Neuropeptide Y receptor subtypes, Y1 and Y2

Characterization of the neuropeptide Y5 receptor in the human hypothalamus: a lack of correlation between Y5 mRNA levels and binding sites

Neuropeptide Y (NPY) is a 36-amino-acid peptide that appears to play a central role in the control of feeding behavior. Recently, a cDNA encoding a novel NPY receptor subtype (Y5) was cloned from the rat and human hypothalamus, and shown to have a pharmacology consistent with NPY-induced feeding. We have subsequently cloned this cDNA from human hypothalamus and stably expressed it in CHO cells. Consistent with earlier reports, hY5 has a high affinity for NPY, [Leu31, Pro34]NPY, and NPY(3-36), but low affinity for larger C-terminal deletions of NPY and BIBP3226. High levels of hY5 mRNA were found in the human testis, brain, spleen and pancreas, with lower levels in several other tissues. In the human brain, hY5 mRNA levels were typically higher than hY2, but lower in comparison to hY1 receptor mRNA. To quantify the relative amounts of hY1, hY2 and hY5 mRNA in the human hypothalamus, we employed competitive RT-PCR. Interestingly, the relative amount of hY5 mRNA was substantially higher than either hY1 or hY2. However, pharmacological characterization of NPY binding sites in human hypothalamus membranes revealed predominantly the hY2 subtype. These data establish that while hY5 mRNA levels are very high in the human hypothalamus, conventional radioligand binding techniques do not detect hY5-like binding site. Whether hY5-like binding sites exist in the other human tissues that express hY5 mRNA (and what function hY5 has in those tissues) awaits future investigation.

Complementary and overlapping expression of Y1, Y2 and Y5 receptors in the developing and adult mouse nervous system

Neuropeptide Y, a 36 amino acid peptide, mediates its biological effects by activating the Y1, Y2, Y5 and Y6 receptors, which are also receptors for the structurally related peptide YY. Different classes of receptors have been suggested to be involved in different neuropeptide Y functions. In this report, we have characterized the developmental regulation and compared the cellular localization of these receptors in the developing and in the adult central and peripheral nervous systems of the mouse. RNase protection assays revealed that Y1, Y2 and Y5 messenger RNAs were expressed very early in spinal cord, brain, cerebellum and dorsal root ganglion development and were often down-regulated at times corresponding to their acquirement of the adult function in neurotransmission. In situ hybridization of the adult brain showed that Y1 was widely expressed, Y2 displayed a more restricted pattern, Y5 was expressed at very low levels and only in a few brain nuclei and Y6 was not expressed. Virtually all areas containing neurons positive for Y5 also expressed Y1, whereas many Y1-positive cells clearly did not express Y5. In contrast, Y2 was not expressed by the neurons expressing Y1 or Y5. These findings suggest that neuropeptide Y signaling in the brain could be mediated by simultaneous Y1 and Y5 activation. Similar results were also obtained in peripheral sensory neurons. Furthermore, our results suggest that neuropeptide Y/peptide YY receptors play an important role in nervous system development and that selective receptor combinations are responsible for signaling the different effects of neuropeptide Y in the peripheral and central nervous systems.

Circulating neuropeptide Y (NPY) and catecholamines in rat under resting and stress conditions. Arguments for extra-adrenal origin of NPY, adrenal and extra-adrenal sources of catecholamines

Neuropeptide Y (NPY) is found in cell bodies of neurons in the brain and co-localized with noradrenaline (NA) in sympathetic nerves as well as with NA and adrenaline (A) in the adrenal chromaffin cells. The purpose of the present work is to determine whether NPY and catecholamines found in the plasma of the rat under resting and stress conditions (ether inhalation, restraint) arise from the adrenals or from extra-adrenal sites. We used adrenalectomized (adx) rats and sham-adx ones. Adrenalectomy increased plasma adrenocorticotrophic hormone (ACTH) levels but decreased drastically circulating corticosterone (B) and A (-97%). However, resting NA was slightly but not significantly decreased and NPY not affected. Ether inhalation (3 min) increased plasma levels of ACTH, B, NA and A in sham-adx rats, ACTH, NA and, weakly, A in adx ones. Restraint (30 min) increased B, NA and A in sham-adx rats, NA and, poorly, A, in adx ones. In contrast, plasma levels of NPY were not significantly affected by these stress conditions. The present data suggest that NA found in rat plasma at rest and during ether or restraint stress could arise from both adrenal medulla and noradrenergic nerve endings while A arises mainly from the adrenergic chromaffin cells of the adrenals. In contrast, NPY found in the circulation, at rest and under stress conditions, is not derived from the adrenals but emanates mainly from an extra-adrenal source.

Modulation of submucosal arteriolar tone by neuropeptide Y Y2 receptors in the guinea-pig small intestine

OBJECTIVES

the aims of this study were to determine if the nerves, both intrinsic and extrinsic, supplying intestinal blood vessels were subject to modulation by a neuropeptide Y2 receptor agonist, N-acetyl[Leu28, Leu31] NPY(24-36).

METHODS

effects of Y2 receptor agonist were examined on (i) responses to acetylcholine (ACh) and intrinsic vasodilator nerve stimulation in normal arterioles and (ii) amplitudes of arteriolar constrictions and smooth muscle membrane potential changes in response to extrinsic perivascular nerve stimulation in both normal and capsaicin-treated arterioles.

RESULTS

(i) neuropeptide Y2 receptor agonist had no significant effect on the relaxing action of exogenous application of ACh but significantly reduced the relaxing action of vasodilator nerve stimulation in arterioles of the isolated submucosa of the guinea-pig small intestine, which were pre-constricted with the thromboxane analogue U46619. (ii) The Y2 agonist significantly decreased the amplitude of excitatory junction potentials (EJPs) evoked by perivascular nerve stimulation in normal arterioles and in arterioles treated with the sensory neurotoxin, capsaicin. On the other hand, the Y2 agonist failed to alter the amplitude of the constrictions obtained by perivascular nerve stimulation in normal arterioles but significantly attenuated the amplitude of constrictions in arterioles treated with capsaicin.

CONCLUSIONS

it is concluded that NPY can modulate release of transmitter from extrinsic sympathetic as well as the intrinsic submucosal vasodilator nerves via prejunctional Y2 receptors.

GR231118 (1229U91) and other analogues of the C-terminus of neuropeptide Y are potent neuropeptide Y Y1 receptor antagonists and neuropeptide Y Y4 receptor agonists

GR231118, BW1911U90, Bis(31/31')[[Cys31, Trp32, Nva34] neuropeptide Y(31-36)] (T-190) and [Trp-Arg-Nva-Arg-Tyr]2-NH2 (T-241) are peptide analogs of the C-terminus of neuropeptide Y that have recently been shown to be antagonists of the neuropeptide Y Y1 receptor. In this study, the activity of these peptides at each of the cloned neuropeptide Y receptor subtypes is determined in radioligand binding assays and in functional assays (inhibition of forskolin-stimulated cAMP formation). GR231118 is a potent antagonist at the human and rat neuropeptide Y Y1 receptors (pA2 = 10.5 and 10.0, respectively; pKi = 10.2 and 10.4, respectively), a potent agonist at the human neuropeptide Y Y4 receptor (pEC50 = 8.6; pKi = 9.6) and a weak agonist at the human and rat neuropeptide Y Y2 and Y5 receptors. GR231118 also has high affinity for the mouse neuropeptide Y Y6 receptor (pKi = 8.8). Therefore, GR231118 is a relatively selective neuropeptide Y Y1 receptor antagonist, but has appreciable activity at the neuropeptide Y Y4 and Y6 receptors as well. BW1911U90, T-190 and T-241 are moderately potent neuropeptide Y Y1 receptor antagonists (pA2 = 7.1, 5.8 and 6.5, respectively; pKi = 8.3, 6.5 and 6.8, respectively) and neuropeptide Y Y4 receptor agonists (pEC50 = 6.8, 6.3 and 6.6, respectively; pKi; 8.3, 7.7 and 8.3, respectively). These data suggest that the C-terminus of neuropeptide Y and related peptides is sufficient for activation of the neuropeptide Y Y4 receptor, but is not sufficient for activation of the neuropeptide Y Y1 receptor. Because BW1911U90, T-190 and T-241 are significantly less potent at the cloned human neuropeptide Y Y1 receptor than at the neuropeptide Y receptor in human erythroleukemia cells, these cells may express a novel neuropeptide Y receptor with high affinity for these peptides.

