Obestatin对血浆ghrelin和nesfatin-1水平及胃排空的影响

目的:探讨侧脑室注射obestatin对大鼠血浆酰基化ghrelin、去酰基化ghrelin、nesfatin-1水平的影响以及对胃排空的调控。方法:侧脑室注射obestatin,采用酶免疫测定(EIA)法检测血浆酰基化ghrelin、去酰基化ghrelin、nesfatin-1水平以及胃排空率的变化。结果:侧脑室分别注射0.1、0.3或1.0 nmol obestatin,大鼠血浆酰基化ghrelin、去酰基化ghrelin以及nesfatin-1水平无显著改变(P0.05),且酰基化ghrelin与去酰基化ghrelin比率无显著改变(P0.05);侧脑室注射obestatin,大鼠摄食量无显著改变,但胃排空率明显增加(P0.05);胃排空率明显延迟(P0.05)。与侧脑室注射1.0 nmol Obestatin组相比,注射1.0 nmol Obestatin+CRF,大鼠摄食量无显著改变,胃排空率明显延迟(P0.05)。各组摄食量及进入十二指肠内食物量无明显差异(P0.05)。结论:中枢obestatin促进大鼠的胃排空,可能与h/r CRF通路有关。     

Does ghrelin explain accelerated gastric emptying in the early stages of diabetes mellitus?

During the early stages of diabetes, gastric emptying is often accelerated, rather than delayed. The mechanism of accelerated gastric emptying in diabetes has not been fully studied. A recent study showed that plasma ghrelin levels were elevated in diabetes. As postprandial antropyloric coordination plays an important role in mediating solid gastric emptying, we hypothesize that the elevated plasma ghrelin levels increase postprandial antropyloric coordination to accelerate emptying in the early stages of diabetes. To test this hypothesis, rats were made diabetic by streptozotocin (STZ; 50 mg/kg) injection, and, 2 wk later, pre- and postprandial plasma ghrelin levels, antropyloric coordination, and solid gastric emptying were determined. In control rats, plasma ghrelin levels were immediately reduced after feeding. In contrast, plasma ghrelin levels remained within the fasted levels in STZ rats after feeding. In STZ rats, gastric emptying was significantly accelerated (77.4 +/- 3.2%, n = 6), compared with that of control rats (58.8 +/- 2.5%, n = 6, P < 0.05). Treatments with anti-ghrelin antibodies attenuated accelerated gastric emptying in STZ rats (50.1 +/- 3.5%, n = 6, P < 0.05), while having little effect in vehicle control rats. The incidence of postprandial antropyloric coordination was significantly increased in STZ rats, compared with that of control rats (P < 0.05). Treatments with anti-ghrelin antibodies suppressed this enhanced antropyloric coordination in STZ rats. Our study suggests that elevated endogenous ghrelin enhances antropyloric coordination, which accelerates gastric emptying in the early stages of diabetes.     

Peripheral urocortin inhibits gastric emptying and food intake in mice: differential role of CRF receptor 2

Intraperitoneal urocortin inhibits gastric emptying and food intake in mice. We investigated corticotropin-releasing factor receptor (CRF-R) subtypes involved in intraperitoneal urocortin actions using selective CRF-R antagonists. Gastric emptying was measured 2 h after a chow meal, and food intake was measured hourly after an 18-h fast in mice. Urocortin (3 microg/kg ip) inhibited gastric emptying by 88%. The CRF-R1/CRF-R2 antagonist astressin B (30 microg/kg ip) and the selective CRF-R2 antagonist antisauvagine-30 (100 microg/kg ip) completely antagonized urocortin action, whereas the selective CRF-R1 antagonist CP-154,526 (10 mg/kg ip) had no effect. Urocortin (1-10 microg/kg ip) dose dependently decreased the 2-h cumulative food intake by 30-62%. Urocortin (3 microg/kg)-induced hypophagia was completely antagonized by astressin B (30 microg/kg ip) and partially (35 and 31%) by antisauvagine-30 (100 or 200 microg/kg ip). The CRF-R1 antagonists CP-154,526 or DMP904 (10 mg/kg ip) had no effect. Capsaicin did not alter urocortin-inhibitory actions while blocking the satiety effect of intraperitoneal CCK. These data indicate that intraperitoneal urocortin-induced decrease in feeding is only partly mediated by CRF-R2, whereas urocortin action to delay gastric emptying of a meal involves primarily CRF-R2.     

