[Leu31, Pro34] NPY, a selective functional postjunctional agonist at neuropeptide-Y receptors in anaesthetised rats

Structural basis of neuropeptide Y signaling through Y1 and Y2 receptors

Neuropeptide Y (NPY), a 36-amino-acid peptide, functions as a neurotransmitter in both the central and peripheral nervous systems by activating the NPY receptor subfamily. Notably, NPY analogs display varying selectivity and exert diverse physiological effects through their interactions with this receptor family. [Pro34]-NPY and [Leu31, Pro34]-NPY, mainly acting on Y1R, reportedly increases blood pressure and postsynaptically potentiates the effect of other vasoactive substances above all, while N-terminal cleaved NPY variants in human body primary mediates angiogenesis and neurotransmitter release inhibition through Y2R. However, the recognition mechanisms of Y1R and Y2R with specific agonists remain elusive, thereby hindering subtype receptor-selective drug development. In this study, we report three cryo-electron microscopy (cryo-EM) structures of Gi2-coupled Y1R and Y2R in complexes with NPY, as well as Y1R bound to a selective agonist [Leu31, Pro34]-NPY. Combined with cell-based assays, our study not only reveals the conserved peptide-binding mode of NPY receptors but also identifies an additional sub-pocket that confers ligand selectivity. Moreover, our analysis of Y1R evolutionary dynamics suggests that this sub-pocket has undergone functional adaptive evolution across different species. Collectively, our findings shed light on the molecular underpinnings of neuropeptide recognition and receptor activation, and they present a promising avenue for the design of selective drugs targeting the NPY receptor family.

Neuropeptide y receptor selective ligands in the treatment of obesity

Obesity is a serious public health problem throughout the world, affecting both developed societies and developing countries. The central nervous system has developed a meticulously interconnected circuitry in order to keep us fed and in an adequate nutritional state. One of these consequences is that an energy-dense environment favors the development of obesity. Neuropeptide Y (NPY) is one of the most abundant and widely distributed peptides in the central nervous system of both rodents and humans and has been implicated in a variety of physiological actions. Within the hypothalamus, NPY plays an essential role in the control of food intake and body weight. Centrally administered NPY causes robust increases in food intake and body weight and, with chronic administration, can eventually produce obesity. NPY activates a population of at least six G protein-coupled Y receptors. NPY analogs exhibit varying degrees of affinity and specificity for these Y receptors. There has been renewed speculation that ligands for Y receptors may be of benefit for the treatment of obesity. This review highlights the therapeutic potential of Y(1), Y(2), Y(4), and Y(5) receptor agonists and antagonists as additional intervention to treat human obesity.

Introduction to the reviews on neuropeptide Y

Neuropeptide Y (NPY) was first reported as an abundant peptide in brain tissue in 1982. Shortly thereafter, NPY was found to be a member of a peptide family consisting of the endocrine peptides pancreatic polypeptide (PP) and peptide YY (PYY). These peptides exert most of their biological effects through five G-protein coupled receptors termed Y1, Y2, Y4, Y5 and y6 that mediate either inhibition adenylate cyclase or increases in intracellular calcium. Since the discovery of NPY, a robust a body of literature has developed around the potential functions of this peptide. While initial findings identified NPY is an important contributor to the regulation of feeding, body weight and blood pressure, more recent work as revealed more subtle functions of this peptide and its potential role in affective disorders, bone formation and cravings. The accompanying twelve reviews detail important developments in our understanding of the functional role of NPY.

Angiotensin II modulates the cardiovascular responses to microinjection of NPY Y1 and NPY Y2 receptor agonists into the nucleus tractus solitarii of the rat

The aim of this work was to investigate the modulation of the cardiovascular effects of neuropeptide Y (NPY) in the nucleus tractus solitarii (NTS) by angiotensin II (Ang II) and to determine the NPY receptor subtype involved in this modulation. Anesthesized Sprague-Dawley rats received microinjections in the NTS of Ang II (threshold and ED(50) doses) with NPY Y(1) agonist Leu(31)Pro(34)NPY and NPY Y(2) agonist NPY(13-36) (threshold and ED(50) doses). The changes in mean arterial pressure (MAP) and heart rate (HR) recorded in the femoral artery were analyzed during 60 min after the microinjections. The injection of threshold doses of Ang II, Y(1) agonist or Y(2) agonist alone did not produce any change in cardiovascular parameters. However, the co-injections into the NTS of threshold doses of both Ang II and the Y(1) agonist elicited significant increases of MAP and HR of about 12 and 10%, respectively. The co-administration of threshold doses of Ang II with the Y(2) agonist also induced a significant vasopressor response. The vasodepressor and bradycardiac effect of an ED(50) dose of the Y(1) agonist was significantly counteracted (P<0.01) by a threshold dose of Ang II. The vasopressor effect elicited by an ED(50) dose of the Y(2) agonist was significantly enhanced by a threshold dose of Ang II (P<0.01). No significant change of cardiovascular responses elicited by an ED(50) dose of Ang II was observed in the presence of threshold doses of the Y(1) agonist or of the Y(2) agonist. The present study gives functional evidences for a differential modulatory activity of Ang II on the cardiovascular responses mediated by Y(1) and Y(2) receptor subtypes, which may be of relevance for central cardiovascular regulation in the NTS.

