Peripheral injection of pancreatic polypeptide enhances colonic transit without eliciting anxiety or altering colonic secretion in rats

Pancreatic polypeptide (PP) is a negative regulator of energy homeostasis that suppresses food intake and lowers body weight. Similar to other gastrointestinal-derived peptides, PP also modulates gastrointestinal motility and may be involved in the regulation of anxiety. Previous studies revealed that PP suppresses gastric emptying but increases colonic motility in mice. In our present study, we assessed the effect of PP on anxiety as well as colonic motility and secretory function. Intracerebroventricular and intravenous routes of PP were administered in conscious rats. Our results showed that intracerebroventricular administration of PP did not affect anxiety in the open field test. Intravenous injection of PP accelerated colonic transit, but did not significantly change fecal amount and fecal fluid composition. On the other hand, intracerebroventricular injection of PP did not alter colonic transit, fecal amount, or fluid composition. In conclusion, peripheral, but not central PP administration enhances colonic motility without eliciting anxiety or altering colonic secretion.

Role of the vagus in the reduced pancreatic exocrine function in copper-deficient rats

Copper plays an essential role in the function and development of the central nervous system and exocrine pancreas. Dietary copper limitation is known to result in noninflammatory atrophy of pancreatic acinar tissue. Our recent studies have suggested that vagal motoneurons regulate pancreatic exocrine secretion (PES) by activating selective subpopulations of neurons within vagovagal reflexive neurocircuits. We used a combination of in vivo, in vitro, and immunohistochemistry techniques in a rat model of copper deficiency to investigate the effects of a copper-deficient diet on the neural pathways controlling PES. Duodenal infusions of Ensure or casein, as well as microinjections of sulfated CCK-8, into the dorsal vagal complex resulted in an attenuated stimulation of PES in copper-deficient animals compared with controls. Immunohistochemistry of brain stem slices revealed that copper deficiency reduced the number of tyrosine hydroxylase-immunoreactive, but not neuronal nitric oxide synthase- or choline acetyltransferase-immunoreactive, neurons in the dorsal motor nucleus of the vagus (DMV). Moreover, a copper-deficient diet reduced the number of large (>11 neurons), but not small, intrapancreatic ganglia. Electrophysiological recordings showed that DMV neurons from copper-deficient rats are less responsive to CCK-8 or pancreatic polypeptide than are DMV neurons from control rats. Our results demonstrate that copper deficiency decreases efferent vagal outflow to the exocrine pancreas. These data indicate that the combined selective loss of acinar pancreatic tissue and the decreased excitability of efferent vagal neurons induce a deficit in the vagal modulation of PES.

Pancreatic polypeptide and peptide YY3-36 induce Ca2+ signaling in nodose ganglion neurons

Peripheral injection of pancreatic polypeptide (PP) and peptide YY(3-36) (PYY(3-36)), the hormones released in response to meals, reduce food intake, in which the rank order of the potency is PP>PYY(3-36). These anorectic effects are abolished in abdominal vagotomized rats, suggesting that PP and PYY(3-36) induce anorexia via vagal afferent nerves. However, it is not clear whether PP and PYY(3-36) directly act on vagal afferent neurons. In this study, we examined the effects of PP and PYY(3-36) on cytosolic Ca(2+) concentration ([Ca(2+)](i)) in isolated nodose ganglion neurons of the mouse vagal afferent nerves. At 10(-11)M, PP but not PYY(3-36) recruited a significant population of nodose ganglion neurons into [Ca(2+)](i) increases. PP at 10(-11) to 10(-7) and PYY(3-36) at 10(-10) to 10(-7)M increased [Ca(2+)](i) in a concentration-dependent manner. At submaximal to maximal concentrations of 10(-10) and 10(-8)M, PP increased [Ca(2+)](i) in approximately twice greater population of nodose ganglion neurons than PYY(3-36). Furthermore, the majority of PP-responsive neurons also exhibited [Ca(2+)](i) responses to cholecystokinin-8, a hormone known to induce satiety through activating nodose ganglion neurons. The results demonstrate that PP and PYY(3-36) directly activate nodose ganglion neurons and suggest that the marked effect of PP on cholecystokinin-8-responsive nodose ganglion neurons could be linked to the regulation of feeding.

