Tachykinin NK1 Receptor Research Articles

Novel 3-phenylpiperidine-4-carboxamides as highly potent and orally long-acting neurokinin-1 receptor antagonists with reduced CYP3A induction

The synthesis and biological evaluation of a series of novel 3-phenylpiperidine-4-carboxamide derivatives are described. These compounds are generated by hybridization of the substructures from two types of tachykinin NK1 receptor antagonists. Compound 42 showed high metabolic stability and excellent efficacy in the guinea-pig GR-73637-induced locomotive activity assay at 1 and 24h after oral administration. It also exhibited good pharmacokinetic profiles in four animal species, and a low potential in a pregnane X receptor induction assay.

3D-Quantitative structure–activity relationship and docking studies of the tachykinin NK3 receptor

The tachykinin NK(3) receptor (NK(3)R) is a novel drug target for schizophrenia and drug abuse. Since few non-peptide antagonists of this G protein-coupled receptor are available, we have initiated this study to gain a better understanding of the structure-activity relationships of NK(3) antagonist compounds. We developed a 3D comparative molecular similarity index analysis (CoMSIA) model that gave cross-validated PLS values with q(2) >0.5 which were validated using a test set. We also describe the development of a homology model of the NK(3)R. The model was then used to develop a pharmacophore for docked ligands. This pharmacophore showed two aromatic, two hydrogen donor and one acceptor/aromatic points. These data will be useful for future structure-based drug discovery of ligands for the NK(3)R.

Peripheral inflammation alters desensitization of substance P-evoked current in rat dorsal root ganglion neurons

The neuropeptide substance P is synthesized in a proportion of neurons of the peripheral and central nervous system, and the receptor for substance P, tachykinin NK₁ receptor, has been identified in numerous areas of the central nervous system including the spinal cord. The present investigation was to confirm the existence of tachykinin NK₁ receptor on rat dorsal root ganglion (DRG) neurons and characterize the adaptation of inward current evoked by substance P during carrageenan-induced peripheral inflammation. Using whole-cell voltage recording technique, our results demonstrated that 1 μM substance P elicited significant inward current in a small population of small-diameter DRG neurons of control rats (7%, n=218) and in a bigger proportion of DRG neurons of carrageenan-inflamed rats (15%, n=203). Desensitization of substance P-evoked current was exhibited in almost all of substance P-responsive DRG neurons in control rats (94%, n=16), while it diminished in a bigger proportion of DRG neurons (35%, n=31) in inflamed rats. Furthermore, desensitization of substance P-evoked current was recovered by the activation of protein kinase C (PKC) by application of phorbol 12,13-dibutyrate, a selective agonist of PKC, in the DRG neurons of the inflamed rats. All these results indicated that tachykinin NK₁ receptor in the primary afferents might contribute to the development and maintenance of inflammatory pain.

Design, structure–activity relationship, and highly efficient asymmetric synthesis of 3-phenyl-4-benzylaminopiperidine derivatives as novel neurokinin-1 receptor antagonists

We synthesized a series of novel 3-phenyl-4-benzylaminopiperidine derivatives that were identified as potent tachykinin NK1 receptor antagonists by structural modification of the 3-benzhydrylpiperidone derivative through high-throughput screening. N-{2-[(3R,4S)-4-({2-Methoxy-5-[5-(trifluoromethyl)-1H-tetrazol-1-yl]benzyl}amino)-3-phenyl-1-piperidinyl]-2-oxoethyl}acetamide ((+)-39) was found to be one of the most potent tachykinin NK1 receptor antagonists with high metabolic stability. Highly efficient asymmetric synthesis of (+)-39 was achieved via dynamic kinetic resolution.

