Modalities of the food intake-reducing effect of sibutramine in humans

Serotonergic anti-obesity agents: past experience and future prospects

The role of serotonin (5-hydroxytryptamine) in appetite control is long established. Serotonergic manipulations reduce food intake in rodents in a manner consistent with satiety. In humans, drugs such as fenfluramine, dexfenfluramine and sibutramine all reduce energy intake, suppress hunger and enhance satiety. Effects on eating behaviour and subjective sensations of appetite are associated with the weight loss-inducing effects of these treatments. Currently, no appetite-suppressing drugs are approved specifically for the treatment of obesity. However, a new generation of serotonergic drugs have progressed through clinical development. The serotonin 5-HT(2C)-receptor selective agonist lorcaserin, a drug specifically developed to target satiety without producing the side effect profiles of its predecessors, has been shown to significantly reduce energy intake and body weight. The weight loss produced by lorcaserin appears modest, and behavioural effects, particularly its supposed satiety-enhancing effects, have yet to be characterized. The monoaminergic re-uptake inhibitor tesofensine has also been shown to produce impressive weight loss in smaller-scale clinical studies. It remains unclear if this drug produces any effects on appetite mediated by serotonin, or whether weight loss is produced largely through enhanced energy expenditure. Evidence indicates that tesofensine strengthens satiety, but behavioural specificity and psychological side effects remain an issue. The serotonergic system remains a viable target for anti-obesity treatment. In this review, we examine the limited behavioural data available on these two new CNS-acting appetite suppressants.

Sibutramine promotes amygdala activity under fasting conditions in obese women

RATIONALE

Sibutramine, a centrally-acting selective monoamine reuptake inhibitor, has been used as an appetite suppressant drug in obesity.

OBJECTIVES

To gain insight into the central nervous actions of sibutramine, brain responses to pictures of food items after sibutramine vs placebo application were assessed by functional magnetic resonance imaging (fMRI) in obese women.

METHODS

In a randomized double-blind crossover design, 10 healthy obese women (BMI 31.8-39.9 kg/m(2)) received 15 mg/d of sibutramine vs placebo for 14 d. Obese participants, and a group of 10 age-matched normal weight controls, viewed pictures of food items and control objects in hungry and satiated states while lying in the MR scanner. The paradigm followed a block design. In obese participants, fMRI measurements were conducted prior and after two weeks of daily sibutramine or placebo administration, whereas control participants were scanned only at one point in time.

RESULTS

Upon food item presentation, obese participants showed increased brain activity in areas related to emotional and reward processing, perceptual processing, and cognitive control as compared to normal weight controls. Sibutramine exerted a divergent satiety-dependent effect on amygdala activity in obese participants, increasing activity in the hungry state while decreasing it under conditions of satiation.

CONCLUSIONS

Our results demonstrate a modulatory influence of sibutramine on amygdala activity in obese women which may underlie the appetite suppressant effects of the drug.

5-HT(2C) receptor agonists and the control of appetite

The role of serotonin (5-HT) in appetite control is well recognised. 5-HT drugs reduce food intake in rodents in a manner consistent with an enhancement of satiety. In humans, they have been shown to reduce caloric intake, an effect associated with reduced hunger and increased satiety. These effects appear to be mediated, at least in part, by the 5-HT(2C) receptor subtype. 5-HT-acting drugs such as fenfluramine, d-fenfluramine, and sibutramine have provided effective anti-obesity treatments in the past. However, more selective agents are needed that produce the same changes in eating behaviour and induce weight loss without unacceptable side effects. Lorcaserin, a selective 5-HT(2C) receptor agonist, is a novel anti-obesity agent that reduces both energy intake and body weight. The effects of lorcaserin on eating behaviour remain to be characterised as does its behavioural specificity.