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.

Comparison between the effects of sigma receptor ligand JO 1784 and neuropeptide Y on immune functions

Recent evidence suggests that sigma receptor ligands and neuropeptide Y may act through the same pathways to modulate centrally mediated immune function. The present study demonstrated that both the sigma receptor ligand igmesine: (+)-N-cyclopropylmethy-N-methyl-1, 4-diphenyl-1-yl-but-3-en-1-ylamine, hydrochloride (JO 1784) (10(-7) and 10(-5) M) and neuropeptide Y (10(-9) and 10(-7) M) in vitro significantly reduced neutrophil phagocytosis and decreased mitogen stimulated lymphocyte proliferation. By contrast, central administration of JO 1784 (0.5 and 5 microg/5 microl) significantly reduced the activity of neutrophil phagocytosis, but enhanced lymphocyte proliferation without changing the serum concentration of corticosterone. Neuropeptide Y (10(-9) and 10(-7) M), following intracerebroventricular infusion, also decreased the neutrophil response, but significantly raised the corticosterone concentration. These results indicate that different mechanisms (involving various neurotransmitters and their receptors, changes in the activity of the hypothalamic-pituitary-adrenal axis, or sigma receptor subtypes) may be involved in the central effects of JO 1784 and neuropeptide Y.

Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurons and cloning of the rat Y2 receptor

1 Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time. 2 More than 70% of the hippocampal neurones were endowed with [125I]-[Leu31,Pro34]PYY Y1-like receptor silver grain accumulations and Y1 receptor immunostaining. These radio- and immuno-labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal-like neuronal cells, as confirmed by neurone-specific enolase and MAP-2 staining. 3 Competition binding profiles revealed that specific [125I]-[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub-type with [Leu31,Pro34]substituted NPY/PYY analogues >> C-terminal fragments = pancreatic polypeptides, with the non-peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]-[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors. 4 The expression of the genuine Y1 receptor was confirmed by RT-PCR in hippocampal cultures. In contrast, negligible levels of Y2-like/[125I]-PYY3-36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT-PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero. 5 Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

Cardiovascular actions of neuropeptide Y and social stress

The role of central neuropeptide Y (NPY) in the cardiovascular response to social stress was evaluated in freely moving rats using telemetry. In unstressed rats, intracerebroventricular (ICV) administration of NPY and the selective Y1 receptor agonist [Leu31, Pro34]-NPY decreased blood pressure and heart rate, while the selective Y2 agonist NPY13-36 transiently raised blood pressure. NPY and [Leu31, Pro34]-NPY blunted elevations in blood pressure and pulse rate following exposure to the resident-intruder procedure, an established social stress paradigm. In contrast, the Y2 agonist significantly augmented stress-induced pressor effects. These observations indicate that the hypotensive effects of ICV NPY appear to be mediated by the Y1 receptor subtype and the NPY receptor subtypes may mediate opposing cardiovascular actions in response to stressful stimuli.

Peptide YY selectively stimulates expression of the colonocytic phenotype

Peptide YY (PYY) is produced by colonic mucosal endocrine cells and modulates gastrointestinal endocrine activity through specific Y-receptors. The direct effects of PYY on intestinal mucosal growth and differentiation remain uncharacterized. The abundance of PYY in colonic mucosa suggests that PYY acts locally to maintain colonocytic differentiation. We tested this hypothesis in human Caco-2 intestinal epithelial cells, which express alkaline phosphatase (AP) and dipeptidyl dipeptidase (DP), brush-border enzymes differentially concentrated in large and small intestinal mucosa, respectively. The effects of PYY on enzyme specific activity were compared with those of pancreatic polypeptide, neuropeptide-Y, vasoactive intestinal peptide, pentagastrin, bombesin, and selective Y1- and Y2-receptor agonists. Brush-border enzyme activity was assessed by AP and DP specific activity in cell lysates quantitated spectrophotometrically following synthetic substrate digestion. PYY, neuropeptide-Y, pancreatic polypeptide, and vasoactive intestinal peptide (10(-7) mol/L) stimulated AP activity. PYY brought about the greatest increase (38.0%+/-11.0%, n=48). Only PYY decreased DP specific activity (7.9%+/-2.2%, n=48). The Y2-agonist but not the Y1-agonist mimicked these PYY effects (increasing AP 28.3%+/-3.5% and decreasing DP 10.4%+/-3.6%). These data suggest that PYY promotes differentiation toward a colonocytic phenotype in Caco-2 intestinal epithelial cells and that this effect may be mediated through the Y2-receptor subtype.

Neuropeptide Y suppresses epileptiform activity in rat hippocampus in vitro

Neuropeptide Y (NPY) potently inhibits glutamate-mediated synaptic transmission in areas CA1 and CA3 of the rat hippocampus without affecting other synaptic inputs onto principal cells of the hippocampal formation, suggesting that its biological role may include the regulation of excitability within the hippocampus. Here we examine NPY's actions in three in vitro models of epilepsy [0 Mg2+-, picrotoxin-, and stimulus-train-induced bursting (STIB)] with the use of extracellular and whole cell patch-clamp recordings from rat hippocampal-entorhinal cortex slices. Perfusion of the slice with saline that had Mg2+ omitted (0 Mg2+) or that had picrotoxin (100 microM) added resulted in brief spontaneous bursts (SBs) resembling interictal discharges. SB frequency is significantly reduced in both models by 1 microM NPY and by the Y2-preferring agonists peptide (P)YY(3-36) (1 microM) and 1-4-(6-aminohexanoic acid)-25-36 ([ahx(5-24)] NPY; 3 microM). The Y1-preferring agonist Leu31-Pro34NPY (1 microM) is considerably less potent, but also reduces burst frequency, even in the presence of the selective Y1 receptor antagonist GR231118, suggesting the involvement of a different receptor. In STIB, high-frequency stimulus trains to stratum radiatum of area CA2/CA3 result in clonic or tonic-clonic ictaform primary afterdischarges (primary ADs) as well as longer, spontaneous secondary ictaform discharges and SBs similar to those in the other models. Primary AD duration is greatly reduced or abolished by Y2- but not Y1-preferring agonists. SBs, although variable, were inhibited by both Y1 and Y2 agonists. In single and dual whole cell recordings from CA3 pyramidal cells, we frequently observed spontaneous, rhythmic synchronous events (SRSEs) arising after several STIB stimuli. Once established, SRSEs persist in the absence of further stimuli and are insensitive to the application of NPY. SRSEs in pyramidal cells typically occur at 2-4 Hz, are outward currents when cells are clamped near rest (>100 pA at a holding potential of -55 mV), reverse between -60 and -70 mV, and are inhibited by 100 microM picrotoxin, indicating involvement of gamma-aminobutyric acid-A receptors. They are inhibited by blockers of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) but not N-methyl-D-aspartate receptors. Whole cell patch-clamp recordings from interneurons in CA3 after STIB reveal NPY-insensitive, rhythmic, inward AMPA-receptor-mediated currents that are similar in frequency to SRSEs seen in pyramidal cells. We conclude that NPY, acting predominantly via Y2 receptors, can dramatically inhibit epileptiform activity in three fundamentally different in vitro models of epilepsy without affecting endogenous inhibitory activity. The results also provide support for the hypothesis that endogenous NPY may normally control excitability in the hippocampus and suggest the potential for NPY receptors as targets for anticonvulsant therapy.