Neuropathic pain as a process: reversal of chronification in an animal model

Peripheral neuropathic pain arises from trauma to sensory nerves. Other types of acute neurotrauma such as stroke and spinal cord injury are treated immediately, largely to prevent secondary damage. To pursue the possibility that neuropathic pain may also be amenable to early treatment, a rat model of neuropathic pain was induced using a 2-mm polyethylene cuff implanted around one sciatic nerve. Within 24 hours, hypersensitivity to von Frey hair stimulation appeared, as indicated by decreased paw withdrawal thresholds. When the cuff was removed 24 hours after implantation, readings returned to pre-implantation levels starting as early as day 18. When the cuff was removed after 4 days, there was a period of initial hypersensitivity, and then an increase toward baseline at two time points near the end of the study; therefore, only a partial recovery toward pre-implantation values occurred. Having established that a temporal reversal can occur, the next step examined possible pharmacological reversal. The tachykinin NK1 receptor antagonist, CP-96,345, produced a minor increase in withdrawal thresholds in animals with the cuff left permanently implanted. To determine the effect of early and repeated administration of CP-96,345, it was given daily on days 1–4. The cuff was removed on day 4. Six days later, readings showed reversal of tactile hypersensitivity. We suggest that persistent neuropathic pain occurs from processes that develop over several hours and days, and that some of these processes may be prevented by early medical intervention. Thus, nerve injury in the context of chronic neuropathic pain should be treated in a similar manner to nerve injury resulting from stroke, spinal cord injury, and other types of neurotrauma. We suggest that effective medical intervention within the first few hours after nerve injury may spare a patient from a chronic debilitating pain that may be refractory to later therapies.

Distribution and pharmacological characterization of primate NK-2 tachykinin receptor in the central nervous system of the rhesus monkey

Tachykinin NK-2 receptor, a cognate receptor for neurokinin A, expressed in the brain has been suggested as a new target for the treatment of psychiatric disorders. In rodents, treatment with NK-2 receptor agonists causes anxiogenic effects, while NK-2 receptor antagonists show anxiolytic and antidepressant-like effects. However, information about the distribution and functions of NK-2 receptors in the central nervous system (CNS) in primates is still lacking. Here, we examined the distribution and pharmacological profile of NK-2 receptors in the rhesus monkey (Macaca mulatta) to clarify the molecular basis of NK-2-mediated tachykininergic functions in the primate CNS. NK-2 receptors cloned from the rhesus monkey brain showed similar pharmacological properties to those of human NK-2 receptors. Substantial expression levels of NK-2 mRNA were observed in all the brain regions examined, including areas pertinent to the emotional networks such as the prefrontal cortex, cingulate cortex and amygdala. These findings suggest that NK-2 receptors may play important roles in the pathophysiology of psychiatric disorders.

Intra-articular administration of tachykinin NK1 receptor antagonists reduces hyperalgesia and cartilage destruction in the inflammatory joint in rats with adjuvant-induced arthritis

Persistent pain associated with inflammatory arthritis is an aggravating factor that decreases patients' quality of life. Current therapies for joint pain have limited effectiveness and produce unwanted negative side effects. Although the involvement of substance P and its cognate tachykinin receptor, NK1, in joint inflammation has been extensively documented through animal experiments, the development of oral tachykinin NK1 receptor antagonists against arthritis-induced pain has been unsuccessful in humans to date. To explore the possibility of using tachykinin NK1 receptor antagonists as local therapeutic agents for inflammatory arthritis, we examined the effects of tachykinin NK1 receptor antagonists administered into the rat ankle joint on hyperalgesia in complete Freund's adjuvant (CFA)-induced inflammatory monoarthritis. Administration of the tachykinin NK1 receptor antagonist WIN 51708 or GR 82334 into the affected ankle joint at day 3 following intra-articular CFA injection reduced the mechanical hyperalgesia 12h after the tachykinin NK1 receptor antagonist injection and their analgesic effects persisted for at least 2days. Histological examinations revealed that intra-articular WIN 51708 reduced the CFA-induced destructive changes in the cartilage. These findings suggest that intra-articular injection of tachykinin NK1 receptor antagonists is a promising strategy for relieving the hyperalgesia that occurs in inflammatory arthritis.

