Naloxone but not CCK-8 may attenuate binge-eating behavior in patients with the bulimia syndrome

Gastrointestinal peptides in eating-related disorders

Food intake is tightly controlled by homeostatic signals sensitive to metabolic need for the regulation of body weight. This review focuses on the peripherally-secreted gastrointestinal peptides (i.e., ghrelin, cholecystokinin, glucagon-like peptide 1, and peptide tyrosine tyrosine) that contribute to the control of appetite and discusses how these peptides or the signals arising from their release are disrupted in eating-related disorders across the weight spectrum, namely anorexia nervosa, bulimia nervosa, and obesity, and whether they are normalized following weight restoration or weight loss treatment. Further, the role of gut peptides in the pathogenesis and treatment response in human weight conditions as identified by rodent models are discussed. Lastly, we review the incretin- and hormone-based pharmacotherapies available for the treatment of obesity and eating-related disorders.

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.

Effects of mu opioid receptor antagonism on cognition in obese binge-eating individuals

RATIONALE

Translational research implicates the mu opioid neurochemical system in hedonic processing, but its role in dissociable high-level cognitive functions is not well understood. Binge-eating represents a useful model of 'behavioural addiction' for exploring this issue.

OBJECTIVE

The aim of this study was to objectively assess the cognitive effects of a mu opioid receptor antagonist in obese individuals with binge-eating symptoms.

METHODS

Adults with moderate to severe binge-eating and body mass index ≥30 kg/m² received 4 weeks of treatment with a mu opioid receptor antagonist (GSK1521498) 2 or 5 mg per day, or placebo, in a double-blind randomised parallel design. Neuropsychological assessment was undertaken at baseline and endpoint to quantify processing bias for food stimuli (visual dot probe with 500- and 2,000-ms stimulus presentations and food Stroop tasks) and other distinct cognitive functions (N-back working memory, sustained attention, and power of attention tasks).

RESULTS

GSK1521498 5 mg/day significantly reduced attentional bias for food cues on the visual dot probe task versus placebo (p = 0.042), with no effects detected on other cognitive tasks (all p > 0.10). The effect on attentional bias was limited to the longer stimulus duration condition in the higher dose cohort alone.

CONCLUSIONS

These findings support a central role for mu opioid receptors in aspects of attentional processing of food cues but militate against the notion of major modulatory influences of mu opioid receptors in working memory and sustained attention. The findings have implications for novel therapeutic directions and suggest that the role of different opioid receptors in cognition merits further research.

Behavioral models of binge-type eating

PURPOSE

To describe and evaluate behavioral models of binge-type eating.

DATA IDENTIFICATION

Studies were identified using Medline and hand searches of bibliographies of identified articles.

STUDY SELECTION

Isomorphic studies were selected that were judged to have some measure of construct validity.

DATA EXTRACTION

Face and construct validity were assessed, as well as simplicity and cost of use.

RESULTS OF DATA SYNTHESIS

Several different models of binge-type eating exist, each with different strengths of validity and use. These include models using sham feeding, restriction/refeeding cycles and/or stress, limited access (LA) to optional foods, and eating induced by operant schedules of behavior.

CONCLUSIONS

We concur with Harry Harlow, who was quoted by Gerry Smith as saying: "You'd be crazy to use animal models, but you'd also be crazy not to use them."

Neuropeptides in eating disorders

The past decade has witnessed a dramatic acceleration in research on the role of the neuropeptides in the regulation of eating behavior and body weight homeostasis. This expanding research focus has been driven in part by increasing public health concerns related to obesity and the eating disorders anorexia nervosa (AN) and bulimia nervosa (BN). Preclinical advances have been facilitated by the development of new molecular and behavioral research methodologies. With a focus on clinical investigations in AN and BN, this article reviews research on selected hypothalamic and gut-related peptide systems with prominent effects on eating behavior. Studies of the orexigenic peptides neuropeptide Y and the opioid peptides have shown state-related abnormalities in patients with eating disorders. With respect to gut-related peptides, there appears to be substantial evidence for blunting in the meal-related release of the satiety promoting peptide cholecystokinin in BN. Fasting plasma levels of the orexigenic peptide ghrelin have been found to be elevated in patients with AN. As discussed in this review, additional studies will be needed to assess the role of nutritional and body weight changes in neuropeptide alterations observed in symptomatic eating disorder patients, and to identify stable trait-related abnormalities in neuropeptide regulation that persist in individuals who have recovered from an eating disorder.