The gut hormone peptide YY regulates appetite

The gut hormone peptide YY (PYY) belongs to the pancreatic polypeptide (PP) family along with PP and neuropeptide Y (NPY). These peptides mediate their effects through the NPY receptors of which there are several subtypes (Y1, Y2, Y4, and Y5). The L cells of the gastrointestinal tract are the major source of PYY, which exists in two endogenous forms: PYY(1-36) and PYY(3-36). The latter is produced by the action of the enzyme dipeptidyl peptidase-IV (DPP-IV). PYY(1-36) binds to and activates at least three Y receptor subtypes (Y1, Y2, and Y5), whereas PYY(3-36) is more selective for Y2 receptor (Y2R). The hypothalamic arcuate nucleus, a key brain area regulating appetite, has access to nutrients and hormones within the peripheral circulation. NPY neurons within the arcuate nucleus express the Y2R. In response to food ingestion plasma PYY(3-36) concentrations rise within 15 min and plateau by approximately 90 min. The peak PYY(3-36) level achieved is proportional to the calories ingested, suggesting that PYY(3-36) may signal food ingestion from the gut to appetite-regulating circuits within the brain. We found that peripheral administration of PYY(3-36) inhibited food intake in rodents and increased C-Fos immunoreactivity in the arcuate nucleus. Moreover, direct intra-arcuate administration of PYY(3-36) inhibited food intake. We have shown that Y2R null mice are resistant to the anorectic effects of peripherally administered PYY(3-36), suggesting that PYY(3-36) inhibits food intake through the Y2R. In humans, peripheral infusion of PYY(3-36), at a dose which produced normal postprandial concentrations, significantly decreased appetite and reduced food intake by 33% over 24 h. These findings suggest that PYY(3-36) released in response to a meal acts via the Y2R in the arcuate nucleus to physiologically regulate food intake.

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.

Sympathetic and parasympathetic interaction in vascular and secretory control of salivary glands in anaesthetised dogs

The present study was undertaken to examine sympathetic-parasympathetic interactions in the regulation of salivary gland function, with special reference to the possible role of the sympathetic cotransmitter neuropeptide Y (NPY). In dogs anaesthetised with pentobarbitone, electrical stimulation of the parasympathetic nerve to the submandibular gland evoked an increase in glandular blood flow and salivary secretion. Sympathetic nerve stimulation evoked a significant prolonged attenuation of vasodilator and secretory responses to subsequent parasympathetic stimulation. This attenuation was not significantly altered by alpha- and beta-adrenoceptor blockade. Systemic administration of the sympathetic cotransmitter, NPY, mimicked the effect of the sympathetic stimulation by significantly attenuating vasodilatation and salivary secretion. The NPY Y1 receptor agonist, [Leu31, Pro34]NPY and the specific NPY Y2 receptor agonist N-acetyl[Leu28, Leu31]NPY 24-36 both significantly attenuated the vasodilatation and salivary secretion evoked by stimulation of the parasympathetic nerve. The NPY Y1 receptor antagonist, GR231118 significantly antagonised the attenuation of vasodilatation caused by both sympathetic stimulation and the NPY Y1 receptor agonist. GR231118 also inhibited the pressor response of NPY. Intra-arterial injection of methacholine and stimulation of the parasympathetic nerve both caused local vasodilatation in the gland which was significantly attenuated by pretreatment with sympathetic stimulation or the NPY Y1 agonist. The NPY Y2-specific agonist did not attenuate methacholine-induced vasodilatation but did attenuate vasodilatation evoked by parasympathetic stimulation. The results indicate that NPY as a sympathetic cotransmitter may have a role in the regulation of vascular secretory function of salivary glands.

Neuropeptide Y1- and Y2-receptor-mediated cardiovascular effects in the anesthetized guinea pig, rat, and rabbit

Neuropeptide Y (NPY) causes vasoconstriction through Y1-receptors and inhibits vagal bradycardia through presynaptic Y2-receptors. These effects of NPY were investigated in anesthetized guinea pigs, rats, and rabbits to find the most suitable species for evaluation of Y1- and Y2-active agents in vivo. The increase in blood pressure (through Y1) of lower doses of NPY was similar in the three species (ED50, 0.9 +/- 0.13, 0.8 +/- 0.39, and 0.6 +/- 0.09 nmol/kg, respectively), but higher doses had depressor effects in four of six rats. Vagal bradycardia, induced by electrical stimulation of the right cervical vagus nerve, was inhibited by NPY in the guinea pig and in the rat (ED35, 3.5 +/- 0.46 and 11.2 +/- 1.79 nmol/kg, respectively; p < 0.05) but not in the rabbit. In the guinea pig, the Y2-receptor-preferring fragment NPY(3-36) and the selective Y1-receptor antagonist H 409/22 were used to confirm that the increase in blood pressure was mediated solely through the Y1-receptor and the vagal inhibition solely through the Y2-receptor. Aside from the cardiovascular effects, NPY caused a decrease in the body temperature and inhibited vagal bronchoconstriction in this species. Considering that NPY may cause depressor effects in the rat and has no effect on the vagal bradycardia in the rabbit, the guinea pig is preferable to both these species for assessment of Y1- and Y2-receptor-active agents in vivo.

