Modulation by neuropeptide Y of parasympathetic nerve-evoked nasal vasodilatation via Y2 prejunctional receptor

Review of Rhinitis: Classification, Types, Pathophysiology

Rhinitis describes a pattern of symptoms as a result of nasal inflammation and/or dysfunction of the nasal mucosa. It is an umbrella entity that includes many different subtypes, several of which escape of complete characterization. Rhinitis is considered as a pathologic condition with considerable morbidity and financial burden on health care systems worldwide. Its economic impact is further emphasized by the fact that it represents a risk factor for other conditions such as sinusitis, asthma, learning disabilities, behavioral changes, and psychological impairment. Rhinitis may be associated with many etiologic triggers such as infections, immediate-type allergic responses, inhaled irritants, medications, hormonal disturbances, and neural system dysfunction. It is basically classified into three major clinical phenotypes: allergic rhinitis (AR), infectious rhinitis, and non-allergic, non-infectious rhinitis (NAR). However, this subdivision may be considered as an oversimplification because a combined (mixed) phenotype exists in many individuals and different endotypes of rhinitis subgroups are overlapping. Due to the variety of pathophysiologic mechanisms (endotypes) and clinical symptoms (phenotypes), it is difficult to develop clear guidelines for diagnosis and treatment. This study aims to review the types of allergic and non-allergic rhinitis, providing a thorough analysis of the pathophysiological background, diagnostic approach, and main treatment options.

Unilateral rhinorrhea after translabyrinthine surgery due to parasympathetic hypersensitive syndrome: differentiation from cerebrospinal fluid leakage

INTRODUCTION

Unilateral rhinorrhea after translabyrinthine surgery for vestibular or facial schwannoma usually suggests cerebrospinal fluid (CSF) leakage and requires specific measures, including revision surgery.

OBJECTIVE

To draw attention to the possibility of postoperative unilateral rhinorrhea with concomitant hyperlacrimation and hypersialorrhea without a CSF origin and reflecting more a neuroplastic phenomenon.

STUDY DESIGN

Retrospective study in a tertiary care center university clinic.

PATIENTS AND INTERVENTION

For 1 case of intratemporal facial schwannoma and 2 cases of vestibular schwannoma, surgery was by a translabyrinthine approach with sacrifice of the facial nerve and hypoglossofacial anastomosis in the first case. Postoperative unilateral hydrorhinorrhea associated with various degrees of lacrimation and/or salivary hypersecretion occurred mainly during exercise or under stressful situations.

CONCLUSION

With unilateral rhinorrhea after translabyrinthine surgery for vestibular or facial schwannoma, concomitant symptoms such as lacrimation or hypersialorrhea may not be explained by CSF leakage through the eustachian tube. Misinterpretation may lead to detrimental revision surgery. The pathophysiogenetic mechanism suggests a neuroplastic phenomenon involving a denervation hypersensitivity reaction of the autonomous system. A simple diagnostic test with a nasal anticholinergic agent may be beneficial.

Modulation of sympathetic neurotransmission by neuropeptide Y Y2 receptors in rats and guinea pigs

We have investigated the effect of the Y2 receptor agonist (Y2 agonist; N-acetyl [Leu28,31] NPY 24-36), on contractions evoked by transmural electrical stimulation of sympathetic nerves of isolated arteries from a range of vascular beds in rats and guinea pigs. Contractions evoked by transmural stimulation of the rat renal, mesenteric and femoral arteries were significantly attenuated in the presence of the Y2 agonist. In these arteries, contractions were significantly inhibited in the presence of an alpha-adrenoceptor antagonist (76-97%). So we conclude that these responses were primarily mediated by noradrenaline and that the Y2 agonist attenuates the release of noradrenaline via presynaptic Y2 receptors. Contractions of the rat carotid artery were not attenuated by the Y2 agonist but were completely abolished in the presence of an alpha-adrenoceptor antagonist suggesting that in this artery the Y2 agonist has no effect on release of noradrenaline. In the guinea pig, carotid arteries contractions evoked by transmural nerve stimulation were attenuated in the presence of the Y2 agonist and inhibited by an alpha-adrenoceptor antagonist 75-87% suggesting that the Y2 agonist attenuates the release of noradrenaline via presynaptic Y2 receptors in this vessel. In the guinea pig femoral artery contractions evoked by transmural stimulation were not modified in the presence of the Y2 agonist but were completely abolished in the presence of an alpha-adrenoceptor antagonist. This suggests that the Y2 agonist does not modify noradrenaline release in this vessel. Contractions of the guinea pig mesenteric artery were significantly potentiated by the Y2 agonist, possibly by potentiation of neuropeptide Y (NPY) at the Y1 receptor. The Y1 antagonist inhibited more than 70 % of the response, indicating that the majority of the contraction was mediated by NPY. The current study demonstrates heterogeneity of neurotransmitter substances in sympathetic nerves supplying vascular beds within and across species and in subsequent functional response.

