The effect of peripheral administration of peptides on food intake, glucose and insulin in wolf pups

In the studies reported here we demonstrate that bombesin decreases food intake in wolf (Canis lupus) pups without altering glucose or insulin levels. A high dose of cholecystokinin-octapeptide (CCK, 5 micrograms/kg) decreased food intake. CCK produced a transient increase in insulin, without altering glucose. Glucagon (0.5 mg/kg) failed to decrease food intake despite producing a marked hyperglycemia and hyperinsulinemia. Calcitonin was ineffective at decreasing food intake, although it did decrease the time spent feeding. These studies suggest a potential role for peripheral peptides in food regulation in the wolf.

Photoperiod-peptide interactions in the energy intake of Siberian hamsters

Siberian hamsters (Phodopus sungorous sungorous) decrease their food intake when exposed to short ("winter-like") photoperiods. The cause of this naturally-occurring hypophagia is unknown, but it may be due to a heightened sensitivity to the factors that normally terminate food intake in long photoperiods, such as the putative satiety peptides. The purpose of the present investigation was to test whether there would be an enhanced sensitivity to the inhibitory effects of some of these peptides on food intake in short relative to long days. Ad lib-fed, adult female Siberian hamsters were housed in a long photoperiod (LD 14:10) and injected with bombesin, glucagon, cholecystokinin octapeptide (CCK-8) and calcitonin (CT). Food intake was monitored 1, 2, 4, 6, and 24 hr post-injection. Bombesin and glucagon had no effect on food intake in long day-housed hamsters. CCK-8 and CT inhibited food intake; however, CCK-8 did so without any apparent behavioral disruption, while CT produced a marked and prolonged depression of behavior. After 10 weeks of exposure to a short photoperiod (LD 8:16) the hamsters were tested again. The previously ineffective dose of bombesin greatly inhibited food intake following short photoperiod exposure. In addition, an increased inhibition of food intake by CCK-8 was also found. In contrast, glucagon did not decrease food intake and CT still produced its non-specific, behaviorally disruptive effects. To our knowledge, this is the first demonstration that the effectiveness of a putative satiety peptide can be dependent upon a change in the photoperiod.(ABSTRACT TRUNCATED AT 250 WORDS)

CRF antagonist partially reverses CRF- and stress-induced effects on feeding

Exogenous corticotropin releasing factor (CRF) causes centrally mediated behavioral changes including decreased feeding and increased grooming. These behavioral changes are also seen in response to some stressors. However, the role of endogenous CRF in the behavioral response to stressors has not been investigated fully. We report below our findings on the behavioral effects of alpha-helical CRF (9-41), a recently discovered competitive antagonist of CRF-induced ACTH release. Alpha-helical CRF (9-41) partially reversed the decrement in feeding induced by CRF. Furthermore, the reduction in food intake due to restraint stress was partially reversed by alpha-helical CRF (9-41). These results indicate that changes in endogenous CRF release induced by the restraint stressor may play a role in stress-induced anorexia.

The effect of cholecystokinin, bombesin and calcitonin on food intake in virgin, lactating and postweaning female rats

During lactation food intake increases greatly without an accompanying large increase in body weight; therefore, this physiological state is an excellent example of non-obese hyperphagia. In the present study, we found that cholecystokinin (CCK-8) decreased food intake in lactating and virgin female rats. However, female rats were more resistant to the effect of CCK on eating following weaning of the pups. Bombesin (BB) suppressed food intake in virgin female rats and in lactating rats during early and mid lactation. Rats were resistant to its satiating effect during late lactation and during the postweaning period. Calcitonin potently suppressed food intake in virgin, lactating and postweaning rats. The present findings suggest that CCK and bombesin decrease food intake more effectively in virgin female rats and during earlier phases of lactation than during late lactation or postweaning.

