Mechanisms of capsaicin- and lactic acid-induced bronchoconstriction in the newborn dog

Pulmonary function as a limiting factor of middle distance race performance

Exercise induced bronchoconstriction (EIB) is common and underdiagnosed phenomenon of yet largely unknown etiology. This study aimed to estimate prevalence of EIB in response to highly demanding skyscraper race and to test its association with race performance and hypothetical predisposing factors. Healthy participants (26 males, 8 females; 31.5 +/- 6.3 years) from mostly running-based amateur sports were measured for forced expiratory volume in first 1 s (FEV1) before and then repeatedly within 10 min after the completion of the 114 m skyscraper upstairs race. Allergy questionnaire (AQUA) data were collected and post-exercise blood lactate was measured. Over 40% of the participants developed >10% decrement in FEV1 shortly after all-out exercise. While EIB response was not associated with questionnaire-based atopic status, training background, gender, age, anthropometrics, pacing and exertion (estimated from the accumulated blood lactate values), participants exhibiting <10% decrement in FEV1 were faster, especially over the later stages of the race. In conclusion, nearly every other participant of the skyscraper race develops EIB not associated with training, demographic, anthropometric and atopic status, pacing and exertion (estimated from postexercise blood lactate), but the responders (FEV1 decrement >10%) were slower indicative of poorer fitness due to EIB developing during the exercise already.

Paradoxical bronchospasm from benzalkonium chloride (BAC) preservative in albuterol nebulizer solution in a patient with acute severe asthma. A case report and literature review of airway effects of BAC

Nebulized bronchodilator solutions are available in the United States as both nonsterile and sterile-filled products. Sulfites, benzalkonium chloride (BAC), or chlorobutanol are added to nonsterile products to prevent bacterial growth. Bronchoconstriction from inhaled BAC is cumulative, prolonged, and correlates directly with basal airway responsiveness. The multi-dose dropper bottle of albuterol sulfate solution contains 50 μg BAC per/2.5 mg of albuterol, which may be below or at the lower limit of the threshold dose for bronchoconstriction. However, with repeated albuterol nebulization, the effect can be additive and cumulative, often exceeding the bronchoconstriction threshold. We report a case of a 17 years old patient, who received 32 mg of BAC via nebulization over a period of 3.5 days that probably caused persistent bronchospasm evidenced by failure to improve clinically and to increase peak expiratory flow rate (PEFR) from 125 L/min (27% of predicted value) to 300 L/min (68% of predicted value) within 2 hours of withdrawing BAC. The patient's respiratory status and PEFR improved dramatically once the nebulization solution was switched to BAC free lev-albuterol solution. The pediatric providers, particularly the emergency department physicians, intensivists and pulmonologists need to be aware of this rare albeit possible toxicity to the respiratory system caused by BAC used as a preservative in albuterol nebulizer solution.

Molecular mechanism of TRP channels

Transient receptor potential (TRP) channels are cellular sensors for a wide spectrum of physical and chemical stimuli. They are involved in the formation of sight, hearing, touch, smell, taste, temperature, and pain sensation. TRP channels also play fundamental roles in cell signaling and allow the host cell to respond to benign or harmful environmental changes. As TRP channel activation is controlled by very diverse processes and, in many cases, exhibits complex polymodal properties, understanding how each TRP channel responds to its unique forms of activation energy is both crucial and challenging. The past two decades witnessed significant advances in understanding the molecular mechanisms that underlie TRP channels activation. This review focuses on our current understanding of the molecular determinants for TRP channel activation.

Acid-sensing by airway afferent nerves

Inhalation of acid aerosol or aspiration of acid solution evokes a stimulatory effect on airway C-fiber and Aδ afferents, which in turn causes airway irritation and triggers an array of defense reflex responses (e.g., cough, reflex bronchoconstriction, etc.). Tissue acidosis can also occur locally in the respiratory tract as a result of ischemia or inflammation, such as in the airways of asthmatic patients during exacerbation. The action of proton on the airway sensory neurons is generated by activation of two different current species: a transient (rapidly activating and inactivating) current mediated through the acid-sensing ion channels, and a slowly activating and sustained current mediated through the transient receptor potential vanilloid type 1 (TRPV1) receptor. In view of the recent findings that the expression and/or sensitivity of TRPV1 are up-regulated in the airway sensory nerves during chronic inflammatory reaction, the proton-evoked irritant effects on these nerves may play an important part in the manifestation of various symptoms associated with airway inflammatory diseases.

