Role of tachykinin NK1 and NK2 receptors in allergen-induced early and late asthmatic reactions, airway hyperresponsiveness, and airway inflammation in conscious, unrestrained guinea pigs

Using a guinea pig model of allergic asthma, we investigated the effects of the inhaled, highly selective nonpeptide tachykinin NK₁ and NK₂ receptor antagonists SR 140333 and SR 48968, respectively, on allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions, and infiltration of inflammatory cells in the airways. Both SR 140333 (100 nM, 3 min) and SR 48968 (100 nM, 3 min) had no effect on the severity of the EAR, while the NK₂ receptor antagonist SR 48968, but not the NK₁ receptor antagonist SR 140333, caused significant inhibition of the LAR. SR 140333 significantly reduced the allergen-induced AHR to histamine, both after the EAR and the LAR. By contrast, SR 48968 did not affect the AHR after the EAR, but significantly attenuated the AHR after the LAR. Bronchoalveolar lavage studies performed after the LAR indicated that SR 140333 caused significant inhibition of allergen-induced infiltration of eosinophils, neutrophils and lymphocytes, while SR 48968 attenuated the infiltration of neutrophils and lymphocytes, but not of eosinophils. Both NK receptor antagonists tended to reduce the accumulation of ciliated epithelial cells in the airways. These results indicate that NK₁ and NK₂ receptors are importantly, but differentially, involved in the development of allergen-induced airways obstruction, AHR and infiltration of inflammatory cells in the airways. Therefore, both NK₁ and NK₂ receptor antagonists, or dual NK₁ and NK₂ antagonists, could be useful in the treatment of allergic asthma.     

气道速激肽在卵蛋白致敏豚鼠模型咳嗽反应中的作用

目的：研究气道速激肽在卵蛋白致敏和激发豚鼠咳嗽发生机制中的作用。 方法： 正常和卵蛋白致敏豚鼠各20只，卵蛋白雾化吸入激发。24 h后，正常组和致敏组豚鼠随机各分为2组，每组10只，分别依次腹腔注射生理盐水，0.1 mg/kg、0.3 mg/kg和1.0 mg/kg的NK1受体拮抗剂SR140333 或NK2受体拮抗剂SR48968，观察吸入10-4 mol/L的辣椒素溶液诱导的咳嗽反应。用非侵入性方法测量正常和卵蛋白致敏豚鼠注射SR140333或SR48968前后吸入辣椒素溶液所产生的特异性气道阻力。 结果： 致敏豚鼠咳嗽反应明显高于正常对照组［(9.3±1.2)times/3 min vs (19.5±5.7)times/3 min，P<0.05］。SR140333不影响正常对照组豚鼠的咳嗽反应，而SR48968则可降低咳嗽频率达30% (P<0.05)，两者均抑制吸入辣椒素后增加的气道阻力。而在卵蛋白致敏豚鼠，SR140333或SR48968均抑制吸入辣椒素溶液诱导的咳嗽频率［(9.9±4.7)times/3 min，(8.0±1.6)times/3 min，P<0.05］和增高的气道阻力。 结论： NK受体拮抗剂抑制致敏豚鼠卵蛋白激发后增高的咳嗽反应。因此，气道速激肽可能是嗜酸性粒细胞性气道炎症所致咳嗽的重要介质。     

The involvement of sensory neuropeptides in airway hyper-responsiveness in rabbits sensitized and challenged to Parietaria judaica

