Multiple neuropeptide Y receptors are involved in cardiovascular regulation. Peripheral and central mechanisms

Human neuropeptide YY1 receptors exert unequal control of the extracellular acidification rate in different cell lines

The ability of the human neuropeptide YY1 receptor subtype to increase the extracellular acidification rate in different cell lines was investigated by using the Cytosensor Microphysiometer. In CHO-Y1 cells (Chinese Hamster Ovary cells expressing the cloned human neuropeptide YY1 receptor), neuropeptide Y increased the acidification rate by up to 15% of the basal level with a -Log(EC50) of 7.42. As expected for neuropeptide YY1 receptors, this response was potently inhibited by the neuropeptide YY1-selective non-peptide antagonist BIBP3226 ((R)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginine amide). Its enantiomer BIBP3435 ((S)-N2-(diphenylacetyl)-N-[(4-hydroxy-phenyl)methyl]-D-arginin amide) was less potent. The antagonists themselves did not affect the extracellular acidification rate at concentrations up to 10 microM. In SK-N-MC cells (a neuroblastoma cell line of human origin that expresses the neuropeptide YY1 receptor) no change of the acidification rate could be observed in the presence of neuropeptide Y at concentrations up to 1 microM. For control, the neuropeptide YY1 receptors were also investigated by assessing whole cell radioligand binding and, at the functional level, by assessing their ability to decrease the forskolin-induced accumulation of cAMP. The specific (i.e., neuropeptide Y-displaceable) binding of [3H]neuropeptide Y was to a homogeneous class of high-affinity sites in both SK-N-MC and CHO-Y1 cells. The equilibrium dissociation constants for [3H]neuropeptide Y, the total number of binding sites and the kinetic constants for association and for dissociation were similar. Neuropeptide Y produced a dose-dependent inhibition of forskolin-induced cAMP accumulation in SK-N-MC cells (-log(EC50) = 9.40) but it did not affect cAMP accumulation in CHO-Y1 cells. Non-transfected CHO-K1 cells were used as negative control throughout the study. No binding or response could be observed in these cells. Our data suggest that the signalling mechanisms of neuropeptide YY1 receptors are closely related to the cell type in which they are expressed.

Localization of neuropeptide Y Y1 receptors in cerebral blood vessels

The localization of neuropeptide Y (NPY) Y1 receptor (R) -like immunoreactivity (LI) has been studied in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence, confocal, and electron microscopy. High levels of Y1-R-LI were observed in smooth muscle cells (SMCs) in the small arterioles of the pial arterial network, especially on the basal surface of the brain, and low levels in the major basal cerebral arteries. The levels of Y1-R-LI varied strongly between adjacent SMCs. Y1-R-LI was associated with small endocytosis vesicles, mainly on the outer surface of the SMCs, but also on their endothelial side and often laterally at the interface between two SMCs. NPY-immunoreactive (Ir) nerve fibers could not be detected in association with the Y1-R-rich small arterioles but only around arteries with low Y1-R levels. A dense network of central NPY-Ir nerve fibers in the superficial layers of the brain was lying close to the strongly Y1-R-Ir small arterioles. The results indicate that NPY has a profound effect on small arterioles of the brain acting on Y1-Rs, both on the peripheral and luminal side of the SMCs. However, the source of the endogenous ligand, NPY, remains unclear. NPY released from central neurons may play a role, in addition to blood-borne NPY.

Non-competitive binding of the nonpeptide antagonist BIBP3226 to rat forebrain neuropeptide Y1 receptors

[3H]Neuropeptide Y labelled neuropeptide Y receptors in rat forebrain membranes as a homogenous class of high-affinity sites. Between 80 and 85% of these receptors showed high affinity for Y1-selective antagonists such as (R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine amide (BIBP3226). While competitive in functional studies, BIBP3226 produced parallel shifts of the Scatchard plots of [3H]neuropeptide Y saturation binding in rat forebrain membranes. Mechanisms which are routinely invoked to explain non-competitive binding do not apply to BIBP3226. Wash-out experiments, involving successive treatment of the membranes with BIBP3226, buffer (wash-out step) and [3H]neuropeptide Y, argue against irreversible or a pseudo-irreversible binding of the antagonist. Allosteric inhibition is also unlikely since BIBP3226 did not affect the rate of dissociation of [3H]neuropeptide Y in isotope dilution experiments. The non-hydrolyzable guanine nucleotide, 5'-guanylylimidodiphosphate (Gpp(NH)p), abolished the binding of [3H]neuropeptide Y and increased its rate of dissociation in isotope dilution experiments. This suggests that the initial [3H]neuropeptide Y-receptor association is a low affinity process and that the observed binding of [3H]neuropeptide Y is related to the formation of a ternary [3H]neuropeptide Y-receptor-G protein complex. Two- or even multistate models (in which BIBP3226 could potentially behave as an inverse agonist) could therefore be needed to explain the non-competitive antagonism of BIBP3226 in broken cell preparations.

