Neuropeptide Y-induced contraction is mediated by neuropeptide Y Y2 and Y4 receptors in the rat colon

Endogenous peptide YY and neuropeptide Y inhibit colonic ion transport, contractility and transit differentially via Y₁ and Y₂ receptors

BACKGROUND AND PURPOSE

Peptide YY (PYY) and neuropeptide Y (NPY) activate Y receptors, targets under consideration as treatments for diarrhoea and other intestinal disorders. We investigated the gastrointestinal consequences of selective PYY or NPY ablation on mucosal ion transport, smooth muscle activity and transit using wild-type, single and double peptide knockout mice, comparing mucosal responses with those from human colon.

EXPERIMENTAL APPROACH

Mucosae were pretreated with a Y₁ (BIBO3304) or Y₂ (BIIE0246) receptor antagonist and changes in short-circuit current recorded. Colonic transit and colonic migrating motor complexes (CMMCs) were assessed in vitro and upper gastrointestinal and colonic transit measured in vivo.

KEY RESULTS

Y receptor antagonists revealed tonic Y₁ and Y₂ receptor-mediated antisecretory effects in human and wild-type mouse colon mucosae. In both, Y₁ tone was epithelial while Y₂ tone was neuronal. Y₁ tone was reduced 90% in PYY⁻/⁻ mucosa but unchanged in NPY⁻/⁻ tissue. Y₂ tone was partially reduced in NPY⁻/⁻ or PYY⁻/⁻ mucosae and abolished in tetrodotoxin-pretreated PYY⁻/⁻ tissue. Y₁ and Y₂ tone were absent in NPYPYY⁻/⁻ tissue. Colonic transit was inhibited by Y₁ blockade and increased by Y₂ antagonism indicating tonic Y₁ excitation and Y₂ inhibition respectively. Upper GI transit was increased in PYY⁻/⁻ mice only. Y₂ blockade reduced CMMC frequency in isolated mouse colon.

CONCLUSIONS AND IMPLICATIONS

Endogenous PYY and NPY induced significant mucosal antisecretory tone mediated by Y₁ and Y₂ receptors, via similar mechanisms in human and mouse colon mucosa. Both peptides contributed to tonic Y₂-receptor-mediated inhibition of colonic transit in vitro but only PYY attenuated upper GI transit.

NPY receptors as potential targets for anti-obesity drug development

The neuropeptide Y system has proven to be one of the most important regulators of feeding behaviour and energy homeostasis, thus presenting great potential as a therapeutic target for the treatment of disorders such as obesity and at the other extreme, anorexia. Due to the initial lack of pharmacological tools that are active in vivo, functions of the different Y receptors have been mainly studied in knockout and transgenic mouse models. However, over recent years various Y receptor selective peptidic and non-peptidic agonists and antagonists have been developed and tested. Their therapeutic potential in relation to treating obesity and other disorders of energy homeostasis is discussed in this review.

Peripheral peptide YY inhibits propulsive colonic motor function through Y2 receptor in conscious mice

Peptide YY (PYY) antisecretory effect on intestinal epithelia is well established, whereas less is known about its actions to influence colonic motility in conscious animals. We characterized changes in basal function and stimulated colonic motor function induced by PYY-related peptides in conscious mice. PYY(3-36), PYY, and neuropeptide Y (NPY) (8 nmol/kg) injected intraperitoneally inhibited fecal pellet output (FPO) per hour during novel environment stress by 90%, 63%, and 57%, respectively, whereas the Y(1)-preferring agonists, [Pro(34)]PYY and [Leu(31),Pro(34)]NPY, had no effect. Corticotrophin-releasing factor 2 receptor antagonist did not alter PYY(3-36) inhibitory action. PYY and PYY(3-36) significantly reduced restraint-stimulated defecation, and PYY(3-36) inhibited high-amplitude distal colonic contractions in restrained conscious mice for 1 h, by intraluminal pressure with the use of a microtransducer. PYY suppression of intraperitoneal 5-hydroxytryptophan induced FPO and diarrhea was blocked by the Y(2) antagonist, BIIE0246, injected intraperitoneally and mimicked by PYY(3-36), but not [Leu(31),Pro(34)]NPY. PYY(3-36) also inhibited bethanechol-stimulated FPO and diarrhea. PYY(3-36) inhibited basal FPO during nocturnal feeding period and light phase in fasted/refed mice for 2-3 h, whereas the reduction of food intake lasted for only 1 h. PYY(3-36) delayed gastric emptying after fasting-refeeding by 48% and distal colonic transit time by 104%, whereas [Leu(31),Pro(34)]NPY had no effect. In the proximal and distal colon, higher Y(2) mRNA expression was detected in the mucosa than in muscle layers, and Y(2) immunoreactivity was located in nerve terminals around myenteric neurons. These data established that PYY/PYY(3-36) potently inhibits basal and stress/serotonin/cholinergic-stimulated propulsive colonic motor function in conscious mice, likely via Y(2) receptors.

