Neuropeptide Y receptor in pig spleen: binding characteristics, reduction of cyclic AMP formation and calcium antagonist inhibition of vasoconstriction

Splanchnic and renal vasoconstrictor and metabolic responses to neuropeptide Y in resting and exercising man

The local clearance of neuropeptide Y (NPY) and whether NPY influences splanchnic and renal metabolism in man have not been investigated previously. The influence of NPY on splanchnic and renal blood flows at physiologically elevated levels has also not been investigated. The effects of a 40-min constant NPY infusion (3 pmol kg-1 min-1) at rest and during 130 min of exercise (50% of VO2max) were studied in six healthy subjects and compared with resting and exercising subjects receiving no NPY. Blood samples were drawn from arterial, hepatic and renal vein catheters for the determination of blood flows (indicators: cardiogreen and para-aminohippuric acid [PAH]), NPY, catecholamines, glucose, lactate and glycerol. NPY infusion was accompanied by: (1) significant fractional extraction of NPY-like immunoreactivity (NPY-Li) by splanchnic tissues at rest (58 +/- 5%) and during exercise (53 +/- 6%), while no arterial-venous differences could be detected across the kidney; (2) a reduction in splanchnic and renal blood flows of up to 18 and 13% respectively (P less than 0.01-0.001) at rest without any additional changes during exercise; and (3) metabolic changes as reflected in: (a) a more marked fall in arterial glucose during exercise compared to the reference group (P less than 0.05); (b) a 35% lower splanchnic glucose release (P less than 0.01) during exercise due to diminished glycogenolysis (P less than 0.01); and (c) a lower arterial lactate level (18% P less than 0.05) together with unchanged splanchnic lactate uptake during exercise, suggesting reduced lactate production by extrahepatic tissues. The disappearance of plasma NPY-Li after the infusions was biphasic with two similar half-lives at rest (4 and 39 min) and during exercise (3 and 43 min).

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

Neuropeptide Y (NPY), a sympathetic cotransmitter, has both prejunctional and postjunctional actions in the cardiovascular system. In the bioassay system used here NPY attenuates cardiac vagal action (an indicator of prejunctional or Y2 action) and increases blood pressure (an indicator of postjunctional or Y1 action). [Leu31,Pro34]NPY has little or no prejunctional activity i.e. does not attenuate cardiac vagal action, but increases blood pressure as effectively as NPY. [Leu31,Pro34]NPY can therefore be used in functional experiments to distinguish between the two types of NPY receptor.

Neuropeptide Y receptor in bovine hippocampus is a Y2 receptor

[125I]NPY bound to a single class of saturable binding sites on bovine hippocampus membranes with a KD of 0.1 mM and Bmax of 165 fmol/mg of protein. The rank order of potency of NPY fragments and other structurally related peptides to inhibit [125I]NPY binding was: PYY greater than or equal to NPY much greater than BPP greater than or equal to APP and NPY greater than NPY-(13-36) greater than NPY-(18-36) greater than or equal to NPY-(20-36) much greater than NPY-(26-36) greater than NPY-(free acid). The identity of the NPY binding site was investigated by affinity labeling. Gel electrophoresis followed by autoradiography revealed a band with a mol mass of 50 kDa. Unlabeled NPY or PYY, but not BPP, HPP and APP, inhibited labeling of [125I]NPY to the 50 kDa protein band. Moreover, labeling was inhibited by NPY greater than NPY-(18-36) greater than or equal to NPY-(13-36) greater than or equal to NPY-(20-36) greater than NPY-(26-36) greater than NPY-(free acid). The binding of [125I]NPY and the intensity of the cross-linked band were reduced in parallel by increasing concentrations of unlabeled NPY (IC50 = 0.7 nM and 0.6 mM, respectively). These studies demonstrate that bovine hippocampal membranes contain a 50 kDa [125I]NPY binding site that has the ligand specificity characteristic of the Y2 receptor subtype.

Neuropeptide Y (NPY) receptors in HEL cells: comparison of binding and functional parameters for full and partial agonists and a non-peptide antagonist

1. We have compared the binding and Ca2+ mobilizing properties of various full agonists, partial agonists and a non-peptide antagonist at the neuropeptide Y (NPY) receptor of human erythroleukemia (HEL) cells. 2. [125I]-NPY binding to intact HEL cells was rapid, saturable, of high affinity and with a specificity typical for the Y1-like subtype: NPY, peptide YY (PYY) and [Pro34]-NPY competed for [125I]-NPY binding with high affinity whereas NPY13-36 and NPY18-36 had only low affinity. 3. NPY, PYY and [Pro34]-NPY potently increased intracellular Ca2+ in HEL cells and had equal efficacy. NPY13-36, vasoactive intestinal peptide (VIP) and pancreatic polypeptide (PP) increased intracellular Ca2+ only poorly. 4. Whereas VIP and PP did not significantly affect NPY-stimulated Ca2+ mobilization, NPY13-36 inhibited NPY-stimulated Ca2+ increases and shifted the NPY concentration-response curve to the right without altering its maximal effect. 5. The agonist (pEC50) potencies of the various peptides corresponded well with the affinities of these compounds in the binding assay (pKi), whereas the antagonist potencies (pKb) of the peptide partial agonists and the pA2 value of the non-peptide NPY antagonist (He 90481), calculated from functional data, were lower than the respective affinities determined in the binding studies. 6. A plot of the fractional Ca2+ response vs the fractional receptor occupancy did not reveal any non-linear receptor-effector coupling for NPY or [Pro34]-NPY; a small receptor reserve might exist for PYY. 7. We conclude that the binding and functional properties of HEL cell NPY receptors are very similar. NPY, PYY and [Pro34]NPY are full agonists at these receptors, whereas NPY13-36 is a partial agonist.

Characteristics of endothelin A and B binding sites and their vascular effects in pig peripheral tissues

The characteristics of endothelin-1 (ET-1) and endothelin-3 (ET-3) binding, and their relationship to second messenger formation in vitro and vascular effects in vivo were studied in the pig. Specific high-affinity binding sites for [125I]ET-1 and [125I]-ET-3 with extremely slow dissociation rates were demonstrated in membrane preparations from the spleen, lung, kidney and spinal cord. Displacement studies showed that receptor populations with much higher affinity for ET-1 than for ET-3 (ETA type) were present in the spleen and renal arteries, while in the whole kidney and spinal cord, receptor populations with similar affinity for ET-1 and ET-3 were found (ETB type). In the lung both receptor subtypes may be present. The precursor forms big ET-1 and big ET-3 were poor ligands although big ET-1 was more active on the ETA site than big ET-3 on the ETB site. Scatchard analysis revealed linear plots in all tissues studied. Both ET-1 and ET-3 increased formation of inositol phosphates in the lung, while ET-1 but not ET-3 was effective in the spleen. Neither ET-1 nor ET-3 were observed to influence basal or stimulated cyclic AMP formation in lung or spleen. ET-1 caused a much more potent and long-lasting increase in splenic and renal vascular resistance in vivo than did ET-3. On the other hand, ET-1 and ET-3 decreased vascular resistance with almost equal potency in the bronchial circulation.