Suppression of inferior alveolar nerve-induced vasoconstrictor response by ongoing cervical sympathetic nerve activity in cat

We examined the effects of ongoing cervical sympathetic trunk (CST) stimulation on the vasoconstrictor responses in the lower lip elicited by electrical stimulation (ES) of the inferior alveolar nerve (IAN) or CST in anaesthetised cats to determine whether (i) the previously reported suppressive effect of ongoing CST activity on IAN-induced vasoconstriction occurs during not only ipsilateral, but also contralateral CST stimulation; and (ii) a vasoconstriction can be elicited by brief CST stimulation during ongoing stimulation of the contralateral CST. The central lower lip blood vessels are innervated by both left and right CST. The fall in central lip blood flow (LBF) elicited by IAN stimulation alone was reduced in a frequency-dependent manner during concurrent CST stimulation at 0.2-2 Hz, and at the high end of this frequency range was transformed to a rise regardless of whether the CST stimulation was ipsilateral or contralateral to the IAN stimulation. The fall in central LBF elicited by stimulation of one CST was not transformed to a rise by ongoing stimulation of the contralateral CST. Possibly, IAN-evoked orofacial vasoconstriction does not occur under physiological conditions (unlike IAN-evoked vasodilatation) because it is suppressed by the spontaneous sympathetic discharge in CST.

Neuropeptide Y inhibits acetylcholine release in human heart atrium by activation of Y2-receptors

Congestive heart failure and other cardiac diseases are characterized by increased activity of the sympathetic nervous system, whereas at the same time parasympathetic activity is often suppressed. Such imbalance may be a result of or at least enhanced by presynaptic inhibitory effects of sympathetic neurotransmitters on acetylcholine release. We investigated whether the sympathetic cotransmitters neuropeptide Y (NPY), norepinephrine (NE), and ATP are capable of modulating acetylcholine release in human heart atrium. Human atrial appendages were incubated with [(3)H]-choline to label cholinergic transmitter stores and placed in superfusion chambers. Electrical field stimulations (S1, S2) induced a tetrodotoxin-dependent [(3)H]-release, which was taken as an index of endogenous acetylcholine release. NE, NPY, ATP, and a P2-receptor analogue were added before S2. NPY (0.05-1.0 micromol/l) concentration dependently inhibited acetylcholine release. This effect was prevented by the NPY-Y(2)-receptor antagonist BIIE 0246 (0.1 micromol/l) but not by the NPY-Y(1)-receptor antagonist BIBP 3226 (10 micromol/l). ATP (10 micromol/l), a stable analogue ADP-beta S (3 micromol/l), and NE (1 micromol/l) had no effect on acetylcholine release. m-RNA for the NPY-receptor subtypes Y(1), Y(2), Y(4), Y(5), and y(6) was demonstrated by reverse transcription-polymerase chain reaction (RT-PCR). The results suggest that the sympathetic neurotransmitter NPY inhibits parasympathetic neurotransmission in the human heart through activation of presynaptic Y(2)-receptors. NE and ATP seem not to play a role. Since NPY plasma levels are high in chronic heart failure patients, NPY may be one component leading to impaired parasympathetic neurotransmission in those patients.

Neuropeptide Y and its receptors as potential therapeutic drug targets

Neuropeptide Y (NPY) is a 36-amino-acid peptide that exhibits a large number of physiological activities in the central and peripheral nervous systems. NPY mediates its effects through the activation of six G-protein-coupled receptor subtypes named Y(1), Y(2), Y(3), Y(4), Y(5), and y(6). Evidence suggests that NPY is involved in the pathophysiology of several disorders, such as the control of food intake, metabolic disorders, anxiety, seizures, memory, circadian rhythm, drug addiction, pain, cardiovascular diseases, rhinitis, and endothelial cell dysfunctions. The synthesis of agonists and antagonists for these receptors could be useful to treat several of these diseases.

Histamine H3 receptor activation inhibits neurogenic sympathetic vasoconstriction in porcine nasal mucosa

