Central apelin-13 inhibits food intake via the CRF receptor in mice

Apelin, the novel identified peptide, is the endogenous ligand for the APJ. Previous studies have reported the effect of apelin on food intake, however the action of acute central injected apelin on food intake in mice remains unknown. The present study was designed to investigate the mechanism as well as the effect of central apelin-13 on food intake in mice. During the dark period, the cumulative food intake was significantly decreased at 4h after the intracerebroventricular (i.c.v.) injection of 1 and 3μg/mouse apelin-13 and the period food intake was significantly reduced during 2-4h after treatment. In the fasted mice, the cumulative food intake was significantly decreased at 2 and 4h after injection of 3μg/mouse apelin-13. The cumulative water intake was significantly reduced by apelin-13 (3μg/mouse) at 4h after injection in freely feeding and fasted mice. However, during light period, apelin-13 had no influence on food and water intake in freely feeding mice. The APJ receptor antagonist apelin-13(F13A) (6μg/mouse) and the corticotrophin-releasing factor (CRF) receptor antagonist α-helical CRF(9-41) (3μg/mouse) could reverse the inhibitory effect on cumulative food intake/0-4h induced by apelin-13 (3μg/mouse) in freely feeding mice during the dark period, whereas the anorexic effect could not be antagonized by the arginie vasopressin (AVP) receptor antagonist deamino(CH(2))(5)Tyr(Me)AVP (0.5μg/mouse). Taken together, these results suggest that central apelin-13 inhibits food intake in mice and it seems that APJ receptor and CRF receptor, but not AVP receptor, might be involved in this process.     

Proadrenomedullin N-terminal 20 peptide (PAMP) inhibits food intake and gastric emptying in mice

We found that proadrenomedullin N-terminal 20 peptide (PAMP) decreased dose-dependently (3-30 nmol/mouse) food intake after intra-third cerebroventricular administration in fasted ddY mice. Gastric emptying also was delayed after central injection of PAMP. In our previous study, PAMP was demonstrated to elicit hyperglycemia via bombesin (BN) receptor. Then, we examined whether the effects of PAMP on feeding and gastric emptying were induced through BN receptor. Surprisingly, PAMP-induced reductions in feeding and gastric emptying rate were not blocked by a BN antagonist, [D-Phe(6), Leu-NHEt(13), des-Met(14)]-BN (6-14). PAMP suppressed feeding in mice lacking gastrin-releasing peptide receptor or BN receptor subtype-3. These results indicate that centrally administered PAMP inhibits food intake, involving the delayed gastric emptying, not through BN receptors but through selective PAMP receptor.     

Peripheral activation of corticotropin-releasing factor receptor 2 inhibits food intake and alters meal structures in mice

The orexigenic effect of urocortins (Ucns), namely Ucn 1, Ucn 2 and Ucn 3 through activation of corticotropin-releasing factor (CRF) receptors, has been well characterized after injection into the brain but not in the periphery. We examined the role of CRF receptor subtype 2 (CRF₂) in the regulation of food intake using intraperitoneal (ip) injection of Ucns and the selective CRF₂ antagonist, astressin₂-B, and CRF₂ knockout (−/−) mice. Meal structures were monitored using an automated episodic solid food intake monitoring system. Ucn 2 (3, 10 or 30 μg/kg, ip) induced a rapid in onset, long lasting and dose-dependent decrease (38%, 66% and 86%, respectively at 4 h) of cumulative food intake after an overnight fast in mice. Ucn 3 anorexic effect was 10-times less potent. Astressin₂-B (30 or 100 μg/kg) injected ip, but not intracerebroventricularly, blocked the inhibitory effect of ip Ucn 1 and Ucn 2 (10 μg/kg). Fasted CRF_2−/− mice did not respond to ip Ucn 1 (10 μg/kg). Meal microstructure analysis of the 4-h re-feeding response to an overnight fast showed that Ucn 2 (10 μg/kg, ip) decreased meal size and duration, but increased meal frequency. In mice fed ad libitum, Ucn 2 (30 μg/kg) injected ip before the dark phase decreased the 4-h nocturnal meal size and duration without influencing meal frequency while the 10 μg/kg dose had no effect. These data indicate that Ucns, through peripheral CRF₂ receptor-mediated induction of satiation, inhibit the eating response to a fast more potently than the physiological nocturnal feeding in mice.     