Evidence for two neuropeptide Y receptors mediating vasoconstriction

The presence of receptor subtypes mediating the vascular and prejunctional effects of neuropeptide Y (NPY) was investigated using the Y2 receptor agonist, NPY-(13-36), and the Y1 agonist, [Leu31,Pro34]NPY. NPY-(1-36) and [Leu31,Pro34]NPY administered i.v. to anesthetized pigs evoked dose-dependent increases in mean arterial blood pressure and splenic and renal vascular resistance, and a decrease in heart rate. The potency of [Leu31,Pro34]NPY was 10-30% that of NPY-(1-36). In the spleen, NPY-(13-36) evoked vasoconstriction similar to that evoked by [Leu31,Pro34]NPY, but did not significantly increase renal vascular resistance or mean arterial blood pressure. Local intra-arterial administration of [Leu31,Pro34]NPY caused an increase in nasal mucosal vascular resistance with a potency similar to that of NPY-(13-36) evoked only a minor (17%) increase in nasal mucosal vascular resistance. The NPY analogues were further characterized in receptor binding studies on pig spleen membranes. Compared to NPY-(1-36), 800 times higher concentrations of [Leu31,Pro34]NPY, and 7 times higher concentrations of NPY-(13-36) were required to achieve the same 50% displacement of [125I]NPY-(1-36). Electrically evoked contractions in rat vas deferens were inhibited by 50% by 0.05 microM NPY-(1-36) and 0.3 microM NPY-(13-36), while [Leu31,Pro34]NPY only slightly attenuated the contractions (by 24% at 1 microM). The present data suggest the existence of subtypes of NPY receptors mediating vasoconstriction. Thus, the splenic vascular bed of the pig contains both Y1 and Y2 receptors while the Y1 subtype predominates in the kidney, nasal mucosa and for blood pressure control. The prejunctional receptor in rat vas deferens seems to be of the Y2 subtype.

Pertussis toxin attenuates postsynaptic actions of neuropeptide Y on the guinea-pig uterine artery

The mechanisms by which neuropeptide Y (NPY) mediates its postsynaptic actions on the guinea-pig uterine artery, were investigated by incubating arterial segments in culture medium containing pertussis toxin (PTX). Arteries were incubated with 0, 0.25 or 1 microgram.ml-1 PTX for 24 or 48 h. Arterial segments incubated in culture medium without PTX showed the three postsynaptic responses to NPY which were reported previously in uncultured arteries: NPY further contracted segments which were precontracted with prostaglandin F2 alpha; NPY reduced the maximum relaxations produced by vasoactive intestinal peptide (VIP); and NPY produced a rightward shift in the VIP concentration-response curves. PTX attenuated the three actions of NPY on the uterine artery to different degrees. PTX also reduced the magnitude of contractions produced by prostaglandin F2 alpha, but did not affect contractions produced by 0.126 M KCl, or relaxations produced by VIP in the absence of NPY. These data indicate that all postsynaptic actions of NPY on the uterine artery, and contractions produced by prostaglandin F2 alpha, are at least partly mediated by pertussis toxin-sensitive GTP-binding proteins. It is not clear whether these multiple actions of NPY are mediated by one, or more than one, GTP-binding protein.

Neuropeptide Y (NPY) metabolism by endopeptidase-2 hinders characterization of NPY receptors in rat kidney

1. Despite the observation of pharmacological responses to neuropeptide Y (NPY) in mammalian kidneys, there are species differences in the ease with which specific NPY binding sites can be demonstrated; we have investigated whether this can be explained by differential metabolism of NPY by a membrane-bound peptidase. 2. NPY receptors were identified on cell membranes isolated from the rabbit kidney (KD = 97 +/- 16 pM, Bmax = 290 +/- 30 fmol mg-1 protein), and this preparation did not degrade [125I]-NPY. However, a similar preparation of cell membranes from the rat kidney exhibited a much lower apparent receptor affinity (IC50 approximately 30 nM); these membranes rapidly degraded [125I]-NPY to fragments which did not bind NPY receptors in either tissue. 3. [125I]-NPY binding sites were revealed in the rat kidney when degradation was inhibited by insulin B chain. Chelating agents also inhibited degradation, but interfered with receptor binding. Binding sites could not be demonstrated in sections of rat kidney, even in the presence of insulin B chain. 4. The difference in degradative activity between rat and rabbit renal cell membranes, inhibition of degradation by chelating agents and insulin B chain, and insensitivity to phosphoramidon suggest that the enzyme responsible was endopeptidase-2, and this was confirmed by comparing the hydrolysis of [125I]-NPY by purified enzyme with rat renal tissue. Activity of this enzyme explains the difficulties encountered demonstrating receptors in the rat kidney. 5. Renal cell membranes from the mouse digested [125I]-NPY in a similar manner and this may be due to the closely related enzyme, meprin. NPY degradation has not previously been reported. The results suggest that NPY should be added to the list of peptides sensitive to these enzymes.

Receptors for neuropeptide Y: multiple subtypes and multiple second messengers

Neuropeptide Y (NPY) can elicit numerous physiological responses by activating specific pre- and postsynaptic receptors. Different orders of potency for agonists in various model systems suggest that there are multiple subtypes of NPY receptors, described here by Martin Michel, but their pharmacological definition remains tentative, awaiting development of specific antagonists and receptor cloning studies. The coupling of NPY receptors to various signal transduction mechanisms is also reviewed, including inhibition of adenylyl cyclase and stimulation or inhibition of increases in intracellular Ca2+, but a link between individual NPY receptor subtypes and specific signal transduction pathways has not been established.

Sympathetic stimulation-evoked overflow of norepinephrine and neuropeptide Y from the heart

Neuropeptide Y (NPY) and norepinephrine are released together on sympathetic activation. To compare the time courses of NPY and norepinephrine washout from cardiac tissues, we measured the overflow of NPY-like immunoreactivity (NPY-LI) and norepinephrine in coronary sinus blood before, during, and after 3-minute trains of ansae subclaviae stimulation in 13 anesthetized dogs. We also measured vagally induced cardiac cycle length responses before and after ansae stimulation. Ansae stimulation increased NPY-LI and norepinephrine overflow from the heart in a frequency-dependent manner (p less than 0.02). After stimulation of the ansae at 5 and 10 Hz, the peak norepinephrine overflows decayed by 90% within 2 minutes, but the NPY-LI overflows required 17 +/- 11 and 35 +/- 21 minutes, respectively, to decay by 90%. Cardiac vagal effects were inhibited after 5- and 10-Hz ansae stimulations, and the peak inhibitions decayed by 90% after 19 +/- 7 and 39 +/- 16 minutes, respectively. The 90% decay times of the NPY-LI overflows were longer (p less than 0.003) than those of the norepinephrine overflows but did not differ significantly (p greater than 0.4) from the 90% decay times of the inhibition of vagal effects. We characterized NPY-LI in coronary sinus and arterial plasma by reversed-phase high-performance liquid chromatography. Before ansae stimulation, the main peak of NPY-LI in the plasma had a retention time similar to that of the oxidized human NPY-(1-36) standard. During ansae stimulation, however, there was a substantial increase in the peak of NPY-LI that eluted in a position similar to that of the monoxidized human NPY-(1-36) standard. These data support the hypothesis that neurally released NPY mediates the sympathetically evoked inhibition of vagal effects and indicate that the time course of removal of NPY from the heart differs substantially from that of norepinephrine. Moreover, under basal conditions, most NPY in the circulation is present in the oxidized form or as a fragment of the 36-amino-acid peptide. In contrast, cardiac sympathetic stimulation evokes the overflow of monoxidized NPY-(1-36) into the coronary sinus plasma.