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.     

Fixed feeding potentiates interdigestive gastric motor activity in rats: importance of eating habits for maintaining interdigestive MMC

Endogenous ghrelin regulates the occurrence of interdigestive gastric phase III-like contractions in rats. However, the fasted motor pattern is not as regular and potent in humans and dogs. We hypothesize that eating habits play an important role in maintaining a regular interdigestive gastric contractions. We studied the effect of fixed-feeding regimen on interdigestive gastric contractions and plasma acyl ghrelin levels. The fixed-fed rats were trained to the assigned meal feeding regimen, once daily at 12:00 PM to 4:00 PM for 14 days. Free-fed rats were maintained with free access to food. As ghrelin regulates gastric emptying as well, solid gastric emptying was also studied in fixed-fed rats and free-fed rats. In free-fed rats, two of six rats did not show interdigestive gastric phase III-like contractions. In contrast, phase III-like contractions were observed in all rats 14 days after starting the fixed-feeding regimen. The maximal amplitude of phase III-like contractions significantly increased from 8.4 +/- 0.6 to 16.3 +/- 1.8 g (n = 6, P < 0.05) 14 days after the start of the fixed feeding. Fasted and postprandial plasma ghrelin levels were significantly increased after 14 days of fixed feeding. Solid gastric emptying was significantly accelerated in fixed-fed rats (72.1 +/- 4.2%) compared with that of free-fed rats (58.7 +/- 2.7%, n = 6, P < 0.05). Our present findings suggest that fixed feeding increases plasma ghrelin levels, potent interdigestive contractions, and acceleration of gastric emptying.     

Abdominal surgery inhibits circulating acyl ghrelin and ghrelin-O-acyltransferase levels in rats: role of the somatostatin receptor subtype 2

Clinical studies are evaluating the efficacy of synthetic ghrelin agonists in postoperative ileus management. However, the control of ghrelin secretion under conditions of postoperative gastric ileus is largely unknown. Peripheral somatostatin inhibits ghrelin secretion in animals and humans. We investigated the time course of ghrelin changes postsurgery in fasted rats and whether somatostatin receptor subtype 2 (sst(2)) signaling is involved. Abdominal surgery (laparotomy and 1-min cecal palpation) induced a rapid and long-lasting decrease in plasma acyl ghrelin levels as shown by the 64, 67, and 59% reduction at 0.5, 2, and 5 h postsurgery, respectively, compared with sham (anesthesia alone for 10 min, P < 0.05). Levels were partly recovered at 7 h and fully restored at 24 h. The percentage of acyl ghrelin reduction was significantly higher than that of desacyl ghrelin at 2 h postsurgery and not at any other time point. This was associated with a 48 and 23% decrease in gastric and plasma ghrelin-O-acyltransferase protein concentrations, respectively (P < 0.001). Ghrelin-positive cells in the oxyntic mucosa expressed sst(2a) receptor and the sst(2) agonist S-346-011 inhibited fasting acyl ghrelin levels by 64 and 77% at 0.5 and 2 h, respectively. The sst(2) antagonist S-406-028 prevented the abdominal surgery-induced decreased circulating acyl ghrelin but not the delayed gastric emptying assessed 0.5 h postinjection. These data show that activation of sst(2) receptor located on gastric X/A-like cells plays a key role in the rapid inhibition of circulating acyl ghrelin induced by abdominal surgery while not being primarily involved in the early phase of postoperative gastric ileus.     