Peripheral administration of CRF and urocortin: effects on food intake and the HPA axis in the marsupial Sminthopsis crassicaudata

The hypothalamic peptides corticotrophin releasing factor (CRF) and urocortin (UCN) decrease food intake and increase energy expenditure when administered either centrally or peripherally to rodents. The effects of CRF and UCN on food intake in other mammals (for example marsupials), however, are not known. Peripherally administered CRF induced cortisol release in the marsupial Sminthopsis crassicaudata via the CRF1 receptor, and central CRF administration potently decreased food intake, as in rodents. When peripherally administered, both CRF and UCN decreased food intake in S. crassicaudata, but UCN was considerably more potent ( approximately 50 fold) in this regard. The anorectic effects of CRF and UCN were not blocked by the CRF1 receptor antagonist antalarmin, suggesting that the peripheral effects of CRF and UCN on food intake are mediated primarily by the CRF2 receptor.     

Behavioral and neuroendocrine effects of the selective CRF2 receptor agonists urocortin II and urocortin III

We compared the in vivo efficacy of two selective CRF2 agonists, mouse urocortin II (mUcn II) and human urocortin III (hUcn III), using food intake, anxious behavior, or ACTH release in CD-1 or Balb/c mice as indices of biological stress responses. All three peptides produced anorexia (Minimal Effective Dose (M.E.D.) for CRF and mUcn II = 0.03 nmol; M.E.D. for hUcn III = 0.3 nmol). Only mUcn II and CRF appeared to increase anxious behaviors in the elevated plus maze test (M.E.D. = 0.3 and 0.01 nmol, respectively). CRF increased the release of plasma ACTH (M.E.D. of 0.3 nmol), while mUcn II and hUcn III had no effect on ACTH release. These data suggest that the CRF2 receptor subtype plays a primary role in the activation of behavioral, but not neuroendocrine, stress responses.     

Intravenous infusion of glucagon-like peptide-1 potently inhibits food intake, sham feeding, and gastric emptying in rats

Glucagon-like peptide-1(7-36)-amide (GLP-1) is postulated to act as a hormonal signal from gut to brain to inhibit food intake and gastric emptying. A mixed-nutrient meal produces a 2 to 3-h increase in plasma GLP-1. We determined the effects of intravenous infusions of GLP-1 on food intake, sham feeding, and gastric emptying in rats to assess whether GLP-1 inhibits food intake, in part, by slowing gastric emptying. A 3-h intravenous infusion of GLP-1 (0.5-170 pmol.kg(-1).min(-1)) at dark onset dose-dependently inhibited food intake in rats that were normally fed with a potency (mean effective dose) and efficacy (maximal % inhibition) of 23 pmol.kg(-1).min(-1) and 82%, respectively. Similar total doses of GLP-1 administered over a 15-min period were less potent and effective. In gastric emptying experiments, GLP-1 (1.7-50 pmol.kg(-1).min(-1)) dose-dependently inhibited gastric emptying of saline and ingested chow with potencies of 18 and 6 pmol.kg(-1).min(-1) and maximal inhibitions of 74 and 83%, respectively. In sham-feeding experiments, GLP-1 (5-50 pmol.kg(-1).min(-1)) dose-dependently reduced 15% aqueous sucrose intake in a similar manner when gastric cannulas were closed (real feeding) and open (sham feeding). These results demonstrate that intravenous infusions of GLP-1 dose-dependently inhibit food intake, sham feeding, and gastric emptying with a similar potency and efficacy. Thus GLP-1 may inhibit food intake in part by reducing gastric emptying, yet can also inhibit food intake independently of its action to reduce gastric emptying. It remains to be determined whether intravenous doses of GLP-1 that reproduce postprandial increases in plasma GLP-1 are sufficient to inhibit food intake and gastric emptying.     

