The effect of the leukotriene receptor antagonist zafirlukast on neurokinin A-induced bronchoconstriction in patients with asthma--A comparison with leukotriene D4 induced broncoconstriction

The bronchoconstriction caused by inhaled neurokinin A (NKA) in patients with asthma is indirect. The mediators involved in NKA-induced bronchoconstriction are unknown. Studies with various H1 receptor antagonists were negative, making an important contribution of histamine unlikely. To study the role of cysteinyl leukotrienes in neurokinin A-induced bronchoconstriction, we performed a randomised, double-blind, cross-over, placebo controlled trial in 12 patients with mild to moderate asthma. Zafirlukast and matching placebo were given orally, 40 mg the evening before and 40 mg the morning of assessment. In one period NKA was administered, in the other period leukotriene D4 (LTD4). Increasing concentrations of NKA and LTD4 were inhaled from a 30 L bag, after nebulization via a Mallinckrodt nebuliser. The difference between log10PC20LTD4 after treatment with placebo or zafirlukast was highly significant (p<0.0001). A trend was observed towards a difference between log10PC20 neurokinin A after treatment with placebo or zafirlukast (p=0.0741). The dose ratio for the neurokinin A provocation was 4.4 and for the LTD4 provocation 67.7. In conclusion, zafirlukast had a large inhibitory effect on LTD4-induced bronchoconstriction, but offered only limited protective effect against neurokinin A-induced bronchoconstriction. We suggest that leukotrienes play a limited role in the bronchoconstrictor effect of neurokinin A in patients with asthma.

Role of NK-1 and NK-2 tachykinin receptor antagonism on the growth of human breast carcinoma cell line MDA-MB-231

We demonstrate that neurokinin A (NKA) and substance P (SP) play a role in the proliferation of the estrogen receptor-negative (ER-) cell line MDA-MB-231, a human breast carcinoma expressing both NK-1 and NK-2 receptors. In vitro experiments showed that the specific receptor antagonists MEN 11,467 (NK-1) and nepadutant (MEN 11,420; NK-2) inhibited tumor cell proliferation, and blocked the stimulatory effect of SP and NKA. Anti-tumoral activity of NK-1 and NK-2 receptor antagonists was demonstrated in nude mice, measuring growth inhibition of MDA-MB-231 tumor cells xenografted s.c. and by using the hollow-fiber assay. In both systems a significant inhibition was found when compounds were administered at 5 mg/kg i.v. every day for 2 weeks. Results obtained from both these models suggest that the in vivo activity of NK-1 and NK-2 antagonists may be a result of a cytostatic effect rather than a cytotoxic effect. Our results suggest that the control of breast carcinoma (ER-) growth by tachykinin receptor antagonists may become a new form of targeted therapy for these human tumors.

Depressed contractile responses to neurokinin A in idiopathic but not neurogenic overactive human detrusor muscle

OBJECTIVE

The role of tachykinins such as neurokinin A in regulating bladder function is unclear, but NK2 receptors seem to mediate contraction in the human bladder and it has been suggested that these peptides may have a role in the pathophysiology of bladder dysfunction. The present study investigates neurokinin receptor-mediated contractility of detrusor muscle in the idiopathic overactive and neurogenic overactive bladder and investigates the neurokinin receptor subtypes involved.

METHODS

Human bladder was obtained from patients undergoing cystectomy (normal) or clam cystoplasty (idiopathic overactive) and from patients with spinal injuries (neurogenic overactive). Strips of isolated detrusor muscle were mounted in physiological Krebs-bicarbonate solution and cumulative concentration-response curves to 1 nM to 300 microM neurokinin A (NKA) were obtained in the absence and presence of neurokinin receptor antagonists, either the NK2 receptor-selective antagonist SR 48968 or the NK3 receptor-selective antagonist SB 223412.

RESULTS

NKA evoked concentration-dependent contraction of normal, idiopathic, and neurogenic overactive detrusor strips. In idiopathic overactive detrusor muscle, NKA-induced contraction was significantly reduced relative to normal detrusor (0.031 +/- 0.005 mg/g, n = 11 versus 0.193 +/- 0.039 mg/g, n = 7). Sensitivity to the peptide was also significantly (p < 0.01) reduced in idiopathic overactive detrusor, with mean pEC50 values (concentration producing 50% maximal response) of 6.62+/-0.16 (n = 11) compared to 7.47+/-0.19 (n = 7) in normal detrusor. In contrast, NKA-induced responses of neurogenic overactive detrusor were similar to those in normal detrusor, with a mean maximum contraction of 0.199 +/- 0.036 mg/g (n = 10) and mean pEC50 value of 7.85+/-0.16 (n = 10). NKA curves in all groups were shifted to the right by the NK2 receptor-selective antagonist SR 48968 with high affinity, pK(B) values being similar in normal, idiopathic, and neurogenic overactive detrusor (8.85 + 0.08, n = 14; 8.97 +/- 0.13, n = 12; 8.73 +/- 0.12, n = 8, respectively). In contrast the NK3 receptor-selective antagonist SB 223412 had a minimal effect on NKA responses and affinity values were low (pK(B) 5.81 +/- 0.11, n = 12 in normal; 5.75 +/- 0.08, n = 12 in idiopathic overactive, and 5.77 +/- 0.13, n = 11 in neurogenic overactive).

CONCLUSION

These data indicate that NKA-induced responses are impaired in detrusor muscle from idiopathic overactive human bladder, but not in detrusor muscle from neurogenic overactive bladder. The NK2 receptor subtype appears to mediate NKA responses in the normal, idiopathic overactive, and neurogenic overactive detrusor. This is important evidence suggesting a difference between the bladder pathophysiology observed in idiopathic versus neurogenic overactive detrusor.

The triple neurokinin-receptor antagonist CS-003 inhibits neurokinin A-induced bronchoconstriction in patients with asthma

Neurokinin A (NKA) causes bronchoconstriction in asthmatic patients. In vitro both NK1 and NK2 receptors can mediate airway contraction. Moreover in guinea pigs, NK3 receptors facilitate cholinergic neurotransmission. Dual tachykinin NK1/NK2 receptor antagonism results in prevention of NKA-induced bronchoconstriction. We have now examined the effect of a single dose of the triple tachykinin receptor antagonist CS-003 on NKA-induced bronchoconstriction in asthmatics. A double blind, crossover, placebo-controlled trial in 16 mild asthmatics was performed. One single dose of CS-003 (200 mg, solution in distilled water) or matched placebo was given orally on the assessment days. NKA-provocation tests were performed pre-dose and 1, 8 and 24 h after dosing. There was a significant shift to the right of the dose-response curve at 1 and 8 h after intake of CS-003. PC20 was not reached in 12/16 patients at 1h post-dose and in 5/16 patients at 8 h post-dose. This did not occur under placebo treatment. A single dose of 200 mg CS-003 protected significantly against NKA-induced bronchoconstriction at 1 and 8h post-dose in mild asthmatics.

Characterization of receptors for two Xenopus gastrointestinal tachykinin peptides in their species of origin

Two tachykinin peptides, bufokinin and Xenopus neurokinin A (X-NKA) were recently isolated from Xenopus laevis. In this study we investigated the tachykinin receptors in the Xenopus gastrointestinal tract. In functional studies using stomach circular muscle strips, all peptides had similar potencies (EC50 values 1-7 nM). The rank order of potency to contract the intestine was physalaemin (EC50 1 nM)> or =bufokinin (EC50 3 nM)>substance P (SP)> or =cod SP>NKA>>X-NKA (EC50 1,900 nM). No maximum response could be obtained for [Sar9,Met(O2)11]SP, eledoisin and kassinin. In stomach strips, the mammalian tachykinin receptor antagonists RP 67580 (NK1) and MEN 10376 (NK2) had agonistic effects but did not antagonize bufokinin or X-NKA. In intestinal strips, RP 67580 (1 microM) reduced the maximal response to X-NKA but not bufokinin, while MEN 10376 was ineffective. [125I]BH-bufokinin bound with high affinity to a single class of sites, of KD 213+/-35 (stomach) and 172+/-9.3 pM (intestine). Specific binding of [125I]BH-bufokinin was displaced by bufokinin> or =SP>NKA> or =eledoisin approximately kassinin>X-NKA, indicating binding to a tachykinin NK1-like receptor. Selective tachykinin receptor antagonists were weak or ineffective. Other iodinated tachykinins ([125I]NKA and [125I]BH-eledoisin) displayed biphasic competition profiles, with the majority of sites preferring bufokinin rather than X-NKA. In conclusion, there is evidence for two different tachykinin receptors in Xenopus gastrointestinal tract. Both receptors may exist in stomach, whereas the bufokinin-preferring NK1-like receptor predominates in longitudinal muscle of the small intestine. Antagonists appear to interact differently with amphibian receptors, compared with mammalian receptors.

Pemirolast potently attenuates paclitaxel hypersensitivity reactions through inhibition of the release of sensory neuropeptides in rats

The effects of anti-allergic agents on the hypersensitivity reactions to paclitaxel, an anti-cancer agent, were examined in rats. Intravenous injection of paclitaxel (15 mg/kg) caused a marked extravasation of plasma protein in lungs and a transient decrease in arterial partial oxygen pressure (PaO(2)). The paclitaxel-induced protein extravasation was inhibited by low doses (0.1-1 mg/kg) of pemirolast or high doses (30-100 mg/kg) of cromoglycate. However, ketotifen was not effective. The decrease in PaO(2) induced by paclitaxel was also significantly reversed by pemirolast. On the other hand, the paclitaxel-induced plasma extravasation was not attenuated by a histamine H(1) blocker diphenhydramine or an H(2) blocker famotidine, but was significantly reduced by a neurokinin NK(1) antagonist LY303870 (0.5 mg/kg) and an NK(2) antagonist SR48968 (1 mg/kg). The concentrations of proteins and sensory peptides such as substance P, neurokinin A and calcitonin gene-related peptide but not histamine in the rat bronchoalveolar lavage fluid were elevated by paclitaxel injection. Both cromoglycate and pemirolast reduced the paclitaxel-induced rise in proteins and sensory peptides. Therefore, we demonstrated for the first time that sensory nerve peptides are involved in paclitaxel hypersensitivity and that an anti-allergic agent pemirolast attenuates the paclitaxel response by inhibiting the release of sensory nerve peptides.

