Neuropeptide Y (18-36) is a competitive antagonist of neuropeptide Y in rat cardiac ventricular membranes

The direct stimulation of Gi proteins by neuropeptide Y (NPY) in the rat left ventricle

Neuropeptide Y (NPY) is a neuropeptide with high distribution in the cardiovascular system of mammals, where it modulates heart and vessel contractility. In the rat heart, the presence of at least three different NPY receptor subtypes has been hypothesised. Notwithstanding this, receptor activation might not be the only mechanism responsible for the complex cardiac effects of the peptide. In this study, we investigated the effect of NPY on the GTPase activity of G-proteins in the rat left ventricle as a possible alternative mechanism of action for the peptide in the rat heart. Our results show that NPY, but also the neuropeptide fragment (18-36) (NPY (18-36)), stimulated the basal, spontaneous GTPase activity of ventricle membranes only when it was measured under the condition of an absence of Mg2+. This stimulation was resistant to BIBP3226 a non-peptidergic antagonist at Y1 receptors, but it was significantly reduced in membranes treated with selective antibodies against the Gialpha subunits. NPYs effect was concentration-dependent with a maximum of activity at 10nM. At this concentration, NPY (and NPY 18-36) was able to inhibit forskolin (FSK)-induced cyclic adenosine-5'-monophosphate (cAMP) elevation in rat left ventricle slices. Our results assess that NPY in the rat heart is able to activate the GTPase activity of Gi proteins, in a receptor-independent way.

Localization and characterization of NPY/PYY receptors in rat frontoparietal cortex during development

Neuropeptide Y (NPY) is present in most cerebrocortical areas during fetal and postnatal development. In the rat frontal cortex, a dense radial fiber network containing NPY immunoreactivity is observed transiently as early as embryonic day 17 (E17) and disappears at the end of the first postnatal week. We have investigated the distribution of NPY receptors in the frontoparietal cortex at 13 stages of development, from E15 fetuses to adults, by in vitro autoradiography, using (125)I-pPYY as a radioligand. Quantitative receptor density was measured through all cortical layers at each developmental stage. Pharmacological identification of (125)I-pPPY binding sites was made by competition experiments using pNPY or [Leu(31),Pro(34)]pNPY and pNPY(13-36), as selective competitors for Y1 and Y2 receptors, respectively. NPY receptors were first detected in the cerebral cortex at low densities at E19 in a thin layer of tissue corresponding to the inner half of the intermediate zone (IZ) and the upper ventricular zone (VZ). The neuroepithelium did not contain binding sites. High densities of sites were observed by E21 onward to P10 in the deep cortical layers corresponding to the IZ and layers V-VI. A decreasing gradient of receptor density was observed from layer VI to the marginal zone (layer I). The distribution of NPY receptors does not match with the perikarya of transient NPY-immunoreactive neurons located in the cortical plate but does coincide with their axonal extension. The receptor density decreased abruptly between P10 and P12 in deep layers, whereas a moderate expression of binding sites is detected from P10 to P12 in layers I-III. By P14, the binding level was the lowest observed in the postnatal period. From P21 onward, receptors were observed in superficial layers I-III, and their density rose by two- to threefold up to adulthood. Competition studies indicated that the NPY receptors located in the deep cortical layers of the E21 or P1 rat cortex exhibit Y2 receptor type characteristics. The binding sites detected in the superficial layers from P10 to P12 rats also show Y2 receptors characteristics, unlike the NPY receptors in layers II-III of the adult, which behave like Y1 receptors. These data show that different NPY receptor types are successively expressed in specific layers during late gestation and early postnatal life in the rat frontoparietal cortex.

Neuropeptide Y effects on murine natural killer activity: changes with ageing and cAMP involvement

Changes in the bidirectional interaction between the nervous and the immune systems have been proposed as a cause of ageing. Neuropeptides, such as neuropeptide Y (NPY), could show different effects on immune function with age. In the present work, we have studied the in vitro action of a wide range of NPY concentrations, i.e. from 10(-13) to 10(-7) M, on natural killer (NK) activity, a function which decreases with age. Spleen, axillary nodes, thymus and peritoneum leukocytes from mice of different ages: young (12+/-2 weeks), adult (24+/-2 weeks), mature (50+/-2 weeks) and old (72+/-2 weeks) were used. Stimulation by NPY of NK activity was observed in adult and mature animals in axillary nodes and thymus, and an inhibition in the spleen from young mice. The specificity of the NPY effect on cytotoxic activity was confirmed using a C-terminal fragment of NPY. Furthermore, cAMP levels in leukocytes were found to be decreased by NPY in adult mice, suggesting an involvement of this messenger system in the NK modulation by this neuropeptide.