Inverse agonism at α2A adrenoceptors augments the hypophagic effect of sibutramine in rats

Because the use of monoamine reuptake inhibitors as weight-reducing agents is limited by adverse effects, novel antiobesity drugs are needed. We studied acute effects of the noradrenaline (NA) and serotonin (5-HT) reuptake inhibitor sibutramine (SIB), alone and after pretreatment with α1- and α2-adrenoceptor (AR), and 5-HT1/2/7, 5-HT1B and 5-HT2C receptor antagonists in order to determine which ARs and 5-HT receptors act downstream of SIB on feeding and locomotion. Acute effects on caloric and water intake, meal microstructure and locomotion were assessed, using an automated weighing system and telemetry in male rats with restricted 18-h access to Western style diet. SIB 3 mg/kg reduced meal size and frequency, which suggests enhanced within- and postmeal satiety. Imiloxan (α2B-AR), WB4101 (α1-AR), SB-224289 (5-HT1B), and modestly BRL 44408 (α2A/D-AR) attenuated SIB's effect on meal size, suggesting that α2B- and α1-ARs and 5-HT1B receptors mediate within-meal satiety, with a modest role for α2A/D-ARs. Only prazosin (α1/2B/2C-AR) counteracted SIB's effect on meal frequency. At 3 mg/kg, SIB modestly increased locomotion. This effect was blocked by metergoline (5-HT1/2/7), WB4101 (α1-AR), and RX821002 (α2-AR). Interestingly, the α2-AR antagonists atipamezole and RX821002 enhanced SIB's effect on caloric intake, probably due to inverse agonistic actions at α2A-autoreceptors that further enhanced release of NA that regulates caloric intake. Thus, an inverse agonist of presynaptic α2A-ARs might beneficially enhance SIB's weight-reducing effect and offer novel treatment for obesity. All in all, the present data supports the ARs and 5-HT receptors involved in the effects of SIB on different aspects of caloric intake and locomotion.

The effects of sibutramine on the microstructure of eating behaviour and energy expenditure in obese women

Given the suggestion that many potential anti-obesity drugs may enhance within-meal satiation, few studies have directly measured the effects of any drug on the microstructure of human eating behaviour. The effects of 7 days dosing with sibutramine 10 mg and 15 mg a day on appetite and energy balance were determined in 30 obese women (BMI 34.6 +/- 3.3 kg/m2, age 46.0 +/- 12.9 years) using a Universal Eating Monitor (UEM) and indirect calorimetry, in a double-blind, placebo-controlled crossover study. At day 7, sibutramine 10 mg and 15 mg reduced food intake by 16.6% and 22.3%, respectively (p < 0.001), compared with placebo. Sibutramine reduced eating rate compared with placebo rather than meal length (10 mg p < 0.05; 15 mg p < 0.001). In addition, sibutramine 10 mg significantly reduced hunger later in the meal (p < 0.05) and sibutramine 15 mg increased fullness early in the meal (p < 0.01), both of which are consistent with enhanced within-meal satiation. Sibutramine had little effect on resting metabolic rate, although 15 mg did significantly reduce respiratory quotient at several time points during the test day. These results provide novel evidence that decreased consumption of a test meal induced by sibutramine is primarily because of reduced eating rate, enhancing the deceleration in cumulative food intake within a meal associated with the development of satiety. Changes in within-meal appetite ratings appear particularly sensitive to drug-induced enhancement of satiation, and may provide key indices for assessing the therapeutic potential of novel anti-obesity drugs.

Comparison of the effects of a liquid yogurt and chocolate bars on satiety: a multidimensional approach

In the context of epidemic obesity, satiety is an important target for nutritional interventions. Using a multidimensional approach, we compared the effect on satiety of two food products frequently consumed in France by young adults as a small mid-afternoon meal called the ‘goûter’. Participants were eighteen healthy young males (aged 20·8 (sd1·8) years) of normal body weight (BMI 21·7 (sd1·7) kg/m2) used to eating four times per d including a ‘goûter’. On two occasions, under laboratory conditions, the time-blinded participants consumed a fixed energy lunch (2·8 MJ) and, 240 min later, either a liquid yogurt or chocolate bars matched for energy (1·2 MJ) and weight (366 g). Then, satiety was assessed by: (1) ratings of hunger, appetite, desire to eat and fullness at 20 min intervals (perception), (2) the delay until the subject requested his dinner meal (duration) and (3) energy intake at this meal (consumption). Results showed that satiety was perceived higher after liquid yogurt than chocolate bars over the 60 min preceding the next meal, as evidenced by hunger (P < 0·005), appetite, (P < 0·005), desire to eat (P < 0·04) and fullness (P < 0·05) ratings. However, its duration was similar between liquid yogurt and chocolate bars (165 (se8) and 174 (se7) min respectively) and this difference was not followed by reduced intake at dinner. In conclusion, this approach of satiety revealed that a liquid yogurt induced a lower subjective motivation to eat than chocolate bars during the hour preceding the spontaneous onset of a meal, without affecting subsequent food intake.