Peptide YY reduces effects of sympathetic nerves and neuropeptide Y on cardiac vagal action

In anesthetized dogs intravenous injection of neuropeptide Y (NPY) or stimulation of the cardiac sympathetic nerve is followed by a period of attenuation of vagal action at the heart lasting from many minutes to over an hour. Peptide YY (PYY), a related peptide (but one not reported to occur in the heart or its autonomic innervation), also inhibits cardiac vagal action but is more powerful and has a longer duration action. In 5 of 9 dogs, cardiac sympathetic nerve stimulation inhibited vagal action on the heart in control conditions, but relieved preexisting inhibition when repeated in the presence of PYY. In 3 dogs, exogenous NPY inhibited cardiac vagal action in control conditions, but failed to augment preexisting inhibition in the presence of PYY. An explanation offered for these results is that when PYY is occupying receptors on vagal nerve terminals, nerve-released NPY or exogenous NPY is either unable to produce an effect, because it cannot gain access to the receptors, or displaces PYY from at least some receptors and, being less powerful than PYY in its inhibitory action, lessens the preexisting vagal attenuation. The results reported are consistent with the proposal that the factor released from the sympathetic nerves following their stimulation and which is responsible for cardiac vagal inhibition is NPY.

G-protein coupling and signalling of Y1-like neuropeptide Y receptors in SK-N-MC cells

We have studied [125I]neuropeptide Y-binding sites and neuropeptide Y-mediated second messenger responses in human SK-N-MC neuroblastoma cells with special reference to the role of G-proteins. Neuropeptide Y stimulated two second messenger responses in SK-N-MC cells, inhibition of cAMP accumulation and mobilization of Ca2+ from intracellular stores. Both effects were completely abolished by pretreatment with pertussis toxin. Binding of [125I]neuropeptide Y to intact cells or SK-N-MC cell membranes was rapid, reversible, characterized by high affinity and low capacity, and had pharmacological characteristics of a homogeneous population of Y1-like neuropeptide Y receptors. In permeabilized cells, [125I] neuropeptide Y binding was inhibited by GTP gamma S in a concentration-dependent manner. Saturation experiments in the absence and presence of GTP gamma S demonstrated a reduction in the number of high-affinity [125I]neuropeptide Y-binding sites without a decrease in affinity of the remaining sites. Pretreatment of intact cells with pertussis toxin completely abolished the inhibition of [125I]neuropeptide Y binding by GTP gamma S. Moreover, pertussis toxin treatment reduced the number of high-affinity [125I]neuropeptide Y binding sites. We conclude that the agonist ligand [125I]neuropeptide Y identifies functional neuropeptide Y receptors in SK-N-MC cells; however, the number of specific [125I]neuropeptide Y-binding sites may not necessarily reflect the number of neuropeptide Y receptors, because the former is affected by the functional state of cellular G-proteins.

Neuropeptide Y receptor in vascular smooth muscle

125I-Bolton-Hunter (125I-BH) neuropeptide Y (NPY) was used to identify specific high-affinity NPY binding sites in porcine aortic smooth muscle membrane fractions and to characterize the binding sites in comparison with those in porcine hippocampal membrane fractions. Ca2+, but not Mg2+ or Mn2+, enhanced specific 125I-BH-NPY binding in aortic smooth muscle, while all of the cations did in hippocampus. The fast, saturable, and selective binding was to a single population of sites, with a KD of 0.99 +/- 0.11 nM and a Bmax of 0.35 +/- 0.06 fmol/mg protein. GTP and its non-hydrolyzable analogues reduced 125I-BH-NPY binding dose dependently. Neither calcium channel blockers nor noradrenaline had any effect on the binding. Among structurally related peptides, peptide YY displaced 125I-BH-NPY binding as potently as NPY, while human, avian, and rat pancreatic polypeptides displaced 125I-BH-NPY binding 100 times less potently than NPY. The C-terminal fragment NPY(13-36) for inhibiting 125I-BH-NPY binding in aortic smooth muscle was approximately 40 times less potent than in the hippocampus. When we examined the effect of these peptides on cytosolic free Ca2+ ([Ca2+]i) in cultured porcine aortic smooth muscle cells, only the peptides showing high affinity for 125I-BH-NPY binding sites increased [Ca2+]i. These results indicate that the NPY binding sites labeled by 125I-BH-NPY in aortic smooth muscle are functional receptors and have different properties from those in the hippocampus with respect to dependency on divalent cations, sensitivity to GTP analogues, and affinity for NPY(13-36) and pancreatic polypeptides.

The role of neuropeptides in cardiovascular regulation

During the past few years more than 30 novel, biologically active peptides have been discovered. Some are produced in endocrine glands and circulate as hormones in the blood; others are contained in the enterochromaffin cells of the gut and may be involved in the regulation of intestinal functions. The vast majority of new peptides, however, have been detected in the central and peripheral nervous systems, where they are synthesized in distinct neurons and stored in neurovesicles. Many of these neuropeptides may be involved in circulatory regulation. There is evidence supporting such a role, especially for centrally located angiotensin, opioid peptides, substance P, neuropeptide Y (NPY), vasopressin, atrial natriuretic peptide (ANP), kinins, corticotropin releasing factor, bombesin, and somatostatin. In this review we discuss the cardiovascular actions of angiotensin, neuropeptide Y, and calcitonin gene related peptide.

[Pro34]neuropeptide Y selectively identifies postjunctional-mediated actions of neuropeptide Y in vivo in rats and dogs

Anaesthetised rats and dogs were used to study the pre- and postjunctional actions of neuropeptide Y (NPY) and [Pro34]NPY simultaneously. Increases in arterial blood pressure indicated postjunctional actions and both NPY and [Pro34]NPY elicited these. Change in pulse interval evoked by stimulation of the cut peripheral end of the right vagus nerve, indicated prejunctional action of the peptides: NPY caused prolonged attenuation of vagal action in rats and dogs but [Pro34]NPY did not attenuate vagal action in rats or dogs.

The effect of neuropeptide Y on mucociliary activity in the rabbit maxillary sinus

The effect of neuropeptide Y (NPY) on mucociliary activity in the rabbit maxillary sinus was investigated in vivo by injecting NPY at increasing dosages into the maxillary artery, response being recorded photoelectrically. At dosages of 0.1-5.0 micrograms/kg, NPY reduced mucociliary activity dose-dependently, the maximum decrease being 14.6 +/- 1.8%, at a dosage of 5.0 micrograms/kg. The NPY-induced reduction of the mucociliary activity manifested brief latency, the peak effect occurring within 3 min followed by a slow return to the baseline value 4-9 min after injection. The response of mucociliary activity to NPY remained unaffected by pretreatment with the alpha-adrenergic antagonists yohimbine (alpha 2) at 100.0 micrograms/kg and phentolamine (alpha 1 + alpha 2) at 0.2-1.0 mg/kg, indicating that the effect of NPY is not mediated via alpha-receptors. Pretreatment with the calcium antagonist nifedipine at 100.0 micrograms/kg inhibited the effect of NPY, suggesting that the NPY-induced decrease may be calcium dependent.