Neuropeptide Y in the paraventricular nucleus of the hypothalamus stimulates colonic transit by peripheral cholinergic and central CRF pathways

There is evidence suggesting that neuropeptide Y (NPY) as well as corticotropin-releasing factor (CRF) in the paraventricular nucleus of the hypothalamus (PVN) are involved in the CNS regulation of gastrointestinal (GI) function. We studied the effects of NPY or Y1-and Y2-receptor agonists microinjected into the PVN on colonic transit. Microinjection of NPY into the PVN at doses of 0.15-1.5 microg decreased the colonic transit time of conscious rats up to 49%. Pretreatment with the peripherally acting cholinergic antagonist atropine methyl nitrate (0.1 mg kg-1 i.p.) blocked the NPY into PVN-induced effect on colonic motor function.The agonist of the Y1-receptor, NPY(Leu31, Pro34), as well as the Y2-receptor agonist, NPY(13-36), dose-dependently decreased colonic transit time when microinjected into the PVN (0.05, 0.15 and 0.5 microg). However, the Y1-receptor agonist was more effective. Intracerebroventricular (ICV) application of the CRF-receptor antagonist, alpha-helical-CRF9-41 (50 microg/rat), blocked the NPY effect in the PVN on colonic motor function. In conclusion, stimulation of colonic transit by NPY acting in the PVN was observed. The PVN is more sensitive to agonists acting on the Y1- than on the Y2-receptor to mediate stimulation of propulsive colonic motility. The effect of NPY in the PVN on colonic motor function depends on central CRF and peripheral cholinergic pathways.

The effect of intrathecal selective agonists of Y1 and Y2 neuropeptide Y receptors on the flexor reflex in normal and axotomized rats

We have examined the effects of intrathecal (i.t.) administration of [Leu31,Pro34]-neuropeptide Y (NPY) or NPY-(13-36), selective agonists of NPY Y1 or Y2 receptors, respectively, on the excitability of the flexor reflex in normal rats and after unilateral transection of the sciatic nerve. In rats with intact and sectioned sciatic nerves, i.t. [Leu31,Pro34]-NPY induced a similar biphasic effect on the flexor reflex with facilitation at low doses and facilitation followed by depression at high doses. In contrast, i.t. NPY-(13-36) only facilitated the flexor reflex in normal rats, and at high dose it caused ongoing discharges in the electromyogram. NPY-(13-36) caused dose-dependent depression of the flexor reflex in rats after sciatic nerve transection, in addition to its facilitatory effect. Topical application of [Leu31,Pro34]-NPY or NPY-(13-36) caused a moderate and brief reduction in spinal cord blood flow. No difference was noted between the vasoconstrictive effect of [Leu31,Pro34]-NPY and NPY-(13-36). It is suggested that activation of Y1 receptors may be primarily responsible for the reflex depressive effect of i.t. neuropeptide Y in rats with intact sciatic nerves, whereas both Y1 and Y2 receptors may be involved in mediating the depressive effect of NPY after axotomy.

Cardiorespiratory responses to intracerebroventricular injection of neuropeptide Y in anaesthetised dogs

Cardiovascular and respiratory effects of intracerebroventricular (icv) administration of neuropeptide Y (NPY) and separate, preferential agonists for NPY Y1 and Y2 receptors were observed in anaesthetised dogs. Central injections of NPY resulted in significant cardiac slowing and decreases in arterial pressure. These cardiovascular effects were blocked by central injection of the NPY Y1- preferring antagonist 1229U91. Central injection of NPY did not have a significant effect on ventilation, but the NPY Y1 antagonist 1229U91 administered alone caused a significant increase in ventilation. The NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreased ventilation while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24--36 significantly increased it. A similar inverse relationship was seen with respect to blood pressure, with the NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreasing blood pressure, while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24-36 significantly increased it. These findings suggest a role for NPY Y1 receptors in pathways mediating decreases in ventilation and blood pressure, and for NPY Y2 receptors in those mediating increased ventilation and blood pressure.

Heterogeneity of prejunctional NPY receptor-mediated inhibition of cardiac neurotransmission

Neuropeptide Y (NPY) has been proposed as the candidate inhibitory peptide mediating interactions between sympathetic and vagal neurotransmission in several species, including man. Here, we have defined the NPY receptors involved in modulation of cardiac autonomic neurotransmission using receptor-selective agonists and antagonists in the rabbit and guinea-pig isolated right atria. In isolated atrial preparations, sympathetically-mediated tachycardia (ST; with atropine 1 microM) or vagally-mediated bradycardia (VB; with propranolol 0.1-1 microM) in response to electrical field stimulation (EFS, 1-4 pulses) were tested 0-30 min after incubation with single concentrations of vehicle, NPY (0.01-10 microM), the Y2 receptor agonist N-Acetyl-[Leu28,31]NPY(24-36) (termed N-A[L]NPY(24-36)) or the Y1 receptor agonist [Leu31,Pro34]NPY (LP). The effect of NPY on the concentration-chronotropic response curves to isoprenaline and bethanechol were also assessed. Guinea-pig atria: NPY and N-A[L]NPY(24-36) caused concentration-dependent inhibition of VB and ST to EFS. Both peptides caused maximal inhibition of VB and ST within 10 min incubation and this remained constant. LP caused a concentration-dependent, transient inhibition of ST which was antagonized by the Y1-receptor antagonist GR231118 (0.3 microM), with apparent competitive kinetics. Rabbit atria: NPY (1 or 10 microM) had no effect on VB at any time point, but both NPY and LP caused a transient (approximately 10 min) inhibition of sympathetic tachycardia. This inhibition could be prevented by 0.3 microM GR231118. N-A[L]NPY(24-36) had no effect on ST. NPY had no effect on the response to beta-adrenoceptor stimulation by isoprenaline nor muscarinic-receptor stimulation by bethanechol in either species. Thus, in the guinea-pig, NPY causes a stable inhibition of both VB and ST to EFS via Y2 receptors and transient inhibition of ST via Y1 receptors. In contrast in the rabbit, NPY has no effect on the cardiac vagus and prejunctional inhibition of ST is transient and mediated by a Y1-like receptor (rather than Y2). Therefore it would be surprising if NPY plays a functional role in modulation of cardiac neurotransmission in the rabbit.