Analogs of pancreatic polypeptide and peptide YY with a locked PP-fold structure are biologically active

Pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY), members of the PP-fold family share a high degree of sequence homology. Nuclear magnetic resonance (NMR) and X-ray crystallography studies have shown these peptides can adopt a tightly organized tertiary structure called the PP-fold, which has long been assumed to be the active structure of this family of peptides. To date, however, no studies have been completed with PYY and PP which confirm if the PP-fold structure is important for their physiological actions. The aim of the study was to test if PYY and PP locked into the PP-fold maintained biological activity. Therefore, we designed and produced analogs of PP and PYY in a cyclic conformation with two cysteine amino acid substitutions at the N-terminus and at position 27. These were oxidized to form a cysteine disulfide bond locking the peptides into the PP-fold structure. Studies demonstrate that the cyclic analogs have both similar in vivo activity to their parent molecules, and affinity for the Y2 and Y4 receptors. Results suggest that the proposed PP and PYY-fold is likely to be their biologically active conformation.

Peptide YY 3-36 and pancreatic polypeptide differentially regulate hypothalamic neuronal activity in mice in vivo as measured by manganese-enhanced magnetic resonance imaging

Peptide YY (PYY) and pancreatic polypeptide (PP) are two appetite suppressing hormones, released post-prandially from the ileum and pancreas, respectively. PYY(3-36) , the major circulating form of the peptide, is considered to reduce food intake in humans and rodents via high affinity binding to the auto-inhibitory neuropeptide Y receptor Y2R, whereas PP is considered to act through the Y4R. Current evidence indicates the anorexigenic effects of both peptides occur via signalling in the brainstem and arcuate nucleus (ARC) of the hypothalamus. Manganese-enhanced magnetic resonance imaging (MEMRI) has previously been used to track hypothalamic neuronal activity in vivo in response to both nutritional interventions and gut hormone treatment. In the present study, we used MEMRI to demonstrate that s.c. administration of PP results in a significant reduction in signal intensity (SI) in the ARC, ventromedial hypothalamus and paraventricular nucleus of fasted mice. Subcutaneous delivery of PYY(3-36) resulted in a nonsignificant trend towards decreased SI in the hypothalamus of fasted mice. We found no SI change in the area postrema of the brainstem after s.c. injection of either peptide. These differences in hypothalamic SI profile between PP and PYY(3-36) occurred despite both peptides producing a comparable reduction in food intake. These results suggest that separate central pathways control the anorexigenic response for PP and PYY(3-36) , possibly via a differential effect of Y4 receptor versus Y2 receptor signalling. In addition, we performed a series of MEMRI scans at 0-2, 2-4 and 4-6 h post-injection of PYY(3-36) and a potent analogue of the peptide; PYY(3-36) (LT). We recorded a significant reduction in the ARC SI 2-4 h after PYY(3-36) (LT) injection compared to both saline and PYY(3-36) in fasted mice. The physiological differences between PYY(3-36) and its analogue were also observed in the long-term effects on food intake, with PYY(3-36) (LT) producing a more sustained anorexigenic effect. These data suggest that MEMRI can be used to investigate the long-term effects of gut peptide delivery on activity within the hypothalamus and brainstem.

Y4 receptors and pancreatic polypeptide regulate food intake via hypothalamic orexin and brain-derived neurotropic factor dependent pathways

Gut-derived peptides are known to regulate food intake by activating specific receptors in the brain, but the target nuclei and neurons influenced are largely unknown. Here we show that peripherally administered pancreatic polypeptide (PP) stimulates neurons in key nuclei of the hypothalamus critical for appetite and satiety regulation. In the lateral hypothalamic area (LHA), also known as the feeding center, neurons expressing the orexigenic neuropeptide orexin co-localize with the early neuronal activation marker c-Fos upon i.p. injection of PP into mice. In the ventromedial hypothalamus (VMH), also known as the satiety center, neurons activated by PP, as indicated by induction of c-Fos immunoreactivity, express the anorexigenic brain-derived neurotrophic factor (BDNF). Activation of neurons in the LHA and VMH in response to PP occurs via a Y4 receptor-dependent process as it is not seen in Y4 receptor knockout mice. We further demonstrate that in response to i.p. PP, orexin mRNA expression in the LHA is down-regulated, with Y4 receptors being critical for this effect as it is not seen in Y4 receptor knockout mice, whereas BDNF mRNA expression is up-regulated in the VMH in response to i.p. PP in the fasted, but not in the non-fasted state. Taken together these data suggest that PP can regulate food intake by suppressing orexigenic pathways by down-regulation of orexin and simultaneously increasing anorexigenic pathways by up-regulating BDNF.

