Potentiation by viral respiratory infection of ovalbumin-induced guinea-pig tracheal hyperresponsiveness: role for tachykinins

Human parainfluenza type 3 virus impairs the efficacy of glucocorticoids to limit allergy-induced pulmonary inflammation in guinea-pigs

Viral exacerbations of allergen-induced pulmonary inflammation in pre-clinical models reportedly reduce the efficacy of glucocorticoids to limit pulmonary inflammation and airways hyper-responsiveness to inhaled spasmogens. However, exacerbations of airway obstruction induced by allergen challenge have not yet been studied. hPIV-3 (human parainfluenza type 3 virus) inoculation of guinea-pigs increased inflammatory cell counts in BAL (bronchoalveolar lavage) fluid and caused hyper-responsiveness to inhaled histamine. Both responses were abolished by treatment with either dexamethasone (20 mg/kg of body weight, subcutaneous, once a day) or fluticasone propionate (a 0.5 mg/ml solution aerosolized and inhaled over 15 min, twice a day). In ovalbumin-sensitized guinea-pigs, allergen (ovalbumin) challenge caused two phases of airway obstruction [measured as changes in sGaw (specific airways conductance) using whole body plethysmography]: an immediate phase lasting between 4 and 6 h and a late phase at about 7 h. The late phase, airway hyper-responsiveness to histamine and inflammatory cell counts in BAL were all significantly reduced by either glucocorticoid. Inoculation of guinea-pigs sensitized to ovalbumin with hPIV-3 transformed the allergen-induced airway obstruction from two transient phases into a single sustained response lasting up to 12 h. This exacerbated airway obstruction and airway hyper-responsiveness to histamine were unaffected by treatment with either glucocorticoid whereas inflammatory cell counts in BAL were only partially inhibited. Virus- or allergen-induced pulmonary inflammation, individually, are glucocorticoid-sensitive, but in combination generate a phenotype where glucocorticoid efficacy is impaired. This suggests that during respiratory virus infection, glucocorticoids might be less effective in limiting pulmonary inflammation associated with asthma.

Neurogenic airway inflammation induced by repeated intra-esophageal instillation of HCl in guinea pigs

This study was conducted to investigate if repeated intra-esophageal acid administrations may induce neurogenic inflammation in the airways and nodose ganglion in a guinea pig model. Guinea pigs were sedated and perfused with 0.1 N HCl in the distal esophagus via a nasoesophageal catheter for 14 consecutive days. Substance P (SP), neurokinin A (NKA), neurokinin B (NKB), and calcitonin gene-related peptide concentration were measured by ELISA or radioimmunoassay. Neuropeptide expression in the airways and nodose ganglion was detected by immunohistochemistry and assessed semi-quantitatively. Inflammation was found in the trachea and bronchi. There was a threefold increase in substance P concentration in the trachea, main bronchi, and lung homogenate and a twofold increase in NKA and NKB concentration in the main bronchi, lung homogenate, and bronchial alveolus lavage fluid, respectively. The SP and NKA expressions in the airways and nodose ganglion were also significantly increased. Chronic intra-esophageal acid instillation induces significant neurogenic inflammation in the airways and nodose ganglion in the vagus nerve in guinea pigs.

Involvement of preprotachykinin A gene-encoded peptides and the neurokinin 1 receptor in endotoxin-induced murine airway inflammation