Preproghrelin-derived peptide, obestatin, fails to influence food intake in lean or obese rodents

Objectives: Obestatin has been initially characterized as a new peptide derived from the ghrelin precursor, which suppresses food intake and inhibits the orexigenic and prokinetic actions of ghrelin when injected peripherally or centrally in lean mice. However, reproducing these data remains controversial. Reasons for the disparity may be the use of different doses, routes, and animal models. We aimed to investigate the effects of peripheral and intracisternal (IC) injection of obestatin on feeding, gastric motility, and blood glucose in rats as well as in diet‐induced obese (DIO) mice. Research Methods and Procedures: Food intake and gastric emptying of a semi‐liquid caloric meal were measured after intraperitoneal (IP) injection of obestatin in rats and DIO mice. Gastric phasic motility and blood glucose were monitored in urethane‐anesthetized rats after IC or intravenous (IV) injection of obestatin. Results: Obestatin injected intraperitoneally at doses ranging from 0.1 to 3 mg/kg influenced neither acute food intake nor gastric emptying in rats. Obestatin injected intravenously at 0.3 or 3 mg/kg and IC at 7.5 or 30 µg/rat modified neither fasted gastric phasic motility nor blood glucose levels, while ghrelin (30 µg/kg, IV) increased and vagotomy suppressed gastric motility, and an oligosomatostatin analog (3 µg/rat, IC) decreased blood glucose. Obestatin, injected intraperitoneally (0.3 mg/kg) in DIO mice, did not alter feeding response to a fast, while urocortin 1 (10 µg/kg, IP) induced a 73.3% inhibition at 2 hours. Discussion: Our data demonstrate that peripheral administration of obestatin did not modify food intake in rats or obese mice or gastric motor function in rats.     

Endogenous brain IL-1 mediates LPS-induced anorexia and hypothalamic cytokine expression

The present study was designed to determine the role of endogenous brain interleukin (IL)-1 in the anorexic response to lipopolysaccharide (LPS). Intraperitoneal administration of LPS (5-10 microgram/mouse) induced a dramatic, but transient, decrease in food intake, associated with an enhanced expression of proinflammatory cytokine mRNA (IL-1beta, IL-6, and tumor necrosis factor-alpha) in the hypothalamus. This dose of LPS also increased plasma levels of IL-1beta. Intracerebroventricular pretreatment with IL-1 receptor antagonist (4 microgram/mouse) attenuated LPS-induced depression of food intake and totally blocked the LPS-induced enhanced expression of proinflammatory cytokine mRNA measured in the hypothalamus 1 h after treatment. In contrast, LPS-induced increases in plasma levels of IL-1beta were not altered. These findings indicate that endogenous brain IL-1 plays a pivotal role in the development of the hypothalamic cytokine response to a systemic inflammatory stimulus.     

Blockade of prostaglandin biosynthesis in intact mice dramatically augments the expansion of committed myeloid progenitor cells (colony-forming units-granulocyte, macrophage) after acute administration of recombinant human IL-1 alpha

Injection of human rIL-1 alpha in intact normal mice has positive and negative effects on myelopoiesis. Within 6 h postinjection, peripheral neutrophilia can be demonstrated. However, bone marrow and spleen cells capable of inhibiting CFU-granulocyte macrophage proliferation are detected between 6 and 48 h postinjection. These myelopoietic suppressor cells belong to the monocytic lineage and are identical to inhibitory cells induced by PGE2. Treatment of mice with indomethacin, a PG synthesis inhibitor, completely blocked the generation of IL-1-alpha-induced myelopoietic suppressor cells, and significantly enhanced femoral and splenic CFU-GM proliferation after a single injection of 0.4 microgram/mouse IL-1. The peripheral blood neutrophilia observed within 6 h after IL-1 injection was delayed to 18 to 24 h postinjection in indomethacin-pretreated mice. In mice treated with four consecutive daily injections of 0.4 microgram IL-1, a sustained peripheral neutrophilia was observed. IL-1 had little effect on femoral CFU-GM in these animals, however, splenic CFU-GM was increased 7- to 10-fold by 4 to 7 days postinjection. In IL-1 plus indomethacin-treated mice, sustained peripheral neutrophilia was observed although to a lesser degree than with IL-1 alone. Marrow CFU-GM were relatively unaffected, however, splenic CFU-GM were increased by 27-fold. These results indicate that the in vivo administration of IL-1 results in neutrophilia and generation of myelopoietic suppressive effects, mediated by cyclo-oxygenase pathway products. Blockade of PG synthesis by using the cyclo-oxygenase inhibitor indomethacin abrogates the myelopoietic suppressive effects associated with IL-1 administration and optimizes its myelopoietic stimulatory capacity. The inclusion of a cyclo-oxygenase inhibitor may have significant relevance to the clinical use of IL-1.     

