CP-96,345 antagonism of NK1 receptors and smoke-induced protein extravasation in relation to its cardiovascular effects

Tissue-specific patterns of neurokinin-1 receptor (NK-1R) gene expression in mice exposed to sidestream cigarette smoke

Neurokinin-1 receptor (NK-1R), a high-affinity plasma membrane-bound receptor for neurokinin substance P, plays important roles in the onset of the pathophysiological responses. To test whether the transcript levels of gene encoding NK-1R in organs are affected by sidestream cigarette smoke (SSCS) exposure, the C57BL/6 mice were randomly assigned to five groups (six/group) in a study of the dose-effect relationship. The mice were exposed to 0 (filtered room air), 2, 4, 8 and 16 mg total particulate matter (TPM) of SSCS/exposure/day, respectively, for seven days through a nose-only exposure chamber (IN-TOX, Albuquerque, NM, USA). The levels of NK-1R mRNA in the lung, heart, liver, kidney and spleen tissues were detected by reverse transcription-polymerase chain reaction (RT-PCR) techniques and normalized against GAPDH expression. NK-1R mRNA in heart tissue showed SSCS-induced dose-dependent downregulation, with minimum expression at a dose of 8.0 mg TPM. Whereas, the levels of NK-1R mRNA in the liver were upregulated to 2.86 and 5.13-fold after exposure to 2.0 and 4.0 mg TPM of SSCS respectively, then returned to 4.19 and 3.93-fold at the exposure doses of 8.0 and 16.0 mg TPM, respectively, when compared to that of the control. In the kidney, SSCS exposure at a dose of 2.0 TPM, but not higher than that level, induced significant elevation of NK-1R mRNA expression. These findings suggest that there are the paracrine and/or autocrine signalling mechanisms through receptor-ligand interactions. No alteration of NK-1R gene expression was observed in the lungs and spleen tissues in this study. The tissue-specific patterns by which SSCS affect NK-1R gene expression in these organs may partially explain dissimilarity of NK-1R activation and the associated toxicity caused by environmental tobacco smoke.

The role of neural inflammation in asthma and chronic obstructive pulmonary disease

The tachykinins substance P and neurokinin A are found within airway nerves and immune cells. They have various effects on the airways that can contribute to the changes observed in asthma and chronic obstructive pulmonary disease. Both tachykinin NK(1) and NK(2) receptors have been involved in the bronchoconstriction and the proinflammatory changes induced by substance P and neurokinin A. Tachykinin NK(1) and NK(2) receptor antagonists have activity in various animal models of allergic asthma and chronic bronchitis. It is suggested that dual NK(1)/NK(2) and triple NK(1)/NK(2)/NK(3) tachykinin receptor antagonists have potential in the treatment of obstructive airway diseases.

Airway inflammation and tachykinins: prospects for the development of tachykinin receptor antagonists

The tachykinins substance P and neurokinin A are contained within sensory airway nerves. Immune cells form an additional source of tachykinins in inflamed airways. Elevated levels of tachykinins have been recovered from the airways of patients with asthma and chronic obstructive pulmonary disease. Airway inflammation leads to an upregulation of tachykinin NK(1) and NK(2) receptors. Preclinical studies have indicated a role for the tachykinin NK(1), NK(2) and NK(3) receptors in bronchoconstriction, airway hyperresponsiveness and airway inflammation caused by allergic and nonallergic stimuli. Compounds that are able to block two or three tachykinin receptors hold promise for the treatment of airways diseases such as asthma and/or chronic obstructive pulmonary disease.