Tachykinins encoded by the preprotachykinin A (TAC1) gene such as substance P (SP) and neurokinin A (NKA) are involved in neurogenic inflammatory processes via predominantly neurokinins 1 and 2 (NK1 and NK2) receptor activation, respectively. Endokinins and hemokinins encoded by the TAC4 gene also have remarkable selectivity and potency for the NK1 receptors and might participate in inflammatory cell functions. The aim of the present study was to investigate endotoxin-induced airway inflammation and consequent bronchial hyper-reactivity in TAC1(-/-), NK1(-/-) and also in double knockout (TAC1(-/-)/NK1(-/-)) mice. Sub-acute interstitial lung inflammation was evoked by intranasal Escherichia coli lipopolysaccharide (LPS) in the knockout mice and their wildtype C57BL/6 counterparts 24 h before measurement. Respiratory parameters were measured with unrestrained whole body plethysmography. Bronchoconstriction was induced by inhalation of the muscarinic receptor agonist carbachol and Penh (enhanced pause) correlating with airway resistance was calculated. Lung interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured with ELISA. Histological evaluation was performed and a composite morphological score was determined. Myeloperoxidase (MPO) activity in the lung was measured with spectrophotometry to quantify the number of infiltrating neutrophils/macrophages. Airway hyper-reactivity was significantly reduced in the TAC1(-/-) as well as the TAC1(-/-)/NK1(-/-) groups. However, LPS-induced histological inflammatory changes (perivascular/peribronchial oedema, neutrophil infiltration and goblet cell hyperplasia), MPO activity and TNF-alpha concentration were markedly diminished only in TAC1(-/-) mice. Interestingly, the concentrations of both cytokines, IL-1beta and TNF-alpha, were significantly greater in the NK1(-/-) group. These data clearly demonstrated on the basis of histology, MPO and cytokine measurements that TAC1 gene-derived tachykinins, SP and NKA, play a significant role in the development of endotoxin-induced murine airway inflammation, but not solely via NK1 receptor activation. However, in inflammatory bronchial hyper-responsiveness other tachykinins, such as hemokinin-1 acting through NK1 receptors also might be involved.

Role of capsaicin-sensitive afferents and sensory neuropeptides in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity in the mouse

Substance P (SP) and calcitonin gene-related peptide (CGRP) released from capsaicin-sensitive afferents induce neurogenic inflammation via NK(1), NK(2) and CGRP1 receptor activation. This study examines the role of capsaicin-sensitive fibres and sensory neuropeptides in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity with functional, morphological and biochemical techniques in mice. Carbachol-induced bronchoconstriction was measured with whole body plethysmography 24 h after intranasal lipopolysaccharide administration. SP and CGRP were determined with radioimmunoassay, myeloperoxidase activity with spectrophotometry, interleukin-1beta with ELISA and histopathological changes with semiquantitative scoring from lung samples. Treatments with resiniferatoxin for selective destruction of capsaicin-sensitive afferents, NK(1) antagonist SR 140333, NK(2) antagonist SR 48968, their combination, or CGRP1 receptor antagonist CGRP(8-37) were performed. Lipopolysaccharide significantly increased lung SP and CGRP concentrations, which was prevented by resiniferatoxin pretreatment. Resiniferatoxin-desensitization markedly enhanced inflammation, but decreased bronchoconstriction. CGRP(8-37) or combination of SR 140333 and SR 48968 diminished neutrophil accumulation, MPO levels and IL-1beta production, airway hyperresponsiveness was inhibited only by SR 48968. This is the first evidence that capsaicin-sensitive afferents exert a protective role in endotoxin-induced airway inflammation, but contribute to increased bronchoconstriction. Activation of CGRP1 receptors or NK(1)+NK(2) receptors participate in granulocyte accumulation, but NK(2) receptors play predominant role in enhanced airway resistance.

Effects of capsaicin on visceral smooth muscle: a valuable tool for sensory neurotransmitter identification

Studying the visceral effects of the sensory stimulant capsaicin is a useful and relatively simple tool of neurotransmitter identification and has been used for this purpose for approximately 25 years in the authors' and other laboratories. We believe that conclusions drawn from experiments on visceral preparations may have an impact on studies dealing with the central endings of primary afferent neurons, i.e. research on nociception at the spinal level. The present review concentrates on the effects of capsaicin--through the transient receptor potential vanilloid receptor type 1 (TRPV1) receptor--on innervated gastrointestinal, respiratory and genitourinary smooth muscle preparations. Tachykinins and calcitonin gene-related peptide (CGRP) are the most widely accepted transmitters to mediate "local efferent" effects of capsaicin-sensitive nerves in tissues taken from animals. Studies more and more frequently indicate a supra-additive interaction of various types of tachykinin receptors (tachykinin NK(1), NK(2), NK(3) receptors) in the excitatory effects of capsaicin. There is also evidence for a mediating role of ATP, acting on P(2) purinoceptors. Non-specific inhibitory actions of capsaicin-like drugs have to be taken into consideration while designing experiments with these drugs. Results obtained on human tissues may be sharply different from those of animal preparations. Capsaicin potently inhibits tone and movements of human intestinal preparations, an effect mediated by nitric oxide (NO) and/or vasoactive intestinal polypeptide.