Pancreatic polypeptide enhances colonic muscle contraction and fecal output through neuropeptide Y Y4 receptor in mice

Pancreatic polypeptide is released mainly from the pancreas, and is thought to be one of the major endogenous agonists of the neuropeptide Y Y(4) receptor. Pancreatic polypeptide has been shown to stimulate colonic muscle contraction, but whether pancreatic polypeptide has in vivo functional activity with respect to colonic transit is unclear. The present report investigated the effects of pancreatic polypeptide on fecal output as an index of colonic transit as well as intestinal motor activity, using wild-type (WT) and neuropeptide Y Y(4) receptor-deficient (KO) mice. Peripheral administration of pancreatic polypeptide increased fecal weight and caused diarrhea in WT mice in a dose-dependent manner (0.01-3mg/kg s.c.). Pancreatic polypeptide-induced increases in fecal weight and diarrhea completely disappeared in KO mice, while basal fecal weights did not differ between WT and KO mice. In longitudinal and circular muscles of mouse isolated colon, pancreatic polypeptide (0.01-1 microM) increased basal tone and frequency of spontaneous contraction in WT mice, but not in KO mice. Atropine did not affect pancreatic polypeptide-induced fecal output or increase in colonic muscle tone, indicating that the actions of pancreatic polypeptide are not mediated through cholinergic mechanisms. The present findings demonstrate that pancreatic polypeptide enhances colonic contractile activity and fecal output through neuropeptide Y Y(4) receptor, and a neuropeptide Y Y(4) receptor agonist might offer a novel therapeutic approach to ameliorate constipation.

Determination of Affinity and Activity of Ligands at the Human Neuropeptide Y Y4Receptor by Flow Cytometry and Aequorin Luminescence

Fluorescence-labeled neuropeptide Y (NPY) has been used in flow cytometric binding assays for the determination of affinity constants of NPY Y1, Y2, and Y5 receptor ligands. Because the binding of fluorescent NPY is insufficient for competition studies at the human Y4 receptor (hY4R), we replaced Glu-4 in hPP with Lys for the derivatization with cyanine-5. Because cy5-[K(4)]hPP has high affinity (Kd 5.6 nM) to the hY4R, it was used as a probe in a flow cytometric binding assay. Specific binding of cy5-[K(4)]hPP to hY4R was visualized by confocal microscopy. The hY(4)R, the chimeric G protein G(qi5) and mitochondrially targeted apoaequorin were stably coexpressed in CHO cells. Aequorin luminescence was quantified in a microplate reader and by a CCD camera. By application of these methods 3-cyclohexyl-N-[(3-1H-imidazol-4-ylpropylamino)(imino)methyl]propanamide (UR-AK49) was discovered as the first nonpeptidic Y4R antagonist (pKi 4.17), a lead to be optimized in terms of potency and selectivity.

Mechanisms and emerging treatments of the metabolic complications of chronic pancreatitis

OBJECTIVES

Exocrine and endocrine abnormalities in chronic pancreatitis contribute to the morbidity and mortality risks of the disease. Complications of exocrine insufficiency include malabsorption, vitamin deficiency syndromes, and weight loss. Oral enzyme replacement therapy is usually effective if attention is paid to factors that affect the bioavailability of enzyme preparations. Complications of endocrine insufficiency can be more difficult to treat due in part to an incomplete knowledge of their etiology.

METHODS

This review focuses on the endocrine aspects of chronic pancreatitis and highlights the observations of our laboratory on the pathogenesis of the metabolic complications of the disease.

RESULTS

In addition to decreased insulin secretory capacity, pancreatogenic (or apancreatic) diabetes is characterized by decreased or absent glucagon and pancreatic polypeptide (PP) secretion, a loss of hepatic insulin receptor (IR) expression/availability, and an impairment in hepatic IR function (phosphorylation and endocytosis). Diminished hepatic IR expression in chronic pancreatitis appears to be because of PP deficiency; laboratory animals and patients with PP deficiency demonstrate decreased hepatic IR availability that is reversed by prolonged (8-hour) PP administration. The impairment in hepatic IR function appears independent of PP deficiency but is reversed by prolonged (28-day) treatment with the insulinotropic/insulinomimetic hormone glucagon-like peptide 1. The endocytosis of hepatic IR is linked to the endocytosis of the glucose transporter 2 from the hepatocyte plasma membrane, and studies suggest that the 2 plasma membrane-bound proteins are complexed noncovalently to function and translocate as a unit after insulin binding to the hepatic IR. The process appears vigorous and sensitive enough to account for a significant reduction in hepatic glucose output and may represent a major mechanism for insulin regulation of hepatic glucose production.

CONCLUSIONS

The regulatory mechanisms of PP-mediated hepatic IR expression and combined IR and GLUT2 endocytosis after insulin binding are defective in chronic pancreatitis and contribute to the apancreatic diabetes, which characterizes this disease.