Neuropeptide Y blocks light-induced phase advances but not delays of the circadian activity rhythm in hamsters

In mammals, the suprachiasmatic nuclei (SCN) are the anatomical site of localization of the light-entrainable circadian clock responsible for the generation of daily rhythms in physiology and behavior. In addition to direct retinohypothalamic innervation, the SCN receive a prominent projection of fibers from the intergeniculate leaflet (IGL) of the thalamus, the geniculohypothalamic tract (GHT), some of which contain the neurotransmitter, neuropeptide Y (NPY). Since the GHT has been suggested to play a role in the modulation of photic entrainment of the SCN circadian clock in rodents, we investigated the effects of local administration of NPY into the region of the SCN on light-induced phase shifts of the free-running activity rhythm in hamsters. Injection of 60 nmol of NPY into the SCN region 10 min prior to light exposure at circadian time 19 completely blocked light-induced phase advances. Similar treatment at circadian time 14 had no significant effect on the magnitude of light-induced phase delays. Injection of NPY at either time point without light exposure did not alter circadian phase. The findings support a modulatory role for NPY in the photic entrainment of the SCN circadian clock.

Identification of multiple neuropeptide Y receptor subtypes in the human frontal cortex

Recently, we found abundant mRNA and binding sites for neuropeptide Y Y1-like receptors in the human cerebral cortex. However, an earlier study using indirect labeling methods failed to detect substantial neuropeptide Y1-like receptor binding in numerous areas of the human brain, including the cerebral cortex. To resolve the disparity in these findings, we characterized the neuropeptide Y receptor subtypes labeled with [125I]peptide YY in homogenates of human frontal cortex. Competition experiments using 100 pM [125I]peptide YY binding to human frontal cortex homogenates indicated predominantly neuropeptide Y Y2 receptors are labeled with this concentration of ligand. However, saturation analysis of [125I]peptide YY binding to frontal cortex membranes resulted in isotherms best characterized by a two-site fit. Binding of [125I]peptide YY to the high affinity (Kd = 40 pM) binding site was prevented using a 100 nM concentration of the neuropeptide Y Y2 receptor agonist peptide YY-(3-36). By masking the higher affinity site, we found a low affinity [125I]peptide YY binding site (Kd = 1.4 nM) exhibiting a pharmacology consistent with a neuropeptide Y Y1-like receptor. It appears that neuropeptide Y Y2 receptors are the predominant subtype labeled with low concentrations of[125I]peptide YY and that the neuropeptide Y Y1 receptor is a low affinity [125I]peptide YY binding site in the human frontal cortex.

Differential modulation of NMDA-stimulated [3H]dopamine release from rat striatum by neuropeptide Y and sigma receptor ligands

Although the identity of the endogenous ligands for sigma (sigma) receptors is unknown, neuropeptide Y (NPY) has been named as a possible candidate for a natural transmitter at these receptors. Using a superfusion system, we compared the effect of NPY on NMDA-stimulated [3H]dopamine release in rat striatum to that of the sigma agonists (+)-pentazocine and BD737. In contrast to (+)-pentazocine- or BD737-mediated inhibition of release, NPY enhanced release. However, the same sigma antagonists (BD1008, DuP734, haloperidol and DTG) that reverse (+)-pentazocine- or BD737-mediated inhibition, as well as a Y receptor antagonist, PYX-1, all reversed the enhancement. PYX-1 also reversed the (+)-pentazocine- and BD737-mediated inhibition of release. Peptide YY (PYY) and [Leu31,Pro34]NPY did not mimic the effect of NPY. NPY13-36 enhanced release to the same extent as NPY but the effect was not reversed by sigma antagonists. Our findings are consistent with the potential role of NPY as an endogenous ligand for a subtype of sigma receptor with characteristics different from Y1, Y2 and Y3 receptors but sensitive to PYX-1.

Distribution of several gut neuropeptides and their effects on motor activity in muscularis mucosae of guinea-pig proximal colon

The distribution of peptide-containing nerve fibers and the effect of their neuropeptides on motor activity were studied in the muscularis mucosae of the guinea-pig proximal colon. In the immunohistochemical study, it was shown that the tachykinin (TK)-containing nerve fibers densely innervated the muscularis mucosae. In the superfusion study, three kinds of TKs, i.e., neurokinin A (NK-A), neurokinin B (NK-B) or substance P (SP), enhanced the spontaneous activity on the strips of muscularis mucosae with a tetrodotoxin (TTX)-insensitive manner. Their potency was in the rank order of NK-A > SP. This suggests that the muscle has a predominant NK2 receptor. Calcitonin gene-related peptide (CGRP)-immunoreactive fibers were commonly observed in the muscle. CGRP induced a potent inhibition on spontaneous activity and a concentration-dependent inhibition on the NK-A-elicited excitation in the presence of TTX, indicating its direct effect on the receptor in the muscle. On the other had, gastrin releasing peptide (GRP), galanin, neuropeptide Y or somatostatin were more or less immunopositive in nerve fibers, but they had no effect on the motility of the muscle except that GRP sometimes showed a faint increase in spontaneous activity. Neither methionine-enkephalin nor gastrin-17/cholecystokinin was immunoreactive and had any effect on the muscle. These neuropeptides other than TKs and CGRP do not seem to be neuromediators of motor activity of muscularis mucosae. The results suggest the possibility that TK-, especially NK-A- and CGRP-containing neurons, participate in the regulation of motor activity of the muscularis mucosae in the guinea-pig proximal colon.

Clonidine administration increases neuropeptide Y immunoreactivity and neuropeptide Y mRNA in the rat cerebral cortex neurons

The effect of alpha 2 adrenoceptor stimulation on neuropeptide Y (NPY) and NPYmRNA expression was studied in the rat cerebral cortex. For receptor stimulation clonidine was used in a dose of 50 micrograms/kg s.c., 3 times at every 8 h; brains were studied 30-40 min after the last dose using radioimmunoassay (RIA), immunocytochemistry and in situ hybridization methods. The RIA of NPY did not show any significant changes in the NPY immunoreactivity (IR) level in the whole cortex, whereas the immunohistochemical analysis demonstrated an increase in the number of NPY-IR neurons in ventral cortical regions, especially in external cortical layers. In situ hybridization histochemistry of NPYmRNA also performed in ventral cortical sections showed that clonidine increased NPY synthesis in some cortical neurons. The obtained results indicate that the alpha 2 adrenoceptor stimulation by clonidine increases the NPY content and synthesis in rat cortical neurons.

Mechanism of the potentiation of vasoconstriction by neuropeptide Y in arterioles from the submucosa of the guinea-pig small intestine

1. Neuropeptide Y (NPY; 3-100 nmol/L) caused a concentration-dependent potentiation of constriction in response to noradrenaline or the thromboxane mimetic U46619 in arterioles from the submucosa of the guinea-pig small intestine. 2. In arterioles permeabilized by exposure to the alpha-toxin of Staphylococcus aureus and maintained in Ca(2+)-buffered medium, NPY potentiated the contractile effects of Ca2+. The magnitude of the potentiation was the same as in intact arterioles. 3. Exposure of arterioles to 1 mumol/L nifedipine to inhibit Ca2+ influx or to 20 mumol/L cyclopiazonic acid to abolish Ca2+ uptake into internal stores had no effect on the potentiating action of NPY.

Multiple NPY receptors coexist in pre- and postsynaptic sites: inhibition of GABA release in isolated self-innervating SCN neurons

Although NPY has been shown to influence the action of many transmitters in the brain, modulation of GABA, the primary inhibitory transmitter, has not been detected with electrophysiology. Using whole-cell patch-clamp recording, we found that NPY has a large modulatory effect on GABAergic neurons of the suprachiasmatic nucleus (SCN) that act as the circadian clock in the mammalian brain. NPY, acting at both Y1- and Y2-like receptors, reduced the frequency of spontaneous miniature inhibitory postsynaptic currents while having little effect on the postsynaptic GABA receptors, suggesting a presynaptic mechanism of NPY action. In single self-innervating neurons, application of either Y1 or Y2 agonists to the same neuron significantly inhibited the evoked autaptic GABA release. The use of single-neuron microcultures has allowed the demonstration that a single peptide, NPY, has two different receptors coded for by different genes in the same axon terminal. The Y1 and Y2 agonists also inhibited whole-cell calcium currents when applied to the same neuron, indicating a coexistence of Y1- and Y2-like receptors in the postsynaptic cell body. The self-innervating cell model we use here may be applicable generally for discriminating presynaptic versus postsynaptic actions of other neurotransmitters and neuromodulators and locating their subtype receptors.