Neuropeptide S inhibits stress-stimulated faecal output in the rat

Neuropeptide S (NPS) is a recently identified bioactive peptide that activates an orphan G-protein coupled receptor, called the NPS receptor (NPSR). In rats, NPS and NPSR constitute a novel neuropeptide system expressed both in the central nervous system and in peripheral tissues, controlling visceromotor, neuroendocrine, nociceptive and behavioural responses. To improve the knowledge of the role of the NPS–NPSR system in the gastrointestinal (GI) tract, we investigated: 1- the supraspinal effect of NPS on motor functions of the upper (gastric emptying and gastrointestinal transit) and lower (distal colonic transit and faecal output) GI tract under basal conditions, 2- during pathological states (restraint stress and corticotropin releasing factor (CRF)-induced defecation) in the rat, and 3- the receptor type involved in treatment with NPS using NPS, tachykinin NK3 and opioid receptor antagonists (([D-Cys(tBu)5]NPS), SR142801 and naloxone, respectively).Intracerebroventricular injection of NPS failed to modify basal gastric emptying, gastrointestinal transit and distal colon propulsion, but significantly and dose-dependently reduced faecal pellet excretion and weight stimulated by restraint stress and CRF. The inhibitory effect of NPS on stress-induced defecation was unmodified by pre-treatment with either the tachykinin or opioid receptor antagonists, but was counteracted by a NPSR antagonist.The present study demonstrates, for the first time, that the supraspinal NPS system, which does not participate in the physiological control of GI motility, plays an inhibitory role on defecation stimulated by restraint stress and CRF. The combination of the ability of NPS to inhibit faecal output together with its known anxiolytic effect may be promising, especially in pathological conditions such as irritable bowel syndrome, where stress and the hyperactivity of the CRF system contribute to the co-morbidity of anxiety with colonic motor symptoms such as diarrhoea.

Role of TRPV1 in nociception and edema induced by monosodium urate crystals in rats

Gout is characterized by the deposition of monosodium urate (MSU) crystals. Despite being one of the most painful forms of arthritis, gout and the mechanisms responsible for its acute attacks are poorly understood. In the present study, we found that MSU caused dose-related nociception (ED50 [ie, the necessary dose of MSU to elicit 50% of the response relative to the control value]=0.04 [95% confidence interval 0.01–0.11]mg/paw) and edema (ED50=0.08 [95% confidence interval 0.04–0.16]mg/paw) when injected into the hind paw of rats. Treatment with the selective TRPV1 receptor (also known as capsaicin receptor and vanilloid receptor-1) antagonists SB366791 or AMG9810 largely prevented nociceptive and edematogenic responses to MSU. Moreover, the desensitization of capsaicin-sensitive afferent fibers as well as pretreatment with the tachykinin NK1 receptor antagonist RP 67580 also significantly prevented MSU-induced nociception and edema. Once MSU was found to induce mast cell stimulation, we investigated the participation of these cells on MSU effects. Prior degranulation of mast cells by repeated treatment with the compound 48/80 decreased MSU-induced nociception and edema or histamine and serotonin levels in the injected tissue. Moreover, pretreatment with the mast cell membrane stabilizer cromolyn effectively prevented nociceptive and edematogenic responses to MSU. MSU induced a release of histamine, serotonin, and tryptase in the injected tissue, confirming mast cell degranulation. Furthermore, the antagonism of histaminergic H1 and serotoninergic receptors decreased the edema, but not the nociception of MSU. Finally, the prevention of the tryptase activity was capable of largely reducing both MSU-induced nociception and edema. Collectively, the present findings demonstrate that MSU produces nociceptive and edematogenic responses mediated by TRPV1 receptor activation and mast cell degranulation.Monosodium urate crystals produce nociceptive and edematogenic response mediated by TRPV1 receptor activation and mast cell degranulation.

Proliferation of sensory C-fibers and subsequent neurogenic inflammation in rat airway induced by inhaled lipopolysaccharide

