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.

Pitfalls using metalloporphyrins in carbon monoxide research.

The proposal that endogenously produced carbon monoxide (CO) may act as a biological messenger has remained controversial. Carbon monoxide is generated by haem oxygenase isoenzymes in the degradation of haem-containing molecules. Certain metalloporphyrins, which are inhibitors of haem oxygenase, have been widely used as pharmacological tools in order to establish a messenger role for CO in the brain and periphery. However, increasing evidence shows that many metalloporphyrins are also associated with a large range of undesired effects, which make the interpretation of results using such compounds very uncertain. In this article, Lars Grundemar and Lars Ny evaluate the properties and describe the nonselective effect profile of such metalloporphyrins.

Effects of various neuropeptide Y/peptide YY fragments on electrically-evoked contractions of the rat vas deferens.

1. The effects of various neuropeptide Y (NPY) and peptide YY (PYY) fragments on electrically-evoked twitches in the rat isolated vas deferens were studied and compared with the effects of full length NPY and PYY. The aim was to identify the shortest NPY/PYY fragments that are capable of suppressing the contractions. 2. NPY (1-36) and C-terminal fragments of NPY (from 11-36 to 22-36) suppressed the electrically-evoked twitches in a concentration-dependent manner. On the whole there seemed to be a gradual lowering of the pIC50 values with progressive shortening of the NPY fragments (except for fragments 16-36 and 22-36 that had rather high pIC50 values). NPY 23-36, 24-36 and 25-36 suppressed the twitches at high concentrations (3 microM). NPY 26-36 was without effect as were C-terminal carboxy-deaminated NPY and glycine extended NPY (NPY-Gly-Lys-Arg). 3. PYY (1-36) and C-terminal fragments of PYY (from 11-36 to 23-36) suppressed the electrically-evoked twitches in a concentration-dependent manner. PYY 1-36 was more potent than any of the fragments. There was a tendency for shorter fragments to have lower pIC50 values. PYY 24-36 and 25-36 suppressed the twitches at high concentrations (3 microM). PYY 26-36 was without effect. 4. The findings suggest that the 12 C-terminal amino acid residues of NPY and PYY are the minimum length required to activate the Y2-receptor.

Neuropeptide Y, peptide YY and C-terminal fragments release histamine from rat peritoneal mast cells.

1. Neuropeptide Y (NPY) and peptide YY (PYY) seem to act on at least two receptor subtypes, Y1 and Y2. The Y1-receptor requires the whole C-terminally amidated NPY/PYY molecule whereas the Y2-receptor in addition recognizes C-terminal fragments of the two peptides. The present study was designed to elucidate whether NPY and related peptides were able to release histamine from isolated peritoneal mast cells of the rat. 2. NPY, NPY 15-36, NPY 22-36, NPY 26-36 and desamido-NPY evoked a concentration-dependent release of mast-cell histamine. The pEC15 values for NPY 15-36 and NPY 22-36 were higher, while the pEC15 value for NPY 26-36 was lower than that for NPY. At the highest concentration tested (0.1 mM), NPY and its C-terminal fragments released between 30 and 40% of the total histamine content. At the same concentration desamido-NPY released about 20%. 3. PYY and PYY 15-36 also evoked a concentration-dependent release of mast-cell histamine. PYY was more effective than PYY 15-36 since, at 0.1 mM, PYY released about 33%, while PYY 15-36 released about 15% of the total histamine content. Pancreatic polypeptide (PP) and the Y1-receptor-selective agonist [Pro34]NPY were virtually inactive. 4. The effect profile of the NPY/PYY-related peptides suggests that they act on the mast cells by a mechanism that does not involve either of the receptor subtypes hitherto described. The kinetics of the NPY-evoked histamine release may suggest that positively charged amino acid residues of NPY/PYY release mast-cell histamine by a non-receptor mechanism, as has been suggested for substance P and other basic peptides.

Vascular effects of helodermin, helospectin I and helospectin II: a comparison with vasoactive intestinal peptide (VIP).