The peptide YY-preferring receptor mediating inhibition of small intestinal secretion is a peripheral Y(2) receptor: pharmacological evidence and molecular cloning

A peptide YY (PYY)-preferring receptor [PYY > neuropeptide Y (NPY)] was previously characterized in rat small intestinal crypt cells, where it mediates inhibition of fluid secretion. Here, we investigated the possible status of this receptor as a peripheral Y(2) receptor in rats. Typical Y(2) agonists (PYY(3-36), NPY(3-36), NPY(13-36), C2-NPY) and very short PYY analogs (N-alpha-Ac-PYY(22-36) and N-alpha-Ac-PYY(25-36)) acting at the intestinal PYY receptor were tested for their ability to inhibit the binding of (125)I-PYY to membranes of rat intestinal crypt cells and of CHO cells stably transfected with the rat hippocampal Y(2) receptor cDNA. Similar PYY preference was observed and all analogs exhibited comparable high affinity in both binding assays. The same held true for the specific Y(2) antagonist BIIE0246 with a K(i) value of 6.5 and 9.0 nM, respectively. BIIE0246 completely abolished the inhibition of cAMP production by PYY in crypt cells and transfected CHO cells. Moreover, the antagonist 1) considerably reversed the PYY-induced reduction of short-circuit current in rat jejunum mucosa in Ussing chamber and 2) completely abolished the antisecretory action of PYY on vasoactive intestinal peptide (VIP)-induced fluid secretion in rat jejunum in vivo. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) experiments showed that Y(2) receptor transcripts were present in intestinal crypt cells (3 x 10(2) molecules/100 ng RNA(T)) with no expression in villus cells, in complete agreement with the exclusive binding of PYY in crypt cells. Finally, a full-length Y(2) receptor was cloned by RT-PCR from rat intestinal crypt cells and also from human small intestine. We conclude that the so-called PYY-preferring receptor mediating inhibition of intestinal secretion is a peripheral Y(2) receptor.

Changes with aging in the modulation by neuropeptide Y of murine peritoneal macrophage functions

Some age-related changes in immune function may be due, at least in part, to a disturbance in the communication between the nervous and immune systems. In the present work, the effects in vitro of neuropeptide Y (NPY) (10(-13) to 10(-7) M) on different peritoneal macrophage functions (adherence to substrate, chemotaxis, phagocytosis, superoxide anion production, and the release of TNFalpha and IL-1beta) have been studied on cells from young (12+/-2 weeks), adult (24+/-2 weeks), mature (50+/-2 weeks) and old (72+/-2 weeks) BALB/c mice. The specificity of these actions was confirmed using two C-terminal fragments of NPY, and the intracellular messengers (protein kinase C and cAMP) involved in the action of the neuropeptide were also analyzed. The results show that the functions studied change with aging and that the effects of NPY on each function, which are carried out through specific receptors, as well as on intracellular pathway, differ depending on age, maintaining the immune functions at physiologically adequate levels in old animals.

The NPY effects on murine leukocyte adherence and chemotaxis change with age. Adherent cell implication

The two-way communication between the nervous and immune system is currently well-known, but the age-related changes in this communication have been scarcely studied. In the present work, we have investigated the in vitro effects of neuropeptide Y (NPY) at concentrations ranging from 10(-13) to 10(-7) M on the adherence and chemotaxis capacities of spleen, axillary node, thymus and peritoneum leukocytes from BALB/c mice. The NPY effect on these functions was examined on cells from animals of four different ages, i.e. young (12+/-2 weeks old), adult (24+/-2 weeks old), mature (50+/-2 weeks old) and old (72+/-2 weeks old). In young animals, NPY stimulates the adherence of leukocytes from spleen, axillary nodes and thymus and inhibits it in cells from peritoneum. In adult animals NPY inhibits the adherence of leukocytes from thymus. These effects disappear with ageing in all locations. Chemotaxis is stimulated by this neuropeptide at all ages in cells from axillary nodes and peritoneum, but this effect is absent in old mice. NPY exerts an inhibitory effect on the chemotaxis of leukocytes from thymus at all ages studied. These NPY effects on leukocytes seem to be carried out through adherent cells.

Myogenic reactivity of rat epineurial arterioles: potential role in local vasoregulatory events

Local control of neural blood flow is considered to reside in innervation of epineurial and endoneurial arterioles rather than in intrinsic autoregulatory mechanisms. With the use of an isolated vessel preparation and an in vivo approach, the present studies examined intrinsic vasomotor responsiveness of epineurial arterioles. Segments of epineurial arterioles, cannulated on glass micropipettes (40 micrometers) and pressurized in the absence of intraluminal flow, showed sustained pressure-dependent (30-90 mmHg) vasoconstriction and acute myogenic reactivity. Myogenic tone was unaffected by phentolamine (10(-6) M). Removal of extracellular Ca(2+) resulted in loss of spontaneous tone and passive behavior. Concentration-response curves for norepinephrine (10(-9)-3 x 10(-6) M) and relaxation to both acetylcholine (10(-8)-10(-5) M) and adenosine (10(-8)-10(-4) M) were obtained. Acetylcholine dilator responses were inhibited by N(G)-nitro-L-arginine methyl ester. Epineurial blood flow was measured in vivo using a laser-Doppler flow probe. Blood flow declined over a 2-h period after surgery, and during this time preparations developed responsiveness to the dilator acetylcholine. Phentolamine blocked vasoconstrictor responses to exogenous norepinephrine but only partially reversed the in vivo baseline tone. The time-dependent decline in epineurial blood flow was observed despite the presence of tetrodotoxin (1 microM), further confirming that tone was predominantly caused by myogenic rather than neurogenic mechanisms. It is concluded that because epineurial arterioles exhibit intrinsic myogenic reactivity, they have the potential to participate in local regulation of neural hemodynamics independently of their own innervation.

Is there really an NPY Y3 receptor?