Histamine release from mast cells is a primary mediator of rhinorrhea, nasal mucosal swelling, increased secretion, sneezing, pruritus and congestion that occur in allergic rhinitis. It is well known that histamine H(1) receptor antagonists inhibit the itch and rhinorhea, but do not block the allergic nasal congestion. A growing body of evidence shows that in addition to histamine H(1) receptors, activation of H(3) receptors may contribute to the procongestant nasal actions of histamine. Activation of the prejunctional histamine H(3) receptor modulates sympathetic control of nasal vascular tone and resistance. The present study was conducted to further characterize the role of histamine H(3) receptors on neurogenic sympathetic vascular contractile responses in isolated porcine nasal turbinate mucosa. We presently found that the histamine H(3) receptor agonist, (R)-alpha-methylhistamine (10-1000 nM), inhibited electrical field stimulation-induced sympathetic vasomotor contractions in a concentration-dependent fashion. Pretreatment with either of the selective histamine H(3) receptor antagonists, thioperamide and clobenpropit, blocked the sympathoinhibitory effect of (R)-alpha-methylhistamine in porcine turbinate mucosa. The effect of compound 48/80, an agent that elicits the release of endogenous histamine from mast cells on nasal sympathetic contractile responses, was also tested. The action of compound 48/80 to release mast cell-derived histamine in the nose mimics many of the nasal responses associated with allergic rhinitis, extravascular leakage and decreased nasal patency. We presently found that compound 48/80 also inhibited the electrical field stimulation-induced sympathetic response. Pretreatment with the H(3) receptor antagonist clobenpropit blocked the sympathoinhibitory action of compound 48/80 on sympathetic contractile responses in nasal mucosa. Taken together, these studies indicate that histamine H(3) receptors modulate vascular contractile responses by inhibition of noradrenaline release from sympathetic nerve terminals in nasal mucosa. It is further suggested that histamine H(3) receptors may play a role in the regulation of vascular tone and nasal patency in allergic nasal congestive disease.

Measurement of nasal patency in anesthetized and conscious dogs

Experiments were undertaken to characterize a noninvasive chronic, model of nasal congestion in which nasal patency is measured using acoustic rhinometry. Compound 48/80 was administered intranasally to elicit nasal congestion in five beagle dogs either by syringe (0.5 ml) in thiopental sodium-anesthetized animals or as a mist (0.25 ml) in the same animals in the conscious state. Effects of mast cell degranulation on nasal cavity volume as well as on minimal cross-sectional area (A(min)) and intranasal distance to A(min) (D(min)) were studied. Compound 48/80 caused a dose-related decrease in nasal cavity volume and A(min) together with a variable increase in D(min). Maximal responses were seen at 90-120 min. Compound 48/80 was less effective in producing nasal congestion in conscious animals, which also had significantly larger basal nasal cavity volumes. These results demonstrate the utility of using acoustic rhinometry to measure parameters of nasal patency in dogs and suggest that this model may prove useful in studies of the actions of decongestant drugs.

Pharmacological characterization of a noninvasive, chronic, experimental dog model of nasal congestion

INTRODUCTION

The present experiments were undertaken to pharmacologically characterize a noninvasive, chronic, experimental dog model of nasal congestion with the overall goal of developing an effective tool for studying the mechanism of action of nasal decongestant drugs.

METHODS

Nasal patency was measured using acoustic rhinometry with chlorpheniramine and d-pseudoephedrine used as test agents. Solubilized compound 48/80 was administered as an intranasal mist to a single naris, to elicit nasal congestion in five conscious beagle dogs. Effects of localized degranulation of mast cells on nasal cavity volume, with and without pretreatment with oral decongestant drugs, were measured before and after compound 48/80 administration. Each series of experiments were repeated with a minimum 2-week rest period between trials.

RESULTS

Compound 48/80 caused a decrease of nasal cavity volume (to about 50% of control). Maximal responses were seen at 90-120 min after 48/80 administration and were of similar magnitude when trials were repeated. Oral administration of the adrenergic agonist, d-pseudoephedrine (3 mg/kg), as well as the histamine H(1) receptor antagonist, chlorpheniramine (10 mg/kg), reduced compound 48/80-induced nasal congestion with the greater effect seen with alpha-adrenoceptor blockade.

DISCUSSION

These results demonstrate the utility of using acoustic rhinometry to measure parameters of nasal patency in the conscious dog, and suggest that this model may provide an effective tool with which to study the actions of decongestant drugs in preclinical investigations using conscious preparations. As this technology is noninvasive, replicate determinations can be made in the same experimental subjects. Both alpha-adrenoceptor agonism and, to a lesser extent, histamine H(1) receptor antagonism appear to block compound 48/80-induced nasal congestion in this model.