Peripheral administration of pancreatic polypeptide inhibits components of food-intake behavior in dogs

Pancreatic polypeptide (PP) belongs to the neuropeptide Y (NPY) family of peptides and is released from pancreatic F cells postprandially. PP functions as a peptide hormone and has been associated with decreased food intake in humans and rodents. Our study describes the effects of PP on feeding behavior in dogs, whose mammalian order (Carnivora) is more distantly related to primates and rodents than these are to each other. Furthermore, obesity is becoming more prevalent in dogs which makes knowledge about their appetite regulation highly relevant. Repeated peripheral administration of physiological doses of PP (three injections of 30 pmol/kg each that were administered within 30 min) to six male beagle dogs prolonged the median time spent eating three servings of food by 19% but resulted in no reduction of food intake. In addition, PP decreased the duration of food-seeking behavior after the first serving by 71%. Thus, a physiological dose of PP seems to decrease both the appetitive and the consummatory drive in dogs.

Critical role of arcuate Y4 receptors and the melanocortin system in pancreatic polypeptide-induced reduction in food intake in mice

Background

Pancreatic polypeptide (PP) is a potent anti-obesity agent known to inhibit food intake in the absence of nausea, but the mechanism behind this process is unknown.

Methodology/Principal Findings

Here we demonstrate that in response to i.p. injection of PP in wild type but not in Y4 receptor knockout mice, immunostaining for the neuronal activation marker c-Fos is induced specifically in neurons of the nucleus tractus solitarius and the area postrema in the brainstem, notably in cells also showing immunostaining for tyrosine hydroxylase. Importantly, strong c-Fos activation is also detected in the arcuate nucleus of the hypothalamus (ARC), particularly in neurons that co-express alpha melanocyte stimulating hormone (α-MSH), the anorexigenic product of the proopiomelanocortin (POMC) gene. Interestingly, other hypothalamic regions such as the paraventricular nucleus, the ventromedial nucleus and the lateral hypothalamic area also show c-Fos induction after PP injection. In addition to c-Fos activation, PP injection up-regulates POMC mRNA expression in the ARC as detected by in situ hybridization. These effects are a direct consequence of local Y4 signaling, since hypothalamus-specific conditional Y4 receptor knockout abolishes PP-induced ARC c-Fos activation and blocks the PP-induced increase in POMC mRNA expression. Additionally, the hypophagic effect of i.p. PP seen in wild type mice is completely absent in melanocortin 4 receptor knockout mice.

Conclusions/Significance

Taken together, these findings show that PP reduces food intake predominantly via stimulation of the anorexigenic α-MSH signaling pathway, and that this effect is mediated by direct action on local Y4 receptors within the ARC, highlighting a potential novel avenue for the treatment of obesity.

Different regulation of atrial ANP release through neuropeptide Y2 and Y4 receptors

Neuropeptide Y (NPY) receptors are present in cardiac membranes. However, its physiological roles in the heart are not clear. The aim of this study was to define the direct effects of pancreatic polypeptide (PP) on atrial dynamics and atrial natriuretic peptide (ANP) release in perfused beating atria. Pancreatic polypeptides, a NPY Y(4) receptor agonist, decreased atrial contractility but was not dose-dependent. The ANP release was stimulated by PP in a dose-dependent manner. GR 23118, a NPY Y(4) receptor agonist, also increased the ANP release and the potency was greater than PP. In contrast, peptide YY (3-36) (PYY), an NPY Y(2) receptor agonist, suppressed the release of ANP with positive inotropy. NPY, an agonist for Y(1, 2, 5) receptor, did not cause any significant changes. The pretreatment of NPY (18-36), an antagonist for NPY Y(3) receptor, markedly attenuated the stimulation of ANP release by PP but did not affect the suppression of ANP release by PYY. BIIE0246, an antagonist for NPY Y(2) receptor, attenuated the suppression of ANP release by PYY. The responsiveness of atrial contractility to PP or PYY was not affected by either of the antagonists. These results suggest that NPY Y(4) and Y(2) receptor differently regulate the release of atrial ANP.