1. Helodermin, helospectin I and helospectin II, peptides recently isolated from the salivary gland venom of Heloderma suspectum, were compared to vasoactive intestinal peptide (VIP) with respect to effects on systemic blood pressure and on isolated femoral arteries in the rat. 2. They all reduced blood pressure in a dose-dependent manner; helodermin was less effective than VIP. However, at doses higher than 1 nmol kg-1 all four peptides reduced blood pressure to about the same extent. 3. The half-life of the hypotensive effect of VIP was longer than that of helodermin and the helospectins. 4. VIP and helodermin were equally potent in relaxing femoral arteries precontracted with phenylephrine or prostaglandin F2 alpha. 5. Helospectin I and II relaxed phenylephrine-contracted vessels to the same extent as VIP but with a lower potency. 6. Addition of VIP 1 microM to preparations exposed to helodermin 1 microM or to either of the helospectins did not produce a further relaxation. 7. The findings indicate that VIP, helodermin and helospectin I and II have a similar profile of action and therefore may act on a common receptor.

Inhibition by zinc protoporphyrin-IX of receptor-mediated relaxation of the rat aorta in a manner distinct from inhibition of haem oxygenase.

1. Carbon monoxide (CO), produced by haem oxygenase through degradation of haem, has been claimed to be a neuromessenger and a possible regulator of vascular tone. We examined whether the haem oxygenase inhibitor, zinc protoporphyrin-IX (ZnPP) and other porphyrins affect the relaxation evoked by various agents in the rat isolated aorta. 2. Pretreatment with ZnPP (0.1 mM) virtually abolished the relaxation evoked by vasoactive intestinal peptide (VIP) and atrial natriuretic peptide (ANP). ZnPP also evoked a rightward shift of the concentration-response curve for the relaxation induced by acetylcholine. 3. In contrast, ZnPP did not affect the relaxation evoked by forskolin and 3-morpholino-sydnonimine, agents which directly activate adenylate and guanylate cyclase, respectively. 4. Although, less effective than ZnPP, tin protoporphyrin-IX (SnPP; 0.1 mM) and protoporphyrin-IX (PP; 0.1 mM) also attenuated the VIP-evoked relaxation. 5. The elevation of cyclic AMP and cyclic GMP levels evoked by VIP and ANP, respectively, were abolished by pretreatment with ZnPP (0.1 mM). 6. ZnPP, SnPP and PP did not affect the contraction evoked by phenylephrine. 7. The results show that ZnPP inhibits relaxation induced by VIP, ANP and acetylcholine, probably by interfering with membrane receptor-coupled signal transduction pathways. This inhibition does not seem to be dependent upon inhibition of haem oxygenase. The lack of specificity of the haem oxygenase inhibiting metalloporphyrins makes them less suitable as pharmacological tools in the investigation of a messenger role for CO.

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.

Ocular inflammation induced by electroconvulsive treatment: contribution of nitric oxide and neuropeptides mobilized from C-fibres.