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.

Opioid peptides and the control of human ingestive behaviour

A variety of evidence suggests that endogenous opioid peptides play a role in the short-term control of eating. More recently, opioid receptor antagonists like naltrexone have been approved as a treatment for alcohol dependence. Here we review the evidence for a role of opioid peptides in both normal and abnormal eating and drinking behaviours and in particular try to identify the nature of the role of opioids in these behaviours. Particular attention is paid to the idea that opioid reward processes may be involved both in the short-term control of eating and hedonic aspects of alcohol consumption, and parallels are drawn between the effects of opiate antagonists on food pleasantness and the experience of drinking alcohol. The review also explores the extent to which data from studies using opiate antagonists and agonists provide evidence for a direct role of endogenous opioids in the control of ingestive behaviour, or alternatively whether these data may be better explained through non-specific effects such as the nausea commonly reported following administration of opiate antagonists. The review concludes that the present data suggests a single opioid mechanism is unlikely to explain all aspects of ingestive behaviour, but also concludes that opioid-mediated reward mechanisms play an important control in hedonic aspects of ingestion. The review also highlights the need for further empirical work in order to elucidate further the role of opioid peptides in human ingestive behaviour.

Naloxone nonselective suppression of drinking of ethanol, sucrose, saccharin, and water by rats

Naloxone, a nonselective opioid antagonist, has been demonstrated to reduce oral self-administration of ethanol (EtOH) in rats. Conflicting conclusions have been drawn about the effects of naloxone on consumption of non-EtOH control liquids. A preliminary meta-analysis found large and homogeneous effects of naloxone on EtOH consumption and heterogeneous effects on the consumption of control liquids. Although many of the authors concluded that their control liquid results were "not significant," when they were combined using meta-analytic techniques, it was apparent that there were some strong, but widely divergent, effect sizes. In the first experiment in the current study, 60 male Sprague-Dawley rats were trained to drink 10% EtOH in tap water over 3 weeks of limited-access sessions. Then, their limited-access consumption was measured in single-bottle tests of four liquids (water, 10% EtOH in water, an isocaloric sucrose solution, and an "equally sweet" saccharin solution) 15 min following an intraperitoneal injection of either saline or 1.0 mg/kg naloxone. Every animal was tested 36 times in a counterbalanced order: three times for each liquid following an injection of naloxone and six times for each liquid following an injection of saline. There were distinct differences in the quantity of each liquid consumed in the saline trials. However, the suppression percentages for each liquid in the naloxone trials were identical ( approximately 50%). There were significant correlations, in the range of.23-.42, between the mean amount of each liquid consumed during saline trials for each animal and the suppression percentage during naloxone trials for the same animal and liquid. When the animals were divided into high, low, and medium drinkers for each liquid, the low drinkers demonstrated a much lower suppression after naloxone treatment than did the other two groups. The data confirm that blockade of opioid receptors suppresses consumption of both EtOH and non-EtOH liquids to a degree that is related to the amount of voluntary, untreated consumption of the liquids.

Effects of aging on the opioid modulation of feeding in humans

OBJECTIVES

To determine whether aging is associated with a reduction in the opioid modulation of feeding, which may be important in the pathogenesis of the "anorexia of aging."

DESIGN

Three studies on separate days, in randomized order and double-blind fashion.

SETTING

Clinical Human Research Laboratory, Department of Medicine, RAH, Adelaide, Australia.

PARTICIPANTS

Twelve older (5 male/7 female) (age 65-84) and 12 young (5 male/7 female) (age 20-26) healthy subjects.

INTERVENTION

Subjects received in double-blinded random order, intravenous bolus (10 minutes) and then continuous (140 minutes) infusions of saline (control), naloxone low dose (LD) (bolus 27 microg/kg; continuous 50 microg/kg/hr), or naloxone high dose (HD) (bolus 54.5 microg/kg; continuous 100 microg/kg/hr).

MEASUREMENTS

After 120 minutes, subjects were offered a buffet meal, and their energy intake was quantified. Hunger, fullness, nausea, and drowsiness were assessed using visual analogue scales.