Effects of Neuropeptides on the Sumatriptan-Disturbed Circulation in the Optic Nerve Head of Rabbits

The purpose of this work was to study 'in vivo' the vascular responses of retinal vessels of New Zealand white rabbits to substance P (SP), neurokinin A (NKA), neurokinin B (NKB), senktide, capsaicin (CAPS), and calcitonin gene related peptide (CGRP) before and after selective antagonist administration. We examined the effects of these neuropeptides on the normal circulation in the optic nerve head of the rabbit. Drugs were injected via pars plana through a micropipette system. Ten minutes before perivascular injection of 10 nmol/l sumatriptan (to contract the vessel), a selective antagonist or its solvent was administered. Then, cumulative injection of the agonist was performed. The other eye was used as control. Direct measurement of retinal arteriole diameters was performed using digital angiography. The quantification of the relaxing effect is expressed as percentage related to the precontracted vascular diameter. Microinjection of SP (NK1 receptor agonist) up to 10 nmol/l induced a dose-dependent arteriolar dilating effect [E(max) (mean +/- SEM) 21.3 +/- 2.3%]. After the perivascular preinjection of 1 nmol/l L-668,169 or 1 nmol/l L-733,060 (NK1 receptor antagonists), the SP dose-response curve was shifted to the right. The same results were obtained with NKA (NK2 receptor agonist) which induced the most potent effect of all neuropeptides (E(max) 53.3+/-2.5%). The NK2 receptor antagonists L-659,877 and GR 159897 (1 nmol/l) strongly inhibited this arteriolar vasodilation. As for CGRP, doses up to 10 nmol/l induced a marked vasodilation (E(max) 41.1+/-0.4%) which decreased after microinjection of the selective antagonist CGRP8-37. The NK3 receptor agonists (senktide and NKB) showed a minor vasodilating effect (E(max) 5.1+/-1.2 and 8.0+/-0.9%, respectively). On the contrary, CAPS showed a marked dose-dependent vasodilating effect (E(max) 43.2+/-2.9%), antagonized by the tachykinin receptor antagonists and CGRP8-37. These results suggest, for the first time, the presence of NK1, NK2, and CGRP receptors on the retinal arteriolar wall of the rabbit.

Pharmacological properties of peptides derived from an antibody against the tachykinin NK1 receptor for the neuropeptide substance P

Two peptides were derived from the structural analysis of a previously described monoclonal antibody [Mol. Immunol. 37 (2000) 423] against the tachykinin NK(1) receptor for the neuropeptide substance P. Here we show that these two peptides were able to inhibit the inositol phosphate transduction pathway triggered both by substance P and neurokinin A, another high-affinity endogenous ligand for the tachykinin NK(1) receptor. They also reduced the cAMP production induced by substance P. By contrast, only one antagonist peptide was able to prevent substance P and neurokinin A from binding the receptor, as revealed both by biochemical and autoradiographic studies. First, these results illustrate the generality of the antibody-based strategy for developing new bioactive peptides. Second, they indicate that antagonists, even exhibiting very close amino acid composition, can interact with the tachykinin NK(1) receptor at different contact sites, some of them clearly distinct from the contact domains for endogenous agonists.

Inhibitory effect of a leukotriene receptor antagonist (montelukast) on neurokinin A-induced bronchoconstriction

BACKGROUND

Tachykinins are potent contractors of human airways producing a dose-related bronchoconstriction when administered by means of inhalation to asthmatic subjects.

OBJECTIVE

The aim of this study was to examine the effective role played by leukotrienes (LTs) in neurokinin A (NKA)-induced bronchoconstriction in asthmatic patients.

METHODS

To address this question, we investigated the protective effect of a selective cysteinyl LT receptor antagonist, montelukast, against inhaled NKA and determined LTE(4) excretion in the urine.

RESULTS

Inhaled NKA in the absence of any drug treatment produced a concentration-related bronchospasm with a geometric mean provocative concentration required to produce a 15% decrease in FEV(1) from the postsaline baseline value (PC(15)) value of 290.9 microg/mL (+SE, 407.1 microg/mL; -SE, 207.84 microg/mL). Montelukast pretreatment significantly increased (P <.01) the PC(15) NKA value (708.8 microg/mL; +SE, 890.47 microg/mL; -SE, 564.15 microg/mL) in comparison with placebo (394.4 microg/mL; +SE, 491.88 microg/mL; -SE, 248.16 microg/mL) and produced a shift of the NKA concentration-response curve to the right in all the subjects studied. When compared with placebo, montelukast did not have a significant protective effect against methacholine challenge; the geometric mean PC(15) values obtained were 0.87 and 0.96 mg/mL with placebo and montelukast, respectively. Although we have not observed any increase in urinary LTE(4) excretion after NKA inhalation, we have shown that pretreatment of asthmatic subjects with montelukast elicits a significant protection against NKA-induced bronchoconstriction.

CONCLUSION

In asthmatic subjects NKA-induced bronchoconstriction is indirectly caused by the release of LTs, and this mechanism could explain some of the antiasthmatic and anti-inflammatory effects of LT antagonists.

Intrathecal histamine induces spinally mediated behavioral responses through tachykinin NK1 receptors

Intrathecal injection of histamine elicited a behavioral response consisting of scratching, biting and licking in conscious mice. Here, we have examined the involvement of substance P (SP) by using intrathecal injection of tachykinin neurokinin (NK)(1) receptor antagonists and SP antiserum. Histamine-induced behavioral response was evoked significantly 5-10 min after intrathecal injection and reached a maximum at 10-15 min. Dose-dependency of the induced response showed a bell-shaped pattern from 200 to 3200 pmol, and maximum effect was observed at 800-1000 pmol. The H(1) receptor antagonist, d-chlorpheniramine and pyrilamine but not the H(2) receptor antagonists, ranitidine and zolantidine, inhibited histamine-induced behavioral response. The NK(1) receptor antagonists, CP-99,994, RP-67580 and sendide, inhibited histamine-induced behavioral response in a dose-dependent manner. A significant antagonistic effect of [D-Phe(7), D-His(9)]SP (6-11), a selective antagonist for SP receptors, was observed against histamine-induced response. The NK(2) receptor antagonist, MEN-10376, had no effect on the response elicited by histamine. Pretreatment with SP antiserum resulted in a significant reduction of the response to histamine. No significant reduction of histamine-induced response was detected in mice pretreated with NK A antiserum. The present results suggest that elicitation of scratching, biting and licking behavior induced by intrathecal injection of histamine may be largely mediated by NK(1) receptors via H(1) receptors in the spinal cord.

Effect of monensin on the levels of tachykinins and their processing enzyme activity in rat dorsal root ganglia

Th effect of monensin, which inhibits trans-Golgi function, on the levels of tachykinins and their processing enzyme activity was examined in organ-cultured rat dorsal root ganglia (DRG). Using an enzyme immunoassay method, we measured neurokinin A and substance P immunoreactivity in the DRG cultured for 72 h with and without 0.1 microM monensin. Both tachykinins were reduced in the DRG treated with monensin. Treatment with monensin also reduced the activity of carboxypeptidase E, which is one of the proteolytic processing enzymes of neuropeptides. These data suggest that proteolytic processing enzymes may in part modulate the biological activity of neuropeptides within a trans-Golgi apparatus.

Tachykinin-stimulated small bowel myoelectric pattern: sensitization by NO inhibition, reversal by neurokinin receptor blockade

Tachykinins stimulate motility whereas NO inhibits motility in the gastrointestinal tract.

AIM

To investigate if inhibition of NO production sensitizes myoelectric activity to subthreshold doses of tachykinins in the small intestine of awake rats.

METHODS

Rats were supplied with a venous catheter and bipolar electrodes at 5, 15 and 25 cm distal to pylorus for electromyography of small intestine. The motor responses were evaluated using pattern recognition. Substance P and neurokinin A dose-dependently stimulated gut motility, with neurokinin A being more potent than substance P. Therefore, neurokinin A was chosen and administered under baseline conditions and 45-60 min after N(omega)-nitro-L-arginine (L-NNA) 1 mg kg(-1), with or without pretreatment with L-arginine 300 mg kg(-1). In addition, myoelectric activity effects of neurokinin A in conjunction with L-NNA were studied before and after administration of the tachykinin receptor antagonists, SR140333 (NK1), SR48968 (NK2) and SR142801 (NK3), each at 2.5 mg kg(-1).

RESULTS

Dose-finding studies verified 10 pmol kg(-1) min(-1) to be the threshold dose at which NKA caused phase II-like activity in a low percentage of experiments (12%, n=41). This dose was therefore used in combination with L-NNA for sensitization experiments of gut myoelectric activity. In experiments where NKA-induced no response, pretreatment with L-NNA led to phase II-like activity in 9 of 18 (50%, p<0.05) experiments. Co-administration of SR140333 and SR48968 abolished this effect.

CONCLUSION

NO counteracts the stimulatory effect of tachykinins on small bowel myoelectric activity in the rat. Inhibition of the L-arginine/NO pathway sensitizes the gut to tachykinin-stimulated motor activity.

2-Aryl indole NK(1) antagonists: optimisation of the amide substituent

The in vivo properties of a series of 2-arylindole NK(1) antagonists have been improved, by modification of the amide substituent. The 1-(2-methoxyphenyl)piperazine amide was identified as a major area of metabolism in the lead compound 1. Replacement of this amine moiety by a 4-benzyl-4-hydroxypiperidine resulted in a compound 18 with reduced clearance and improved central duration of action.