The pancreatic polypeptide family and the migrating motor complex of the rat: differential effects in the duodenum and jejunum

AIM

To investigate the effects of members of the pancreatic polypeptide family on migrating myoelectric complexes in rats in vivo.

METHODS

Rats were supplied with bipolar electrodes at 5 (duodenum), 15 and 25 cm (jejunum) distal to pylorus for electromyography. The natural ligands neuropeptide Y, pancreatic polypeptide, peptide YY1-36 and peptide YY3-36 were infused IV at doses of 0.5-400 pmol kg(-1) min(-1). The mechanisms of action were studied after pre-treatment with N(omega)-nitro-L-arginine (L-NNA) 1 mg kg(-1), guanethidine 3 mg kg(-1) and in bilaterally vagotomized animals.

RESULTS

PP inhibited myoelectrical activity dose-dependently in both the duodenum (ED50 5.8 pmol kg(-1) min(-1)) and jejunum (2.6 pmol kg(-1) min(-1)). PYY1-36 and PYY3-36 also had inhibitory effect in the jejunum (4.4 and 130 pmol kg(-1) min(-1), respectively). PYY1-36 had no significant effect in the duodenum, whereas PYY3-36 stimulated myoelectrical activity at the highest doses. NPY was without effect. In the jejunum neither L-NNA, guanethidine or vagotomy had any significant influence on the inhibitory effects of PP, PYY1-36 and PYY3-36. In the duodenum, the effect of PP was inhibited by guanethidine, but not L-NNA or vagotomy. The stimulatory effect of PYY3-36 in the duodenum was blocked by L-NNA and vagotomy, whereas guanethidine was without effect.

CONCLUSION

Peptides of the PP family modulate small bowel motility differentially. Whereas their general effect is inhibitory in the jejunum, the mixing duodenal compartment is stimulated by PYY3-36, suggested to reflect receptor distribution distinction in the gut. This implicates distribution of distinct receptors in the gut being activated by either peptide.

Neuropeptide Y receptors; antisecretory control of intestinal epithelial function

This paper reviews the cellular localisation, mechanisms of release and intestinal absorptive actions of neuropeptide Y and its related peptides, peptide YY, pancreatic polypeptide and major fragments NPY(3-36) and PYY(3-36). While NPY is commonly found in inhibitory enteric neurons that can be interneurons, motor neurons or secretomotor-nonvasodilator in nature, its analogue, peptide YY in contrast, is located in neuroendocrine L-cells that predominate in the colorectal mucosa. Peptide YY is released from these cells when nutrients arrive in the small or large bowel, exerting paracrine as well as hormonal actions. Pancreatic polypeptide is found in relatively few, scattered intestinal endocrine cells, the majority of this peptide being produced by, and released from pancreatic islet F-cells in response to food intake. An introduction to the current pharmacology of this family of peptides is provided and the different types of neuropeptide Y (termed Y) receptors, their agonist preferences, antagonism, and preferred signalling pathways, are described. Our current understanding of specific Y receptor localisation within the intestine as determined by immunohistochemistry, is presented as a prelude to an assessment of functional studies that have monitored ion transport across isolated mucosal preparations. It is becoming clear that three Y receptor types are significant functionally in human colon, as well as particular rodent models (e.g. mouse) and these, namely the Y(1), Y(2) and Y(4) receptors, are discussed in detail. Their presence within the basolateral aspect of the epithelial layer (Y(1) and Y(4) receptors) or on enteric neurons (Y(1) and Y(2) receptors) and their activation by endogenous neuropeptide Y, peptide YY (Y(1) and Y(2) receptors) or pancreatic polypeptide (which prefers Y(4) receptors) results consistently in antisecretory/absorptive responses. The recent use of novel mouse knockouts has helped establish loss of specific intestinal functions including Y(1) and Y(2) receptor-mediated absorptive tone in colon mucosa. Progress in this field has been rapid recently, aided by the availability of selective antagonists and mutant mice lacking either one (e.g. Y(4)-/-, for which no antagonists exist at present) or more Y receptor types. It is therefore timely to review this work and present a rational basis for developing stable synthetic Y receptor agonists as novel anti-diarrhoeals.

Differential expression of Y receptors and signaling pathways in intestinal circular and longitudinal smooth muscle

The expression and mechanisms of action of Y receptors were examined in dispersed intestinal smooth muscle cells of the rabbit. The mixed Y1/Y2 agonists, NPY and PYY, and the Y2 agonist, NPY13-36, elicited concentration-dependent contraction of circular muscle cells that was inhibited by the selective Y2 antagonist, BIIE 0246. The Y4 agonist, PP, elicited similar, though weaker, contraction that was insensitive to Y1 and Y2 antagonists. The Y1 agonist, [Leu31, Pro34]NPY, did not elicit contraction of circular muscle cells. All Y receptor agonists inhibited cAMP formation in a PTx-sensitive fashion. In contrast, none of the agonists caused contraction of longitudinal muscle cells, and only the mixed Y1/Y2 agonists, NPY and PYY, and the Y1 agonist, [Leu31, Pro34]NPY, inhibited cAMP formation and VIP-induced muscle cell relaxation. 125I-PYY binding in longitudinal muscle cells was inhibited by NPY, PYY, [Leu31, Pro34]NPY and the Y1 antagonist, BIBP 3226. Contraction of circular but not longitudinal muscle cells by Y2 and Y4 agonists was observed also in cells isolated from human jejunum. The results indicate that Y2 and Y4 receptors are present only in intestinal circular muscle cells where they mediate contraction that is insensitive to PTx or Ca2+ channel blockers. Y1 receptors, negatively coupled to adenylyl cyclase, are present in cells from both layers.