Characterization of neuropeptide Y receptor subtypes in the normal human brain, including the hypothalamus

The aim of the present study was to investigate the existence and distribution of neuropeptide Y receptor subtypes in various regions of the normal human brain using the peptide YY derivative receptor probes, [125I][Leu31,Pro34]polypeptide YY/Y1 and [125I]polypeptide YY(3-36)/Y2, in addition to the non-selective ligand [125I]polypeptide YY. Membrane binding assays performed with post mortem frontal cortex homogenates revealed that [125I]polypeptide YY and [125I]polypeptide YY(3-36) bound in a time- and protein concentration-dependent manner. Very low amounts of specific [125I][Leu31,Pro34]polypeptide YY binding could be detected even in the presence of high amounts of protein, contrasting with results obtained with [125I]polypeptide YY and [125I]polypeptide YY(3-36), a preferential Y2 receptor probe. Analysis of saturation isotherms revealed that [125I]polypeptide YY(3-36) bound to a single class of high-affinity sites (0.5-2 nM). Significantly higher binding capacities were evident for [125I]polypeptide YY(3-36) as compared to [125I][Leu31,Pro34]polypeptide YY, suggesting that the human frontal cortex, in contrast to the rat, is mostly enriched with Y2 receptors. Ligand selectivity profile confirmed the hypothesis that polypeptide YY(3-36), neuropeptide Y and polypeptide YY but not the [Leu31,Pro34] derivatives are potent competitors of [125I]polypeptide YY and [125I]polypeptide YY(3-36) binding sites. Autoradiographic studies demonstrated further that cortical areas, as well as most other regions of the human brain, are particularly enriched with Y2/[125I]polypeptide YY(3-36) sites, while only low to very low amounts of Y1 binding were detected except in the dentate gyrus of the hippocampal formation. In the human hypothalamus, a preponderance of Y2 binding sites was also noted. Taken together, these results clearly establish that the distribution of the Y1 and Y2 receptor subtypes in human is different from the rodent brain, the Y2 subtype being most abundant in the human brain.

Increased potency of neuropeptide Y to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat

The regulation by neuropeptide Y of alpha2-adrenoceptors in the nucleus tractus solitarii was evaluated in the adult normotensive Wistar Kyoto rat and the adult spontaneously hypertensive rat. The microinjection of a submaximal dose of l-noradrenaline (800 pmol in 50 nl) alone into the nucleus tractus solitarii produced a significant reduction in the mean arterial blood pressure in either strain. The threshold dose (1 pmol in 50 nl) of neuropeptide Y(1-36) for the vasodepressor response in the Wistar Kyoto rat was five times higher than that (0.2 pmol in 50 nl) in the spontaneously hypertensive rat. Furthermore, neuropeptide Y(1-36) at 0.2 pmol in 50 nl could significantly counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl) in the spontaneously hypertensive rat, but not in the Wistar Kyoto rat, in which 1 pmol in 50 nl of neuropeptide Y(1-36) must be employed to counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl), although the vasodepressor responses are of a similar magnitude. The in situ hybridization and quantitative receptor autoradiographical experiments showed that the alpha2A-adrenoceptor messenger RNA levels and the B(max) value of the alpha2-adrenoceptor agonist [3H]p-aminoclonidine binding sites measured in the nucleus tractus solitarii of the spontaneously hypertensive rat were substantially lower than those in the Wistar Kyoto rat. The quantitative receptor autoradiographical results were consistent with the cardiovascular results and showed that in the spontaneously hypertensive rat, neuropeptide Y(1-36) at 1 nM led to a significant increase in the K(d) value of [3H]p-aminoclonidine binding sites. In the Wistar Kyoto rat, neuropeptide Y(1-36) produced this effect only at 10 nM. The present study provides evidence for an increase of the potency of neuropeptide Y(1-36) to antagonistically modulate alpha2-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat. This enhanced antagonistic action may partly be related to a reduction in the number of alpha2A-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat, since a decrease has been observed in the alpha2A-adrenoceptor messenger RNA levels and the alpha2-adrenoceptor binding sites in the spontaneously hypertensive rat. This increased potency of neuropeptide Y(1-36) to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat may contribute to the development of high blood pressure in this hypertensive strain.