Potent and selective agonism of the melanocortin receptor 4 with MK-0493 does not induce weight loss in obese human subjects: energy intake predicts lack of weight loss efficacy

MK-0493 is a novel, potent, and selective agonist of the melanocortin receptor 4 (MC4R), one of the best-validated genetic targets and considered one of the most promising for the development of antiobesity therapeutics. An ad libitum energy-intake model was qualified with excellent reproducibility: the geometric mean ratio (GMR) with 95% confidence interval (CI) for total energy intake over a period of 24 h for 30 mg sibutramine/placebo was 0.82 (0.76, 0.88), and for 10 mg sibutramine/placebo it was 0.98 (0.91, 1.05). MK-0493 showed a small and marginally significant effect on 24-h energy intake, whereas 30 mg of sibutramine caused a significant reduction in total 24-h energy intake; specifically, the GMR (95% CI) for 30 mg sibutramine/placebo was 0.79 (0.74, 0.85). MK-0493 was associated with modest weight reduction from baseline but had only small, statistically insignificant effects relative to placebo after 12 weeks in a fixed-dose study and also after 18 weeks of stepped-titration dosing. We conclude that agonism of MC4R is not likely to represent a viable approach to the development of antiobesity therapeutics.

Acute effects of pharmacological modifications of fatty acid metabolism on human satiety

The role of NEFA in eating behaviour is still poorly known. Our objective was to examine whether etomoxir (ETO), an inhibitor of NEFA oxidation, or ( − )-hydroxycitrate (HCA), an inhibitor of lipogenesis which may indirectly stimulate NEFA oxidation, alters satiety. Post-lunch satiety was measured in eight normal-weight male subjects who were deprived of time cues and received on three occasions either ETO (320 mg), HCA (2 g) or placebo (PLA) in random order. Between lunch and dinner, blood was withdrawn continuously and collected every 10 min for measures of plasma concentrations of glucose, insulin, lactate, TAG, NEFA, β-hydroxybutyrate (BHB), leptin and ghrelin. Results showed that HCA began to decrease hunger and desire to eat compared to PLA and ETO 210 min after lunch and increased satiety duration compared to PLA by 70 (se23) min (P < 0·05), but did not modify energy intake at dinner. ETO did not affect any variable of satiety. HCA increased NEFA concentrations during the pre-dinner period, whereas ETO increased and decreased plasma concentrations of NEFA and BHB, respectively. Mean differences in plasma NEFA concentrations between HCA and PLA were predictive of the differences in satiety duration between treatments (r20·71,P < 0·01). Among treatments, plasma leptin concentration at dinner onset was the only blood variable correlated with energy intake at this meal (r− 0·75,P < 0·0005). In healthy, normal-weight men, acute HCA increased the intensity and duration of satiety possibly via increased NEFA disposal for oxidation.

Modafinil decreases food intake in humans subjected to simulated shift work

In a limited number of studies modafinil has been shown to decrease food intake by laboratory animals and humans. The present study represents a secondary data analysis, in which the effects of modafinil on several measures of food intake were determined in humans living in a residential laboratory during simulated shift work. During this 23-day study, a wide selection of food items and beverages were freely available. During this double-blind, within-participant study, volunteers (N = 11) received oral modafinil dose (0, 200, or 400 mg) 1 h after waking for three consecutive days under two shift conditions: day shift and night shift. Shifts alternated three times during the study, and shift conditions were separated by an "off" day. Modafinil (200, 400 mg) dose-dependently decreased total caloric intake by approximately 18% and approximately 38%, respectively, regardless of shift condition, without selectively altering the proportion of total calories derived from carbohydrate, fat and protein. Ratings of "Hungry" were also significantly decreased by both active doses, but only immediately before the lunch break period. In addition, tolerance to the anorexic effects of modafinil was not apparent, as these effects remained stable across the three days of modafinil dosing. These findings show that modafinil produced clear reductions in food intake and suggest that future prospective studies should examine the drug in obese participants.