Sympathetic control of nasal blood flow in the rat mediated by alpha(1)-adrenoceptors

Experiments were undertaken, using laser-Doppler flowmetry, to determine the nature of adrenoceptors mediating sympathetic nerve evoked nasal vasoconstrictor responses in anesthetized rats. Presence of sympathetic tone was confirmed by a large (330%) increase of nasal blood flow following section of the ipsilateral preganglionic cervical sympathetic nerve. Electrical nerve stimulation produced reproducible, frequency-related nasal vasoconstrictor responses with near maximal response, observed at less than 10 Hz. Evoked nasal vasoconstrictor responses were largely blocked with intravenous treatment with the non-selective alpha-adrenoceptor antagonists, phentolamine (5 mg kg(-1)) and phenoxybenzamine (2 mg kg(-1)), as well as with the selective alpha(1)-adrenoceptor antagonist, prazosin (300 microg kg(-1)). alpha(2)-Adrenoceptor antagonism with rauwolscine (500 microg kg(-1)) potentiated neurally evoked nasal vasoconstriction. Neither atropine (1 mg kg(-1)) nor propranolol (1 mg kg(-1)) altered the evoked responses. Rats with intact cervical sympathetic nerves responded to rauwolscine with a modest constriction. Subsequent prazosin administration produced an increase of nasal blood flow of approximately 275%. These results suggest that the nasal vasculature of the rat is under intense sympathetic tone and that the resulting neurogenic vasoconstriction is mediated exclusively by activation of alpha(1)-adrenoceptors.

Effects of a selective neuropeptide Y Y2 receptor antagonist, BIIE0246, on Y2 receptors at peripheral neuroeffector junctions

1. This study investigated the effects of BIIE0246, a novel neuropeptide Y (NPY) Y2 receptor antagonist, on the inhibition of cholinergic neuroeffector transmission in rat heart and guinea-pig trachea and purinergic neuroeffector transmission in guinea-pig vas deferens produced by the NPY Y2 receptor agonist, N-acetyl [Leu28,31] NPY 24-36. 2. In pentobarbitone anaesthetized rats, supramaximal stimulation every 30 s, of the vagus nerve innervating the heart, increased pulse interval by approximately 100 ms. This response was attenuated by intravenous administration of N-acetyl [Leu28,31] NPY 24-36 (10 nmol x kg(-1)). 3. Transmural stimulation of segments of guinea-pig trachea at 1 min intervals with 5 s trains of stimuli at 0.5, 5, 10, 20 and 40 Hz evoked contractions which were reduced in force by N-acetyl [Leu28,31] NPY 24-36 (2 microM). 4. In guinea-pig vasa deferentia, the amplitude of excitatory junction potentials evoked by trains of 20 stimuli at 1 Hz was reduced in the presence of N-acetyl [Leu28,31] NPY 24-36 (1 microM). 5. In all preparations BIIE0246 attenuated the inhibitory effect of N-acetyl [Leu28,31] NPY 24-36 but had no effect when applied alone. 6. The findings support the view that the nerve terminals of postganglionic parasympathetic and sympathetic neurones possess neuropeptide Y Y2 receptors which, when activated, reduce neurotransmitter release.

NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY24-36, reduces renal vasoconstrictor activity in anaesthetised dogs

The actions of neuropeptide Y (NPY) at the autonomic neuroeffector junction have been attributed to two main receptor subtypes. At NPY Y1 receptors, located postsynaptically, NPY has been shown to produce vasoconstriction, or to potentiate the action of other vasoconstrictor agents. At NPY Y2 receptors, located presynaptically on nerve terminals, NPY inhibits the release of neurotransmitter from autonomic nerve terminals. In these experiments we have used the specific NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY, which lacks local constrictor activity, and have demonstrated inhibition of nerve-evoked vasoconstriction in the renal circulation of anaesthetised dogs in a way that suggests an intra-renal regional specificity. Under control conditions stimulation of the renal sympathetic nerves over a range of frequencies (1-5 Hz) reduced renal vascular conductance and glomerular filtration rate (GFR). Following the injection of the selective NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31]NPY24-36, nerve-evoked reductions in renal conductance were reduced by over 45%. At the lowest stimulation frequencies, reduced vasoconstrictor activity was associated with a marked increase in GFR in the presence N-acetyl [Leu28,Leu31]NPY24-36. At both higher levels of stimulation N-acetyl [Leu28,Leu31]NPY24-36 significantly inhibited vasoconstrictor activity and attenuated the nerve-evoked reductions in GFR. Full recovery of both variables was observed 20 min after N-acetyl [Leu28,Leu31]NPY24-36 injection. N-acetyl [Leu28,Leu31]NPY24-36 produced a similar inhibition of renal vasoconstrictor activity when the renal nerves were left intact and activated reflexly. These results suggest that NPY can act via NPY Y2 receptors to inhibit sympathetic vasoconstrictor activity in the renal circulation of dogs. On the basis of the demonstrated dissociation of effects on vascular conductance and GFR, we suggest that this might result from a preferential action of the NPY Y2 agonist on sympathetic nerves supplying the afferent arteriole of the kidney.