Coexpression of Y1, Y2, and Y4 receptors in smooth muscle coupled to distinct signaling pathways

Coexpression of Y1, Y2, and Y4 receptors on smooth muscle cells was determined by reverse transcription-polymerase chain reaction, and the receptors were characterized by radioligand binding, selective receptor protection, and functional analysis of signaling pathways. 125I-peptide YY (PYY) binding was completely inhibited by neuropeptide Y (NPY) and PYY, and partially inhibited by the Y1 agonist [Leu31, Pro34]NPY or the Y2 agonist NPY13-36. In cells where Y1 receptors were preserved by selective receptor protection, 125I-PYY binding was selectively inhibited by the Y1 agonist or antagonist BIBP 3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amide]. Conversely, in cells where Y2 receptors were preserved, 125I-PYY binding was selectively inhibited by the Y2 agonist or antagonist BIIE 0246 [(S)N2-[1-[2-[4-[(R,S)-5,11-dihydro-6(66H)-oxodibenz[b,e]azepin-11-y]-1piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-35(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide]. All Y receptors activated preferentially Gi2, but only Y2 and Y4 receptors activated Gq. Consequently, Y2 agonists (NPY, PYY, and NPY13-36) and the Y4 agonist (pancreatic polypeptide) induced concentration-dependent contraction, inositol 1,4,5-trisphosphate (IP3) formation, and increase in cytosolic free Ca2+. Contraction induced by Y2 and Y4 agonists was not affected by 0 Ca2+, Ca2+ channel blockers, or pertussis toxin (PTx), but it was abolished by thapsigargin, U73122 [1-(6-(17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-25-dione], or the myosin light chain kinase inhibitor ML-9 [1-(5-chloronaphthalene-1-sulfonyl)homopiperazine, HCl]. Y2-mediated contraction was inhibited by the selective Y2 antagonist BIIE 0246. Insensitivity to PTx implied that the coupling to Gi did not initiate (Y1) or contribute (Y2 and Y4) to contraction. All Y receptor agonists inhibited cAMP formation in a PTx-sensitive manner. The patterns of contraction and inhibition of cAMP by various Y receptors were corroborated by selective receptor protection. The study demonstrates coexpression of Y1, Y2, and Y4 receptors on smooth muscle negatively coupled to adenylyl cyclase via Gi2. Coupling of Y2 and Y4 receptors to Gq determines their ability to induce IP3-dependent Ca2+ release and initiate contraction.

Physiological role of neuropeptide Y in the regulation of the ascending phase of the peristaltic reflex

The physiological role of neuropeptide Y (NPY) and of specific NPY receptors in regulating the intestinal peristaltic reflex was examined in three-compartment flat-sheet preparations of rat colon. Graded muscle stretch or mucosal stimulation applied to the central compartment inhibited NPY release in the orad compartment where ascending contraction was measured. NPY and the Y1-receptor agonist [Leu31, Pro34]NPY inhibited, whereas the selective Y1-receptor antagonist BIBP 3226 augmented ascending contraction and substance P (SP) release in the orad compartment induced by muscle stretch or mucosal stimulation. Neither agonist nor antagonist had any effect on descending relaxation or VIP release in the caudad compartment. The Y2-receptor agonist NPY13-36 and antagonist BIIE 0246 had no effect on peptide release or mechanical response. The results indicate that suppression of a tonic inhibitory influence of NPY neurons on excitatory neurotransmitter release contributes substantially to the orad contractile phase of the peristaltic reflex. The effect of NPY on neurotransmitter release is mediated by Y1 receptors.