C-terminal modifications of neuropeptide Y and its analogs leading to selectivity for the mouse brain receptor over the porcine spleen receptor

Neuropeptide Y (NPY) is known to bind to at least two types of receptors (Y1 & Y2). One type (Y2) is able to bind and undergo activation by both NPY and its C-terminal fragments with good potency while the other (Y1) requires the full length of NPY for good potency. For most NPY analogs that have been examined, potency for the Y2 system (porcine spleen) is greater than or equal to that for the Y1 system (mouse brain), since the Y2 system is generally less selective. However, modifications of NPY and its analogs at position 34 can lead to materials with some Y1 selectivity. For example, [Pro34]-pNPY binds to mouse brain with an affinity of 0.14 nM. Its affinity for porcine spleen is 140 nM. [His34]-pNPY was also found to be Y1 selective (19-fold), but not to the degree of the [Pro34] analog (1000-fold). The Pro34 modification in the Y2 selective C-terminal fragment NPY (20-36) converted it into an essentially non-selective analog. The selectivity from the Pro34 substitution results from a loss of Y2 binding potency along with little effect on the Y1-receptor binding. Therefore, Y1 and Y2 receptors have differing requirements for the C-terminal region of NPY in addition to their different requirements for NPY's N-terminus.

Neuropeptide Y and sympathetic neurotransmission

The coexistence of neuropeptide Y (NPY) with noradrenaline (NA) in perivascular nerves as well as in sympathetic nerves to muscle in the heart, spleen and vas deferens suggests a role for NPY in autonomic transmission. Sympathetic nerve stimulation or reflexogenic activation in experimental animals or man are associated with NPY release as revealed by overflow mainly upon strong activation. This difference between NPY and NA secretion may be related to the partly separate subcellular storage whereby NPY seems to be exclusively present in the large dense-cored vesicles. The NPY secretion is likely to be regulated by the local biophase concentrations of NA acting on prejunctional alpha-2-adrenoceptors since alpha-2 agonists inhibit and antagonists enhance NPY overflow, respectively. Furthermore, after NA has been depleted by reserpine, the nerve stimulation-evoked release of NPY is enhanced leading to a progressive depletion of tissue content of NPY. Exogenous NPY binds to both pre- and postjunctional receptors, inhibits NA and NPY release, enhances NA-evoked vasoconstriction and induces vasoconstriction per se. The prejunctional action of NPY which is especially noticeable in the vas deferens may serve to reduce transmitter secretion upon excessive stimulation. The long-lasting vasoconstriction evoked by sympathetic stimulation in several tissues including skeletal muscle, nasal mucosa and spleen, which remains in animals pretreated with reserpine (to deplete NA) combined with preganglionic denervation (to prevent the concomitant excessive NPY release and depletion), is mimicked by NPY and highly correlated to NPY release. Under these circumstances the NPY content in the local venous effluent reaches levels at which exogenous NPY evokes vasoconstriction.

The effects of neuropeptide Y and its fragments upon basal and electrically stimulated ion secretion in rat jejunum mucosa

1. The effects of neuropeptide Y (NPY) and a range of C terminal fragments were investigated both on basal short circuit current (s.c.c.) and electrical field stimulated responses in voltage clamped preparations in rat jejunal mucosa. 2. Most of the NPY fragments tested had direct effects upon the mucosa, reducing baseline s.c.c. with EC50 values of 1 micron or more. NPY was 30 times more effective than any of the fragments tested and the order of potency was: NPY much greater than NPY (11-36) greater than or equal to (12-36) greater than or equal to (13-36) greater than or equal to (14-36). NPY (15-36), (16-36), (20-36) and (22-36) were still less effective and complete concentration-response curves could not be constructed. NPY (26-36), des amido NPY and the C-terminal flanking peptide of NPY (CPON) were all inactive and did not significantly alter responses to NPY. 3. Electrical field stimulation (EFS) of mucosal preparations elicited rapid transient secretory responses in the presence of hexamethonium and atropine. NPY and fragments attenuated these secretory responses and where concentration-response relationships could be compared at a given time point the following order of potency was obtained: NPY much greater than NPY (11-36) greater than NPY (13-36). Again NPY (26-36), des amido NPY and CPON were ineffective, while at single concentrations (300 nM) a graded attenuation of EFS responses was obtained with NPY (14-36) greater than or equal to NPY (15-36) greater than NPY (16-36) greater than or equal to NPY (20-36) greater than NPY (22-36). 4. The attenuation of EFS responses by these peptides was not dependent upon the basal secretory state. Pretreatment of tissues with piroxicam reduced s.c.c. and attenuated further reductions in s.c.c. by NPY, but had no effect upon NPY-mediated inhibition of electrically-stimulated secretory responses. 5. NPY fragments attenuated both basal and EFS generated secretion. Since fragments are effective these receptors must, by definition be Y2-like. NPY (11-36) and NPY (13-36) at 300nm and 1 microM did not significantly attenuate secretory responses to either carbachol (CCh) or substance P (SP). A 1 microM concentration of either fragment was equivalent in effect to 30nm NPY upon basal current, but NPY at this concentration significantly reduced both CCh- and SP-induced secretion. The reduced spectrum of fragment activity together with the different order and potency ratios obtained with these three peptides indicates a presynaptic action for NPY and the fragments.

Structure-function studies on neuropeptide Y and pancreatic polypeptide--evidence for two PP-fold receptors in vas deferens

The biological effects of neuropeptide Y (NPY), rat pancreatic polypeptide (rPP), hybrid analogs of NPY and PP, and C-terminal fragments of NPY were studied in the field-stimulated rat vas deferens model. The results were correlated with peptide binding experiments in Y1 and PP receptor assays on rat PC-12 cells and Y2 receptors on porcine hippocampal membranes. NPY and rPP inhibited the electrically induced contractions in the vas deferens with an IC50 of 25 and 22 nM respectively. However, in contrast to NPY, rPP could not totally block muscle activity. The inhibitory action of the long C-terminal fragment of NPY, NPY-(19-36) and NPY-(11-36), indicated that NPY acts through a Y2 receptor in the vas deferens. The structural basis for the differential recognition of NPY and PP by Y2 receptors and partly also by PP receptors, could be defined with hybrid analogs of PP and NPY. The analogs, [Ile31,Gln34]PP and [Leu31,Pro33]NPY reacted in the vas deferens preparation in accordance with their relative potency in the Y2 and PP receptor assays. [Ile31,Gln34]PP, which bound to the Y2 receptor like NPY, was also able to block the part of the contractile response which was resistant to rPP. It is concluded that in the vas deferens, PP-fold peptides act through two types of receptors: Y2 and PP, and that residues in the C-terminal part of the molecules determine the differential recognition of the peptides by these receptor types.