Comparative vascular responses in elasmobranchs to different structures of neuropeptide Y and peptide YY

The vascular responses to neuropeptide Y (NPY) and peptide YY (PYY) were tested in several species of elasmobranchs to assess whether changes in sequence in these neuropeptides from elasmobranchs to mammals are associated with different physiological responses. NPY-like immunoreactivity was detected in the gut and in nerve fibres surrounding some, but not all, blood vessels of six species. Intravenous injection of dogfish, frog and human NPY in anaesthetised fish caused similar vasopressor effects in the three species tested, except human NPY which lowered blood pressure in one of the three. Dogfish NPY and PYY were equipotent pressor agents in two species, but PYY was significantly more potent than NPY in one species. NPY and PYY both contracted isolated gut arteries from three species, but had no effect on isolated efferent arteries tested. In conclusion, differential vascular responses in elasmobranchs are not associated with changes in NPY sequence across vertebrates, but may be with changes in PYY in some species.

Exogenous NPY modulation of cardiac autonomic reflexes and its pressor effect in the conscious rabbit

1. Neuropeptide Y (NPY) may inhibit sympathetic and vagal transmission via presynaptic Y2 receptors and cause vasoconstriction via postsynaptic Y1 receptors. We examined the effects of NPY and related peptides on cardiovascular parameters and autonomic reflexes in the conscious rabbit. Further, the postjunctional effects of NPY and related peptides were assessed on acetylcholine (ACh) and isoprenaline agonist dose-chronotropic response curves. 2. In conscious rabbits the cardiac baroreceptor-heart rate reflex (baroreflex), Bezold-Jarisch like and nasopharyngeal reflexes were assessed in control, propranolol-treated or methscopolamine-treated (baroreflex only) groups, before and 30 min after i.v. administration of NPY (10 microg kg[-1] + 5 microg kg[-1] min[-1]) or vehicle (saline, 10 ml h[-1]). The effects of equivalent pressor doses of [Leu31, Pro34]NPY or methoxamine on the baroreflex were also examined. In separate animals, dose-heart rate (HR) response curves to isoprenaline or ACh were constructed before and 15 min after administration of NPY, [Leu31,Pro34]NPY (ACh only) or [Leu31,Pro34]NpY + sodium nitroprusside (ACh only). 3. Administration of NPY-receptor agonists caused sustained bradycardia (in the absence of methscopolamine) and rightward shifts of the barocurves in all 3 groups. The range of sympathetically-mediated tachycardia was significantly decreased by NPY or [Leu31,Pro34]NPY in the methscopolamine-treated group. However, these changes in the baroreflex were no different from those elicted by equipressor doses of methoxamine. There was no vagal inhibition by any NPY-receptor agonist in all three autonomic reflexes examined. ACh or isoprenaline dose-HR response curves were not affected by NPY peptide administration. 4. We conclude that in the conscious rabbit, at a single dose that elicits a significant pressor response, exogenous NPY has no direct effect on modulation of cardiac and autonomic reflexes. Non-specific effects of exogenous NPY on the baroreflex may be fully explained by its pressor action. There was no effect of NPY on postjunctional ACh or isoprenaline agonist dose-response curves. Therefore, it is unlikely that endogenous NPY has a functional role in directly modulating cardiac autonomic neurotransmission in the rabbit.

Evidence for Y1 and Y2 subtypes of neuropeptide Y receptors linked to opposing postjunctional effects observed in rat cardiac myocytes

The aim of this study was to confirm the existence of and identify the receptor subtypes for neuropeptide Y that are present post-junctionally in myocardium. The effects of the selective agonists, [Leu31, Pro34] neuropeptide Y (neuropeptide Y Y1 receptors), neuropeptide Y-(13-36) and peptide YY-(3-36) (neuropeptide Y Y2 receptors), and neuropeptide Y and the related peptide YY, which have differential action at neuropeptide Y Y3 receptors, on amplitudes of contraction of adult rat ventricular cardiomyocytes were studied. Also, the effect of the neuropeptide Y Y1-selective antagonist, bis(31/31')[[Cys31, Trp32, Nva34] neuropeptide Y-(31-36)] on neuropeptide Y-mediated changes in myocyte contraction was investigated. Neuropeptide Y, peptide YY, neuropeptide Y-(13-36) and peptide YY-(3-36) attenuated the isoprenaline (10(-7) M)-stimulated contractile response, and the EC50 values were 9.0 x 10(-9), 4.3 x 10(-10), 3.1 x 10(-11) and 8.5 x 10(-11) M, respectively. [Leu31, Pro34] neuropeptide Y increased the contractile response of cardiomyocytes, and the EC50 values were 8.1 x 10(-9) and 1.5 x 10(-9) M, in the absence and presence of isoprenaline, respectively. Since [Leu31, Pro34] neuropeptide Y caused a positive effect on ventricular myocyte contraction and neuropeptide Y-(13-36) and peptide YY (3-36) produced the most potent negative effects, it is proposed that both neuropeptide Y Y1 and neuropeptide Y Y2 receptors, linked respectively to the positive and negative responses, are expressed in cardiomyocytes. The finding of receptors with neuropeptide Y Y2 characteristics on cardiomyocytes represents a further example of a postjunctional location for this subtype. As there was no significant discrepancy between the potencies of peptide YY and neuropeptide Y to attenuate the contractile response, it appears that neuropeptide Y Y3-like receptors are not linked principally to contractile function in rat cardiomyocytes. Bis(31/31')[[Cys31, Trp32, Nva34] neuropeptide Y-(31-36)] antagonised the neuropeptide Y-mediated stimulation of contractile activity through neuropeptide Y Y1 receptors, but the compound also inhibited the attenuation of isoprenaline-stimulated contraction, apparently by acting as a partial agonist at the neuropeptide Y Y2 receptors.