Neurogenic mechanisms in bronchial inflammatory diseases

Neurogenic inflammation encompasses the release of neuropeptides from airway nerves leading to inflammatory effects. This neurogenic inflammatory response of the airways can be initiated by exogenous irritants such as cigarette smoke or gases and is characterized by a bi-directional linkage between airway nerves and airway inflammation. The event of neurogenic inflammation may participate in the development and progression of chronic inflammatory airway diseases such as allergic asthma or chronic obstructive pulmonary disease (COPD). The molecular mechanisms underlying neurogenic inflammation are orchestrated by a large number of neuropeptides including tachykinins such as substance P and neurokinin A, or calcitonin gene-related peptide. Also, other biologically active peptides such as neuropeptide tyrosine, vasoactive intestinal polypeptide or endogenous opioids may modulate the inflammatory response and recently, novel tachykinins such as virokinin and hemokinins were identified. Whereas the different aspects of neurogenic inflammation have been studied in detail in laboratory animal models, only little is known about the role of airway neurogenic inflammation in human diseases. However, different functional properties of airway nerves may be used as targets for future therapeutic strategies and recent clinical data indicates that novel dual receptor antagonists may be relevant new drugs for bronchial asthma or COPD.

Vanilloid receptor activation by 2- and 10-microm particles induces responses leading to apoptosis in human airway epithelial cells

Exposure to airborne particulate matter (PM) is associated with increased mortality and morbidity. It has been previously shown that PMs and synthetic particles (PC10 and PC2) that have similar characteristics to PMs induced depolarizing currents and increases in intracellular calcium ([Ca2+]i) in capsaicin- and acid-sensitive sensory neurons and in TRPV1-expressing HEK 293 cells. To determine whether such mechanisms also underlie PM-induced toxicity in epithelial cells lining the human airways, we tested the responses of PCs on BEAS-2B (immortalized human bronchial epithelial cells), NHBE (normal human bronchial/tracheal epithelial cells), and SAEC (normal human small airway epithelial cells from the distal airways). RT-PCR revealed that all these cell types expressed TRPV1 (VR1), ASIC1a, and ASIC3 subunits of proton-gated ion channels. Calcium imaging studies revealed that in all three cell types approximately 30% were activated by both capsaicin and acid. In these cells, PCs induced an increase in [Ca2+]i that was inhibited by capsazepine, a TRPV1 antagonist, and/or by amiloride, an ASIC antagonist. The capsazepine-sensitive contribution to PC-induced increases in [Ca2+]i was approximately 70%. Measurements of apoptosis revealed that exposure to PCs induced a time-dependent increase in the number of apoptotic cells. After incubation for 24 (PC10) or 48 h (PC2) approximately 60% of these cells were apoptotic. Pretreatment with capsazepine as well as removal of external calcium completely (approximately 100%) prevented PC-induced apoptosis. These data suggest that pharmacological inhibition of calcium-permeable vanilloid receptors could be used to prevent some of the pathological actions of PMs.

Neurogenic inflammation and particulate matter (PM) air pollutants

Exposure to a class of airborne pollutants known as particulate matter (PM) is an environmental health risk of global proportions. PM is thought to initiate and/or exacerbate respiratory disorders, such as asthma and airway hyper-responsiveness and is epidemiologically associated with causing death in the elderly and those with pre-existing respiratory, or cardiopulmonary disease. Plausible mechanisms of action to explain PM inflammation and its susceptible sub-population component are lacking. This review describes a series of published studies which indicate that PM initiates airway inflammation through sensory neural pathways, specifically by activation of capsaicin-sensitive vanilloid (e.g. VRI) irritant receptors. These acid-sensitive receptors are located on the sensory C nerve fibers that innervate the airways as well as on various immune and non-immune airway target cells. The activation of these receptors results in the release of neuropeptides from the sensory terminals that innervate the airways. Their interactions with airway target cells, result in signs of inflammation (e.g. bronchoconstriction, vasodilation, histamine release, mucous secretion etc.). Our data have linked the activation of the VR1 receptors to the surface charge carried on the colloidal particulates which constitute PM pollution. Related studies have examined how genetic and non-genetic factors modify the sensitivity of these irritant receptors and enhance the inflammatory responsiveness to PM. In summary, this review proposes a mechanism by which neurogenic elements initiate and sustain PM-mediated airway inflammation. Although neurogenic influences have been appreciated in normal airway homeostasis, they have not, until now, been associated with PM toxicity. The sensitivity of the sensory nervous system to irritants and its interactions with pulmonary target tissues, should encourage neuroscientists to explore the relevance of neurogenic influences to toxic disorders involving other peripheral target systems.