Exaggerated Pressor Response in Relation to Attenuated Muscle Temperature Response during Contraction in Ischemic Heart Failure

It is known that muscle temperature (T_m) increases with exercise. The purpose of this study was to examine if contraction-induced increase in T_m was altered in rats with heart failure (HF) induced by chronic myocardial infraction (MI) as compared with healthy control animals. A temperature probe was inserted in the triceps surae muscle to continuously measure T_m throughout experiments. Static muscle contraction was induced by electrical stimulation of the sciatic nerve for 1 min. As baseline T_m was 34°C, contraction increased temperature by 1.6 ± 0.18°C in nine health control rats and by 1.0 ± 0.15°C in 10 MI rats (P < 0.05 vs. control). Note that there were no differences in developed muscle tension and muscle weight between the two groups. In addition, muscle contraction increased mean arterial pressure by 23 ± 3 mmHg in control rats and by 31 ± 3 mmHg in MI rats (P < 0.05 vs. control). A regression analysis further shows that there is an inverse liner relationship between the pressor response and static contraction-induced increase in T_m. Our data suggest that T_m increase evoked by contraction is impaired in MI rats. The abnormal alteration in T_m likely modifies the reflex cardiovascular responses in MI via mechanisms of temperature-sensitive receptors on muscle afferent nerves.

Airway irritation and cough evoked by acid: from human to ion channel

Inhalation or aspiration of acid solution evokes airway defense responses such as cough and reflex bronchoconstriction, resulting from activation of vagal bronchopulmonary C-fibers and Aδ afferents. The stimulatory effect of hydrogen ion on these sensory nerves is generated by activation of two major types of ion channels expressed in these neurons: a rapidly activating and inactivating current mediated through ASICs, and a slow sustaining current via activation of TRPV1. Recent studies have shown that these acid-evoked responses are elevated during airway inflammatory reaction, revealing the potential convergence of a wide array of inflammatory signaling on these ion channels. Since pH in the airway fluid drops substantially in patients with inflammatory airway diseases, these heightened stimulatory effects of acid on airway sensory nerves may play a part in the manifestation of airway irritation and excessive cough under those pathophysiological conditions.

Apnea of prematurity: pathogenesis and management strategies

Apnea of prematurity (AOP) is a significant clinical problem manifested by an unstable respiratory rhythm reflecting the immaturity of respiratory control systems. This review will address the pathogenesis of and treatment strategies for AOP. Although the neuronal mechanisms leading to apnea are still not well understood, recent decades have provided better insight into the generation of the respiratory rhythm and its modulation in the neonate. Ventilatory responses to hypoxia and hypercarbia are impaired and inhibitory reflexes are exaggerated in the neonate. These unique vulnerabilities predispose the neonate to the development of apnea. Treatment strategies attempt to stabilize the respiratory rhythm. Caffeine remains the primary pharmacological treatment modality and is presumed to work through blockade of adenosine receptors A(1) and A(2). Recent evidences suggest that A(2A) receptors may have a greater role than previously thought. AOP typically resolves with maturation suggesting increased myelination of the brainstem.

Dyspnoea in children. Does development alter the perception of breathlessness?

Dyspnoea, the perception of an unpleasant and/or uncomfortable sensation of breathlessness, offers several physiological, anatomical and teleological analogies with pain. Pain perception has been shown to exist in the newborn, suggesting that dyspnoea may also occur from birth onwards. The perception of breathlessness will be subservient to developmental changes in the behaviour of sensors and lung and muscular receptors implicated in dyspnoea, some of which are known to be active at time of birth. For example, perinatal resetting of the arterial chemoreceptor could lead to transient depression of the dyspnoeic response to hypoxia. However, though early evoked ventilatory responses and peripheral receptor maturation do exist, dyspnoea will only occur if the corresponding central neural circuitry undergoes parallel maturation. Our knowledge of dyspnoea in later childhood is based on a small number of clinical or psychophysical studies, predominantly dealing with asthma and exercise. There is a thus a clear need for systematic assessment of the existence and severity of dyspnoea sensing in younger children that takes into account its role as an alarm mechanism for triggering adaptive and/or protective responses.