Effects of pre-contraction with endothelin-1 on alpha 2-adrenoceptor- and (endothelium-dependent) neuropeptide Y-mediated contractions in the isolated vascular bed of the rat tail

1. The pressor effects to bolus doses of the alpha 2-adrenoceptor agonist UK-14,304 were studied in the isolated vascular bed of the perfused rat tail before and after increasing the perfusion pressure with infusions of endothelin-1. Those of neuropeptide Y were studied before and after pre-constriction with endothelin-1 or 5-hydroxytryptamine. The pressor effects of neuropeptide Y were studied before and after functional disruption of the endothelium with the detergent CHAPS. 2. Endothelin-1 and the alpha 1-adrenoceptor agonist phenylephrine induced dose-dependent vasoconstriction, endothelin-1 being some 10(4) times more potent than phenylephrine [log dose (mol) of the ED50 for endothelin-1 and phenylephrine: -11.8 +/- 0.2 (n = 7), -8.2 +/- 0.2 (n = 5) respectively]. 3. Under control conditions, at basal perfusion pressures, UK-14,304 and neuropeptide Y were virtually inactive as vasoconstrictors. Following a sustained increase in perfusion pressure by infusions of endothelin-1 (2.5-10 nM at 0.8 ml min-1), however, both UK-14,304 and neuropeptide Y induced dose-dependent pressor responses and both were some 10(2) times more potent than phenylephrine [log dose (mol) of the ED50 for UK-14304 and neuropeptide Y: -10 +/- 0.5 (n = 6), -10.3 +/- 0.4 (n = 6) respectively]. Responses to neuropeptide Y also were uncovered when vascular tone was increased with 5-hydroxytryptamine (5-20 nM) [log dose (mol) of the ED50 for neuropeptide Y: -10.2 +/- 0.2 (n = 6)]. 4. Pre-constriction-induced pressor responses to UK-14,304 were inhibited by 1 microM rauwolscine whilst those to neuropeptide Y were inhibited by disruption of the endothelium. Removal of the endothelium had no significant effect on the pressor responses to 4pmol or 8pmol endothelin-1 and had no effect on the increase in perfusion pressure induced by the endothelin-1 infusions but did decrease the time-course of pressor responses to bolus injections of endothelin-1. Endothelial disruption had no significant effect on the vasoconstriction induced by all but one of the doses of phenylephrine administered [log dose (mol) of the ED5o for phenylephrine after CHAPS: -8.6 + 0.2 (n = 5)], indicating that the responsiveness of the vascular smooth muscle was not destroyed by CHAPS. This treatment did, however, slow the onset and prolong the time course of the phenylephrine-induced responses. 5. These results indicate that, in the isolated vascular bed of the rat tail, pressor responses to both alpha 2-adrenoceptor- and neuropeptide Y receptor-activation are uncovered by agonist-induced preconstriction including that to endothelin-1. Neuropeptide Y-induced vasoconstriction was endotheliumdependent.

Characterization of functional neuropeptide Y receptors in a human neuroblastoma cell line

We identified receptors for neuropeptide Y (NPY) on an established human neuroblastoma cell line, SK-N-MC, which are functionally coupled to adenylate cyclase through the inhibitory guanine nucleotide-binding protein of adenylate cyclase, Gi. Intact SK-N-MC cells bound radiolabeled NPY with a KD of 2 nM and contained approximately 83,000 receptors/cell. Unlabeled porcine and human NPY and structurally related porcine peptide YY (PYY) competed with labeled NPY for binding to the receptors. NPY inhibited cyclic AMP accumulation in SK-N-MC cells stimulated by isoproterenol, dopamine, vasoactive intestinal peptide, cholera toxin, and forskolin. NPY inhibited isoproterenol-stimulated cyclic AMP production in a dose-dependent manner, with half-maximal inhibition at 0.5 nM NPY. Porcine and human NPY and porcine PYY gave similar dose-response curves. NPY also inhibited basal and isoproterenol-stimulated adenylate cyclase activity in disrupted cells. Pertussis toxin treatment of the cells completely blocked the ability of NPY to inhibit cyclic AMP production and adenylate cyclase activity. The toxin catalyzed the ADP-ribosylation of a 41-kDa protein in SK-N-MC cells that corresponds to Gi. The receptors on SK-N-MC cells appeared to be specific for NPY, as other neurotransmitter drugs, such as alpha-adrenergic, dopaminergic, muscarinic, and serotonergic antagonists, did not compete for either NPY binding or NPY inhibition of adenylate cyclase. Thus, SK-N-MC cells may be a useful model for investigating NPY receptors and NPY-mediated signal transduction.

Effect of neuropeptide Y on alpha 2-adrenoceptor-mediated cardiovascular responses in the pithed rat

1. The effects of neuropeptide Y (NPY) on the cardiovascular responses induced by stimulation of pre and postjunctional alpha 2-adrenoceptors were studied in the pithed normotensive rat. 2. The increase in diastolic blood pressure induced by cumulative injection of xylazine (1-1000 micrograms kg-1, i.v.) were potentiated by NPY (5 micrograms kg-1) but not affected by a lower dose (0.75 micrograms kg-1) of this peptide. 3. Xylazine (1-100 micrograms kg-1) inhibited in a dose-dependent manner the tachycardia induced by continuous electrical stimulation (0.2 Hz, 2 ms, 60 V) of the spinal cord (C7-Thl). 4. NPY (5 micrograms kg-1 but not 0.75 micrograms kg-1) enhanced the inhibitory effect of xylazine on the tachycardia induced by electrical stimulation without having any direct effect on heart rate. 5. These results suggest that there may be a positive interaction between NPY receptors, postjunctional alpha 2-adrenoceptors and between NPY receptors and postjunctional alpha 2-adrenoceptors in the cardiovascular system of the rat.

Pharmacology of noradrenaline and neuropeptide tyrosine (NPY)-mediated sympathetic cotransmission

Pharmacological and physiological aspects for neuropeptide Y (NPY) and noradrenaline (NA) cotransmission have been studied in the peripheral sympathetic nervous control of blood vessels, heart, spleen and vas deferens. NPY coexists with NA in large dense cored vesicles and is released compared to NA mainly upon high frequency stimulation or strong reflex sympathetic activation. NPY release is inhibited via prejunctional alpha-2 adrenoceptors and adenosine receptors but facilitated by angiotensin II or beta-receptor activation. NPY exerts prejunctional inhibitory actions on both NA and NPY release, enhances the vasoconstrictor effect of NA and evokes potent, long-lasting vasoconstriction. Specific receptor mechanisms for NPY exist at both the pre- and postjunctional levels; a large amidated C-terminal portion of NPY is necessary for receptor binding, inhibition of cyclic AMP formation and vasoconstrictor effects. Denervation results in supersensitivity for both NA and NPY-evoked vasoconstriction. Reserpine pretreatment is associated with depletion of NA as well as NPY; the effect on NPY is entirely dependent on an intact nerve activity. Reserpine treatment combined with preganglionic denervation depletes NA by 99% while NPY levels are maintained intact. The characteristic appearance of the nerve stimulation evoked vasoconstrictor response with a high correlation to NPY outflow after reserpine treatment, suggests that NPY may be involved as a transmitter in a variety of vascular beds. NPY-synthesis in ganglia seems to be regulated by nicotinic receptor activity; secondary stimulation by eg reserpine stimulates and nicotine antagonists decrease NPY-synthesis. Many classical pharmacological agents including guanethidine, clonidine, yohimbine, angiotensin II, nicotine and desipramine influence NPY release. A complex interplay therefore seems to occur at both the pre- and postjunctional levels of transmission for the classical transmitter NA and the coexisting peptide NPY, creating a great diversity of chemical signalling potential.