Urocortin 2 acts centrally to delay gastric emptying through sympathetic pathways while CRF and urocortin 1 inhibitory actions are vagal dependent in rats

We characterized the influence of the selective corticotropin-releasing factor 2 (CRF(2)) receptor agonist human urocortin 2 (Ucn 2), injected intracisternally, on gastric emptying and its mechanism of action compared with intracisternal CRF or urocortin (Ucn 1) in conscious rats. The methylcellulose phenol red solution was gavaged 20 min after peptide injection, and gastric emptying was measured 20 min later. The intracisternal injection of Ucn 2 (0.1 and 1 microg) and Ucn 1 (1 microg) decreased gastric emptying to 37.8 +/- 6.9%, 23.1 +/- 8.6%, and 21.6 +/- 5.9%, respectively, compared with 58.4 +/- 3.8% after intracisternal vehicle. At lower doses, Ucn 2 (0.03 microg) and Ucn 1 (0.1 microg) had no effect. The CRF(2) antagonist astressin(2)-B (3 microg ic) antagonized intracisternal Ucn 2 (0.1 microg) and CRF (0.3 microg)-induced inhibition of gastric emptying. Vagotomy enhanced intracisternal Ucn 2 (0.1 or 1 microg)-induced inhibition of gastric emptying compared with sham-operated group, whereas it blocked intracisternal CRF (1 microg) inhibitory action (45.5 +/- 8.4% vs. 9.7 +/- 9.7%). Sympathetic blockade by bretylium prevented intracisternal and intracerebroventricular Ucn 2-induced delayed gastric emptying, whereas it did not influence intravenous Ucn 2-, intracisternal CRF-, and intracisternal Ucn 1-induced inhibition of gastric emptying. Prazosin abolished the intracisternal Ucn 2 inhibitory effect, whereas yohimbine and propranolol did not. None of the pretreatments modified basal gastric emptying. These data indicate that intracisternal Ucn 2 induced a central CRF(2)-mediated inhibition of gastric emptying involving sympathetic alpha(1)-adrenergic mechanisms independent from the vagus contrasting with the vagal-dependent inhibitory actions of CRF and Ucn 1.     

Peptide YY(3-36) inhibits gastric emptying and produces acute reductions in food intake in rhesus monkeys

Peptide YY3-36 [PYY(3-36)], a gastrointestinal peptide that is released into the circulation in response to ingesting a meal, has recently been suggested to play a role in controlling food intake. PYY(3-36) has been reported to inhibit food intake following peripheral administration in rodents and in human subjects. To more fully characterize the potential feeding actions of PYY(3-36), we examined the ability of a dose range of PYY(3-36) (0.3-3.0 nmol/kg) to affect liquid gastric emptying and daily 6-h food intake in male rhesus monkeys. Intramuscular PYY(3-36) produced a dose-related inhibition of saline gastric emptying that was maximal at a dose of 3 nmol/kg. Intramuscular PYY(3-36) administered before daily 6-h food access produced significant feeding reductions at doses of 1 and 3 nmol/kg. Analyses of the patterns of food intake across the 6-h period of food access revealed that PYY(3-36) increased the latency to the first meal and reduced average meal size without altering meal number. Although single doses of PYY(3-36) reduced intake, a suppressive effect on food intake was not sustained over multiple administrations across successive days. Together, these data suggest that PYY(3-36) has the ability to reduce food intake in acute test situations in nonhuman primates. Whether this is a physiological action of the endogenous peptide remains to be determined.     

Comparative effects of amylin and cholecystokinin on food intake and gastric emptying in rats

CCK is a physiological inhibitor of gastric emptying and food intake. The pancreatic peptide amylin exerts similar actions, yet its physiological importance is uncertain. Objectives were to compare the dose-dependent effects of intravenous infusion of amylin and CCK-8 on gastric emptying and food intake in rats, and to assess whether physiological doses of amylin are effective. Amylin and CCK-8 inhibited gastric emptying with mean effective doses (ED(50)s) of 3 and 35 pmol x kg(-1) x min(-1) and maximal inhibitions of 60 and 65%, respectively. Amylin and CCK-8 inhibited food intake with ED(50)s of 8 and 14 pmol x kg(-1) x min(-1) and maximal inhibitions of 78 and 69%, respectively. The minimal effective amylin dose for each effect was 1 pmol x kg(-1) x min(-1). Our previous work suggests that this dose increases plasma amylin by an amount comparable to that produced by a meal. These results support the hypothesis that amylin acts as a hormonal signal to the brain to inhibit gastric emptying and food intake and that amylin produces satiety in part through inhibition of gastric emptying.     