Functional consequences of neuropeptide Y Y 2 receptor knockout and Y2 antagonism in mouse and human colonic tissues

1 Neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP) differentially activate three Y receptors (Y(1), Y(2) and Y(4)) in mouse and human isolated colon. 2 The aim of this study was to characterise Y(2) receptor-mediated responses in colon mucosa and longitudinal smooth muscle preparations from wild type (Y(2)+/+) and knockout (Y(2)-/-) mice and to compare the former with human mucosal Y agonist responses. Inhibition of mucosal short-circuit current and increases in muscle tone were monitored in colonic tissues from Y(2)+/+ and Y(2)-/- mice+/-Y(1) ((R)-N-[[4-(aminocarbonylaminomethyl)phenyl)methyl]-N(2)-(diphenylacetyl)-argininamide-trifluoroacetate (BIBO3304) or Y(2) (S)-N(2)-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide (BIIE0246) antagonists. 3 Predictably, Y(2)-/- tissues were insensitive to Y(2)-preferred agonist PYY(3-36) (</=100 nM), but unexpectedly Y(4)-preferred PP responses were right-shifted probably as a consequence of elevated circulating PP levels, particularly in male Y(2)-/- mice (Sainsbury et al., 2002). 4 BIBO3304 and BIIE0246 elevated mucosal ion transport, indicating blockade of inhibitory mucosal tone in Y(2)+/+ tissue. While BIBO3304 effects were unchanged, those to BIIE0246 were absent in Y(2)-/- mucosae. Neither antagonist altered muscle tone; however, BIIE0246 blocked NPY and PYY(3-36) increases in Y(2)+/+ basal tone. BIBO3304 abolished residual Y(1)-mediated NPY responses in Y(2)-/- smooth muscle. 5 Tetrodotoxin significantly reduced BIIE0246 and PYY(3-36) effects in Y(2)+/+ mouse and human mucosae, but had no effect upon Y-agonist contractile responses, indicating that Y(2) receptors are located on submucosal, but not myenteric neurones. 6 Tonic activation of submucosal Y(2) receptors by endogenous NPY, PYY or PYY(3-36) could indirectly reduce mucosal ion transport in murine and human colon, while direct activation of Y(2) receptors on longitudinal muscle results in contraction.

Recent developments in our understanding of the physiological role of PP-fold peptide receptor subtypes

The three peptides pancreatic polypeptide (PP), peptide YY (PYY), and neuropeptide Y (NPY) share a similar structure known as the PP-fold. There are four known human G-protein coupled receptors for the PP-fold peptides, namely Y1, Y2, Y4, and Y5, each of them being able to bind at least two of the three endogenous ligands. All three peptides are found in the circulation acting as hormones. Although NPY is only released from neurons, PYY and PP are primarily found in endocrine cells in the gut, where they exert such effects as inhibition of gall bladder secretion, gut motility, and pancreatic secretion. However, when PYY is administered in an experimental setting to animals, cloned receptors, or tissue preparations, it can mimic the effects of NPY in essentially all studies, making it difficult to study the effects of PP-fold peptides and to delineate what receptor and peptide accounts for a particular effect. Initial studies with transgenic animals confirmed the well-established action of NPY on metabolism, food-intake, vascular systems, memory, mood, neuronal excitability, and reproduction. More recently, using transgenic techniques and novel antagonists for the Y1, Y2, and Y5 receptors, NPY has been found to be a key player in the regulation of ethanol consumption and neuronal development.

Functional mapping of NPY/PYY receptors in rat and human gastro-intestinal tract

Peptide YY (PYY) is involved in the regulation of several gastro-intestinal functions, including motility. The aims of the present study were (i) to characterize the effects of PYY on smooth muscle strips obtained from the different gastro-intestinal segments in rats and in humans and (ii) to realize a map of the Y receptors expression. Contractions of strips were recorded under isometric conditions, using PYY and acetylcholine as control. We observed that PYY induced a contraction of muscle strips from rat proximal colon, but displayed no effect on other gut segments. Using RT-PCR, mRNA encoding the Y1 and Y4 receptors were detected in muscle strips depending on the segment. In humans, the muscle preparations responded to ACh but not to PYY. Moreover, only Y2 receptor mRNA was found in the ileum and the left colon, but not in other segments. Our study shows the heterogeneity in the expression of Y receptors along the gastro-intestinal tract, and reveals great discrepancies between rats and humans both concerning the expression of Y receptor, and the response of smooth muscle strips to PYY.

Pharmacology of neuropeptide Y receptor antagonists. Focus on cardiovascular functions

Neuropeptide Y is one of the most abundant mammalian neuropeptides identified to date. The possible actions of neuropeptide Y, that is co-localized and released with noradrenaline, as a sympathetic co-transmitter has attracted much attention during the last decade. In recent years, several non-peptide antagonists with high subtype selectivity for neuropeptide Y receptors have been introduced. With them, the status of neuropeptide Y as a sympathetic transmitter has been established, and so have profound cardiovascular effects mediated by neuropeptide Y Y(1) and Y(2) receptors. Significant release of neuropeptide Y occurs especially upon stronger sympathetic activation, and recent data suggest that the importance of neuropeptide Y seems enhanced in stress-related cardiovascular disorders. The true significance of neuropeptide Y has thus started to unfold, owing to the presence of the first generation of selective neuropeptide Y receptor antagonists. This review concerns the pharmacology of these agents, what we have learnt from them, and might find out in the future.