Distinction of NPY receptors in vitro and in vivo. I. NPY-(18-36) discriminates NPY receptor subtypes in vitro

We studied the possibility of multiple neuropeptide Y (NPY) receptor subtypes. NPY-stimulated Ca2+ mobilization in human erythroleukemia (HEL) cells was used to screen a number of NPY analogues. The potencies of three of these analogues [peptide YY (PYY), [D-Tyr-36]NPY, and NPY-(18-36)] were compared with that of NPY in the following model systems: Ca2+ mobilization and inhibition of adenosine 3',5'-cyclic monophosphate accumulation in HEL cells, potentiation of vasoconstriction in the isolated rabbit ear artery, reduction of cutaneous microvascular perfusion in the rat digit, and inhibition of [3H]serotonin release in rat brain. In each of the five models, PYY was a full agonist that exhibited a similar or slightly higher potency than NPY, whereas [D-Tyr-36]NPY and NPY-(18-36) were partial agonists with lower potencies: NPY-(18-36) had a lower potency and efficacy than [D-Tyr-36]NPY in HEL cells and the rabbit ear artery, but was more effective than [D-Tyr-36]NPY for constricting cutaneous microvasculature and inhibiting serotonin release. Because of its weak partial agonism, we also tested NPY-(18-36) as an antagonist of NPY-stimulated Ca2+ mobilization in HEL cells. NPY-(18-36) shifted the NPY concentration-response curve to the right with a KB affinity value of 297 nM. In summary, [D-Tyr-36]NPY and NPY-(18-36) are partial agonists, the relative potency of which varies between systems. These data demonstrate the presence of multiple NPY receptor subtypes. We propose a modified classification scheme of NPY receptor subtypes.

Characterization of neuropeptide Y binding sites in rat cardiac ventricular membranes

Neuropeptide Y (NPY) binding sites in rat cardiac ventricular membranes have been characterized in detail. 125I-NPY bound to the membranes with high affinity. Binding was saturable, reversible and specific, and depended on time, pH and temperature. Analysis of the binding data obtained under optimal conditions, 2 hr, 18 degrees C and at pH 7.5, revealed the presence of low and high affinity binding sites. The high affinity binding sites had an apparent dissociation constant (Kd) of 0.38 nM and a binding capacity (Bmax) of 7.13 fmol/mg protein. The apparent Kd and Bmax for low affinity binding sites were 22.34 nM and 261.25 fmol/mg protein, respectively. Peptides unrelated to NPY did not compete with 125I-NPY for the binding sites even at 1 microM concentrations, whereas homologous peptides, peptide YY (PYY) and pancreatic polypeptide (PP), and NPY(13-36) inhibited 125I-NPY binding but with lower potency compared to NPY. 125I-NPY binding was sensitive to the nonhydrolyzable GTP analog, Gpp(NH)p, suggesting that the NPY receptor is coupled to the adenylate cyclase system. The ventricular membrane receptor characterized in this study may play an important role in mediating the physiological effects of NPY in the heart.

Neuropeptide Y binding and inhibition of cAMP accumulation in human neuroepithelioma cells

The specific binding of 125I-labeled neuropeptide Y (NPY) and the biological response to NPY receptor activation were measured in cultured human neuroepithelioma (SK-N-MC) cells. A single class of high-affinity binding sites [dissociation constant (KD) = 0.2 nM] was characterized both by equilibrium binding of 125I-NPY concentrations less than 1 nM and kinetically by the initial rates of 125I-NPY association and dissociation. Specific 125I-NPY binding was decreased in a concentration-dependent manner by inclusion of guanine nucleotides in the incubation medium. The existence of multiple affinity states or NPY receptor subtypes was suggested by 1) a Hill coefficient of less than 1.0 obtained when analyzing equilibrium binding with 125I-NPY concentrations greater than 1 nM, 2) biphasic dissociation of 125I-NPY, 3) an increase in the component of rapid dissociation and decrease in the component of slow dissociation when guanine nucleotides were present during dissociation of 125I-NPY, and 4) displacement of 125I-NPY by unlabeled peptide with a slope factor of 0.6. Exposure of intact cells to NPY caused a concentration-dependent pertussis toxin-sensitive inhibition of forskolin-stimulated cellular adenosine 3',5'-cyclic monophosphate (cAMP) accumulation [50% effective concentration (EC50) = 0.4 nM]. In contrast, NPY had no effect on cellular inositol phosphate content or protein kinase C activation. These results demonstrate that NPY binds specifically to a G protein-linked receptor that inhibits adenylate cyclase in SK-N-MC cells.

Interaction of 125I-neuropeptide Y with rat cardiac membranes

125I-Neuropeptide Y (NPY) bound specifically with high affinity to rat atrial and ventricular membranes. Scatchard analysis revealed the presence of single class of binding sites in both atrial and ventricular membranes. The apparent Kd and Bmax for atrial membranes were 0.63 nM and 70 fmol/mg protein, respectively; ventricular membranes had an apparent kd of 0.39 nM and a Bmax of 283 fmol/mg protein. NPY structural homologues peptide YY (PYY) and pancreatic polypeptide (PP) bound to the ventricular membranes NPY receptor, but with several fold lower potency compared to NPY. Binding of 125I-NPY to ventricular membranes was sensitive to guanosine triphosphate (GTP) suggesting that the NPY receptor is linked to adenylate cyclase system. The receptor characterized in this system may play a crucial role in mediating the cardiac effects of NPY.

Neuropeptide Y inhibits relaxations of the guinea pig uterine artery produced by VIP

Interactions between neuropeptides contained in autonomic vasodilator neurons supplying the guinea pig uterine artery were investigated in isolated segments of the artery precontracted with prostaglandin F2 alpha. Neither somatostatin-14 (10(-6) mol.l-1) nor dynorphin A(1-17) (10(-6) mol.l-1) had direct effects on vascular tone, and did not affect relaxations produced by guinea pig vasoactive intestinal peptide (gpVIP). Both the porcine and the guinea pig forms of neuropeptide Y (NPY; 10(-7)-10(-5) mol.l-1) caused transient contraction of the precontracted arteries. NPY also inhibited relaxations of the artery produced by gpVIP, an action which was not directly related to the NPY contractions. NPY caused both a concentration-dependent rightward shift in the gpVIP concentration-response curve, and a reduction in size of the maximum relaxation to gpVIP. NPY (10(-6) mol.l-1) also produced a rightward shift in the concentration-response curves for the vasodilators forskolin and glyceryl trinitrate, but did not reduce the maximum relaxations to these compounds. Thus NPY, which is colocalized with VIP in vasodilator neurons supplying the uterine artery, can greatly reduce the vasodilator potency of VIP.