NPY is an abundant neuropeptide that is widely distributed throughout the central and peripheral nervous systems. Based on pharmacological and cloning data, there are believed to be six different types of NPY receptors. The Y3 receptor is the only one of the six that has not been cloned or well characterized. Y3 receptors have been shown to be important in the regulation of visceral afferents within the nucleus tractus solitarius (NTS). In the present experiments, we have compared the effects of NPY and various analogs on Ba2+ currents in acutely dissociated neurons from the NTS and the neighboring area postrema (AP). No neurons from either NTS or AP responded to [D-Trp32]NPY suggesting that these areas lack Y5 receptors. However, we found a group of NTS neurons that only responded to NPY and not PYY or any other analogs. This agonist profile corresponds to that described for NPY Y3 receptors. No AP neurons showed this type of agonist profile. Other neurons responded to a variety of NPY analogs indicating the presence of Y1, Y2, and Y4 receptors in both nuclei.

Neuropeptide Y Y1 receptors in vascular pharmacology

The existence of neurogenic mediator candidates apart from noradrenaline and acetylcholine involved in the control of vascular tone has attracted enormous attention during the past few decades. One such mediator is neuropeptide Y (NPY), which is co-localized with noradrenaline in sympathetic perivascular nerves. Stimulation of sympathetic nerves in vitro and in vivo causes non-adrenergic vasoconstriction which can be blocked by experimental manipulations that inhibit NPY mechanisms. Thus, the vasopressor response to stimulation of sympathetic nerves can be attenuated by chemical or surgical sympathectomy, treatment with reserpine or other pharmacological agents, and tachyphylaxis to NPY or by NPY antagonists. The NPY field was long plagued by a lack of specific antagonists, but with the recently developed, selective, non-peptide and stable NPY antagonists it has now become possible to study subtypes of this receptor family. For instance, it has become clear that the NPY Y1 receptor mediates most of the direct peripheral effects of NPY on vascular tone. These antagonists promise to stimulate NPY research and will likely unravel the true significance of NPY in cardiovascular control under physiological conditions as well as in pathophysiological states.

Localization of neuropeptide Y Y1 receptor mRNA in human tooth pulp

With immunocytochemistry numerous nerve fibres containing neuropeptide Y (NPY) were found in human molar pulp tissue, often around small blood vessels. Reverse transcriptase-polymerase chain reaction, using specific primers, detected mRNA of the human NPY Y1 receptor in the human pulp tissue. Thus, both NPY-containing nerve fibres and NPY Y1 receptor mRNA are present in human tooth pulp, possibly regulating vascular tone and pain perception.

Neuropeptide Y2 receptors on nerve endings from the rat neurohypophysis regulate vasopressin and oxytocin release

Neuropeptide Y and peptide YY are important central and peripheral modulators of cardiovascular and neuroendocrine functions, that act through multiple receptor subtypes, Y1 through Y5. A neuropeptide Y-binding site of the Y2 type was characterized by ligand-binding studies in isolated nerve terminals from the rat neurohypophysis. Functionally, neuropeptide Y and peptide YY dose-dependently triggered arginine 8-vasopressin and oxytocin release from perfused isolated terminals, and potentiated the arginine-8-vasopressin release induced by depolarization. Osmotic stimulation by salt loading of rats for two and seven days caused a more than three-fold increase in the neuropeptide Y content of the nerve endings. However, the Y2 receptor expression and arginine-8-vasopressin content declined, showing that the neuropeptide Y system is dynamic and suggesting that it plays a physiological role in salt and water homeostasis. Two sets of observations suggest the arginine-8-vasopressin release by neuropeptide Y may not be explained by neuropeptide Y effects on intracellular Ca2+. First, absence of Ca2+ from the perfusion medium did not affect the arginine-8-vasopressin release, and secondly neuropeptide Y did not change intraterminal Ca2+ concentrations. Pretreatment with pertussis toxin blocked arginine-8-vasopressin secretion by neuropeptide Y, suggesting activation of Gi or Go heterotrimeric G-proteins are required for secretion. It is concluded, that the nerve endings of the neurohypophysis contain a complete neuropeptide Y system with ligand and receptors. Neuropeptide Y may act in an autocrine fashion via activation of Y2 neuropeptide Y receptors to stimulate the release of vasopressin and oxytocin via a Gi/Go dependent secretory mechanism.

Ozone-induced stimulation of pulmonary sympathetic fibers: a protective mechanism against edema

Tropospheric ozone exerts well-described toxic effects on the respiratory tract. Less documented, by contrast, is the ability of ozone to induce protective mechanisms against agents that are toxic to the lungs. In particular, interactions between ozone and the sympathetic nervous system have never been considered. Using a model of permeability edema in isolated perfused rabbit lungs, we report here that, immediately after exposure of rabbits to 0.4 ppm ozone for 4 hr, the pulmonary microvascular responses to acetylcholine and substance P are completely blocked. Several lines of evidence, including partial inhibition of the ozone-induced protective effect by several drugs (alpha2- and beta-adrenergic antagonists, neuropeptide Y antagonist, guanethidine), measured levels of released catecholamines in blood and urine and the in vitro response of isolated lungs exposed to 0.4 ppm ozone all seem to suggest that ozone can stimulate pulmonary adrenergic fibers and induce the local release of catecholamines and neuropeptide Y, this resulting in transient protection against pulmonary edema. We also showed that, 48 hr after the exposure, ozone increased the baseline microvascular permeability and the response to low concentrations of acetylcholine.