Effects of urocortin 2 and 3 on motor activity and food intake in rats

Urocortin 2 (Ucn 2) and Ucn 3 are new members of the corticotropin-releasing factor (CRF) family and bind selectively to the CRF type 2 receptor (CRF2). The effects of these peptides on behavioral changes induced by CRF were examined in rats. In a familiar environment, intracerebroventricular injection of Ucn 2 attenuated the stimulatory effect of CRF on motor activity, although it alone produced no effect. Ucn 3 suppressed motor activity and attenuated the stimulatory effect of CRF. In an open field, CRF decreased locomotion and rearing but increased grooming behavior. Ucn 2 attenuated the inhibition of locomotor activity induced by CRF without affecting other activities, such as rearing or grooming behavior. Ucn 3 had no effect on the behavioral changes induced by CRF, although it alone decreased locomotion and rearing in a manner similar to CRF. Ucn 2 was thus found to have an antagonistic effect on bi-directional motor activation induced by CRF, while Ucn 3 had a suppressive effect on motor activity. Both Ucn 2 and Ucn 3 suppressed food intake in freely-fed rats, but not immediately after injection. These results suggest that the CRF2 receptor is involved in motor suppressive effects as well as anxiolytic and anorectic effects of Ucn 2 and Ucn 3.     

Arg-Ile-Tyr (RIY) derived from rapeseed protein decreases food intake and gastric emptying after oral administration in mice

We previously reported that a bioactive tripeptide Arg-Ile-Tyr (RIY), which has been isolated as an inhibitor for angiotensin I-converting enzyme from the subtilisin digest of rapeseed protein, decreased blood pressure. In this study, we also found that RIY dose-dependently decreased food intake at a dose of 150 mg/kg after oral administration in fasted ddY male mice. The anorexigenic action of RIY was blocked by a cholecystokinin-1 CCK1 receptor antagonist, lorglumide. RIY also decreased the gastric emptying rate at a dose of 150 mg/kg and the RIY-induced delay of gastric emptying was blocked by lorglumide. However, RIY had no affinity for CCK1 receptor. Taken together, RIY decreased food intake and gastric emptying by stimulating CCK release.     

Intravenous urocortin II decreases blood pressure through CRF(2) receptor in rats

Urocortin II (Ucn II) is a new member of the corticotropin-releasing factor (CRF) family that binds selectively to the CRF subtype 2 receptor (CRF(2)). CRF or urocortin injected intravenously (i.v.) induced hypotension. We investigated the influence of iv human Ucn II (hUcn II) on basal mean blood pressure (MAP) and on the sympathetic mediated hypertensive response to TRH analog, RX-77368 injected intracisternally (i.c.) 20 min after hUcn II in urethane-anesthetized rats. Ucn II (3, 10, and 30 microg/kg, i.v.) significantly decreased basal MAP from baseline by -20.9+/-6.5, -21.3+/-5.4 and -46.8+/-6.5 mm Hg, respectively, after 10 min. RX-77368 (30 ng, i.c.) elevated MAP for over 90 min with a maximal hypertensive response at 20 min. Ucn II (3, 10, and 30 microg/kg, i.v.) did not alter the 20 min net rise in MAP induced by RX-77368 (35.7+/-7.1, 32.6+/-3.3 and 24.6+/-6.9 mm Hg, respectively) compared with vehicle (33.6+/-4.3 mm Hg). The selective CRF(2) antagonist, astressin(2)-B (60 microg/kg, i.v.) abolished hUcn II hypotensive action while having no effect on basal MAP. These data show that iv hUcn II induces hypotension through peripheral CRF(2) receptor while not altering the responsiveness to sympathetic nervous system-mediated rise in MAP.     

Leptin inhibits gastric emptying in rats: role of CCK receptors and vagal afferent fibers

