Endogenous tachykinins facilitate transmission through parasympathetic ganglia in guinea-pig trachea

Eosinophil and airway nerve interactions in asthma

Airway eosinophils are increased in asthma and are especially abundant around airway nerves. Nerves control bronchoconstiction and in asthma, airway hyperreactivity (where airways contract excessively to inhaled stimuli) develops when eosinophils alter both parasympathetic and sensory nerve function. Eosinophils release major basic protein, which is an antagonist of inhibitory M₂ muscarinic receptors on parasympathetic nerves. Loss of M₂ receptor inhibition potentiates parasympathetic nerve-mediated bronchoconstriction. Eosinophils also increase sensory nerve responsiveness by lowering neurons' activation threshold, stimulating nerve growth, and altering neuropeptide expression. Since sensory nerves activate parasympathetic nerves via a central neuronal reflex, eosinophils' effects on both sensory and parasympathetic nerves potentiate bronchoconstriction. This review explores recent insights into mechanisms and effects of eosinophil and airway nerve interactions in asthma.

Bilateral vagotomy as a tool for determining autonomic involvement in airway responses in mouse models of asthma

This chapter describes the use of bilateral vagotomy as a tool for determining autonomic regulation of airway responses to the exogenous bronchoconstrictor thromboxane mimetic U46619 in an acute model of asthma in the mouse. Mice receive a sensitization of ovalbumin (OVA) and adjuvant followed by 3 days of OVA aerosol to induce allergic airway disease characterized by bronchoalveolar lavage (BAL) eosinophilia, increased mucus production, and elevated IgE and IL-13. Using a small animal ventilator (Flexi-vent) and the forced oscillatory technique fit to the constant phase model of the lung, a variety of features associated with human asthma can be evaluated in mouse models. For example, this protocol describes the methods to evaluate central and peripheral airway mechanics, airway resistance (R aw) and tissue damping (G), and tissue elastance (H) in response to U46619. The contribution of autonomic nerves in this response is determined by severing both the left and right vagus nerves prior to aerosol challenge.

Neuromodulation mediated by the tachykinin NK3-receptor agonist [MePhe7]-neurokinin B in the isolated perfused lung of nonsensitized nonchallenged and ovalbumin-sensitized and -challenged guinea pig

The neuromodulatory action of the tachykinin NK(3)-receptor agonist [MePhe(7)]-neurokinin B ([MePhe(7)]-NKB) was evaluated on vagal stimulation-induced bronchoconstriction in nonsensitized nonchallenged and ovalbumin (OVA)-sensitized and -challenged guinea pig using the isolated perfused lung preparation. Lungs were placed inside a warmed (37°C) glass chamber and suspended from a force displacement transducer (Grass FT-03) with both vagi connected to a stimulating electrode. Isolated lungs were stimulated at a constant voltage (20 V) and pulse duration (5 ms) with electrical stimulation frequencies ranging from 1 to 128 Hz. The authors demonstrated that vagal stimulation produced frequency-dependent bronchoconstriction and [MePhe(7)]-NKB, at a dose (0.1 μM) that does not produce bronchoconstriction by itself, potentiated the vagally induced bronchoconstriction at all frequencies in nonsensitized nonchallenged animals and to a greater extent in OVA-sensitized and -challenged guinea pigs; the potentiations were totally inhibited by the tachykinin NK(3)-receptor antagonist SR 142801 (1 μM). In a second set of experiments, [MePhe(7)]-NKB produced bronchoconstriction in a dose-dependent (1 to 300 μg/mL) manner with similar potencies and maximum responses in nonsensitized nonchallenged (EC(50) = 8.6 ± 1.1 μM; E(Max) = 61.1 ± 3.5 mm Hg) and OVA-sensitized and -challenged (EC(50) = 8.5 ± 1.3 μM; E(Max) = 63.5 ± 3.7 mm Hg) animals. In conclusion, these results demonstrated that [MePhe(7)]-NKB potentiated vagal stimulation-induced bronchoconstriction via the tachykinin NK(3)-receptors and OVA sensitization caused development of airway hyperresponsiveness in these potentiations. However, OVA sensitization had no effect on airway responsiveness of vagal stimulation-and [MePhe(7)]-NKB-induced bronchoconstrictions.

Neurokinin receptors in recurrent airway obstruction: a comparative study of affected and unaffected horses

The purpose of the study was to compare in vitro airway responses to neurokinin A & B (NKA and NKB) and expression of NK-2 receptors in airways of horses affected and unaffected with recurrent airway obstruction (RAO). Neurokinin-A, an inflammatory mediator belonging to the tachykinin family of neuropeptides, causes bronchoconstriction by binding to NK-2 receptors. Neurokinin-B is a lesser-known neuropeptide that acts on NK-3 receptors. Horses were placed into RAO-affected and RAO-unaffected groups based on their history, clinical scoring, and pulmonary function testing. Lung tissue from each lobe was collected for immunohistochemical staining for NK-2 receptors. Cumulative concentration-response relationships were determined on bronchial rings (4-mm wide) collected and prepared from the right diaphragmatic lung lobe to graded concentrations (half log molar concentrations 10(-7)M to 10(-4)M) of NKA and NKB. The results showed that NKA caused significantly greater contraction than NKB in both groups. In RAO-affected horses, both agents produced significantly greater bronchial contractions than those in the RAO-unaffected horses. Immunohistochemical staining showed that the overall NK-2 receptor distribution was significantly increased in bronchial epithelium and smooth muscles of bronchi and pulmonary vessels of RAO-affected than RAO-unaffected horses. The findings indicate that NK-2 receptors are up-regulated in RAO, suggesting that NK-2 receptor antagonists may have some therapeutic value in controlling the progression of airway hyperreactivity in horses affected with RAO.