BACKGROUND: C-fibres have received considerable attention in the context of airway hyper-responsiveness (AHR), in fact several lines of evidence suggest that tachykinins might be involved in the pathogenesis of AHR. OBJECTIVE: The aim of this study was to investigate the role of capsaicin-sensitive sensory C-fibres and tachykinins in rabbits sensitized to the major allergen of Parietaria judaica pollen (Par j1). METHODS: Airway responsiveness was determined by exposing sensitized rabbits to cumulative concentrations of aerosolized histamine before and after an allergic challenge and after a pre-treatment with either vehicle or capsaicin or tachykinin receptor antagonists. Bronchoalveolar lavage was performed following histamine challenge and total and differential cell counts were performed. RESULTS: In sensitized rabbits, an AHR to inhaled histamine was observed 24 h after a Par j1 challenge. Capsaicin pre-treatment inhibited the AHR achieved 24 h following antigen exposure (P < 0.01). Pre-treatment with the tachykinin NK2 receptor antagonist, SR 48968, significantly reduced the antigen-induced AHR (P < 0.05), while pre-treatment with tachykinin NK1 (SR 140333) and NK3 (SR 142801) receptor antagonists did not significantly modify it. Bronchoalveolar lavage fluid obtained from vehicle and capsaicin-treated rabbits challenged with Par j1 exhibited no significant differences in total and differential cell counts. CONCLUSIONS: Parietaria judaica-induced AHR in immunized rabbits was shown to be inhibited by pre-treatment with capsaicin, an effect that is not related to an action on the associated pulmonary infiltration of eosinophils. The involvement of NK2 receptor stimulation in this phenomenon also suggests that NK2 receptor antagonists may be useful for investigating mechanisms of bronchopulmonary alterations in asthmatic patients.     

Inhibitory effect of inhaled FK-506 on increased bronchial responsiveness and eosinophil infiltration in the airway mucosa]

We examined the effects of inhaled FK-506, a potent immunosuppressive agent, on increased bronchial responsiveness to acetylcholine and on eosinophil infiltration in a guinea pig models of asthma. The guinea pigs were sensitized by repeated inhalation of ovalbumin (OA). Twenty four hours after antigen challenge, bronchial responsiveness to acetylcholine significantly increased and a marked accumulation of eosinophils in the airways was observed. However, when the guinea pigs were treated with aerosolized FK (10 mg/ml) for 5 min per day for 6 successive days before antigen challenge, the increase in bronchial responsiveness was significantly suppressed and the eosinophil accumulation was strikingly reduced. Since inhaled FK significantly suppressed these responses, there is a possibility that inhaled FK may be a useful therapy for patients with chronic bronchial asthma in the future.     

Sensory neuropeptides are not directly involved in bronchial hyperresponsiveness induced by interleukin-8 in guinea-pigs in vivo

Background Interleukin-8 (IL-8) hus been shown to be a chemotactic factor for netitrophils, T-lymphocytes and eosinophils. Repeated intranasal administration of IL-8 enhances bronchial responsiveness to inhaled histamine in guinea-pigs. Neuropeptides which arc released trotn C-fibre nerve-endings have been postulated to induce bronchial hyperresponsiveness through neurogenic inflammation. Objective This study was conducted to examine whether sensory neuropeptides are involved in the IL-8-induced bronchial hyperresponsiveness. Methods IL-8 at a dose of 5μg/kg was administered intranasally to guinea-pigs twice a week for 3 weeks. One day after the last administration, animals were anesthetized and artificially ventilaled through tracheal cannula, and lateral pressure at the tracheal cannula (Pao) was measured as an overall index of airway responses lo increasing concentrations of inhaled histamine (25, 50, 100, and 200 μg/mL). A NKI and NK2 dual antagonist FK224(10mg/kg), a selective NK1 antgonist FK888 (10mg/kg) or vehicle was intravenously administered 10min before measurement of bronchial responsiveness. Result The IL-8 treatment significantly enhanced bronchial responsiveness to histamine (ANOVA P < 0.01). FK224 or FK888 did not alter the IL-8-induced bronchial hyperresponsiveness. Conclusion We conclude that repeated intranasal administratioti of IL-8 causes bronchial hyperresponsiveness (BHR) and that neuropeptides such as neurokinin A and substance P do not directly contribute to the development of BHR induced by IL-8.     