Lipopolysaccharide (LPS) is associated with the development and exacerbation of airway inflammation. Increases in innervation of sensory C-fibers and tachykinin receptors, which mainly involve overproduction of neurotrophins such as nerve growth factor (NGF), may enhance neurogenic inflammation. Expression of NGF and its receptors in rat lungs is known to decline with age. We examined whether inhaled LPS causes proliferation of sensory C-fibers, increased expression of tachykinin receptors and subsequent enhancement of neurogenic inflammation in the airways of preweaning rats. Wistar male rats aged 2 weeks inhaled aerosolized LPS derived from Escherichia coli (0.1mg/ml) for 30min. Evans blue dye leakage into the trachea induced by gaseous formaldehyde or intravenous capsaicin was measured as an index of tachykinin NK1 receptor-mediated vascular permeability. Expression of substance P-immunoreactive nerves, tachykinin NK1 receptors, tumor necrosis factor (TNF)-α and NGF in the trachea was also assessed immunohistochemically. Neurogenic plasma leakage in the trachea increased significantly between 7 and 21 days after LPS inhalation. Expression of TNF-α, NGF, substance P-immunoreactive nerves and tachykinin NK1 receptors was enhanced, peaking at 28h, 7 days, 14 days and 14 days after LPS inhalation, respectively. Pretreatment with infliximab, a blocking antibody for TNF-α, almost completely abolished the airway changes seen after LPS inhalation. In conclusion, inhaled LPS increased innervation of sensory C-fibers and expression of tachykinin NK1 receptors in the airway, probably resulting in enhancement of neurogenic airway inflammation. These airway responses may be caused by overproduction of neurotrophins including NGF, mainly through a TNF-α-mediated pathway.

SR 48968 selectively prevents faecal excretion following activation of tachykinin NK2 receptors in rats.

We tested the ability of SR 48968, (S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichloropheny l)butyl ) benzamide, a non-peptide antagonist highly selective for tachykinin NK2 receptors, to prevent defecation induced in rats by several agents. The tachykinin agonists substance P, [MePhe7]neurokinin B and [beta-Ala8]neurokinin A (4-10) all promoted defecation and increased faecal water content, the last compound being over ten times more potent than the other two (intraperitoneal dose inducing the excretion of 1 g faeces dry weight = 6.7 micrograms kg-1). SR 48968 given either orally (p.o.) or subcutaneously (s.c.) was similarly potent in dose-dependently inhibiting faecal output stimulated by the selective NK2-agonist [beta-Ala8]neurokinin A (4-10) (doses causing 50% inhibition 0.4 microgram kg-1, p.o. and 0.3 microgram kg-1, s.c.). This inhibition was long-lasting (more than 18 h after 1 microgram kg-1 SR 48968 either s.c. or p.o.). At the higher doses tested, SR 48968 also significantly prevented the increase in faecal water content produced by [beta-Ala8]neurokinin A (4-10). In rats treated with SR 48968, stimulation of faecal output by the alpha 2-adrenergic antagonist idazoxan and by salmonella endotoxin (LPS), but not by the 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino) tetralin, 5-HT, carbachol or platelet-activating factor, was partially prevented. The present results suggest that activation of intestinal NK2 receptors, either directly by the selective agonist [beta-Ala8]neurokinin A (4-10) or indirectly through the release of endogenous neurokinin A (by idazoxan or LPS), promotes defecation, presumably as a consequence of increased gut motility or secretion, or both. SR 48968 should therefore be useful for studying the role of neurokinin A-dependent mechanisms in health and disease, including those of the gastrointestinal system, and possibly for developing new therapeutic agents.

A substance P antagonist improves outcome when administered 4 h after onset of ischaemic stroke

Previous studies have suggested that substance P (SP) plays a critical role in the development of brain oedema and functional deficits following traumatic brain injury and that SP receptor antagonism may improve outcome. No studies have described such a role in ischemic stroke. The present study characterized the effects of the NK1 tachykinin receptor antagonist, n-acetyl-l-tryptophan (NAT), on blood–brain barrier (BBB) breakdown, oedema formation, infarct volume and functional outcome following reversible ischemic stroke in rats. Ischemia was induced using a reversible thread model of middle cerebral artery occlusion where occlusion was maintained for 2h before reperfusion. Animals received either NAT or equal volume saline vehicle intravenously at 2h post-reperfusion. Ischaemic stroke resulted in increased perivascular SP immunoreactivity at 24h. Administration of NAT significantly reduced oedema formation and BBB permeability at 24h post-ischemia and significantly improved functional outcome as assessed over 7days. There was no effect on infarct volume. We conclude that inhibition of SP activity with a NK1 tachykinin receptor antagonist is effective in reducing cerebral oedema, BBB permeability and functional deficits following reversible ischemia and may therefore represent a novel therapeutic approach to the treatment of ischaemic stroke.