Interleukin (IL)-1 regulates ozone-enhanced tracheal smooth muscle responsiveness by increasing substance P (SP) production in intrinsic airway neurons of ferret

Exposure to ozone induces airway hyperresponsiveness (AHR) mediated partly by substance P (SP) released from nerve terminals of intrinsic airway neurons. Our recent studies showed that interleukin (IL)-1, an important multifunctional proinflammatory cytokine, increases synthesis and release of SP from intrinsic airway neurons. The purpose of this study is to investigate the possible involvement of endogenous IL-1 in modulating neural responses associated with ozone-enhanced airway responsiveness. Ferrets were exposed to 2ppm ozone or filtered air for 3h. IL-1 in the bronchoalveolar lavage (BAL) fluid was significantly increased in ozone-exposed animals and responses of tracheal smooth muscle to methacholine (MCh) and electrical field stimulation (EFS) were elevated significantly. Both the SP nerve fiber density in tracheal smooth muscle and the number of SP-containing neurons in airway ganglia were significantly increased following ozone exposure. Pretreatment with IL-1 receptor antagonist (IL-1 Ra) significantly diminished ozone-enhanced airway responses to EFS as well as ozone-increased SP in the airway. To selectively investigate intrinsic airway neurons, segments of ferret trachea were maintained in culture conditions for 24h to eliminate extrinsic contributions from sensory nerves. The segments were then exposed to 2ppm ozone in vitro for 3h. The changes of ozone-induced airway responses to MCh and EFS, and the SP levels in airway neurons paralleled those observed with in vivo ozone exposure. The ozone-enhanced airway responses and neuronal SP levels were inhibited by pretreatment with IL-1 Ra. These findings show that IL-1 is released during ozone exposure enhances airway responsiveness by modulating SP expression in airway neurons.

Calcitonin gene-related peptide affects synaptic and membrane properties of bronchial parasympathetic neurons

Calcitonin gene-related peptide (CGRP) is located with substance P in nerve varicosities in close apposition to principal neurons in airway parasympathetic ganglia. Substance P has multiple effects on airway parasympathetic neurons but the role of CGRP is unknown. Using intracellular current clamp recording of ganglionic neurons, stimulation of vagal afferent nerves in the presence of neurokinin receptor antagonists evoked hyperpolarization of the membrane potential which was blocked by the CGRP-1 receptor antagonist, CGRP(8-37). Exogenous application of alpha-CGRP (0.001-0.1 microM) hyperpolarized the membrane potential, which was either blocked or reversed to depolarization in the presence of CGRP(8-37), whereas higher concentrations of alpha-CGRP (1.0-10.0 microM) caused depolarization. Action potential accommodation in phasic-type neurons decreased in the presence of alpha-CGRP (0.1-10 microM). The co-localization of substance P- and CGRP-immunoreactivity was observed in nerve varicosities within ganglia; prolonged exposure to capsaicin in vitro depleted substance P and CGRP immunostaining in nerve varicosities. These results demonstrate that CGRP has multiple effects on the excitability of airway parasympathetic neurons and may alter their activity, ultimately affecting parasympathetic tone in the lower airways.

Alteration of airway neuropeptide expression and development of airway hyperresponsiveness following respiratory syncytial virus infection

The mechanisms by which respiratory syncytial virus (RSV) infection causes airway hyperresponsiveness (AHR) are not fully established. We hypothesized that RSV infection may alter the expression of airway sensory neuropeptides, thereby contributing to the development of altered airway function. BALB/c mice were infected with RSV followed by assessment of airway function, inflammation, and sensory neuropeptide expression. After RSV infection, mice developed significant airway inflammation associated with increased airway resistance to inhaled methacholine and increased tracheal smooth muscle responsiveness to electrical field stimulation. In these animals, substance P expression was markedly increased, whereas calcitonin gene-related peptide (CGRP) expression was decreased in airway tissue. Prophylactic treatment with Sendide, a highly selective antagonist of the neurokinin-1 receptor, or CGRP, but not the CGRP antagonist CGRP(8–37), inhibited the development of airway inflammation and AHR in RSV-infected animals. Therapeutic treatment with CGRP, but not CGRP(8–37) or Sendide, abolished AHR in RSV-infected animals despite increased substance P levels and previously established airway inflammation. These data suggest that RSV-induced airway dysfunction is, at least in part, due to an imbalance in sensory neuropeptide expression in the airways. Restoration of this balance may be beneficial for the treatment of RSV-mediated airway dysfunction.

A Novel Role for Tachykinin Neurokinin-3 Receptors in Regulation of Human Bronchial Ganglia Neurons

The neuropeptide tachykinins and their receptors have been implicated in the pathogenesis of lung disease, although the role of the tachykinin neurokinin-3 receptor has not been elucidated. Using confocal microscopy, we identified tachykinin neurokinin-3 receptors on human bronchial parasympathetic ganglion neurons. Electrophysiologic recordings demonstrated that activation of sensory nerve fibers, either by antidromic stimulation or capsaicin, depolarized these neurons. This response was mimicked by exogenously applied tachykinin neurokinin-3 receptor-selective agonist, senktide analogue, but not significantly by tachykinin neurokinin-1 or neurokinin-2 receptor-selective agonists. Responses to endogenous tachykinins or exogenous selective tachykinin neurokinin-3 receptor activation with senktide analogue were inhibited by the selective tachykinin neurokinin-3 receptor antagonists, SB 223412 or SB 235375. We provide the first evidence that tachykinin neurokinin-3 receptors regulate human bronchial parasympathetic ganglion neurotransmission by activation of a peripheral reflex. This pathway may play a significant role in controlling bronchomotor tone and air flow to the lung.

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.

Greater involvement of neurokinins found in Guinea pig models of severe asthma compared with mild asthma

BACKGROUND

Involvement of neurokinins in asthma has been previously pointed out by several reports. However, the relationship between neurokinins and the severity of asthma has remained unclear. We developed a model of mild asthma (model I) and severe asthma (model II) in guinea pigs, and investigated the function of neurokinins in both models.

METHODS

In models I and II, systemically sensitized guinea pigs were made to inhale ovalbumin once and three times, respectively. Substance P (SP) and neurokinin A (NKA) concentrations in the bronchoalveolar lavage fluid (BALF) were measured in models I and II. Then, the effects of a capsaicin pretreatment, which depletes neurokinins, in both animal models on airway narrowing induced by the last ovalbumin inhalation, airway hyperresponsiveness to inhaled methacholine, and eosinophil accumulation in BALF, were investigated.