Role of zinc supplementation in type II diabetes mellitus

Zinc is required for normal immune function and taste acuity and enhances the in vitro effectiveness of insulin. Impaired immune function and taste have been reported in diabetic subjects, and decreased serum zinc levels and hyperzincuria occur in some diabetic subjects and animals. Subjects with type II diabetes were examined to determine whether the similar effects of zinc depletion and diabetes are causally related. Low serum zinc levels were found in 16 of 180 subjects (9 percent). There was no correlation between serum zinc and glycosylated hemoglobin levels. Natural killer cell activity did not differ between diabetic subjects (n = 28) and control subjects (n = 38) and did not correlate with serum zinc levels. T lymphocyte response to phytohemagglutinin was lower in diabetic subjects than in control subjects (70 +/- 10 versus 103 +/- 7 X 10(3) counts per minute) but was not lowest in those with the lowest zinc levels. Taste thresholds for hydrochloric acid, sucrose, sodium chloride, and urea were elevated in diabetic subjects (n = 28) versus control subjects (n = 10), but thresholds did not correlate with glycosylated hemoglobin or serum zinc levels. Zinc supplementation in nine diabetic subjects had no effect on the glycosylated hemoglobin level, natural killer cell activity, or taste thresholds, but it did increase mitogen activity in those with the lowest initial phytohemagglutinin responses. It is concluded that zinc deficiency occurs in a subset of subjects with type II diabetes but is not related to diabetes control and does not explain decreased taste acuity. Zinc deficiency may play a role in abnormal immune function in type II diabetes mellitus.

Abnormal intestinal permeability to sugars in diabetes mellitus

A test of intestinal mucosal function which utilizes the differential permeability of L-rhamnose and lactulose has been reported to be helpful in the diagnosis of gluten-sensitive enteropathy. We have applied this test to 48 male subjects with diabetes mellitus to evaluate its usefulness as a screening test in diabetic patients and to further study sugar absorption in these individuals. Total urinary lactulose excretion in the 13 healthy control subjects was 54.5 +/- 8.5 mg/5 h, while excretion by diabetic patients was increased at 116.1 +/- 15.7 mg/5 h (p less than 0.01). Similarly, total L-rhamnose excretion by diabetic patients was significantly higher (139.7 +/- 14.3 mg/5 h vs 84.3 +/- 18.4 mg/5 h, p less than 0.05). The ratio of percent urinary excretion for lactulose/L-rhamnose (L/R ratio) for diabetic patients (0.197 +/- 0.024) was not different from the control subjects (0.151 +/- 0.2). Nine out of 48 diabetic patients studied had lactulose/L-rhamnose ratios higher than the mean plus two standard deviations of the control group, which might lead to the diagnosis of small bowel mucosal disease. Although we may have been detecting subclinical mucosal disease or gluten sensitive enteropathy in a subgroup, it appears that this test of intestinal mucosal function should be interpreted with caution in diabetic patients.

Opioid-induced feeding: localization of sensitive brain sites

These experiments were designed to identify brain sites at which opioids might act to influence ingestive behavior and to determine which opioid receptor types are involved. After food deprivation, rats were given microinjections of naloxone into several brain regions and food intake was measured. Injections into or near the paraventricular (PVN) or ventromedial (VMH) hypothalamic nuclei or the globus pallidus (GP) reduced food intake; injections into the striatum or lateral hypothalamus (LH) were ineffective. A second study examined the ingestive effects of roughly equimolar doses (1.43-1.75 nmol) of dynorphin A (DYN), beta-endorphin (beta-END), and D-Ala2,D-Leu5-enkephalin (DADLE) when injected into 4 different brain regions. Only DYN significantly increased food intake, and this effect was seen only with injections into the PVN and VMH. Beta-END stimulated water intake when injected into the PVN, VMH and GP but not the LH. Further studies indicated that with PVN injections, DYN was effective at a dose as low as 0.47 nmol, and that a higher dose of DADLE (4.39 nmol) did stimulate food intake. These studies support an important role for dynorphin and the kappa opioid receptor in the regulation of feeding and suggest that the opioid regulation of food and water intake can be differentiated both by sites of action and by effective agonists.

The stimulation of food intake by selective agonists of mu, kappa and delta opioid receptors

It is known that under some conditions the administration of opioid agonists will stimulate food intake. However, the lack of receptor selectivity of some of the agonists which produce this effect leaves open the question of which receptor types are actually involved. In the experiments presented here, rats were given intracerebroventricular injections of Dynorphin 1-17 (DYN), [D-ala2MePhe4,-Gly-ol5]enkephalin (DAGO), and [D-ser2, leu5]enkephalin-thr6 (DSLET); these peptides are thought to be selective agonists at kappa, mu and delta opioid receptors, respectively. All three peptides stimulated food intake in non-deprived rats at doses in the 3-10 nmol range; water intake was also increased in some cases. Generally, DYN stimulated feeding at a lower dose than DAGO or DSLET and the magnitude of the effect tended to be greater. On the other hand, DAGO more consistently increased water intake. In some cases, DYN also caused episodes of "barrel-rolling" and postural abnormalities, whereas DAGO had sedative and/or cataleptic effects. These results are interpreted as an involvement of more than one opioid receptor types in the regulation of appetite, possibly with separate opioid systems contributing to food and water intake.