Role of tachykinins in enhancement of bradykinin-induced bronchoconstriction by captopril

In anesthetized, mechanically ventilated guinea pigs, infusion of captopril (1 mg/kg/h), an angiotensin converting enzyme inhibitor, significantly enhanced bronchoconstriction induced by intravenous injection of bradykinin (BK; 0.1–30 nmol/kg). Pretreatment of guinea pigs with capsaicin (100 g/kg) slightly suppressed the bronchoconstriction by BK alone and almost all of the enhancement of BK-induced bronchoconstriction by captopril was suppressed. Intravenous injection of substance P (SP; 0.1–100 nmol/kg), neurokinin A (NKA; 0.1–30 nmol/kg) and neurokinin B (NKB; 0.1–30 nmol/kg) also induced dose-dependent bronchoconstriction but captopril treatment enhanced only the bronchoconstriction induced by SP. BK degradation in bronchoalveolar lavage fluid (BALF) in vitro was significantly suppressed by captopril (p<0.05). Captopril infusion to guinea pigs significantly increased the levels of BK, SP, and NKA in BALF after BK injection (p<0.05). FK224, an NK1 and NK2 receptor antagonist and SR 48968, an NK2 receptor antagonist, significantly suppressed the broncoconstriction induced by BK alone (p<0.01 and p<0.05, respectively) as well as the enhancement by captopril (p<0.01). It can be concluded that the enhancement of BK-induced bronchoconstriction by captopril was attributable to inhibition of the degradation of BK itself and thereby enhanced release of NKA and partly of SP from sensory nerves by BK.accepted by M. J. Parnham     

Chronic smoking enhances tachykinin synthesis and airway responsiveness in guinea pigs

This study tests the hypothesis that the bronchial hyperreactivity induced by chronic cigarette smoke (CS) exposure involves the increased expression and release of tachykinins and calcitonin gene-related peptide (CGRP) from afferent nerve fibers innervating the airways. In guinea pigs chronically exposed to CS (20 min twice daily for 14-17 d), peak response in total lung resistance to capsaicin (1.68 microg/kg, intravenously) was significantly greater than that evoked by the same dose of capsaicin in control (air-exposed) animals. This augmented response in CS-exposed animals was abolished after treatment with CP-99994 and SR-48968, the neurokinin (NK)-1 and NK-2 receptor antagonists, suggesting the involvement of tachykinins in chronic CS-induced airway hyperresponsiveness (AHR). Further, substance P (SP)-like immunoreactivity (LI) and CGRP-LI in the airway tissue were significantly greater in the CS animals than in the control animals. Finally, beta-preprotachykinin (PPT, a splice variant from the PPT A gene encoding tachykinins including SP and NKA) messenger RNA levels as measured by in situ hybridization histochemistry displayed a significant increase in jugular ganglion neurons but not in dorsal root or nodose ganglion neurons. These data suggest that chronic CS-induced AHR is related to an increase in SP synthesis and release in jugular ganglion neurons innervating the lungs and airways.     

The NK-2 receptor antagonist SR 48968C does not improve adenosine hyperresponsiveness and airway obstruction in allergic asthma

When stimulated, excitatory nonadrenergic noncholinergic (e-NANC) nerves locally release tachykinins like Neurokinin (NK) A and Substance P, causing neurogenic inflammation and airway obstruction via activation of specific NK-1 and NK-2 receptors. The recently developed nonpeptide NK-2 receptor antagonist SR 48968C has a high affinity for the NK-2 receptor, and is a strong and selective antagonist of NK-2 receptor mediated airway obstruction. In a placebo-controlled cross-over study, we investigated the effect of SR 48968C, administrated orally once-daily in a dosage of 100 mg during 9 days, on airway responsiveness to adenosine 5'-monophosphate (AMP) in 12 allergic asthmatic patients. Furthermore, we assessed its effect on airway obstruction, by measuring FEV1 on the first and last day of each treatment period and by peak flow registration at home throughout the study period. SR 48968C had no significant effect on PC20AMP or on FEV1 measured on day 1 and 9, and morning and evening peakflow measured at home on day 2-8. Thus, although SR 48968C was administrated in a dosage that might cause a demonstrable blocking effect on airway NK-2 receptors in asthma, it did not have a significant bronchodilatory or bronchoprotective effect against adenosine hyperresponsiveness in this study. Further studies are needed to assess the value of SR 48968C and other NK receptor antagonists in the treatment of asthma     