RESULTS

SP concentration tended to increase and the NKA concentration increased significantly in model II, but not in model I. Capsaicin pretreatment significantly inhibited the late bronchial response that was observed 2-6 h after the last ovalbumin inhalation, airway hyperresponsiveness and eosinophil accumulation in model II. On the other hand, it had no effects on the responses in model I.

CONCLUSION

It is suggested that the more severe the disease, the greater the involvement of neurokinins.

Substance P released from intrinsic airway neurons contributes to ozone-enhanced airway hyperresponsiveness in ferret trachea

Exposure to ozone (O3) induces airway hyperresponsiveness mediated partly through the release of substance P (SP) from nerve terminals in the airway wall. Although substantial evidence suggests that SP is released by sensory nerves, SP is also present in neurons of airway ganglia. The purpose of this study was to investigate the role of intrinsic airway neurons in O3-enhanced airway responsiveness in ferret trachea. To remove the effects of sensory innervation, segments of ferret trachea were maintained in culture conditions for 24 h before in vitro exposure to 2 parts/million of O3 or air for 1 h. Sensory nerve depletion was confirmed by showing that capsaicin did not affect tracheal smooth muscle responsiveness to cholinergic agonist or contractility responses to electrical field stimulation (EFS). Contractions of isolated tracheal smooth muscle to EFS were significantly increased after in vitro O3 exposure, but the constrictor response to cholinergic agonist was not altered. Pretreatment with CP-99994, an antagonist of the neurokinin 1 receptor, attenuated the increased contraction to EFS after O3 exposure but had no effect in the air exposure group. The number of SP-positive neurons in longitudinal trunk ganglia, the extent of SP innervation to superficial muscular plexus nerve cell bodies, and SP nerve fiber density in tracheal smooth muscle all increased significantly after O3 exposure. The results show that release of SP from intrinsic airway neurons contributes to O3-enhanced tracheal smooth muscle responsiveness by facilitating acetylcholine release from cholinergic nerve terminals.

Interleukin-1beta-induced airway hyperresponsiveness enhances substance P in intrinsic neurons of ferret airway

Interleukin (IL)-1beta causes airway inflammation, enhances airway smooth muscle responsiveness, and alters neurotransmitter expression in sensory, sympathetic, and myenteric neurons. This study examines the role of intrinsic airway neurons in airway hyperresponsiveness (AHR) induced by IL-1beta. Ferrets were instilled intratracheally with IL-1beta (0.3 microg/0.3 ml) or saline (0.3 ml) once daily for 5 days. Tracheal smooth muscle contractility in vitro and substance P (SP) expression in tracheal neurons were assessed. Tracheal smooth muscle reactivity to acetylcholine (ACh) and methacholine (MCh) and smooth muscle contractions to electric field stimulation (EFS) both increased after IL-1beta. The IL-1beta-induced AHR was maintained in tracheal segments cultured for 24 h, a procedure that depletes SP from sensory nerves while maintaining viability of intrinsic airway neurons. Pretreatment with CP-99994, an antagonist of neurokinin 1 receptor, attenuated the IL-1beta-induced hyperreactivity to ACh and MCh and to EFS in cultured tracheal segments. SP-containing neurons in longitudinal trunk, SP innervation of superficial muscular plexus neurons, and SP nerve fiber density in tracheal smooth muscle all increased after treatment with IL-1beta. These results show that IL-1beta-enhanced cholinergic airway smooth muscle contractile responses are mediated by the actions of SP released from intrinsic airway neurons.

Endogenous neurokinins facilitate synaptic transmission in guinea pig airway parasympathetic ganglia

Neurokinin-containing nerve fibers were localized to guinea pig airway parasympathetic ganglia in control tissues but not in tissues pretreated with capsaicin. The purpose of the present study was to determine whether neurokinins, released during axonal reflexes or after antidromic afferent nerve stimulation, modulate ganglionic synaptic neurotransmission. The neurokinin type 3 (NK(3)) receptor antagonists SB-223412 and SR-142801 inhibited vagally mediated cholinergic contractions of bronchi in vitro at stimulation voltages threshold for preganglionic nerve activation but had no effect on vagally mediated contractions evoked at optimal voltage or field stimulation-induced contractions. Intracellular recordings from the ganglia neurons revealed that capsaicin-sensitive nerve stimulation potentiated subsequent preganglionic nerve-evoked fast excitatory postsynaptic potentials. This effect was mimicked by the NK(3) receptor agonist senktide analog and blocked by SB-223412. In situ, senktide analog markedly increased baseline tracheal cholinergic tone, an effect that was reversed by atropine and prevented by vagotomy or SB-223412. Comparable effects of intravenous senktide analog on pulmonary insufflation pressure were observed. These data highlight the important integrative role played by parasympathetic ganglia and indicate that activation of NK(3) receptors in airway ganglia by endogenous neurokinins facilitates synaptic neurotransmission.

Mechanisms of wood smoke-induced increases in nasal airway resistance and reactivity in rats

We investigated the mechanisms of wood smoke-induced increases in nasal airway resistance (RNA) and airway reactivity in anesthetized rats. Delivery of wood smoke into a functionally isolated nasal airway produced an increase in RNA, which was attenuated by CP-96,345 [a tachykinin NK(1) receptor antagonist; (2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-azabicyclo(2.2.2.)-octan-3-amine] or atropine. Additionally, smoke pre-exposure animals displayed a greater amplitude and a longer duration of RNA responses to capsaicin or histamine provocation, as compared to air controls. This enhanced airway reactivity to capsaicin or histamine was largely alleviated by CP-96,345 or atropine. The nasal secretory responses to capsaicin or histamine in smoke pre-exposure animals were similar to those in air controls. We concluded that (1) reflex cholinergic and tachykininergic mechanisms play important roles in wood smoke-induced increases in nasal airway resistance and airway reactivity, and (2) this nasal airway hyperreactivity might not be due to an exaggerated secretory response, but is presumably due to augmented nasal swelling.