Effect of peripherally administered ghrelin on gastric emptying and acid secretion in the rat

Ghrelin is a gut peptide that is secreted from the stomach and stimulates food intake. There are ghrelin receptors throughout the gut and intracerebroventricular ghrelin has been shown to increase gastric acid secretion. The aim of the present study was to examine the effects of peripherally administered ghrelin on gastric emptying of a non-nutrient and nutrient liquid, as well as, basal and pentagastrin-stimulated gastric acid secretion in awake rats. In addition, gastric contractility was studied in vitro. Rats equipped with a gastric fistula were subjected to an intravenous infusion of ghrelin (10-500 pmol kg(-1) min(-1)) during saline or pentagastrin (90 pmol kg(-1) min(-1)) infusion. After administration of polyethylene glycol (PEG) 4000 with 51Cr as radioactive marker, or a liquid nutrient with (51)Cr, gastric retention was measured after a 20-min infusion of ghrelin (500 pmol kg(-1) min(-1)). In vitro isometric contractions of segments of rat gastric fundus were studied (10(-9) to 10(-6) M). Ghrelin had no effect on basal acid secretion, but at 500 pmol kg(-1) min(-1) ghrelin significantly decreased pentagastrin-stimulated acid secretion. Ghrelin had no effect on gastric emptying of the nutrient liquid, but significantly increased gastric emptying of the non-nutrient liquid. Ghrelin contracted fundus muscle strips dose-dependently (pD2 of 6.93+/-0.7). Ghrelin IV decreased plasma orexin A concentrations and increased plasma somatostatin concentrations. Plasma gastrin concentrations were unchanged during ghrelin infusion. Thus, ghrelin seems to not only effect food intake but also gastric motor and secretory function indicating a multifunctional role for ghrelin in energy homeostasis.     

Endotoxin induced increases in rat plasma pituitary-adrenocortical hormones are better reflected by alterations in tumor necrosis factorα than interleukin-1β

In order to assess the relative cytokine contribution to endotoxin stimulation of pituitary-adrenocortical hormone secretion, we measured plasma levels of interleukin-1β (IL-Iβ), tumor necrosis factorα (TNFα), adrenocorticotropin (ACTH) and corticosterone following lipopolysaccharide (LPS) challenge in rats. LPS administration induced robust increases in both plasma ACTH and corticosterone levels at 3 h after i.p. injection; while ACTH decreased towards control levels, corticosterone remained at peak concentrations at 6 h after LPS injection. Basal levels of plasma IL-1β were below the sensitivity of the ELISA and basal levels of plasma TNFα were 0.25 ± 0.12 pM. Small but highly variable non-significant increases in plasma IL-1β levels were seen at 3 h and 6 h after injection of LPS. The lack of functional consequences of the small increases in IL-1β levels was demonstrated by unchanged levels of [¹²⁵I]IL-1α binding in liver at 3 h after LPS injection. In contrast, dramatic increases in plasma TNFα concentrations were observed at 3 h and decreased to non-injected control levels at 6 h after LPS injection. There was a significant positive correlation between ACTH and TNFα after LPS injection, while no correlation was seen between ACTH and IL-1β. These data demonstrate differential regulation of IL-1β and TNFα by endotoxin treatment and suggest that TNFα may be a more potent mediator of LPS-induced ACTH secretion in rat.     

Lipopolysaccharide increases gastric and circulating NUCB2/nesfatin-1 concentrations in rats