Role of TRPV receptors in respiratory diseases

Transient receptor potential vanilloid type channels (TRPVs) are expressed in several cell types in human and animal lungs. Increasing evidence has demonstrated important roles of these cation channels, particularly TRPV1 and TRPV4, in the regulation of airway function. These TRPVs can be activated by a number of endogenous substances (hydrogen ion, certain lipoxygenase products, etc.) and changes in physiological conditions (e.g., temperature, osmolarity, etc.). Activation of these channels can evoke Ca(2+) influx and excitation of the neuron. TRPV1 channels are generally expressed in non-myelinated afferents innervating the airways and lungs, which also contain sensory neuropeptides such as tachykinins. Upon stimulation, these sensory nerves elicit centrally-mediated reflex responses as well as local release of tachykinins, and result in cough, airway irritation, reflex bronchoconstriction and neurogenic inflammation in the airways. Recent studies clearly demonstrated that the excitability of TRPV1 channels is up-regulated by certain autacoids (e.g., prostaglandin E(2), bradykinin) released during airway inflammatory reaction. Under these conditions, the TRPV1 can be activated by a slight increase in airway temperature or tissue acidity. Indirect evidence also suggests that TRPV channels may play a part in the pathogenesis of certain respiratory diseases such as asthma and chronic cough. Therefore, the potential use of TRPV antagonists as a novel therapy for these diseases certainly merits further investigation.

TRPV1 Receptor Mediates Glutamatergic Synaptic Input to Dorsolateral Periaqueductal Gray (dl-PAG) Neurons

The purpose of this study was to determine the role of transient receptor potential vanilloid type 1 (TRPV1) receptor in modulating neuronal activity of the dorsolateral periaqueductal gray (dl-PAG) through excitatory and inhibitory synaptic inputs. First, whole cell voltage-clamp recording was performed to obtain the spontaneous miniature excitatory postsynaptic currents (mEPSCs) and inhibitory postsynaptic currents (mIPSCs) of the dl-PAG neurons. As 1 μM of capsaicin was applied into the perfusion chamber, the frequency of mEPSCs was increased from 3.21 ± 0.49 to 5.64 ± 0.64 Hz ( P < 0.05, n = 12) without altering the amplitude and the decay time constant of mEPSCs. In contrast, capsaicin had no distinct effect on mIPSCs. A specific TRPV1 receptor antagonist, iodo-resiniferatoxin (i-RTX, 300 nM), decreased the frequency of mEPSCs from 3.51 ± 0.29 to 2.01 ± 0.2 Hz ( P < 0.05, n = 8) but did not alter the amplitude and decay time. In addition, i-RTX applied into the chamber abolished the effect of capsaicin on mEPSC of the dl-PAG. In another experiment, spontaneous action potential of the dl-PAG neurons was recorded using whole cell current-clamp methods. Capsaicin significantly elevated the discharge rate of the dl-PAG neurons from 3.03 ± 0.38 to 5.96 ± 0.87 Hz ( n = 8). The increased firing activity was abolished in the presence of glutamate N-methy-d-aspartate (NMDA) and non-NMDA antagonists, 2-amino-5-phosphonopentanoic acid, and 6-cyano-7-nitroquinoxaline-2,3-dione. The results from this study provide the first evidence indicating that activation of TRPV1 receptors increases the neuronal activity of the dl-PAG through selective potentiation of glutamatergic synaptic inputs.

Transduction mechanisms in airway sensory nerves

The induction of action potentials in airway sensory nerves relies on events leading to the opening of cation channels in the nerve terminal membrane and subsequent membrane depolarization. If the membrane depolarization is of sufficient rate and amplitude, action potential initiation will occur. The action potentials are then conducted to the central nervous system, leading to the initiation of various sensations and cardiorespiratory reflexes. Triggering events in airway sensory nerves include mechanical perturbation, inflammatory mediators, pH, temperature, and osmolarity acting through a variety of ionotropic and metabotropic receptors. Action potential initiation can be modulated (positively or negatively) through independent mechanisms caused mainly by autacoids and other metabotropic receptor ligands. Finally, gene expression of sensory nerves can be altered in adult mammals. This neuroplasticity can change the function of sensory nerves and likely involve both neurotrophin and use-dependent mechanisms. Here we provide a brief overview of some of the transduction mechanisms underlying these events.