Comparison of the effect of imidaprilat and ramiprilat on bronchoconstriction and hypotension induced by bradykinin in guinea pigs

OBJECTIVE: To demonstrate tissue selective brady-kinin (BK) potentiating action of angiotensin converting enzyme inhibitors, we studied effects of imidaprilat and ramiprilat, active metabolites of imidapril and ramipril, respectively, on bronchoconstriction and hypotension both induced by BK in vasopressin-infused anesthetized guinea pigs. METHODS: We measured pulmonary inflation pressure and blood pressure in vasopressin-infused anesthetized guinea pigs at the same time. BK-induced changes in pulmonary inflation pressure and blood pressure before and after the administration of ACE inhibitor were compared. RESULTS: Imidaprilat and ramiprilat enhanced BK-induced hypotension comparably, and this effect was inhibited by Nomega-nitro-L-arginin-methylester (L-NAME, a nitric oxide synthetase inhibitor). Although imidaprilat did not affect BK-induced bronchoconstriction, ramiprilat enhanced the broncho-constriction significantly. SR48968, a selective NK2 receptor antagonist, significantly inhibited the enhancing effect of ramiprilat on BK-induced bronchoconstriction. CONCLUSION: These results suggest that enhancement of BK-induced hypotension by imidaprilat and ramiprilat is mediated by nitric oxide (NO), but the mediator of the enhancing action of ramiprilat on BK-induced bronchoconstriction is mainly neurokinin A.     

Analysis of the inflammatory response in the rat paw caused by the venom of <Emphasis Type="Italic">Apis melifera</Emphasis> bee

OBJECTIVE: This study examines the pro-inflammatory action caused by subcutaneous (s.c.) injection of the bee venom (BV) Apis melifera in the rat paw. METHODS: Male Wistar rats were used. The venom of Apis melifera was injected s.c. into the rat paw and the oedema formation and the activity of myeleperoxidase (MPO) were measured. RESULTS: Subcutaneous injection of BV caused dose-and time-dependent paw oedema (ED50 of 1.5 microg/paw) with peak at 30 min. The MPO activity increased about 1.6, 4.2 and 8.9 folds at 0.5, 4 and 6 h after s.c. injection of BV. The mast cell degranulating drug 48/80, pyrilamine or metysergide, inhibited BV-mediated oedema formation (88, 62 and 96%, respectively). Likewise, L-NAME, the NK1 antagonist FK 888, the B1 des-Arg9-[Leu8]-BK or B2 kinin antagonist Hoe 140 also antagonised the paw oedema induced by BV (60, 59, 49, and 49%, respectively). SR48968 and SR14280, respectively NK2 and NK3 antagonists and also indomethacin, inhibited by 31, 29 and 22%, respectively BV-induced oedema formation. In contrast, the PAF antagonist WEB 2086 or valeryl salycilate, did not affect the BV-induced paw oedema. The levels of MPO were inhibited by compound 48/80, cyproheptadine, Hoe 140, or by des-Arg9[Leu8]-BK (85, 61, 59, and 53%, respectively) measured 6 h after. CONCLUSION: These results indicate that the BV from Apis melifera causes a marked dose-and time-dependent oedema formation in the rat paw, an effect that is accompanied by intense leukocyte migration. The pro-inflammatory response induced by BV is mediated by several mechanisms, namely the release of histamine and/or serotonin from mast cells, activation of H1 histamine receptor, production of nitric oxide, the involvement of kinins through the activation of B1 and B2 receptors, and also tachykinins acting at NK1 receptor or and to a lesser extent at NK2 and NK3 receptors.     