Direct evidence that stimulation of neuropeptide Y Y5 receptor activates hypothalamo-pituitary-adrenal axis in conscious rats via both corticotropin-releasing factor- and arginine vasopressin-dependent pathway

An abundance of data suggests a crucial role of neuropeptide Y (NPY) as an activator of the hypothamamo-pituitary-adrenal (HPA) axis. However, there is quite limited evidence regarding receptors that mediate this response. Here, we address the possibility that Y(5) receptor subtype may be responsible for NPY-induced activation of HPA axis. For this purpose, the effects of an intracerebroventricular injection of Y(5)-selective agonist, [cPP(1-7), NPY(19-23), Ala(31), Aib(32), Gln(34)]-human pancreatic polypeptide (hPP), on circulating ACTH and corticosterone in conscious rats were evaluated. Central injection of hPP (100 pmol) produced significant increases in plasma ACTH and corticosterone compared with artificial cerebrospinal fluid, and previous treatment with a novel Y(5)-selective antagonist, FMS586 [3-(9-isopropyl-6,7,8,9-tetrahydro-5H-carbazol-3-yl)-1-methyl-1-(2-pyridin-4-yl-ethyl)-urea hydrochloride] (25 mg/kg, po), completely blocked these alterations. Pretreatment with corticotropin-releasing factor (CRF) receptor antagonist (astressin, 10-50 microg/rat, iv) or arginine vasopressin (AVP) receptor antagonist ([deamino-Pen(1), O-Me-Tyr(2), Arg(8)] vasopressin; 3-30 microg/rat, iv) differentially suppressed these increases by 70-80 or 40-50%, respectively. The combined treatment showed no additive effect of these antagonists. Furthermore, an exogenous AVP (0.3 microg/rat, iv)-induced HPA activation was fully inhibited by astressin, suggesting a convergent pathway of AVP receptor signals onto CRF neurons. Central injection of hPP also evoked marked up-regulation of mRNA expression for CRF and AVP in the hypothalamus, which, likewise, were completely reversed by FMS586. Our observations provide the first evidence that selective stimulation of Y(5) receptor provokes activation of the HPA axis and its downstream pathway is chiefly composed of both CRF (primary regulator) and AVP (subordinate to the former) with distinct relative contribution.

Low-dose pancreatic polypeptide inhibits food intake in man

Pancreatic polypeptide (PP) is a gut hormone released from the pancreas in response to food ingestion and remains elevated for up to 6 h postprandially. Plasma levels are elevated in patients with pancreatic tumours. An intravenous infusion of PP has been reported to reduce food intake in man, suggesting that PP is a satiety hormone. We investigated whether a lower infusion rate of PP would induce significant alterations in energy intake. The study was randomised and double-blinded. Fourteen lean fasted volunteers (five men and nine women) received 90 min infusions of PP (5 pmol/kg per min) and saline on two separate days. The dose chosen was half that used in a previous human study which reported a decrease in appetite but at supra-physiological levels of PP. One hour after the end of the infusion, a buffet lunch was served and energy intake measured. PP infusion was associated with a significant 11 % reduction in energy intake compared with saline (2440 (se 200) v. 2730 (se 180) kJ; P < 0·05). Preprandial hunger as assessed by a visual analogue score was decreased in the PP-treated group compared to saline. These effects were achieved with plasma levels of PP within the pathophysiological range of pancreatic tumours.

Y(4) receptors mediate the inhibitory responses of pancreatic polypeptide in human and mouse colon mucosa