Antinociceptive effects of neuropeptide Y and related peptides in mice

This study compares the antinociceptive and orexigenic activities of NPY and analogs after intracerebroventricular administration in mice. NPY had an antinociceptive action in the mouse writhing test which was not affected by prior treatment with naltrexone, yohimbine, idazoxan or reserpine. A detailed examination revealed that NPY (0.023-0.7 nmol), PYY (0.007-0.07 nmol), NPY2-36 (0.023-0.23 nmol) and the Y1 agonist [Leu31, Pro34]-NPY (0.07-0.7 nmol) all produced a dose-dependent and complete suppression of acetic acid-induced writhing. In contrast, the Y2 agonist, NPY13-36, had little or no antinociceptive effect. As shown by their ED50 values, the relative potency of the peptides was PYY > NPY2-36 > or = NPY > [Leu31, Pro34]-NPY > > NPY13-36, suggesting that a Y1 rather than a Y2 or Y3 receptor subtype was implicated in the antinociceptive action. Thereafter, all peptides were assessed for their effects on food intake. With respect to dose and peptide specificity, the hyperphagic effects of NPY and related peptides paralleled those on nociception, suggesting a common receptor mechanism. However, a purported NPY antagonist, [D-Trp32]-NPY, attenuated NPY's effect on feeding yet this same peptide elicited a dose-dependent inhibition of acetic acid-induced writhing, suggesting some molecular distinction between antinociception and stimulation of food intake.

Cloning and functional expression of cDNAs encoding human and rat pancreatic polypeptide receptors

PCR was used to isolate nucleotide sequences that may encode novel members of the neuropeptide Y receptor family. By use of a PCR product as a hybridization probe, a full-length human cDNA was isolated that encodes a 375-aa protein with a predicted membrane topology identifying it as a member of the G-protein-coupled receptor superfamily. After stable transfection of the cDNA into human embryonic kidney 293 cells, the receptor exhibited high affinity (Kd = 2.8 nM) for 125I-labeled human pancreatic polypeptide (PP). Competition binding studies in whole cells indicated the following rank order of potency: human PP = bovine PP > or = human [Pro34]peptide YY > rat PP > human peptide YY = human neuropeptide Y. Northern blot analysis revealed that human PP receptor mRNA is most abundantly expressed in skeletal muscle and, to a lesser extent, in lung and brain tissue. A rat cDNA clone encoding a high-affinity PP receptor that is 74% identical to the human PP receptor at the amino acid level was also isolated. These receptor clones will be useful in elucidating the functional role of PP and designing selective PP receptor agonists and antagonists.

Ligand binding and functional effects of systematic double D-amino acid residue substituted neuropeptide Y analogs on Y1 and Y2 receptor types

In order to identify the signal epitopes of the neuropeptide Y (NPY) molecule, the conformation of the NPY molecule was pertubated by a systematic double D-amino acid replacement of neighbouring residues. These NPY-analogs were examined for receptor affinity and on biological activity. The rat cerebral cortex and hippocampus were used for binding characteristics on Y1 and Y2 binding sites, respectively, while the isolated guinea pig caval vein and rat vas deferens were used in functional characterization of Y1 and Y2 receptors, respectively. The NPY analogs were examined as ligands at [3H]NPY binding sites in homogenates of the rat brain. Pairwise D-substitutions of either of the first 6 amino acid residues in the N-terminal part of the molecule resulted in a 20-100-fold loss of affinity for Y1 binding sites compared with the native peptide. In comparison, the same analogs displayed affinities, which were about 8-40 times lower than NPY itself at Y2 binding sites. Especially [D-Ser3,D-Lys4]NPY had a low affinity to Y1 and Y2 binding sites. For many of the pairwise D-amino acid substituted NPY analogs, there were similar affinities for Y1 and Y2 binding sites in the cerebral cortex and hippocampus, respectively. D-Amino acid residue substitutions in positions 7 and 8 did essentially not affect the affinity to either type of binding site, while such replacements in positions 19 and 20 resulted in a drastic loss of affinity to both types of NPY binding site. In contrast, [D-Tyr21,D-Ser22]NPY was only slightly less potent than NPY itself on either type of binding site. Pairwise D-amino acid substitutions in the C-terminal (positions 27 to 36) decreased the affinity to Y1 and Y2 binding sites by 2 to 3 orders of magnitude. In the guinea pig vena cava the D-amino acid substituted NPY analogs evoked a concentration-dependent contraction with an rank order of potency similar to that of the respective analog at Y1 binding sites in the cerebral cortex. Similarly, in the rat vas deferens the D-amino acid substituted NPY analogs evoked a concentration-dependent inhibition of the electrically-stimulated twitches with a rank order of potency similar to that of the respective analog at Y2 binding sites in the hippocampus. However, D-amino acid replacements in positions 25 and 26 resulted in an analog which was virtually inactive in the vas deferens, but almost equipotent with NPY in the vena cava. In conclusion, the present study has shown that N-terminal double D-amino acid substitutions in the NPY molecule reduced the binding affinity to and activation more of the Y1 receptor, than of the Y2 receptor, while both receptors were quite sensitive to double D-amino acid changes in positions 19 and 20 and in the C-terminal end of the NPY molecule.