Examination of the role of the amphipathic alpha-helix in the interaction of neuropeptide Y and active cyclic analogues with cell membrane receptors and dimyristoylphosphatidylcholine

To test the potential importance of the putative C-terminal amphipathic alpha-helical region of neuropeptide Y (NPY) in receptor binding, the interactions of porcine NPY and several peptide analogues with lipid and cell membrane receptors were compared. Cyclic analogues were designed to constrain the N- and C-terminal regions of the peptide and to retain the folded conformation of NPY predicted from its sequence analogy with pancreatic polypeptide and its similar spectral behavior. The three cyclic peptides were [Cys2, 8-aminooctanoic acid5-24, D-Cys27]-NPY (C2-NPY), [Cys5, 8-aminooctanoic acid7-20, D-Cys24]-NPY (C5-NPY), and [D-Cys7, 8-aminooctanoic acid8-17, Cys20]-NPY (C7-NPY). All of the peptides bind with high affinity to pig spleen membranes, but only NPY and [Glu16, Ser18, Ala22, Leu28,31]-NPY (ESALL-NPY) bind quantitatively to dimyristoylphosphatidylcholine (DMPC) liposomes. C7-NPY and NPY20-36 bind with moderate affinity to liposomes, but only NPY and C7-NPY bind with high affinity to mouse brain receptors. Thus, lipid binding and receptor binding are not correlated in this series of peptides, and binding to the pig spleen receptor appears to require only the C-terminal region of the peptide. Simple lipid binding, as in NPY20-36, is insufficient for binding to the mouse brain receptor, suggesting that the N-terminal region of the peptide is required for high-affinity binding to this receptor. Data from fluorescence, differential scanning calorimetry, and liposome clearing experiments suggest that, although the interaction of NPY with lipid is consistent with formation of an amphipathic alpha-helix, a simple amphipathic alpha-helical model for the interaction with the high-affinity NPY receptor is insufficient to explain the data.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement by neuropeptide Y (NPY) of the dihydropyridine-sensitive component of the response to alpha 1-adrenoceptor stimulation in rat isolated mesenteric arterioles

1. The mechanism by which neuropeptide Y (NPY) potentiates the vasoconstriction induced by alpha 1-adrenoceptor agonists was investigated in 3rd generation mesenteric arterioles of the rat. 2. At a maximally active concentration, nitrendipine (10(-6) M) displaced to the right the concentration-response curves to noradrenaline (pD2 decreased from 6.2 +/- 0.06 to 5.7 +/- 0.03) and phenylephrine (pD2 decreased from 5.6 +/- 0.03 to 5.3 +/- 0.03). Diltiazem (10(-5) M) also shifted to the right the concentration-response curve to phenylephrine (pD2 decreased from 6.0 +/- 0.06 to 5.5 +/- 0.04). In addition, the maximal response to phenylephrine was significantly decreased in the presence of either nitrendipine or diltiazem. 3. In the absence of a calcium channel blocking agent, NPY (100 nM) produced a leftward shift of the concentration-response curves to noradrenaline (pD2 increased from 6.2 +/- 0.06 to 6.5 +/- 0.05) and phenylephrine (pD2 increased from 5.6 +/- 0.03 to 6.0 +/- 0.06 and from 6.0 +/- 0.06 to 6.3 +/- 0.11). In the presence of either nitrendipine (10(-6) M) or diltiazem (10(-5) M), NPY (100 nM) did not alter the concentration-response curves to either noradrenaline or phenylephrine. 4. NPY was added to arterioles brought to the same level of tension (40% of the maximal contraction) either by phenylephrine alone (1.5 x 10(-6) M) or by a higher concentration of phenylephrine (3 x 10(-6) M) followed by the addition of prazosin (1.3 x 10(-9) M; a concentration at which it partially blocks alpha 1-adrenoceptors). In these conditions, the response to phenylephrine was completely abolished by nitrendipine (10-6 M) or by diltiazem (10-5M). Furthermore, NPY (10-1" to 10-7M) increased the arteriolar tension up to the maximal contractile capacity of the vessels with pD2 values of 8.6 + 0.02 and 8.7 + 0.01, in the absence and presence of prazosin, respectively. 5. Prazosin was replaced in the above protocol by other vasodilator agents acting through different mechanisms. Whether in the presence of 2 x 10-7M forskolin, 6 x 10-7M sodium nitroprusside (which stimulate adenylate cyclase or guanylate cyclase, respectively) or 2 x 10- 7M diltiazem (a concentration at which calcium entry is partially blocked), NPY enhanced phenylephrine-induced contraction to the maximum level with an identical potency (pD2 values of the peptide ranged from 8.3 to 8.7). 6. The results show that, in rat mesenteric arterioles, NPY potentiates only the calcium entry blockersensitive component of contraction induced by stimulation of alpha,-adrenoceptors. In addition, they provide evidence that the peptide counteracts with an equal potency the inhibitory effect of partial block of alpha,-adrenoceptors and of relaxing agents acting through different mechanisms. It is suggested that NPY enhances calcium entry induced by stimulation of alpha l-adrenoceptors in this tissue.

Y1 receptors for neuropeptide Y are coupled to mobilization of intracellular calcium and inhibition of adenylate cyclase

Two types of binding sites have previously been described for neuropeptide Y (NPY), called Y1 and Y2 receptors. The intracellular events following Y1 receptor activation was studied in the human neuroblastoma cell line SK-N-MC. Both NPY and the specific Y1 receptor ligand, [Leu31,Pro34]-NPY, caused a rapid and transient increase in the concentration of free calcium in the cytoplasm as measured by the fluorescent probe, Fura-2. The effect of both peptides was independent of extracellular calcium as addition of EGTA or manganese neither changed the size nor the shape of the calcium response. The calcium response to NPY was abolished by pretreatment with thapsigargin, which can selectively deplete a calcium store in the endoplasmic reticulum. Y1 receptor stimulation, by both NPY and [Leu31,Pro34]NPY, also inhibited the forskolin-stimulated cAMP production with an EC50 of 3.5 nM. There was a close relation between the receptor binding and the cellular effects as half-maximal displacement of [125I-Tyr36]monoiodoNPY from the receptor was obtained with 2.1 nM NPY. The Y2-specific ligand NPY(16-36)peptide had no effect on either intracellular calcium or cAMP levels in the SK-N-MC cells. It is concluded that Y1 receptor stimulation is associated with both mobilization of intracellular calcium and inhibition of adenylate cyclase activity.

Neuropeptides in hypertension: role of neuropeptide Y and calcitonin gene related peptide

1. The effect of neuropeptide Y (NPY) on cardiovascular function at three levels of the noradrenergic axis where the peptide is known to co-exist with noradrenaline (NA) and or adrenaline (A) was studied in normotensive Sprague-Dawley (SD), Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHR). 2. In the perfused mesenteric arterial bed, NPY and the structurally similar peptide intestinal polypeptide (PYY) decreased the periarterial nerve stimulation induced release of NA and potentiated the increase in perfusion pressure to nerve stimulation or exogenously applied agonists (e.g. angiotensin, vasopressin, phenylephrine). In contrast to NPY and PYY, C-terminal NPY fragments inhibited NA release and produced a parallel decrease in perfusion pressure thus supporting the concept of Y1 (post) and Y2 (pre) NPY receptors. 3. In the mesenteric artery of SHR the prejunctional inhibitory effect of NPY was attenuated while the postjunctional response was enhanced. 4. Following intrathecal (Int) injection of NPY, there was a decrease in blood pressure, total peripheral resistance (predominantly by a decrease in mesenteric vascular resistance) and renal nerve activity. The depressor effect of Int NPY was attenuated in the SHR. 5. Unilateral injections of NPY into the posterior hypothalamic nucleus increased blood pressure, hindquarter and renal vascular resistance and renal nerve activity. The pressor effect was enhanced in the SHR. 6. Periarterial nerve stimulation of the perfused mesenteric artery produced a frequency dependent vasodilation in beds pretreated with guanethidine and precontracted with methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

125I-neuropeptide Y binding activity of pig spleen cell membranes: effect of solubilisation

Crude preparations of pig spleen cell membranes were obtained by differential centrifugation. 125I-NPY bound specifically to these membranes with a KD of 56 +/- 13 pM and Bmax of 44 +/- 4.0 fmols/mg protein. After treatment with 1% CHAPS* and 10 mM 2-mercaptoethanol in the presence of 2 microM leupeptin, 2 microM pepstatin A, 10 microM phosphoramidon, 200 microM PMSF and 0.1% bacitracin, followed by centrifugation at 100,000 g a soluble preparation was obtained that contained a single population of specific 125I-NPY binding sites. The KD of the soluble receptor was significantly higher at 1.38 +/- 0.2 nM (P less than 0.01) but the Bmax of 59.6 +/- 6.6 fmols/mg protein was similar (N.S.). This is the first description of a method for obtaining NPY receptors in soluble form and should enable their purification and characterisation, though the low affinity of the soluble receptor may reflect disruption of the ligand binding site upon removal of the receptor from the membrane.