Effect of naltrexone on mood and cognitive functioning among overweight men

The effects of naltrexone on both mood and cognition were examined in overweight male subjects. Subjects were randomly prescribed, in a double-blind fashion, either placebo or naltrexone for 8 weeks. The results of the study showed that a chronic administration of a high dose of naltrexone (300 mg/day) does not significantly change mood or cognitive functioning among overweight adult men.

Effects of manipulations of glucoregulation on feeding in the ground squirrel

Insulin and 2-deoxy-D-glucose (2-DG) stimulate feeding in rats, while glucagon inhibits feeding. We report here their effects on food intake in the 13-lined ground squirrel (Spermophilus tridecumlinectus). These hibernating animals are an interesting model for studying appetite regulation because of the marked seasonal variations in food consumption. Food intake reached a peak of 286 +/- 7 g/kg/day in mid July, decreasing to 16.1 +/- 3 g/kg/day in September. Studies during the hyperphagic period showed that glucagon (0.5 to 1 mg/kg) decreased feeding 30 minutes post injection (p less than 0.01) whereas at 4 hours glucagon produced a 37% increase in feeding (p less than 0.05). During the hypophagic period, glucagon failed to alter food consumption. Insulin (5-100 Units/kg) produced no effect on feeding in hyperphagic animals despite a decrease in glucose from 193 +/- 10 mg/dl to 55 +/- 4 mg/dl after 100 Units/kg. However, insulin (50 and 100 Units/kg) resulted in significant increases in food consumption at 2 and 4 hours (p less than 0.01 and 0.05, respectively) when administered while the animals were hypophagic. 2-DG (250-750 mg/kg) increased food consumption (hyperphagic phase) by 76% at 20 hours (p less than 0.01) with significant increases being present as early as 4 hours, although when 2-DG was given to hypophagic animals it resulted in decreased food intake at 4 hours (p less than 0.05). We conclude that the effects of glucoregulatory manipulations on food consumption are markedly influenced by the circannual rhythm of feeding in the 13-lined ground squirrel.

Alterations in calmodulin levels in tissues from aged animals

We measured the levels of calmodulin in brain tissue as well as in other tissues by a specific radioimmunoassay. Fisher-344 rats with ages of 3, 13, 23, and 29 months were used. IR-calmodulin levels were reduced in the cortex, striatum, and anterior pituitary but not in the hypothalamus (although there was a tendency for reduction in the latter tissue). No significant decreases in IR-calmodulin were observed in gastrocnemius, kidney, or heart of the oldest group of rats, and, in fact, the levels in the heart were significantly higher in the oldest age group when compared with the 13- and 23-month-old rats. These data agree with the decline in cyclic nucleotide phosphodiesterase activity observed in the cortex and striatum of aged animals.

Seasonal variation in opioid modulation of feeding in the 13-lined ground squirrel

Opioids are well recognized to modulate ingestive behaviors in a variety of species. To study the potential role of opioids in the alteration of ingestive behaviors that occur prior to hibernation, we have administered opiate agonists and the antagonist, naloxone, to the 13-lined ground squirrel (Spermophilus tridecemlineatus) during periods when they were hyperphagic and hypophagic. Naloxone consistently reduced feeding during both phases of the feeding cycle. Hypophagic animals, however, were 10 times more sensitive to the effects of naloxone. The effect of the opiate agonists (morphine and butorphanol, 1 and 10 mg/kg) on feeding also varied between seasons. The low dose of morphine produced a slight, but significant increase in feeding at one hour in hyperphagic animals, while the high doses tended to decrease feeding. When administered to hypophagic animals, feeding was decreased by both doses of each agonist. Immunoreactive (IR)-dynorphin levels in the cortex, hypothalamus and striatum were higher during the hypophagic phase compared with the hyperphagic phase. These data indicate that the 13-lined ground squirrel possesses an opiate sensitive feeding system which is affected by season.

