determined, all rats were tested for feeding responses to subcutaneous injections of morphine (0, 2 and 10 mg/kg). Significant positive correlations were found between baseline daily intake of a given diet and the effect of morphine on the intake of that diet. Generally, morphine increased carbohydrate intake in carbohydrate-preferring rats, and increased fat intake in fat-preferring rats. These results suggest that the effect of morphine is to increase intake of a preferred diet rather than to increase intake of a specific macronutrient.

High-fat diet preference in developing and adult rats

Diet preference tests in rats have yielded equivocal results, as some investigators have reported a strong preference for diets high in fat over those containing less fat, while others have failed to see this preference. To further explore this unresolved problem, two diet preference experiments were conducted. In Experiment 1, adult rats were maintained for at least three months on one of three powdered diets (control, high-carbohydrate or high-fat). Rats were then given a preference test with all three diets available. Animals from each group overwhelmingly preferred the high-fat diet. To determine whether this preference was also present in younger, developing rats, in Experiment 2, weanling animals were tested with the same three diets as in Experiment 1. As observed with adult animals, weanling rats also showed a strong preference for the high-fat diet. The idea that rats prefer a diet with a relatively high level of fat is supported. Possible explanations for these findings are discussed.

Dietary hyperphagia in rats: role of fat, carbohydrate, and energy content

Dietary energy, fat and carbohydrate content were varied to determine the nutritional factors responsible for hyperphagia induced by feeding rats high-fat diets. In the first experiment, rats were fed isoenergetic high-fat or high-carbohydrate diets for 2 weeks. Weight gain and energy intake were lower in rats given the high-fat diet. When some of the rats were switched to a diet that was high in fat, carbohydrate and energy, gram food intake was initially unchanged, resulting in a substantial increase in energy intake and weight gain. Energy intake gradually declined over the 4 weeks following the switch to the high-energy diet. In the second experiment, rats were fed high-fat diets that were either high or low in carbohydrate content and either high or low in energy content (kcal/g). Rats fed a high-fat diet that was high in energy and carbohydrate ate the most energy and gained the most body weight and carcass fat. In the third experiment, rats were fed high-carbohydrate diets varying in fat and cellulose content. Energy intake and body weight gain varied directly as a function of caloric density regardless of the fat or cellulose content of the diets. It is concluded that hyperphagia induced by feeding high-fat diets is not due to the high dietary fat content alone. Rather, high levels of fat, carbohydrate, and energy interact to produce overeating and obesity in rats fed high-fat diets.

Satiation due to CCK-8 derivative infusion into VMH is related to a specific macronutrient selection

Diet self-selection from carbohydrate, protein and lipid offered simultaneously was studied in adult male rats infused for 8 days with pyroglutamyl-CCK-8 (pGlu-CCK-8) (0.8 pmol/hr), a derivative of the COOH-terminal octapeptide of cholecystokinin (CCK), or vehicle bilaterally into the ventromedial hypothalamus (VMH). Infusion with pGlu-CCK-8 markedly decreased total daily energy intake mainly due to a suppressed carbohydrate intake. Both pGlu-CCK-8 and vehicle infusions caused a nonspecific decrease in protein intake, but the vehicle infusion caused a compensatory increase in lipid intake as well as carbohydrate intake, so their total energy intake was well maintained. These results suggest that the process of infusion into the VMH elicited itself a suppressive effect on protein intake, but that pGlu-CCK-8 infusion elicited a more specific suppressive effect on carbohydrate intake and, to a lesser extent, on lipid intake. These results also support the prediction that centrally administered CCK may suppress food intake and show in addition that such a suppression occurs selectively. The similarities and the differences in the patterns of macronutrient selection produced by vehicle of pGlu-CCK-8 infusions into the VMH provide further evidence of the unique functions of VMH and CCK in the feeding process.

Intake of individual macronutrients following IP injections of BBS and CCK in rats

The effects of injections of either bombesin (BBS) or cholecystokinin octapeptide (CCK-8) on patterns of food intake of macronutrients were examined in adult male rats, and compared to the effects following saline injections. The animals were food deprived for 18 hours and then offered one of three isocaloric dietary components (protein, carbohydrate or fat). During the first 30 minutes following injections of BBS, protein intake was decreased. Suppression of carbohydrate intake, significant between 30 and 60 minutes, was sustained up to two hours following injections. During the first 30 minutes following injections of CCK, animals reduced their intake of each macronutrient. Reductions in the consumption of fat and protein were sustained up to one and six hours, respectively. The availability of particular macronutrients is proposed as a possible factor accounting for differences among studies with respect to self-selection profiles and duration effects.