Leptin regulates energy homeostasis and body weight by balancing energy intake and expenditure. It was recently reported that leptin, released into the gut lumen during the cephalic phase of gastric secretion, is capable of initiating intestinal nutrient absorption. Vagal afferent neurons also express receptors for both CCK and leptin, which are believed to interact in controlling food intake. The present study was undertaken to investigate the central and peripheral effects of leptin on gastric emptying rate. Under anesthesia, male Sprague-Dawley rats (250-300 g) were fitted with gastric Gregory cannulas (n=12) and some had additional cerebroventricular cannulas inserted into their right lateral ventricles. Following recovery, the rate of gastric emptying of saline (300 mOsm/kg H(2)O) was determined after instillation into the gastric fistula (3 ml, 37 degrees C, containing phenol red, 60 mg/l as a non-absorbable dilution marker). Gastric emptying rate was determined from the volume and phenol red concentrations recovered after 5 min. Leptin, injected intraperitoneally (i.p.; 10, 30, 60, 100 microg/kg) or intracerebroventricularly (i.c.v.; 5, 15 microg/rat) 15 min before the emptying, delayed gastric emptying rate of saline at the dose of 30 microg/kg or 15 microg/rat (p<0.001). When CCK(1) receptor blocker L-364,718 (1 mg/kg, i.p.), CCK(2) receptor blocker L-365,260 (1 mg/kg, ip) or adrenergic ganglion blocker bretylium tosylate (15 mg/kg, i.p.) was administered 15 min before ip leptin (30 microg/kg) injections, leptin-induced delay in gastric emptying was abolished only by the CCK(1) receptor blocker (p<0.001). However, the inhibitory effect of central leptin on gastric emptying was reversed by adrenergic blockade, but not by either CCK antagonists. Our results demonstrated that leptin delays gastric emptying. The peripheral effect of leptin on gastric motility appears to be mediated by CCK(1) receptors, suggesting the release of CCK and the involvement of vagal afferent fibers. On the other hand, the central effect of leptin on gastric emptying is likely to be mediated by adrenergic neurons. These results indicate the existence of a functional interaction between leptin and CCK receptors leading to inhibition of gastric emptying and short-term suppression of food intake, providing an additional feedback control in producing satiety.     

Dietary daidzein decreases food intake accompanied with delayed gastric emptying in ovariectomized rats

ABSTRACT

We previously found that equol, a metabolite of intestinal bacterial conversion from soy isoflavone daidzein, has female-specific anorectic effects. In the present study, we used seven-week-old female ovariectomized (OVX) Sprague Dawley rats to test the hypothesis that the anorectic effect of dietary daidzein may be attributed to delayed gastric emptying. Results suggest that dietary daidzein delays gastric emptying and that it has an anorectic effect with residual gastric contents, but not without gastric contents. Dietary equol significantly decreased daily food intake in the OVX rats without sleeve gastrectomy, but not in those with sleeve gastrectomy, suggesting that the accumulation of food in the stomach is required for the anorectic effect of equol to occur. These results support the hypothesis that the anorectic effect of dietary daidzein is attributed to delayed gastric emptying.     

Effects of amylin-related peptides on food intake, meal patterns, and gastric emptying in rats

We previously demonstrated that amylin inhibits food intake and gastric emptying in rats with half-maximal effective doses (ED(50)s) of 8 and 3 pmol x kg(-1) x min(-1) and maximal inhibitions of 78 and 60%, respectively. In this study of identical design, rats received intravenous infusions of salmon calcitonin (sCT), rat calcitonin (rCT), rat calcitonin gene-related peptide (rCGRP), and rat adrenomedullin (rADM) for 3 h at dark onset, and food intake was measured for 17 h or for 15 min and gastric emptying of saline was measured during the final 5 min. sCT, rCGRP, and rADM inhibited food intake with estimated ED(50)s of 0.5, 26, and 35 pmol x kg(-1) x min(-1) and maximal inhibitions of 88, 90, and 49%, respectively. rCT was not effective at doses up to 100 pmol x kg(-1) x min(-1). sCT, rCGRP, rADM, and rCT inhibited gastric emptying with ED(50)s of 1, 130, 160, and 730 pmol x kg(-1) x min(-1) and maximal inhibitions of 60, 66, 60, and 33%, respectively. These results suggest that amylin and sCT may act by a common mechanism to decrease food intake, which includes inhibition of gastric emptying.     