RESULTS

The naloxone LD and HD infusions had no significant effect on ratings of hunger, fullness, or nausea, but increased drowsiness (P < .01) compared with the control infusion in both age groups. Older subjects ate less (P < .001) at the buffet meal than young subjects during all three infusions. Naloxone infusions reduced energy intake compared with control (P < .001), LD by 13.2 +/- 5.0% and HD by 10.7 +/- 5.0%, with no difference between the doses (P = .71). Overall, naloxone suppressed energy intake in both young and older subjects (P < .01). This suppression was slightly, but not significantly, greater in young than in older subjects (mean of LD and HD 16.4 +/- 4.9% vs 7.5 +/- 4.9%, P = .42), because of a trend to reduced suppression in older women.

CONCLUSIONS

We conclude that healthy older adults retain their sensitivity to the suppressive effects of naloxone on food intake. Possible gender differences in this sensitivity warrant further investigation. A decline in opioid activity is unlikely to contribute substantially to the physiological anorexia of aging observed in older people.

Hormonal regulation of appetite and food intake

Several clinical disorders are strongly influenced by hormones involved in appetite and weight regulation. Obesity and eating disorders are of major importance, because they are associated with severe morbidity and considered to be among the greatest health problems in the Western world today. This review describes recent findings in hormonal regulation of food intake by substances acting both centrally, such as corticotropin-releasing factor, neuropeptide Y and leptin, and peripherally, such as cholecystokinin and somatostatin. Sex hormones and glucocorticoids play an important role in long-term regulation of metabolism. The role of these hormones in appetite and weight changes during life as well as during pregnancy and lactation is discussed. Furthermore, the development of obesity and eating disorders is influenced, in particular, by steroid hormones. Treatment with sex hormones, as in hormone replacement therapy, affects appetite and weight and may have beneficial effects in preventing android obesity. Currently, there is great effort in developing endogenous neurohumoral substances into effective drugs for the treatment of obesity and eating disorders. Leptin and neuropeptide Y analogues are of interest as potential antiobesity agents.

Food cravings, endogenous opioid peptides, and food intake: a review

Extensive research indicates a strong relationship between endogenous opioid peptides (EOPs) and food intake. In the present paper, we propose that food cravings act as an intervening variable in this opioid-ingestion link. Specifically, we argue that altered EOP activity may elicit food cravings which in turn may influence food consumption. Correlational support for this opioidergic theory of food cravings is provided by examining various clinical conditions (e.g. pregnancy, menstruation, bulimia, stress, depression) which are associated with altered EOP levels, intensified food cravings, and increased food intake.

Investigational drugs for eating disorders

Anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED) each occur in about 0.5-1.5% of the population in westernised countries, and primarily affect women. At present, a variety of pharmacological treatments are used in addition to psychotherapy, with antidepressants being most the common. Currently available drugs, while helpful, fall far short of desired levels of efficacy. Based on current knowledge about neural mechanisms that regulate feeding behaviour, several classes of compounds are in development to treat eating disorders. These include cholecystokinin (CCK) antagonists, corticotropin-releasing hormone (CRH) antagonists, histamine-3 (H3) receptor antagonists, neuropeptide Y (NPY) antagonists, and a variety of serotonin uptake inhibiting drugs. Based on currently available effective treatments, it seems reasonable that the serotonin uptake inhibiting drugs might hold the greatest likelihood of benefit for these illnesses, but the receptor antagonists in development might provide substantial improvement in response rates.

New aspects of diagnosis and pharmacotherapy of eating disorders

This paper points out recent diagnostic features of bulimia and anorexia nervosa and of the recently defined 'binge eating disorder'. The pharmacologic treatment approaches for these conditions will be reviewed by discussing the results of randomized controlled studies. For anorexia nervosa (AN), the outcome of pharmacotherapy has been poor, in contrast to bulimia nervosa (BN) and binge eating disorder (BED), where pharmacological treatment, primarily with antidepressants, has proved to be effective, at least in the short run. However, long-term outcome studies are still awaited. (MJ Psych Clin Pract 1997; 1: 21-35).