Role of tachykinins in asthma

The sensory neuropeptides substance P (SP) and neurokinin A (NKA) are localized to sensory airway nerves, from which they can be released by a variety of stimuli, including allergen, ozone, or inflammatory mediators. Sensory nerves containing these peptides are relatively scarce in human airways, but it is becoming increasingly evident that inflammatory cells such as eosinophils, macrophages, lymphocytes, and dendritic cells can produce the tachykinins SP and NKA. Moreover, immune stimuli can boost the production and secretion of SP and NKA. SP and NKA have potent effects on bronchomotor tone, airway secretions, and bronchial circulation (vasodilation and microvascular leakage) and on inflammatory and immune cells. Following their release, tachykinins are degraded by neutral endopeptidase (NEP) and angiotensin-converting enzyme. The airway effects of the tachykinins are largely mediated by tachykinin NK1 and NK2 receptors. Tachykinins contract smooth muscle mainly by interaction with NK2 receptors, while the vascular and proinflammatory effects are mediated by the NK1 receptor. In view of their potent effects on the airways, tachykinins have been put forward as possible mediators of asthma, and tachykinin receptor antagonists are a potential new class of antiasthmatic medication.

Effect of tachykinin receptor antagonists in experimental neuropathic pain

The intrathecal effect of 0.1 to 10 microg of RP-67,580 (3aR,7aR)-7,7-diphenyl-2[1-imino-2(2-methoxyphenyl)-ethyl]++ +perhydroisoindol-4-one hydrochloride, CP-96,345 (2S,3S)-cis-(2(diphenylmethyl)-N-[(2-methoxyphenyl) methyl]-1-azabicyclo[2.2.2]octan-3-amine), SR-140,333 (S)-(1-¿2-[3-(3,4-dichlorophenyl)- 1-(3-isopropoxyphenylacetyl)piperidin-3-yl]ethyl¿-4-phenyl-1 -azonia-bicyclo[2.2.2.]-octane,chloride), all neurokinin (NK)1-receptor antagonists, SR-48,968 (S)-N-methyl-N[4-(4-acetylamino-4-[phenylpiperidino)-2-(3,4-dichlorophen yl)-butyl]benzamide, a tachykinin NK2 receptor antagonist and SR-142,801 (S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl) piperidin-3-yl)propyl)-4-phenylpiperidin-4-yl)-N-methyl acetamide, a tachykinin NK3 receptor antagonist, and of their respective inactive enantiomers on thresholds of vocalization due to a mechanical stimulus in mononeuropathic (sciatic nerve ligature) and diabetic rats, was examined. The tachykinin NK1 and the NK2 receptor antagonists were antinociceptive in both models, with a higher effect of the former in diabetic rats. The tachykinin NK3 receptor antagonist was weakly effective in diabetic rats only. This indicates a differential involvement of the tachykinins according to the model of neuropathic pain, suggesting a potential role for tachykinin receptor antagonists in the treatment of neuropathic pain.

The tachykinin NK1 receptor. Part II: Distribution and pathophysiological roles

The tachykinin NK1 receptor is widely distributed in both the central and peripheral nervous system. In the CNS, NK1 receptors have been implicated in various behavioural responses and in regulating neuronal survival and degeneration. Moreover, central NK1 receptors regulate cardiovascular and respiratory function and are involved in activating the emetic reflex. At the spinal cord level, NK1 receptors are activated during the synaptic transmission, especially in response to noxious stimuli applied at the receptive field of primary afferent neurons. Both neurophysiological and behavioural evidences support a role of spinal NK1 receptors in pain transmission. Spinal NK1 receptors also modulate autonomic reflexes, including the micturition reflex. In the peripheral nervous system, tachykinin NK1 receptors are widely expressed in the respiratory, genitourinary and gastrointestinal tracts and are also expressed by several types of inflammatory and immune cells. In the cardiovascular system, NK1 receptors mediate endothelium-dependent vasodilation and plasma protein extravasation. At respiratory level, NK1 receptors mediate neurogenic inflammation which is especially evident upon exposure of the airways to irritants. In the carotid body, NK1 receptors mediate the ventilatory response to hypoxia. In the gastrointestinal system, NK1 receptors mediate smooth muscle contraction, regulate water and ion secretion and mediate neuro-neuronal communication. In the genitourinary tract, NK1 receptors are widely distributed in the renal pelvis, ureter, urinary bladder and urethra and mediate smooth muscle contraction and inflammation in response to noxious stimuli. Based on the knowledge of distribution and pathophysiological roles of NK1 receptors, it has been anticipated that NK1 receptor antagonists may have several therapeutic applications at central and peripheral level. At central level, it is speculated that NK1 receptor antagonists could be used to produce analgesia, as antiemetics and for treatment of certain forms of urinary incontinence due to detrusor hyperreflexia. In the peripheral nervous system, tachykinin NK1 receptor antagonists could be used in several inflammatory diseases including arthritis, inflammatory bowel diseases and cystitis. Several potent tachykinin NK1 receptor antagonists are now under evaluation in the clinical setting, and more information on their usefulness in treatment of human diseases will be available in the next few years.