Human colonic anti-secretory activity of the potent NK(1) antagonist, SR140333: assessment of potential anti-diarrhoeal activity in food allergy and inflammatory bowel disease

1. This in vitro study was designed to determine the potential use of the NK(1) antagonist, SR140333 as an anti-diarrhoeal treatment for food allergy or inflammatory bowel disease. The effect of various immune and neuronal stimuli on human colonic substance P (SP) release and the effect of SR140333 on subsequently stimulated mucosal ion transport was investigated. 2. Submucosal and sensory nerve fibre stimulation using electrical field stimulation (1 ms/7 Hz/7 V) and capsaicin (50 microM) respectively, mast cell activation by anti-IgE (1/250 dilution) and granulocyte stimulation using fMLP (50 microM) each released SP and evoked a secretory response. 3. SP and the NK(1) selective agonist, Sar-SP (0.1 - 1000 nM) stimulated an increase in colonic secretion which was antagonized by SR140333 (pD'(2)=6.7 and 7.25 versus SP and Sar-SP respectively). 4. SR140333, at a concentration that blocked NK(1)-mediated secretion (500 nM), also reduced the secretory response to both alphaIgE and capsaicin. This suggests a pathophysiologic role for NK(1) receptors. 5. Capsaicin evoked SP release was increased in tissue taken from Crohn's disease but not ulcerative colitis patients. The response to SP was however reduced by 70 and 89% respectively. 6. Mast cells and sensory afferents contribute to allergic diarrhoea. Since SR140333 reduced the secretory response to mast cell and afferent stimulation this compound may be particularly useful in reducing the symptoms of food allergy.

Differential role of neurokinin receptors in human lymphocyte and monocyte chemotaxis

The precise nature of neurokin receptor involvement in human immune cell chemotaxis is unclear. This study therefore sought to directly compare the chemotactic effects of neurokinins on human T lymphocytes and monocytes. Substance P was found to have a similar dose-dependent chemotactic action on T lymphocyte and monocyte populations. In contrast, T lymphocytes were found to be more responsive than monocytes both to the highly selective NK-1 agonist, [Sar(9)Met O(2)(11)]-substance P, and also to the NK-2 selective agonist, beta-alanine neurokinin A((4-10)). Consistent with these findings, substance P-induced chemotaxis of both T lymphocyte and monocytes was attenuated by the selective NK-1 antagonist LY303870. However, the selective NK-2 antagonist MEN 10,376 was only effective in inhibiting the T lymphocyte response. The study confirms that neurokinins have chemotactic actions on immune cells and indicates important functional differences between human T lymphocyte and monocyte responses. This provides a potential mechanism by which the nervous system can selectively influence cellular recruitment in inflammatory disease.

Bicyclic peptides as type I/type II beta-turn scaffolds

We recently reported the rational design, synthetics, and structural characterization of the most potent and selective peptide-based neurokinin A antagonist thus far described: cyclo(Met1-Asp2-Trp3-Phe4-Dap5-Leu6)cyclo(2 beta-5 beta). Its bicyclic structure is characterized by a type I and a type II two beta-turn around Trp3-Phe4 and Leu6-Met1, respectively. In order to understand whether the two different beta-turned structures are determined by the bicyclic structure or by the amino acid type at the corner positions, we have synthesized the pseudo-symmetrical analogue cyclo(Phe1-Asp2-Trp3-Phe4-Dap5-Trp6)cyclo(2 beta-5 beta). The structural characterization in the crystal state and in solution, here reported, gives an experimental evidence that the backbone of the bicyclic structure is a rigid scaffold that can be used to build both a type I and type II beta-turn independently from the amino acid composition.

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.

Role of nitric oxide and septide-insensitive NK(1) receptors in bronchoconstriction induced by aerosolised neurokinin A in guinea-pigs

The tachykinin, neurokinin A (NKA), contracts guinea-pig airways both in vitro and in vivo, preferentially activating smooth muscle NK(2) receptors, although smooth muscle NK(1) receptors may also contribute. In vitro evidence suggests that NKA activates epithelial NK(1) receptors, inducing the release of nitric oxide (NO) and subsequent smooth muscle relaxation. A number of selective NK(1) receptor agonists have been reported to activate both smooth muscle and epithelial NK(1) receptors, however septide appears only to activate smooth muscle NK(1) receptors. The aim of the present study was to investigate whether NKA-induced bronchoconstriction in guinea-pigs in vivo may be limited by NO release via NK(1) receptor activation, and whether selective NK(1) receptor agonists may activate this mechanism differently. Aerosolized NKA caused an increase in total pulmonary resistance (RL) that was markedly reduced by the NK(2) receptor antagonist, SR 48968, and abolished by the combination of SR 48968 and the NK(1) receptor antagonist, CP-99, 994. The increase in RL evoked by NKA was potentiated by pretreatment with the NO synthase (NOs) inhibitor, L-NAME, but not by the inactive enantiomer D-NAME. Potentiation by L-NAME of NKA-induced increase in RL was reversed by L-Arginine, but not by D-Arginine. Pretreatment with L-NAME did not affect the increase in RL induced by the selective NK(2) receptor agonist, [beta-Ala(8)]NKA(4-10), and by the selective NK(1) receptor agonist, septide, whereas it markedly potentiated the increase in RL caused by a different NK(1) selective agonist, [Sar(9),Met(O(2))(11)]SP. Dose-response curves showed that septide was a more potent bronchoconstrictor than [Sar(9),Met(O(2))(11)]SP to cause bronchoconstriction. Pretreatment with the NK(1) receptor antagonist, CP-96,994, abolished the ability of L-NAME to increase bronchoconstriction to aerosolized NKA. Bronchoconstriction to aerosolized NKA was increased by L-NAME, after pretreatment with the NK(3) receptor antagonist, SR 142801. The present study shows that in vivo bronchoconstriction in response to the aerosolized naturally occurring tachykinin, NKA, is limited by its own ability to release relaxant NO via NK(1) receptor activation. This receptor is apparently insensitive to septide, thus justifying, at least in part, the high potency of septide to cause bronchoconstriction in guinea-pigs.

Nociceptin-induced scratching, biting and licking in mice: involvement of spinal NK1 receptors

1. Intrathecal (i.t.) injection of nociceptin at small doses (fmol order) elicited a behavioural response consisting of scratching, biting and licking in conscious mice. Here we have examined the involvement of substance P-containing neurons by using i.t. injection of tachykinin neurokinin (NK)1 receptor antagonists and substance P (SP) antiserum. 2. Nociceptin-induced behavioural response was evoked significantly 5 - 10 min after i.t. injection and reached a maximum at 10 - 15 min. Dose-dependency of the induced response showed a bell-shaped pattern from 0.375 - 30.0 fmol, and the maximum effect was observed at 3.0 fmol. 3. The behavioural response elicited by nociceptin (3.0 fmol) was dose-dependently inhibited by intraperitoneal (i.p.) administration of morphine. 4. The NK1 receptor antagonists, CP-96,345, CP-99,994 and sendide, inhibited nociceptin-induced behavioural response in a dose-dependent manner. A significant antagonistic effect of [D-Phe7, D-His9]SP (6 - 11), a selective antagonist for SP receptors, was observed against nociceptin-induced response. The NK2 receptor antagonist, MEN-10376, had no effect on the response elicited by nociceptin. 5. Pretreatment with SP antiserum resulted in a significant reduction of the response to nociceptin. No significant reduction of nociceptin-induced response was detected in mice pretreated with NKA antiserum. 6. The N-methyl-D-aspartate (NMDA) receptor antagonists, dizocilpine (MK-801) and D(-)-2-amino-5-phosphonovaleric acid (APV) (D-APV), and L-NG-nitro arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, failed to inhibit nociceptin-induced behavioural response. 7. off present results suggest that SP-containing neurons in the mouse spinal cord may be involved in elicitation of scratching, biting and licking behaviour following i.t. injection of nociceptin.

Defects of tyrosine289phenylalanine mutation on binding and functional properties of the human tachykinin NK2 receptor stably expressed in chinese hamster ovary cells

A point mutation was made at position 289 in the transmembrane segment 7 of the human tachykinin NK2 receptor to yield a tyrosine/phenylalanine (Tyr/Phe) substitution. Chinese hamster ovary cells stably transfected with the wild-type or Tyr289Phe mutant NK2 receptor both bound neurokinin A (NKA) and the synthetic NK2 receptor-selective agonists, GR 64349 and [betaAla8]NKA(4-10), with high and even affinities. Neurokinin B (NKB) and substance P (SP) also displayed sizeable binding affinities, albeit with lower affinity as compared to NKA. In a functional assay (production of inositol-1,4,5-trisphosphate, IP3), NKA, GR 64349, and [betaAla8]INKA(4-10) stimulated IP3 accumulation via the wild-type and mutant receptors with similar potencies. On the other hand, NKB and SP exhibited a dramatic reduction in their agonist efficacies at the mutant receptor, NKB acting as a partial agonist (maximum effect = 50% of the response to NKA) and SP being totally inactive. The results obtained with phenoxybenzamine inactivation experiments indicated that a large and similar receptor reserve existed for both the wild-type and the mutant receptor. SP, which displayed sizeable binding affinity for the mutant receptor but did not stimulate IP3 accumulation, antagonized the agonist effect of NKA. The antagonist action of SP at the mutant NK2 receptor cannot be ascribed to receptor internalization. The Tyr/Phe replacement at position 289 markedly reduced the binding affinity and antagonist potency of the non-peptide ligand, SR 48968, without affecting the binding affinity and antagonist potency of the bicyclic peptide antagonist MEN 11420. The results indicate that the hydroxyl radical function of Tyr289 in transmembrane segment 7 of the human NK2 receptor is, directly or indirectly, involved in stimulus transduction when the NK2 receptor is occupied by NKB or SP, but not when using NKA or NK2 receptor-selective agonists.