Intracerebroventricular administration of MK-801 increases food intake through mechanisms independent of gastric emptying

Systemic or hindbrain administration of MK-801, a noncompetitive N-methyl-D-aspartate receptor antagonist, increases meal size. To examine whether MK-801 enhances intake by increasing gastric emptying, we administered MK-801 (2.0 microg/3.0 microl) into the fourth ventricle [intracerebroventricular (ICV)] and measured feeding and gastric emptying of 5-ml NaCl or 15% sucrose loads. In a parallel experiment, we examined food intake and gastric emptying following intraperitoneal (IP) injection of MK-801 (100 microg/kg). MK-801, either IP or ICV, increased 30-min sucrose intake compared with control (12.3 +/- 0.7 vs. 9.8 +/- 0.5 and 16.6 +/- 2.0 vs. 10.7 +/- 0.7 ml, for IP and ICV administration, respectively). Also, IP MK-801 increased 5-min gastric emptying of NaCl (4.13 +/- 0.1 ml emptied) and sucrose (3.11 +/- 0.1 ml emptied) compared with control (3.75 +/- 0.2 and 2.28 +/- 0.1 ml emptied for NaCl and sucrose loads, respectively). In contrast, ICV MK-801 did not alter NaCl emptying (3.82 +/- 0.1 ml emptied) compared with control (3.82 +/- 0.3 ml emptied) and actually reduced gastric emptying of sucrose (2.1 +/- 0.2 and 2.94 +/- 0.1 ml emptied, for MK and vehicle, respectively). These data confirm previous results that systemic as well as hindbrain injection of MK-801 increases food intake. However, because ICV MK-801 failed to increase gastric emptying, these results indicate that MK-801 increases food intake through mechanisms independent of altered gastric emptying.     

5-HT3 receptors participate in CCK-induced suppression of food intake by delaying gastric emptying

Serotonin type 3 (5-HT(3)) receptors have been shown to participate in the negative-feedback control of food intake. We previously reported that cholecystokinin (CCK)-induced suppression of food intake is partly mediated through 5-HT(3) receptors when rats were tested on a preferred liquid diet, but whether such an effect occurs when they are tested on a solid maintenance diet is unknown. In the present study, we examined the effects of ondansetron, a selective 5-HT(3) antagonist, on CCK-induced suppression of solid chow intake. Intraperitoneal administration of ondansetron significantly attenuated 30- and 60-min CCK-induced reduction of food intake, with suppression being completely reversed by 120 min. It is not known whether 5-HT(3) receptors directly mediate CCK-induced satiation or whether their participation depends on CCK acting as part of a feedback cascade to inhibit ongoing intake. Because CCK-induced inhibition of sham feeding does not depend on additive gastric/postgastric-feedback signals, we examined the ability of ondansetron to reverse CCK-induced satiation in sham-feeding rats. Ondansetron did not attenuate reduction of sham feeding by CCK, suggesting that ondansetron does not directly antagonize CCK-satiation signals. CCK suppresses real feeding through a delay in gastric emptying. Ondansetron could attenuate CCK-induced reduction of food intake by reversing CCK-induced inhibition of gastric emptying. We found that blockade of 5-HT(3) receptors attenuates CCK-induced inhibition of gastric emptying of a solid meal, as well as saline and glucose loads. We conclude that 5-HT(3) receptors mediate CCK-induced satiation through indirect mechanisms as part of a feedback cascade involving inhibition of gastric emptying.     

Inhibitory effects of intestinal electrical stimulation on food intake, weight loss and gastric emptying in rats

The aim was to investigate the effects of intestinal electrical stimulation (IES) on food intake, body weight, and gastric emptying in rats. An experiment on food intake and weight change was performed in 22 rats on a control diet and 10 diet-induced obese (DIO) rats for 4 wk with IES or sham IES. The effect of IES on gastric emptying was performed in another 20 rats in the control group. We found that 1) in control rats, 4-wk IES resulted in a reduction of 18.2% in the total amount of food intake compared with sham-IES (P = 0.02); the rats treated with IES had a weight change of -1 +/- 7.8g (P = 0.03), which was equivalent to a weight loss of 6.2% due to IES when adjusted for normal growing. 2) Acute IES delayed gastric emptying by 20% in the control rats (P < 0.01). 3) In the DIO rats, 1-wk IES with the same parameters as those used in the control rats resulted in a significant reduction in the total amount of food intake (126.6 +/- 6.3 g vs. 116.9 +/- 3.2 g, P < 0.01). More reduction in food intake was noted, and a significant weight change was also observed when stimulation energy was increased. 4) No adverse events were observed in any of the experiments. In conclusion, IES delays gastric emptying, reduces food intake, and decreases weight gain in control growing rats. These data suggest that it is worthy to explore therapeutic potentials of IES for obesity.