Pharmacology of the peptidomimetic, MEN 11149, a new potent, selective and orally effective tachykinin NK1 receptor antagonist

In this study we investigated the pharmacological properties of MEN 11149, 2-(2-naphthyl)-1-N-[(1R,2S)-2-N-[1(H)indol-3-ylcarbonyl]aminocy clohexanecarbonyl]-1-[N'-methyl-N'-(4-methylphenylacetyl)]di aminoethane, a novel partially retro-inverse pseudo peptide antagonist of tachykinin NK1 receptors. MEN 11149 potently inhibits the binding of [3H]substance P to tachykinin NK1 sites in IM9 cells (pKi = 8.5 +/- 0.1). The compound is highly specific for the human tachykinin NK1 receptors, since it has negligible effects (pKi < 6) on the binding of specific ligands to tachykinin NK2, NK3 receptors and a battery of central and peripheral receptors or ion channels. The tachykinin NK1 receptor antagonism of MEN 11149 appears to be insurmountable since, in saturation binding experiments, both K(D) and Bmax are significantly affected by incubation with the compound (1-30 nM). In isolated guinea-pig ileum, MEN 11149 (0.1-100 nM) shifts to the right in a non-parallel way the substance P methyl ester-induced cumulative concentration-response curve with progressive inhibition of the maximal response (pK(B) = 9.6 +/- 0.1). When tested for reversibility at 5 nM in the same preparation, the compound displays a slow dissociation rate compared to the fast dissociation rate with FK888 (N2-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl)carbonyl-L-prolyl]-N-methy l-N-phenylmethyl-L-3-(2-naphthyl)alaninamide) at 5 nM. In the same preparation, MEN 11149 (10 microM) did not affect the cumulative concentration-response curve to acetylcholine. In vivo, MEN 11149 dose dependently antagonizes [Sar9,Met(O2)11]substance P-induced bronchoconstriction in anaesthetized guinea-pigs (ID50 = 83 +/- 31 nmol/kg i.v.). The duration of the effect exceeds 3 h. MEN 11149 does not affect the bronchoconstriction induced by neurokinin A. The compound dose dependently inhibits [Sar9,Met(O2)11]substance P-induced plasma protein extravasation in guinea-pig bronchi whether administered intravenously (ID50 = 0.22 +/- 0.02 micromol/kg) or orally (ID50 = 0.97 +/- 0.21 micromol/kg). These results demonstrate that MEN 11149 is a potent, highly selective and orally effective insurmountable antagonist of tachykinin NK1 receptors with a long duration of action.

Role of tachykinins in airway narrowing induced by cigarette smoke in guinea pigs

To investigate the mechanism of the airway narrowing induced by cigarette smoke, anaesthetized guinea pigs were exposed to 200 puffs of smoke for 10 min. Airway narrowing was assessed by monitoring the total pulmonary resistance (R(L)). Plasma extravasation was determined by measuring the amount of Evans blue dye extravasated into the trachea and main bronchi. Exposure to cigarette smoke caused a marked airway narrowing and plasma extravasation. Pretreatment with the dual NK(1) and NK(2) receptor antagonist, FK224, abolished such airway narrowing and significantly inhibited the extravasation. While the NK(1) receptor antagonist, FK888, inhibited the extravasation, it had no effect on airway narrowing. Atropine partially inhibited airway narrowing without affecting extravasation. Results suggest that the airway narrowing induced by cigarette smoke is caused by tachykinins, and that a cholinergic pathway is involved. Thickening of the airway walls induced by NK(1) receptor-mediated extravasation may not be involved in such airway narrowing.