1. Electroconvulsive treatment (ECT) of rabbits produced ocular inflammation consisting of conjunctival hyperaemia, miosis and protein extravasation into the aqueous humour, reflected by the so-called aqueous flare response (AFR): the maximal reduction in pupil size was 3.8 +/- 0.1 mm (s.e. of mean, n = 16) while the maximal AFR was 28.1 +/- 2.8 (arbitrary units). 2. ECT also caused release of substance P (SP), pituitary adenylate cyclase-activating peptide (PACAP)-27, -38 and calcitonin gene-related peptide (CGRP). The concentrations of SP and CGRP in the aqueous humour of normal, untreated eyes were 10.6 +/- 1.4 and 117.4 +/- 12.4 pmol l-1, respectively, while the concentrations of PACAP-27 and -38 were below the detection limit. After ECT the concentrations of SP, PACAP-27, -38 and CGRP were 65.0 +/- 9.6, 46.9 +/- 8.4, 50.2 +/- 5.4 and 1109.9 +/- 133.1 pmol l-1, respectively (s.e. of mean, n = 12). Conceivably, ECT evoked an antidromic activation of sensory neurones in the trigeminal ganglion with the consequent release of neuropeptides from C-fibres in the uvea and the development of neurogenic inflammation. 3. Rabbits received the nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME, 200 mg kg 1, i.v.). This pretreatment inhibited the ECT-evoked conjunctival hyperaemia, miosis and AFR: under these circumstances the maximal reduction in pupil size was 1.9 +/- 0.1 mm while the maximal AFR was 2.7 +/- 0.9 (n = 16). L-NAME also inhibited the ECT-evoked release of SP, PACAP-27, -38 and CGRP into the aqueous humour; the concentrations of SP and CGRP were 13.2 +/- 1.5 and 204.8 +/- 33.5 pmol l-1, respectively, while PACAP-27 and -38 were below the detection limit (n = 12). 4. The ECT-evoked miosis was also inhibited by pretreatment with the tachykinin receptor antagonist D-Pal9 spantide 11 (90 nmol, intravitreal injection); under these circumstances the maximal reduction in pupil size was only 0.7 +/- 0.03 mm, indicating an important role for SP in the miotic response. Pretreatment of the eye with capsaicin, which is known to cause functional ablation of C-fibres, inhibited the conjunctival hyperaemia, miosis and AFR by 40-50%; the maximal reduction in pupil size being 2.2 +/- 0.2 mm and the maximal AFR 13.8 +/- 2.1 (arbitrary units) (n = 8). 5. The results suggest (1) that ECT evokes ocular inflammation through antidromic C-fibre activation; (2) that SP contributes to the ECT-evoked miosis; and (3) that NO contributes to the antidromic C-fibre activation and possibly to the vascular responses mediated by the C-fibre transmitters.

Characterization of vascular neuropeptide Y receptors.

1. In the present study we compared neuropeptide Y (NPY) and NPY-related analogues for their ability to activate or bind to vascular NPY receptors in four experimental set-ups. Previous results have suggested the existence of different receptor subtypes, Y1 receptors requiring full-length NPY (1-36) or [Pro34]-NPY, and Y2 receptors recognizing also N-terminally truncated forms of NPY but not [Pro34]-NPY. 2. NPY 1-36 and [Pro34]-NPY dose-dependently increased arterial pressure in the anaesthetized rat with a similar magnitude and potency. NPY 2-36 was much less potent than NPY 1-36. NPY 4-36 and NPY 11-36 were inactive even at a dose as high as 10 nmol kg-1. 3. NPY 1-36, [Pro34]-NPY, NPY 2-36 and NPY 5-36 concentration-dependently increased the coronary resistance in the Langendorff preparation of the rat. NPY 1-36 and [Pro34]-NPY were equipotent, while NPY 2-36 and NPY 5-36 were about 7 and 20 times less potent. At 0.3 microM, NPY 11-36, NPY 20-36 and NPY 22-36 induced a slight contraction while NPY 23-36 was inactive. 4. NPY 1-36, [Pro34]-NPY, NPY 2-36, NPY 4-36, NPY 5-36 and NPY 11-36 evoked concentration-dependent contractions in the isolated inferior caval vein of the rat and guinea-pig. [Pro34]-NPY was more potent than NPY 1-36. NPY 2-36 was equipotent with NPY 1-36, while NPY 4-36, NPY 5-36 and NPY 11-36 were approximately 30 times less potent.5. [Pro34]-NPY was equipotent with NPY 1-36 in displacing the '25I-labelled gut hormone peptide([1251]-PYY) from rat aortic smooth muscle cells, while NPY 2-36 and shorter forms of NPY were much less potent or inactive.6. In caval vein smooth muscle cells of the rat, the displacement pattern was more complex than in aortic smooth muscle cells, in that both [Pro34]-NPY and NPY 13-36 effectively displaced the radioligand,albeit none of them completely.7. In conclusion, the NPY-evoked pressor response in the whole rat and coronary vessels seems to be mediated by vascular Y1 receptors and the binding characteristics of the NPY-related peptides in the aortic smooth muscle cells correspond to a population of such receptors. In the caval vein, the profile of the bioactivity and the binding affinity of the NPY-related peptides suggest a mixed population of Y1/Y2 receptors.