Effects of sibutramine on gastric emptying, intestinal motility and rectal tone in dogs

The aim of this study was to evaluate the effects of sibutramine on gastric emptying, small-bowel contractions, rectal tone and compliance, and gastrointestinal myoelectrical activity. The study was performed in 14 dogs. It was composed of three separate experiments: gastric emptying of liquids and gastrointestinal slow waves; small-bowel contractions; and rectal tone and rectal compliance. Each experiment included two sessions: a control session and a treatment session with sibutramine (5 mg/kg orally) administrated 2 h before the study. Sibutramine significantly accelerated liquid gastric emptying at 75 and 90 min after the meal but did not alter gastrointestinal slow waves. Gastric emptying at 75 and 90 min was 61.42 +/- 7.71 and 66.32 +/- 7.67% in the control session, and increased to 71.27 +/- 5.14 and 75.93 +/- 5.29% in the session with sibutramine (p < 0.05, vs. control). Sibutramine significantly inhibited postprandial small-bowel contractions. Sibutramine did not alter the rectal tone, but significantly increased rectal compliance. Sibutramine accelerates gastric emptying of liquids but inhibits small-bowel contractions. These findings suggest the peripheral mechanisms of sibutramine in reducing food intake and causing weight loss in obesity patients.

Driving earlier clinical attrition: if you want to find the needle, burn down the haystack. Considerations for biomarker development

Drug development attrition rates are rising and late phase attrition remains high, contributing to an unsustainable increase in R&D spending. Consequently, there is much effort to identify the potentially successful molecules earlier in development with the use of biomarkers to predict potential efficacy and safety. However, focussing only on picking the winners earlier will not solve the problem. It is essential that the evaluation of these biomarkers also enables the earlier termination of the molecules that will not have the required activity.

Serotonergic drugs : effects on appetite expression and use for the treatment of obesity

Over 35 years of research suggests that endogenous hypothalamic serotonin (5-hydroxytryptamine) plays an important part in within-meal satiation and post-meal satiety processes. Thus, the serotonin system has provided a viable target for weight control, critical to the action of at least two effective anti-obesity treatments, both producing clinically significant weight loss over a year or more. Numerous serotonin receptor subtypes have been identified; of these, serotonin 5-HT1B and 5-HT2C receptors have been specifically recognised as mediators of serotonin-induced satiety.A number of serotonergic drugs, including selective serotonin reuptake inhibitors (SSRIs), dexfenfluramine and 5-HT2C receptor agonists, have been shown to significantly attenuate rodent bodyweight gain. This effect is strongly associated with marked hypophagia and is probably mediated by the hypothalamic melanocortin system. Additionally, sibutramine, dexfenfluramine, fluoxetine and the 5-HT2C receptor agonist chlorophenylpiperazine (mCPP) have all been shown to modify appetite in both lean and obese humans, resulting in reduced caloric intake. Clinical studies demonstrate serotonergic drugs specifically reduce appetite prior to and following the consumption of fixed caloric loads, and cause a reduction in pre-meal appetite and caloric intake at ad libitum meals. Weight loss in the obese has also been produced by treatment with both the serotonin precursor 5-hydroxytryptophan and the preferential 5-HT2C receptor agonist mCPP.A new generation of 5-HT2C receptor selective agonists have been developed and at least one, lorcaserin (APD356), is currently undergoing clinical trials. In addition, 5-HT6 receptor antagonists such as PRX-07034 and BVT74316 have been shown to potently reduce food intake and bodyweight gain in rodent models and have recently entered clinical trials. However, the role of the 5-HT6 receptor in the expression of appetite remains to be determined. The hope is that these drugs will not only be free of their predecessors' adverse effect profiles, but will also be equally or more effective at regulating appetite and controlling bodyweight.

Consequence of omitting or adding a meal in man on body composition, food intake, and metabolism

OBJECTIVE

To investigate in man the consequence on body composition and related biological and metabolic parameters of omitting or adding a meal.