Functional roles played by the sympathetic supply to lip blood vessels in the cat

In the anesthetized cat we used laser-Doppler flowmetry to investigate the part played by cervical superior sympathetic trunk (CST) fibers in the control of blood vessels in an orofacial area (the lower lip). The blood flow increase (antidromic vasodilatation) elicited by inferior alveolar nerve (IAN) stimulation was not affected by ongoing repetitive CST stimulation over the frequency range examined (0.2-10 Hz), although reflex parasympathetic vasodilatation was attenuated. The vasoconstrictor responses elicited by IAN stimulation in some preparations were reduced in a frequency-dependent manner (at 0.2-1 Hz) during ongoing CST stimulation (and replaced by vasodilator responses). The vasoconstrictor response evoked directly by brief CST stimulation was attenuated, but not transformed to a vasodilator response, by ongoing CST stimulation. Thus in the cat lower lip 1) sympathetic stimulation attenuated one type of vasodilator response (parasympathetic-mediated vasodilatation), but not another (antidromic vasodilatation), and 2) ongoing sympathetic (CST) stimulation at low frequencies (<1 Hz) prevented further sympathetic-mediated vasoconstriction.

Escape of parasympathetic vasodilatation from sympathetic attenuation in oro-facial areas in the cat

We examined the effects of concurrent repetitive stimulation of the cervical sympathetic trunk (CST) on the parasympathetically mediated reflex blood flow increase in the orofacial area of cats. In urethane plus alpha-chloralose anaesthetized cats, parasympathetic reflex vasodilatation in the ipsilateral lower lip was elicited by electrical stimulation of the central cut end of the lingual nerve (LN). This blood flow increase was attenuated in a frequency-dependent manner when CST was stimulated concurrently at 0.5-10 Hz for 10 minutes. When we applied repeated LN stimulation (using identical parameters, each time) at intervals during a 30-minutes period of 10 Hz CST stimulation, the attenuation of the blood flow increase gradually weakened in a time-dependent manner even though the direct vasoconstrictor effect of CST stimulation showed no such decline.

Nervous control of blood flow in the orofacial region

The blood vessels of orofacial tissues are innervated by cranial parasympathetic, superior cervical sympathetic, and trigeminal nerves, a situation somewhat different from that seen in body skin. This review summarizes our current knowledge of the nervous control of blood flow in the orofacial region, and focuses on what we know of the respective roles of sympathetic, parasympathetic, and trigeminal sensory nerves in the regulation of blood flow in this region, with particular attention being paid to the mutual interaction between them.

Influence of TASP-V, a novel neuropeptide Y (NPY) Y2 agonist, on nasal and bronchial responses evoked by histamine in anaesthetized pigs and in humans

1. In nine anaesthetized pigs we have studied the influence of intranasal or intrabronchial pretreatment with TASP-V, a neuropeptide Y (NPY) Y2 agonist formed by the attachment of NPY 21-36 to a template-assembled synthetic peptide (TASP), on the functional responses to subsequent intranasal or intrabronchial histamine challenge. 2. In a parallel study, subjective and objective nasal airway resistance (NAR) increase following intranasal histamine challenge was evaluated in 11 healthy volunteers after TASP-V or placebo pretreatment. 3. In pigs, increase in sphenopalatine blood flow induced by histamine dihydrochloride nasal spray (0.25 mg kg(-1) in 3 ml of saline) was significantly reduced by 65% (P<0.05) following intranasal pretreatment with 10 microg kg(-1) of TASP-V. Bronchoconstriction induced by histamine dihydrochloride nebulization (0.5 mg kg(-1) in 3 ml of saline) was significantly attenuated by 25 and 55% following aerosolized pretreatment with TASP-V analogue at 10 and 20 microg kg(-1), respectively. 4. In healthy volunteers, objective increase in NAR and reduction in nasal minimal cross section area (MCSA) induced by intranasal spray of histamine dihydrochloride (15 microg kg(-1) in 200 microl of saline) were significantly attenuated by 50% following local pretreatment with 1.275 microg kg(-1) of TASP-V when compared with saline. 5. It is concluded that intranasal or intrabronchial pretreatment with TASP-V reduced nasal obstruction and bronchoconstriction evoked by histamine challenge in the pig. In healthy human volunteers, this agent attenuated NAR increase and MCSA reduction induced by intranasal application of histamine.

Inhibition of vagal vasodilatation by a selective neuropeptide Y Y2 receptor agonist in the bronchial circulation of anaesthetised dogs