Localization and activity of haem oxygenase and functional effects of carbon monoxide in the feline lower oesophageal sphincter.

1. In the feline lower oesophageal sphincter (LOS), the distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO)-1 and -2 was studied by immunohistochemistry and confocal microscopy, the HO activity was measured and the possible role for CO as a mediator of relaxation was investigated. 2. HO-2 immunoreactivity was abundant in nerve cell bodies of the submucosal and myenteric plexus. Approximately 50% of the HO-2-containing myenteric cell bodies were also nitric oxide synthase- and vasoactive intestinal peptide (VIP)-immunoreactive. In addition, HO-2 immunoreactivity was seen in nerve fibres, in non-neuronal cells dispersed in the smooth muscle and in arterial endothelium. HO-1 immunoreactivity was confined to non-neuronal cells in the smooth muscle, similar to those positive for HO-2. 3. Activity of HO, measured as CO production, was observed in LOS homogenates at a rate of 1.00 +/- 0.05 nmol mg-1 protein h-1. This production was inhibited by the HO inhibitor, zinc protoporphyrin-IX (ZnPP). 4. In isolated circular smooth muscle strips of LOS, developing spontaneous tone, exogenously administered CO evoked a concentration-dependent relaxation reaching a maximum of 93 +/- 3%. This relaxation was accompanied by an increase in cyclic GMP, but not cyclic AMP levels. The relaxant response was attenuated by methylene blue, but unaffected by tetrodotoxin. Repeated exposure to CO resulted in a progressive reduction of the relaxant response. 5. ZnPP caused a rightward-shift of the concentration-response curves for the relaxant responses to VIP, peptide histidine isoleucine, and pituitary adenylate cyclase activating peptide 27. 6. ZnPP and tin protoporphyrin-IX (another inhibitor of HO) did not affect nonadrenergic, noncholinergic relaxations induced by electrical field stimulation. Nor did ZnPP affect relaxations induced by 3-morpholino-sydnonimine or forskolin. 7. The present findings, showing localization of HO immunoreactivity to both neuronal and nonneuronal cells of the feline LOS, ability of LOS to produce CO and a relaxant effect of CO in circular LOS muscle, suggest a role for CO as a peripheral messenger.

Suppression by neuropeptide Y of capsaicin-sensitive sensory nerve-mediated contraction in guinea-pig airways.

1. In the present study we have examined whether neuropeptide Y (NPY) interferes with non-adrenergic, non-cholinergic nerve-mediated contractions and relaxations in the guinea-pig airways. In these experiments we have used ring preparations of bronchi and trachea, incubated in the presence of atropine, propranolol and indomethacin (each 1 microM). 2. The contractile response to electrical stimulation of non-adrenergic, non-cholinergic nerve fibres was suppressed by NPY and NPY 13-36 in a concentration-dependent manner, these agents having similar inhibitory potencies. NPY caused a more complete inhibition than the C terminal fragment. 3. NPY affected neither the basal tension nor the substance P-evoked contraction in the bronchi and trachea and did not interfere with nerve-mediated, non-adrenergic relaxation in the trachea. 4. On the basis of these results, it is suggested that NPY may act on the terminals of sensory neurones in the airways to prevent antidromic, excitatory neurotransmission by inhibiting transmitter release.

Characterization of Y3 receptor-mediated synaptic inhibition by chimeric neuropeptide Y-peptide YY peptides in the rat brainstem.