Attenuation of acid induced oesophagitis in VR-1 deficient mice

BACKGROUND AND AIMS

Activation of the vanilloid receptor subtype 1 (VR-1) results in release of proinflammatory peptides which initiate an inflammatory cascade known as neurogenic inflammation. We investigated its role in an acute model of surgically induced oesophagitis.

METHODS

Oesophagitis was induced by pyloric ligation in wild-type and VR-1 deficient mice. A subset of animals were administered the VR-1 antagonist capsazepine, famotidine, or omeprazole one hour before surgery. Five hours after surgery, myeloperoxidase activity (MPO), histological damage scores, intragastric pH, and immunocytochemical analysis of substance P (SP) receptor endocytosis were determined.

RESULTS

Oesophagitis induced knockout mice exhibited significantly lower levels of MPO activity, histological damage scores, and SP receptor endocytosis than wild-type mice. Inflammatory parameters were significantly reduced by acid inhibition and capsazepine in wild-type mice.

CONCLUSIONS

We conclude that acute acid induced oesophagitis is reduced in animals lacking VR-1. This suggests that acid induced oesophagitis may act through VR-1 and that inhibition of the receptor may reduce inflammation.

Development of mechanics and pulmonary reflexes

The mechanical properties of the respiratory system are paramount in converting neural output into ventilation. The highly compliant chest wall of the newborn results in chest distortion and volume loss during inspiration and, as the chest is also unable to resist the inward recoil of the lung, there is a reduction in lung volume at end expiration (functional residual capacity) and a tendency for alveoli to collapse. Vagal innervation of the lungs and airways is responsible for eliciting various reflexes that result in the dynamic modification of respiratory mechanics and an improvement in ventilation. From the first breath, the newborn increases the frequency of augmented breaths to improve lung compliance and prolongs the expiratory time constant in order to increase the amount of air remaining in the lung at end expiration and help prevent lung collapse. This review examines the respiratory mechanics of the mammalian neonate at birth and during early development together with the vagal reflexes that are responsible for the dynamic modification of respiratory mechanics in order to ensure that effective gas exchange occurs from birth.

Influence of maturation on constrictive response to stimulation of C-fiber afferents in isolated guinea pig airways

We investigated whether the airway constrictive response to stimulation of bronchopulmonary C-fiber afferents is altered during the maturation process. Isometric tension was measured in airway rings isolated from three tracheobronchial locations (intrathoracic trachea and main and hilar bronchi) and compared in mature [M, 407 ± 10 (SE) g body wt, n = 36] and immature (IM, 161 ± 5 g body wt, n = 35) guinea pigs. Our results showed no difference in the ACh (10−5 M)- or KCl (40 mM)-induced contraction between M and IM groups, regardless of the airway location. In sharp contrast, the concentration-response curves of 10−8–10−6 M capsaicin were distinctly lower in IM hilar bronchi; for example, response to the same concentration of capsaicin (10−6 M) was 89.2 ± 15.3% of the response to 10−5 M ACh in IM and 284.7 ± 43.2% in M animals. Similar, but smaller, differences in the bronchoconstrictive response to capsaicin between IM and M groups were also observed in the trachea and main bronchus. Electrical field stimulation induced airway constriction in all three locations in M and IM groups. However, after administration of 10−6 M atropine and 10−6 M propranolol, electrical field stimulation-induced contraction was significantly smaller in the hilar bronchus of IM than M animals, and this difference was not prevented by pretreatment with 5 × 10−5 M indomethacin. Although radioimmunoassay showed no difference in the tissue content of substance P between M and IM airways, the constrictive responses to exogenous substance P and neurokinin A were markedly greater in M airways at all three locations. In conclusion, the constriction of isolated airways evoked by C-fiber stimulation was significantly weaker in the IM guinea pigs, probably because of a less potent effect of tachykinins on the airway smooth muscle.