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

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

Y-receptor subtypes--how many more?

The Y-receptors belong to the G protein-coupled receptor superfamily and mediate a wide variety of physiological effects, such as regulation of blood pressure, anxiety, memory retention, hormone release and food intake. Since the first human Y-receptor was cloned in 1992, the search for additional subtypes has been an area of intense study. Recently four new NPY-receptor subtypes have been isolated, revealing surprisingly limited sequence identity with values as low as 30%. Several reports indicate further heterogeneity of this receptor family, for example a peripheral Y2 receptor. However, since many studies have been carried out with different peptide analogs and radioligands in different species, there is substantial confusion regarding the pharmacological profile of the receptors. This may have led to an exaggeration of the potential number of discrete receptors.

Neuropeptide Y treatment and food deprivation increase cyclic AMP response element-binding in rat hypothalamus

Intrahypothalamic (IHT) administration of neuropeptide Y (NPY) induces a robust feeding response in rats. We have shown previously that NPY-induced feeding is mediated by a pertussis-toxin-sensitive G protein in rats. NPY receptors are coupled to cAMP and Ca2+. Because these second messengers are known to activate cAMP response element binding proteins, (CREB), cAMP response element modulators, or activating transcription factor 1, we investigated the involvement of these transcription factors in NPY-induced feeding in rats. Compared with control injections of cerebrospinal fluid (1 microl), IHT administration of NPY increased cAMP response element (CRE) binding to rat hypothalamic nuclear extracts in a time-dependent manner, as detected by an electrophoretic mobility shift assay. In contrast, IHT administration of the anorectic neuropeptide, pituitary adenylate cyclase activating polypeptide, strongly inhibited the CRE binding. Food deprivation for 48 hr also increased CRE binding, whereas 8 hr of refeeding normalized CRE activity. Preincubation of the hypothalamic nuclear extracts of NPY-treated and unfed rats with antibody specific to CREB blocked CRE binding, whereas preincubation with phosphoCREB antibody retarded the migration of CRE-protein complex, indicating that phosphoCREB is involved in this process. Consistently, immunohistochemical studies with food-deprived rats showed an intense phosphoCREB signal in the paraventricular nuclei and ventromedial hypothalamus in comparison to rats fed ad libitum. Hypothalamic calcium/calmodulin-dependent protein kinase II activity was also increased by IHT-NPY. These results suggest that calcium/calmodulin-dependent protein kinase II induced phosphorylation of CREB may be involved in regulating feeding behavior induced by NPY.

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.

Structure-affinity studies of C-terminally modified analogs of neuropeptide Y led to a novel class of peptidic Y1 receptor antagonist

A novel type of C-terminally modified analogs of the 36-mer peptide hormone neuropeptide Y has been synthesized, characterized and tested with respect to receptor affinity and biological activity in various systems. The compounds were obtained by synthesizing the fully protected peptide fragment NPY 1-35 or analogs of this, and coupling it in solution to various amines, alcohols, and modified tyrosine residues. It could be confirmed, that the C-terminal tyrosineamide of NPY is essential for its affinity to the Y1 receptor subtype. Obviously, the amino group of the amide part is more important than the oxygene atom of the carbonyl group, as NPY 1-35-tyrosinol has a lower affinity than NPY 1-35-tyrosinethioamide. NPY 1-35-tyramide could be shown to act as an antagonist in a Ca2+ release assay in human neuroblastoma cells. Analogs of NPY 1-35-tyramide showed the same structure-affinity relationships as NPY itself, suggesting, that there exists the same binding mode for the agonist and the antagonist.

Conformational analysis of neuropeptide Y segments by CD, NMR spectroscopy and restrained molecular dynamics

Neuropeptide Y (NPY), a peptide amide comprising 36 residue has been shown to act as a potent vasoconstrictor. In order to shed light on the structural requirements for the biological activities with respect to the different prerequisites for affinity to the NPY receptor subtypes Y1 and Y2, in the present study the syntheses and conformational analyses of two C-terminal segments, NPY(18-36) and NPY(13-36), are described. The results obtained by CD measurements, two-dimensional NMR spectroscopy and a conformational refinement of the NMR-derived structure by molecular mechanics stimulations support the findings of previously published structure-activity relationship studies for biologically active and selective compounds. In particular, the alpha-helical conformation as well as an appropriate exposure of the side chains of the critical C-terminal dipeptide within NPY(18-36) are in agreement with the prerequisites proposed for Y2 receptor binding of that segment.

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.

Role of neuropeptide Y and its receptor subtypes in neurogenic pulmonary edema

The effect of neuropeptide Y on the number of perivascular carbon deposits, assessed as a measure of lung vascular permeability, was examined in isolated perfused lung preparations of rats. The number of carbon particle deposits after bronchial application of neuropeptide Y was increased in a dose-dependent manner. In the presence of a beta-adrenoceptor antagonist, norepinephrine augmented the effects of neuropeptide Y. Peptide YY, an analog of neuropeptide Y, demonstrated a much lower potency for increasing the number of carbon deposits, and neuropeptide Y-(18-36), which elicits a weak antagonist action on the neuropeptide Y Y3 receptor, significantly decreased the neuropeptide Y-induced increase. Furthermore, examination of the influence of neuropeptide Y-(18-36) pretreatment on fibrin-induced neurogenic pulmonary edema, in rats, revealed a reduction of the protein concentration ratio of tracheal fluid to serum. Therefore, we conclude that neuropeptide Y may elevate vascular permeability in the pulmonary circulation, conceivably through the neuropeptide Y Y3 receptor, and that neuropeptide Y may in fact play a physiological role even in the in-situ pulmonary circulation.