Bacterial lipopolysaccharide (LPS) is an established animal model to study the innate immune response to Gram-negative bacteria mimicking symptoms of infection including reduction of food intake. LPS decreases acyl ghrelin associated with decreased concentrations of circulating ghrelin-O-acyltransferase (GOAT) likely contributing to the anorexigenic effect. We also recently described the prominent expression of the novel anorexigenic hormone, nucleobindin2 (NUCB2)/nesfatin-1 in gastric X/A-like cells co-localized with ghrelin in different pools of vesicles. To investigate whether LPS would affect gastric and circulating NUCB2/nesfatin-1 concentration, ad libitum fed rats were equipped with an intravenous (iv) catheter. LPS was injected intraperitoneally (ip, 100 μg/kg) and blood was withdrawn before and at 2, 5, 7 and 24 h post injection and processed for NUCB2/nesfatin-1 radioimmunoassay. Gastric corpus was collected to measure NUCB2 mRNA expression by RT-qPCR and NUCB2/nesfatin-1 protein concentration by Western blot. Injection of LPS increased plasma NUCB2/nesfatin-1 concentrations by 43%, 78% and 62% compared to vehicle at 2 h, 5 h and 7 h post injection respectively (p < 0.05) and returned to baseline at 24 h. The plasma NUCB2/nesfatin-1 increase at 2 h was associated with increased corpus NUCB2 mRNA expression (p < 0.01), whereas NUCB2 mRNA was not detectable in white blood cells. Likewise, gastric NUCB2 protein concentration was increased by 62% after LPS compared to vehicle (p < 0.01). These data show that gastric NUCB2 production and release are increased in response to LPS. These changes are opposite to those of ghrelin in response to LPS supporting a differential gastric regulation of NUCB2/nesfatin-1 and ghrelin expression derived from the same cell by immune challenge.     

Inhibitory effect of ghrelin on food intake is mediated by the corticotropin-releasing factor system in neonatal chicks

It is known that, in rats, central and peripheral ghrelin increases food intake mainly through activation of neuropeptide Y (NPY) neurons. In contrast, intracerebroventricular (ICV) injection of ghrelin inhibits food intake in neonatal chicks. We examined the mechanism governing this inhibitory effect in chicks. The ICV injection of ghrelin or corticotropin-releasing factor (CRF), which also inhibits feeding and causes hyperactivity in chicks. Thus, we examined the interaction of ghrelin with CRF and the hypothalamo-pituitary-adrenal (HPA) axis. The ICV injection of ghrelin increased plasma corticosterone levels in a dose-dependent or a time-dependent manner. Co-injection of a CRF receptor antagonist, astressin, attenuated ghrelin-induced plasma corticosterone increase and anorexia. In addition, we also investigated the effect of ghrelin on NPY-induced food intake and on expression of hypothalamic NPY mRNA. Co-injection of ghrelin with NPY inhibited NPY-induced increase in food intake, and the ICV injection of ghrelin did not change NPY mRNA expression. These results indicate that central ghrelin does not interact with NPY as seen in rodents, but instead inhibits food intake by interacting with the endogenous CRF and its receptor.     

Peripheral ghrelin injections stimulate food intake, foraging, and food hoarding in Siberian hamsters

Fasting triggers many effects, including increases in circulating concentrations of ghrelin, a primarily stomach-derived orexigenic hormone. Exogenous ghrelin treatment stimulates food intake, implicating it in fasting-induced increases in feeding, a consummatory ingestive behavior. In Siberian hamsters, fasting also stimulates appetitive ingestive behaviors such as foraging and food hoarding. Therefore, we tested whether systemic ghrelin injections (3, 30, and 200 mg/kg) would stimulate these appetitive behaviors using a running wheel-based food delivery system coupled with simulated burrow housing. We also measured active ghrelin plasma concentrations after exogenous ghrelin treatment and compared them to those associated with fasting. Hamsters had the following: 1) no running wheel access, free food; 2) running wheel access, free food; or 3) foraging requirement (10 revolutions/pellet), no free food. Ghrelin stimulated foraging at 0-1, 2-4, and 4-24 h postinjection but failed to affect wheel running activity not coupled to food. Ghrelin stimulated food intake initially (200-350%, first 4 h) across all groups; however, in hamsters with a foraging requirement, ghrelin also stimulated food intake 4-24 h postinjection (200-250%). Ghrelin stimulated food hoarding 2-72 h postinjection (100-300%), most markedly 2-4 h postinjection in animals lacking a foraging requirement (635%). Fasting increased plasma active ghrelin concentrations in a time-dependent fashion, with the 3- and 30-mg/kg dose creating concentrations of the peptide comparable to those induced by 24-48 h of fasting. Collectively, these data suggest that exogenous ghrelin, similar to fasting, increases appetitive behaviors (foraging, hoarding) by Siberian hamsters, but dissimilar to fasting in this species, stimulates food intake.     