Neuropeptide Y (NPY) is both co-stored and co-released with noradrenaline from sympathetic nerve terminals. In the cardiovascular system, NPY acts on two main receptor subtypes. At postjunctional, or Y1 receptors, NPY can cause both direct vasoconstriction and the potentiation of various constrictor agents. NPY acting at the presynaptic, or Y2 receptor, inhibits the release of neurotransmitter from autonomic nerves. In the present paper, we have used both sympathetic stimulation and the selective NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31] NPY24-36, to examine the role of NPY in the inhibition of vagally mediated vasodilatation in the bronchial circulation of the anaesthetised dog. Stimulation of the cardiac end of the cervical vagus nerve at 1 Hz for 15 s (1 ms, 70 V) increased bronchial vascular conductance by 45%. This increase in flow was abolished by atropine. Sympathetic stimulation for 2.5 min at 16 Hz (1 ms, 20 V) produced a significant (P < 0.05) and prolonged (9 min) inhibition of the subsequent parasympathetically evoked vasodilatation. Similarly, the NPY Y2 receptor agonist, N-acetyl [Leu28,Leu31] NPY24-36, produced a significant (P < 0.05) and prolonged (15 min) inhibition of parasympathetically evoked vasodilatation. When vagus was stimulated at 2.5 Hz for 30 s (1 ms, 70 V), an atropine-resistant, but capsaicin-sensitive vasodilatation was observed. Neither sympathetic stimulation nor the NPY Y2 receptor agonist could be demonstrated to inhibit this vasodilatation. These results suggest that NPY can inhibit cholinergic parasympathetic vasodilatation in the bronchial circulation by an action on NPY Y2 receptors.

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

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

Sympathetic attenuation of parasympathetic vasodilatation in oro-facial areas in the cat

1. The present study was designed to examine the interaction between sympathetic and parasympathetic influences on blood flow in oro-facial areas such as lower lip, palate and submandibular gland (SMG) and in the common carotid artery (CCA) in anaesthetized cats. 2. Section of the ipsilateral superior cervical sympathetic trunk (CST) increased the basal CCA blood flow significantly. The control level with the nerve intact was comparable with that seen at 0.5-1 Hz CST stimulation, suggesting a spontaneous discharge of around 0. 5-1 Hz in the CST fibres innervating the beds supplied by the CCA. The basal blood flow at all sites examined was reduced by CST stimulation in a frequency-dependent manner. 3. Electrical stimulation of the central end of the lingual nerve (LN) evoked blood flow increases in the lower lip and palate. These blood flow increases were markedly reduced by concurrent CST stimulation in a manner that was frequency dependent, but not simply related to the vasoconstrictor effect of CST stimulation. This effect of CST stimulation was not observed in tongue or SMG, even though CST stimulation evoked vasoconstriction in these tissues. A significant reduction in the level of CCA blood flow attained during LN stimulation was observed on repetitive CST stimulation only at 10 Hz, indicating that this response behaved in a fashion different from that seen in the lower lip, palate, tongue and SMG. 4. The present study suggests that concurrent repetitive CST stimulation reduces parasympathetically mediated blood flow increases in certain oro-facial areas (such as the lower lip and palate), but not in the tongue and SMG. This inhibitory action was not a simple additive effect (between vasoconstriction and vasodilatation) and it disappeared rapidly after the cessation of CST stimulation.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Inhibition of sympathetic cholinergic vasodilatation by a selective NPY Y2 receptor agonist in the gracilis muscle of anaesthetised dogs

Neuropeptide Y (NPY) is known to be co-stored and co-released from sympathetic nerve terminals. In the cardiovascular system NPY acts on two main receptor subtypes. At the postjunctional or Y1 receptor NPY causes constriction directly in addition to potentiating other vasoconstrictor agents. NPY acting at the prejunctional, or Y2 receptor, inhibits the release of neurotransmitter from autonomic nerve terminals. In these experiments we used the selective Y2 receptor agonist N-acetyl[Leu28,Leu31]NPY24-36 to examine the role of NPY in the modulation of sympathetic vascular control in skeletal muscle in anaesthetised dogs. No systemic pressor or local constrictor activity was observed in response to N-acetyl[Leu28, Leu31]NPY24-36 administration, therefore allowing us to examine the neuroinhibitory actions of NPY in the absence of direct vascular effects on blood flow. Stimulation of the sympathetic nerves to the gracilis muscle engages both sympathetic cholinergic and sympathetic adrenergic fibres and produces an initial vasodilatation followed by a slower vasoconstriction. Nerve evoked vasodilatation was inhibited by over 50% in the presence of the selective NPY Y2 agonist N-acetyl[Leu28,Leu31]NPY24-36. This dilatation was abolished by atropine, confirming its cholinergic nature. N-Acetyl[Leu28,Leu31]NPY24-36 was found to have no effect on nerve evoked vasoconstriction. The results demonstrate a NPY Y2-receptor mediated inhibition of nerve evoked sympathetic cholinergic vasodilatation but not of sympathetic vasoconstriction.