Analysis of the mechanisms involved in the inflammatory response induced by des-Arg9-bradykinin in the rat pleural cavity

OBJECTIVE: The present study investigates some of the mechanisms underlying the inflammatory responses caused by the selective B1 kinin receptor agonist, des-Arg9-bradykinin (des-Arg9-BK), in the rat pleural cavity. MATERIAL: Male Wistar rats were used (N = 4-10 per group). TREATMENT: A fixed volume (100 microl) of PBS or des-Arg9-BK (10-60 nmol) was injected into the rat pleural cavity. Animals were treated with the B1 des-Arg9[Leu8]-BK (60 nmol/cav.) and R715 (65 nmol/cav.), B2 HOE 140 (3 nmol/cav.), NK1 FK888 (1 nmol/cav.), NK2 SR 48968 (20 nmol/cav) or NK3 SR142801 (10 nmol/cav.) receptor antagonists, or with either cyproheptadine (40 mg/kg, i.p.) or compound 48/80 (0.6 mg/kg, i.p., twice a day/3 days, 1.2 mg/kg/4th day). RESULTS: des-Arg9-BK (30 nmol/cavity) induced a time-dependent leukocyte migration. The increase in total leukocytes was not significantly reduced by the treatment with any of the B1, B2, NK1, NK2 or NK3 receptor antagonists. Treatment of animals with cyproheptadine or with compound 48/80 markedly inhibited des-Arg9-BK-induced cell migration (77 +/- 7 and 82 +/- 4%, respectively). CONCLUSION: These findings suggest that inflammatory responses caused by the B1 agonist des-Arg9-BK in the rat pleural cavity are mediated by a receptor-independent mechanism, being largely dependent on the activation of resident mast cells and release of histamine and/or serotonin.     

Delayed-type asthmatic response induced by repeated intratracheal exposure to toluene-2,4-diisocyanate in guinea pigs

BACKGROUND: A toluene-2,4-diisocyanate (TDI)-induced asthma model, in which delayed-type hypersensitivity-like asthmatic airway obstruction is elicited restrictively in the lung, has never been developed. METHODS: Guinea pigs were percutaneously sensitized with TDI. For the challenges, once every 2 weeks for a total of 5 times, TDI mists were delivered directly to the lung through an oral cannula, with its tip being positioned in the opening of the trachea. Time-course changes in specific airway resistance (sRaw) were measured by double-flow plethysmography. Basic mechanisms underlying TDI-induced asthma were analyzed. RESULTS: After the 2nd-5th challenges, induction of both an early increase in sRaw that peaked at 10 min and a delayed-type sRaw elevation that peaked at 22 h were observed. Interestingly, in the sensitized/challenged animals, baseline sRaw was elevated by repeated challenge as compared to that seen for non-sensitized animals. Intratracheal administration of a bronchodilator, salbutamol, strongly suppressed the early asthmatic response (EAR) but not the delayed-type asthmatic response (DAR). During DAR, both albumin leakage and fucose secretion into the bronchoalveolar lavage fluid were increased. The cysteinyl leukotriene antagonist pranlukast failed to inhibit either EAR or DAR while the corticosteroid dexamethasone significantly suppressed DAR, without significantly affecting EAR. CONCLUSIONS: Effective delivery of TDI to the lung may induce reproducible DAR in sensitized guinea pigs with chronicity that is reflected by an increase in the sRaw baseline. DAR is not mediated by constriction of airway smooth muscles and is probably due to the concurrent presence of mucosal edema and mucus hypersecretion in the airways.     

A role for tachykinins in the regulation of human sperm motility

BACKGROUND: Tachykinins and tachykinin receptors are widely distributed in the male reproductive tract and appear to be involved in reproduction. However, the function and expression of tachykinins and their receptors in human spermatozoa remain poorly studied. We analysed the effects of tachykinins on sperm motility and characterized the population of tachykinin receptors in human spermatozoa. METHODS AND RESULTS: Motility analysis was performed following World Health Organization guidelines and we found that substance P (SP), human hemokinin-1 (hHK-1), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-dependent increases in sperm progressive motility. The effects of tachykinins were antagonized by the NK(1) receptor-selective antagonist SR 140333, the NK(2) receptor-selective antagonist, SR 48968 and, to a lesser extent, also by the NK(3) receptor-selective antagonist SR 142801. Immunocytochemistry studies showed expression of the NK(1), NK(2) and NK(3) tachykinin receptor proteins in spermatozoa with different major sites of localization for each receptor. Western blot analysis confirmed the presence of tachykinin receptors in sperm cell homogenates. RT-PCR demonstrated expression of the genes that encode SP/NKA (TAC1), NKB (TAC3) and hHK-1 (TAC4) but not the genes TACR1, TACR2 and TACR3 encoding NK(1), NK(2) and NK(3) receptors, respectively. CONCLUSIONS: These results show for the first time that the NK(1), NK(2) and NK(3) tachykinin receptor proteins are present in human spermatozoa. Our findings suggest that tachykinins, probably acting through these three tachykinin receptors, play a role in the regulation of human sperm motility.     