Activity of centrally truncated analogues of neuropeptide Y at Y1 and Y2 receptor subtypes in vivo

Neuropeptide Y (NPY), a sympathetic cotransmitter, has both prejunctional and postjunctional actions in the cardiovascular system. In anaesthetized rats, the bioassay system used here, NPY attenuates cardiac vagal action (a prejunctional or Y2 action) and increases blood pressure (a postjunctional or Y1 action). Several NPY analogues were tested against NPY. In these, centrally located amino acid sequences of various lengths were removed, and replaced with simpler 'spacers'. As the parent NPY molecule is considered to exist in a U-shape, these central truncations were intended to shorten the depth of the U, while maintaining the integrity of its two ends. The centrally truncated NPY analogues examined here retain activity at both receptor subtypes in vivo. These findings indicate that the U-shape of the parent molecule probably exists to assist stability, but that receptor binding occurs through sequences closer to the termini.

Neuropeptide Y Y2 receptor-mediated attenuation of neurogenic plasma extravasation acting through pertussis toxin-sensitive mechanisms

1. The effects of neuropeptide Y (NPY) receptor agonists (administered intravenously) were examined on plasma protein ([125I]-bovine serum albumin) leakage within dura mater evoked by unilateral trigeminal ganglion stimulation (0.6 mA, 5 ms, 5 Hz, 5 min), capsaicin (1 mumol kg-1, i.v.) or substance P (1 nmol kg-1, i.v.) in anaesthetized Sprague-Dawley rats. 2. NPY (EC50: 5.6 nmol kg-1) and NPY fragment 13-36 [NPY (13-36)] (ED50: 4.3 nmol kg-1), an NPY Y2 receptor agonist, dose-dependently attenuated [125I]-bovine serum albumin extravasation from meningeal vessels when administered 10 min prior to electrical stimulation. [Leu31, Pro34]-NPY, an NPY Y1 and Y3 receptor agonist, inhibited the response at a higher dose only (23 nmol kg-1) (P < 0.05). 3. NPY also significantly decreased plasma protein extravasation induced by capsaicin (1 mumol kg-1) but not by substance P (1 nmol kg-1). 4. Pertussis toxin (20 micrograms kg-1, administered intracisternally 48 h prior to stimulation) blocked completely the inhibitory effect of NPY and NPY (13-36) but did not inhibit extravasation alone. 5. We conclude that NPY inhibits neurogenically-mediated plasma protein extravasation acting through presynaptic pertussis toxin-sensitive NPY Y2 receptors, possibly by inhibition of neuropeptide release from perivascular trigeminovascular afferents.

Cutaneous vasomotor effects of neuropeptide Y

The effects of neuropeptide Y (NPY) were examined on the cutaneous microvascular blood flow (CMF) of the hindpaws in anesthetized rats. NPY (0.5-50 nmol/kg), infused intra-arterially into the hindpaw circulation, produced sustained dose-dependent increases in CMF (29 +/- 7% to 210 +/- 52%) indicating cutaneous vasodilation. Denervation of a hindpaw, ganglionic or alpha-adrenergic blockade significantly elevated the resting CMF indicating tonic vasoconstrictor sympathetic input to the cutaneous vasculature. In the denervated hindpaw or following ganglionic blockade, NPY produced sustained decreases in CMF (up to 51 +/- 8%) indicating vasoconstriction. Effects of the Y1 receptor agonist, (Leu31, Pro34) NPY were identical to those of NPY. The Y2 receptor agonist, NPY13-36 increased CMF of the intact hindpaw (24 +/- 10%-68 +/- 16% at 5-150 nmol/kg, i.a.) but did not affect CMF of the denervated hindpaw. NPY and (Leu31, Pro34)NPY, but not NPY13-36, produced significant pressor effects. These data suggest that: 1) NPY produces neurogenic cutaneous vasodilation via presynaptic Y2 receptor-mediated inhibition of sympathetic tone, 2) Y1 receptors may also exist presynaptically, however, it is likely that (Leu31, Pro34)NPY does not distinguish between Y1 and Y2 receptors, and 3) activation of postsynaptic Y1 receptors produces vasoconstriction which is unmasked only when the noradrenergic tone is eliminated.

