Effect of naloxone on food consumption in obesity

Peptides that regulate food intake: antagonism of opioid receptors reduces body fat in obese rats by decreasing food intake and stimulating lipid utilization

Agonists to opioid receptors induce a positive energy balance, whereas antagonists at these receptors reduce food intake and body weight in rodent models of obesity. An analog of 3,4-dimethyl-4-(3-hydroxyphenyl)piperidine, LY255582, is a potent non-morphinan antagonist for mu-, kappa-, and delta-receptors (K(i) of 0.4, 2.0, and 5.2 nM, respectively). In the present study, we examined the effects of oral LY255582 treatment on caloric intake, calorie expenditure, and body composition in dietary-induced obese rats. Acute oral treatment of LY255582 produced a dose-dependent decrease in energy intake and respiratory quotient (RQ), which correlated with the occupancy of central opioid receptors. Animals receiving chronic oral treatment with LY255582 for 14 days maintained a negative energy balance that was sustained by increased lipid use. Analysis of body composition revealed a reduction in fat mass accretion, with no change in lean body mass, in animals treated with LY255582. Therefore, chronic treatment with LY255582 reduces adipose tissue mass by reducing energy intake and stimulating lipid use.

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.

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.

Effect of naltrexone on food intake, hunger, and satiety in obese men

Increasing doses of naltrexone (25 to 200 mg) given over 4 consecutive days reduced intake of laboratory luncheon meals by 30% in 17 obese men. Meal size remained suppressed in the laboratory during the week following naltrexone administration. Water intake in the laboratory and body weight were not affected. Rates of ingestion and subjective ratings suggested that naltrexone reduced appetite rather than promoted early satiation. Nausea and other side effects occurred on 1 or 2 days during the naltrexone week in seven subjects whose food intake was reduced. Food intake was also reduced in seven of the remaining 10 subjects who reported no adverse reactions. These results suggest that a conditioned taste aversion or a conditioned anorexia may have developed in some subjects.

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

We undertook a study to see if putative anorectic agents could attenuate binge eating episodes in bulimic patients. Bolus intravenous administration, followed by continuous intravenous infusion of naloxone, resulted in a significant decrease in the amount of food consumed during binge-eating episodes, whereas bolus followed by continuous intravenous infusion of CCK-8 failed to significantly suppress binge eating behavior. These results suggest that the endogenous opioid system is involved in the maintenance of binge eating behavior in patients with bulimia.