Repeated exposure to low levels of sulfur dioxide (SO2) enhances the development of ovalbumin-induced asthmatic reactions in guinea pigs.

BACKGROUND: Sulfur dioxide (SO2) is one of the major air pollutants. It is known to aggravate asthma symptoms in human beings, but few studies have focused on the effects of SO2 upon the development of bronchial asthma in animal models. OBJECTIVE: This study was undertaken to evaluate the role of SO2 upon the development of ovalbumin (OA)-induced asthmatic reactions in guinea pigs. METHODS: Guinea pigs were divided into four groups: (1) OA- and SO2-exposed group (n = 12), (2) SO2-exposed group (n = 12), (3) OA-exposed group (n = 11), and (4) saline-exposed group (n = 7). Guinea pigs of the first and second groups were exposed to 0.1 ppm SO2 for 5 hours a day on 5 consecutive days. Guinea pigs in the first and third groups inhaled 0.1% OA aerosols for 45 minutes a day on days 3, 4, and 5. One week after the sensitization procedure, all the guinea pigs underwent bronchial challenge with 1.0% OA aerosols, using unrestricted whole-body plethysmography. Bronchoalveolar lavage and histopathologic examination were performed 24 hours after the bronchial challenge. RESULTS: Increases in enhanced pause (Penh), as an index of airway obstruction, after the bronchial challenge was significantly higher in OA- and SO2-exposed group (group 1) than the other groups (P < .05, respectively). Eosinophil counts in bronchoalveolar lavage fluids were also significantly higher in group 1 than in the other groups (P < .05, respectively). Histopathologic findings of bronchial and lung tissue in the group 1 showed an infiltration of inflammatory cells, bronchiolar epithelial damage, and mucus and cell plug in the lumen, but no significant abnormalities were observed in the other groups. CONCLUSIONS: These results indicate that repeated exposure to low levels of sulfur dioxide may enhance the development of ovalbumin-induced asthmatic reactions in guinea pigs.     

Involvement of thromboxane A2 and peptide leukotrienes in early and late phase nasal blockage in a guinea pig model of allergic rhinitis

OBJECTIVE AND DESIGN: We investigated the effects of the thromboxane (TX) A2 antagonist seratrodast, the peptide leukotriene (p-LT) antagonist pranlukast, the antihistaminic drug terfenadine and the glucocorticoid dexamethasone on antigen-induced sneezing, biphasic nasal blockage and nasal hyperresponsiveness to histamine using a guinea pig model of allergic rhinitis. SUBJECTS: Male Hartley guinea pigs were used. TREATMENT: Intranasally sensitized guinea pigs were challenged once every week for 13 weeks by inhalation of Japanese cedar pollen as the antigen. Dexamethasone and other agents were administered orally 3 and 1 h, respectively, before the 4th, 6th and 13th challenge. METHODS: Sneezing frequency and the change in specific airway resistance (sRaw) were measured at these challenges. Two days after the 13th challenge, nasal responsiveness to histamine was evaluated by measuring sRaw after intranasal instillation of increasing doses of histamine. Moreover, the levels of TXB2, p-LTs and histamine were estimated in nasal cavity lavage fluid (NCLF) collected at the 13th challenge. RESULTS: Only terfenadine (10 mg/kg) significantly inhibited sneezing at any challenge time. Seratrodast (3 and 10 mg/ kg), pranlukast (30 mg/kg) and dexamethasone (10 mg/kg), but not terfenadine, suppressed both the early and late phase elevation of sRaw (biphasic nasal blockage), although the degree of inhibition on the early phase response varied with the challenge time. In contrast, the development of nasal hyperresponsiveness to histamine was inhibited by only dexamethasone. Furthermore, biphasic increases in TXB2, p-LTs and histamine in NCLF were observed after the challenge in sensitized animals. CONCLUSIONS: These results suggest that TXA2 and p-LTs, but not histamine, play important roles in both the early and the late phase nasal blockage in this model of allergic rhinitis.     