Synthesis, structure, and antagonistic properties of des-Asn29[D-Trp28,32]NPY(27-36)

We have previously reported that [D-Trp32]NPY and its centrally truncated analogues such as des-AA7-24[D-Trp5,32,Aoc6]NPY can competitively antagonize NPY effects on rat hypothalamus and Y1 (SK-N-MC AND HEL) cells, respectively. In continuation of this work, we performed structure-activity studies with C-terminal decapeptide sequence keeping D-Trp at position 32 to develop lower molecular weight Y1-selective antagonists. This study led to the development of des-Asn29[D-Trp28,32]NPY(27-36), which bound to both Y1 (SK-N-MC, Ki > or = 10 microM) and Y2 (SK-N-BE2, Ki = 1.01 +/- 0.03 microM) receptors. This peptide did not exhibit any agonist activity at Y1 receptors, and exhibited comparable potencies in antagonizing the effects of NPY on the synthesis of cAMP and mobilization of [Ca2+]i in HEL cells. However, in SK-N-MC cells, it was more potent in antagonizing the mobilization of [Ca2+]i than inhibition of cAMP synthesis. Substitution of Nva for Gln34 to increase the hydrophobicity without altering the carbon skeleton substantially increased Y1 affinity (Ki = 0.33 +/- 0.15 microM) and imparted Y1 selectivity (Ki for Y2 affinity = 3.16 +/- 0.50). Moreover, this peptide exhibited good antagonistic potency in HEL cells. 2D NMR studies of des-Asn29[D-Trp28,32]NPY(27-36) revealed the existence of a fairly stable loop-like structure between residues 27 and 32 and a less stable one between residues 32 and 36. The increased Y1 affinity of des-Asn29[D-Trp28,32,Nva34]NPY(27-36) may be due to the stabilization of the 32-36 loop by Nva34. It appears therefore that stabilization of the loop structures in these peptides should result in the development of more potent Y1 receptor antagonists. Our investigations also suggest that HEL cells express a homogeneous population of NPY Y1 receptors whereas SK-N-MC cells express high- and low-affinity Y1 receptors coupled to Ca2+ and cAMP, respectively.

Autoradiographic analysis of neuropeptide Y receptor binding sites in the rat hippocampus after kainic acid-induced limbic seizures

Changes in peptide YY receptor binding were investigated at various intervals after limbic seizures induced in rats by an intraperitoneal injection of kainic acid (10-12 mg/kg). Six to 24 h after kainic acid, specific peptide YY binding, representing Y1 and Y2 neuropeptide Y receptor subtypes, was markedly enhanced in the strata radiatum and oriens CA3 (increase by up to 185% and 178% of control values, respectively). Seven and 30 days after kainic acid, a reduction by up to 63% was found. The basal and kainic acid-induced changes in peptide YY binding were mainly represented by Y2 receptor sites. In the hilus of the dentate gyrus, an increase of global peptide YY binding by up to 400% was observed after 24 h which became attenuated to 125% after 30 days. In the molecular layer of the dentate gyrus global peptide YY binding increased by up to 87% between six and 24 h after kainic acid injection and was reduced by 37% after 30 days. Similar changes were observed in the cerebral cortex. Whereas in the hilus of the dentate gyrus peptide YY binding consisted mainly of Y2 sites, it represented predominantly Y1 receptors in the molecular layer and the cortex. The decline in global and Y2 specific peptide YY binding observed at 30 days in the hippocampus proper was prevented in animals protected from seizure-induced brain damage by an anticonvulsant dose of phenobarbital 3 h after injection of kainic acid. In the stratum moleculare of the dentate gyrus, Y2 specific binding was significantly enhanced while global peptide YY binding was slightly decreased compared to controls. These results show lasting changes in neuropeptide Y receptor binding sites after the acute seizures induced by kainic acid. Since neuropeptide Y modulates glutamatergic neurotransmission, these modifications may play an important role in the hippocampal excitability of chronically epileptic rats.

Neuropeptide Y inhibits depolarization-stimulated catecholamine synthesis in rat pheochromocytoma cells

In PC12 rat pheochromocytoma cells differentiated with nerve growth factor (NGF), neuropeptide Y inhibited depolarization-stimulated catecholamine synthesis as determined by in situ measurement of 3,4-dihydroxyphenylalanine (DOPA) production in the presence of the decarboxylase inhibitor m-hydroxybenzylhydrazine (NSD-1015). The inhibition by neuropeptide Y was concentration-dependent and was prevented by pretreatment with pertussis toxin, suggesting the involvement of a GTP-binding protein of the Gi or Go subtype. The neuropeptide Y analog [Leu31,Pro34]neuropeptide Y also caused inhibition of DOPA production, but was less potent than neuropeptide Y itself, while peptide YY and neuropeptide Y-(13-36) had no significant effect. This pattern is most consistent with the involvement of the neuropeptide Y Y3 receptor subtype. In PC12 cells differentiated with dexamethasone, neuropeptide Y also caused a concentration-dependent inhibition of DOPA production, while peptide YY was again without effect. Neuropeptide Y had no effect on DOPA production in undifferentiated PC12 cells. These results indicate that neuropeptide Y can modulate catecholamine synthesis in addition to its modulatory effects on catecholamine release.