Neurochemical modulation of cardiovascular control in the nucleus tractus solitarius

The central control of cardiovascular function has been keenly studied for a number of decades. Of particular interest are the homeostatic control mechanisms, such as the baroreceptor heart-rate reflex, the chemoreceptor reflex, the Bezold-Jarisch reflex and the Breuer-Hering reflex. These neurally-mediated reflexes share a common termination point for their respective centrally-projecting sensory afferents, namely the nucleus tractus solitarius (NTS). Thus, the NTS clearly plays a critical role in the integration of peripherally initiated sensory information regarding the status of blood pressure, heart rate and respiratory function. Many endogenous neurochemicals, from simple amino acids through biogenic amines to complex peptides have the ability to modulate blood pressure and heart rate at the level of the NTS. This review will attempt to collate the current knowledge regarding the roles of neuromodulators in the NTS, the receptor types involved in mediating observed responses and the degree of importance of such neurochemicals in the tonic regulation of the cardiovascular system. The neural pathway that controls the baroreceptor heart-rate reflex will be the main focus of attention, including discussion of the identity of the neurotransmitter(s) thought to act at baroafferent terminals within the NTS. In addition, this review will provide a timely update on the use of recently developed molecular biological techniques that have been employed in the study of the NTS, complementing more classical research.

Neuropeptide Y. A novel sympathetic stress hormone and more

Several lines of evidence suggest that NPY is a neurotransmitter and neurohormone intricately involved in stress responses of the body, and as such should be considered a "stress molecule." Thus, circulating plasma NPY levels are increased by stress particularly if it is severe or prolonged. Stress stimulates the release of NPY from the sympathetic nerves and the adrenal medulla (in some species also from platelets), and in addition, modulates NPY inactivation. Stress-induced plasma NPY levels may reach the concentrations that are vasoconstrictive per se in addition to potentiating the actions of catecholamines. Reciprocally, elevated circulating levels of catecholamines during stress appear to induce hypersensitivity of blood vessels to NPY. Consequently, the peptide may be responsible for stress-induced regional vasoconstriction (splanchnic, coronary, and cerebral) but also may exert other actions that may be a part of the stress response: facilitate platelet aggregation, leukocyte adhesion, and macrophage activation. NPY release and actions appear to be up-regulated by testosterone and down-regulated by estrogens; therefore, NPY may be of particular importance to stress-induced cardiovascular events in men. In addition to acute vasoconstrictive effects, NPY exerts chronic actions and stimulates vascular smooth muscle proliferation and vascular hypertrophy, and hence, may be a link between stress and potential chronic changes in blood vessels.

Characterization of neuropeptide Y (NPY) receptors in human cerebral arteries with selective agonists and the new Y1 antagonist BIBP 3226

1. We have characterized pharmacologically the receptor subtype(s) responsible for the neuropeptide Y (NPY)-induced vasoconstriction in human cerebral arteries. NPY, PYY and several of their derivatives with well defined affinities at the known Y1 and Y2 receptor subtypes were used. Moreover, we tested the ability of the new Y1 receptor antagonist, BIBP 3226, to antagonize the NPY-induced cerebral vasoconstriction. 2. NPY, PYY and their agonists with high affinities at the Y1 receptor subtype ([Leu31-Pro34]-NPY and [Leu31-Pro34]-PYY) elicited strong, long lasting and concentration-dependent contractions of human cerebral arteries. Compounds with Y2 affinity such as PYY3-36 or NPY13-36 either elicited a submaximal contraction at high concentrations or failed to induce any significant vasomotor response. Also, the application of NPY or the specific Y1 agonist, [Leu31-Pro34]-NPY, to human cerebral vessels pretreated with the Y1 agonist, NPY13-36, resulted in contractile responses identical to those obtained when these compounds were tested without prior application of NPY13-36. 3. The order of agonist potency at the human cerebrovascular receptor was: [Leu31-Pro34]-NPY = [Leu31-Pro34]-PYY > or = NPY > PYY > PYY3-36 > > > NPY13-36, which corresponded to that reported previously at the neuronal and vascular Y1 receptors. 4. Increasing concentrations (10(-9)-10(-6) M) of the Y1 receptor antagonist, BIBP 3226, to human cerebral vessels caused a parallel and rightward shift in the NPY dose-response curves without any significant change in the maximal contractile response. The calculated pA2 was 8.52 +/- 0.13, a value compatible with the reported affinity at the rodent and human Y1 receptor. 5. We conclude that Y1 receptors exclusively, mediate the NPY-induced contraction in human cerebral arteries and we show that BIBP 3226 is a potent and competitive antagonist of this YI-mediated vasoconstriction.