Role of adenylate cyclase in modulatory effect of neuropeptide Y on [3H]noradrenaline release in guinea-pig vas deferens

1. The effect of neuropeptide Y (NPY) on [3H]noradrenaline ([3H]NA) release-evoked by 5-Hz electrical stimulation or 5 microns calcium ionophore A23187 was studied in vitro in guinea-pig vas deferens. 2. The evoked tritium overflow (which reflected [3H]NA release) was determined by liquid scintillation spectrometry. 3. NPY, 1 microM, reduced electrically-evoked tritium overflow. NPY reduction was more pronounced upon 20-sec, 3 msec continuous stimulation (73.2 +/- 4.4%) and upon 5-min, 1 msec intermittent stimulation (47.8 +/- 2.4%) as compared to the reduction upon 5-min, 1 msec continuous stimulation (24.3 +/- 3.8%). Forskolin (0.1-1 microM) and theophylline (0.65-1.25 mM) dose-dependently diminished this NPY reducing effect. 4. NPY, 1 microM, reduced A23187-evoked tritium overflow by 52.3 +/- 7.1%. Forskolin (5 microM) and theophylline (1.25 mM) significantly decreased the effect of NPY. 5. It is concluded that in guinea-pig vas deferens NPY reduces [3H]NA release through affecting adenylate cyclase and the processes responsible for calcium mobilization.

[Leu31, Pro34]neuropeptide Y: a specific Y1 receptor agonist

Two types of binding sites have previously been described for 36-amino acid neuropeptide Y (NPY), called Y1 and Y2 receptors. Y2 receptors can bind long C-terminal fragments of NPY-e.g., NPY-(13-36)-peptide. In contrast, Y1 receptors have until now only been characterized as NPY receptors that do not bind such fragments. In the present study an NPY analog is presented, [Leu31, Pro34]NPY, which in a series of human neuroblastoma cell lines and on rat PC-12 cells can displace radiolabeled NPY only from cells that express Y1 receptors and not from those expressing Y2 receptors. The radiolabeled analog, [125I-Tyr36] monoiodo-[Leu31, Pro34]NPY, also binds specifically only to cells with Y1 receptors. The binding of this analog to Y1 receptors on human neuroblastoma cells is associated with a transient increase in cytoplasmic free calcium concentrations similar to the response observed with NPY. [Leu31, Pro34]NPY is also active in vivo as it is even more potent than NPY in increasing blood pressure in anesthetized rats. It is concluded that [Leu31, Pro34]NPY is a specific Y1 receptor agonist and that the analog or variants of it can be useful in delineating the physiological importance of Y1 receptors.

Modulation of noradrenaline and neuropeptide Y (NPY) release in the pig kidney in vivo: involvement of alpha 2, NPY and angiotensin II receptors

The modulation of the release of noradrenaline (NA) and neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in the pig kidney in vivo. Under control conditions a reproducible co-release of NA and NPY-LI was obtained upon stimulation of the renal nerves with 5 Hz for 1 min. Infusion of peptide YY (PYY, 1 microgram/kg/min i.v.), which binds to NPY receptors, caused renal vasoconstriction and reduced the stimulation-evoked overflow of NA and NPY-LI by 24 +/- 4 and 33 +/- 11%, respectively (P less than 0.01). The PYY effect was reversible and was absent 1 h after the infusion. The alpha 2-adrenoceptor antagonist yohimbine (0.2 mg/kg i.v.) enhanced the overflow of NA and NPY-LI 2- to 3-fold. The angiotensin converting enzyme inhibitor captopril (5 mg/kg i.v.) did not significantly affect the overflow of NA or NPY-LI evoked by the nerve stimulation. Angiotensin II (0.5 microgram/kg/min i.v.), on the other hand, induced a reversible enhancement of the overflow of both NA and NPY-LI by 71 and 77%, respectively (P less than 0.01). Infusion of endothelin (0.2 microgram/kg/min i.v.), which reduced renal blood flow by a magnitude similar to that evoked by angiotensin II, did not significantly alter the nerve stimulation-evoked overflow of NA or NPY-LI. None of the administered drugs did significantly affect the percentage reduction in renal blood flow evoked by nerve stimulation. It is concluded that the release of NA and NPY-LI from sympathetic nerves in the pig kidney is inhibited in parallel via activation of NPY receptors by PYY and via alpha 2-adrenoceptors by endogenous NA.(ABSTRACT TRUNCATED AT 250 WORDS)

Centrally truncated and stabilized porcine neuropeptide Y analogs: design, synthesis, and mouse brain receptor binding

Porcine neuropeptide Y (pNPY) has been proposed to form an intramolecularly stabilized structure characterized by N- and C-terminal helical regions arranged antiparallel due to a central turn region. Analogs based on this structural model that have the central turn region and various amounts of the helical regions removed, yet retain the N and C termini in a similar spatial orientation were designed. The gap formed by removal of the central residues (residues 8-17 or 7-20) was spanned with a single 8-aminooctanoic acid residue (Aoc) and the structure was further stabilized by the introduction of a disulfide bridge. [D-Cys7,Aoc8-17,Cys20]pNPY and [Cys5,Aoc7-20,D-Cys24]pNPY were synthesized and found to have receptor binding affinities of 2.3 nM and 150 nM, respectively, in mouse brain membranes (pNPY affinity is 3.6 nM in this assay). It is proposed that the central region (residues 7-17) of pNPY serves a structural role in the peptide and is not involved in direct receptor interaction.

Pre- and postjunctional actions of neuropeptide Y and related peptides

The effects of neuropeptide Y (NPY) and related peptide fragments on blood pressure and vagal action at the heart were compared in the anaesthetized rat. A change in vagal action was taken as a measure of presynaptic activity and a change in blood pressure was taken as a measure of postsynaptic activity. NPY, NPY-(13-36), PYY-(13-36), des-Ser22-NPY-(13-36) and a stabilized 13-36 analogue of NPY (ANA NPY) all exerted pressor actions and attenuated vagal action at the heart. The maximum vagal inhibitory or presynaptic action in order of potency was NPY, ANA-NPY, PYY-(13-36) significantly greater than NPY-(13-36), des-Ser22-NPY-(13-36). The order of potency for the half time of this effect was NPY, ANA-NPY significantly longer than PYY-(13-36) and NPY-(13-36), which were significantly longer than des Ser22-NPY-(13-36). For the pressor or postsynaptic effects, NPY increased blood pressure significantly more and for a longer duration than all the 13-36 fragments, which were not demonstrably different in this respect. These results are consistent with the proposal that there are two populations of NPY receptors. The C-terminal flanking peptide of NPY (CPON) and desamido-NPY had no effect on either vagal action at the heart or on blood pressure.