Analysis of NPY receptor subtypes in the human frontal cortex reveals abundant Y1 mRNA and binding sites

Receptors for neuropeptide Y (NPY) are widely distributed throughout the mammalian brain. Using indirect labeling methods, the human brain was reported to contain predominantly the Y2 receptor subtype, whereas the rat brain contains a mixture of Y1 and Y2 receptor subtypes. To more accurately assess NPY receptors in the human brain, we used type Y1- and Y2-selective radioligands [125I] [Leu31,Pro34]PYY and [125I]PPY (3-36), respectively, to examine NPY receptors in the human frontal cortex. Contrary to an earlier report, abundant Y1 binding sites were found in homogenates of human frontal cortex. Moreover, saturation analysis showed similar densities of both Y1 (Kd = 433 +/- 36 pM, Bmax = 313 +/- 15 fmol/mg protein) and Y2 (Kd = 444 +/- 39 pM, Bmax = 458 +/- 22 fmol/mg protein) receptor subtypes in the human frontal cortex. Subsequently, Northern blot analysis revealed abundant expression of Y1 mRNA, with very low levels of Y2 mRNA, in cerebral cortex and in other areas of the human brain. These findings were confirmed by competitive RT-PCR in the human frontal cortex. Therefore, it appears that Y1 binding sites and mRNA are expressed abundantly in the human frontal cortex and, earlier findings, suggest that the human brain contains a mixture of Y1 and Y2 receptor subtypes.

Does the neuropeptide Y Y1 receptor contribute to blood pressure control in the spontaneously hypertensive rat?

OBJECTIVE

To study the effects of the selective neuropeptide Y (NPY) Y1 receptor antagonist BIBP 3226 in spontaneously hypertensive rats (SHR) in order to elucidate whether NPY function may be altered in the SHR and whether the NPY Y1 receptor plays a specific role in the maintenance of high blood pressure in this genetic form of hypertension.

METHODS

Pithed and conscious SHR were studied after intravenous administration of 0.125-1 mg/kg BIBP 3226. The cardiovascular effects were evaluated under baseline conditions, under acute stress and after exogenous administration of 20 microg/kg NPY. The potentiating effects of NPY on pressor responses to phenylephrine and tyramine were studied in the SHR.

RESULTS

Intravenous administration of 0.125-1 mg/kg BIBP 3226 dose-dependently inhibited the pressor response to exogenous NPY in pithed SHR. At higher doses BIBP 3226 had an effect duration of 20-40 min. In the pithed SHR, a 0.5 mg/kg bolus injection of BIBP 3226 shifted the pressor response curve for exogenous NPY significantly to the right It also inhibited significantly the potentiating effects of NPY on pressor responses to phenylephrine and tyramine. In conscious SHR, 0.125-1 mg/kg BIBP 3226 did not reduce the basal blood pressure. In combination with a hypotensive dose of prazosin, administration of 0.5 mg/kg BIBP 3226 had no added effects lowering the basal blood pressure. A stressful stimulus, namely an air jet, caused a brief increase in blood pressure and heart rate in the conscious SHR. In this model, 0.5 mg/kg BIBP inhibited the heart rate response slightly but had no effect on the blood pressure response.

CONCLUSIONS

Our results demonstrate that, although the selective NPY Y1 receptor antagonist BIBP 3226 may shift the pressor response to exogenous NPY potently, it does not influence basal blood pressure significantly in the SHR.

Neuropeptide Y family of hormones: receptor subtypes and antagonists

Neuropeptide Y (NPY) is the most abundant peptide present in the mammalian central and peripheral nervous system. NPY exhibits a variety of potent central and peripheral effects including those on feeding, memory, blood pressure, cardiac contractility and intestinal secretions. Classical pharmacological studies have shown that NPY effects are mediated by four different receptor subtypes, Y-1, Y-1-like, Y-2, and Y-3. However, the existence of numerous atypical activities provide strong evidence for the occurrence of additional NPY receptor subtypes. Pharmacological studies have further been facilitated by the recent cloning and expression of Y-1, Y-2, Y-4 (PP-1) and Y-5 receptors. Moreover, the cloned Y-5 receptor has been suggested to be the long awaited Y-1-like receptor involved in feeding. Structure-activity studies have laid a good foundation towards the development of receptor selective compounds, and to date potent Y-1 selective peptide and nonpeptide antagonists have been developed. The need to clone numerous receptor subtypes and to develop receptor selective compounds for physiological and perhaps clinical use is expected to keep NPY research active for many years to come.

Neuropeptide Y-mediated long-term depression of excitatory activity in suprachiasmatic nucleus neurons

A brief exposure to light can shift the phase of mammalian circadian rhythms by 1 hr or more. Neuropeptide Y (NPY) administration to the hypothalamic suprachiasmatic nucleus, the circadian clock in the brain, also causes a phase shift in circadian rhythms. After a phase shift, the neural clock responds differently to light, suggesting that learning has occurred in neural circuits related to clock function. Thus, certain stimuli can produce effects that last for an extended period, but possible mechanisms of this long-term effect have not been previously examined at the cellular level. Here, we report that NPY caused a long-term depression in both electrical activity and intracellular calcium levels of neurons, as studied with whole-cell patch-clamp recording and Fura-2 digital imaging. In contrast to the immediate (1 sec) recovery after relief from glutamate receptor blockade, a brief single application of NPY (100 nM) depressed cytosolic Ca2+ for > 1 hr. The mechanism of this long-term calcium depression, a form of cellular learning, is dependent on the simultaneous release of glutamate and activation of NPY receptors, because both the extended response to NPY and any aftereffect were blocked by coapplication of glutamate receptor antagonists. Postsynaptic actions of NPY, mediated by both Y1- and Y2-like receptors, were short term and recovered rapidly. The primary site of long-term NPY actions may be on presynaptic glutamatergic axons, because the frequency of miniature excitatory postsynaptic currents in the presence of tetrodotoxin was reduced by transient exposure to NPY in both cultures and slices.

Hormonal response to enteral feeding and the possiblerole of peptide YY in pathogenesis of enteral feeding-related diarrhoea

Diarrhoea is a common complication of enteral feeding. Previous studies have demonstrated a secretion of water and electrolytes in the ascending colon during intragastric but not intraduodenal enteral feeding. The cause of this secretion is likely to be neurohumoral in origin. This study was designed to examine the hormonal responses to enteral feeding. In vivo segmental colonic perfusion studies were undertaken. Before and at hourly intervals during these studies serum was taken for estimations of neurotensin (NT), pancreatic glucagon (PG), peptide YY (PYY) and vasoactive intestinal polypeptide (VIP). During fasting there was a median ascending colonic absorption of water in all groups. During feeding there was a net secretion in the ascending colon in both gastric groups and in the high load duodenal group, but not in the low load duodenal group. During these studies the PYY levels remained unchanged from fasting in the low and high load gastric groups. In the low and high load duodenal groups the PYY levels increased. The NT levels increased only in the high load duodenal group. There were no other changes in NT or in PG or VIP levels either between fasting and feeding, or between the gastric and duodenal groups. PYY is known to stimulate intestinal absorption. The absence of a rise during intragastric feeding may be important in the underlying mechanisms of enteral feeding-induced colonic secretion and hence enteral feeding-related diarrhoea.

Neuropeptide Y potentiates noradrenaline-induced contraction through the neuropeptide Y Y1 receptor

To elucidate which neuropeptide Y receptor subtype is responsible for the neuropeptide Y-induced potentiation of the noradrenaline-evoked contraction in human omental arteries we used antisense oligodeoxynucleotide (Antisense), the new selective neuropeptide Y Y1 receptor antagonist, BIBP3226 {(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl) methyl]-D-arginine-amide} and the reverse transcriptase-polymerase chain reaction (RT-PCR). Neuropeptide Y significantly potentiated the noradrenaline-induced contraction in non-incubated vessels (pEC50 6.4 +/- 0.2 vs. 5.9 +/- 0.2) and in vessels incubated with 1 microM Sense oligodeoxynucleotide (Sense) (pEC50 6.0 +/- 0.1 vs. 5.6 +/- 0.2). In vessels incubated with 1 microM Antisense the potentiating effect of neuropeptide Y was completely abolished. BIBP3226 (1 microM) inhibited the neuropeptide Y-induced potentiation in human omental arteries (pEC50 5.8 +/- 0.3 vs. 6.4 +/- 0.2). Finally, messenger RNA for the neuropeptide Y Y1 receptor was detected using RT-PCR. On the basis of our results we conclude that the neuropeptide Y-induced potentiation of the noradrenaline-induced contraction is mediated by the neuropeptide Y Y1 receptor.