Sympathetic and parasympathetic interaction in vascular and secretory control of the nasal mucosa in anaesthetized dogs

1. In dogs anaesthetized with pentobarbitone, electrical stimulation of the parasympathetic nerve fibres to the nasal mucosa evoked frequency dependent increases in both nasal arterial blood flow and nasal secretion. Blood flow was measured using a transonic flow probe placed around the artery. 2. Sympathetic nerve stimulation for 3 min at 10 Hz evoked significant and prolonged (> 30 min) attenuation of the vasodilator and secretory responses to subsequent parasympathetic stimulation. 3. Intravenous and intranasal administration of the neuropeptide Y (NPY) analogue N-acetyl [Leu28,Leu31] NPY 24-36, a selective NPY Y2 receptor agonist (20 nmol kg-1), significantly attenuated both vasodilator and secretory effects of subsequent parasympathetic nerve stimulation. When given intravenously, the inhibitory effect of this Y2 receptor agonist on vascular and secretory effects of parasympathetic nerve stimulation was rapid in onset (5 min) and lasted for more than 60 min. The modulatory effect of the Y2 receptor agonist was also seen with intranasal administration, but was slower in onset (15 min), and lasted less than 45 min. The effects of the intranasal pretreatment with the Y2 receptor agonist were significantly prolonged in the presence of the endopeptidase inhibitor phosphoramidon (10 nM). 4. Atropine pretreatment did not significantly reduce the change in vascular conductance evoked by parasympathetic nerve stimulation. Subsequent pretreatment with the NPY Y2 receptor agonist N-acetyl [Leu28,Leu31] NPY 24-36 reduced the stimulation induced increase in conductance by 30%. Nasal secretion was reduced by 70% following pretreatment with atropine and a further 30% by pretreatment with the NPY Y2 receptor agonist. Dose dependent vasodilator and secretory effects of local intra-arterial infusion of acetylcholine and vasoactive intestinal peptide were not modified by the NPY Y2 agonist. 5. Total protein and albumin concentration were measured in nasal lavage fluid collected after nerve stimulation. Atropine pretreatment increased the percentage of the total protein that was albumin in nasal lavage fluid. Neither sympathetic nerve stimulation nor Y2 receptor agonist pretreatment further modified the albumin exudation (a marker of vascular permeability) in nasal fluid lavage collected after parasympathetic nerve stimulation. 6. We propose that sympathetic nerve stimulation releases NPY, which acts on Y2 receptors, probably located on parasympathetic nerve endings, to attenuate both vasodilatation and nasal secretion evoked by subsequent parasympathetic nerve stimulation. This effect is also observed after pretreatment with the Y2-selective NPY analogue N-acetyl [Leu28,Leu31] NPY 24-36.

A role for neuropeptide Y in rat iridial arterioles

A role for neuropeptide Y (NPY) in neurotransmission in rat iridial arterioles has been investigated. Reverse transcription-polymerase chain reaction analysis has demonstrated mRNA expression for both Y1 and Y2 receptors in the superior cervical ganglion and iris. The Y1 agonist [Leu31,Pro34]NPY caused a dose-dependent constriction of iris arterioles (50% effective concentration of 10(-8) M), but, at low concentrations (10(-9) and 10(-10) M), it failed to potentiate either submaximal responses to norepinephrine (10(-6) M) or submaximal, noradrenergic responses to nerve stimulation. In contrast, 10(-7) M [Leu31,Pro34]NPY potentiated submaximal, noradrenergic responses to nerve stimulation (10 Hz, < or = 1 s) and to a concentration of norepinephrine (10(-7) M) which produced only small contractions. The Y1 antagonist 1229U91 blocked contractions induced by [Leu31,Pro34]NPY. Stimulation of the nerves for longer periods (10 or 20 Hz; 5, 30, or 60 s) revealed a component of the response which was reduced by 1229U91. This component was not apparent after brief stimuli (10 Hz, < or = 1 s), even when opposing receptor pathways were blocked. The Y2 agonist N-acetyl-[Leu28,Leu31]NPY24-36 had little effect on arterioles preconstricted with either high potassium or an alpha 2-adrenoceptor agonist, or on nerve-mediated contractions. Results suggest that NPY, released from sympathetic nerves during long-duration, high-frequency stimulation, activates Y1 receptors on iris arterioles to produce vasoconstriction and to potentiate responses to low concentrations of norepinephrine.

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

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

Post-exercise nasal vasoconstriction and hyporeactivity: possible involvement of neuropeptide Y

Neuropeptide Y (NPY) is co-localized with noradrenaline (NA) in perivascular sympathetic nerve and is a vasoconstrictor. Pre-treatment with exogenous NPY markedly reduced nasal airway obstruction and rhinorrhea induced by the irritant capsaicin in control subjects. The aim of the present experiments was to study the time course variations of plasma concentrations of NA and NPY during and after intense exercise in 17 healthy volunteers. In parallel, changes in nasal airway resistance (NAR) were recorded. Nasal obstruction and rhinorrhea induced by capsaicin were compared after 30 min of rest and after 30 min of exercise. Both subjective and objective NAR were significantly reduced (p < 0.05) for over 15 min after the end of exercise. Plasma levels of NPY remained increased for more than 15 min after exercise whereas NA returned to basal values within less than 10 min. The increases of NAR and mucus production evoked by capsaicin were markedly attenuated for 30 min after exercise (p < 0.05). Variations of plasma NPY concentrations over time correlated better with post-exercise nasal vasoconstriction and hyporeactivity to capsaicin than NA. These observations suggest that endogenous NPY could be involved in the prolonged post-exercise nasal vasoconstriction and acts as a modulator of nasal airways reactivity.