Neuropeptide Y2-type receptor-mediated activation of large-conductance Ca(2+)-sensitive K+ channels in a human neuroblastoma cell line

We have proposed recently that a pertussistoxin-insensitive Ca2+ influx stimulated by Y2-type receptor activation in CHP-234 human neuroblastoma cells underlies increases in intracellular free Ca2+ concentration ([Ca2+]i) induced by neuropeptide Y (NPY), which were strictly dependent on extracellular Ca2+ and independent of internal Ca2+ stores. We describe here the actions of NPY in these same cells, using the activity of Ca(2+)-activated K+ channels as an indicator of [Ca2+]i. The elementary slope conductance of these channels was 110 +/- 3 pS (with an asymmetrical K+ gradient), their activity was greatly increased by application of ionomycin, and they were reversibly blocked by 1 mM tetraethylammonium (TEA) and 100 nM charybdotoxin. Application of 100 nM NPY, in the presence but not in the absence of extracellular Ca2+, increased the channel open probability. ATP applied in the absence of external Ca2+ caused rises both in channel open probability and [Ca2+]i. Inositol trisphosphate production was stimulated by ATP but not by NPY. In outside-out patches, NPY increased channel open probability, indicating that NPY-associated Ca2+ influx does not require all the intracellular machinery present in intact cells. Channel activation by NPY was unaffected by the replacement of guanosine 5'-triphosphate (GTP) by (guanosine 5'-O-(2-thiodiphosphate) (GDP[ beta S]), a non-hydrolysable GDP analogue, in the pipette internal solution, consistent with the lack of involvement of G-proteins in the coupling of Y2-type receptors to Ca2+ influx in CHP-234 cells.

Plasma neuropeptide Y and catecholamines in women and men with essential hypertension

Neuropeptide-Y (NPY) is a peptide proposed to modulate the effect of the sympathetic nervous system on blood pressure control and contribute to the development of essential hypertension. To assess the possible influence of gender on its role, we evaluated plasma NPY, noradrenaline (NA) and adrenaline (A) concentrations in men and women with essential hypertension. No difference in NPY concentration was found between genders, but NPY concentration was elevated in both hypertensive men and women. NA levels were similar in all investigated hyper- and normotensives, while A was increased only in hypertensive men. These results suggest various patterns of sympatho-adrenal activity in gender subgroups of patients with essential hypertension.

Discrimination by benextramine between the NPY-Y1 receptor subtypes present in rabbit isolated vas deferens and saphenous vein

1. In order to characterize the neuropeptide Y (NPY) Y1 receptors known to be present in rabbit isolated vas deferens and saphenous vein, the pharmacological activity of the selective NPY Y1 receptor agonists, [Leu31,Pro34] NPY and various other peptide agonists, together with the putative NPY antagonist, benextramine, were compared in the two tissues. 2. In rabbit isolated saphenous vein, cumulative dose-response curves to various NPY agonists were obtained. All the peptides tested caused contractions which developed quite slowly. The rank order of potency obtained was: PYY > NPY > [Leu31,Pro34] NPY = NPY2-36 > hPP >> NPY13-36 = NPY18-36. Incubation with benextramine (BXT) at 100 microM for 30 min irreversibly abolished the contractile response to [Leu31,Pro34] NPY but was ineffective against NPY18-36-induced contractions. 3. Cumulative dose-response curves to [Leu31,Pro34] NPY were performed in the same preparation before and after incubation with 100 microM BXT for 20 min in order to inactivate NPY Y1 receptors. The pKA (-logKA) estimation for [Leu31,Pro34] NPY was 7.60 +/- 0.30 using the operational model and 7.20 +/- 0.33 using the null method; the difference between the two methods was not statistically significant (P = 0.36). 4. Prostatic segments of rabbit vas deferens were electrically stimulated with single pulses. Immediately after stabilization of the contractile response, a cumulative dose-response curve to various NPY agonists was obtained in each tissue. The rank order of potency for twitch inhibition was: PYY> [Leu31,Pro34]NPY > NPY > hPP>NPY2- 36 >>NPY13-36>> NPY 18-36 which indicates the presence of a prejunctional NPY Y1 receptor. BXT at 100 microM incubated for 10 or 60 min did not antagonize the response to[Leu31,Pro34] NPY.5. We conclude that rabbit isolated saphenous vein contains a population of post-junctional NPY Y1 receptors irreversibly blocked by BXT, as well as a population of post-junctional NPY Y2 receptors,which are insensitive to BXT. In contrast, the rabbit isolated vas deferens express a pre-junctional NPYY1 receptor subtype which is not blocked by BXT. Tetramine disulphides such as BXT could be useful tools in classifying NPY receptors.