Peptides as neurotransmitters in vascular autonomic neurons

1. Neuropeptides are present in the majority of autonomic neurons projecting to blood vessels, where they are co-localized with non-peptide transmitters and sometimes with other peptides. 2. Neuropeptides are released from vasoconstrictor and vasodilator nerve terminals after high frequency stimulation ( > 2-5Hz) with trains of impulses. 3. Neuropeptides can have potent post-synaptic effects on vascular tone, but often these effects are restricted to selected regions of the vasculature. 4. Post-synaptic effects of neuropeptides tend to be more slowly-developing and more long-lasting than those of non-peptide transmitters. 5. Autonomic vasoconstrictor and vasodilator responses often have multiple phases, with the faster phases being mediated by non-peptide transmitters and the slower phases medicated predominantly by one or more neuropeptides. 6. Some neuropeptides do not seem to have post-synaptic effects in a particular vascular bed, but can have presynaptic actions on neurotransmitter release. 7. Neuropeptides form an important component of the repertoire of neurotransmitters used by vascular autonomic neurons to regulate regional blood flow in response to a range of physiological stimuli.

Increased vasopressor actions of intraventricular neuropeptide Y-(13-36) in spontaneously hypertensive versus normotensive Wistar-Kyoto rats. Possible relationship to increases in Y2 receptor binding in the nucleus tractus solitarius

The C-terminal NPY fragment (13-36)[NPY-(13-36)], a Y2 receptor agonist, elicits vasopressor responses upon central administration. The cardiovascular responses of NPY-(13-36) together with the distribution of NPY receptor subtypes within the nucleus tractus solitarius (nTS) have therefore been studied in spontaneously hypertensive rats (SHR). NPY-(13-36) was injected intracerebro-ventricularly in different doses (7.5 to 3000 pmol) in awake, unrestrained rats to evaluate the cardiovascular effects. NPY receptor subtypes were studied by autoradiography using [125I]peptide YY ([125I]PYY) as a radioligand and by masking the NPY Y1 and Y2 receptor subtypes with unlabelled [Leu31,Pro43]NPY and NPY-(13-36) respectively. In both male SHR and age-matched male normotensive Wistar-Kyoto rats (WKY) NPY-(13-36) injections elicited vasopressor effects. In WKY this effect was dose-dependent and became significant at doses from 75 pmol, whereas in the SHR the vasopressor effect had a longer duration than in the WKY and became significant at lower doses (25 pmol) but associated with the development of an early ceiling effect. The heart rate was unaffected in both groups of rats. Total specific [125I]PYY binding in the nTS was 25% higher in SHR than in WKY rats. By masking the Y1 and Y2 receptor subtypes respectively it could be shown that this difference was due to an increase in Y2 receptor binding within the nTS. The present results give evidence for an increased potency but not an increased efficacy of NPY-(13-36) in inducing a pressor response in the SHR associated with a longer duration as compared with the WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog ANA-NPY

Neuropeptide Y analog ANA-NPY or [Leu-17, Gln-19, Ala-20, Ala-23, Leu-28, Leu-31]NPY(13-36)-amide binds to postjunctional or Y1 receptors to raise blood pressure and to prejunctional or Y2 receptors to inhibit neurotransmitter release. ANA-NPY affects Y2 receptors in the same way as intact NPY but exhibits far less potent effects on Y1 receptors. The structure of ANA-NPY was examined using two-dimensional proton nuclear magnetic resonance spectroscopy. Complete assignment of all backbone and side chain hydrogens was accomplished with totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), providing the through-space and sequential backbone connectivities. The tertiary solution structure of the peptide was performed using distance geometry and dynamic simulated annealing. ANA-NPY exhibits a helical structure with strong amphipathic character with a bend around Glu-24 indicating that the C-terminal segment 25-35 forms a single alpha-helical motif.

Neuropeptide Y and galanin binding sites in rat and monkey lumbar dorsal root ganglia and spinal cord and effect of peripheral axotomy

Using monoiodinated peptide YY (PYY) and galanin as radioligands, and neuropeptide Y (NPY) fragments, the distribution of NPY binding sites and its subtypes Y1 and Y2, and of galanin binding sites, was investigated in rat and monkey lumbar (L) 4 and L5 dorsal root ganglia (DRG) and spinal cord before and after a unilateral sciatic nerve cut, ligation or crush. Receptor autoradiography revealed that [125I]PYY bound to some DRG neurons and a few nerve fibres in normal rat DRG, and most of these neurons were small. NPY binding sites were observed in laminae I-IV and X of the rat dorsal horn and in the lateral spinal nucleus, with the highest density in laminae I-II. [125I]PYY binding was most strongly attenuated by NPY13-36, a Y2 agonist, and partially inhibited by [Leu31,Pro34]NPY, a Y1 agonist, in both rat DRG and the dorsal horn of the spinal cord. These findings suggest that Y2 receptors are the main NPY receptors in rat DRG and dorsal horn, but also that Y1 receptors exist. After sciatic nerve cut, PYY binding markedly increased in nerve fibres and neurons in DRG, especially in large neuron profiles, and in laminae III-IV of the dorsal horn, as well as in nerve fibres in dorsal roots and the sciatic nerve. Incubation with NPY13-36 completely abolished PYY binding, which was also reduced by [Leu31,Pro34] NPY. However, the increase in PYY binding seen in laminae I-IV of the ipsilateral dorsal horn after axotomy was not observed after coincubation with [Leu31,Pro34] NPY. NPY binding sites were seen in a few neurons in monkey DRG and in laminae I-II, X and IX of the monkey spinal cord. The intensity of PYY binding in laminae I-II of the dorsal horn was decreased after axotomy. Galanin receptor binding sites were not observed in rat DRG, but were observed in the superficial dorsal horn of the spinal cord, mainly in laminae I-II. Axotomy had no effect on galanin binding in rat DRG and dorsal horn. However, galanin receptor binding was observed in many neurons in monkey L4 and L5 DRG and in laminae I-IV and X of monkey L4 and L5 spinal cord, with the highest intensity in laminae I-II. No marked effect of axotomy was observed on the distribution and intensity of galanin binding in monkey DRG or spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Peripheral hyperalgesia in experimental neuropathy: exacerbation by neuropeptide Y