Neuropeptide Y 3-36 is an endogenous ligand selective for Y2 receptors

Neuropeptide Y (NPY 1-36) binds to Y1 and Y2 receptors with similar affinity. No endogenous molecular form of NPY with selectivity for Y1 or Y2 receptors has been described so far. We report the presence of an endogenous fragment of NPY in porcine brain, NPY 3-36, which lacks the amino-terminal dipeptide Tyr-Pro of NPY 1-36. NPY 3-36 accounts for 35% of NPY-like immunoreactivity in porcine brain. We have compared binding of NPY 3-36 and NPY 1-36 in model systems of Y1-like (SK-N-MC cells) and Y2-like receptors (CHP234 cells). NPY 3-36 and NPY 1-36 had similarly high affinity for Y2-like receptors on CHP234 cells, but NPY 3-36 had a 1000-fold lower affinity than NPY 1-36 for Y1-like receptors on SK-N-MC cells. Thus amino-terminal cleavage of NPY 1-36 generating NPY 3-36 converts an unselective Y1/Y2 receptor ligand into a highly Y2 selective ligand. This may be a means of fine tuning NPY biological actions.

Inhibitory effect of neuropeptide Y on growth hormone secretion in rats is mediated by both Y1- and Y2-receptor subtypes and abolished after anterolateral deafferentation of the medial basal hypothalamus

Neuropeptide Y (NPY) may play a physiological role in the regulation of growth hormone (GH) secretion by acting via somatostatin (SS) in the periventricular nucleus (PeV), as well as via the GH-releasing factor in the arcuate nucleus (ARC) of the medial basal hypothalamus (MBH). The objectives of the present study were to determine the neuron structures and receptor subtypes necessary for mediating the inhibitory effect of NPY on GH secretion in unanesthetized male rats. To eliminate the influence of hypophyseotropic SS, anterolateral deafferentation (ALC) of the hypothalamus was performed. Intracerebroventricular (i.c.v.) administration of 1.17 nmol of NPY decreased the blood level of GH for 3-4 h in sham-operated rats, while the procedure was without effect in ALC rats. The i.c.v. administration of 1.17 nmol of a Y1-receptor agonist ([Leu31, Pro34]-NPY) or a Y2-receptor agonist (NPY 13-36 and NPY 3-36) similarly suppressed the blood GH level. The data support the hypothesis that neuron structures anterolateral to the MBH are required for NPY-induced inhibition of GH secretion that is mediated via Y1- and Y2-receptor subtypes. Combined with data of other investigators, SS is likely the neurohumoral mediator of the effect of NPY on GH secretion.

Metabolism and functions of neuropeptide Y

Neuropeptide Y is one of the most abundant neuropeptides in the central and peripheral nervous systems and its sequence is highly conserved among species. A number of key physiological roles for NPY are now emerging, especially in the control of feeding and energy homeostasis. Other physiological actions of NPY are also reviewed. The metabolism of NPY has been examined by employing certain purified ectopeptidases and by using different membrane preparations. These approaches reveal that NPY is processed at its N-terminus by two proline-preferring aminopeptidases: aminopeptidase P and dipeptidyl peptidase IV. The action of the latter enzyme generates NPY (3-36) which has previously been shown to be a selective agonist at the Y2 class of NPY receptor. Thus, post-secretory processing of NPY can modify receptor selectivity. NPY is found to be resistant to the action of two other membrane aminopeptidases (N and W), and to the action of angiotensin converting enzyme. However, it is a substrate for endopeptidase-24.11 (K(m) = 15.4 microM) which can cleave the Tyr20-Tyr21 and Leu30-Ile31 bonds consistent with the known specificity of the enzyme. In striatal synaptic and renal brush border membranes, NEP is shown to be the major NPY hydrolysing activity but plays a lesser role in intestinal brush border membranes. Knowledge of the proteolytic processing of NPY should aid in the design of stable analogues of this neuropeptide.

Antagonistic effect of D-myo-inositol-1,2,6-trisphosphate (PP56) on neuropeptide Y-induced vasoconstriction in the feline dental pulp

Intra-arterial injection of neuropeptide Y (NPY) (1.3-2.0 micrograms/kg) resulted in decreases of pulpal blood flow by 37.7 +/- 5.7% (mean +/- SEM). The intra-arterial injection of D-myo-inositol-1,2,6-trisphosphate (PP56) (0.3 mg/kg) alone changed pulpal blood flow by 1.0%. The effect of NPY in the presence of PP56 resulted in significantly smaller decreases in pulpal blood flow ranging from 27.2 +/- 5.4 to 16.6 +/- 3.5% from control as compared with NPY alone. In effect, PP56 partially blocked the decreases in pulpal blood flow caused by NPY. The electrical stimulation of the sympathetic nerve alone resulted in decreases in pulpal blood flow of 41.7 +/- 6.2%. The electrical stimulation of the sympathetic nerve following the intra-arterial administration of PP56 decreased pulpal blood flow by 23.1 +/- 6.0% from control, significantly less than the sympathetic nerve stimulation alone. PP56 attenuated the decrease in pulpal blood flow caused by the sympathetic nerve stimulation by 44.4 +/- 11.0%. Similarly, the combination of PP56 and phentolamine followed by electrical stimulation of the sympathetic nerve reduced the decrease in pulpal blood flow caused by the sympathetic nerve stimulation alone by 43.0 +/- 8.6%. These results provide evidence that the non-peptide PP56 is capable of antagonizing vasoconstriction caused by NPY in the feline dental pulp. In addition, they show functional evidence that NPY as well as noradrenaline are released from the sympathetic nerve endings during its stimulation and cause vasoconstriction.

Localization and characterization of neuropeptide Y/peptide YY receptors in the brain of the smooth dogfish (Mustelis canis)

Multiple receptor subtypes specific for the neuropeptide Y (NPY)/peptide Y (PYY) family of peptides exist in mammals, but little is known about the distribution of this receptor family in other vertebrates. Saturable binding sites for 125I-labeled porcine PYY were localized in frozen sections of the brain of the smooth dogfish (Mustelis canis) by radioligand binding and autoradiography. Saturable 125I-porcine PYY binding sites were distributed widely in the cerebral hemispheres, optic lobes, hypothalamus, cerebellum and hindbrain. Binding was saturable, specific for PYY and related peptides, and of high affinity (Kd = 2.53 nM). The specificity of the binding site was analyzed by performing competitive inhibition experiments with nonradioactive PYY, NPY, and [Leu31, Pro34]-NPY and NPY13-36, synthetic peptide analogs specific for the mammalian Y1 and Y2 receptor subtypes, respectively. Saturable 125I-porcine PYY binding sites in all regions of the dogfish brain closely resembled the mammalian Y1 NPY receptor subtype in specificity for these substances. There was no evidence for expression of multiple receptor subtypes. We conclude that a single receptor specific for the NPY/PYY family of peptides is widely expressed in the smooth dogfish brain and that this receptor closely resembles the mammalian Y1 receptor subtype, suggesting that the Y1 receptor is the ancestral receptor in this family.