Antagonists of sensory neuropeptides inhibit the secondary phase of increased circulation following thermally induced inflammation

A model of thermally induced inflammation in the anesthetized rat was used to measure acute microcirculatory reactions after heat exposure. The thermal injury was inflicted by dipping the right hindpaw into hot water at 60 degrees for 20 s. Local blood flow was recorded simultaneously in both hindpaws and continuously by laser Doppler flowmetry before, during and for 2 h after the thermal injury and the mean arterial blood pressure (MAP) was displayed on a chart recorder. To assess the contribution of the nervous system to the vascular changes seen, neuropeptide antagonists directed toward substance P (SP), neurokinin A (NKA), and calcitonin gene-related peptide (CGRP) were administered. The neurokinin antagonists (NK1, NK2) and the CGRP antagonist (CGRP8-37) were injected via a catheter into the jugular vein. During the first few minutes after thermal injury to the controls, an immediate increase in blood perfusion of about 351% was recorded, followed by a slow decrease of circulation. At 30 min after thermal injury, there was a secondary phase of increased microcirculation of approximately 329%. A slow decline of cutaneous circulation then followed and, after another 30 min, the value stabilized at a level about 100% above the level before injury. Pretreatment with intravenous injections of the NK1 antagonist, NK2 antagonist, and CGRP8-37 attenuated the first phase and almost abolished the secondary phase. No significant change of perfusion was observed on the unscalded paw. The MAP remained at a stable level throughout the experiment and was not affected by the thermal injury or by the administration of the antagonists as compared to controls. Our results show that sensory neuropeptides play a significant role in the blood flow increase seen following thermal injury.

The peripheral NK-1/NK-2 receptor antagonist MDL 105,172A inhibits tachykinin-mediated respiratory effects in guinea-pigs

1. Stimulation of sensory nerves causes release of tachykinins, including substance P (SP) and neurokinin A (NKA), which produce a variety of respiratory effects via NK-1 and NK-2 receptors, respectively. Hence, development of a compound which could potently and equivalently antagonize both receptors was pursued. 2. MDL 105,172A ((R)-1-[3-(3,4-dicholorophenyl)-1-(3,4,5-trimethoxybenzoyl)- 3-pyrrolidinyl]-4- phenyl-piperidine-4-morpholinecarboxamide) exhibited high affinity for NK-1 (4.34 nM) and NK-2 (2.05 nM) receptors. In vitro, the compound antagonized SP (pA2 = 8.36) or NKA (pA2 = 8.61)-induced inositol phosphate accumulation in tachykinin monoreceptor cell lines. 3. In anaesthetized guinea-pigs, MDL 105,172A inhibited SP-induced plasma protein extravasation (ED50 = 1 mg kg-1, i.v.) and [beta-Ala8]NKA 4-10-induced bronchoconstriction (ED50 = 0.5 mg kg-1, i.v.) indicating NK-1 and NK-2 antagonism, respectively. 4. Capsaicin was used to elicit respiratory effects in anaesthetized and conscious guinea-pigs; the latter were inhibited by MDL 105,172A following i.v. (ED50 = 1 mg kg-1) or oral (ED50 = 20 mg kg-1) administration. Hence, MDL 105,172A can inhibit pulmonary responses to tachykinins released endogenously in the airways. 5. At doses up to 200 mg kg-1, p.o., MDL 105,172A failed to inhibit repetitive hind paw tapping induced by i.c.v GR 73632, and NK-1 selective agonist, in gerbils, whereas CP-99,994 (0.87 mg kg-1, s.c.) completely ablated the effect. These data suggest that MDL 105,172A does not penetrate the central nervous system (CNS) and its tachykinin antagonism is restricted to the periphery. 6. MDL 105,172A is a non-peptide, potent, equivalent antagonist of NK-1 and NK-2 receptors. Its ability to inhibit both exogenously administered as well as endogenously released tachykinins support its use in examining the role of sensory neuropeptides in diseases associated with neurogenic inflammation including asthma.

[Mechanisms of tolerance to sulfur dioxide and sodium metabisulfite]

Inhalation of sulphur dioxide (250 ppm), (SO2) or sodium metabisulfite (80 mM) (MBS) aerosol or perfusion with MBS (3 mM) induced a reduction in compliance and conductance in the isolated, perfused and ventilated guinea pig lung. Pretreatment of the lung with sodium sulfite (3 mM), a dissolution product of SO2 and MBS, reduced the bronchoconstriction induced by SO2 and MBS. Bronchoconstriction induced by SO2 and MBS in associated to increased levels of Calcitonin gene-Related Peptide (CGRP) in the perfusate effinent, indicating activation of sensory nerves. The release of CGRP induced by SO2 and MBS was not affected by sodium sulfite. Sulfite treatment did not modify lung reactivity towards acethylcholine, bradykinin, serotonin, histamine and substance P (fragment 5-11). An inhibitory effect by sulfite was observed on bronchoconstriction induced by neurokinin A (fragment 4-10). Since bronchoconstriction induced by SO2 and MBS appears to be mediated by neurokinin A release and action, sulfite may act by affecting its signal transduction pathway. In conclusion, the results indicate that during exposure to some environmental and occupational pollutants, e.g. SO2 and MBS, critical modifications of sulfhydryl groups on smooth muscle receptors may occur. We hypothesise this as a possible step in the development of tolerance and hyperreactivity.

Experimental treatments for asthma

There has been increased recognition of the importance of inflammatory cells and their products in the pathogenesis of asthma. From this recognition has evolved a number of new approaches to treat the various components of the asthmatic inflammatory response. Nonselective anti-inflammatory agents such as cyclosporine and gold appear to decrease symptoms and allow a steroid-sparing effect in many cases, though side effects from cyclosporine often necessitate dose reduction. Novel oral compounds as the 5-lipoxygenase inhibitors have been effective in controlling asthma symptoms triggered by various stimuli, and the cysteinyl leukotriene receptor antagonists have shown promise in this regard as well. Neurokinin antagonists, inhaled loop diuretics, and lidocaine may play significant roles in asthma therapy through inhibition of neurogenic inflammation and possibly mast cell function. Inhibition of mast cell products by existing drugs such as heparin or the development of specific inhibitors of mast cell tryptase may also be effective agents, as are selective phosphodiesterase inhibitors, which appear to have anti-inflammatory properties. Finally, specific cytokine antagonists, agonists, inhibitors of T-cell function, selective inducible nitric oxide synthase inhibitors, and even gene-directed strategies may provide not only insights into the pathogenesis of asthma but also novel therapeutic approaches to treat the inflammation in this disease.

Role of sensory neuropeptides in post-allergic propranolol-induced bronchoconstriction in guinea pigs in vivo

BACKGROUND

Administration of propranolol can provoke bronchoconstriction in asthmatic patients. We hypothesized that such bronchoconstriction may result from the inflammatory mediators released by an allergic reaction. We recently developed a guinea pig model for propranolol-induced bronchoconstriction (PIB). Neuropeptides which are released from C-fibre nerve endings have been postulated to induce bronchial hyperresponsiveness through neurogenic inflammation.

OBJECTIVE

The purpose of this study was to examine whether sensory neuropeptides are involved in the development of PIB after allergic reaction.

METHODS

Propranolol at a concentration of 10 mg/ml was inhaled 20 min after antigen challenge in passively sensitized, anaesthetized and artificially ventilated guinea pigs. The animals were treated intravenously with a NK1 and NK2 dual antagonist, FK224, in a dose of 1 or 10 mg/kg or vehicle or a selective NK1 antagonist, FK888, in a dose of 1 or 10 mg/kg or vehicle 10 min before or 15 min after antigen challenge.

RESULTS

Propranolol inhaled 20 min after antigen challenge caused bronchoconstriction. FK224 or FK888 administered 15 min after antigen challenge as well as 10 min before antigen challenge did not reduce the PIB.

CONCLUSION

We conclude that neuropeptides such as neurokinin A and substance P do not directly contribute to the development of PIB after allergic reaction.

Tachykinin inhibition of acid-induced gastric hyperaemia in the rat

1. Primary afferent neurones releasing the vasodilator, calcitonin gene-related peptide, mediate the gastric hyperaemic response to acid back-diffusion. The tachykinins neurokinin A (NKA) and substance P (SP) are located in the same neurones and are co-released with calcitonin gene-related peptide. In this study we investigated the effect and possible role of tachykinins in the acid-evoked gastric vasodilatation in urethane-anaesthetized rats. 2. Gastric acid back-diffusion, induced by perfusing the stomach with 15% ethanol in the presence of 0.05 M HCl, increased gastric mucosal blood flow by 60-90%, as determined by the hydrogen clearance technique. NKA and SP (0.14-3.78 nmol min-1 kg-1, infused intra-aortically) inhibited the gastric mucosal hyperaemic response to acid back-diffusion in a dose-dependent manner, an effect that was accompanied by aggravation of ethanol/acid-induced macroscopic haemorrhagic lesions. 3. The inhibitory effect of NKA (1.26 nmol min-1 kg-1) on the acid-induced gastric mucosal vasodilatation was prevented by the tachykinin NK2 receptor antagonists, MEN 10,627 (200 nmol kg-1) but left unaltered by the NK1 receptor antagonist, SR 140,333 (300 nmol kg-1) and the mast-cell stabilizer, ketotifen (4.6 mumol kg-1). 4. Under basal conditions, with 0.05 M HCl being perfused through the stomach, NKA (1.26 nmol min-1 kg-1) reduced gastric mucosal blood flow by about 25%, an effect that was abolished by SR 140,333 but not MEN 10,627 or ketotifen. 5. SR 140,333, MEN 10,627 or ketotifen had no significant effect on basal gastric mucosal blood flow nor did they modify the gastric mucosal hyperaemic reaction to acid back-diffusion. 6. The effect of NKA (1.26 nmol min-1 kg-1) in causing vasoconstriction and inhibiting the vasodilator response to acid back-diffusion was also seen when blood flow in the left gastric artery was measured with the ultrasonic transit time shift technique. 7. Arginine vasopressin (AVP, 0.1 nmol min-1 kg-1) induced gastric mucosal vasoconstriction under basal conditions but was unable to inhibit the dilator response to acid back-diffusion. 8. These data show that NKA has two fundamentally different effects on the gastric circulation. Firstly, NKA reduces gastric blood flow by activation of NK1 receptors. Secondly, NKA inhibits the gastric hyperaemic response to acid back-diffusion through an NK2 receptor-mediated mechanism. These two tachykinin effects appear to take place independently of each other since they are mediated by different receptors. This concept is further supported by the inability of AVP to mimic tachykinin inhibition of the gastric vasodilator response to acid back-diffusion.