On lung nerves and neurogenic injury

Information accumulated in recent years has begun to unveil a previously unsuspected complexity in the innervation of the lungs. We know now that the conducting airways receive a highly redundant supply of vagal motor and sensory fibers; that many of these fibers cross over from the contralateral side of the brain to reach distant portions of the lung, thereby assuring the symmetry and simultaneity of the bronchomotor responses; and that, perhaps in recognition of the different functions and properties of proximal and distal airways, vagal motor fibers have a distinctive segmental distribution. Both sensory and motor neurons serve as the input and output elements of a complex brain stem neuronal network, which integrates the regulation of airway smooth muscle tone into the control of ventilation. This network has a local counterpart in the airway walls, where a heterogeneous population of intrinsic neurons may act not only as a relay for cholinergic stimuli, but also as a local mechanism of inflammatory modulation. The interruption of the nerve supply to the lungs (for instance after lung transplantation) abolishes the integration of bronchomotor and ventilatory activities, and, by increasing airway deformation, may initiate fibroproliferative responses in the airway walls. In addition, the destruction of vagal motor and sensory fibers leaves behind a surviving population of denervated intrinsic neurons, which may act as a disregulated mechanism of inflammatory amplification.

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

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

Role of intrinsic airway neurons in ozone-induced airway hyperresponsiveness in ferret trachea

Exposure to ozone (O(3)) enhances airway responsiveness, which is mediated partly by the release of substance P (SP) from airway neurons. In this study, the role of intrinsic airway neurons in O(3)-induced airway responses was examined. Ferrets were exposed to 2 ppm O(3) or air for 1 h. Reactivity of isolated tracheal smooth muscle to cholinergic agonists was significantly increased after O(3) exposure, as were contractions to electrical field stimulation at 10 Hz. Pretreatment with CP-99994, a neurokinin type 1 receptor antagonist, partially abolished the O(3)-induced reactivity to cholinergic agonists and electrical field stimulation. The O(3)-enhanced airway responses were present in tracheal segments cultured for 24 h, a procedure shown to deplete sensory nerves while maintaining viability of intrinsic airway neurons, and all the enhanced smooth muscle responses were also diminished by CP-99994. Immunocytochemistry showed that the percentage of SP-containing neurons in longitudinal trunk and the percentage of neurons innervated by SP-positive nerve fibers in superficial muscular plexus were significantly increased at 1 h after exposure to O(3). These results suggest that enhanced SP levels in airway ganglia contribute to O(3)-induced airway hyperresponsiveness.

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.

Modulation of acetylcholine release in the guinea-pig trachea by the nitric oxide donor, S-nitroso-N-acetyl-DL-penicillamine (SNAP)

The effects of the nitric oxide (NO) donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) and the NO synthase inhibitor L-N(G)-nitroarginine (L-NOARG) on the electrically evoked [(3)H]-acetylcholine release were studied in an epithelium-free preparation of guinea-pig trachea that had been preincubated with [(3)H]-choline. SNAP (100 and 300 microM) caused small but significant increases of the electrically evoked [(3)H]-acetylcholine release (121+/-4% and 124+/-10% of control). Resting outflow of [(3)H]-ACh was not affected by SNAP. The increase by SNAP was abolished by the specific inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3-alpha]quinoxalin-1-one (ODQ, 1 microM). The facilitatory effect of SNAP (100 and 300 microM) was reversed into inhibition of release (to 74+/-4% and to 78+/-2%) after pretreatment of the trachea with capsaicin (3 microM). ODQ prevented the inhibition. Capsaicin pretreatment alone did not significantly alter the release of [(3)H]-acetylcholine. A significant inhibition by SNAP (100 microM) of [(3)H]-acetylcholine release (78+/-3%) was also seen in the presence of the NK(2) receptor antagonist SR 48968 (30 nM). L-NOARG (10 and 100 microM) significantly enhanced the electrically-evoked smooth muscle contractions, but caused no significant increases of the evoked release from capsaicin pretreated trachea strips. This might indicate that the inhibitory effect of endogenous NO on acetylcholine release is too small to be detected by overflow studies. It is concluded that NO has dual effects on the evoked acetylcholine release. NO enhances release in the absence of modifying drugs, but NO inhibits acetylcholine release after blockade of the NK(2) receptor or after sensory nerve depletion with capsaicin. This suggests that NO and endogenous tachykinins act in series to produce an increase in acetylcholine release.

Substance P-induced airway hyperreactivity is mediated by neuronal M(2) receptor dysfunction

Neuronal muscarinic (M(2)) receptors inhibit release of acetylcholine from the vagus nerves. Hyperreactivity in antigen-challenged guinea pigs is due to blockade of these M(2) autoreceptors by eosinophil major basic protein (MBP) increasing the release of acetylcholine. In vivo, substance P-induced hyperactivity is vagally mediated. Because substance P induces eosinophil degranulation, we tested whether substance P-induced hyperreactivity is mediated by release of MBP and neuronal M(2) receptor dysfunction. Pathogen-free guinea pigs were anesthetized and ventilated. Thirty minutes after intravenous administration of [Sar(9),Met(O(2))(11)]- substance P, guinea pigs were hyperreactive to vagal stimulation and M(2) receptors were dysfunctional. The depletion of inflammatory cells with cyclophosphamide or the administration of an MBP antibody or a neurokinin-1 (NK(1)) receptor antagonist (SR-140333) all prevented substance P-induced M(2) dysfunction and hyperreactivity. Intravenous heparin acutely reversed M(2) receptor dysfunction and hyperreactivity. Thus substance P releases MBP from eosinophils resident in the lungs by stimulating NK(1) receptors. Substance P-induced hyperreactivity is mediated by blockade of inhibitory neuronal M(2) receptors by MBP, resulting in increased release of acetylcholine.