Neuropeptide Y inhibits 3[H]noradrenaline release in the rat vas deferens independently of cAMP levels

The purpose of the present investigation was to ascertain the functional significance of the reduction in cyclic AMP (cAMP) levels in the inhibitory action of neuropeptide Y (NPY) on [3H]noradrenaline ([3H]NA) release, as well as to further characterize the subtype(s) of NPY receptors involved in the peptide's actions in the rat vas deferens. We studied the effects of NPY, carboxyterminal fragments of this peptide and the NPY analog (Leu31,Pro34)-NPY on three functional responses, namely, the release of [3H]NA and the associated muscle contractions evoked by electrical stimulation, and the accumulation of cAMP stimulated by forskolin. NPY, a known inhibitor of the electrically-evoked [3H]NA release and neurogenic contractions is also a potent inhibitor of the forskolin-stimulated cAMP synthesis in the prostatic portion of the rat vas deferens. However, the ability of NPY to inhibit cAMP accumulation is lost upon tissue denervation, suggesting that this is likely to be a prejunctional effect. Elevation of cAMP levels by the use of the cell permeant analog of cAMP, 8-(p-chlorophenylthio)-cAMP (8pCPTcAMP) increases the electrically-evoked release of [3H]NA. However, the inhibition of [3H]NA release by NPY is not prevented by 8pCPTcAMP. Structure-activity relationship studies reveal that NPY and related peptides inhibit the release of [3H]NA, the muscle contractions and the synthesis of cAMP with a similar pharmacological profile. NPY is the most potent inhibitory agent, whereas [Leu31,Pro34]-NPY and NPY13-36, the respective Y1 and Y2 selective agonists, display similar potencies to inhibit the three responses. It is concluded that NPY inhibits neurotransmission in the rat vas deferens through the activation of a peptide receptor different from the known NPY-Y1 or NPY-Y2 receptor subtypes. NPY receptor activation in the vas deferens is negatively coupled to adenylyl cyclase activity. This intracellular signalling pathway is, however, not likely to mediate the peptide effects on the prejunctional regulation of noradrenaline release.

Antagonistic properties of centrally truncated analogs of [D-Trp(32)]NPY

We have previously shown that [D-Trp(32)]NPY can competitively antagonize NPY-induced feeding in rats (Balasubramaniam et al. J. Med. Chem. 1994, 37, 811-815). This peptide, however, did not bind to SK-N-MC cells with Y-1 receptors. Since centrally truncated NPY analogs have been shown to bind Y-1 receptors, we synthesized similar analogs of [D-Trp(32)]NPY and investigated their Y-1 (SK-N-MC) and Y-2 (SK-N-BE2) receptor affinities and their properties in human erythroleukemia (HEL) cells. None of the analogs with D-Trp(32) mobilized intracellular calcium, [Ca2]i, in HEL cells. Although Des-AA(6-24)[Aoc(6)]NPY and the corresponding D-Trp(32) analog exhibited no affinity to Y-1 receptors, Des-AA(7-24)[Aoc(6),D-Trp(32)] NPY(6) exhibited weak binding. Replacing Pro(5) in 6 with D-Ala to stabilize the central chain reversal, and hence the antiparallel alignment of the N- and C-terminal regions known to be important for Y-1 binding, resulted in an analog, Des-AA(7-24)[D-Ala(5),Aoc(6),D-Trp(32)]NPY (7), which exhibited moderate antagonist potency in attenuating NPY effects on cAMP and [Ca2+]i, in SK-N-MC and HEL cells, respectively. This analog also shifted the dose-response curve of NPY on blood pressure in anesthetized rats. Deletion of only the 7-17 and/or the incorporation of N-Me-Ala(5), superior beta-turn stabilizer, in 7 did not improve the Y-1 receptor affinity. Des-AA(7-24)[D-Ala(5), Gly(6),D-Trp(32)]NPY exhibited an affinity similar to that of 7, suggesting that a long spacer arm is not necessary for efficient Y-1 receptor interaction. Locking the antiparallel alignment via a 2/26 or 2/27 lactam bridge did not improve the binding. Finally, replacement of D-Ala(5) in 7 with D-Trp dramatically increased both the binding and the antagonistic potencies. Modeling based on the avian pancreatic polypeptide X-ray structure suggested that analogs which have the N- and C-terminal regions in close proximity might exhibit good binding, and that the D-Trp(32) substitution may induce a beta-turn that could be important for exhibiting antagonism. A systematic investigation has resulted in the development of relatively potent Y-1 receptor antagonists. Further structure-activity studies with these compounds and those previously reported by us and other investigators should result in the development of long-acting and receptor selective antagonists.

Broad spectrum antibiotic activity of the skin-PYY

Neuropeptide Y (NPY) and polypeptide YY (PYY) are two ubiquitous neuropeptides, found in brain and intestines, respectively, where they exert important regulatory functions. In this study, a new member of the YY family recently isolated from amphibian skin, skin-PYY (SPYY), is reported to inhibit irreversibly the proliferation of a broad spectrum of pathogenic microorganisms. NPY and PYY are shown to be endowed with the same activity. Their potency is similar to that of other antibacterial peptides which have been shown to exert their function by disintegrating the bacterial membrane. These findings and the fact that the C-terminal alpha-helical domain SPYY14-36, which is highly conserved among family members, was responsible for killing microorganisms and for permeation of phospholipid vesicles, suggested that the antibiotic activity may emerge via a membrane permeation mechanism. These findings also raise the question whether NPY and PYY exert in vivo a similar function in mammals.

Inhibitory effect of intrahippocampal NPY injection on amphetamine-induced behavioural activity

The aim of the present study was to investigate the influence of intrahippocampal neuropeptide Y (NPY) administration on the rats' behaviour. The CA1 field or dentate area (GD) of the dorsal hippocampus was chronically implanted with intracerebral cannulae. NPY (or redistilled water in the control group) was injected bilaterally or unilaterally in a volume of 1 microliter to each hippocampus, in a dose of 1 or 2 micrograms per rat. A separate group of rats was pretreated with amphetamine (1 mg/kg, s.c.), 15 min before a bilateral microinjection of NPY (2 micrograms) into the CA1 region. Immediately after the intrahippocampal injection, the rats' behaviour was tested in an open field box. It was found that NPY did not change the locomotor and the exploratory activity after either CA1 or GD administration to non-pretreated animals. In amphetamine pretreated rats, NPY injected into the CA1 field inhibited the amphetamine induced increase in sniffing and rearing and, to a lesser extent, the number of line-crossings. The obtained results may suggest an inhibitory action of NPY in the CA1 hippocampal field on the behavioural hyperactivity.

Proteases involved in the metabolism of angiotensin II, bradykinin, calcitonin gene-related peptide (CGRP), and neuropeptide Y by vascular smooth muscle cells

To understand the regulation of the vasoactive peptides bradykinin, angiotensin II, calcitonin gene-related peptide (CGRP), and neuropeptide Y (NPY), their proteolytic catabolism by cultured rat aortic vascular smooth muscle cells and A7r5 cells was investigated. Endopeptidase-24.11 (EC 3.4.24.11, CD 10) was responsible for the final inactivation of bradykinin, angiotensin II, and CGRP, but not of NPY, which was degraded by a different metallo-endopeptidase. Exopeptidases, namely the aminopeptidases A (EC 3.4.11.7), N (EC 3.4.11.2, CD 13), and P (EC 3.4.11.9) and the carboxypeptidases M (EC 3.4.17.12) and P (EC 3.4.17.16), were important for their differential, receptor subtype-specific activation or inactivation. Aminopeptidase A and N generated angiotensins III and IV from angiotensin II. Aminopeptidase P liberated the terminal amino acids from bradykinin and NPY, yielding the Y2 receptor specific-agonist NPY(2-36). Carboxypeptidase P produced AT II(1-7) and carboxypeptidase M produced the BK1 receptor agonist [des-Arg9]bradykinin. Thus, peptidases at the surface of vascular smooth muscle cells exert a complex influence on the level of biologically active vasoactive peptides.

alpha-Trinositol: a functional (non-receptor) neuropeptide Y antagonist in vasculature

Neuropeptide Y is a sympathetic co-neurotransmitter released with noradrenaline upon sympathetic nerve stimulation. This study describes the ability of a synthetic inositol phosphate, alpha-trinositol(D-myo-inositol 1,2,6-triphosphate; PP 56) to antagonize vasoconstrictor responses to neuropeptide Y in-vitro as well as in-vivo. In human and guinea-pig isolated arteries alpha-trinositol potently (10 nM to 1 microM extracellular concentration) suppressed the constriction evoked by neuropeptide Y alone, the potentiation by neuropeptide Y of noradrenaline-evoked constriction, and the neuropeptide Y-induced inhibition of relaxation. Moreover, in the pithed (areflexive) rat, a non-adrenergic portion of the pressor response to preganglionic sympathetic nerve stimulation was sensitive to alpha-trinositol. As studied in the recently cloned human (vascular-type) Y1 receptor, the action of alpha-trinositol does not occur through antagonism at the neuropeptide Y recognition site nor does it induce allosteric changes of this receptor. However, we found alpha-trinositol to inhibit the rise in intracellular Ca2+ as well as inositol triphosphate concentrations induced by neuropeptide Y. It is, therefore, proposed that alpha-trinositol represents a non-receptor, but yet selective antagonist of neuropeptide Y in vasculature, opening up the possibility to investigate involvement of neuropeptide Y in sympathetic blood pressure control and in cardiovascular disorders.