Neuropeptide Y receptor subtypes

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

Hypotensive effects of [D-Tyr27,36, D-Thr32]Neuropeptide Y (27-36)

An analogue of the 10 C-terminal amino acids of neuropeptide Y (NPY) containing three D-isomeric substitutions (27-36-D) has been synthesized and its cardiovascular activity studied in Sprague-Dawley (SD) and spontaneously hypertensive (SHR) rats. Intravenous administration of 1000 nmol/kg 27-36-D decreases MAP in SHR (-59.9 +/- 5.0 mmHg) and SD rats (-44.4 +/- 4.7 mmHg). The hypotension produced by 1000 nmol/kg 27-36-D diminished by 71.2% following pretreatment with the histamine receptor antagonist diphenhydramine, although histamine depletion with compound 48/80 does not significantly alter this hypotension. These data suggest that NPY (27-36)-D produces a profound and sustained hypotension in two strains of rat which is partially attributable to activity at histamine receptors.

Neuropeptide Y inhibits potassium-stimulated glutamate release through Y2 receptors in rat hippocampal slices in vitro

1. We investigated the effects of neuropeptide Y (NPY), peptide YY (PYY), NPY13-36, NPY18-36, [Leu31][Pro34]NPY and of pancreatic polypeptide Y (PPY) on calcium-dependent, potassium-stimulated glutamate release in superfused rat hippocampal slices. 2. NPY, PYY and the Y2 receptor agonist NPY13-36 equipotently inhibited the release of glutamate. The half-maximal response was observed at about 10 nM in a dose-dependent manner (3 to 100 nM). Maximal inhibition of 50 to 60% was obtained at 100 nM. At higher concentrations of the peptides (300 nM and 1 microM) this inhibition was partially or entirely reversed. Porcine NPY13-36 and NPY18-36 inhibited glutamate release by about 44% at 100 nM. 3. The specific Y1 receptor agonist, [Leu31][Pro34]NPY, caused an insignificant increase in glutamate release at 100 to 300 nM concentrations. PPY had no effect on potassium-evoked glutamate release in hippocampal slices at concentrations of 30 nM to 1 microM. 4. The experiments support previous electrophysiological data. They suggest a potent inhibitory action of NPY through NPY-Y2 receptors on the release of the excitatory amino acid glutamate in rat hippocampus. Especially under conditions of increased NPY synthesis, such as in epilepsy, this mechanism may be of pathophysiological relevance.

Neuropeptide Y in sympathetic co-transmission: recent advances in the search for neuropeptide Y antagonists

Since the discovery of neuropeptide Y which is co-stored and co-operate with noradrenaline (NA) in sympathetic nerve fibers, several scientific groups have searched for structures with neuropeptide Y antagonistic properties. Research has mainly focused on various peptide fragments which originate from or are related to the neuropeptide Y sequence. Some non-peptide antagonists have been proposed but they are mostly of low potency and non-selective. Our recent observations that alpha-trinositol (D-myo-inositol 1.2.6-trisphosphate) is an inhibitor of neuropeptide Y effects will hopefully lead to the development of useful non-peptide neuropeptide Y inhibitors. As a novel approach the highly selective approach of down-regulating neuropeptide Y receptors with antisense oligodeoxynucleotides is also discussed. Neuropeptide Y antagonistic agents would help us to understand the physiological role of neuropeptide Y and may serve as useful medication in circulation disorders.

Modulation of intracellular calcium transients and dopamine release by neuropeptide Y in PC-12 cells

In PC-12 cells differentiated with nerve growth factor, neuropeptide Y (NPY) potentiated the K(+)-evoked increase in intracellular calcium, but this potentiation was not mediated by classical Y1 or Y2 NPY receptors. The potentiation by NPY appeared to occur through the mobilization of calcium from intracellular stores because thapsigargin successfully blocked the potentiation. In contrast, the Y2 agonist, NPY-(13-36), attenuated the K(+)-evoked increase in intracellular calcium by decreasing the influx of extracellular calcium. The effect of NPY-(13-36) on dopamine release from PC-12 cells was next studied. NPY-(13-36) significantly attenuated the K(+)-evoked dopamine release in a concentration-dependent manner. Nifedipine and omega-conotoxin also attenuated the evoked dopamine release. In the presence of nifedipine or omega-conotoxin, NPY-(13-36) produced further inhibition of the evoked dopamine release. Furthermore, NPY-(13-36)-induced inhibition of dopamine release was abolished by pertussis toxin pretreatment. We conclude that the regulatory effects of NPY and analogues on intracellular calcium are mediated by multiple NPY receptor subtypes. Y2 receptor-mediated pertussis toxin-sensitive inhibition of the evoked dopamine release does not seem to be due to interactions with L- or N-type Ca2+ channels.