Structural requirements for neuropeptide Y in mast cell and G protein activation

Incubation of neuropeptide Y or its C-terminal fragments with rat peritoneal mast cells resulted in a dose-dependent histamine release. Fragment 18-36 of neuropeptide Y was the most biologically active peptide. EC25 value on rat mast cells was 7.2 +/- 2.2 nM. Neuropeptide Y was also able to induce a flare response after intradermal injection in humans. The histamine releasing effects of neuropeptide Y related peptides were greatly inhibited by pretreatment of rat mast cells with pertussis toxin or benzalkonium chloride. Neuropeptide Y and C-terminal related peptides also stimulated the GTPase activity of purified heterotrimeric G proteins in a dose-dependent manner from 1 to 50 microM. Binding studies with [125I]neuropeptide Y were unable to provide evidence for the presence of specific binding sites on the surface of mast cells. The alpha helical conformation of neuropeptide Y fragments was studied by measuring the circular dichroism spectra. Neuropeptide Y-(18-36) was the smallest fragment having a strong helical conformation. Our results demonstrate that neuropeptide Y activates mast cells through a non-specific process leading to G protein activation.

Neuropeptide Y receptor subtypes

Neuropeptide Y (NPY) is an amidated 36-amino acid peptide with a wide distribution in the central and peripheral nervous system. It can evoke numerous physiological responses by activating specific receptors. Studies using NPY analogs in various model systems and cell types demonstrate different orders of ligand potency and receptor binding affinity. These studies suggest the existence of multiple subtypes of NPY receptors. NPY has been described to bind to at least three different receptors, Y1, Y2 and Y3. NPY has also been shown to interact with sigma receptor in vivo and in vitro. There are indications that more subtypes might exist. Ligand binding studies reveal that Y1, Y2 and Y3 receptors are all G-protein coupled. It is not yet confirmed whether the sigma receptor that interacts with NPY is G-protein coupled. Some studies show that NPY receptors may interact with other classical receptors, including alpha- and beta-adrenoceptors and cholinergic receptors. In the case of alpha- and beta-adrenoceptors, the receptor-receptor interaction is possibly via a pertussis toxin-sensitive G-protein. NPY receptors are coupled to various signal transduction mechanisms including inhibition of adenylate cyclase, and stimulation or inhibition of increases in intracellular Ca2+. Specific links between individual NPY receptor subtype and a particular signal transduction pathway are not established.

Structure-activity relationships of neuropeptide Y analogues with respect to Y1 and Y2 receptors

Secondary structure investigations, affinities, and activities of neuropeptide Y analogues with respect to the Y1 and the Y2 receptor are reviewed. The results are discussed with respect to the different prerequisites for affinities to both receptor subtypes. The results from a systematic scanning of the hormone using L-alanine and from a large variety of discontinuous and cyclic analogs suggest that two different conformations of neuropeptide Y are adopted at the Y1 and Y2 receptors. Whereas a C-terminal turn structure is suggested for Y1 receptor affinity, an alpha-helical conformation of the C-terminus is afforded for good binding to the Y2 receptor.