Tachykinins and neuro-immune interactions in asthma

Excitatory non-adrenergic-non-cholinergic neuropeptides, such as the tachykinins substance P and neurokinin A, and its receptors are present in human and animal airways. Tachykinins are biologically active at extremely low concentrations. These peptides can cause potent inflammatory effects and can affect airway function in a way that resembles features of asthma. Local release of tachykinins affects blood vessels (vasodilatation and increased vascular permeability) and bronchial smooth muscle (bronchoconstrition and hyperresponsiveness). Neuropeptide research has revealed that tachykinins also play an important modulatory role in immune reactions. Tachykinins stimulate immune cells, such as mast cells, lymphocytes, and macrophages and are chemotactic for neutrophils and eosinophils. Vice versa, a range of immune cell mediators can also induce the release of tachykinins from excitatory NANC nerve endings in the airways. In the last 20 years, significant advances have been made in investigations of the interaction between immune cells and nervous systems in chronic inflammatory diseases such as asthma.

Neurogenic inflammation in the airways

Release of neuropeptides, including tachykinins and calcitonin gene-related peptide, from sensory nerves via an axon or local reflex may have inflammatory effects in the airways. This neurogenic inflammation may be initiated by activation of sensory nerves by inflammatory mediators and irritants. Neurogenic inflammation is well developed in rodents and may contribute to the inflammatory response to allergens, infections and irritants in animal models. However, the role of neurogenic inflammation in airway inflammatory diseases, such as asthma and COPD is still uncertain as there is little direct evidence for the involvement of sensory neuropeptides in human airways. Initial clinical studies using strategies to block neurogenic inflammation have not been encouraging, but it is important to study more severe forms of airway disease in more prolonged studies in the future to explore the role of neurogenic inflammation.

Excitatory non-adrenergic-non-cholinergic neuropeptides: key players in asthma

Professor David de Wied first introduced the term 'neuropeptides' at the end of 1971. Later peptide hormones and their fragments, endogenous opioid (morphine-like) peptides and a large number of other biogenic peptides became classified as neuropeptides. All of these peptides are united by a number of common features including their origin (nervous system and peptide-secreting cells found in various organs such as skin, gut, lungs), biosynthesis, secretion, metabolism, and enormous effectiveness. Neuropeptides are biologically active at extremely low concentrations. The past decade, neuropeptide research has revealed that neuropeptides also participate strongly in immune reactions. The neuro-immune concept has opened up a whole new research area. In the last 20 years, significant advances have been made in investigations of the interaction between immune and nervous systems in chronic inflammatory diseases such as asthma. The goal of this review is to bring together the functional relevance of excitatory non-adrenergic-non-cholinergic (NANC) nerves and the interaction with the immune system in asthma.

The role of respiratory viruses in acute and chronic asthma

Respiratory infections can have dual effects related to asthma. First, there is increasing evidence that severe infections with RSV and PIV in infancy can alter lung development and physiology to increase the risks of subsequent wheezing and asthma. Second, infections with common cold viruses and influenza commonly precipitate wheezing symptoms in children and adults who already have established asthma, and RV appears to be the most important virus in producing exacerbations of the disease. The principal mechanisms by which this occurs appears to be viral replication in epithelial cells, triggering a cascade of inflammation involving granulocytes, macrophages, T cells, and secreted cytokines and mediators. The inflammatory process, although essential to clear the infection, augments pre-existing airway inflammation in asthma, leading to increased airway obstruction and lower respiratory tract symptoms. Greater understanding of virus-induced changes in inflammation and corresponding changes in airway physiology may lead to new therapeutic approaches to the treatment and prevention of virus-induced airway dysfunction.