Blockade of neuropeptide Y(2) receptors and suppression of NPY's anti-epileptic actions in the rat hippocampal slice by BIIE0246

Neuropeptide Y (NPY) has been shown to suppress synaptic excitation in rat hippocampus by a presynaptic action. The Y(2) (Y(2)R) and the Y(5) (Y(5)R) receptors have both been implicated in this action. We used the non-peptide, Y(2)R-selective antagonist, BIIE0246, to test the hypothesis that the Y(2)R mediates both the presynaptic inhibitory and anti-epileptic actions of NPY in rat hippocampus in vitro. NPY and the Y(2)R-selective agonist, [ahx(5-24)]NPY, both inhibited the population excitatory postsynaptic potential (pEPSP) evoked in area CA1 by stratum radiatum stimulation in a concentration-dependent manner. BIIE0246 suppressed the inhibitory effects of both agonists, suppressing the maximal inhibition without causing a change in the agonist EC(50), in a manner inconsistent with competitive antagonism. BIIE0246 washed out from hippocampal slices extremely slowly. Application of agonist at high concentrations (1 - 3 microM) for prolonged periods did not alter the rate of washout, but did partially overcome the antagonism, inconsistent with an insurmountable antagonism by BIIE0246. In the stimulus train-induced bursting (STIB) model of ictal activity in hippocampal slices, both NPY and [ahx(5-24)]NPY inhibited primary afterdischarge (1 degrees AD) activity. BIIE0246 (100 nM) completely suppressed the actions of NPY and [ahx(5-24)]NPY in this model. In contrast, the potent Y(5)R-selective agonist, Ala(31)Aib(32)NPY, affected neither 1 degrees AD activity in the presence of BIIE0246, nor, by itself, even the pEPSP in CA1. BIIE0246 potently suppresses NPY actions in rat hippocampus, suggesting a dominant role for Y(2)R there. The apparently insurmountable antagonism observed may result from the lipophilic nature of the antagonist.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Neuropeptide Y Y(1) receptor regulates protein turnover and constitutive gene expression in hypertrophying cardiomyocytes

Increased levels of neuropeptide Y correlate with severity of left ventricular hypertrophy in vivo. At cardiomyocyte level, hypertrophy is characterised by increased mass and altered phenotype. The aims were to determine the contributions of increased synthesis and reduced degradation of protein to neuropeptide Y-mediated increase in mass, assess effects on gene expression, and characterise neuropeptide Y Y receptor subtype involvement. Neuropeptide Y (10 nM) increased protein mass of adult rat ventricular cardiomyocytes maintained in culture (24 h) (16%>basal) and de novo protein synthesis (incorporation of [(14)C]phenylalanine) (18%>basal). Neuropeptide Y (100 nM) prevented degradation of existing protein at 8 h. Actinomycin D (5 microM) attenuated increases in protein mass to neuropeptide Y (< or = 1 nM) but not to neuropeptide Y (10 nM). [Leu(31), Pro(34)]neuropeptide Y (10 nM), an agonist at neuropeptide Y Y(1) receptors, increased protein mass (25%>basal) but did not stimulate protein synthesis. Neuropeptide Y-(3-36) (10 nM), an agonist at neuropeptide Y Y(2) receptors, increased protein mass (29%>basal) and increased protein synthesis (13%>basal), respectively. Actinomycin D (5 microM) abolished the increase in protein mass elicited by neuropeptide Y-(3-36) but not that by [Leu(31), Pro(34)]neuropeptide Y. BIBP3226 [(R)-N2-(diphenylacetyl)-N-(4-hydroxyphenylmethyl)-D-arginine amide] (1 microM), a neuropeptide Y Y(1) receptor subtype-selective antagonist, and T(4) [neuropeptide Y-(33-36)](4), a neuropeptide Y Y(2) receptor subtype-selective antagonist, attenuated the increase in protein mass to 100 nM neuropeptide Y by 68% and 59%, respectively. Neuropeptide Y increased expression of the constitutive gene, myosin light chain-2 (MLC-2), maximally at 12 h (4.7-fold>basal) but did not induce (t< or = 36 h) expression of foetal genes (atrial natriuretic peptide (ANP), skeletal-alpha-actin and myosin heavy chain-beta). This increase was attenuated by 86% and 51%, respectively, by BIBP3226 (1 microM) and T(4) [neuropeptide Y-(33-36)](4) (100 nM). [Leu(31), Pro(34)]neuropeptide Y (100 nM) (2.4-fold>basal) and peptide YY-(3-36) (100 nM) (2.3 fold>basal) increased expression of MLC-2 mRNA at 12 h. In conclusion, initiation of cardiomyocyte hypertrophy by neuropeptide Y requires activation of both neuropeptide Y Y(1) and neuropeptide Y Y(2) receptors and is associated with enhanced synthesis and attenuated degradation of protein together with increased expression of constitutive genes but not reinduction of foetal genes.