Heterogeneity of prejunctional neuropeptide Y receptors inhibiting noradrenaline overflow in the portal vein of freely moving rats

The effects of intraportal infusions of different doses of neuropeptide Y, its selective neuropeptide Y Y1 receptor analogue, [Leu31,Pro34]neuropeptide Y, and the Y2-selective C-terminal fragment, neuropeptide Y-(18-36), on basal and electrically evoked noradrenaline overflow in the portal vein as well as on mean arterial pressure and heart rate were investigated in permanently instrumented freely moving rats. Neuropeptide Y dose dependently (2-2000 ng/kg/min) attenuated the electrically evoked noradrenaline overflow and almost complete blockade was reached at the highest dose used. [Leu31,Pro34]Neuropeptide Y also dose dependently (20-20,000 ng/kg/min) attenuated the evoked overflow, reaching a maximum of 55% inhibition at the highest dose (20,000 ng/kg/min). Neuropeptide Y-(18-36) attenuated the evoked release only at 20,000 ng/kg/min (by 46%). Only at the highest dose did neuropeptide Y (2000 ng/kg/min) and [Leu31,Pro34]neuropeptide Y (20,000 ng/kg/min) significantly enhance mean arterial pressure and decrease heart rate and basal plasma noradrenaline levels, the latter two effects being due to the baroreceptor reflex. Neuropeptide Y-(18-36) did not influence these parameters at all doses used. The results indicate the presence of prejunctional neuropeptide Y Y1 receptors, and possibly the coexistence of Y1 and Y2 receptors, in the portal vein of freely moving rats, which in conjunction are able to inhibit markedly electrically evoked noradrenaline overflow. Postjunctional neuropeptide Y receptors mediating an increase in blood pressure in the freely moving rat are solely of the Y1 subtype.

Selective modulation of the NPY receptors of the Y2 subtype by alpha 2 receptors in the nucleus tractus solitarii of the rat. A cardiovascular and quantitative receptor autoradiographical analysis

The modulation of neuropeptide Y (NPY) receptors by alpha 2 receptors in the nucleus tractus solitarii (Sol) of the rat was evaluated using quantitative receptor autoradiography and measurements of mean arterial blood pressure and heart rate. The receptor autoradiographical experiments showed that clonidine (10 nM), a selective alpha 2 receptor agonist, induced a 59% increase in the B0 value and a 47% decrease in the IC50 value of NPY(1-36) when competing for [125I]peptide YY ([125I]PYY)-binding sites in the presence of [Leu31, Pro34]NPY (100 nM), a selective NPY Y1 receptor agonist, to block the binding to NPY Y1 receptors. In contrast, when NPY(13-36) (300 nM), a selective NPY Y2 receptor agonist, was used to block the binding to NPY Y2 receptors, clonidine (1-30 nM) did not affect the B0 value and the IC50 value of NPY(1-36) when competing for [125I]PYY-binding sites, suggesting that the stimulation of alpha 2 receptors can selectively increase the affinity of NYP(1-36) for the NPY Y2 receptor. Microinjections of threshold doses of adrenaline or clonidine into the Sol not only counteracted the vasopressor action of a close to ED50 dose of coinjected NPY(13-36), but also changed the vasopressor and tachycardic response produced by NPY(13-36) into a vasodepressor and bradycardic response. However, threshold doses of adrenaline or of clonidine microinjected into the Sol did not modify the vasodepressor responses to a close to ED50 dose of NPY(1-36) or of [Leu31, Pro34]NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y and truncated neuropeptide Y analogs evoke histamine release from rat peritoneal mast cells. A direct effect on G proteins?

Several regulatory peptides, including neuropeptide Y, can release histamine from mast cells. In the present study we investigated which parts of the neuropeptide Y molecule are required to evoke the release of histamine from isolated rat peritoneal mast cells. In addition, we examined whether the histamine release evoked by neuropeptide Y (and by compound 48/80) is sensitive to the G protein inhibitors pertussis toxin and benzalkonium chloride. Neuropeptide Y released histamine in a concentration-dependent manner. Also a neuropeptide Y analog with the center part substituted by 8-aminooctanoic acid, [Aoc2-27]neuropeptide Y, and the cyclic form of the C-terminal hexapeptide, cyclic neuropeptide Y-(31-36), released histamine. The three peptides were equally effective and equally potent. Neuropeptide Y-(1-24)NH2 also released histamine, but its efficacy was low. The rank order of potency of the analogs tested did not agree with that of any of the previously known or postulated neuropeptide Y receptors. Pretreatment of mast cells with pertussis toxin or benzalkonium chloride markedly inhibited the histamine release evoked by neuropeptide Y, [Aoc2-27]neuropeptide Y and compound 48/80. In conclusion, most of the histamine-releasing activity of neuropeptide Y resides in the six C-terminal amino acid residues. The release appears to be G protein-dependent and is probably not receptor mediated.