The antisecretory effects of several Y agonists, including pancreatic polypeptide (PP), indicate the presence of Y(1), Y(2), and Y(4) receptors in mouse and human (h) colon mucosae. Here, we used preparations from human and from wild-type (WT), Y(4), and Y(1) receptor knockout ((-/-)) mice, alongside Y(4) receptor-transfected cells to define the relative functional contribution of the Y(4) receptor. First, rat (r) PP antisecretory responses were lost in murine Y(4)(-/-) preparations, but hPP and Pro(34) peptide YY (PYY) costimulated Y(4) and Y(1) receptors in WT mucosa. The Y(1) antagonist/Y(4) agonist GR231118 [(Ile,Glu,Pro,Dpr,Tyr,Arg,Leu,Arg,Try-NH(2))-2-cyclic(2,4'),(2',4)-diamide] elicited small Y(4)-mediated antisecretory responses in human tissues pretreated with the Y(1) antagonist, BIBO3304 [(R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N(2)-(diphenylacetyl)-argininamide trifluoroacetate)], and attenuated Y(4)-mediated hPP responses in mouse and human mucosa. GR231118 and rPP were also antisecretory in hY(4)-transfected epithelial monolayers but were partial agonists compared with hPP at this receptor. In Y(4)-transfected human embryonic kidney (HEK) 293 cells, Y(4) ligands displaced [(125)I]hPP binding with orders of affinity (pK(i)) at human (hPP = rPP > GR231118 > Pro(34)PYY = PYY) and mouse (rPP = hPP > GR231118 > Pro(34)PYY > PYY) Y(4) receptors. GR231118- and rPP-stimulated guanosine 5'-3-O-(thio)triphosphate binding through hY(4) receptors with significantly lower efficacy than hPP. GR231118 marginally increased basal but abolished further PP-induced hY(4) internalization to recycling (transferrin-labeled) pathways in HEK293 cells. Taken together, these findings show that Y(4) receptors play a definitive role in attenuating colonic anion transport and may be useful targets for novel antidiarrheal agents due to their limited peripheral expression.

Mechanisms of neuropeptide Y, peptide YY, and pancreatic polypeptide inhibition of identified green fluorescent protein-expressing GABA neurons in the hypothalamic neuroendocrine arcuate nucleus

The fast inhibitory transmitter GABA is robustly expressed in the arcuate nucleus (ARC) and appears to play a major role in hypothalamic regulation of endocrine function and energy homeostasis. Previously, it has not been possible to record selectively from GABA cells, because they have no defining morphological or physiological characteristics. Using transgenic mice that selectively express GFP (green fluorescent protein) in GAD67 (glutamic acid decarboxylase 67)-synthesizing cells, we identified ARC GABA neurons (n > 300) and used whole-cell recording to study their physiological response to neuropeptide Y (NPY), the related peptide YY(3-36) (PYY(3-36)), and pancreatic polypeptide (PP), important modulators of ARC function. In contrast to other identified ARC cells in which NPY receptor agonists were reported to generate excitatory actions, we found that NPY consistently reduced the firing rate and hyperpolarized GABA neurons including neuroendocrine GABA neurons identified by antidromic median eminence stimulation. The inhibitory NPY actions were mediated by postsynaptic activation of G-protein-linked inwardly rectifying potassium (GIRK) and depression of voltage-gated calcium currents via Y1 and Y2 receptor subtypes. Additionally, NPY reduced spontaneous and evoked synaptic glutamate release onto GABA neurons by activation of Y1 and Y5 receptors. The peptide PYY(3-36), a peripheral endocrine signal that can act in the brain, also inhibited GABA neurons, including identified neuroendocrine cells, by activating GIRK conductances and depressing calcium currents. The endogenous Y4 agonist PP depressed the activity of GABA-expressing neurons mainly by presynaptic attenuation of glutamate release. Together, these results show that the family of neuropeptide Y modulators reduces the activity of inhibitory GABA neurons in the ARC by multiple presynaptic and postsynaptic mechanisms.

BODIPY-conjugated neuropeptide Y ligands: new fluorescent tools to tag Y1, Y2, Y4 and Y5 receptor subtypes

N-terminal labelled fluorescent BODIPY-NPY peptide analogues were tested in Y1, Y2, Y4 and Y5 receptor-binding assays performed in rat brain membrane preparations and HEK293 cells expressing the rat Y1, Y2, Y4 and Y5 receptors. BODIPY TMR/FL-[Leu31, Pro34]NPY/PYY were able to compete for specific [125][Leu31, Pro34]PYY-binding sites with an affinity similar to that observed for the native peptide at the Y1 (Ki=1-6 nM), Y2 (Ki>1000 nM), Y4 (Ki=10 nM) and Y5 (Ki=1-4 nM) receptor subtypes. BODIPY FL-PYY(3-36) was able to compete for specific Y2 (Ki=10 nM) and Y5 (Ki=30 nM) binding sites, but had almost no affinity in Y1 and Y4 assays. BODIPY FL-hPP was able to compete with high affinity (Ki; 1 and 15 nM) only in Y4 and Y5 receptor-binding assays. BODIPY TMR-[cPP(1-7), NPY(19-23), Ala31, Aib32, Gln34]hPP and BODIPY TMR-[hPP(1-17), Ala31, Aib32]NPY were potent competitors only on specific Y5-binding sites (Ki=0.1-0.6 nM). As expected, these fluorescent peptides inhibited forskolin-induced cAMP accumulation, demonstrating that they retained their agonist properties. When tested in confocal microscopy imaging, fluorescent Y1 and Y5 agonists internalized in a time-dependent manner in Y1 and Y5 transfected cells, respectively. These results demonstrate that BODIPY-conjugated NPY analogues retain their selectivity, affinity and agonist properties for the Y1, Y2, Y4 and Y5 receptor subtypes, respectively. Thus, they represent novel tools to study and visualize NPY receptors in living cells.