The effect of calcitonin gene-related peptide on food intake involves aversive mechanisms

Calcitonin gene-related peptide (CGRP), the product of the calcitonin gene produced primarily in the central nervous system, has been shown to decrease food intake when administered intracerebroventricularly (ICV). Testing of CGRP (ICV) in both single bottle conditioned-aversion and differential starvation paradigms was done. In both paradigms, results using CGRP were consistent with those predicted for aversive agents. Therefore, CGRP apparently decreases feeding via aversive mechanisms.

Opiates and medial hypothalamic knife cuts cause hyperphagia through different mechanisms

Several experiments were performed to determine whether the hyperphagia caused by medial hypothalamic knife cuts and that induced by opiate agonists are mediated by a common mechanism. In the first set of experiments, male Sprague-Dawley rats were given bilateral parasagittal medial hypothalamic knife cuts or a sham procedure and fed a high-fat Crisco-chow diet. Knife-cut and sham-operated rats were approximately equally sensitive to the suppressive effects of naloxone on food intake. The kappa opiate receptor agonist ketocyclazocine generally increased daytime food intake in sham-operated rats; in contrast, the normal hyperphagia of knife-cut rats was in most cases either unchanged or decreased by ketocyclazocine. In a second set of experiments, neither diet composition nor hypothalamic knife cuts significantly affected the feeding responses to naloxone or the stimulatory effects of the kappa agonist butorphanol tartrate. It was hypothesized that the differential effects of ketocyclazocine in knife-cut and sham-operated rats are a consequence of the sedative effects of the drug combined with the elevated baseline of the knife-cut subjects. This hypothesis was supported by a third experiment, in which ketocyclazocine also reduced nocturnal intake in unoperated rats and butorphanol increased intake. That feeding responses to naloxone and butorphanol were essentially unchanged by hypothalamic knife cuts suggests that the opioid feeding system is independent of the longitudinal feeding inhibitory pathway believed to be involved in knife-cut-induced hyperphagia.

Effect of butorphanol tartrate on food and water consumption in humans

There is much evidence that endogenous opioid peptides are involved in the regulation of food and water intake in a variety of species. We report here that the exogenous opiate agonist, butorphanol tartrate (1 microgram/kg), significantly increases food, but not water, intake in normal humans. The major effect on food intake was seen within the first 2 h after the administration of drug. These findings suggest that this drug may be therapeutically useful in patients with cancer anorexia.

Opiates and medial hypothalamic knife cuts cause hyperphagia through different mechanisms

Several experiments were performed to determine whether the hyperphagia caused by medial hypothalamic knife cuts and that induced by opiate agonists are mediated by a common mechanism. In the first set of experiments, male Sprague-Dawley rats were given bilateral parasagittal medial hypothalamic knife cuts or a sham procedure and fed a high-fat Crisco-chow diet. Knife-cut and sham-operated rats were approximately equally sensitive to the suppressive effects of naloxone on food intake. The kappa opiate receptor agonist ketocyclazocine generally increased daytime food intake in sham-operated rats; in contrast, the normal hyperphagia of knife-cut rats was in most cases either unchanged or decreased by ketocyclazocine. In a second set of experiments, neither diet composition nor hypothalamic knife cuts significantly affected the feeding responses to naloxone or the stimulatory effects of the kappa agonist butorphanol tartrate. It was hypothesized that the differential effects of ketocyclazocine in knife-cut and sham-operated rats are a consequence of the sedative effects of the drug combined with the elevated baseline of the knife-cut subjects. This hypothesis was supported by a third experiment, in which ketocyclazocine also reduced nocturnal intake in unoperated rats and butorphanol increased intake. That feeding responses to naloxone and butorphanol were essentially unchanged by hypothalamic knife cuts suggests that the opioid feeding system is independent of the longitudinal feeding inhibitory pathway believed to be involved in knife-cut-induced hyperphagia.

Effects of opiate antagonists on feeding and spontaneous locomotion in deer

The effects of opioid antagonists on seasonal changes in feeding behavior of white-tailed deer (Odocoileus virginianus) during fall, winter, and summer, as well as in bottle-fed fawns are described. Naltrexone had no effect on the amount of milk ingested by bottle-fed fawns. After weaning naltrexone significantly decreased feeding in both the summer and winter, with no difference in the effect for either season, indicating that opioids do not play a role in the winter hypophagia or the summer hyperphagia in deer. Similarly there was no seasonal effect on the ability of naloxone to decrease feeding in yearlings during summer, fall, and winter. Naltrexone significantly decreased spontaneous locomotion in the fawns in winter and the fall. In yearlings there was a tendency for the high dose of naloxone to decrease spontaneous locomotion in winter whereas in summer and fall it tended to enhance time spent moving. These data suggest that the endogenous opioid control of feeding in deer is independent of the seasonal effect on feeding and endogenous opioids do not play a role in the seasonal rhythmicity of feeding in deer. The effects of endogenous opioids on spontaneous locomotion do appear to be linked to changes in seasonal activity patterns.