Distribution and functional effects of neuropeptide Y on equine ureteral smooth muscle and resistance arteries

The distribution of neuropeptide Y (NPY)-immunoreactive (IR) nerves, as well as the functional effects of NPY and the Y1- and Y2-receptor agonists, [Leu31,Pro34]NPY and NPY(13-36), respectively, have been investigated in vitro in both visceral and arterial smooth muscle of the horse intravesical ureter. NPY-IR nerve fibres were widely distributed along the entire length of the ureter, although the intravesical part was the most richly innervated region, and the only one where NPY-IR ganglion cells were found. NPY (10(-7) M) did not affect either basal tone or spontaneous rhythmic contractions of the isolated intravesical ureter, but significantly enhanced the increases in both tone and frequency of phasic activity elicited by noradrenaline (10(-6) and 10(-5) M). The Y1-receptor agonist, [Leu31,Pro34]NPY (10(-7) and 10(-6) M) did not significantly alter either ureteral basal tone or the contractile activity induced by noradrenaline, whereas the Y2-receptor agonist, NPY(13-36) (10(-7) M), mimicked the potentiating effect of NPY on noradrenaline responses. In ureteral resistance arteries (effective lumen diameters of 130-300 microm), NPY (10(-10) to 10(-7) M) elicited concentration-dependent contractions, which were inversely correlated with the arterial lumen diameter. Submaximal concentrations of NPY (10(-8) M) significantly increased the sensitivity of ureteral arteries to noradrenaline. [Leu31,Pro34]NPY (10(-10) to 10(-7) M), but not NPY(13-36), induced a contractile effect of similar magnitude and potency as those of NPY, and also potentiated noradrenaline responses. The present results demonstrate a rich NPY-innervation in the intravesical ureter and reveal functional effects of the peptide enhancing motor activity in both ureteral and arterial smooth muscles, although the receptors mediating such effects seem to be different. Thus, NPY potentiates the phasic contractions and tone elicited by noradrenaline through Y2-receptors, whereas it both contracts and potentiates noradrenaline vasoconstriction in ureteral arteries via Y1-receptors.

Intranasal administration of neuropeptide Y in man: systemic absorption and functional effects

1. Exogenous neuropeptide Y (NPY, 10 nmol, 50 nmol and 100 nmol) and its vehicle (NaCl 0.9%) were administered in a double blind, randomized and controlled manner by intranasal spray in 7 healthy volunteers. Variations of plasma NPY concentration over time were measured during 120 min. Forty min after the administration of 50 nmol and 100 nmol of exogenous NPY, plasma NPY increased from 5.5 +/- 1.1 pM to 9.8 +/- 2.3 pM (P < 0.05) and from 9.06 +/- 5.1 pM to 20.8 +/- 6.16 pM (P < 0.001), respectively. There was no significant modification of the mean arterial blood pressure and no subjective discomfort was reported. 2. Nasal airway resistance (NAR) was measured by anterior rhinomanometry and was reduced by 25 +/- 3% and 32 +/- 5% after the spray of 50 nmol and 100 nmol, respectively, for about 90 min. 3. Double-blind, randomized, placebo-controlled and 3-way crossover design experiments were performed in 8 healthy volunteers to evaluate the influence of intranasal pretreatment with NPY (20 nmol) and the mixed alpha 1/alpha 2-adrenoceptor agonist oxymetazoline (20 nmol) on the functional effects of subsequent local irritation evoked by capsaicin (3.3 x 10(-4) mol). Subjective evaluation of NAR and local intensity of discomfort were evaluated by means of a visual analogue scale. Nasal secretions were collected and objective NAR was recorded by rhinomanometry. 4. Subjective NAR, nasal secretions and rhinomanometry recordings were not modified by intranasal application of saline, NPY or oxymetazoline. Subjective nasal obstruction, local discomfort, nasal secretions and NAR increase evoked by capsaicin were markedly reduced by NPY pretreatment (P < 0.05) when compared to saline or oxymetazoline. 5. It is concluded that intranasal application of exogenous NPY has very low systemic absorption but induced long lasting nasal vasoconstriction without cardiovascular effects. Pretreatment of the nasal mucosa with exogenous NPY reduces both secretagogue and vasodilator responses to subsequent application of capsaicin.

Cutaneous vasomotor effects of neuropeptide Y

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