Neuropeptide Y effector systems: perspectives for drug development

Neuropeptide Y was isolated in 1982 and has since attracted considerable interest. It is widely distributed in central and peripheral neurones and can produce a multitude of biological effects in the brain and the periphery. For example, the peptide has been associated with stimulation of food and water intake, control of mood, and regulation of central autonomic functions. In the periphery, sympathetic neuropeptide Y plays a role as a vasopressor and vasoconstrictor. Neuropeptide Y acts on at least three distinct receptor types, referred to a Y1, Y2 and Y3. This review by Lars Grundemar and Rolf Håkanson focuses on some neuropeptide Y-dependent mechanisms that may be implicated in certain disorders and may be promising targets for drugs active at neuropeptide Y receptors.

Functional effects and ligand binding of chimeric galanin-neuropeptide Y (NPY) peptides on NPY and galanin receptor types

1. The effects and binding characteristics of a series of chimeric galanin-neuropeptide Y (NPY) peptides were examined in various preparations known to contain a predominant population of either Y1 or Y2 receptors for NPY or galanin receptors. 2. NPY suppressed the electrically stimulated twitches of the rat vas deferens (Y2 receptors), while galanin enhanced the electrically stimulated twitches. The galanin-NPY peptides M 32 (galanin(1-13)-NPY(25-36)), M69A (galanin(1-13)-Lys-[epsilon NH-Gly-NPY(4-1)]NPY(25-36)) and M88 (galanin(1-12)-Ala-NPY(25-36)) evoked a concentration-dependent suppression of the electrically stimulated twitches. These chimeric peptides were about equipotent with NPY, while NPY (13-36) was about five times less potent than NPY itself. Also a stochiometric combination of the N- and C-terminal fragments NPY (1-24)NH2 and NPY (25-36) (each at 1 microM) was inactive in vas deferens. M120 (galanin (1-13)-NPY(14-36) (1 microM) did not affect the NPY-mediated suppression of the stimulated twitches. 3. NPY evoked a concentration-dependent contraction in the guinea-pig isolated caval vein (Y1 receptors), while galanin (< or = 1 microM) was inactive. M32, M69A and M88 induced a slight contraction at very high concentrations only (> or = 0.3 M), while M120 was inactive at 1 microM. None of the four chimeric peptides affected the contraction evoked by NPY. 4. Since the number of NPY receptors in the rat vas deferens and guinea-pig caval vein were too low,the affinities of the galanin-NPY peptides for [3H]-NPY binding sites were examined in membranes from rat brain areas known to contain predominant populations of Y1 receptors (cerebral cortex) and Y2 receptors (hippocampus), respectively. The chimeric peptides M32, M69A, M88, M120 and NPY (13-36)all had higher affinities for hippocampal binding sites than for cerebral cortical binding sites. These peptides were 90-440 times less potent than NPY at cerebral cortical binding sites and 15-125 times less potent than NPY at hippocampal binding sites. The most selective chimeric peptide was M32, which had a 20 fold higher affinity for hippocampal than for cerebral cortical binding sites.5. At hypothalamic [125I]-galanin binding sites M32, M88 and M69A were equipotent with galanin,while M120 was about 10 times less potent than galanin. M32, M88 and M69A, like galanin contracted the rat isolated jejunum.6. The N-terminal portion (1-12) of galanin seems to permit a steric conformation of the attached NPY (25-36) part of the chimeric galanin-NPY peptides, which results in a facilitated Y2 but not Y1.receptor recognition and activation. None of the galanin-NPY peptides appeared to act as antagonists at either type of NPY receptor, probably due to their low affinity. Instead, they displayed a very high affinity for hypothalamic galanin receptors and probably act as galanin agonists in the rat jejunum.

Subtypes of receptors for neuropeptide Y: implications for the targeting of therapeutics

Neuropeptide Y is a 36 amino acid peptide that was originally discovered in extracts of porcine brain. The peptide has a broad distribution in the central or peripheral nervous system. Receptors for this peptide were originally subdivided into postsynaptic Y-1 receptors and presynaptic Y-2 receptors. The Y-1 receptor has recently been cloned and appears to mediate several effects of NPY including vasoconstriction and an anxiolytic effect in animal models of anxiety. The Y-2 receptor inhibits the release of neurotransmitters in the CNS by the inhibition of the mobilization of intracellular calcium. Additional receptors have been proposed including a Y-3 receptor that recognizes NPY but not the related endocrine peptide, PYY. The functional importance of these newer receptors remains to be established. The absence of useful antagonists has made the study of NPY a challenge for investigators in the field. The potential utility of such molecules is discussed.