Injury of peripheral nerves often results in hyperalgesia (an increased sensitivity to painful stimuli). This hyperalgesia is mediated in part by sympathetic neurotransmitters. We examined the effect of neuropeptide Y (NPY), specific Y1 and Y2 agonists, and an NPY antagonist on peripheral hyperalgesia in rats whose sciatic nerves had been partially transected. NPY and the Y2 agonist, N-acetyl [Leu28,Leu31] NPY 24-36 exacerbated both mechanical and thermal hyperalgesia, while the Y1 agonist, [Leu31, Pro34]NPY relieved thermal hyperalgesia. Mechanical and thermal hyperalgesia were both relieved by alpha-trinositol (PP56), a non-competitive antagonist of the actions of neuropeptide Y. Hyperalgesia was also relieved by surgical sympathectomy, which eliminated the effects of NPY and its agonists. These results suggest that neuropeptide Y contributes to peripheral hyperalgesia by actions at Y2 receptors, which may be located on postganglionic sympathetic terminals.

Antagonistic regulation of alpha 2-adrenoceptors by neuropeptide Y receptor subtypes in the nucleus tractus solitarii

The modulation of alpha 2-adrenoceptors by neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtypes has been studied in the nucleus tractus solitarii of the male rat. The autoradiographical experiments showed that neuropeptide Y-(1-36), neuropeptide Y-(13-36), a selective neuropeptide Y Y2 receptor agonist, and [Leu31,Pro34]neuropeptide Y, a selective neuropeptide Y Y1 receptor agonist, in the nanomolar range increased the Kd value of the [3H]p-aminoclonidine binding sites in the above rank order of potency without changing the Bmax values. In contrast, in the competition experiments, the neuropeptide Y Y1 and the neuropeptide Y Y2 receptor agonists decreased and increased, respectively, with the same potency the IC50 value of l-adrenaline and especially of clonidine for the alpha 2-adrenoceptor agonist binding sites associated with an increase and a decrease of the B0 value, respectively. Cardiovascular experiments showed that microinjections of clonidine into the nucleus tractus solitarii induced dose-dependent vasodepressor and bradycardiac responses. Threshold doses for vasodepressor effects of neuropeptide Y-(1-36) and of the neuropeptide Y Y1 receptor agonist and for vasopressor effects of the neuropeptide Y Y2 receptor agonist significantly counteracted the vasodepressor action elicited by an ED50 dose of clonidine in the nucleus tractus solitarii, the bradycardiac action of clonidine also being counteracted by the neuropeptide Y Y2 but not the neuropeptide Y Y1 receptor agonist. The present results give indications for the existence of an antagonistic modulation of high affinity alpha 2-adrenoceptors by the neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtype in the nucleus tractus solitarii which may contribute to a reduction of alpha 2-adrenoceptor-mediated cardiovascular depression.

Stabilized structure of the presynaptic (Y2) receptor-specific neuropeptide Y analog N-acetyl[Leu-28,Leu-31]NPY(24-36)

Neuropeptide Y analog N-acetyl[Leu-28,Leu-31]NPY(24-36)-amide binds specifically to prejunctional or Y2 receptors acting to inhibit neurotransmitter release. The structure of this biologically active mutant was studied by two-dimensional proton nuclear magnetic resonance spectroscopy. Assignments of all backbone and side chain hydrogens were made by using totally correlated spectroscopy (TOCSY) experiments providing through-bond 1H-1H connectivities, and nuclear Overhauser effect spectroscopy (NOESY), which provided through-space and sequential backbone connectivities. Structure analysis of the peptide was performed using distance geometry and dynamic simulated annealing revealing the presence of a helical structure exhibiting an amphiphilic character and slight constriction in the segment 24-29.

A novel neuropeptide Y analog, N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36), with functional specificity for the presynaptic (Y2) receptor

We have carried out functional and in vitro studies on a novel analog of neuropeptide Y which shows selectivity for the prejunctional or neuropeptide Y Y2 receptor. In anaesthetised rats N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) attenuates cardiac vagal action (a prejunctional or neuropeptide Y Y2 action) and has no significant pressor effects (postjunctional or neuropeptide Y Y1 action). In the human neuroblastoma cell line (SMS-KAN) which expresses and endogenous Y2-like neuropeptide Y receptor, N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) competes with peptide YY for binding sites with an IC50 of 0.5 +/- 0.1 nM. In contrast in a fibroblast Chinese hamster ovary cell line which expresses the cloned human neuropeptide Y Y1 receptor and is used to study changes in cytosolic calcium evoked by (a neuropeptide Y Y1 effect), N-acetyl [Leu28,Leu31]neuropeptide Y-(24-36) showed no activity even at high concentrations. The steric structure for this novel compound has been determined using proton nuclear magnetic resonance (NMR) spectroscopy and it is consistent with the C-terminal end of published structures of neuropeptide Y. We suggest acetylation and amino acid substitutions stabilise the molecule and allow it to bind only to the neuropeptide Y Y2 receptor.