1. Neuropeptide Y (NPY) and peptide YY (PYY) act at receptors referred to as Y1 and Y2, while the Y3 receptor is specific to NPY and does not recognize PYY. The effects of NPY, its related peptides and a series of newly constructed chimeric NPY-PYY peptides were examined on excitatory and inhibitory postsynaptic currents (e.p.s.cs and i.p.s.cs, respectively) in rat dorsomedial nucleus tractus solitarius (NTS) neurones recorded in coronal brainstem slices. Monosynaptic activity was evoked by electrical stimulation in the region of the tractus solitarius. 2. NPY (5-500 nM) inhibited e.p.s.cs and i.p.s.cs in a concentration-dependent manner. In contrast, PYY (500 nM) failed to affect either e.p.s.cs or i.p.s.cs. The N- and C-terminal parts of a series of chimeric NPY-PYY peptides were joined at positions where NPY and PYY sequences differ. In binding experiments the chimeric peptides were all about equipotent with NPY and PYY in displacing [125I]-PYY from Y1 and Y2 binding sites on SK-N-MC cells and rat hippocampus respectively. 3. In the whole cell voltage clamp recordings of NTS neurones, NPY(1-23)-PYY(24-36) and NPY(1-14)-PYY(15-36) evoked a concentration-dependent inhibition of e.p.s.cs and i.p.s.cs, while NPY(1-7)-PYY(8-36) and NPY(1-3)-PYY(4-36) were inactive. The only differences in amino acid residues between NPY(1-14)-PYY(15-36) and NPY(1-7)-PYY(8-36) reside in positions 13 and 14. 4. Furthermore, [Pro34]NPY (500 nM) was equivalent in potency to NPY itself at inhibiting monosynaptic transmission in NTS, while [Leu31,Pro34]NPY and pancreatic polypeptide (both at 500 nM) failed to affect synaptic transmission. 5. The present study has shown that NPY acts at Y3 receptors to suppress both excitatory and inhibitory currents in the NTS. The different efficacy of the chimeric NPY-PYY peptides suggests that positions 13 and 14 are of great importance for Y3 receptor recognition. Finally, this receptor type readily recognizes [Pro34]NPY, but not [Leu31,Pro34]NPY.

Neuropeptide Y receptor subtypes, Y1 and Y2.

Heterogeneity among NPY (and PYY) receptors was first proposed on the basis of studies on sympathetic neuroeffector junctions, where NPY (and PYY) can exert three types of action: 1) a direct (e.g., vasoconstrictor) response; 2) a postjunctional potentiating effect on NE-evoked vasoconstriction; and 3) a prejunctional suppression of stimulated NE release; the two latter phenomena are probably reciprocal, since NE affect NPY mechanisms similarly. It was found that amidated C-terminal NPY (or PYY) fragments, e.g., NPY 13-36, could stimulate selectively prejunctional NPY/PYY receptors, which were termed Y2-receptors. Consequently, the postjunctional receptors which were activated poorly by NPY/PYY fragments, were termed Y1-receptors. Later work has indicated that the Y2-receptor may occur postjunctionally in selected sympathetic effector systems. The central nervous system appears to contain a mixture of Y1- and Y2-receptors as indicated by functional as well as binding studies. For instance, NPY and NPY 13-36 produced diametrically opposite effects on behavioral activity, indicating the action of the parent peptide on two distinct receptors. Cell lines, most importantly neuroblastomas, with exclusive populations of Y1- or Y2-receptors, have been characterized by binding and second messenger studies. In this work, selective agonists for the two receptor subtypes were used. Work of many investigators has formed the basis for subclassifying NPY/PYY effects being mediated by either Y1- or Y2-receptors. A preliminary subclassification based on effects of NPY, PYY, fragments and/or analogs is provided in Table 6. It is, however, to be expected that further receptor heterogeneity will be revealed in the future. It is argued that mast cells possess atypical NPY/PYY receptors. The histamine release associated with stimulation of the latter receptors may, at least in part, underlie the capacity of NPY as well as of short C-terminal fragments to reduce blood pressure. Fragments, such as NPY 22-36, appear to be relatively selective vasodepressor agents because of their weak vasopressor properties.(ABSTRACT TRUNCATED AT 400 WORDS)

Modulation of carbon monoxide production and enhanced spatial learning by tin protoporphyrin.