[Pharmacological profiles of a novel tachykinin NK-2 receptor antagonist, TAC-363]

We examined the pharmacological profiles of a novel tachykinin NK-2 receptor antagonist, Na-(tert-butylcarbamoyl)-L-glutaminyl-L-tryptophyl-alpha-azap++ + henylalanine 2-benzyloxyethylamide (TAC-363). In vitro studies showed that TAC-363 caused a rightward shift of the contraction response curve with a slight inhibition of maximal response for the neurokinin A (NKA)-induced contraction of the hamster trachea and parallel rightward shift of the curve for the substance P (SP)-induced contraction of the guinea-pig ileum. The pA2 values were 9.82 and 8.42 on the contraction by NKA and SP, respectively. The selectivity of TAC-363 to NK-2 receptor was 25 times higher than that to NK-1 receptor. The compound did not affect the histamine and acetylcholine-induced bronchoconstriction in guinea-pig ileum. Intravenous administration (0.1-1 mg/kg) of the compound inhibited dose-dependently both NKA- and capsaicin-induced bronchoconstriction in guinea-pigs. The inhibitory effect of the compound lasted up to 60 min on NKA-induced bronchoconstriction in guinea-pigs. These results suggest that TAC-363 is a potent and selective NK-2 receptor antagonist, which is effective in vitro and in vivo. It may be useful in the treatment of NKA-dependent pathology, especially bronchial asthma.

In vivo exposure to nitrogen dioxide (NO2) induces a decrease in calcitonin gene-related peptide (CGRP) and tachykinin immunoreactivity in guinea-pig peripheral airways

The mammalian respiratory tract is densely innervated by sensory and autonomic fibres. Subsets of the nerves contain bioactive regulatory peptides, such as substance P, calcitonin gene-related peptide (CGRP), and neurokinins. The sensory nervous system responds to inhaled irritants, resulting in a release of neuropeptides and, thus, a decrease in the peptide immunoreactivity of the fibres. We examined the effects of inhaled nitrogen dioxide (NO2), a well-known indoor and outdoor air pollutant, on pulmonary sensory neuropeptides. Guinea-pigs were exposed for 4 h to 18 parts per million (ppm) NO2 or to air (n = 5 each). At the end of the exposure, they were killed with urethane and their lungs were fixed in 1% paraformaldehyde in phosphate-buffered saline. Cryostat sections were stained with antisera to an anatomical nerve marker, protein gene product (PGP) 9.5, and to CGRP and tachykinins, utilizing the avidin-biotinylated peroxidase method. In the noncartilaginous airways (diameter < 250 microns) of NO2-exposed animals, less tachykinin- and CGRP-immunoreactive nerve fibres were found compared with controls. No change was seen in the total nerve fibre distribution (PGP 9.5). It is concluded that the peptidergic nerves of guinea-pig peripheral airways are a sensitive indicator of exposure to nitrogen dioxide.

Characterization of substance P release from the intermediate area of rat thoracic spinal cord

Substance P (SP) nerve terminals innervate the intermediolateral cell column (IML) of the thoracic spinal cord, where SP coexists with serotonin (5-HT), neurokinin A (NKA) and thyrotropin-releasing hormone (TRH). Neither the depolarization-induced release of SP nor the presence of other neurochemicals in the regulation of SP release has been directly studied in this system. In the present study, basal and K(+)-stimulated release of SP from the microdissected intermediate area (including the IML, intercalated nucleus and central autonomic nucleus) of the rat thoracic spinal cord, and the regulation of SP release by presynaptic autoreceptors and by coexisting neurochemicals (5-HT, NKA and TRH) were studied using an in vitro superfusion system. Potassium evoked a concentration- and extracellular Ca(2+)-dependent release of SP. In rats pretreated with the serotoninergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), both SP content and the absolute amount of SP released were decreased. However, the fraction of the remaining tissue content of SP released by K+ depolarization was not changed subsequent to 5,7-DHT treatment. Moreover, 5-HT, 5-HT1B agonists (CGS-12066B and RU 24969) and a 5-HT3 agonist (2-methyl-5-HT) did not alter the K(+)-evoked release of SP. These data demonstrate that SP is released from the intermediate area of the rat thoracic spinal cord and some of the SP released comes from serotoninergic nerve terminals. Although 5-HT coexists with SP in the IML, neither endogenous 5-HT nor 5-HT receptor ligands appear to regulate the release of SP. Other colocalized neuropeptides (NKA and TRH) are not involved in the regulation of SP release because neither NKA, a NK2 agonist (GR 64349) nor a TRH analog (MK-771) changed the K(+)-evoked release of SP. A neurokinin-1 (NK1) antagonist (GR 82334) dose-dependently (10(-9)-10(-7) M) increased the K(+)-stimulated release of SP. These data suggest the presence of presynaptic inhibitory NK1 autoreceptors. Whereas, NK1 agonists, [GR 73632 (10(-9)-10(-6) M) and [Sar9, Met (O2)11]SP (10(-8)-10(-6) M)], increased the basal and K(+)-stimulated release of SP, the excitatory effects of GR 73632 were not blocked by the NK1 antagonist. Moreover, GR 73632 increased the efflus of SP to a greater extent in the absence of peptidase inhibitors. Thus, the effect of NK1 agonists on the release of SP may be related to an inhibition of peptide degradation rather than activation of NK1 autoreceptors.

Tachykinin receptors mediate atropine-resistant rat duodenal reflex contractions in vivo

The study aimed to establish the possible role of tachykinins as mediators of atropine-resistant reflex contractions evoked by balloon distension in the proximal duodenum of urethane-anesthetized, guanethidine (34 mumol/kg s.c.)-pretreated rats. Distension of the balloon with a small amount (0.2-0.3 ml) of saline induced the appearance of phasic rhythmic contractions (about 11 mmHg in amplitude) which were promptly suppressed by either atropine (3 mumol/kg i.v.) or hexamethonium (28 mumol/kg i.v.). Despite the continuous i.v. infusion of atropine (2 mumol/h), low-amplitude rhythmic phasic contractions recovered, which were promptly suppressed by hexamethonium, to indicate the involvement of an atropine-resistant excitatory reflex. The amplitude of these atropine-resistant contractions was increased to about 4-5 mmHg by further distension of the balloon (0.4-0.6 ml) : under these conditions, the atropine-resistant contractions undergo a progressive fading. The fading was prevented by i.v. administration of the nitric oxide (NO) synthase inhibitor, L-nitroarginine methyl ester (L-NAME, 55 mumol/h), to provide a suitable baseline (amplitude of contractions was 7-8 mmHg) for studying the effect of tachykinin receptor antagonists. I.v. administration of the selective tachykinin NK2 receptor antagonists, MEN 10,627 (10-100 nmol/kg) and SR 48968 (100-300 nmol/kg) or of the selective NK1 antagonist SR 140333 (100 nmol/kg), at doses which do not affect the duodenal contractions induced by acetylcholine (5.5 mumol/kg i.v.), produced a prompt and long lasting suppression of the atropine-resistant reflex duodenal contractions produced by balloon distension in urethane-anesthetized rats, whilst SR-48965 (300 nmol/kg), the enantiomer of SR-48968 devoid, of NK2 receptor blocking activity, was without effect. I.v. administration of the selective NK1 receptor agonists [Sar9] substance P sulfone and septide or of the NK2 receptor selective agonist, [beta Ala8] neurokinin A(4-10) produced dose-dependent contractions of the duodenum. SR 140333 (100 nmol/kg i.v.) selectively antagonized the duodenal contractions produced by [Sar9] substance P sulfone and septide without affecting those produced by [beta Ala8] neurokinin A(4-10). On the other hand, MEN 10,627 (30-100 nmol/kg i.v.) and SR 48968 (100-300 nmol/kg i.v.) but not SR 48965 (300 nmol/kg i.v.) antagonized, at a comparable extent, duodenal contractions induced by both the selective NK2 and NK1 receptor agonists. We conclude that endogenous tachykinins are involved in mediating atropine-resistant reflex contractions evoked by distension of the rat duodenum in vivo: both NK1 and NK2 receptors are activated by endogenous ligands to produce NANC contractions of rat duodenum in vivo. However, the contractile response to i.v. administered NK1 receptor agonists, [Sar9] substance P sulfone and septide, may involve the release of mediators producing smooth muscle contraction via NK2 receptors.