Neuropeptide Y Y(5) receptor antagonist CGP71683A: the effects on food intake and anxiety-related behavior in the rat

The effects of neuropeptide Y Y(5) receptor antagonist (trans-naphtalene-1-sulphonic acid [4-[(4-amino-quinazolin-2-ylamino)-methyl]-cyclohexylmethyl]-amide hydrochloride; CGP71683A), on food intake, anxiety and locomotor activity were studied. CGP71683A (1-10 mg/kg, i.p.) dose-dependently decreased nocturnal and fasting-induced food intake. CGP71683A did not have an anxiogenic-like effect in the rat social interaction test. In the elevated plus-maze test, where novel neuropeptide Y Y(1) receptor antagonist (2R)-5-([amino(imino)methyl)amino)-2-[(2.2-diphenylacetyl)-amino]-N-[(1R)-1-(4-hydroxyphenyl)ethyl-pentanamide (H 409/22) had anxiogenic-like effect, CGP71683A was inactive. In the open-field test, carried out immediately after the elevated plus-maze test, CGP71683A inhibited horizontal and vertical activity. CGP71683A did modify the habituation of locomotor response in novel environment. These data show that the inhibition of food intake induced by CGP71683A could not be explained by increased fearfulness, a state that is induced by neuropeptide Y Y(1) receptor antagonists. Thus, our data, obtained with first neuropeptide Y Y(5) receptor antagonist CGP71683A, suggest that in contrast to the neuropeptide Y Y(1) receptor, Y(5) receptor is not involved in tonic neuropeptide Y-induced anxiolysis.

Multiple Y receptors mediate pancreatic polypeptide responses in mouse colon mucosa

A functional study has been performed to characterise the Y receptors responsible for NPY, PYY and PP-stimulated responses in mouse colonic mucosal preparations. Electrogenic ion secretion was stimulated with VIP following which NPY, PYY and PP analogues were, to varying degrees, inhibitory. PYY(3-36), hPP, Gln(23)hPP and rPP were effective but less potent than full length PYY, NPY or their Pro(34)-substituted analogues, while the Y(5) agonist Ala(31), Aib(32)hNPY was the least active peptide tested. The Y(1) antagonists, BIBP3226 and BIBO3304 virtually abolished Pro(34)PYY and PYY responses while PYY(3-36) responses were selectively inhibited by the Y(2) antagonist, BIIE0246. A combination of BIBO3304 and BIIE0246 also partially attenuated hPP responses, leaving residual effects that were most probably Y(4)-mediated. Thus we conclude that Y(1), Y(2) and Y(4) receptors attenuate ion secretion in mouse colon.

Effects of a selective neuropeptide Y Y2 receptor antagonist, BIIE0246, on Y2 receptors at peripheral neuroeffector junctions

1. This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y2 receptor antagonist, on the inhibition of cholinergic neuroeffector transmission in rat heart and guinea-pig trachea and purinergic neuroeffector transmission in guinea-pig vas deferens produced by the NPY Y2 receptor agonist, N-acetyl [Leu28,31] NPY 24-36. 2. In pentobarbitone anaesthetized rats, supramaximal stimulation every 30 s, of the vagus nerve innervating the heart, increased pulse interval by approximately 100 ms. This response was attenuated by intravenous administration of N-acetyl [Leu28,31] NPY 24-36 (10 nmol x kg(-1)). 3. Transmural stimulation of segments of guinea-pig trachea at 1 min intervals with 5 s trains of stimuli at 0.5, 5, 10, 20 and 40 Hz evoked contractions which were reduced in force by N-acetyl [Leu28,31] NPY 24-36 (2 microM). 4. In guinea-pig vasa deferentia, the amplitude of excitatory junction potentials evoked by trains of 20 stimuli at 1 Hz was reduced in the presence of N-acetyl [Leu28,31] NPY 24-36 (1 microM). 5. In all preparations BIIE0246 attenuated the inhibitory effect of N-acetyl [Leu28,31] NPY 24-36 but had no effect when applied alone. 6. The findings support the view that the nerve terminals of postganglionic parasympathetic and sympathetic neurones possess neuropeptide Y Y2 receptors which, when activated, reduce neurotransmitter release.

Constitutive neuropeptide Y Y(4) receptor expression in human colonic adenocarcinoma cell lines

1. Three human adenocarcinoma cell lines, Colony-24 (Col-24), Col-6 and Col-1 have been studied as confluent epithelial layers able to transport ions vectorially in response to basolateral vasoactive intestinal polypeptide (VIP) and pancreatic polypeptides (PP). 2. Different species PP stimulated responses in Col-24 with Y(4)-like pharmacology. Bovine (b)PP, human (h)PP and porcine (p)PP were equipotent (EC(50) values 3.0--5.0 nM) while rat (r)PP, avian (a)PP and [Leu(31), Pro(34)]PYY (Pro(34)PYY) were significantly less potent. PYY was inactive. The PP pharmacology in Col-1 was comparable with Col-24. However, Col-6 cells were different; pPP had an EC(50) intermediate (22.0 nM) between that of bPP (3.0 nM) and hPP (173.2 nM), with aPP and rPP being at least a further fold less potent. 3. Deamidation of Tyr(36) in bPP (by O-methylation or hydroxylation) or removal of the residue resulted in significant loss of activity in Col-24. 4. GR231118 (1 microM) had no PP-like effects. In Col-24 and Col-1, GR231118 significantly attenuated bPP (30 nM) or hPP (100 nM) responses, but it did not alter bPP responses in Col-6. BIBP3226 and GR231118 both inhibited Y(1)-mediated responses which were only present in Col-6. 5. RT--PCR analysis confirmed the presence of hY(4) receptor mRNA in Col-24 and Col-1 epithelia but a barely visible hY(4) product was observed in Col-6 and we suggest that an atypical Y(4) receptor is expressed in this cell line.