A role for pancreatic polypeptide in the regulation of gastric emptying and short-term metabolic control

CONTEXT

Previous studies using pancreatic polypeptide (PP) infusions in humans have failed to show an effect on gastric emptying, glucose metabolism, and insulin secretion. This might be due to the use of nonhuman sequences of the peptide.

OBJECTIVE

The objective of this study was to use synthetic human PP to study gastric emptying rates of a solid meal and postprandial hormone secretion and glucose disposal as well as the gastric emptying rate of water.

DESIGN

This was a single-blind study.

SETTING

The study was performed at a university hospital.

PARTICIPANTS

Fourteen healthy adult subjects were studied.

INTERVENTIONS

Infusion of saline or PP at 0.75 or 2.25 pmol/kg.min was given to eight subjects (gastric emptying of solid food), and infusion of saline or PP at 2.25 pmol/kg.min was given to six subjects (gastric emptying of water).

MAIN OUTCOME MEASURES

The main outcome measures were gastric emptying of solids (scintigraphy), hunger ratings (visual analog scale), and plasma concentrations of PP, insulin, glucagon, somatostatin, glucagon-like peptide 1, glucose, and gastric emptying of plain water (scintigraphy).

RESULTS

PP prolonged the lag phase and the half-time of emptying of the solid meal. The change in hunger rating, satiety, desire to eat after the meal, or prospective consumption was not affected. The postprandial rise in plasma glucose was prolonged by PP. The postprandial rise in insulin was also delayed by PP. PP had no significant effect on the emptying of water.

CONCLUSIONS

PP inhibits gastric emptying of solid food and delays the postprandial rise in plasma glucose and insulin. PP is suggested to have a physiological role in the pancreatic postprandial counterregulation of gastric emptying and insulin secretion.

Effects of pancreatic polypeptide on pancreas-projecting rat dorsal motor nucleus of the vagus neurons

We investigated the pre- and postsynaptic effects of pancreatic polypeptide (PP) on identified pancreas-projecting neurons of the rat dorsal motor nucleus of the vagus in thin brain stem slices. Perfusion with PP induced a TTX- and apamin-sensitive, concentration-dependent outward (22% of neurons) or inward current (21% of neurons) that was accompanied by a decrease in input resistance; PP was also found to affect the amplitude of the action potential afterhyperpolarization. The remaining 57% of neurons were unaffected. PP induced a concentration-dependent inhibition in amplitude of excitatory (n = 22 of 30 neurons) and inhibitory (n = 13 of 17 neurons) postsynaptic currents evoked by electrical stimulation of the adjacent nucleus of the solitary tract, with an estimated EC(50) of 30 nM for both. The inhibition was accompanied by an alteration in the paired pulse ratio, suggesting a presynaptic site of action. PP also decreased the frequency, but not amplitude, of spontaneous excitatory (n = 6 of 11 neurons) and inhibitory currents (n = 7 of 9 neurons). In five neurons, chemical stimulation of the area postrema (AP) induced a TTX-sensitive inward (n = 3) or biphasic (outward and inward) current (n = 2). Superfusion with PP reversibly reduced the amplitude of these chemically stimulated currents. Regardless of the PP-induced effect, the vast majority of responsive neurons had a multipolar somata morphology with dendrites projecting to areas other than the fourth ventricle or the central canal. These results suggest that pancreas-projecting rat dorsal motor nucleus of the vagus neurons are heterogeneous with respect to their response to PP, which may underlie functional differences in the vagal modulation of pancreatic functions.