Impaired ghrelin signaling is associated with gastrointestinal dysmotility in rats with gastroesophageal reflux disease

Gastroesophageal reflux disease (GERD) is often associated with decreased upper gastrointestinal motility, and ghrelin is an appetite-stimulating hormone known to increase gastrointestinal motility. We investigated whether ghrelin signaling is impaired in rats with GERD and studied its involvement in upper gastrointestinal motility. GERD was induced surgically in Wistar rats. Rats were injected intravenously with ghrelin (3 nmol/rat), after which gastric emptying, food intake, gastroduodenal motility, and growth hormone (GH) release were investigated. Furthermore, plasma ghrelin levels and the expression of ghrelin-related genes in the stomach and hypothalamus were examined. In addition, we administered ghrelin to GERD rats treated with rikkunshito, a Kampo medicine, and examined its effects on gastroduodenal motility. GERD rats showed a considerable decrease in gastric emptying, food intake, and antral motility. Ghrelin administration significantly increased gastric emptying, food intake, and antral and duodenal motility in sham-operated rats, but not in GERD rats. The effect of ghrelin on GH release was also attenuated in GERD rats, which had significantly increased plasma ghrelin levels and expression of orexigenic neuropeptide Y/agouti-related peptide mRNA in the hypothalamus. The number of ghrelin-positive cells in the gastric body decreased in GERD rats, but the expression of gastric preproghrelin and GH secretagogue receptor mRNA was not affected. However, when ghrelin was exogenously administered to GERD rats treated with rikkunshito, a significant increase in antral motility was observed. These results suggest that gastrointestinal dysmotility is associated with impaired ghrelin signaling in GERD rats and that rikkunshito restores gastrointestinal motility by improving the ghrelin response.     

Different responses of circulating ghrelin, obestatin levels to fasting, re-feeding and different food compositions, and their local expressions in rats

Obestatin, a sibling of ghrelin derived from preproghrelin, opposes several physiological actions of ghrelin. Our previous study has demonstrated that both plasma ghrelin and obestatin levels were decreased significantly 2h after food intake in human. To further expand current knowledge, we investigated the temporal profiles of their levels in ad libitum fed rats, 48h fasted rats and 48h fasted rats refed 2h with a standard chow, crude fiber, 50% glucose or water, and their expressions in stomach, liver and pancreatic islets immunohistochemically. Plasma ghrelin and obestatin levels were measured by EIA. Plasma leptin, insulin and glucose levels were also evaluated. Both plasma ghrelin and obestatin levels increased significantly in fasted rats compared with ad libitum fed rats. The ingestion of standard chow produced a profound and sustained suppression of ghrelin levels, whereas plasma obestatin levels decreased significantly but recovered quickly. Intake of crude fiber or 50% glucose, however, produced a more profound and sustained suppression of obestatin levels, though they had relatively less impact on ghrelin levels. Plasma glucose was the only independent predictor of ghrelin levels, obestatin levels, and ghrelin to obestatin ratios. Obestatin immunoreactivity was detected in the fundus of stomach, liver and pancreatic islets, with roughly similar patterns of distribution to ghrelin. These data show quantitative and qualitative differences in circulating ghrelin and obestatin responses to the short-term feeding status and nutrient composition, and may support a role for obestatin in regulating metabolism and energy homeostasis.     