Phase II trial of a complex polyriboinosinic-polyribocytidylic acid with poly-L-lysine and carboxymethyl cellulose in the treatment of children with acute leukemia and neuroblastoma: a report from the Children's Cancer Study Group

Therapeutic efficacy and toxicity were evaluated in 28 children with acute lymphoblastic leukemia, in ten with acute nonlymphoblastic leukemia (ANLL), and in 13 with metastatic neuroblastoma. All were refractory to standard chemotherapeutic agents and 25 were refractory to an investigational drug. The initial dose was 12 mg/m2/day and was based on an established maximal dose tolerated in adults. This dose was found to be intolerable in 5 of 5 children with leukemia. Similarly an initial dose of 9 mg/m2/day was intolerable in 4 of 5 patients with leukemia. The starting dose in the next 28 children with leukemia or neuroblastoma was 3 mg/m2. This drug was gradually increased to the highest tolerated dose by 3-mg/m2 increments. Fifteen children with acute lymphoblastic leukemia, 3 children with ANLL, and 2 children with neuroblastoma received the drug daily. Seven patients with ANLL and 7 patients with neuroblastoma received the drug biweekly. Seventeen patients with acute lymphoblastic leukemia, 6 patients with ANLL, and 5 patients with neuroblastoma had an adequate trial of the drug. An adequate trial was defined as a minimum of 5 weeks of therapy unless progressive disease developed. Side effects of the drug were striking and included fever, hypotension, myalgia, bone pain, arthralgia, arthritis, abdominal pain, liver toxicity, thrombocytopenia, and neurotoxicity. No complete remission occurred although interferon levels above 100 units/ml were induced in nearly 50% of the patients.

Phase II trial of poly(I,C)-LC, an interferon inducer, in the treatment of children with acute leukemia and neuroblastoma: a report from the Children's Cancer Study Group

A Phase II study of poly(I,C)-LC was performed in 28 children and adolescents with acute lymphoblastic leukemia (ALL), 10 with acute nonlymphoblastic leukemia (ANLL), and 13 with metastatic neuroblastoma. All were refractory to standard chemotherapeutic agents and 25 to an investigational drug. Initial doses of 12 mg/m2 and 9 mg/m2 were intolerable. However, 9 mg/m2 was tolerable in the majority of patients when the drug was started at 3 mg/m2 and increased by 3 mg/m2 increments. Fifteen children with ALL, three with ANLL, and two with neuroblastoma received the drug daily. Seven patients with ANLL and seven children with neuroblastoma received the drug biweekly. Twenty-eight patients received an adequate trial, which was defined as a minimum of 5 weeks at the maximal tolerated dose, unless there was progressive disease at the maximal tolerated dose. Side effects of the drug were striking, and included fever, hypotension, myalgia, bone pain, arthralgia, arthritis, abdominal pain, liver toxicity, thrombocytopenia, and neurotoxicity. No complete remissions occurred in spite of interferon levels above 100 U in nearly 50% of patients.

Poly(I,C)-LC as an interferon inducer in refractory multiple myeloma

Seven patients with refractory multiple myeloma (readily evaluable for response) were treated in a Phase II trial with poly(I,C)-LC using a 3 times per week intravenous schedule. Serial immunologic testing included assessment of natural killer (NK) cell activity, antibody-dependent cytotoxicity, delayed hypersensitivity, and in vitro mitogen responses. One patient had a partial response (PR) of 6-month duration, and 3 other patients had objective responses (less than PR). Significant interferon induction occurred, but levels dropped substantially with serial dosing. Major toxicity included hypertension, hypotension, fever, and myelosuppression. The demonstration of modulation of myeloma progression in this refractory population was encouraging.