Tachykinin NK(2) receptors facilitate acetylcholine release from guinea-pig isolated trachea

The release of newly synthesised [3H]acetylcholine was evoked by electrical field stimulation (5 Hz, 600 pulses) of epithelium-deprived guinea-pig trachea strips after sensory neuropeptides depletion with 3 microM capsaicin. The selective tachykinin NK(2) receptor agonist [betaAla(8)]neurokinin A-(4-10) increased in a concentration-dependent manner the electrically-induced release of [3H]acetylcholine. The facilitatory effect was antagonised by the selective non-peptide tachykinin NK(2) receptor antagonist, SR 48968 (apparent pK(B) 8.9). The tachykinin NK(1) and NK(3) receptor agonists substance P methyl ester and senktide (both 10 and 100 nM), respectively, did not affect the evoked release of [3H]acetylcholine. It is concluded that the cholinergic nerves of guinea-pig trachea are endowed with prejunctional facilitatory tachykinin receptors of the NK(2) subtype.

Wood smoke-induced airway hyperreactivity in guinea pigs: time course, and role of leukotrienes and hydroxyl radical

A prior airway exposure to wood smoke induces a tachykinin-dependent increase in airway responsiveness to the subsequent smoke inhalation in guinea pigs (Life Sci. 63: 1513, 1998). To further investigate the time course of, and the contribution of other chemical mediators to, this smoke-induced airway hyperresponsiveness (SIAHR), two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs of anesthetized guinea pigs by a respirator. In the control animals, the SIAHR was evidenced by the bronchoconstrictive response to the second smoke challenge (SM2) which was approximately 5.2-fold greater than that to the first challenge (SM1). This SIAHR was alleviated by shortening the elapsed time between SM1 and SM2 to 10 min or by extending it to 60 min, and was abolished by extending it to 120 min. This SIAHR was reduced by pretreatment with either MK-571 (a leukotriene D4-receptor antagonist) or dimethylthiourea (a hydroxyl radical scavenger), but was not affected by pretreatment with either pyrilamine (a histamine H1-receptor antagonist) or indomethacin (a cyclooxygenase inhibitor). The smoke-induced reduction in the neutral endopeptidase activity (a major enzyme for tachykinin degradation) measured in airway tissues excised 30 min post SM1 was largely prevented by pretreatment with dimethylthiourea. However, this reduction was not seen in airway tissues excised 120 min post SM1. These results suggest that 1) the SIAHR to inhaled wood smoke has a rapid onset time following smoke inhalation and lasts for less than two hours, 2) leukotrienes and hydroxyl radical may play contributory roles in the development of this SIAHR, and 3) hydroxyl radical is the major factor responsible for the smoke-induced inactivation of airway neutral endopeptidase, which may possibly participate in the development of this SIAHR.

Substance P and neurokinin-1 receptor expression by intrinsic airway neurons in the rat

Tachykinins and their receptors are involved in the amplification of inflammation in the airways. We analyzed the expression of preprotachykinin-A (PPT-A) and neurokinin-1 (NK-1) receptor genes by intrinsic airway neurons in the rat. We also tested the hypothesis that PPT-A-encoded peptides released by these neurons fulfill the requisite role of substance P in immune complex injury of the lungs. We found that ganglion neurons in intact and denervated airways or in primary culture coexpress PPT-A and NK-1 receptor mRNAs and their protein products. Denervated ganglia from tracheal xenografts (nu/nu mice) or syngeneic lung grafts had increased PPT-A mRNA contents, suggesting preganglionic regulation. Formation of immune complexes in the airways induced comparable inflammatory injuries in syngeneic lung grafts, which lack peptidergic sensory fibers, and control lungs. The injury was attenuated in both cases by pretreatment with the NK-1 receptor antagonist LY-306740. We conclude that tachykinins released by ganglia act as a paracrine or autocrine signal in the airways and may contribute to NK-1 receptor-mediated amplification of immune injury in the lungs.

Airway hyperresponsiveness induced by chronic exposure to cigarette smoke in guinea pigs: role of tachykinins

This study was carried out to determine whether tachykinins released from lung C-fiber afferents play a part in the bronchial hyperreactivity induced in guinea pigs by chronic exposure to cigarette smoke (CS). Two matching groups of young guinea pigs were exposed to either mainstream CS (CS group) or air (control group) for 20 min twice daily for 14-17 days. There was no difference in the baseline total pulmonary resistance (RL) between the two groups, but the baseline dynamic lung compliance was reduced ( approximately 19%) in CS animals. The responses of RL to intravenous injections of ACh, neurokinin (NK) A, and capsaicin were all markedly increased in CS animals; for example, ACh at the same dose of 5.06 microg/kg increased RL by 207% in the control group and by 697% (n = 8; P < 0. 001) in the CS group. The increased responsiveness was accompanied by significant increases in the numbers of neutrophils, eosinophils, and macrophages in the bronchoalveolar lavage fluid in CS animals. Pretreatment with SR-48968 and CP-99994, antagonists of NK(1) and NK(2) receptors, respectively, did not alter the response of RL to ACh in control animals, but it abolished the elevated bronchoconstrictive response in the CS animals. Furthermore, the immunoreactivities of substance P and calcitonin gene-related peptide in the bronchoalveolar lavage fluid collected after capsaicin challenge were significantly increased in CS animals. These results show that chronic exposure to CS induced airway mucosal inflammation accompanied by bronchial hyperreactivity in guinea pigs and that the tachykininergic mechanism plays an important role in this augmented responsiveness.

Involvement of tachykinin NK1 receptor in the development of allergen-induced airway hyperreactivity and airway inflammation in conscious, unrestrained guinea pigs