Differences in the neuropeptide Y-like immunoreactivity of the plasma and platelets of human volunteers and depressed patients

In this study, patients with recurrent major depression were found to have significantly lower neuropeptide Y-like immunoreactivity (NPY-LI) in platelet-poor plasma (p < 0.01) and significantly higher NPY-LI in platelets (p < 0.001) compared to controls. Also, qualitative differences in the NPY-LI in platelet-poor plasma (PPP) and platelets were detected when the samples were analyzed by HPLC followed by RIA of the collected fractions.

Neuropeptide Y gene expression and receptor autoradiography in hypertensive and normotensive rat brain

Neurones containing neuropeptide Y (NPY) may participate in central cardiovascular control by tonically influencing barosensitive neurones within the nucleus tractus solitarius. The present study has employed both in situ hybridisation histochemistry and receptor autoradiography, to visualise the expression of prepro-NPY mRNA in the forebrain and to determine the NPY receptor subtype(s) in the brainstem, respectively. Prepro-NPY gene expression was visualised in the hypothalamus, cortex, dentate gyrus and lateral reticular thalamus from age-matched spontaneously hypertensive rats (SHR) and normotensive Don Ryu rats (DRY) and Wistar Kyoto rats (WKY). Quantitative densitometry revealed an increase in the NPY transcript in the arcuate nucleus of SHR rats compared to their normotensive counterparts. Autoradiography using [125I]Bolton-Hunter-NPY (BH-NPY, 15 pM) demonstrated NPY binding sites in the area postrema, the commissural nucleus tractus solitarius (cNTS) and the inferior olivary complex. NPY (1 microM) and peptide YY (1 microM), but not [Leu31,Pro34]NPY (10-100 nM), fully inhibited the binding of [125I]BH-NPY. These results indicate that NPY receptors of the Y2 subtype predominate in the dorsal vagal complex. Unilateral nodose ganglionectomy resulted in a partial loss of NPY binding sites in the commissural NTS, but not the area postrema, suggesting that a proportion of binding sites (Y2 subtype) are present on central vagal terminals. While all three rat strains appear to have the same relative proportions of NPY receptor subtypes in the brainstem, the relevance of the differential NPY gene expression in the arcuate nucleus regarding central cardiovascular control mechanisms and/or the pathogenesis of hypertension remains to be elucidated.

Neuropeptide Y is a vasoconstrictor and adrenergic modulator in the hamster microcirculation by acting on neuropeptide Y1 and Y2 receptors

The microvascular effects of neuropeptide Y, and two analogs with preferential affinity for different neuropeptide Y receptor subtypes, were assessed by intravital microscopy on the hamster cheek pouch. The interaction of neuropeptide Y and its analogs with noradrenaline was also studied. Superfusion with 0.1-300 nM neuropeptide Y caused a concentration-dependent reduction in microvascular conductance that was paralleled by reductions in arteriolar and venular diameters. These effects of neuropeptide Y were equipotent with noradrenaline, but slower to develop and longer-lasting than that of noradrenaline. Neuropeptide Y did not affect permeability to macromolecules, as measured by extravasation of fluorescent dextran. The neuropeptide Y Y1 receptor agonist, [Leu31,Pro34]neuropeptide Y, mimicked neuropeptide Y with similar potency but shorter duration, while neuropeptide Y-(13-36), a neuropeptide Y Y2 receptor agonist, was at least 10-fold less potent than neuropeptide Y to induce a delayed and prolonged reduction in microvascular conductance. The joint superfusion of 1 nM neuropeptide Y plus 0.1 mu M noradrenaline did not cause synergism, nor even summation of effects, but reduced the contractile effect of noradrenaline. No synergism was observed after a 10 min priming with 1 nM neuropeptide Y, followed by its joint application with 0.1 mu M noradrenaline, but a significant vasodilation and hyperemia ensued upon stopping noradrenaline application. Priming with 1 nM [Leu31,Pro34]neuropeptide Y prolonged noradrenaline vasoconstriction without evidence of hyperemia. In contrast, priming with 1 nM neuropeptide Y-(13-36) significantly antagonized noradrenaline vasoconstriction. These findings indicate that both neuropeptide Y receptor subtypes are present in arterioles and venules of the hamster, and suggest that their activation with neuropeptide Y induces a rapid (Y1 receptor subtype activation) and a delayed (Y2 receptor subtype activation) vasocontractile response. The interaction with noradrenaline is complex, without evidence for synergism, but neuropeptide Y Y2 receptor activation seems to antagonize noradrenaline and/or to facilitate auto-regulatory vasodilation after the catecholamine-induced vasoconstriction.

Neuropeptide Y accounts for sympathetic vasoconstriction in guinea-pig vena cava: evidence using BIBP 3226 and 3435

The ability of the novel, non-peptide, neuropeptide Y Y1 receptor antagonist, BIBP 3226 ((R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininami de), to antagonize neuropeptide Y- and sympathetic-mediated vasoconstriction was examined in isolated segments of the thoracic vena cava of guinea-pigs. Increasing concentrations (10(-9) - 10(-6) M) of BIBP 3226 caused a parallel and rightward shift in the neuropeptide Y dose-response curve but did not significantly change the effect of noradrenaline. The calculated pA2 value for BIBP 3226 was 8.0 +/- 0.08, a value fully compatible with the reported affinity at rodent and human neuronal Y1 receptors. BIBP 3226 (10(-6) M) also readily reversed the established vasocontraction induced by neuropeptide Y. BIBP 3226 (10(-6) M) markedly inhibited the slow long-lasting contraction evoked by high frequency electrical field stimulation, leaving a rapid component which was abolished by phentolamine. Its enantiomer, BIBP 3435 ((S)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-argininami de), which exerts a much weaker action on neuropeptide Y Y1 receptors, had no such inhibitory effect. In propranolol-pretreated vessels, the vasoconstriction evoked by nerve stimulation was enhanced; then BIBP 3226 inhibited the peak response by 44%, and the integrated contractile effect by 90%. We conclude that BIBP 3226 is a potent and competitive antagonist of neuropeptide Y Y1 receptor-mediated vasoconstriction in guinea-pig vena cava and that endogenous neuropeptide Y acting on the neuropeptide Y Y1 receptor is likely to account for the long-lasting component of the sympathetic vasoconstriction in response to high-frequency stimulation in this vessel.

Vascular reactivity to noradrenaline and neuropeptide Y in the streptozotocin-induced diabetic rat

The study aimed to assess vascular reactivity to noradrenaline with and without neuropeptide Y in diabetic rats, and to determine whether any abnormality could be attributed to insulin deficiency or to hyperglycaemia per se. The authors compared non-diabetic rats (n = 9) and rats with streptozotocin-induced diabetes that were either untreated (n = 10), or treated with insulin (n = 9) or food restriction (n = 8) to restore near-normoglycaemia. After 4 weeks of diabetes, contractile responses to noradrenaline (0.24-48 mumol L-1), without and with neuropeptide Y (0.1 mumol L-1), were assessed using an isometric myograph in two mesenteric arteries from each rat. Vessels from untreated diabetic rats were significantly more reactive to noradrenaline than the control vessels when tested without (P < 0.0001) but not with (P = NS) neuropeptide Y. Diabetic rats rendered nearly normoglycaemic through food restriction showed dose-response curves that were very similar to the untreated diabetic group (P = NS). By contrast, insulin-treated diabetic vessels showed reduced sensitivity to noradrenaline, with and without neuropeptide Y, compared with both the diet-restricted and untreated vessels (both P < 0.0001). The authors conclude that vascular sensitivity to noradrenaline, without or with neuropeptide Y, is reduced over a wide dose range in vessels taken from rats treated in vivo with insulin; furthermore, vessels taken from diabetic rats not treated with insulin (hypoinsulinaemic) tended to be more reactive than either control vessels or those taken from the insulin-treated rats. The latter group of rats were probably hyperinsulinaemic for much of the time; the results may therefore support the hypothesis that insulin acts as a vasodilator.