Tachykinins, sensory nerves, and asthma--an overview

Tachykinin peptides, substance P (SP) and neurokinin A (NKA), are released from airway sensory nerves upon exposure to irritant chemicals and endogenous agents including bradykinin, prostaglandins, histamine, and protons, The released neuropeptides are potent inducers of a cascade of responses, including vasodilatation, mucus secretion, plasma protein extravasation, leukocyte adhesion--activation, and bronchoconstriction. Neurokinin 1 receptors (preferably activated by SP) seem to be most important for inflammatory actions, while neurokinin 2 receptors (preferably activated by NKA) mediate bronchoconstriction. Species differences exist whereby rat and guinea-pig have a more developed neurogenic inflammation response than normal human airways. However, disease states such as inflammation or viral infections lead to enhanced peptide synthesis and (or) increased sensory nerve excitability. Together with increased neurokinin 1 receptor synthesis and loss of major tachykinin-degrading enzymes such as neutral endopeptidase in airway inflammation, this suggests that recently developed, orally active nonpeptide neurokinin receptor antagonists could have a therapeutic potential in asthmatic patients.

Antagonism of nociceptive responses of cat spinal dorsal horn neurons in vivo by the NK-1 receptor antagonists CP-96,345 and CP-99,994, but not by CP-96,344

Extracellular and intracellular studies were undertaken to test the effects of the non-peptide, substance P (NK-1) receptor antagonists CP-96,345 and CP-99,994, and of CP-96,344, the inactive enantiomer of CP-96,345, on the responses of spinal dorsal horn neurons to peripheral noxious and non-noxious cutaneous stimuli in spinalized cats anesthetized with alpha-chloralose. The effect of these agents on the response of dorsal horn neurons to iontophoretic application of substance P was also tested in extracellular studies. The substance P-induced slow, prolonged discharge of dorsal horn neurons was blocked by administration (0.5 mg/kg, i.v.) of CP-96,345 (n = 10) or CP-99,994 (n = 9), but was unaffected by CP-96,344 (n = 9). The response of substance P-sensitive neurons to noxious thermal stimulation of the cutaneous receptive field, especially the late afterdischarge phase, was also significantly inhibited by CP-96,345 (n = 10) and by CP-99,994 (n = 7). The response of such neurons to noxious pinch stimulation of the receptive field was also significantly inhibited by CP-96,345 (n = 7) and CP-99,994 (n = 8), but the response of three other substance P-sensitive neurons to pinch was unaffected by CP-96,345. CP-96,344 did not affect the response of any neuron tested to either of these noxious stimuli (noxious thermal, n = 7; pinch, n = 6). The response to hair afferent stimulation was unaffected by any of these compounds (CP-96,345, n = 16; CP-96,344, n = 5; CP-99,994, n = 6). In intracellular studies, the effect of these antagonists was tested on responses of dorsal horn neurons to noxious pinch stimulation or to a train of high intensity electrical stimulation of the superficial peroneal nerve. Both stimuli produced an initial fast depolarization followed by a slow and prolonged depolarization with corresponding discharge patterns. CP-96,345 (n = 3) and CP-99,994 (n = 6) selectively blocked the late, slow components of the stimulus-evoked response without affecting the early components. Responses to single electrical pulses of the same intensity and duration were not affected. CP-96,344 did not affect any of the responses tested (n = 5). The data indicate that nociceptive responses of a subset of spinal dorsal horn cells are selectively blocked by the NK-1 receptor antagonists, CP-96,345 and CP-99,994, thus confirming the involvement of NK-1 receptors in these responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Differences in the distribution and characteristics of tachykinin NK1 binding sites between human and guinea pig lung