Muscle pressor reflex: potential role of vanilloid type 1 receptor and acid-sensing ion channel

Reflex cardiovascular responses to muscle contraction are mediated by mechanical and metabolic stimulation of thin muscle afferent fibers. Metabolic stimulants and receptors involved in responses are uncertain. Capsaicin depolarizes thin sensory afferent nerves that have vanilloid type 1 receptors (VR1). Among potential endogenous ligands of thin fibers, H+ has been suggested as a metabolite mediating the reflex muscle response as well as a potential stimulant of VR1. It has also been suggested that acid-sensing ion channels (ASIC) mediate H+, evoking afferent nerve excitation. We have examined the roles of VR1 and ASIC in mediating cardiovascular reflex responses to acid stimulation of muscle afferents in a rat model. In anesthetized rats, injections of capsaicin into the arterial blood supply of triceps surae muscles evoked a biphasic response (n = 6). An initial fall in mean arterial pressure (from baseline of 95.8 +/- 9.5 to 70.4 +/- 4.5 mmHg, P < 0.05 vs. baseline) was followed by an increase (to 131.6 +/- 11.3 mmHg, P < 0.05 vs. baseline). Anandamide (an endogenous substance that activates VR1) induced the same change in blood pressure as did capsaicin. The pressor (but not depressor) component of the response was blocked by capsazepine (a VR1 antagonist) and section of afferent nerves. In decerebrate rats (n = 8), H+ evoked a pressor response that was not blocked by capsazepine but was attenuated by amiloride (an ASIC blocker). In rats (n = 12) pretreated with resiniferatoxin to destroy muscle afferents containing VR1, capsaicin and H+ responses were blunted. We conclude that H+ stimulates ASIC, evoking the reflex response, and that ASIC are likely to be frequently found on afferents containing VR1. The data also suggest that VR1 and ASIC may play a role in processing of muscle afferent signals, evoking the muscle pressor reflex.

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.

Postnatal maturation of vagal respiratory reflexes in preterm and full-term lambs

The postnatal development of ventilatory reflexes originating from bronchopulmonary receptors was assessed in preterm vs. full-term lambs. Ventilation and arterial pressure were repeatedly measured in 10 preterm (gestational age, 132 days) and 7 full-term lambs without sedation from day 1 to day 42. The Hering-Breuer inhibitory reflex (slowly adapting stretch receptors) was assessed by the increase in expiratory time during end-inspiratory occlusion. The pulmonary chemoreflex (C-fiber endings) was assessed by the initial apnea + bradycardia + systemic hypotension and the secondary tachypnea after capsaicin intravenous injection. Results show the following. 1) Premature birth did not modify the maturation of the Hering-Breuer reflex. 2) Whereas a classic pulmonary chemoreflex was observed in the very first hours of life in preterm lambs, the tachypneic component of this reflex was weaker than in full-term lambs on day 1. 3) Premature birth led to a reversed postnatal maturation of this tachypneic response (tendency to increase with postnatal age). Our findings suggest that premature birth in lambs modifies postnatal maturation of the pulmonary chemoreflex.

Mechanisms of acid-induced activation of airway afferent nerve fibres in guinea-pig

The mechanisms underlying the response of airway afferent nerves to low pH were investigated in an isolated guinea-pig airway nerve preparation. Extracellular recordings were made from single jugular or nodose vagal ganglion neurons that projected their sensory fibers into the airways. The airway tissue containing the mechanically sensitive receptive fields was exposed into acidic solutions. Rapid and transient (approximately 3 s) administration of 1 mM citric acid to the receptive field consistently induced action potential discharge in nociceptive C-fibers (41/44) and nodose Adelta fibres (29/30) that are rapidly adapting low threshold mechanosensors (RAR-like fibres). In contrast, citric acid activated only 8/17 high threshold mechanosensitive jugular Adelta fibres. The RAR-like fibres were slightly more sensitive than C-fibres to acidic solutions (pH threshold > 6.7). The RAR-like fibres response to the approximately 3 s acid treatment was not affected by a vanilloid receptor 1 (VR1) antagonist, capsazepine (10 microM), and was rapidly inactivating (action potential discharge terminated before the acid administration was completed). Gradual reduction of pH did not activate the RAR-like fibres even when the pH was reduced to approximately 5.0. The C-fibres responded to the gradual reduction of pH with persistent action potential discharge that was nearly abolished by capsazepine (10 microM) and inhibited by over 70 % with another VR1 antagonist iodo-resiniferatoxin (1 microM). In contrast the C-fibre response to the transient approximately 3 s exposure to pH approximately 5.0 was not affected by the VR1 antagonists. We conclude that activation of guinea-pig airway afferents by low pH is mediated by both slowly and rapidly inactivating mechanisms. We hypothesize that the slowly inactivating mechanism, present in C-fibres but not in RAR-like fibres, is mediated by VR1. The rapidly inactivating mechanism acts independently of VR1, has characteristics similar to acid sensing ion channels (ASICs) and is found in the airway terminals of both C-fibres and RAR-like fibres.