Urocortin 1 reduces food intake and ghrelin secretion via CRF(2) receptors

Although it is known that urocortin 1 (UCN) acts on both corticotropin-releasing factor receptors (CRF(1) and CRF(2)), the mechanisms underlying UCN-induced anorexia remain unclear. In contrast, ghrelin, the endogenous ligand for the growth hormone secretagogue receptor, stimulates food intake. In the present study, we examined the effects of CRF(1) and CRF(2) receptor antagonists (CRF(1)a and CRF(2)a) on ghrelin secretion and synthesis, c-fos mRNA expression in the caudal brain stem, and food intake following intracerebroventricular administration of UCN. Eight-week-old, male Sprague-Dawley rats were used after 24-h food deprivation. Acylated and des-acylated ghrelin levels were measured by enzyme-linked immunosorbent assay. The mRNA expressions of preproghrelin and c-fos were measured by real-time RT-PCR. The present study provided the following important insights into the mechanisms underlying the anorectic effects of UCN: 1) UCN increased acylated and des-acylated ghrelin levels in the gastric body and decreased their levels in the plasma; 2) UCN decreased preproghrelin mRNA levels in the gastric body; 3) UCN-induced reduction of plasma ghrelin and food intake were restored by CRF(2)a but not CRF(1)a; 4) UCN-induced increase of c-fos mRNA levels in the caudal brain stem containing the nucleus of the solitary tract (NTS) was inhibited by CRF(2)a; and 5) UCN-induced reduction of food intake was restored by exogenous ghrelin and rikkunshito, an endogenous ghrelin secretion regulator. Thus, UCN increases neuronal activation in the caudal brain stem containing NTS via CRF(2) receptors, which may be related to UCN-induced inhibition of both ghrelin secretion and food intake.     

Reduced ghrelin production induced anorexia after rat gastric ischemia and reperfusion

The gastrointestinal (GI) tract is one of the most susceptible organs to ischemia. We previously reported altered gastric motility after gastric ischemia and reperfusion (I/R). However, there have also been few reports of alterations in the eating behavior after gastric I/R. Ghrelin is a GI peptide that stimulates food intake and GI motility. Although ghrelin itself has been demonstrated to attenuate the mucosal injuries induced by gastric I/R, the endogenous ghrelin dynamics after I/R has not yet been elucidated. The present study was designed to investigate the relationship between food intake and the ghrelin dynamics after gastric I/R. Wistar rats were exposed to 80-min gastric ischemia, followed by 12-h or 48-h reperfusion. The food intake, plasma ghrelin levels, gastric preproghrelin mRNA expression levels, and the histological localization of ghrelin-immunoreactive cells were evaluated. The effect of exogenous ghrelin on the food intake after I/R was also examined. Food intake, the plasma ghrelin levels, the count of ghrelin-immunoreactive cells corrected by the percentage areas of the remaining mucosa, and the expression levels of preproghrelin mRNA in the stomach were significantly reduced at 12 h and 48 h after I/R compared with the levels in the sham-operated rats. Intraperitoneal administration of ghrelin significantly reversed the decrease of food intake after I/R. These data show that gastric I/R evoked anorexia with decreased plasma ghrelin levels and ghrelin production, which appears to be attributable to the I/R-induced gastric mucosal injuries. The decrease in the plasma ghrelin levels may have been responsible for the decreased food intake after gastric I/R.     

Exogenous ghrelin attenuates endotoxin fever in rats

Ghrelin is a gut-derived peptide that plays a role in energy homeostasis. Recent studies have implicated ghrelin in systemic inflammation, showing increased plasma ghrelin levels after endotoxin (lipopolysaccharide, LPS) administration. The aims of this study were (1) to test the hypothesis that ghrelin administration affects LPS-induced fever; and (2) to assess the putative effects of ghrelin on plasma corticosterone secretion and preoptic region prostaglandin (PG) E₂ levels in euthermic and febrile rats. Rats were implanted with a temperature datalogger capsule in the peritoneal cavity to record body core temperature. One week later, they were challenged with LPS (50 μg/kg, intraperitoneal, i.p.) alone or combined with ghrelin (0.1 mg/kg, i.p.). In another group of rats, plasma corticosterone and preoptic region PGE₂ levels were measured 2 h after injections. In euthermic animals, systemic administration of ghrelin failed to elicit any thermoregulatory effect, and caused no significant changes in basal plasma corticosterone and preoptic region PGE₂ levels. LPS caused a typical febrile response, accompanied by increased plasma corticosterone and preoptic PGE₂ levels. When LPS administration was combined with ghrelin fever was attenuated, corticosterone secretion further increased, and the elevated preoptic PGE₂ levels were relatively reduced, but a correlation between these two variables (corticosterone and PGE₂) failed to exist. The present data add ghrelin to the neurochemical milieu controlling the immune/thermoregulatory system acting as an antipyretic molecule. Moreover, our findings also support the notion that ghrelin attenuates fever by means of a direct effect of the peptide reducing PGE₂ production in the preoptic region.