Endogenous carbon monoxide (CO), produced by haem oxygenase (HO), may play a role in hippocampal long-term potentiation (LTP). Its role in learning and memory in intact animals is less well known. Tin protoporphyrin (Sn-PP; 25 mg kg-1, i.p.) effectively but transiently inhibited HO activity in brain homogenates, and improved acquisition in the Morris water maze. Locomotor activity was unaffected, indicating a behavioural specificity of the learning effect. The analogue zinc protoporphyrin (25 mg kg-1, i.p.), which does not pass the blood-brain barrier, did not affect learning. If the observed memory effect is related to inhibition of HO, the role of CO in spatial learning may be different from that suggested by LTP studies.

Carbon monoxide as a putative messenger molecule in the feline lower oesophageal sphincter of the cat.

The distribution of the carbon monoxide (CO) producing enzymes haem oxygenase (HO) type 1 and 2 were studied in the feline lower oesophageal sphincter (LOS), as were HO activity and functional effects of CO. HO-2 immunoreactivity was observed in nerve cell bodies in the submucosal and myenteric plexus, nerve fibres, non-neuronal cells surrounding smooth muscle bundles, and in arterial endothelium, HO-1 immunoreactivity was confined to non-neuronal cells in the smooth muscle layer. CO production, indicating HO activity, was demonstrated in tissue homogenates. CO relaxed the LOS, and activated the cyclic GMP system. These results show that HO is present in the LOS, and suggest that CO can be generated by neuronal and non-neuronal structures and may have a role as a peripheral messenger.

The cloned guinea pig neuropeptide Y receptor Y1 conforms to other mammalian Y1 receptors.

We have cloned the guinea pig neuropeptide Y (NPY) Y1 receptor and found it to be 92-93% identical to other cloned mammalian Y1 receptors. Porcine NPY and peptide YY (PYY) displayed affinities of 43 pM and 48 pM, respectively. NPY2-36 and NPY3-36 had 6- and 46-fold lower affinity, respectively, than intact NPY. Functional coupling was measured by using a microphysiometer. Human NPY and PYY were equipotent in causing extracellular acidification with EC50 values of 0.59 nM and 0.69 nM, respectively, whereas NPY2-36 and NPY3-36 were about 15-fold and 500-fold less potent, respectively, than NPY. The present study shows that the cloned guinea pig Y1 receptor is very similar to its orthologues in other mammals, both with respect to sequence and pharmacology. Thus, results from previous studies on guinea pig NPY receptors might imply the existence of an additional Y1-like receptor sensitive to B1BP3226.

Suppression of sensory C fiber-mediated contractions by neuropeptide Y Y1 receptors in the guinea pig bronchi.

The aim of the study was to examine which neuropeptide Y (NPY) receptor types that are coupled to inhibition of sensory C fiber-mediated contractions of the guinea pig bronchi. NPY and PYY evoked a concentration-dependent inhibition of the electrically stimulated contractions. The Y1 receptor-selective antagonist BIBP3226 (1 microM) evoked a rightward shift of the NPY-induced response. Also the Y1 (and Y4-Y6) receptor agonist [Leu31,Pro34]NPY suppressed the stimulated contractions with a potency similar to the parent molecule. BIBP3226 (1 microM) also attenuated the response induced by [Leu31,Pro34]NPY. The Y2 receptor agonist [Cys2, Aoc524, D-Cys27]NPY suppressed the stimulated contractions at 1 microM only. NPY 2-36 was much less potent than NPY itself and pretreatment with BIBP3226 did not affect the inhibitory response. Human pancreatic polypeptide (Y4-Y6 receptor agonist) was inactive (< or = 1 microM). In conclusion, NPY is capable of suppressing sensory nerve-mediated contractions in the guinea pig bronchi mainly via Y1 receptors.

Characterization of the receptor response for the neuropeptide Y-evoked suppression of parasympathetically-mediated contractions in the guinea pig trachea.