It has been suggested that tachykinin NK1 receptor-mediated neurogenic inflammation, characterized by microvascular leakage, mucus secretion, and infiltration and activation of inflammatory cells in the airways, may be involved in allergic asthma. Therefore, in a guinea pig model of allergic asthma, we investigated the involvement of the NK1 receptor in allergen-induced early (EAR) and late (LAR) asthmatic reactions, airway hyperreactivity (AHR) after these reactions and airway inflammation, using the selective nonpeptide NK1 receptor antagonist SR140333. On two different occasions, separated by 1 wk interval, OA-sensitized guinea pigs inhaled either saline (3 min) or SR140333 (100 nM, 3 min) at 30 min before as well as at 5.5 h after OA provocation (between the EAR and LAR) in a random crossover design. A control group, receiving saline inhalations before and at 5.5 h after the two OA provocations, was included as well. SR140333 had no significant effect on either the EAR or the LAR compared with saline control inhalations. However, the NK1 receptor antagonist significantly reduced the OA-induced AHR to histamine, both after the EAR at 5 h after OA challenge (1.77 +/- 0.13-fold increase in histamine reactivity versus 2.50 +/- 0.25-fold increase in the control animals, p < 0.01) and after the LAR at 23 h after OA challenge (1.15 +/- 0.12-fold increase versus 1.98 +/- 0. 34-fold increase, respectively, p < 0.05). Moreover, bronchoalveolar lavage studies performed at 25 h after the second OA provocation indicated that SR140333 significantly inhibited the allergen-induced infiltration of eosinophils, neutrophils, and lymphocytes in the airways (p < 0.05 for all observations), whereas a tendency to reduced accumulation of ciliated epithelial cells in the airway lumen was observed (p = 0.10). These results indicate that the NK1 receptor is involved in the development of allergen-induced AHR to histamine, and that NK1 receptor-mediated infiltration of inflammatory cells in the airways may contribute to this AHR.

Smoke-induced airway hyperresponsiveness to inhaled wood smoke in guinea pigs: tachykininergic and cholinergic mechanisms

The smoke-induced airway hyperresponsiveness (SIAHR) to inhaled wood smoke was investigated in anesthetized guinea pigs. Two smoke challenges (each 10 ml) separated by 30 min were delivered into the lungs by a respirator. In control animals, SIAHR was evidenced by an average bronchoconstrictive response (an increase in total lung resistance) to the second smoke challenge (SM2) that was approximately 4.3-fold greater than that to the first challenge (SM1). Pretreatment with CP-96,345 and SR-48,968 (neurokinin-1 and -2 receptor antagonists; each 1 mg/kg) in combination totally prevented this SIAHR, while pretreatment with CP-96,344 and SR48,965 (inactive enantiomers of CP-96,345 and SR-48,968, each 1 mg/kg) in combination failed to do so. Pretreatment with CP-96,345 (1 mg/kg), SR48,968 (1 mg/kg), or atropine (50 microg/kg) significantly alleviated this SIAHR. Pretreatment with phosphoramidon [an inhibitor of neutral endopeptidase (NEP); 2 mg/kg], which suppresses the degradation of tachykinins, induced an increase in airway reactivity that largely mimicked this SIAHR. The NEP activity measured in airway tissues excised 30 min after SM1 was significantly lower than that in air control value. These results suggest that 1) a prior wood smoke exposure induces an airway hyperresponsiveness to the subsequent wood smoke inhalation, 2) a tachykininergic mechanism involving both neurokinin-1 and -2 receptors is essential for, and a cholinergic mechanism is also involved in the development of this SIAHR, and 3) inactivation of airway NEP by wood smoke may contribute to this SIAHR.

Acetylcholine and tachykinin receptor antagonists attenuate wood smoke-induced bronchoconstriction in guinea pigs

To study the mechanisms of wood smoke-induced bronchoconstriction, we measured total lung resistance (RL) and dynamic lung compliance (Cdyn) in anesthetized and mechanically ventilated guinea pigs. Airway exposure to various doses of wood smoke (lauan wood; 5, 10, and 15 breaths) resulted in a dose-dependent increase in RL and decrease in Cdyn. The smoke-induced changes in RL and Cdyn were significantly attenuated by pretreatment with atropine, CP-96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N-((2-methoxyphenyl)-methyl)-1-aza bicyclo(2.2.2.)-octan-3-amine; a tachykinin NK1 receptor antagonist], and SR-48,968 [(S)-N-methyl-N(4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophen yl)-butyl)benzamide; a tachykinin NK2 receptor antagonist] in combination, atropine alone, and SR-48,968 alone, but were not significantly affected by pretreatment with the inactive enantiomers of CP-96,345 and SR-48,968, CP-96,345 alone, indomethacin (a cyclooxygenase inhibitor), and MK-571 [((3-(3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl((3-dimethyl amino-3-oxo-propyl)thio)methyl)propanoic acid; a leukotriene D4 receptor antagonist]. The activity of airway neutral endopeptidase, a major enzyme for tachykinin degradation, was not significantly influenced by wood smoke during the development of bronchoconstriction. We conclude that: (1) both cholinergic mechanisms and endogenous tachykinins, but not cyclooxygenase products or leukotriene D4, play an important role in the acute bronchoconstriction induced by wood smoke, and (2) the contribution of tachykinins to this airway response is primarily mediated via the activation of tachykinin NK2 receptors, but is not associated with inactivation of the airway neutral endopeptidase.

Involvement of tachykinin NK3 receptors in citric acid-induced cough and bronchial responses in guinea pigs

Aerosolized citric acid induces several pulmonary effects including bronchoconstriction, airway inflammation, and cough. Evidence from the use of tachykinin NK1 and NK2 receptor antagonists, as well as chronic treatment with high doses of capsaicin, have suggested that these effects are mediated through the release of tachykinins from sensory nerve endings. In the present study, we have investigated the effects of a tachykinin NK3 receptor antagonist, SR 142801 (osanetant), on cough, bronchoconstriction, and bronchial hyperresponsiveness induced by aerosolized citric acid (0.4 M) in guinea pigs. SR 142801, at 0.3 and 1 mg . kg-1 by intraperitoneal route, significantly inhibited cough in conscious guinea pigs by 57 +/- 3 and 62 +/- 10% (n = 8), respectively. In anaesthetized guinea pigs, it failed to inhibit the bronchoconstriction induced by citric acid when given alone but abolished it when combined with the tachykinin NK2 receptor antagonist, SR 48968 (saredutant). In guinea pigs pretreated with thiorphan (1 mg . kg-1), aerosolized citric acid (0.4 M, 1 h) induced airway hyperresponsiveness 24 h later, displayed by an exaggerated response to the bronchoconstrictor effect of acetylcholine. A microvascular leakage hypersensitivity also occurred and was demonstrated by a potentiation of the plasma protein extravasation from bronchial vessels induced by histamine. When given once intraperitoneally at 1 mg . kg-1 30 min before the citric acid exposure, SR 142801 inhibited both hyperresponsiveness to acetylcholine and the potentiation of histamine-induced increase in microvascular permeability. The results suggest that tachykinin NK3 receptors are involved in citric acid-induced effects on airways.