RESEARCH METHODS AND PROCEDURES

Twenty-four young normal-weight male subjects were recruited, 12 usual four-meal and 12 usual three-meal eaters, differing only in the consumption of an afternoon meal. They omitted or added a fourth meal during a 28-day habituation period and were asked to report their intake on three 3-day occasions. Before and after this habituation period, subjects participated in a session with a time-blinded procedure, and blood was collected continuously from lunch to the spontaneously requested dinner. Body composition, respiratory quotient, and biochemical parameters were measured in the late evening preceding each session.

RESULTS

Omitting a meal was followed by increases in fat mass (360 +/- 115 grams, p < 0.05), late evening leptin concentration (20.7 +/- 11.0%, p < 0.05), and respiratory quotient (3.7 +/- 1.4%, p < 0.05). Increase in the percentage of dietary fat during the habituation period (+4.1 +/- 2.0%, p < 0.05) was correlated with fat mass (r = 0.66, p < 0.05). Adding a meal had no effect, but, in both groups, the change in energy content at this fourth eating occasion was correlated with the change in adiposity.

DISCUSSION

Our results suggest that adiposity may increase when young lean male subjects switch from a four- to a three-meal pattern by removing their usual afternoon meal. This effect could be partly mediated by a change in the macronutrient composition of the diet.

Effects of sibutramine on the appetitive and consummatory aspects of feeding in non-human primates

This study examined how sibutramine (0.06-4.0 mg/kg, i.m.), a clinically effective weight-loss medication which increases extracellular serotonin and norepinephrine levels, affected the appetitive and consummatory aspects of feeding of non-human primates. The effects were compared to the effects of the positive control dexfenfluramine (2.0-6.0 mg/kg, p.o.), which primarily increases extracellular serotonin levels. Baboons had access to food 24 h each day, but they had to complete a two-phase operant procedure in order to eat. Responding on one lever during a 30-min appetitive phase was required before animals could start a consumption phase, where responding on another lever led to food delivery, i.e., a meal. Responding during the appetitive phase resulted in presentations of food-related stimuli only. Sibutramine increased the latency to the first meal of the session in females, and decreased consummatory behavior without affecting other appetitive behavior in males and females. In contrast, dexfenfluramine, increased the latency to the first meal of the session, and decreased both appetitive and consummatory behavior in males and females. The behavioral mechanism by which sibutramine decreases food intake is distinct from other anorectic drugs, including dexfenfluramine, that have been tested in this paradigm.

Sibutramine and the management of obesity

Sibutramine is a selective serotonin and noradrenaline re-uptake inhibitor approved for the long-term management of obesity. Its primary mechanism of action is increased satiety, although some evidence also suggests increased energy expenditure could play a role in sibutramine-induced weight loss. It has established general efficacy in long-term trials, with clinically-approved doses of 10 and 15 mg. Sibutramine has also been studied in a number of unique populations, including obese controlled hypertensives, diabetics and ethnic minorities, further establishing its effectiveness. However, it does have a consistent effect of increasing blood pressure and pulse. Thus, blood pressure and heart rate should be monitored in patients using sibutramine and it may not be applicable in obese patients with significant cardiovascular disease.

A review of the metabolic effects of sibutramine

BACKGROUND

Obesity is associated with an increased incidence of diabetes, hypertension, dyslipidaemia and coronary artery disease. Current management strategies of obesity include lifestyle management strategies of obesity include lifestyle interventions and pharmaco therapy. Sibutramine is a drug with established efficacy in weight reduction and maintenance of weight loss. It reduces food intake and attenuates the fall in reduces food intake and attenuates the fall in metabolic rate associated with weight loss.

OBJECTIVE

To review the metabolic effects associated with sibutramine use.

METHODS

Relevant articles were identified through a Medline search (up to December 2004).

RESULTS

Weight loss with sibutramine treatment is associated with improved insulin sensitivity and a fall in glycosylated haemoglobin levels in type 2 diabetic patients. In most trials sibutramine exerted favourable effects on lipids, especially exerted favourable effects on lipids, especially on high density lipoprotein (HDL) cholesterol and triglycerides, as well as on the total:HDL cholesterol ratio. Sibutramine also lowers serum uric acid concentrations. Furthermore, this drug seems to favourably influence adipocytokines; it reduces serum leptin and resistin levels and increases adiponectin levels. Sibutramine also exerts a beneficial effect on hyper androgenaemia in obese women with polycystic ovary syndrome. Preliminary findings also suggest that weight loss following treatment with sibutramine is useful in patients with non-alcoholic fatty liver disease (NAFLD).