BIIE0246, a potent and highly selective non-peptide neuropeptide Y Y(2) receptor antagonist

1. BIIE0246, a newly synthesized non-peptide neuropeptide Y (NPY) Y(2) receptor antagonist, was able to compete with high affinity (8 to 15 nM) for specific [(125)I]PYY(3 - 36) binding sites in HEK293 cells transfected with the rat Y(2) receptor cDNA, and in rat brain and human frontal cortex membrane homogenates. 2. Interestingly, in rat brain homogenates while NPY, C2-NPY and PYY(3 - 36) inhibited all specific [(125)I]PYY(3 - 36) labelling, BIIE0246 failed to compete for all specific binding suggesting that [(125)I]PYY(3 - 36) recognized, in addition to the Y(2) subtype, another population of specific NPY binding sites, most likely the Y(5) receptor. 3. Quantitative receptor autoradiographic data confirmed the presence of [(125)I]PYY(3 - 36)/BIIE0246-sensitive (Y(2)) and-insensitive (Y(5)) binding sites in the rat brain as well as in the marmoset monkey and human hippocampal formation. 4. In the rat vas deferens and dog saphenous vein (two prototypical Y(2) bioassays), BIIE0246 induced parallel shifts to the right of NPY concentration-response curves with pA(2) values of 8.1 and 8.6, respectively. In the rat colon (a Y(2)/Y(4) bioassay), BIIE0246 (1 microM) completely blocked the contraction induced by PYY(3 - 36), but not that of [Leu(31), Pro(34)]NPY (a Y(1), Y(4) and Y(5) agonist) and hPP (a Y(4) and Y(5) agonist). Additionally, BIIE0246 failed to alter the contractile effects of NPY in prototypical Y(1) in vitro bioassays. 5. Taken together, these results demonstrate that BIIE0246 is a highly potent, high affinity antagonist selective for the Y(2) receptor subtype. It should prove most useful to establish further the functional role of the Y(2) receptor in the organism.

Potent and selective tools to investigate neuropeptide Y receptors in the central and peripheral nervous systems: BIBO3304 (Y1) and CGP71683A (Y5)

We have evaluated 3 newly developed neuropeptide Y receptor antagonists in various in vitro binding and bioassays: BIBO3304 (Y1), T4[NPY33-36]4 (Y2), and CGP71683A (Y5). In rat brain homogenates, BIBO3304 competes for the same population of [125I][Leu31,Pro34] peptide YY (PYY) binding sites (75%) as BIBP3226, but with a 10 fold greater affinity (IC50 of 0.2 ± 0.04 nM for BIBO3304 vs. 2.4 ± 0.07 nM for BIBP3226),while CGP71683A has high affinity for 25% of specific [125I][Leu31,Pro34]PYY binding sites. Both BIBO3304 and CGP71683A (at 1.0 µM) were unable to compete for a significant proportion of specific [125I]PYY3-36/Y2 sites. The purported Y2 antagonist T4[NPY33-36]4 competed against [125I]PYY3-36 binding sites with an affinity of 750 nM. These results were confirmed in HEK 293 cells transfected with either the rat Y1, Y2, Y4, or Y5 receptor cDNA. BIBO3304, but not CGP71683A, competed with high affinity for [125I][Leu31,Pro34]PYY binding sites in HEK 293 cells transfected with the rat Y1 receptor cDNA, whereas the reverse profile was observed upon transfection with the rat Y5 receptor cDNA. Additionally, both molecules were inactive at Y2 and Y4 receptor subtypes expressed in HEK 293 cells. Receptor autoradiographic studies revealed the presence of [125I][Leu31,Pro34]PYY/BIBO3304-insensitive sites in the rat brain as reported previously for BIBP3226. Finally, the selective antagonistic properties of BIBO3304 were demonstrated in a Y1 bioassay (rabbit saphenous vein; pA2 value of 9.04) while being inactive in Y2 (rat vas deferens) and Y4 (rat colon) bioassays. These results confirm the high affinity and selectivity of BIBO3304 and CGP71683A for the Y1 and Y5 receptor subtypes, respectively, while the purported Y2 antagonist, T4[NPY33-36]4 possesses rather low affinity for this receptor.Key words: NPY receptor antagonist, receptor subtypes, bioassays, receptor binding assays, autoradiographic studies, receptor distribution.