The effect of opiates and naloxone on food intake in virgin and lactating rats

Lactation provides an excellent model of non-obese hyperphagia. There is accumulating evidence that endogenous opioids play a role in the modulation of the hormonal changes that occur during lactation. Because endogenous opioids appear also to play a role in the regulation of feeding, we studied the effects of the opiate agonist, butorphanol tartrate, and an opiate antagonist, naloxone, on food intake in virgin female rats and in rats during early, mid and late lactation and during post-weaning. It has been reported that female rats are less sensitive to the suppressant effects of nalmefene, an opioid antagonist, than male rats. Therefore, we also examined the effect of naloxone, an opioid antagonist, on spontaneous nocturnal feeding and 24 hour food deprivation-induced food intake in virgin female rats. We found that female rats were relatively insensitive to the food suppressant effects of naloxone following 24 hour food deprivation, while male rats tested under similar conditions had a decreased intake in response to naloxone. Despite the marked hyperphagia that occurred during lactation, there were minimal alterations in the response to opiate agonists and antagonists during this time period. Our data suggest that endogenous opioids may not play a pivotal role in the hyperphagia of lactation.

Peptide YY (PYY), a potent orexigenic agent

Peptide YY (PYY) enhances feeding and drinking more potently than does neuropeptide Y after central administration. Chronic administration of PYY every 6 h for 48 h causes massive food ingestion. Tolerance to this effect of PYY does not appear to develop. This data suggests that PYY is one of the most potent orexigenic substances yet to be identified. PYY may play a role in the pathogenesis of bulimic syndromes.

The level of expression of adenovirus type 2 transforming genes governs sensitivity to nonspecific immune cytolysis and other phenotypic properties of adenovirus 2-simian virus 40-transformed cell hybrids

Syrian hamster embryo cells transformed by adenovirus type 2 (Ad2) or simian virus 40 (SV40) differ markedly in morphology, tumorigenicity, and susceptibility to in vitro lysis by nonspecific cytotoxic cells. Hybrid cells formed by fusing Ad2- and SV40-transformed Syrian hamster embryo cells may express only SV40 T antigens or both SV40 and Ad2 T antigens. Hybrids that express only SV40 T antigens are indistinguishable from the nonhybrid SV40-transformed phenotype, whereas hybrid cells that express T antigens from both viruses closely resemble the nonhybrid parental Ad2-transformed phenotype. Because these hybrid cells have been useful in the study of neoplastic transformation, we determined the amount of viral antigens that they accumulate in an attempt to correlate the level of expression of the transforming viral genes with some of their phenotypic properties. Hybrid cells that expressed proteins from both viruses showed reduced levels of SV40 T antigens compared with those of hybrid cells that did not express Ad2 T antigens. We also found that the production of several cellular proteins that influence cytomorphology was inhibited in hybrid and nonhybrid cells that expressed Ad2 T antigens, and the repression of these cellular proteins correlated with a change in cytomorphology from fibroblastic to spherical. Finally, we showed that the susceptibility of our hybrid cells to in vitro lysis by natural killer cells and activated macrophages, two putative host-effector cells involved in defense against neoplasia, correlated closely with the level of expression of a 58,000-dalton Ad2 protein. The results reported here, together with the results of previous studies, indicate that the oncogenic potential of hybrid cells that express both Ad2 and SV40 antigens is extremely sensitive to Ad2 expression, whereas other phenotypic properties depend on Ad2 expression in a dose-dependent manner.

Opioids and consummatory behavior

Since the second decade of this century it has been known that opiates can influence ingestive behaviors. Generally, opioid agents enhance feeding and opioid antagonists decrease feeding. The present paper reviews the responsiveness of different animal species to opiates in relation to ingestive behaviors, the opioid receptors involved in such consummatory behaviors, the site of action of opioid modulation of feeding, the role of glucose in opioid induced feeding, and endocrine effects on opioid feeding systems. We emphasize the finding that more than one opioid receptor is involved in the modulation of feeding. A large body of evidence indicates a major role for the dynorphin/alpha-neo-endorphin kappa opioid receptor as one of the receptors involved in feeding modulation. Opioids appear to exert their effect predominantly within the central nervous system, though peripheral effects on taste and gastrointestinal function may play a role in opioid-induced feeding. Although opioid blockade acutely blocks food intake, chronic administration of opiate antagonists to humans and laboratory animals has not proven to be an effective means of decreasing body weight. Chronic opiate administration decreases body weight and autosensitization of beta-endorphin increases body weight. Thus, although it is clear that opioids can effect food intake, it is not clear what effect chronic administration of opioids has no food intake or body weight.