CONCLUSION

Weight loss following sibutramine administration is associated with several favourable metabolic effects.

The utility of animal models of human energy homeostasis

The prevalence of obesity among adults and children has increased steadily over the last few years worldwide, reaching epidemic proportions. Particularly alarming is the link between obesity and the development of chronic disorders such as heart disease, type 2 diabetes, hypertension and some cancers (Bjorntorp, 1997). Environmental causes of obesity are thought to include a sedentary lifestyle and an abundance of highly palatable energy-dense foods (Hill et al. 2003). Genetic factors also contribute to susceptibility to obesity, although the genetic basis of most human obesities is thought to be polygenic (Comuzzie & Allison, 1998; Barsh et al. 2000). The present paper considers some of the animal models used to infer aspects of human obesity, with an emphasis upon their usefulness.

Effect of sibutramine on macronutrient selection in male and female rats

Sibutramine, a serotonin-noradrenaline reuptake inhibitor (SNRI), has been shown to be a safe and effective weight-loss drug. The purpose of the present study was to examine whether sibutramine has an effect on macronutrient selection in both female and male rats in addition to total food intake. Wistar rats of both sexes were divided into three groups, and each group was offered a different set of three sensorily contrasting macronutrient-specific diets, each set including carbohydrate-, protein-, and fat-rich diets. Sibutramine (10 mg/kg) was shown to consistently decrease carbohydrate and fat intake at all data points regardless of gender and diet. Intake of carbohydrate differed between male and female rats at 2 h post administration with 2.5 and 5 mg/kg of sibutramine. The effect of sibutramine on protein intake was diet- and gender-specific. All doses of sibutramine decreased total food intake regardless of gender and diet group beginning at 6 h post administration. In conclusion, sibutramine affected macronutrient selection and emphasis on dietary recommendations, as well as appropriate dosage according to gender should be considered during therapy.

Use of sibutramine to treat obesity

Medications are useful adjuncts to diet and exercise and may help patients lose weight and maintain significant weight loss (5%-10% from baseline). Pharmacologic approaches are indicated in those patients who have had prior weight-loss attempts, who have a body mass index greater than or equal to 30 kg/m2 or greater than or equal to 27 kg/m2 with comorbidity, and who are motivated and ready to undertake dietary and physical activity changes. This article provides a treatment algorithm to help physicians measure meaningful weight loss and proposes conservative blood pressure limits to guide the long-term prescription of sibutramine. Sibutramine can be a useful tool in the obesity treatment toolbox if used by knowledgeable practitioners.

Methamphetamine attenuates disruptions in performance and mood during simulated night-shift work

RATIONALE

Increased sleepiness while working and sleep disruptions are common complaints among shift workers. Consequently, shift workers may be more susceptible to diminished performance and work-related accidents.

OBJECTIVE

To examine the effects of the central nervous system stimulant methamphetamine on psychomotor task performance, subjective effects, and food intake during shift work under laboratory conditions.

METHODS

Seven participants completed this 23-day, within-participant design, residential laboratory study. They received a single oral methamphetamine dose (0, 5, 10 mg) 1 h after waking for three consecutive days under two shift conditions: (1) during the day shift, participants performed computerized psychomotor tasks from 0830 hours to 1730 hours and went to bed at 2400 hours and (2) during the night shift, participants performed tasks from 0030 hours to 0930 hours and went to bed at 1600 hours. Shifts alternated three times during the study; shift conditions were separated by an "off" day during which participants were not on a schedule and data were not collected.

RESULTS

When participants received placebo, psychomotor task performance and subjective effects were disrupted during the night shift, relative to the day shift. Changing shift conditions did not alter food intake significantly. Methamphetamine reversed performance and subjective-effects disruptions, and decreased food intake during the night shift.