SR 48968 specifically depresses neurokinin A- vs. substance P-induced hyperalgesia in a nociceptive withdrawal reflex

To determine the role of neurokinin A and tachykinin NK2 receptors in processing of nociceptive information at the spinal level, the selective NK2 receptor antagonist, SR 48968 (S)-N-methyl-N [4-(4-acetylamino-4-[phenyl piperidino)-2-(3,4-dichlorophenyl)-butyl] benzamide, was tested for its effects on the hyperalgesia produced in the tail flick reflex by intrathecal administration of neurokinin A and of substance P. SR 48968 was also tested in a model in which noxious peripheral stimulation has been shown to produce hyperalgesia via a substance P mechanism. SR 48968 given intrathecally had a dose-dependent inhibitory effect on both the behaviour and the hyperalgesia induced by neurokinin A but not on either of these effects produced by substance P. In addition, systemic administration of SR 48968 depressed the hyperalgesic effect of intrathecal administration of neurokinin A. First, this evidence indicates a unique role for neurokinin A in the spinal cord as distinct from that of its homologue, substance P. and confirms that neurokinin A acts via the tachykinin NK2 receptor, rather than non-specifically via the NK1 receptor. Second, the data indicate that in this model substance P does not express any of its effects non-selectively via activation of NK2 receptors. Third, SR 48968 appears to have access to the spinal cord upon systemic administration. Fourth, intrathecal administration of the NK1 receptor antagonist, CP-96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N-[(2-methoxy-phenyl)-methyl]-1- azabicyclo [2.2.2]-octan-3-amine], had no effect on the responses to intrathecal administration of neurokinin A. Finally, the hyperalgesia produced by sustained noxious thermal stimulation of the tip of the tail was unaffected by intrathecal administration of SR 48968; thus, it remains to find a physiological response in which endogenous neurokinin A and NK2 receptors at the spinal level are involved in the rat in vivo.

The effect of inhaled FK224, a tachykinin NK-1 and NK-2 receptor antagonist, on neurokinin A-induced bronchoconstriction in asthmatics

The tachykinins substance P and neurokinin A (NKA) are present in sensory airway nerves and have been implicated in the pathogenesis of asthma. FK224 is a cyclopeptide tachykinin antagonist previously shown to inhibit both tachykinin NK-1 and NK-2 receptor mediated airway responses in guinea pigs. Inhaled FK224 protected against bradykinin-induced bronchoconstriction and cough in asthmatics. In this study we examined the reproducibility of the NKA challenge and the effect of inhaled FK224 on NKA-induced bronchoconstriction in 10 patients with stable asthma. On Day 1 baseline lung function and PC20 methacholine were determined. On Days 2 and 3 increasing doubling concentrations of NKA (3.3 x 10(-9) to 1.0 x 10(-6) mol/ml) were administered via inhalation, with intervals of 10 min. On both days NKA caused a concentration-dependent decrease in specific airways conductance (sGaw) and FEV1. Mean +/- SEM, log PC35, sGaw NKA (mol/ml) was -6.61 +/- 0.10 on Day 2 and -6.57 +/- 0.14 on Day 3 (not significant [NS]). On Days 4 and 5 FK224 (4 mg) or placebo (P) was administered via metered-dose inhaler 30 min before NKA challenge in a double-blind, crossover manner. The study medication was well tolerated. FK224 had no significant effect on baseline lung function. After P and FK224, NKA caused a comparable concentration-dependent bronchoconstriction. The mean +/- SEM log PC35 sGaw NKA (mol/ml) was -6.04 +/- 0.18 after P and -6.19 +/- 0.23 after FK224 (NS). In conclusion, inhaled FK224 had no effect on baseline lung function and offered no protection against NKA-induced bronchoconstriction in a group of mild asthmatic patients.

In vitro and in vivo characterization of MDL 105,212A, a nonpeptide NK-1/NK-2 tachykinin receptor antagonist

We have identified and characterized a novel, potent, nonselective tachykinin receptor antagonist, MDL 105,212A [(R)-1-[2-[3-(3,4- dichlorophenyl)-1-(3,4,5-trimethoxybenzoyl)-pyrrolidin-3-yl] -ethyl]- 4-phenylpiperidine-4-carboxamide, hydrochloride]. The compound binds with low nanomolar affinity and species specificity to human NK-1 and NK-2 receptors as well as to guinea pig NK-3 receptors. In vitro functional assays are consistent with potent competitive antagonism of substance P-(SP) or neurokinin A-(NKA) induced [3H]-inositol phosphate accumulation in NK-1 or NK-2 monoreceptor cell lines with pA2 values of 8.19 and 8.67, respectively. Its ability to inhibit SP, NKA and capsaicin-mediated respiratory effects was examined in guinea pigs in vivo. MDL 105,212A attenuated SP-induced airway plasma protein extravasation (ED50 = 0.20 mg/kg, i.v.), NKA-induced respiratory collapse (ED50 = 5 mg/kg, i.v) and inhibited capsaicin-induced increases in pulmonary insufflation pressure (ED50 = 0.5 mg/kg, i.v.). Conscious guinea pigs responded to capsaicin aerosol exposure with dyspnea, coughs and gasps (significant respiratory events) and plasma protein extravasation. MDL 105,212A inhibited these responses in a dose-dependent manner after i.v. (ED50 = 5 mg/kg) or oral (ED50 = 50 mg/kg) administration. These data suggest that MDL 105,212A is a potent NK-1 and NK-2 receptor antagonist based on in vitro activity and its ability to inhibit SP and NKA mediated respiratory effects in vivo after exogenous administration or endogenous release and hence may be a useful therapeutic agent in neuroinflammatory disorders such as asthma in which a role for both tachykinins in the pathogenesis of the disease has been postulated.

Augmentation of neurally evoked cholinergic bronchoconstrictor responses by prejunctional NK2 receptors in the guinea-pig

1. We examined the effect of exogenously administered tachykinins, neurokinin A (NKA), substance P (SP) and neurokinin B (NKB) on neurally mediated cholinergic bronchoconstrictor responses in guinea-pigs. 2. Electrical stimulation of regions in the dorsal medulla oblongata produced a cholinergic bronchospasm that was not affected by depletion of endogenous tachykinins with capsaicin pretreatment (50 mg kg-1, s.c., 1 week earlier) or by pretreatment with the neutral endopeptidase inhibitor, phosphoramidon (3 mg kg-1, i.v.). 3. Infusion of NKA (0.03-0.1 microgram kg-1 min-1), SP (1 microgram kg-1 min-1) or NKB (1 microgram kg-1 min-1) potentiated the bronchoconstrictor response to electrical stimulation of the dorsal medulla. The doses of tachykinins tested were subthreshold for direct activation of airway smooth muscle, because they were devoid of direct bronchoconstrictor effects. The relative rank order potency for augmentation of centrally induced bronchospasm was NKA > NKB approximately SP, suggesting activation of the NK2 receptor subtype. 4. Infusion of NKA, SP and NKB had no effect on bronchoconstrictor responses to i.v. methacholine (1 microgram kg-1) indicating that a prejunctional neural mechanism of action was responsible for the effects on CNS stimulation-induced bronchospasm. 5. Potentiation of the bronchoconstrictor response to dorsal medullary stimulation produced by infusion of NKA was blocked by pretreatment with the NK2 antagonist SR 48968 (1 mg kg-1, i.v.) but not by the NK1 antagoinst CP 96,345 (1 mg kg-1, i.v.). 6. The potentiation of CNS-induced bronchospasm produced by infusion of SP was partially inhibited by CP 96,345 (1 mg kg-1, i.v.) but not by SR 48968 (1 mg kg-1, i.v.). Treatment with combined SR 48968 (1 mg kg-1, i.v.) and CP 96,345 (1 mg kg-1, i.v.) completely blocked the SP-induced potentiation of CNS-stimulated bronchospasm. 7. These results identify an important modulatory role for NK2 receptors, located at prejunctional sites on parasympathetic nerves, on cholinergic bronchoconstrictor responses in guinea-pigs. 8. It is proposed that substances that release tachykinins from airway sensory nerves, e.g. inflammatory mediators or irritants, may induce hyperresponsiveness of cholinergic bronchomotor responses by activation of NK2-receptors on parasympathetic airway nerves. Furthermore, these studies indicate that endogenous tachykinins are not involved in the maintenance of basal cholinergic bronchomotor tone in the intact guinea-pig.

Temperature and agonist dependency of tachykinin NK1 receptor antagonist potencies in rat isolated superior cervical ganglion

Using rat isolated superior cervical ganglion we have further characterised tachykinin NK1 receptors and investigated the possible existence of tachykinin NK1 receptor subtypes. At 37 degrees C, tachykinin NK1 receptor antagonists GR82334 ([D-Pro9[spiro-gamma- lactam]Leu10,Trp11]physalaemin-1(1-11)), CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine) and (+/-)-RP67580 (7,7-diphenyl-2[1-imino-2(2-methoxy- phenyl)-ethyl]perhydroisoindol-4-one (3aR,7aR)) antagonised more potently depolarisation responses evoked by GR73632 (delta Ava]L-Pro9,N-MeLeu10]SP-(7-11)), septide ([pGlu6,Pro9]SP-(6-11)) and neurokinin A than those evoked by substance P, substance P O-methyl ester and [Sar9,Met(O2)11]substance P. GR73632 and substance P O-methyl ester evoked depolarisation responses of similar magnitude, unaffected by addition of tetrodotoxin, but which cross-desensitised. At 22 degrees C, the ability of GR82334 and (+/-)-RP67580 to inhibit substance P O-methyl ester-evoked but not GR73632-evoked responses was enhanced greatly. These results suggest a single population of tachykinin NK1 receptors in this preparation. The agonist and temperature dependency of tachykinin NK1 receptor antagonist potency in rat isolated superior cervical ganglion may reflect different conformational changes in the tachykinin NK1 receptor induced by partial or full sequence substance P analogues.