Virus- and bradykinin-induced airway hyperresponsiveness in guinea pigs

The involvement of bradykinin in virus-induced airway hyperresponsiveness (AHR) in guinea pig airways in vivo was determined with the B(2)-receptor antagonist Hoe 140. The efficacy of Hoe 140 treatment was assessed through its effect on the bradykinin-induced (up to 2.5 microgram/100 g B.W. administered intravenously) decrease in blood pressure (BP). Hoe 140 (0.1 micromol/kg), administered subcutaneously twice a day for 5 d almost completely blocked bradykinin-induced changes in BP. Four days after parainfluenza-3 (PI-3) virus infection, guinea pigs showed AHR; excessive airway contraction was found with histamine-receptor stimulation. This hyperresponsiveness was completely inhibited by pretreatment with Hoe 140 (0.1 micromol/kg) administered subcutaneously twice a day for five consecutive days, starting 1 d before virus inoculation. Interestingly, nebulized delivery of bradykinin itself to captopril-treated animals induced an AHR comparable to that observed in virus-treated guinea pigs. Viral infection also caused influx of bronchoalveolar cells into the lungs. Both histologic examinations and lung lavage experiments showed that this cell influx could not be inhibited by pretreatment with Hoe 140. In summary, the results of the study show that bradykinin is involved in a cascade of events leading to AHR after a viral infection in guinea pigs, without affecting bronchoalveolar cell influx.

Particulate matter initiates inflammatory cytokine release by activation of capsaicin and acid receptors in a human bronchial epithelial cell line

Recent experiments have shown that human bronchial epithelial cells (i.e., BEAS-2B) release pro-inflammatory cytokines (i.e., IL-6 and TNFalpha) in a receptor-mediated fashion in response to the neuropeptides, substance P (SP), calcitonin gene-related protein (CGRP), and the prototype botanical irritant capsaicin. In the present experiments, we examined the relevance of these receptors to particulate matter (PM)-associated cellular inflammation. BEAS-2B cells, exposed to residual oil fly ash particles (ROFA), responded with an immediate (<30 s) increase in intracellular calcium levels ([Ca2+]i), increases of key inflammatory cytokine transcripts (i.e., IL-6, IL-8, TNFalpha) within 2 h exposure, and subsequent release of IL-6 and IL-8 cytokine protein after 4 h exposure. Pretreatment of BEAS-2B cells with pharmacological antagonists selective for the SP or CGRP receptors reduced the ROFA-stimulated IL-6 cytokine production by approximately 25 and 50%, respectively. However, pretreatment of these cells with capsazepine (CPZ), an antagonist for capsaicin (i.e., vanilloid) receptors, inhibited the immediate increases in [Ca2+]i, diminished transcript (i.e., IL-6, IL-8, TNFalpha) levels and reduced IL-6 cytokine release to control levels. BEAS-2B cells exposed to ROFA in calcium-free media failed to demonstrate increases of [Ca2+]i and showed reduced levels of cytokine transcript (i.e., IL-6, IL-8, TNFalpha) and IL-6 release, suggesting that ROFA-stimulated cytokine formation was partially dependent on extracellular calcium sources. A final set of experiments compared the inflammatory properties of the soluble and acidic insoluble components of ROFA. BEAS-2B cells, exposed to ROFA or ROFA that had been filtered through a 0.2-micrometer pore filter, produced equivocal IL-6. BEAS-2B cells exposed to pH 5.0 media for 15 min released moderate amounts of IL-6, 4 h later. This cytokine release could be blocked by amiloride, a pH receptor antagonist, but not by CPZ. BEAS-2B cells, pretreated with amiloride before ROFA exposure, showed a partial (approximately 25%) reduction of IL-6. Together, these data indicate that the acidic, soluble components of ROFA initiate cytokine release in BEAS-2B cells through activation of both capsaicin- and pH-sensitive irritant receptors.