Feeding, drug abuse, and the sensitization of reward by metabolic need

The incentive-motivating effects of external stimuli are dependent, in part, upon the internal need state of the organism. The increased rewarding efficacy of food as a function of energy deficit, for example, has obvious adaptive value. The enhancement of food reward extends, however, to drugs of abuse and electrical brain stimulation, probably due to a shared neural substrate. Research reviewed in this paper uses lateral hypothalamic electrical stimulation to probe the sensitivity of the brain reward system and investigate mechanisms through which metabolic need, induced by chronic food restriction and streptozotocin-induced diabetes, sensitizes this system. Results indicate that sensitivity to rewarding brain stimulation varies inversely with declining body weight. The effect is not mimicked by pharmacological glucoprivation or lipoprivation in ad libitum fed animals; sensitization appears to depend on persistent metabolic need or adipose depletion. While the literature suggests elevated plasma corticosterone as a peripheral trigger of reward sensitization, sensitization was not reversed by meal-induced or pharmacological suppression of plasma corticosterone. Centrally, reward sensitization is mediated by opioid receptors, since the effect is reversed by intracerebroventricular (i.c.v.) infusion of naltrexone, TCTAP (mu antagonist) and nor-binaltorphimine (kappa antagonist). The fact that these same treatments, as well as i.c.v. infusion of dynorphin A antiserum, block the feeding response to lateral hypothalamic stimulation suggests that feeding and reward sensitization are mediated by a common opioid mechanism. Using in vitro autoradiography, radioimmunoassays and a solution hybridization mRNA assay, brain regional mu and kappa opioid receptor binding, levels of prodynorphin-derived peptides, and prodynorphin mRNA, respectively, were measured in food-restricted and diabetic rats. Changes that could plausibly be involved in reward sensitization are discussed, with emphasis on the increased dynorphin A1-3 and prodynorphin mRNA levels in lateral hypothalamic neurons that innervate the pontine parabrachial nucleus, where mu binding decreased and kappa binding increased. Finally, the possible linkage between metabolic need and activation of a brain opioid mechanism is discussed, as is evidence supporting the relevance of these findings to drug abuse.

Metabolic determinants of binge eating

Binge-eating behavior is often thought to be the consequence of energy restriction and dietary restraint. However, evidence is accumulating that recurrent eating binges may be one behavioral mechanism in the expression of familial obesity, and may therefore precede the onset of dieting. The profile of patients with the DSM-IV binge-eating disorder resembles that of patients with familial obesity. There is further evidence for the involvement of the endogenous opiate peptide system. Binge-type foods are often rich in fat, sugar, or both. The opiate antagonist naloxone reduced the consumption of sweet high-fat foods in obese and lean female binge-eaters, though not in nonbinging controls. In contrast, obese as opposed to lean subjects were not differentially affected by naloxone. These data provide a psychobiological validation of the DSM-IV binge eating disorder and suggest that binge eating may be triggered by physiological events. As opposed to being the outcome of dieting, binge-eating episodes should be considered as its possible cause.

A review of anorexia nervosa and bulimia nervosa

Eating disorders remain an important health care problem for clinicians working with children and adolescents. Although the cause of these illnesses remains obscure, information about the effectiveness of different forms of treatment is available to guide the clinician. Individuals involved in the treatment of such patients should be aware of the means of diagnosing the conditions, the common complications of both anorexia and bulimia, the management of these, and the indications for specific treatment modalities. Although the outcome is variable, effective treatment delivered early in the course of illness provides the most likely route to recovery.

Role of neuropeptides in the regulation of feeding behavior: a review of cholecystokinin, bombesin, neuropeptide Y, and galanin

The purpose of this report is to provide a review of four peptides (cholecystokinin, bombesin, neuropeptide Y, galanin) and their role in feeding behavior. Cholecystokinin (CCK) and bombesin (BBS) are considered satiety peptides, and neuropeptide Y (NPY) and galanin (GAL) have been proposed as appetite peptides. For the purposes of this review, satiety refers to the physiological cessation of feeding, and appetite refers to the drive to eat and exists in gradations.

Sensitization and conditioning of feeding following multiple morphine microinjections into the nucleus accumbens

The effects of repeated morphine infusions (10 micrograms/0.5 microliter) into the nucleus accumbens on feeding were studied in sated rats. As shown previously, intra-accumbens morphine infusions induced a large increase in food intake. After undergoing repeated morphine treatment, animals consumed significant quantities of food in response to a saline or sham injection, compared to their pre-morphine baseline. This conditioned feeding was present up to 18 days after the final drug infusion. Additionally, repeated morphine administration caused a progressive sensitization of feeding; the final morphine infusion elicited nearly double the amount of food intake as the first. Multiple saline infusions had no behavioral effects. Repeated stimulation of opiate receptors may enhance associative mechanisms such that previously neutral environmental stimuli acquire the ability to elicit feeding. Abnormal activation of this system may be a possible neural substrate for compulsive feeding and bulimia.