Receptors for gut regulatory peptides

Receptors for regulatory peptides (hormones or neurotransmitters) play a pivotal role in the ability of cells to taste the rich neuroendocrine environment of the gut. Recognition of low concentration of peptides with a high specificity and translation of the peptide-receptor interaction into a biological response through different signalling pathways (adenylyl cyclase-cAMP or phospholipase C-phosphatidylinositol) are crucial properties of receptors. While many new receptors have been identified and thereafter characterized functionally during the 1980s, molecular biology now emerges as the privileged way for the structural characterization and discovery of receptors. Different strategies of receptor cloning have been developed which may or may not require prior receptor purification. Among cloning strategies that do not require receptor purification, homology screening of cDNA libraries, expression of receptor cDNA or mRNA in Xenopus laevis oocytes or in COS cells, and the polymerase chain reaction method achieved great success, e.g. cloning of receptors for cholecystokinin, gastrin, glucagon-like peptide 1, gastrin-releasing peptide/bombesin, neuromedin K, neuropeptide Y, neurotensin, opioids, secretin, somatostatin, substance K, substance P and vasoactive intestinal peptide. All these receptors belong to the superfamily of G-protein-coupled receptors which consist of a single polypeptide chain (350-450 amino acids) with seven transmembrane segments, an N-terminal extracellular domain and a C-terminal cytoplasmic domain. In this chapter, we have detailed the properties of three receptors which play an important role in digestive tract physiology and illustrate various signal transduction pathways: pancreatic beta-cell galanin receptors which mediate inhibition of insulin release and intestinal epithelial receptors for vasoactive intestinal peptide and peptide YY, which mediate the stimulation and inhibition of water and electrolyte secretion, respectively.

Actions of vasoactive intestinal peptide and neuropeptide Y on the pacemaker current in canine Purkinje fibers

We have investigated the actions of vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) on the pacemaker current (I(f)) in canine Purkinje fibers. On voltage pulses to the middle of the I(f) activation range, VIP reversibly increases I(f), whereas NPY reversibly decreases I(f). A three-pulse voltage protocol suggests that VIP shifts I(f) activation in the positive direction and that NPY shifts I(f) activation in the negative direction on the voltage axis without changing maximal I(f) conductance. These effects of VIP and NPY on I(f) are exerted through their specific peptide receptors, since the effects are blocked by VIP and NPY receptor antagonists. VIP and NPY are colocalized in cardiac parasympathetic and sympathetic nerve endings, respectively, and can be released preferentially on high and long-lasting nerve stimulation. Given this colocalization and frequency-dependent release, these results suggest a role for these neuropeptides in controlling cardiac I(f) and consequently heart rate.

Vasoconstrictor effects of various neuropeptide Y analogues on the rat tail artery in the presence of phenylephrine

1. The increase in perfusion pressure induced by neuropeptide Y (NPY), peptide YY (PYY) and related peptides were compared in the perfused rat tail artery precontracted by a submaximal concentration (1 microM) of the vasoconstrictor, phenylephrine. 2. NPY, PYY, [Leu31,Pro34]NPY, [Glu16,Ser18,Ala22,Leu28,31]NPY (ESALL-NPY) and the centrally truncated and stabilized analogues [D-Cys5,8-aminooctanoic acid7-20, Cys24]-NPY (D-Cys5-NPY) and [D-Cys7, 8-aminooctanoic acid8-17,Cys20]-NPY (D-Cys7-NPY) produced a concentration-dependent enhancement of the vasoconstrictor response induced by 1 microM phenylephrine. PYY was two times more potent than NPY and [Leu31,Pro34]NPY while ESALL-NPY, D-Cys7-NPY and D-Cys5-NPY were approximately 3, 5 and 16 times less potent than NPY respectively. NPY, D-Cys5-NPY and D-Cys7-NPY gave similar maximal responses whereas those observed for PYY, [Leu31,Pro34]NPY and ESALL-NPY were much greater than that of NPY. 3. NPY 13-36 and [des-Ser3,Lys4,Cys2,8-aminooctanoic acid3-24, D-Cys27]-NPY ([es-Ser3,Lys4]Cys2-NPY) were practically inactive at concentrations up to 3 microM, whereas [des-Ser3,Lys4,D-Cys2,8-aminooctanoic acid3-24,Cys27]-NPY ([des-Ser3,Lys4]D-Cys2-NPY), which differs from [des-Ser3,Lys4]Cys2-NPY in the disulphide bridge (a D-Cys in position 2 for [des-Ser3,Lys4]D-Cys2-NPY instead of an L-CYs for [des-Ser3,Lys4]Cys2-NPY) was a weak agonist the maximal effect of which could not be ascertained. 4. The contractile effects of [des-Ser3,Lys4]D-Cys2-NPY were additive with those of NPY and [Leu31,Pro34]NPY demonstrating that it is not a partial agonist but may simply not interact competitively with the receptor binding site for NPY. NPY and PYY interacted in a manner expected of agonists competing for the same binding site.5. PYY, NPY and [Leu31,Pro34]NPY were equipotent in displacing the I125-labelled PYY from binding sites on membranes from Y1-receptor expressing SK-N-MC cells, while the centrally truncated analogues were much less potent. The rank order of potencies for displacement of the I125-PYY binding by these peptides in SK-N-MC cells correlated with their activity in enhancing the vasoconstrictor response of phenylephrine in the tail artery. For the [des-Ser3,Lys4]D-Cys2-NPY analogue, the displacement pattern was more complex in that the displacement analysis revealed the presence of two binding sites.6. In conclusion, these data provide no evidence for other than postjunctional Y1-receptors mediating the enhancement of the contractile response elicited by phenylephrine in the perfused rat tail artery. The effects of [des-Ser3,Lys4]D-Cys2-NPY indicate that the Y1-receptor may possess an allosteric binding site.