Neuropeptide Y (NPY) acts via several distinct receptor types. The aim of the present study was to examine which NPY receptors are coupled to inhibition of parasympathetically-mediated contractions of the isolated guinea pig trachea. Electrical field stimulation of tracheal rings evoked a rapid twitch, which was abolished by atropine (1 microM). NPY, the structurally related hormone peptide YY (PYY), the Y2 receptor agonist [Cys2, Aoc5-24, D-Cys27]NPY, as well as NPY 5-36 and NPY 13-36 evoked a concentration-dependent inhibition of the electrically-stimulated twitches. Pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) failed to prevent the NPY-induced inhibition. Although less potent than NPY, the Y1 (and Y4-Y6) receptor agonist [Leu31, Pro34]NPY also inhibited the electrically-stimulated twitches. Another NPY-related peptide, pancreatic polypeptide, which recognizes Y4-Y6 receptors did not affect the stimulated twitches at concentrations up to 1 microM. However, pretreatment with the Y1 receptor-selective antagonist BIBP3226 (1 microM) virtually abolished the inhibition evoked by [Leu31, Pro34]NPY. None of the peptides affected the baseline tension and BIBP3226 (1 microM) per se did not affect the amplitude of the electrically-stimulated twitches. In conclusion, it seems that NPY and PYY are capable of suppressing parasympathetically mediated contractions in the guinea pig trachea mainly via Y2 receptors, but there is also a small contribution from Y1 receptors.

Unlike VIP, the VIP-related peptides PACAP, helodermin and helospectin suppress electrically evoked contractions of rat vas deferens.

We have compared the effects of vasoactive intestinal peptide (VIP) and of the VIP-related peptides pituitary adenylate cyclase activating peptide (PACAP) 1-27 and 1-38, helodermin, helospectin I and helospectin II, on the electrically evoked twitches in the isolated vas deferens of the rat. While VIP was virtually without effect, PACAP 1-38 suppressed the electrically evoked twitches effectively and in a concentration-dependent manner (pIC50 value 7.5). The naturally occurring N-terminal fragment PACAP 1-27 was less effective than PACAP 1-38 (Imax values 37.2% suppression compared to 76.5%) and less potent. The C-terminal fragment PACAP 16-38 was virtually inactive. Also helodermin and helospectin I+II suppressed the electrically evoked twitches effectively and in a concentration-dependent manner (pIC50 values 6.9; 7.2; 6.8, respectively). The three peptides produced similar maximum reduction of the twitches (74-80%). The findings suggest that PACAP, helodermin and helospectin suppress the electrically evoked contractions in the rat vas deferens via receptors distinct from VIP receptors.

Neuropeptide Y suppresses the neurogenic inflammatory response in the rabbit eye; mode of action.

Ocular injury in the rabbit causes miosis and breakdown of the blood aqueous barrier (aqueous flare response, AFR), reflecting a sensory nerve-mediated inflammatory response, elicited by the release of tachykinins and calcitonin gene-related peptide (CGRP) from C-fibers. Neuropeptide Y (NPY) occurs in sympathetic fibers in the eye. The study was designed to examine whether NPY and related peptides interfere with the inflammatory response to ocular injury in the rabbit in vivo. The isolated rabbit iris was studied with respect to NPY binding sites and second messenger coupling. The AFR and the miotic response to a standardized injury (infrared irradiation (IR) of the iris) were suppressed dose-dependently by NPY (0.01-1.0 nmol) injected intravitreally 30 min prior the trauma. The treated eye was compared with the contralateral eye, which received 0.9% saline and IR. The Y1 receptor agonist [Pro34]NPY, the Y2 receptor agonist NPY 13-36 and the structurally related peptide YY (1 nmol each) suppressed the AFR in response to IR. Injection of either NPY or the Y1 and Y2 receptor agonists (0.3 nmol each) suppressed the AFR evoked by exogenously applied CGRP (0.15 nmol). Saturation studies with 125I-NPY revealed both high and 'moderate' affinity binding sites in the iris. The Bmax values were 26 and 321 fmol/mg protein, respectively. NPY suppressed the forskolin-stimulated adenylate cyclase activity (IC50 value 19 nM). NPY did not affect basal or noradrenaline-induced accumulation of inositol phosphates in the iris. In conclusion, the rabbit iris seems to be rich in NPY receptors linked to inhibition of adenylate cyclase activity.(ABSTRACT TRUNCATED AT 250 WORDS)