Pancreatic polypeptide administration reduces insulin requirements of artificial pancreas in pancreatectomized dogs

An artificial endocrine pancreas is a mechanical device that frequently measures blood glucose and adjusts the rate of insulin infusion to maintain normoglycemia. In this study, we evaluated the effect of pancreatic polypeptide (PP) on insulin requirements after total pancreatectomy. However, other endocrine hormones are needed not only to facilitate the effect of insulin, but also to regulate insulin functions in vivo. In this study, the effect of PP infusion on insulin requirements after total pancreatectomy in dogs is examined. After total pancreatectomy, five dogs were supported by artificial endocrine pancreas model STG-22 for 72 h. In a second group of five dogs, both insulin and PP were infused. Mean blood glucose levels and insulin requirements were compared between the two groups. There was no difference in mean plasma glucose levels between the two groups. In all 10 dogs, the mean blood glucose level for 72 h was 110 +/- 4 mg/dL and was tightly controlled between 65 and 190 mg/dL. However, the insulin requirement for the first and second postoperative days in the group treated with PP was significantly less than that of the control group (90.0 +/- 20.8 mU/kg vs. 445.0 +/- 151.9 mU/kg; P < 0.05, and 562.7 +/- 126.5 mU/kg vs. 1007.7 +/- 144.9 mU/kg; P < 0.05, respectively). We conclude that infusion of PP reduces the insulin requirement for the initial 48 h in pancreatectomized dogs treated with an artificial endocrine pancreas.

Y2 receptor-selective agonist delays the estrogen-induced luteinizing hormone surge in ovariectomized ewes, but y1-receptor-selective agonist stimulates voluntary food intake

Neuropeptide Y (NPY) plays a major role in the regulation of food intake, regulation of homeostasis, and neuroendocrine function. We have previously shown that third ventricular infusion of this peptide delays the estradiol benzoate-induced surge in LH secretion in ovariectomized ewes. To determine the receptor subtype that transmits this effect, we have now used the same model to infuse a Y1 receptor agonist [NPY Leu31 Pro34], a Y2 receptor agonist (PYY3-36), and a Y4 receptor agonist (pancreatic polypeptide). We monitored the surges in animals given these agonists or artificial cerebrospinal fluid by measuring plasma LH levels, and we also measured daily voluntary food intake (VFI). A low (7 microg/h) dose of Y2 agonist delayed the surge but did not affect VFI, whereas a higher dose (14 microg/h) stimulated VFI. A dose of 18 microg/h of the Y1 agonist did not affect surge generation but also stimulated VFI. A dose of 24 microg/h of Y4 agonist affected neither surge generation nor VFI. These specificities are different from those reported for the rat and human (in which a Y2 agonist causes reduction in VFI). We conclude that, in sheep, the negative regulation of the reproductive axis by NPY and Y-receptor agonists is effected via the Y2 receptors, whereas the orexigenic effects are most likely effected via the Y1 receptors.

Pancreatic polypeptide reduces appetite and food intake in humans

Pancreatic polypeptide (PP) is a gut hormone released from the pancreas in response to ingestion of food. Plasma PP has been shown to be reduced in conditions associated with increased food intake and elevated in anorexia nervosa. In addition peripheral administration of PP has been shown to decrease food intake in rodents. These findings suggest that PP may act as a circulating factor that regulates food intake. Therefore we investigated the effect of intravenous infusion of PP (10 pmol/kg/min) on appetite and food intake in a randomised double-blind placebo-controlled crossover study in ten healthy volunteers. Infusion of PP reduced appetite and decreased the energy intake at a buffet lunch two hours post-infusion by 21.8 +/- 5.7% (P < 0.01). More importantly the inhibition of food intake was sustained, such that energy intake, as assessed by food diaries, was significantly reduced both the evening of the study and the following morning. Overall PP infusion reduced cumulative 24-hour energy intake by 25.3 +/- 5.8%. In conclusion our data demonstrates that PP causes a sustained decrease in both appetite and food intake.

Characterization of the effects of pancreatic polypeptide in the regulation of energy balance

BACKGROUND & AIMS

Pancreatic polypeptide (PP) belongs to a family of peptides including neuropeptide Y and peptide YY. We examined the role of PP in the regulation of body weight as well as the therapeutic potential of PP.