Eosinophilic leukocyte accumulation during vagally induced bronchoconstriction

Eosinophilic leukocytes (eosinophils) are important effector cells in allergic inflammatory diseases such as asthma, in which significant accumulation of these cells is observed in the bronchial mucosa. However, there is little information about the relationships between bronchoconstriction and accumulation of eosinophils. We hypothesized that eosinophils are retained in the bronchial vasculature in the inner airway wall during bronchoconstriction because of deformation of the mucosal membrane. To test this hypothesis we induced unilateral bronchoconstriction in open chest guinea pigs by stimulating the right vagus nerve and compared the accumulation of eosinophils in the airway wall of the constricted and contralateral unconstricted lungs using histologic specimens. Results show that the density of eosinophils (number of cells/wall area) significantly increased in the inner wall and decreased in the adventitia of the constricted airways compared with the contralateral unconstricted airways. There was a positive relationship between the amount of smooth muscle shortening and the eosinophil density in the inner wall. On the other hand, this relationship was significantly negative in the adventitia. Atropine completely inhibited the eosinophil accumulation in the inner wall. These data suggest that eosinophils can accumulate in the airway inner wall during bronchoconstriction because of geometrical factors.

Morphology and electrophysiology of guinea-pig paratracheal neurones

BACKGROUND

Although guinea-pig tracheal preparations are used as models of asthma, the morphological and electrophysiological characteristics of its associated ganglion neurones (paratracheal neurones) have not been characterized.

METHODS

Intracellular staining and electrophysiological recording techniques have been applied to guinea-pig paratracheal neurones in isolated preparations.

RESULTS

Most (32/35) neurones were multipolar, with many short (< 70 microns), finely tapering processes and one or more long processes; the latter, which were traced for up to 400 microns, travelled along the interconnecting nerve trunks, often in pairs, or over smooth muscle bundles. About 20% (6/32) of neurones had conspicuous somal extensions that gave rise to 3-8 processes. The soma morphology of neurones of the intrinsic ganglionated plexus close to the trachealis muscle were usually more complex than those in or associated with recurrent or vagal nerve trunks. Two types of neurone were identified electrophysiologically; neurones with fast excitatory synaptic potentials were found only in ganglia located very close to the smooth muscle, whereas > 90% of neurones lacking synaptic inputs were associated with recurrent nerve trunks. Transmural or focal electrical stimulation failed to evoke either slow inhibitory or slow excitatory (cholinergic or non-cholinergic) synaptic potentials in either electrophysiological type.

CONCLUSIONS

It is tentatively concluded that the neurones of the intrinsic ganglionated plexus receiving synaptic input probably provided the para-sympathetic innervation to effector cells (such as trachealis muscle). Both these and the spiking neurones located in or near nerve trunks showed little potential for synaptic modulation of their excitability.

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.

The distribution and co-localization of immunoreactivity to nitric oxide synthase, vasoactive intestinal polypeptide and substance P within nerve fibres supplying bovine and porcine female genital organs

The distribution of nitric oxide synthase-immunoreactive (NOS-IR) axons and their relationship to structures immunoreactive to vasoactive intestinal polypeptide (VIP), substance P (SP) and tyrosine hydroxylase (TH) were studied by means of the nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) technique or double-labelling immunofluorescence in the genital organs of cow and pig. Relevant neurons were also investigated in the pig. NOS-containing neural structures were TH-immunonegative in bovine or porcine genital organs, or in the studied ganglia. In the bovine ovary, NOS-IR nerves were neither VIP-IR nor SP-IR, whereas in the pig, most NOS-containing axons were also VIP-IR. The oviduct was supplied by single NOS/VIP- or NOS/SP-containing nerves, whereas in the uterus, NOS-IR axons were moderate in number, often being immunoreactive for VIP or SP. Numerous NOS/VIP-IR and NOS/SP-IR nerves were found in the vagina of both species. In all tissues studied, NOS-IR axons were mainly related to vascular smooth muscle. Most of the neurons of the paracervical ganglia and some neurons in dorsal root ganglia exhibited strong NOS activity. Only single neurons in sympathetic ganglia were NADPH-d-positive. Most nitrergic neurons in the autonomic ganglia were VIP-IR but SP-immunonegative. The sensory neurons were mostly NOS/SP-IR, whereas only single neurons co-expressed NOS and VIP immunoreactivity.

Tachykinin NK2 receptors further characterized in the lung with nonpeptide receptor antagonists

Two nonpeptide tackykinin NK2 receptor antagonists have now been described, SR 48968 and GR 159897. These drugs are highly specific and very potent antagonists with affinity (binding and in vitro study) for NK2 receptors in the subnanomolar range (pKi = 9-10), without intrinsic activity. They act preferentially on the human NK2A receptor subtype. These drugs exert potent and long-acting antagonism by both i.v. and oral administration. Their use has first confirmed the preponderant role of NK2 receptors in airway smooth muscle contraction, especially in human bronchi. A role for NK2 receptor stimulation has also been clearly demonstrated in bronchoconstriction induced by various agents known to induce the release of tachykinins (capsaicin, resiniferatoxin, citric acid, sodium metabisulfite diethyl ether, serotonin, and bradykinin), in allergen-induced airway constriction in the guinea pig sensitized to ovalbumin, and in hyperpnea-induced bronchoconstriction. Inhibition of neurokinin A mediated or capsaicin-mediated dyspnea by SR 48968 has also been demonstrated in the guinea pig. SR 48968 also is very efficient in inhibiting cough induced by citric acid or capsaicin. Finally, SR 48968 is able to abolish in guinea pigs in vivo the bronchial hyperreactivity induced after 24 or 48 h by a citric acid challenge or an ovalbumin challenge, respectively. Thus, nonpeptide, long-acting NK2 receptor antagonists can be regarded as suitable tools for investigations in humans. They may shortly allow a precise determination of the role of tachykinins in asthmatic patients.