1. The distribution and characteristics of tachykinin NK1 binding sites have been compared in human and guinea pig lung using quantitative in vitro receptor autoradiography with [125I]-Bolton Hunter-labelled substance P ([125I]-BH-SP). In addition, the effects on these sites of ovalbumin sensitization and challenge have been determined in guinea pig lung. 2. [125I]-BH-SP bound specifically and with high affinity to microvascular endothelium in both human and guinea pig lung, but to bronchial smooth muscle and pulmonary artery media in only guinea pig lung. 3. Specific binding of [125I]-BH-SP to guinea pig bronchial smooth muscle was positively correlated with airway diameter in the range 150-800 microns and was less dense in trachea than in main bronchi. 4. [125I]-BH-SP binding was inhibited by tachykinins with rank orders of affinity of SP > NKA > NKB (human microvessels) and SP > NKA = NKB (guinea pig bronchi and pulmonary arteries). NKA displayed a higher affinity for [125I]-BH-SP binding sites in human microvessels than in guinea pig tissues (P < 0.0001), indicating differences in selectivity for tachykinins between human and guinea pig NK1 receptors. 5. In both human and guinea pig lung, [125I]-BH-SP binding was inhibited by the specific tachykinin receptor antagonists FK888 (NK1 selective antagonist) and FK224 (mixed NK1/NK2 antagonist), with FK888 displaying equal affinity to SP and > 500 times higher affinity than FK224. SP, NKA, NKB and FK888 exhibited similar affinities for [125I]-BH-SP binding sites in both guinea pig arteries and bronchi. 6. Similar distributions, densities and characteristics of [I251]-BH-SP binding sites were demonstrated in oval bumin-sensitized and -challenged guinea-pig lung and in naive animals.7. Differences in the distribution and characteristics of NKI binding sites labelled with [125I]-BH-SP between guinea pig and human lung suggest limitations in the use of guinea pig models for studying roles of tachykinins in pulmonary disease. However, the similar microvascular distributions of NK,binding sites in human and guinea pig lung suggest that the selective tachykinin receptor antagonistsFK888 and FK224 may be useful in the management of airway inflammation in man.

Effects of NK1 receptor antagonists on vasodilation induced by chemical and electrical activation of sensory C-fibre afferents in different organs

The effects of the non-peptide NK1 receptor antagonists, CP 96,345 and RP-67,580, were investigated in a model using anaesthetized pigs. Both the blood flow in the internal maxillary and the bronchial artery (ultrasonic flowmetry) and the superficial blood flow in nasal mucosa and the skin (laser-Doppler flowmetry) were monitored simultaneously. Vasodilation induced by substance P administered i.v. systemically was blocked by pretreatment with CP-96,345, 3 mg kg-1 but not by RP-67,580. CP-96,345 had no effects on the vasodilation induced by calcitonin gene-related peptide or vasoactive intestinal polypeptide. The capsaicin-induced vasodilation in the superficial blood flow of the nasal mucosa and the skin, was reduced after the CP-96,345 pretreatment. The vasodilation induced by capsaicin infusion in the internal maxillary or the bronchial artery was not affected by the CP-96,345 pretreatment. Electrical stimulation of the vagal nerve induced a vasodilation in the bronchial circulation which was not attenuated by pretreatment with CP-96,345. In the nasal mucosa and the skin NK1 receptors seem to be involved in the vasodilation in the superficial small vessels, due to chemical activation of sensory C-fibre afferents. Furthermore, CP-96,345 is a useful tool in the evaluation of NK1 receptor-mediated responses. RP-67,580 which has been shown to have NK1 antagonistic properties in the rat has no such effects in the domestic pig.