CONCLUSION

These data indicate that shift changes produce performance impairments and mood alterations, and that a single low to moderate dose of methamphetamine attenuates many shift change-related disruptions in performance and mood.

Effects of preexposure to dexfenfluramine, phentermine, dexfenfluramine-phentermine, or fluoxetine on sibutramine-induced hypophagia in the adult rat

The antiobesity drug sibutramine suppresses food intake via inhibition of reuptake of both norepinephrine (NE) and serotonin (5-HT) into brain terminals. The present study examined whether preexposure to other antiobesity drugs (fluoxetine [FLUOX], phentermine [PHEN], and dexfenfluramine [DEX]) that alter noradrenergic and/or serotonergic activity in brain induces tolerance or sensitization to the subsequent hypophagic action of sibutramine. Accordingly, adult male rats were treated (administered orally once per day for 21 days) with DEX (0, 1, or 3 mg/kg) and/or PHEN (0, 5, or 10 mg/kg), alone and in combination, or with the selective 5-HT reuptake inhibitor FLUOX (0, 15, or 30 mg/kg). Daily administration of PHEN persistently reduced food intake and body weight whereas tolerance developed to the hypophagic action of DEX or of FLUOX within the first week of daily administration. Moreover, low doses of DEX (1 mg/kg) and PHEN (5 mg/kg) interacted in a supra-additive manner to inhibit food intake and water intake and decrease body weight over the 21-day exposure period. After a recovery period of 9 days, a series of food intake trials were conducted to assess the hypophagic action of sibutramine (0, 1, 3, and 9 mg/kg po). Preexposure to PHEN (5 or 10 mg/kg), DEX (3 mg/kg), or FLUOX (30 mg/kg) resulted in a significant attenuation of the hypophagia induced by sibutramine over an 8-h, but not a 2-h, testing period. The pattern of cross-tolerance noted in this study is consistent with the observation that sibutramine inhibits eating via an interaction with noradrenergic and serotonergic mechanisms. Whether PHEN and DEX preexposure in humans alters subsequent sibutramine effectiveness is unknown.

Pharmacotherapy of obesity

The growing recognition of the health risks of obesity coupled with the difficulties in treating it successfully by lifestyle modification predicates a need for effective drug treatment. The history of drug treatment in the second half of the 20th century is, however, one of disappointment and concern over drug toxicity. However, the advances in our understanding of the mechanism of weight control, together with improved ways of evaluating anti-obesity drugs, has resulted in two effective compounds, sibutramine and orlistat, becoming available for clinical use. Sibutramine has actions on both energy intake and expenditure and had been shown to enhance weight loss and weight maintenance achieved by diet, in simple obesity as well as when accompanied by complications of diabetes or hypertension. About 50-80% of patients can achieve a >5% loss, significantly more than if patients receive the same lifestyle intervention with placebo. Orlistat, which acts peripherally to block the absorption of dietary fat, has had similar results in clinical trials; a recent study (XENDOS) has just reported results which show that the enhanced, albeit modest, weight loss achieved with orlistat delays the development of diabetes over a 4-year period. A number of other compounds are expected to complete or enter clinical trials over the next decade. There is considerable optimism that we will soon have the pharmacological tools needed to make the treatment of obesity feasible.

Serotonin receptor blockade increases food intake and body weight after total gastrectomy in rats

BACKGROUND

Total gastrectomy often results in early satiety and loss of body weight. Serotonin inhibits food intake, and postprandial serotonin release is increased after total gastrectomy. Serotonin might contribute to early satiety and loss of body weight after total gastrectomy.

METHODS AND MATERIALS

Food intake and body weight were investigated with an automated recording system in gastrectomized rats 1-12 months postoperatively. Rats were treated with metergoline, a 5-hydroxytryptamine (5-HT)(1/2) receptor antagonist, two different 5-HT(3) receptor antagonists, a combination of metergoline and devazepide, a cholecystokinin (CCK) a receptor antagonist, or vehicle. In addition, metergoline or vehicle was applied continuously by an intraperitoneal osmotic minipump for 7, 28, or 84 days after total gastrectomy.