Neuropeptide modulation of chemically induced skin irritation

This study addresses the hypothesis that the early symptoms of chemically induced skin irritation are neurally mediated. Several approaches were used to affect nerve transmission in adult Balb/c female mice. These included general anesthesia (i.e., sodium pentobarbital), systemic capsaicin treatment, and pretreatment with specific pharmacological antagonists of the neuropeptides substance P (SP) and neurokinin A (NKA). After these treatments, a strongly irritating dose of dinitrofluorobenzene (DNFB) was applied to the ear and its swelling was measured over several postexposure times as an index of tissue irritation. Ear swelling in Nembutal (30 mg/kg)-anesthetized mice was depressed 62 and 76% at 4 and 24 hr postexposure compared to DNFB-treated unanesthetized animals measured at the same time points. Multiple injections of capsaicin (cumulative dose 30 mg/kg) depressed DNFB-ear swelling relative to non-capsaicin, DNFB-treated controls by 15, 40 (ip), and 44 and 43% (sc) at 4 and 24 hr postexposure, respectively. In mice exposed to acute or multiple injections of the SP antagonist CP-96,345 before DNFB application, ear swelling was depressed (relative to DNFB-treated animals) by 64 and 36% (acute, sc, 10 mg/kg) and 91 and 88% (multiple, ip, cumulative 35 mg/kg) at 0.5 and 1 hr postexposure, respectively. Mice exposed to the NKA antagonist, SR 48968, alone and in combination with the SP antagonist CP-96,345 were also examined after DNFB application. Ear swelling was diminished in mice pretreated with the NKA antagonist (1.0 mg/kg) by 17, 24, 34, and 40% at 0.5, 1, 4, and 24 hr postexposure. When used in combination with the SP antagonist, DNFB-induced ear swelling was reduced by 95% compared to unantagonized, DNFB-exposed mice at the 0.5- and 1-hr time points and remained significantly depressed by 33 and 46% at 4 and 24 hr postexposure. Taken in concert, these data suggest that neuropeptides, especially the tachykinins SP and NKA, modulate the early stages of chemically induced skin irritation.

Enantiospecific inhibition of emesis induced by nicotine in the house musk shrew (Suncus murinus) by the neurokinin1 (NK1) receptor antagonist CP-99,994

Effects of the NK1 receptor antagonist CP-99,994 on nicotine-induced emesis were examined in Suncus murinus. CP-99,994 (3 and 10 mg/kg i.p.) attenuated emesis to (-)nicotine (4 mg/kg s.c.). CP-100,263 (3 and 10 mg/kg i.p.), the enantiomer of CP-99,994 with 1000 fold lower affinity for the NK1 receptor was without effect and RP67580 reduced emesis only at a dose of 30 mg/kg i.p. Responses to NK1 antagonists were ranked according to their affinities for the Suncus murinus NK1 receptor.

Effect of a new dual neurokinin antagonist on airway smooth muscle in situ

The effect of FK224 (N-(N2-[N-¿N-(N-2,3-didehydro-N-methyl-N-[N-3- (2-pentylphenyl)-propionyl¿-L-threonyl]tyrosyl-L-leucynyl)-D -phenylalanyl¿-L-allothreonyl]-L-asparaginyl)-L-serine-v-lacto ne, CAS 125787-94-2) on isometric contraction of canine tracheal smooth muscle in situ was studied. Contraction was induced by administration of substance P, neurokinin A, and neurokinin B intra-arterially into the tracheal circulation in five mongrel dogs. FK224 inhibited substance P- and neurokinin A-induced contraction in a dose-dependent manner, but it did not inhibit neurokinin B-induced contraction significantly. These data suggest that FK224 is a dual antagonist of both neurokinin 1 and neurokinin 2 receptors, with a similar potency in in vivo experiments.

Analysis of the mechanisms underlying the contractile response induced by the hydroalcoholic extract of Phyllanthus urinaria in the guinea-pig urinary bladder in-vitro

The hydroalcoholic extract of Phyllanthus urinaria (Euphorbiaceae), substance P and substance P methyl ester all caused graded contractions in the guinea-pig urinary bladder. Responses to hydroalcoholic extract and substance P were markedly inhibited in calcium-free Krebs solution, this effect being reversed by reintroduction of calcium in the medium. The contraction in response to hydroalcoholic extract was unaffected by atropine, propranolol, prazosin, yohimbine, tetrodotoxin, w-conotoxin, nicardipine, HOE 140, guanethidine, staurosporine, phorbol ester or indomethacin, excluding the involvement of nervous mediated responses, or action via cholinergic, adrenergic, kinins, cyclo-oxygenase metabolites, protein kinase C or activation of L or N-type calcium channels. The selective NK1 tachykinin antagonist (FK 888), but not NK2 (SR 48968) antagonized substance P-induced contraction, but both drugs failed to effect Phyllanthus urinaria-induced contraction. Prolonged desensitization of guinea pig urinary bladder with capsaicin (10 microM) or preincubation of guinea-pig urinary bladder with capsazepine did not affect contraction caused by hydroalcoholic extract. Ruthenium red almost completely abolished capsaicin-induced contraction, but had no effect on hydroalcoholic extract-mediated contraction. Substance P and the hydroalcoholic extract caused marked potentiation of the twitch response in the preparations field stimulated. The facilitatory effect of substance P, but not that of hydroalcoholic extract, was prevented by the NK1 (FK 888), but not by NK2 (SR 48968) antagonist. We concluded that contraction induced by hydroalcoholic extract of Phyllanthus urinaria in the guinea pig urinary bladder involves direct action on smooth muscle and relies on the mobilization of extracellular calcium influx unrelated to activation of L- and N-type calcium channels or activation of protein kinase C mechanisms. In addition contraction caused by the hydroalcoholic extract of Phyllanthus urinaria in guinea-pig urinary bladder does not involve the activation of tachykinin or vanilloid receptors.

Effects of neurokinin receptor antagonists on L-dopa induced bladder hyperactivity in normal conscious rats

PURPOSE

The urodynamic effects of intrathecal neurokinin (NK) receptor blockade on L-dopa-induced bladder hyperactivity were investigated in a rat model.

MATERIALS AND METHODS

Continuous cystometry was performed in normal, conscious, female Sprague-Dawley rats.

RESULTS

In rats pretreated with intraperitoneal carbidopa 50 mg./kg., intraperitoneal L-dopa 50 mg./kg. caused bladder hyperactivity that could be attenuated by intrathecal administration of the NK1 receptor selective antagonist SR 140,333 (2 nmol.), whereas the NK2 receptor selective antagonist SR 48,968 (2 nmol.) failed to do so. Combination of SR 140,333 (2 nmol.) and SR 48,968 (2 nmol.), which by itself decreased micturition pressure, practically abolished the L-dopa-induced hyperactivity.

CONCLUSIONS

The present results suggest that tachykinins, via stimulation of NK1 (and/or NK2) receptors, are involved in L-dopa-induced bladder hyperactivity, most probably at the spinal level. This implies tachykinin involvement in the supraspinal pathways that control the sacral parasympathetic center innervating the urinary bladder. It also implies that spinal NK receptors are a possible target for drugs aimed for elimination of bladder hyperactivity mediated via these pathways.

New spiropiperidines as potent and selective non-peptide tachykinin NK2 receptor antagonists

The synthesis of a series of 2-(5-fluoro-1H-indol-3-yl)ethyl spiropiperidines is described together with their tachykinin NK2 receptor affinities measured in a rat colon binding assay. Equivalent NK2 receptor binding affinity was observed for the spirooxazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1-oxa-3,8-diazaspiro[4.5] decan-2-one (3a), the imidazolidinone 3-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-1,3,8-triazaspiro[4.5 ] decan-2-one (3s), and the pyrrolidinone 2-benzyl-8-[2-(5-fluoro-1H-indol-3-yl)ethyl]-2,8-diazaspiro[4.5]decan -3 - one (3t). Substitution in the phenyl ring of compound 3a produced no significant enhancement in NK2 binding affinity. Replacement of the phenyl ring in 3a with other aromatic rings resulted in a significant loss in binding affinity. Compound 3a was shown to be a potent NK2 receptor antagonist in guinea pig trachea where it also demonstrated 1000-fold selectivity for NK2 receptors over NK1. In the anesthetized guinea pig, compound 3a administered by the intravenous or oral route displayed potent and long-lasting antagonist activity against NK2 receptor agonist induced bronchoconstriction.

Identification of residues involved in ligand binding to the neurokinin-2 receptor

Several residues of the human neurokinin-2 receptor have been identified to be critical for the binding of peptide agonists and non-peptide antagonists. Amino acid substitutions in the first and second extracellular segments and the second transmembrane segment led to substantial reduction in peptide affinity without affecting the affinity of antagonist SR48968. These effects are identical to those observed for homologous residues in the neurokinin-1 receptor, suggesting that these three regions are involved in high-affinity peptide binding to both receptor subtypes. On the other hand, some conserved residues in the fourth to seventh transmembrane segments are required for peptide binding to only one receptor subtype but not both. The conserved nature and location of these receptor residues suggest that the distance between bound peptide and helices 4-7 varies depending on the receptor subtype. It is likely that the conformational compatibility between a ligand and a given receptor determines the magnitude of binding affinity, and thus receptor subtype selectivity. While many single-residue substitutions did not affect the binding affinity of the antagonist SR48968, two double mutants in the sixth and seventh transmembrane segments were found to reduce its affinity substantially. Therefore, receptor residues participate cooperatively in the binding of SR48968. These results demonstrate the usefulness of combining single-residue substitutions in studying and confirming the role of receptor residues in ligand binding. Finally, the overlapping nature of agonist and antagonist binding sites is consistent with the observation that substitutions of some residues modify the binding affinities of both peptide agonists and non-peptide antagonists.