Role of vagal C-fiber afferents in the bronchomotor response to lactic acid in the newborn dog

We addressed the hypothesis that vagal C-fiber afferents and cyclooxygenase products are the mechanisms responsible for lactic acid (LA)-induced bronchoconstriction in the newborn dog. Perineural capsaicin and indomethacin were used to block conduction of vagal C fibers and production of cyclooxygenase products, respectively. Perineural capsaicin eliminated (85%) the increase in lung resistance (Rl; 45 ± 5.6%) due to capsaicin (25 μg/kg), whereas the increase in Rl (54 ± 6.9%) due to LA (0.4 mmol/kg) was only inhibited by 37 ± 4.7% ( P < 0.05). Atropine reduced LA-induced bronchoconstriction (42 ± 2.1%) by an amount similar to that obtained with perineural capsaicin. However, inhibition was significantly increased when atropine was combined with indomethacin (61 ± 2.7%; P < 0.05), implicating cyclooxygenase products in the LA-induced bronchoconstrictor response. We conclude that the mechanisms responsible for LA-induced bronchoconstriction in the newborn are 1) activation of vagal C-fibers, which, through projections to medullary respiratory centers, leads to activation of vagal cholinergic efferents; 2) production of cyclooxygenase products, which cause bronchoconstriction independent of medullary involvement; and 3) an unknown bronchoconstrictor mechanism, putatively tachykinin mediated. On the basis of our data, pharmaceutical targeting of pulmonary afferents would prevent multiple downstream mechanisms that lead to airway narrowing due to inflammatory lung disease.

Respiratory and cardiovascular reflexes elicited by nasal instillation of capsaicin to anesthetized, spontaneously breathing dogs

Cardiopulmonary reflexes elicited by capsaicin (CAPS) instilled into the nasal passages were determined in 6 anesthetized dogs breathing spontaneously. Nasal instillation of CAPS (10 microg/ml, 10 ml) induced: 1) apneic response characterized by an increase in expiration time; 2) bronchoconstrictor response characterized by an increase in lung resistance and a decrease in dynamic compliance; and 3) cardiovascular response characterized by a decrease in heart rate and an increase in arterial blood pressure. These reflex responses to CAPS were attenuated by pretreatment with a higher dose of CAPS (100 microg/ml, 10 ml), suggesting desensitization of CAPS-sensitive endings. These results suggest that marked cardiopulmonary reflexes are produced by nasal CAPS instillation, which may result, at least in part, from stimulation of nasal CAPS-sensitive sensory afferents.

Neuropeptide-induced chemotaxis of eosinophils in pulmonary diseases

Eosinophilic lung diseases include various disease entities, and the incidence of pulmonary infiltration with eosinophilia is on the rise. Because eosinophils, well known as inflammatory cells, respond to peripheral neuropeptides in vitro and in vivo, and these peptides are also present in human airway nerves, their interactions are thought to play a major role in the initiation and perpetuation of inflammatory lung diseases. This article reviews the current literature on eosinophil biology and interactions of these cells with the neuroendocrine system. Also, implications of tachykinins and other neuropeptides in eosinophilic pulmonary diseases is discussed based on recently investigated mechanisms. Eosinophils and sensory nerves most likely influence each other in a two-directional way in the pathogenesis of pulmonary diseases. Although release of sensory neuropeptides is involved in most conditions of airway hyperresponsiveness, increased bronchial resistance, and lung eosinophilia, the role of these nervous system-derived mediators in pulmonary diseases may be underestimated.