Substance P binding sites on intestinal lymphoid aggregates and blood vessels in inflammatory bowel disease correspond to authentic NK-1 receptors

Previous reports have described the ectopic expression of substance P binding sites on lymphoid aggregates and small blood vessels in inflammatory bowel disease. In this report, three non-peptide NK-1 receptor antagonists, CP-96,345, RP-67,580, and L-703,606 abolished saturable 125I-Bolton-Hunter substance P binding to the ectopically expressed receptors in frozen sections of surgically resected bowel from five patients with either Crohn's disease or ulcerative colitis. The rank order of affinity was approximately substance P approximately CP-96,345 approximately L-703,606 > RP-67,580. These results suggest that: (i) the ectopically expressed substance P binding sites in inflammatory bowel disease are authentic NK-1 receptors, (ii) all ectopically expressed receptors on small blood vessels, and lymphoid aggregates as well as normally expressed receptors on the bowel circular muscle have similar receptor affinities and specificities for substance P and the non-peptide antagonists, and (iii) non-peptide antagonists may be therapeutically beneficial in inflammatory bowel disease by inhibiting the pro-inflammatory effects of substance P acting via the NK-1 receptor.

Involvement of substance P but not nitric oxide or calcitonin gene-related peptide in neurogenic plasma extravasation in rat incisor pulp and lip

The possible involvement of the neuropeptides substance P and calcitonin gene-related peptide (CGRP) in the development of neurogenic plasma extravasation in the lower lip, gingiva and incisor pulp was examined in anaesthetized rats by means of the Evans blue method and by using newly developed blockers of substance P (CP-96,345) and CGRP (CGRP8-37). Electrical stimulation of the inferior alveolar nerve (15 V, 2 ms, 10 Hz) for 5 min significantly increased the Evans blue content of the ipsilateral lip, gingiva and pulp by 60 (p < 0.01), 62 (p < 0.01) and 92% (p < 0.05), respectively (n = 8). Pretreatment with CP-96,345 (total dose: 1.5 mg/kg, intravenously) counteracted the dye leakage in the lip and pulp but not in the gingiva (n = 6). The inactive enantiomer (CP-96,344, 1.5 mg/kg, n = 8) or the nitric oxide synthesis inhibitor (N omega-nitro-L-arginine methyl ester hydrochloride, 10 mg/kg, n = 7) did not reduce the stimulation-induced dye extravasation in any of the tissues. Pretreatment with CGRP8-37 (0.3 mg/kg, n = 7) did not significantly influence the development of neurogenic extravasation in the lip and incisor pulp, but it slightly attenuated extravasation in the gingiva. The results indicate that the afferent nerve-induced dye extravasation in the lip and pulp, but not in the gingiva, is to a large extent mediated by substance P acting via neurokinin-1 receptors. There was no evidence for an involvement of nitric oxide or CGRP in neurogenic extravasation in rat incisor and lip.

CGRP (8-37) reduces the duration but not the maximal increase of antidromic vasodilation in dental pulp and lip of the rat

In this study the newly developed blockers of substance P (CP-96,345) and calcitonin gene-related peptide (CGRP8-37) were used to examine whether substance P and CGRP are involved in the afferent nerve induced vasodilation in the rat lower incisor pulp and lip. Electrical stimulation of the inferior alveolar nerve (10 V, 2 ms, 10 Hz, 30 s) in the presence of phenoxybenzamine (3 mg kg-1) induced an immediate vasodilation in the pulp and lip (52 and 186% increase in blood flow respectively, n = 12) with a long duration. Infusion of 2 mg kg-1 CP-96,345, a dose that inhibited the vasodilator effects of substance P (5-25 ng kg-1) in oral tissues, did not have any effect on antidromic vasodilation in either tissue. After infusion of CGRP8-37 (0.3 mg kg-1) the duration of the antidromic vasodilation in the pulp and lip was significantly reduced by 72 and 67% respectively (P < 0.05, n = 4), whereas the maximal increase of the response was unaffected. The blocking effect of the drug was short-lasting. When combined infusions of CP-96,345 and CGRP8-37 were given, a similar reduction in the duration of antidromic vasodilation in the pulp and lip occurred but in this case the amplitude of vasodilation in the pulp was reduced (from 35 +/- 9 to 12 +/- 3%, P < 0.05, n = 4). However, in the lip, the amplitude of vasodilation was not significantly reduced. The present findings indicate an involvement of CGRP in the mediation of the late phase of antidromic vasodilation in rat oral tissues and a role of substance P in the initiation of antidromic vasodilation in the incisor pulp.