Contractile effect of tachykinins on rabbit small intestine

To study the role of the tachykinin receptors in spontaneous contractions of longitudinal and circular smooth muscle from rabbit small intestine and to determine the mechanism of action of Substance P (SP). Rabbit duodenum, jejunum and ileum segments were prepared. The spontaneous contractions of longitudinal and circular smooth muscle were recorded using a computer via an isometric force transducer. The specific agonists and antagonists of tachykinin receptors were added into the organ bath. The agonists of tachykinin NK1 receptor (SP and [Sar9] SP), NK2 receptor (NKA and (β-Ala8)-NKA), and NK3 receptor (NKB and Senktide) all induced contractions in the small intestine. The contractions were diminished by NK1 receptor antagonist L-733,060, NK2 receptor antagonist GR-94800, and NK3 receptor antagonist SB 218795. Contractions caused by SP were also reduced by atropine, verapamil, PKC inhibitor staurosporine, and PLC inhibitor U73122. Ttachykinin NK1, NK2, and NK3 receptors mediate the contractions of the smooth muscle in rabbit intestine. Furthermore, SP acts directly on smooth muscle cells through the tachykinin NK1 receptor.

Effects of Systemic Capsaicin Treatment on TRPV1 and Tachykinin NK1 Receptor Distribution and Function in the Nucleus of the Solitary Tract of the Adult Rat

Vanilloids including capsaicin and resiniferatoxin (RTX) have been identified as potential novel anti-inflammatory and analgesic compounds. We have previously shown that systemic capsaicin administration to neonatal rats evokes profound long-term alterations in transient receptor potential vanilloid 1 (TRPV1)- and neurokinin 1 (NK₁) receptor-mediated respiratory responses in the commissural nucleus of the solitary tract (cNTS). Whether this effect of capsaicin is unique to developmentally immature animals is unknown. Therefore, in the present study, we investigated the effects of systemic capsaicin administration to adult rats on NK₁ receptor binding sites, TRPV1 and NK₁ immunoreactivity and function in the cNTS. Microinjection of capsaicin (1 nmol) or RTX (75 pmol) into the cNTS of vehicle-pretreated rats produced a profound bradypnoea (maximum change: –45 breaths·min^–1) and a small increase in tidal volume (VT). Similarly, microinjection of the selective NK₁ receptor agonists [Sar⁹, Met(O₂)¹¹]substance P (SP; 66 pmol) and septide (20 pmol) decreased respiratory frequency and increased VT. Thirteen to 18 days after systemic administration of capsaicin (125 mg·kg^–1 s.c.), the bradypnoeic responses to both capsaicin and RTX were absent (p < 0.05), indicative of sensory neuron ablation/desensitisation. Systemic capsaicin pretreatment significantly (p < 0.05) reduced the density of both [¹²⁵I]Bolton-Hunter SP binding sites (NK₁ receptors) and NK₁ receptor immunoreactivity in the cNTS, but did not alter the respiratory responses evoked by microinjection of [Sar⁹, Met(O₂)¹¹]SP and septide into this region. These studies show that systemic capsaicin administration reduces NK₁ receptor density in the cNTS without adversely affecting NK₁ receptor function at this site. We speculate that adult rats may be more resistant than neonatal rats to the neuroplastic effects of systemic capsaicin administration.

Staphylococcal Enterotoxin B Causes Proliferation of Sensory C-Fibers and Subsequent Enhancement of Neurogenic Inflammation in Rat Skin

Staphylococcal enterotoxin B (SEB) may be associated with the exacerbation of atopic dermatitis. We investigated whether SEB causes proliferation of sensory C-fibers and subsequent enhancement of plasma leakage induced by sensorineural stimulation in rat skin. SEB was applied intracutaneously to the abdomen of preweaning and adult rats. Evans blue dye leakage into the skin induced by topical 10% formalin was measured as an index of neurogenic skin vascular permeability. Local expression of substance P, tachykinin NK1 receptors, and nerve growth factor was assessed immunohistochemically. In addition, we assessed the effects of topical tacrolimus on these skin responses induced by SEB. Increased neurogenic skin plasma leakage was seen 7 days after SEB treatment in 2 different age groups. Innervation of substance P-immunoreactive nerves and expression of tachykinin NK1 receptors and nerve growth factor were also promoted by SEB, peaking at 7 days, 7 days, and 56 h after SEB treatment, respectively. Tacrolimus markedly inhibited these skin changes. SEB increased the innervation of sensory C-fibers and tachykinin NK1 receptors in rat skin, probably because of upregulated production of neurotrophins, including nerve growth factor, leading to enhancement of neurogenic skin inflammation. T cell activation induced by SEB may initiate these changes.