Opioid dysregulation in anorexia nervosa: naloxone effects on preprandial and postprandial growth hormone response to growth hormone-releasing hormone

Previously, we have shown that in the opposite extremes of nutritional status, obesity and anorexia nervosa (AN), growth hormone (GH) response to growth hormone-releasing hormone (GH-RH) is not inhibited by the ingestion of a normal 800-cal meal consumed at lunch time (1 PM), which is at variance with results in normal subjects. However, in obese patients the postprandial increase in GH response to GH-RH is inhibited by an infusion of naloxone (NAL). In this study we have tested anorectic patients, performing the following tests at 1 PM: GH-RH test (50 micrograms IV) or, in a different day session, NAL (1.6 mg/h, starting 30 minutes before GH-RH) + GH-RH test (50 micrograms IV). The tests were performed in the following three different experimental conditions: (1) short-term fasting studies (lasting from breakfast), (2) long-term fasting studies (from midnight of the day before) and (3) postprandial studies (after a standard meal consumed 1 hour before the test). In AN, the GH response to GH-RH was not influenced by NAL infusion at 1 PM, in both short- and long-term fasting studies (short-term fasting: peak values after GH-RH alone, 26.5 +/- 6.5 ng/mL, during NAL, 28.0 +/- 3.3 ng/mL; long-term fasting: peak values after GH-RH alone, 32.2 +/- 6.8 ng/mL, during NAL, 30.6 +/- 4.0 ng/mL). A partial NAL-inhibitory effect was instead observed in postprandial studies, as evidenced by the calculation of areas under the curve ([AUCs] 1,662.1 +/- 90.0 after GH-RH alone v 1,090.5 +/- 245.4 ng/mL/h during NAL).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

A review of the controlled trials of pharmacotherapy and psychotherapy in the treatment of bulimia nervosa

The treatment literature on bulimia nervosa includes several double-blind placebo controlled studies, the majority of which examine the use of antidepressants in bulimia nervosa. The psychotherapy literature has focused heavily on the use of cognitive behavioral therapy (CBT) in the treatment of this eating disorder. Some studies have compared CBT to other types of therapy or waiting list controls. The following review will examine the methodology and outcome of the pharmacotherapy and psychotherapy treatment studies of bulimia nervosa. The authors conclude that while the studies indicate treatment is somewhat effective, there remains uncertainty regarding the long-term effectiveness of most of the reported treatments.

Measurement of CSF dynorphin A 1-8 immunoreactivity in anorexia nervosa and normal-weight bulimia

Twenty-one patients with anorexia nervosa and 35 normal-weight patients with bulimia underwent a series of CSF studies involving measurement of CSF dynorphin A 1-8 immunoreactivity during hospitalization in an eating-disorder treatment and research program. The control group consisted of 17 healthy volunteers. There were no statistically significant differences in CSF dynorphin A 1-8 measurements among groups or within a group at various stages of treatment. These results regarding dynorphin A 1-8 immunoreactivity are discussed in light of other evidence for altered opiate function in some eating-disorder patients.

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.

Influence of naloxone infusion on prolactin and growth hormone response to growth hormone-releasing hormone in anorexia nervosa

Anorexia nervosa (AN) is frequently associated with anomalies of growth hormone (GH) and prolactin (PRL) secretion. We studied the GH and PRL responses to GHRH1-44 (50 micrograms IV) and the effect of a naloxone infusion (1.6 mg/hr), started 1 hr before GHRH administration, on this response in 12 female patients with AN, aged 15-30 yr, and in seven normal women, aged 19-27 yr, during the follicular phase as controls. In AN, GHRH induced an increase in GH levels similar to that observed in normal subjects. A significant inhibition of the GH response to GHRH was observed during naloxone infusion, similar to the inhibition in normal female subjects during the follicular phase. PRL levels showed a significant increment after GHRH alone and a slight, nonsignificant, PRL increment after GHRH during naloxone infusion in AN patients. In contrast a slight PRL decrease was observed after GHRH, both before and during naloxone infusion, in the normal subjects. Our study demonstrates that endogenous opioids play a role in influencing PRL secretion in patients with AN different from their role in normal subjects.

Current perspectives on the eating disorders: I. History, psychological and biological aspects

An ongoing, major effort in psychiatry throughout the 1980s has been the study of anorexia and bulimia. In spite of ample effort on the part of researchers and clinicians, the etiology of these disorders remains elusive. Because of the multiple biological, sociocultural, and psychological forces involved and the early genesis of the disorder, an understanding of the eating disorders is tantamount to an appreciation of the developmental process itself. Part I of this paper presents a historical view of the eating disorders and reviews recent progress in classification criteria, epidemiology, biology, psychology, developmental, and analytic theory. Part II will focus on treatment, outcome, and research priorities.