Airway hyperresponsiveness: first eosinophils and then neuropeptides

Airway hyperreactivity to bronchoconstrictor mediators is a main characteristic in the majority of asthmatic patients and correlates well with the severity of the disease. The airways of asthmatic patients are characterized by an inflammatory state resulting in activation of lung tissue cells and attraction and infiltration of leukocytes from the blood. The accumulation of eosinophilic leukocytes is a prominent feature of inflammatory reactions that occurs in allergic asthma. The increase in number of eosinophils is important since it correlates in time with an increase in bronchial hyperresponsiveness. Viral respiratory infections can also induce eosinophilia and airway hyperresponsiveness in humans and animals and can worsen asthmatic reactions. This report reviews current opinions on the relationship between inflammation-induced eosinophil accumulation/activation and the development of airway hyperresponsiveness and the possible role for sensory neuropeptides in this process. Firstly, CC chemokines play an important role in allergic airway inflammation and respiratory viral infections leading to eosinophil recruitment. Secondly, it can be concluded that IL5 is involved in the development in airway hyperresponsiveness. IL5 has profound effects on eosinophils as promoter of growth, differentiation and proliferation, chemoattractant, activator and primer. However, it is conceivable that in animal models for allergic asthma besides IL5 other regulatory mediators may be involved in eosinophil migration and activation in the lung, which in turn will lead to airway hyperresponsiveness. Recent data support the possible role of eotaxin and its eosinophil-specific receptor CCR-3 in eosinophil chemotaxis and activation in allergic asthma. Moreover, it is suggested that the development of airway eosinophilia in vivo involves a two-step mechanism, elicited by eotaxin and IL5. The precise mechanism by which eosinophils induce bronchial hyperresponsiveness is at present unknown. Sensory neuropeptides could be important mediators in this process, since it has been demonstrated that airway nerves are surrounded by and infiltrated with eosinophils after antigen challenge. Sensory neuropeptides could be the final, more downstream, common pathway after eosinophil infiltration and activation in inducing airway hyperresponsiveness due to allergen inhalation or respiratory viral infections. In conclusion, in the process of the development of airway hyperresponsiveness observed during viral infections or in allergic asthma, the IL5/eotaxin-induced infiltration and activation of eosinophils in the airways is evident. Following this step, eosinophil-derived inflammatory mediators will induce the release of sensory neuropeptides (possibly NK2-receptor activating tachykinins) which in turn will lead to airway hyperresponsiveness.

Role for neurokinin-2 receptor in interleukin-5-induced airway hyperresponsiveness but not eosinophilia in guinea pigs

In the guinea pig, interleukin-5 (IL-5) has been shown to induce airway hyperresponsiveness as well as eosinophilia, which are important symptoms in asthma. IL-5 seems to be a critical cytokine since it selectively affects eosinophil functions. The mechanism of action by which IL-5 leads to airway hyperresponsiveness may be important for our understanding of the pathogenesis of asthma. Neurogenic inflammation, which is mediated by nonadrenergic noncholinergic nerves (NANC), may play a role in the IL-5-induced effects in guinea pig airways. In this study, the role of neuropeptides in the IL-5-induced airway hyperresponsiveness and eosinophilia in the guinea pig was examined using selective neurokinin receptor antagonists. Intra-airway application of IL-5 (1 microgram, twice) induces a selective eosinophil migration (control: 12 [8-22] x 10(5) cells and IL-5: 90 [67-187] x 10(5) cells, p < 0.05) and activation (control: 6.3 +/- 0.9 ng eosinophil peroxidase [EPO]/ml bronchoalveolar lavage [BAL] fluid and IL-5: 29.3 +/- 4.9 ng EPO/ml BAL fluid, p < 0.05) and a pronounced airway hyperresponsiveness in vivo. The maximal responses to histamine are increased by 160 +/- 16% (p < 0.05) after IL-5. Treatment of guinea pigs with either the nonselective neurokinin (NK)-receptor antagonist, FK224, or the selective NK2-receptor antagonist, SR48968, results in a complete inhibition of the in vivo hyperresponsiveness found after application of IL-5. Vice versa, intra-airway administration of substance P (10 micrograms, twice) results in an airway hyperresponsiveness (increased maximal response after substance P: 166 +/- 15% [p < 0.05]) without inducing migration or activation of eosinophils. All examined NK-receptor antagonists do not influence the IL-5-induced eosinophil accumulation. In addition, no effect of the NK-receptor antagonists is observed on the IL-5-induced eosinophil activation, as determined by BAL fluid EPO levels. The release of NK2-receptor active tachykinins plays an important role in the development of IL-5-induced airway hyperresponsiveness. This feature appears to be a step following eosinophil infiltration and activation since there are no effects on eosinophil function by pretreatment of the used NK-receptor antagonists.