Lactic acid-induced plasma protein extravasation in rat airways by stimulation of sensory nerves and NK1 receptor activation

Locally applied lactic acid and capsaicin caused extravasation of Evans blue dye in trachea, main bronchi and nasal mucosa of anaesthetized rats. In animals pretreated with capsaicin to deplete sensory neuropeptides, the lactic acid response was abolished in main bronchi and highly reduced in trachea. Pretreatment with the NK1 receptor antagonist, RP 67580 (3 mg x kg-1 intravenously), markedly inhibited the lactic acid-induced extravasation at all levels; similar pretreatment with NK2 receptor antagonist, SR 48968 (0.5 mg x kg-1 intravenously), was ineffective. Locally applied ruthenium red (a transmembrane Ca2+ fluxes inhibitor), capsazepine (a capsacin receptor antagonist) and diclofenac intraperitoneally (a cyclooxygenase blocker) did not change the lactic acid effect, while the capsaicin response was only diminished in bronchi by local pretreatment with ruthenium red. In conclusion locally applied lactic acid in rat trachea and nasal cavity activated capsaicin sensitive sensory nerve endings producing plasma protein extravasation. This reaction was shown to be mediated by tachykinins acting on the NK1 receptor through a mechanism which appeared to be resistant to capsazepine and ruthenium red and independent of cyclooxygenase products. In comparison the effect of capsacin was partially ruthenium red-sensitive but not influenced by capsazepine.

Postjunctional inhibitory effect of the NK2 receptor antagonist, SR 48968, on sensory NANC bronchoconstriction in the guinea-pig

1 The effects of a selective NK2 receptor antagonist, SR 48968, on non-adrenergic non-cholinergic (NANC) bronchoconstriction in the guinea-pig were investigated in both in vitro and in vivo studies. 2 In isolated bronchus, the electrical field stimulation (EFS, 1 Hz for 1 min)-induced NANC bronchoconstriction was inhibited by 83% after preincubation with SR 48968 (10(-7) M) for 1 h. The selective NK1 receptor antagonist, CP 96,345 (10(-6) M), together with SR 48968 completely abolished the remaining EFS-evoked NANC bronchial contraction. ST 48968 (10(-7) M) totally blocked the bronchial contraction caused by neurokinin A (NKA), but reduced only slightly the bronchoconstriction caused by high concentrations of substance P (SP) and did not influence the response to acetylcholine (ACh). 3 In the guinea-pig isolated perfused lung, SR 48968 (5 x 10(-7) M) perfusion for 30 min markedly reduced, by 95% and 68% respectively, the increase in lung resistance (RL) and the decrease in dynamic compliance (CDyn) evoked by vagal stimulation (1 Hz for 1 min). Capsaicin (10(-8) M)-evoked bronchoconstriction was also significantly inhibited by SR 48968 (5 x 10(-7) M). However, the same concentration of SR 48968 did not affect the release of neuropeptide calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) evoked by either vagal stimulation or capsaicin in the isolated perfused lung, suggesting no prejunctional action. SR 48968 (5 x 10-7 M) caused a parallel shift of the concentration response curve to the right by a factor of 10 for the bronchoconstriction evoked by NKA(l0-9-3 x 10-7 M) in the isolated lung, while it abolished the contraction induced by the selective NK2 receptor agonist, Nle10 NKA(4-10) (10-9-3 x 10- 7 M).4. In in vivo studies, ST 48968 (0.3 mg kg-1, i.v.) also greatly inhibited the increase in insufflation pressure evoked by either capsaicin (10 microg kg-'1 i.v.) or NKA (1 microg kg-1, i.v.), without any measurable effect on the accompanying hypotensive responses.5. The results suggest: (i) ST 48968 is a selective and potent NK2 postjunctional receptor antagonist both in vitro and in vivo in the guinea-pig, and (ii) the NANC bronchoconstriction evoked by sensory nerve activation either by antidromic nerve stimulation or by capsaicin is mediated mainly via NK2 receptors and only to a minor extent via NK, receptors.