Effects of naltrexone on food preference and concurrent behavioral responses in food-deprived rats

Naltrexone (0.05-5.0 mg/kg, SC) was administered to food-deprived rats prior to a 15-min food-preference test. Total food intake and feeding duration was reduced following administration of the opiate antagonist. However, while naltrexone reduced the consumption of the initially-preferred chocolate-coated cookies, the ingestion of the nonpreferred standard laboratory chow pellets was significantly enhanced. These data cannot be explained in terms of a general anorexic effect and nonspecific suppression of feeding responses. Instead, they indicate that naltrexone reduced preference for the highly palatable cookies, so that a feeding response to the chow pellets emerged. Under the conditions of test-familiarity, naltrexone did not reduce grooming, locomotion or rearing duration. An increase in locomotion may have been secondary to the reduction in feeding. The results agree with previous data from animal and human studies in suggesting that endogenous opioid peptide activity is involved in the palatability of preferred foods.

Neuroendocrine profile in bulimia nervosa

The neuroendocrinology of bulimia nervosa has only recently been investigated, with initial research suggesting some biological overlap with both anorexia nervosa (AN) and depression. Similarities among AN, depression, and bulimia include a nonsuppressed Dexamethasone Suppression Test and an abnormal growth hormone (GH) response to thyrotropin-releasing hormone (TRH). Bulimics and anorectics both tend to have a delayed thyrotropin (TSH) response to TRH and elevated basal GH levels. Bulimics, however, have a normal GH response to clonidine, a nonblunted TSH response to TRH, low basal prolactin (PRL) levels, and may have an exaggerated PRL response to TRH. Unpublished data suggest bulimics may have a gonadotropin profile distinct from either AN or depression, as well as a variety of other endocrinopathies. Although many of these abnormalities may reflect malnutrition despite normal weight, other factors that are as yet unidentified are likely to be contributing to the neuroendocrine abnormalities seen in bulimia.

Impaired cholecystokinin secretion in bulimia nervosa

Bulimia nervosa is a prevalent disorder of unknown cause, characterized by recurrent episodes of uncontrollable eating. In the light of recent evidence that the gastrointestinal hormone cholecystokinin induces satiety and reduces food intake in laboratory animals and humans, we investigated the hypothesis that abnormalities in cholecystokinin secretion and satiety may occur in patients with bulimia and contribute to their disturbed eating patterns. Blood levels of cholecystokinin and subjective satiety were measured in 14 women with bulimia and 10 normal women before and after a mixed-liquid meal. The total integrated plasma cholecystokinin response to eating was significantly impaired in patients with bulimia (P less than 0.05) as was postprandial satiety. Fasting cholecystokinin levels were similar in both populations (approximately 0.8 pmol per liter). After eating, however, mean (+/- SEM) peak plasma cholecystokinin levels increased to 4.1 +/- 0.9 pmol per liter in normal controls but to only 2.1 +/- 0.2 pmol per liter in patients with bulimia nervosa (P less than 0.05). After an open trial of tricyclic antidepressants in a subgroup of five patients with bulimia, the postprandial cholecystokinin response to eating increased significantly, to 6.6 +/- 1.2 pmol per liter (P less than 0.05), and there was an increase in the satiety response. We conclude that patients with bulimia do not have normal satiety and have impaired secretion of cholecystokinin in response to a meal. Preliminary evidence suggests that both these abnormalities may be improved by treatment with tricyclic antidepressants.

The use of opiate antagonists in treating bulimia: a study of low-dose versus high-dose naltrexone

Sixteen individuals with bulimia consented to a 6-week trial of naltrexone, receiving either standard dosages of 50-100 mg each day or high dosages of 200-300 mg each day. At the end of 6 weeks, individuals in the low-dose group had no significant change in their frequency of binge eating or purging, while individuals in the high-dose group had significant reductions in both behaviors. Four individuals in the low-dose group who were crossed over to high-dose naltrexone at the end of the study went on to experience significant reductions in binge eating and purging. These findings support the potential utility of opiate blockade in treating bulimia, but suggest that dosages of naltrexone greater than those needed to block exogenous opiates may be required for therapeutic efficacy in reducing binge eating and purging.