METHODS

We measured food intake, gastric emptying, oxygen consumption, and gene expression of hypothalamic neuropeptides, gastric ghrelin, and adipocytokines in mice after administering PP intraperitoneally. Peptide gene expression was also examined in PP-overexpressing mice. Vagal and sympathetic nerve activities were recorded after intravenous administration in rats. Effects of repeated administrations of PP on energy balance and on glucose and lipid metabolism were examined in both ob/ob obese mice and fatty liver Shionogi (FLS)-ob/ob obese mice.

RESULTS

Peripherally administered PP induced negative energy balance by decreasing food intake and gastric emptying while increasing energy expenditure. The mechanism involved modification of expression of feeding-regulatory peptides (decrease in orexigenic neuropeptide Y, orexin, and ghrelin along with an increase in anorexigenic urocortin) and activity of the vagovagal or vagosympathetic reflex arc. PP reduced leptin in white adipose tissue and corticotropin-releasing factor gene expression. The expression of gastric ghrelin and hypothalamic orexin was decreased in PP-overexpressing mice. Repeated administrations of PP decreased body weight gain and ameliorated insulin resistance and hyperlipidemia in both ob/ob obese mice and FLS-ob/ob obese mice. Liver enzyme abnormalities in FLS-ob/ob obese mice were also ameliorated by PP.

CONCLUSIONS

These observations indicate that PP may influence food intake, energy metabolism, and the expression of hypothalamic peptides and gastric ghrelin.

Design and synthesis of the potent, orally available, brain-penetrable arylpyrazole class of neuropeptide Y5 receptor antagonists

Novel arylpyrazole derivatives were synthesized and evaluated as neuropeptide Y (NPY) Y5 receptor antagonists. Compound (-)-7, which features a novel chiral 2,3-dihydro-1H-cyclopenta[a]naphthalene moiety, showed good binding affinity and antagonistic activity for the Y5 receptor. After intracerebroventricular administration in SD rats, (-)-7 significantly inhibited food intake that was induced by the centrally administered Y5-preferring agonist, bovine pancreatic polypeptide, but had only a negligible effect on NPY-induced feeding.

In vitro and in vivo characterization of 3-[2-[6-(2-tert-butoxyethoxy)pyridin-3-yl]-1H-imidazol-4-yl]benzonitrile hydrochloride salt, a potent and selective NPY5 receptor antagonist

To investigate the anorectic potential of NPY5 receptor antagonists, we have profiled the in vitro and in vivo properties of 3-[2-[6-(2-tert-butoxyethoxy)pyridin-3-yl]-1H-imidazol-4-yl]benzonitrile hydrochloride salt (1). This compound was found to have excellent NPY5 receptor affinity and selectivity, potent functional antagonism, and good peripheral and central nervous system exposure in rats. This compound attenuated bovine pancreatic polypeptide induced food intake in rats but failed to demonstrate anorectic activity in rodent natural feeding models.

Orexin neurons express a functional pancreatic polypeptide Y4 receptor

The receptor subtypes that mediate the effects of neuropeptide Y (NPY) on food intake have not been clearly defined. The NPY Y4 receptor has been identified recently as a potential mediator of the regulation of food intake. The purpose of the present study was to characterize the central site of action of the Y4 receptor using a combination of neuroanatomical and physiological approaches. Using immunocytochemistry, Y4-like immunoreactivity was found to be colocalized with orexin cell bodies in the lateral hypothalamic area (LHA) and orexin fibers throughout the brain. In situ hybridization confirmed the expression of Y4 mRNA in orexin neurons. To determine the functional interaction between Y4 receptors and orexin neurons, we examined the effects of rat pancreatic polypeptide (rPP), a Y4-selective ligand, or NPY, a nonselective ligand, administered directly into the LHA on the stimulation of food and water intake and c-Fos expression. Both rPP and NPY significantly increased food and water intake when they were administered into the LHA, although NPY was a more potent stimulator of food intake. Furthermore, both NPY and rPP significantly stimulated c-Fos expression in the LHA. However, whereas rPP stimulated c-Fos expression in orexin neurons, NPY did not. Neither rPP nor NPY stimulated c-Fos in melanin-concentrating hormone neurons, but both activated neurons of an unknown phenotype in the LHA. These results suggest that a functional Y4 receptor is expressed on orexin neurons and that these neurons are activated in response to a ligand with high affinity for the Y4 receptor (rPP). Although these data suggest a role for central Y4 receptors, the endogenous ligand for this receptor has yet to be clearly established.