Effect of peripheral axotomy on expression of neuropeptide Y receptor mRNA in rat lumbar dorsal root ganglia

Using in situ hybridization, the expression of the mRNA for a neuropeptide Y (NPY) receptor, was studied in lumbar (L) 4 and 5 dorsal root ganglia (DRGs) of normal rats and at various intervals after unilateral sciatic nerve transection. Twenty percent of all normal DRG neurons were NPY receptor mRNA-positive, and the majority of these neurons were of the small type, with only a few labelled medium-sized and large neurons. In L5 normal ganglia NPY receptor mRNA colocalized with substance P, calcitonin gene-related peptide and galanin mRNAs in small neurons, but not in medium-sized or large neurons containing these peptides. NPY receptor mRNA was not observed in somatostatin or nitric oxide synthase mRNA-positive neurons. Sciatic nerve transection induced a marked decrease in NPY receptor mRNA levels. However, in parallel there was a transient increase in the number of NPY receptor mRNA-positive small neuron profiles, but the intensity of labelling was mostly very low, although a few strongly labelled, small neuron profiles were also encountered. In addition, axotomy caused a marked increase in the number of NPY receptor mRNA-positive large neuron profiles in the ipsilateral DRGs, and they constituted 15-20% of counted DRG neuron profiles and 45-65% of counted large neuron profiles, 7-28 days after axotomy. In L5 DRGs, ipsilateral to the axotomy, NPY receptor mRNA colocalized with NPY mRNA in many large and some medium-sized neuron profiles, with galanin mRNA in some small, medium-sized and large neuron profiles and with vasoactive intestinal polypeptide mRNA in some small and medium-sized neuron profiles and a few large profiles. Occasionally, NPY receptor mRNA was observed in nitric oxide synthase mRNA-positive small neurons. In the dorsal horn, NPY receptor mRNA-positive small neurons were concentrated in lamina II at L4 and L5 levels, and were scattered in deeper laminae. No marked changes were observed ipsilateral to the axotomy. No NPY receptor mRNA-positive cells were found in the normal rat gracile nucleus, or in this nucleus after axotomy. These results show that a NPY receptor may be a prejunctional receptor in primary afferent neurons and play a role in the modulation of somatosensory information, both in normal and lesioned primary afferent DRG cells. However, axotomy induced a distinct shift in NPY receptor mRNA expression from small to large neurons, indicating that sensitivity to NPY is switched from one modality to another.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the NPY receptors mediating vasoconstriction of the guinea-pig uterine artery and thoracic vena cava using a range of NPY analogues

The ability of analogues of neuropeptide Y (NPY) to produce direct vasoconstriction, or to antagonize NPY constrictions, was examined in isolated segments of the thoracic vena cava and the uterine artery of guinea-pigs, where NPY mediates a slow phase of sympathetic vasoconstriction. [Leu31,Pro34]NPY, NPY(13-36) and NPY(18-36) all contracted the uterine artery and the vena cava. Contractions produced by [Leu31,Pro34]NPY were similar in time course to those produced by porcine NPY (pNPY), although contractions produced by NPY(13-36) or NPY(18-36) typically were slower than pNPY contractions. In both vessels the order of potency of the agonists was pNPY > or = [Leu31,Pro34]NPY > NPY(13-36) > NPY(18-36). High concentrations (10(-5)mol.l-1) of pNPY or [Leu31,Pro34]NPY produced desensitization of contractions of the uterine artery produced by NPY(13-36). The reported NPY receptor antagonists, PYX-1 and PYX-2 (5 x 10(-6)mol.l-1), slightly reduced (by 21-47%) the magnitude of constrictions produced by exogenous pNPY (1-3 x 10(-8) mol.l-1) in both the uterine artery and the vena cava. These results show that the NPY receptors mediating slow sympathetic vasoconstriction of both the uterine artery and the vena cava are likely to be predominantly Y1 receptors, despite differences between the adrenoceptors mediating sympathetic responses in the two blood vessels.

Antagonism of pre- and postjunctional responses to neuropeptide Y and sympathetic stimulation by D-myo-inositol-1,2,6-trisphosphate in the anaesthetised dog

Pre- and postjunctional responses to nerve released or exogenous neuropeptide Y (NPY) were measured in the anaesthetised dog before and after administration of D-myo-inositol-1,2,6-trisphosphate (PP56) a putative NPY antagonist. The inhibition of the increase in pulse interval evoked by vagal stimulation was used as a measure of prejunctional action of NPY and the magnitude of increase in blood pressure was used as a measure of postjunctional action of NPY (direct action or constrictor potentiating). Elevated plasma levels of PP56 were maintained throughout the course of the experiment. PP56 significantly reversed the inhibitory effect of NPY (nerve released or exogenous) on cardiac vagal action, and significantly inhibited the pressor response to exogenous NPY. PP56 did not affect the pressor response to intravenous phenylephrine, a selective alpha-adrenoceptor agonist. PP56 therefore significantly antagonises both pre- and postjunctional effects of NPY (nerve released and exogenous) and, with respect to its postjunctional antagonism, this action is selective for NPY.