RESULTS

Metergoline treatment resulted in a dose-dependent increase in food intake in gastrectomized rats. 5-HT(3) receptor antagonist treatment had no effect, and devazepide in addition to metergoline did not further stimulate food intake. Metergoline increased food intake at 1, 3, and 6 months postoperatively by up to 45% (24-h cumulative food intake [FI], 6 months: vehicle 3.83 +/- 0.10, metergoline 5.52 +/- 0.15 g/100 g body weight (BW), P < 0.0001). Chronic metergoline treatment for 7, 28, or 84 days significantly increased food intake after total gastrectomy compared to vehicle treatment (FI 7 days: vehicle 30.83 +/- 0.71, metergoline 36.27 +/- 0.85 g/100 g BW; P < 0.0002; average weekly FI during 28 days; vehicle 31.23 +/- 0.22, metergoline 36.83 +/- 0.33 g/100 g BW, P < 0.0001; average weekly FI during 84 days: vehicle 33.02 +/- 0.59, metergoline 35.07 +/- 0.48 g/100g BW, P < 0.008), and there was a significant body weight increase compared to vehicle treatment (7 days: DeltaBW vehicle -0.7 +/- 1.2 g vs DeltaBW metergoline 9.0 +/- 2.1 g, P < 0.001; 28 days: DeltaBW vehicle 0.3 +/- 2.2 vs DeltaBW metergoline 13.0 +/- 2.3, P < 0.001; 84 days: DeltaBW vehicle 25.7 +/- 10.2 vs DeltaBW metergoline 49.5 +/- 7.2, P < 0.04). Treatment for 84 days resulted in a significant body weight gain, while vehicle treatment had no effect (vehicle: 438 +/- 11 g vs 464 +/- 12 g, P < 0.2, n.s.; metergoline: 448 +/- 9 g vs 498 +/- 10 g, P < 0.007).

CONCLUSIONS

Inhibition of food intake by serotonin might contribute to early satiety and loss of body weight after total gastrectomy.

Combining behavioral and pharmacological treatments for obesity

Weight-loss medications are currently recommended for use only as an adjunct to diet, exercise, and behavior modification. Little, however, is known about the benefits of combining behavioral and pharmacological therapies or about the mechanisms that would make these combined approaches more effective than either used alone. This article reviews the effects of adding pharmacotherapy (i.e., principally sibutramine and orlistat) to a modest program of lifestyle modification. Studies revealed that the addition of medication typically improved short- and long-term weight loss compared with lifestyle modification alone. The best results, however, were obtained when medications were combined with an intensive, group program of lifestyle modification. The two approaches may have additive effects; behavioral treatment seems to help obese individuals control the external (i.e., food-related) environment, whereas pharmacotherapy may control the internal environment by reducing hunger, cravings, or nutrient absorption. The article examines possible methods of sequencing behavioral and pharmacological therapies and offers suggestions for future research.

Regulation of body weight and carcass composition by sibutramine in rats

OBJECTIVE

We examined the effectiveness of sibutramine to modulate food intake and body composition in rats with two levels of adiposity imposed by the duration of their maintenance on a moderate-fat diet.

RESEARCH METHODS AND PROCEDURES

Male Sprague--Dawley rats were fed a 32% fat diet from weaning until 2 or 4 months of age, at which point, body fat was either 15% or 25%, respectively, as measured by DXA. Sibutramine (0.6 or 2 mg/kg, orally) was then given daily for 2 weeks.

RESULTS

Food intake and body weight decreased acutely in a dose-related manner in both groups with sibutramine treatment. In all rats, food intake suppression was attenuated after multiple days of sibutramine. Both 15%- and 25%-fat rats had a persistent decrease in weight gain over the 2-week period in response to sibutramine. The older, 25%-fat rats were more sensitive to sibutramine than the younger, 15%-fat rats with regard to the magnitude of overall food intake inhibition, decrease in body weight gain, and caloric efficiency. Despite these differences, sibutramine produced the same relative reductions in fat mass and had no effect on lean mass in the two groups.

DISCUSSION

Thus, sibutramine produced equivalent efficacy on carcass fat loss in both groups, despite less inhibition of feeding and body weight gain in leaner rats. Whether these changes are a result of the leaner rats being younger and on a steeper growth curve compared with older, fatter rats or whether this is a direct function of their level of adiposity remains to be determined.