Characterizing the role of the neuropeptide substance P in experimental subarachnoid hemorrhage

Background: Raised intracranial pressure (ICP) following SAH predicts poor outcome and is due to hemorrhage volume and possibly, brain edema, hydrocephalus and increased volume of circulating intracranial blood. Interventions that reduce edema may therefore reduce ICP and improve outcome. The neuropeptide substance P (SP) mediates vasogenic edema formation in animal models of ischemic stroke, intracerebral hemorrhage and brain trauma, and may contribute to development of increased ICP. SP (NK1 tachykinin receptor) blockade using n-acetyl-l-tryptophan (NAT) reduces edema and improves outcome in these models. This study therefore assessed whether SP mediates edema formation in experimental SAH. Methods: SAH was induced in rats by either injection of autologous blood into the prechiasmatic cistern (injection SAH) or by arterial puncture of the Circle of Willis (filament SAH). NAT was injected (i.v.) 30 min after SAH induction. Subgroups were assessed for brain water content, SP and albumin immunoreactivity, and functional outcome at 5, 24 and 48 h or ICP over 5 h. Results: A secondary ICP increase occurred within 2 h of SAH. Brain edema followed filament SAH ( p < 0.001) and correlated with functional deficits ( r = 0.8, p < 0.01). Increased albumin immunoreactivity ( p < 0.001) indicated vasogenic edema. However, NAT treatment did not improve ICP, edema or outcome. Conclusions: Experimental SAH produced secondary ICP elevation, vasogenic brain edema and functional deficits, although it is unclear if edema contributed to ICP. Blockade of SP did not improve any outcome parameters, suggesting that neurogenic inflammation may be less critical than other factors in these models.

Bidirectional Regulation of Human Colonic Smooth Muscle Contractility by Tachykinin NK2 Receptors

In this study, we attempted to clarify the mechanism of tachykinin-induced motor response in isolated smooth muscle preparations of the human colon. Fresh specimens of normal colon were obtained from patients suffering from colonic cancer. Using mucosa-free smooth muscle strips, smooth muscle tension with circular direction was monitored isometrically. Substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) produced marked contraction. All of these contractions were inhibited by saredutant, a selective NK(2)-R antagonist, but not by CP122721, a selective NK(1)-R antagonist or talnetant, a selective NK(3)-R antagonist. βAla(8)-NKA(4-10) induced concentration-dependent contraction similar to NKA, but Sar(9)-Met(11)-SP and Met-Phe(7)-NKB did not cause marked contraction. Colonic contraction induced by βAla(8)-NKA(4-10) was completely blocked by saredutant, but not by atropine. Tetrodotoxin or N(G)-nitro-L-arginine methyl ester pretreatment significantly enhanced βAla(8)-NKA(4-10)-induced contraction. Immunohistochemical analysis showed that the NK(2)-R was expressed on the smooth muscle layers and myenteric plexus where it was also co-expressed with neuronal nitric oxide synthase in the myenteric plexus. These results suggest that the NK(2)-R is a major contributor to tachykinin-induced smooth muscle contraction in human colon and that the NK(2)-R-mediated response consists of an excitatory component via direct action on the smooth muscle and an inhibitory component possibly via nitric oxide neurons.