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.

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.

Cloning and functional expression of a cDNA encoding a human type 2 neuropeptide Y receptor

Neuropeptide Y (NPY) is a 36-amino acid polypeptide that is widely distributed in the central nervous system and periphery. Pharmacological studies have suggested that there are at least three receptor subtypes, Y1, Y2, and Y3. Cloning of the Y1 subtype has been reported previously. Here we report the isolation by expression cloning of a cDNA encoding a human NPY receptor displaying a pharmacology typical of a Y2 receptor. COS-7 cells transfected with the cDNA express high affinity binding sites for NPY, peptide YY, and NPY13-36, whereas [Leu31,Pro34]NPY binds with lower affinity. The receptor is 381 amino acids in length and has seven putative transmembrane regions typical of G-protein-coupled receptors. Comparison of the amino acid sequence of this Y2 receptor to that of the human Y1 receptor indicates that the two receptors are 31% identical at the amino acid level. Northern blot analyses reveal a single 4-kilobase mRNA species and indicate that the messenger RNA is present in many areas of the central nervous system. NPY induced calcium mobilization and inhibited forskolin-stimulated cAMP accumulation in Chinese hamster ovary cells that stably express the Y2 receptor cDNA, indicating that the recombinant Y2 receptor is functionally coupled to second messenger systems.

Cardiovascular and renal effects of alpha-trinositol in ischemic heart failure rats

Previous studies have demonstrated that alpha-trinositol (D-myo-inositol-1.2.6-trisphosphate; PP56) may act as a functional neuropeptide Y (NPY) inhibitor. Because NPY is known to be a potent vasoconstrictor, the effects of alpha-trinositol on renal function, vascular responses and the potentiating effects of NPY were investigated in rats with congestive heart failure (CHF) induced by ligation of the left coronary artery. Incremental doses of alpha-trinositol were given to conscious rats (bolus 2, 4 or 10 mg/kg i.v. followed by a 15-minute infusion 20, 40 and 100 mg/kg/h, respectively). Urinary volume, sodium and potassium excretions were significantly increased in both CHF and sham-operated control animals after alpha-trinositol administration compared with saline. Diuresis and natriuresis were observed also during co-administration of alpha-trinositol with NPY but not with norepinephrine (NE). In the pithed CHF rats, threshold doses of NPY potentiated the pressor effects of endothelin-1 (ET-1) and angiotensin II (AII), but not preganglionic nerve stimulation or phenylephrine administration. Alpha-trinositol antagonized both the pressor response to NPY and the potentiation by NPY of pressor responses to effects of ET-1 and AII. Our data show that alpha-trinositol exhibis diuretic and natriuretic effects as well as vascular antagonistic effects on NPY in normal and CHF rats. These effects of alpha-trinositol may be due to an interaction with NPY mediated antidiuresis and antinatriuresis.

The effect of neuropeptide Y on sodium, chloride and potassium transport across the rat distal colon

1. Neuropeptide Y (NPY; 10(-10)-10(-7) mol l-1) reduced basal short-circuit current (Isc) in a concentration-dependent manner in the rat distal colon but was ineffective in the proximal colon. 2. The action of NPY was dependent upon the presence of Cl- and HCO3- anions and was blocked by prior treatment of the tissue with a Cl- channel blocker. The decrease in Isc was associated with an increase in mucosa-to-serosa fluxes of Na+, Rb+ (K+) and Cl-, whereas the serosa-to-mucosa flux of Cl- was decreased. 3. The size of the inhibitory NPY effect was linearly correlated with the height of the basal Isc, i.e. it inhibited 55% of basal secretory Isc. 4. The action of NPY was unaffected by indomethacin and tetrodotoxin, when given alone, but was abolished, when the basal Isc was decreased to values near zero by a combination of both inhibitors. This inhibition could be overcome by restoring basal Isc with prostaglandin E2, indicating that the effect of NPY is not mediated by nerves or prostaglandins, but that NPY is only effective, when anion secretion is stimulated by the spontaneous release of neurotransmitters and prostaglandins. 5. NPY inhibited the increase in Isc induced by veratridine and prostaglandin E2, but it had no effect on the Isc induced by direct stimulation of the adenylate cyclase with forskolin, or on Isc induced by stimulation of the Ca(2+)-pathway with carbachol. Inhibition of the response to veratridine or prostaglandin E2 by NPY showed the same dependence on the height of the ISC just prior to addition of NPY as seen in control conditions, i.e. NPY inhibited 55% of cyclic AMP-mediated secretion.6. These results suggest that the effect of NPY is mediated by an inhibition of cyclic AMP-stimulated secretion, which is stimulated in the rat distal colon by a continuous release of prostaglandins and neurotransmitters.

Involvement of the Y2 receptor subtype in the regulation of prolactin gene expression by neuropeptide Y in the male rat

In order to determine the influence of neuropeptide Y (NPY) on the biosynthesis of prolactin (PRL), we have studied the effects of NPY and some NPY analogs on PRL gene expression in the male rat anterior pituitary gland. The following peptides (4 micrograms/100 g body wt): NPY, peptide YY (PYY), NPY13-36 (a Y2 receptor agonist) and [Leu31,Pro34]NPY (a Y1 receptor agonist) were injected into the left lateral ventricle of adult male rats. Control animals received only the vehicle (0.9% NaCl). All the animals were perfused with 4% paraformaldehyde 4 h after injection and processed for in situ hybridization. The intracerebroventricular injection of NPY, PYY, and NPY13-36 induced a significant increase in the hybridization signal (22-40% over control). On the other hand, the Y1 receptor agonist [Leu31,Pro34]NPY did not influence PRL mRNA levels. These data then suggest that activation of the Y2 NPY receptor subtype at the central level can positively regulate PRL gene expression.

Reduction of vasoconstriction mediated by neuropeptide Y Y2 receptors in arterioles of the guinea-pig small intestine

Brief applications of a high-K+ solution were used to evoke transient constrictions of arterioles from the guinea-pig small intestine. Analogues of neuropeptide Y (NPY) selective for Y2-receptors reduced the constrictions, whereas NPY or a Y1-selective analogue potentiated the constrictions. We conclude that arteriolar smooth muscle has both Y1 and Y2 receptors, and suggest that Y2 receptors inhibit vasoconstriction by modulating the opening of voltage-sensitive Ca2+ channels. This may be related to the role of NPY that is present in some vasodilator nerves.

Differential mechanism of peptide YY and neuropeptide Y in inhibiting motility of guinea-pig colon

The effect of peptide YY on contractility, acetylcholine release and noradrenaline release was examined in the isolated guinea-pig colon, and findings were compared with those for neuropeptide Y. Peptide YY and neuropeptide Y inhibited the twitch contractions mediated by the stimulation of cholinergic neurons. Peptide YY, neuropeptide Y, [Leu31,Pro34]neuropeptide Y and neuropeptide Y-(13-36) inhibited the electrically stimulated release of acetylcholine. Neuropeptide Y, but not peptide YY, inhibited the high K(+)-stimulated tetrodotoxin-resistant release of acetylcholine, while the inhibitory effect of neuropeptide Y disappeared after treatment with yohimbine. Neuropeptide Y, but not peptide YY or neuropeptide Y analogues, evoked the release of noradrenaline. After desensitization to the effects of neuropeptide Y, peptide YY inhibited electrically stimulated acetylcholine release. Thus, peptide YY inhibits acetylcholine release through stimulation of a receptor, distinct from the site of action of neuropeptide Y, located on cholinergic neurons as well as the neuropeptide Y Y1 and Y2 receptors in the guinea-pig colon. Neuropeptide Y inhibits acetylcholine release due to the noradrenaline release mediated by stimulation of a receptor distinct from neuropeptide Y Y1 and Y2 receptors, located on adrenergic neurons.