Ionic basis of neurokinin-A-induced depolarization in single smooth muscle cells isolated from guinea-pig trachea

Neurokinin A (NKA) caused single tracheal smooth muscle cells (TSMCs) to contract. The effects of NKA on the electrical activity of guinea-pig TSMCs were examined using the tight-seal whole-cell patch-clamp technique. Under current-clamp conditions at rest, the membrane potential of TSMCs spontaneously oscillated at about -40 mV and NKA rapidly depolarized the membrane potential to nearly 0 mV, which then gradually repolarized to about -20 mV in the presence of NKA. The oscillations in potential disappeared transiently during the rapid phase of depolarization in response to NKA and reappeared during the sustained phase of depolarization. Under voltage-clamp conditions, NKA evoked an inward current which faded quickly. Subsequently, the cell conductance in the presence of NKA at potentials greater than -40 mV decreased gradually. The reversal potential of the NKA-induced inward current was about 0 mV, and shifted with changes in the Cl- equilibrium potential. The Cl- current was not elicited by NKA when using a pipette solution containing 10 mM ethylenebis(oxonitrilo)tetraacetic acid (EGTA). During the sustained phase, K+ currents evoked by depolarizing voltage steps were inhibited by NKA. The present results indicate that NKA causes rapid and sustained depolarization of TSMCs by two distinct mechanisms: (1) initial transient activation of the Ca(2+)-dependent Cl- current, and (2) sustained inhibition of K+ currents.

Tachykinin effects on bladder activity in conscious normal rats

When instilled intravesically in normal, unanesthetized rats, neurokinin A (NKA), but not substance P (SP) and neurokinin B (NKB), stimulated micturition. The effect of NKA was inhibited by the NK2 receptor selective antagonists SR 48,968 and MEN 10,627, but not by the NK1 receptor selective antagonist RP 67,580, suggesting that the effect was mediated by stimulation of NK2 receptors. Given intra-arterially near the bladder, NKA produced an increase in basal intravesical pressure before initiating micturition, indicating that the tachykinin had a direct contractant effect on the detrusor smooth muscle. Such a contractile effect was not observed when NKA was given intravesically. The effect of intra-arterial NKA could not be blocked by the NK1 receptor selective antagonist SR 140,333 or the NK2 receptor selective antagonist SR 48,968, but by their combination. Also intra-arterial NKB stimulated micturition, but was less potent than NKA. Intra-arterial SP had only weak stimulating effects. The results suggest that intravesically administered NKA can initiate micturition in the normal rat by stimulation of superficially located NK2 receptors in the urothelium. Intra-arterially administered NKA caused bladder hyperactivity via stimulation of both NK1 and NK2 receptors.

Proliferation of guinea pig tracheal epithelial cells in coculture with rat dorsal root ganglion neural cells

Neuropeptides secreted by sensory afferent nerves in airways may modulate growth of airway epithelial cells. To determine whether airway sensory C-fiber nerves secrete neuropeptides that stimulate airway epithelial cell proliferation, we measured S-phase traversal in guinea pig tracheal epithelial (GPTE) cells after coculture with rat dorsal root ganglion (DRG) cells. GPTE cells were grown in subconfluent culture on collagen-coated filters for 2 days. DRG cells were harvested from newborn rat pups and grown in primary culture for 7-10 days in separate wells. GPTE and DRG cells then were cocultured for 48 h, and 10 mM bromodeoxyuridine (BrdU), a thymidine analogue, was added in the final 24 h. Control GPTE cells were grown under similar conditions but without DRG cells. Coculture with DRG cells stimulated GPTE cell traversal of S phase. BrdU labeling in cocultured GPTE cells was 42.8 +/- 5.8 compared with 18.1 +/- 7.2% in control GPTE cells (P < 0.001, n = 6). Coculture in the presence of either the neurokinin (NK)1 receptor antagonists LY-297911 or CP-99,994, the NK2 receptor antagonist SR-48,968, or the calcitonin gene-related peptide (CGRP) receptor antagonist hCGRP-(8-37) (10(-7) M of each) during coculture attenuated proliferation of GPTE cells. Treatment with all three antagonists together during coculture decreased BrdU labeling to 2.4 +/- 0.9% of labeled cells vs. 8.5 +/- 0.5% of labeled cells during coculture without antagonists (n = 4, P < 0.02). DRG cells in coculture secreted substantial concentrations of CGRP [71.0 +/- 11.3 (+/- SE) pmol/ml], substance P (1.26 +/- 0.35 pmol/ml), and neurokinin A (0.45 +/- 0.10 pmol/ml) (n = 19 for each).(ABSTRACT TRUNCATED AT 250 WORDS)

Galanin and somatostatin inhibition of neurokinin A and B induced airway mucus secretion in the rat

Neurokinin A and B are present in neurons situated in lung and NK-1 receptors have been described on tracheal submucosal gland cells. In the present study we compared the ability of substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) to stimulate airway mucus secretion. Furthermore, we characterized the interaction of NKA and NKB with galanin and somatostatin. The rank order of the tachykinins to stimulate airway mucus secretion was SP > NKA > NKB suggesting that NK-1 receptors mediate these effects(EC50:SP: 50 nmol/l, NKA: 200 nmol/l, NKB: 400 nmol/l). Galanin and somatostatin were equally potent to inhibit NK-A and NK-B stimulated airway mucus release. These results suggest that NK-A and NK-B are potent stimulators of airway macromolecule secretion. Galanin and somatostatin potently inhibit these actions of the tachykinins. Therefore, airway mucus secretion is controlled by a complex network of several different mediators.

Passive immunization with an anti-substance P antibody prevents substance P- and neurokinin A-induced bronchospasm in anesthetized guinea-pigs

In a guinea-pig model of asthma, active immunization against substance P (SP) prevented the development of airways' hyperresponsiveness and reduced bronchospastic responses to SP (i.v.). The rat-mouse heterohybridoma NC1/34 secretes a specific, rat IgG1, anti-substance P antibody (alpha-SP Ab) which was isolated and purified by passing supernatant from cultures through thiophilic gel. Purity of antibody was about 50% (SDS-PAGE). The relative affinities of the alpha-SP Ab for SP, neurokinin A (NKA) and calcitonin gene-related peptide (CGRP) were estimated by ELISA using a constant amount of SP coupled (glutaraldehyde) to bovine serum albumin (BSA) to capture the antibody, alone and in the presence of increasing concentrations of the neuropeptides. At alpha-SP Ab dilutions of 1 in 5,000 to 1 in 32,000, CGRP did not prevent antibody binding to SP-BSA conjugate bound to the plates, but both SP and NKA prevented binding. In this system, the relative affinity of the alpha-SP Ab, at dilutions of 1 in 5,000 and 1 in 10,000, was about 50 times greater for SP than NKA. Whether passive immunization with alpha-SP Ab prevented bronchospastic responses to SP and NKA (i.v.), in vivo, was determined in groups of anesthetized guinea-pigs by recording pulmonary flow resistance (RL) and dynamic pulmonary elastance (EL). Injection of alpha-SP Ab (i.v., 5:1 molar ratio: alpha-SP Ab:SP total dose) did not alter baseline values of RL and EL, but markedly inhibited increases in RL and EL induced by SP and NKA (i.v.) without affecting responses to methacholine (i.v.). A control, "irrelevant" rat IgG-type antibody at a similar concentration had no effect on responses to SP or NKA. These findings indicate that passive immunization with a monoclonal alpha-SP Ab can prevent the bronchospastic effects of exogenous SP and NKA in guinea-pigs.

Neurokinin depletion attenuates pulmonary changes induced by antigen challenge in sensitized guinea pigs

The role of neurokinins in the acute pulmonary response to antigen was studied in guinea pigs that received ovalbumin (50 mg/kg ip) on days 1 and 3 and capsaicin (50 mg/kg sc) on day 21 (OAC); ovalbumin on days 1 and 3 (OA1); capsaicin on day 1 and OA on days 8 and 10 (COA); and ovalbumin on days 8 and 10 (OA2). On day 28, guinea pigs were submitted to ovalbumin aerosol challenge. Maximal values of pulmonary dynamic elastance (Edyn) and pulmonary resistance (RL) were significantly lower in OAC and COA groups compared with OA1 and OA2 groups (P < 0.001). There was no difference between maximal Edyn and RL values obtained in OAC and COA groups. Morphometric analysis of lungs showed significantly (P < 0.05) lower values of contraction index of airways, peribronchial edema, and alveoli over inflation in guinea pigs that received capsaicin compared with intact guinea pigs. Capsaicin treatment did not influence the formation of specific IgG1 anaphylactic antibodies. We conclude that neurokinin depletion results in a decrease in the pulmonary mechanical and inflammatory responses to antigen challenge in sensitized guinea pigs. These effects are observed when capsaicin is given either before or after sensitization.

Comparison of the effects of sumatriptan and the NK1 antagonist CP-99,994 on plasma extravasation in Dura mater and c-fos mRNA expression in trigeminal nucleus caudalis of rats

Dural plasma extravasation produced by electrical stimulation of the trigeminal ganglion was measured in rats and the concomitant expression of c-fos mRNA produced in the trigeminal nucleus caudalis (NtV) was measured using in situ hybridization techniques. The non-peptide NK1 receptor selective antagonist CP-99,994 (1-3000 micrograms kg-1) and the 5HT1D receptor agonist sumatriptan (1-1000 micrograms kg-1) reduced dural plasma extravasation dose-dependently with ID50S of 52 micrograms kg-1 and 30 micrograms kg-1 respectively. CP-99,994 (1000 micrograms kg-1). a compound known to have good brain penetration, decreased c-fos mRNA expression in the NtV by 37 +/- 7% without disruption of the blood brain barrier (BBB). Sumatriptan (1000 micrograms kg-1), known to be poorly brain penetrant, had no significant effect on c-fos mRNA expression in the NtV unless the BBB was disrupted by infusion of a hyperosmolar mannitol solution after which sumatriptan decreased c-fos mRNA expression by 65 +/- 11%. The results suggest that brain penetrant NK1 receptor antagonists may have anti-migraine effects peripherally through blockade of dural extravasation and centrally by inhibition of nociceptive pathways. Furthermore the data indicates that the anti-migraine action of sumatriptan must be predominantly peripherally mediated, be it via inhibition of plasma extravasation or direct vasoconstriction, since it had little effect on the activation of neurones in the NtV unless the BBB was disrupted.