Structure-activity studies of peptide YY(22-36): N-alpha-Ac-[Phe27]PYY(22-36), a potent antisecretory peptide in rat jejunum

Peptide YY (PYY) and its homologous peptide, neuropeptide Y (NPY), are known to exhibit potent antisecretory effects in the intestine. To determine the structural requirements to elicit antisecretory effects, we have synthesized several analogs of the PYY active site, PYY(22-36), and compared their binding affinities and antisecretory potencies in rat jejunum. These investigations revealed that the hydroxyl groups of Ser23 and Thr32, as well as the imidazole group of His26, are important for activity in the intestine. N-alpha-acetylation of PYY(22-36) increased both the binding affinity and antisecretory potency. Structure-activity studies with N-alpha-Ac-PYY(22-36) showed that substitution of His26 with parachlorophenylalanine (pCl-Phe) or Tyr36 with N-Me-Tyr reduced receptor affinity, while replacement of Tyr27 with Phe increased the activity substantially. Furthermore, acylation of the alpha-NH2 group with hydrophobic groups, myristic and naphthaleneacetic acids, substantially reduced the antisecretory potencies but not the binding affinities. Further modification of N-alpha-Ac-[Phe27]PYY(22-36) may lead to the development of more potent agonist compounds, which may provide a framework for the design of a new class of antidiarrheal drugs.

Characterization of amylin binding sites in a human hepatoblastoma cell line

Amylin binding sites in a human hepatoblastoma cell line (HepG2) have been characterized in detail. 125I-Amylin (rat) bound to HepG2 cells with high affinity. Binding was reversible and selective, and dependent on time and temperature. Scatchard analysis revealed the presence of high (Kd = 0.11 +/- 0.04 nM) and low (Kd = 1.3 +/- 0.4 microM) affinity binding sites for 125I-amylin in HepG2 cells. The dissociation experiments also showed that 125I-amylin dissociated from high- and low-affinity sites. The association data, however, indicated the presence of only one binding site. Rat amylin was more potent than human amylin and rat calcitonin gene-related peptide (CGRP) in displacing 125I-amylin bound to HepG2 cells. Nonhomologous peptides did not displace 125I-amylin. Rat amylin was, however, less potent than rat CGRP in displacing 125I[Tyr0]CGRP from HepG2 cells. Pretreatment of HepG2 cells with rat amylin (10 nM) reduced the specific binding of 125I-amylin by 75%, whereas rat CGRP (10 nM) pretreatment had no effect on amylin binding. Calcitonin gene-related peptide, as well as rat and human amylin, stimulated the adenylate cyclase activity of HepG2 cell membrane preparation in a dose-dependent manner, with an order of potency of CGRP > rat amylin > human amylin. A CGRP antagonist, CGRP(8-37), significantly attenuated the stimulatory effect of both amylin and CGRP on adenylate cyclase activity. These investigations show that distinct receptors of amylin and CGRP are present in HepG2 cells, and that amylin stimulates adenylate cyclase activity through CGRP receptors. This system could now be exploited for studying amylin receptors and amylin-mediated signal transduction.

NPY-(18-36) and pertussis toxin distinguish between the negative and positive contractile effects of neuropeptide Y (NPY) in ventricular cardiomyocytes

The mechanism of action of NPY to produce contractions of adult rat ventricular myocytes was investigated. Positive effects were mediated through an L-type Ca2+ channel. Negative effects, linked through an inhibitory G-protein to a transient outward K+ channel, could be antagonised by NPY-(18-36).

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.

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.

N-alpha-biotinylated-neuropeptide Y analogs: syntheses, cardiovascular properties, and application to cardiac NPY receptor visualization

Two monobiotinylated analogs of neuropeptide Y (NPY) were synthesized by coupling the N-hydroxysuccinimidyl esters of biotin and (6-biotinylamido)-hexanoic acid, respectively, to the free alpha-NH2 group of the side chain protected NPY peptide resin. Crude peptides obtained by HF cleavage were purified by RPLC and their integrities were confirmed by amino acid and mass spectral analysis. As with NPY, both biotinylated analogs inhibited 125I-NPY binding and adenylate cyclase activity of rat cardiac ventricular membranes in a dose-dependent manner. N-alpha-[(6-biotinylamido)-hexanoyl]-NPY exhibited potencies comparable to that of NPY whereas N-alpha-biotinyl-NPY was slightly less potent. In the in vivo experiments, however, both the biotinylated analogs exhibited responses comparable to NPY in increasing arterial blood pressure and decreasing heart rate in anesthetized rats. The responses of the biotinyl analogs were longer lasting than those of NPY. Histochemical studies revealed that N-alpha-[(6-biotinylamido)-hexanoyl]-NPY could label the NPY receptors in rat cardiac ventricular tissues. This labeling was specific since intact NPY inhibited the staining. These studies show that biotinyl-NPY analogs exhibit biological potencies comparable to intact NPY and can therefore be used to further probe the NPY-receptor interaction.