Adenosine receptor subtypes in the airways responses to 5'-adenosine monophosphate inhalation of sensitized guinea-pigs

Background Endogenous adenosine levels are raised in the lungs during asthma attacks. 5′‐adenosine monophosphate (5′‐AMP) inhalation in asthmatics causes bronchoconstriction and in sensitized guinea‐pigs induces early (EAR) and late asthmatic responses (LAR), airway hyper‐reactivity (AHR) and inflammatory cell recruitment to the lungs. Objective The aim of this study was to investigate the roles of A₁, A_2A, A_2B and A₃ adenosine receptors in these responses to inhaled 5′‐AMP in sensitized guinea‐pigs. Comparisons were made with the effect of dexamethasone treatment on 5′‐AMP‐induced responses. Methods Functional airways responses to inhaled 5′‐AMP (3 and 300 mm ) of actively sensitized, conscious guinea‐pigs were determined by whole‐body plethysmography following administration of selective adenosine receptor antagonists or their vehicles. AHR to inhaled histamine (1 mm ) and inflammatory cell influx in bronchoalveolar lavage fluid were determined. Results 5′‐AMP at 3 mm caused an immediate bronchoconstriction (EAR), whereas 300 mm caused bronchodilatation. Both responses were followed at 6 h by a LAR, together with inflammatory cell influx and AHR to histamine. The A_2A receptor antagonist, ZM241385, further enhanced cell influx after 5′‐AMP inhalation (3 and 300 mm ), and blocked the immediate bronchodilator response to 300 mm 5′‐AMP, exposing an EAR. The A_2B receptor antagonist, MRS1706 (in the presence of ZM241385), inhibited the LAR, AHR and cell influx, following inhalation of 5′‐AMP (300 mm ). The A₃ receptor antagonist, MRS1220, inhibited 5′‐AMP‐induced inflammatory cell influx. The A₁ receptor antagonist, DPCPX (in the presence of ZM241385), inhibited the EAR following 5′‐AMP inhalation (300 mm ). Dexamethasone inhibited the LAR, AHR and cell influx following inhalation of 5′‐AMP (300 mm ). Conclusion All four adenosine receptor subtypes play various roles in the airways responses to inhaled 5′‐AMP in sensitized guinea‐pigs.     

Antagonism by NKP608 of substance P-induced plasma protein exudation in a novel preparation of perfused trachea in rats and guinea-pigs in vivo

OBJECTIVE: To examine whether NKP608, a novel 1-benzoyl-2-benzyl-4-aminopiperidine NK1 receptor antagonist, inhibits substance P (SP)-induced airway plasma protein exudation in vivo. MATERIAL: Anaesthetised English shorthair guinea-pigs and Wistar rats. TREATMENT: Tachykinin peptides were applied topically onto the trachea and antagonists administered intravenously. METHODS: Tracheal segments isolated in situ were perfused with saline and plasma-derived protein assayed in the perfusate. RESULTS: SP (1 microM) caused plasma protein exudation, which was abolished by an NK1 antagonist (RP 67580,1.75 micromol/kg) but unaffected by an NK2 antagonist (SR 48968, 1.75 micromol/ kg) indicating the response is NK1-receptor-mediated. This was confirmed with a response to an NK1 agonist ([Sar9, Met(O2)11]-SP, 1 microM) but none to an NK2 agonist ([betaAla8]-neurokinin A(4-10), 1 microM). NKP608 inhibited SP responses with estimated ID50 values (micromol/kg) of 0.0044 (guinea-pigs) and 0.19 (rats). CONCLUSIONS: NKP608 is an antagonist in vivo of NK1 receptor-induced tracheal plasma protein exudation and is more potent in guinea-pigs than rats.