Suppressive Effects of Glycyrrhetinic Acid Derivatives on Tachykinin Receptor Activation and Hyperalgesia

Glycyrrhetinic acid (GA), an aglycone of glycyrrhizin, isolated from the licorice root (Glycyrrhizia), and its semi-synthetic derivatives have a wide range of pharmacological effects. To investigate whether GA derivatives may be used as a new class of analgesics, we examined the effects of these compounds on human tachykinin receptors expressed in CHO-K1 cells. Among the GA derivatives examined, the disodium salt of olean-11,13(18)-dien-3β,30-O-dihemiphthalate inhibited the mobilization of [Ca(2+)](i) induced by substance P, neurokinin A, and neurokinin B in CHO-K1 cells expressing the human NK(1), NK(2), and NK(3) tachykinin receptors, respectively. In an inflammatory pain model, Compound 5 suppressed the capsaicin-induced flinching behavior in a dose-dependent manner. Compound 5 was also effective in suppressing pain-related behaviors in the late phase of the formalin test and reducing thermal hyperalgesia in the neuropathic pain state caused by sciatic nerve injury. Collectively, Compound 5 may be an analgesic candidate via tachykinin receptor antagonism.

Nitrergic Inhibition of Tachykininergie Neuro-Muscular Transmission via Cyclic GMP in the Hamster Ileum

The present study was designed to explore the inhibitory mechanism by nitric oxide (NO) of the tachykininergic neuro-muscular transmissions in the hamster ileum. In the presence of guanethidine (1 µM), atropine (0.5 µM), nifedipine (0.1 µM) and apamin (100 nM), electrical field stimuli (EFS; 0.5 ms duration, 15 V) evoked non-adrenergic, non-cholinergic excitatory junction potentials (EJPs) in circular smooth muscle cells. The EJPs were markedly inhibited by the tachykinin NK1 receptor antagonists [D-Pro(4), D-Trp(7,9)]-SP(4-11) (3 µM). Both the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 200 µM) and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 µM), did not affect on the resting membrane potentials, but enhanced the tachykininergic EJPs. In the presence of L-NAME (200 µM), exogenously applied NO (10 µM) and the membrane permeable analogue of guanosine 3',5'-cyclic monophosphate (cGMP), 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP, 3 mM), significantly inhibited the tachykininergic EJPs. Application of EFS (0.5 msec duration, 15 V) with trains of 20 pulses at 20 Hz increased amount of released substance P (SP). The release of SP was further increased by the treatment of L-NAME or ODQ, but markedly reduced by exogenously applied NO and 8-Br-cGMP. These results suggest that the endogenous NO may inhibit the tachykininergic neuro-muscular transmissions by the decrease of SP release from the tachykininergic neurons, possibly through a guanylate cyclase-cGMP-dependent mechanism in the hamster ileum.

Bronchoconstrictor effect of the tachykinin NK3-receptor agonists [MePhe7]-neurokinin B and senktide in the isolated guinea pig lung

ABSTRACTTo determine whether bronchoconstriction can be mediated via the tachykinin NK3 receptors, isolated guinea pig lungs were challenged with the exogenous tachykinin NK3-receptor agonists [MePhe7]-neurokinin B ([MePhe7]-NKB) and senktide. [MePhe7]-NKB induced bronchoconstriction (EC50 = 11.8 ± 1.7 μM) that was significantly inhibited by the tachykinin NK3-receptor antagonist SB 223412 at 10 μM (EC50 = 24.4 ± 4.5 μM). Senktide also induced bronchoconstriction (EC50 = 96.2 ± 20.3 μM) and the bronchoconstriction was significantly reduced by SB 223412 at 1 and 10 μM (EC50 = 270.8 ± 78.9 μM and 388.3 ± 105.5 μM, respectively). Although the authors demonstrated that SB 223412, [MePhe7]-NKB, and senktide are potent and selective for the tachykinin NK3 receptors in binding and functional (Ca2+ mobilization) assays, the tachykinin NK1-receptor antagonist CP 99,994 at 1 μM (EC50 = 32.7 ± 8.5 μM) produced inhibition of [MePhe7]-NKB–induced bronchoconstriction, whereas the tachykinin NK2-receptor antagonist SR 48968 at 0.1 μM (EC50 = 213.2 ± 42.9 μM) blocked senktide-induced bronchoconstriction. These data suggest that [MePhe7]-NKB and senktide caused bronchoconstriction in guinea pig through activation of the tachykinin NK3-receptors but the tachykinin NK1- and/or NK2-receptors are also involved in the response.