Tachykinins, sensory nerves, and asthma--an overview

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

Activation of the micturition reflex by NK2 receptor stimulation in the anaesthetized guinea-pig

1. The mechanisms underlying stimulation of bladder contractions and bronchoconstriction by the selective NK2 receptor agonist, [beta-Ala8]NKA(4-10), were examined in the anaesthetized guinea-pig. 2. Atropine, alpha,beta-methylene-ATP and ganglion blocking agents were used to examine the contribution of reflex arc activation and/or potentiation of efferent mechanisms to the NK2 receptor-mediated responses seen in these two tissues. 3. [beta-Ala8]NKA(4-10)-induced bronchoconstriction was immediate, dose-dependent and was unaffected by pretreatment with ganglion blockers (hexamethonium or chlorisondamine), blockade of muscarinic receptors by atropine, or desensitization of P2 purinoceptors by alpha,beta-methylene-ATP. 4. At does of 5 micrograms kg-1 and above, [beta-Ala8]NKA(4-10) induced bladder contractions that appeared to be of an 'all-or-nothing' nature. These contractions occurred after a delay of 10 to 30 s and were often biphasic, comprised of an initial rapid component followed by a slower tonic component. 5. Pretreatment of the animals with either atropine or the desensitizing purinoceptor agonist alpha,beta-methylene-ATP, resulted in partial inhibition of bladder contractile responses to [beta-Ala8]NKA(4-10). The combination of atropine and alpha,beta-methylene-ATP pretreatment resulted in additive inhibition leading to complete blockade of the response. 6. The bladder responses to [beta-Ala8]NKA(4-10) (5 micrograms kg-1) were inhibited by pretreatment with the ganglion blockers, hexamethonium and chlorisondamine, indicating a preganglionic mechanism of action. 7. These findings demonstrate the indirect nature of the bladder contractions induced by activation of NK2 receptors in the anaesthetized guinea-pig. Contractions occur secondary to the release of endogenous cholinergic and NANC transmitters by activation of neuronal NK2 receptors located at apreganglionic site, possibly on capsaicin-sensitive sensory afferent nerves, where NK2 sites have been demonstrated autoradiographically. In contrast, [beta-Ala8]NKA(4- 10)-induced bronchoconstriction in the anaesthetized guinea-pig is a direct smooth muscle contractile response that is unaffected by ganglionblockade or blockade of muscarinic receptors.

Opposite modulation by tachykinin (NK1) and CGRP receptors of sympathetic control of mouse vas deferens motility

Electrical field stimulation of isolated mouse vas deferens elicited sympathetic twitch whose amplitude was transiently enhanced by the selective tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P (0.3-30 nM), but not by selective NK2 and NK3 receptor agonists. Potentiation by [Sar9,Met(O2)11]substance P was antagonized by (+/-)-CP 96,345 [(2S,3S)-cis-2-(diphenylmethyl)-N- [(2-methoxyphenyl)-methyl]-1-azabicyclo[2.2.2]octan-3-amine] (IC50 = 0.1 microM). On the other hand, electrical field stimulation-induced contractions were inhibited by calcitonin gene-related peptide, CGRP (0.1-30 nM), and this action was reduced by its antagonist, human CGRP-(8-37) (3 microM). [Sar9,Met(O2)11]substance P (3 nM) did not affect either high-K+ or noradrenaline-induced contraction, while CGRP (3 nM) significantly reduced the noradrenaline-induced motor response. Capsaicin (1 microM) inhibited sympathetic twitches, and this effect was partially antagonized by human CGRP-(8-37). In the presence of this antagonist, capsaicin induced a short-living and (+/-)-CP 96,345-sensitive twitch enhancement. These data suggest that the sympathetic control of mouse vas deferens motility can be modulated in an opposite manner by tachykinin NK1 (prejunctionally located) and by CGRP (pre- and/or postjunctionally located) receptors.

Characterization and autoradiographic mapping of [3H]CP96,345, a nonpeptide selective NK1 receptor antagonist in guinea pig lung

We have studied binding and distribution of NK1 receptors in guinea pig lung using [3H]CP96,345. Kinetic studies showed that specific binding of [3H]CP96,345 was rapid and reversible, giving a kinetic dissociation constant (Kd) of 0.28 +/- 0.05 nM. The specific binding was also saturable and Scatchard analysis indicated a single class of binding site with an equilibrium Kd of 0.12 +/- 0.03 nM and maximum binding capacity (Bmax) of 107.0 +/- 10.3 fmol/mg of protein. Competition studies showed the rank order of affinity for agonists and antagonists as follows: SP > NKA = septide >> NKB = senktide; CP96,345 > FK888 > FK224 > L668169. NK3 agonists, NK2-selective antagonists, and a calcium channel blocker, diltiazem, showed no displacement, indicating high selectivity for NK1 receptors. Autoradiographic mapping showed specific labeling over airway smooth muscle from central to peripheral airways, submucosal glands, and nerve fibers of trachea. The labeling of airway epithelium was increased with diminishing size of airways. Pulmonary blood vessels were also moderately labeled and there was sparse labeling over alveolar walls. [3H]CP96,345 may provide a useful tool to evaluate NK1 receptor expression in peripheral organs.

Facilitatory effects of selective agonists for tachykinin receptors on cholinergic neurotransmission: evidence for species differences

1. Exogenous tachykinins modulate cholinergic neurotransmission in rabbit and guinea-pig airways. We have investigated the effect of selective tachykinin receptor agonists and antagonists on cholinergic neurotransmission evoked by electrical field stimulation (EFS) of bronchial rings in rabbit, guinea-pig and human airways in vitro to assess which type of tachykinin receptor is mediating this facilitatory effect. 2. Bronchial rings were set up for isometric tension recording. Contractile responses to EFS (60 V, 0.4 ms, 2 Hz for 10 s every min) and exogenous acetylcholine (ACh) were obtained and the effects of selective tachykinin agonists and antagonists were investigated. 3. In rabbit bronchi the endogenous tachykinins, substance P (SP) and neurokinin A (NKA) (10 nM) potentiated cholinergic responses to EFS (by 287.6 +/- 121%, P < 0.01 and 181.4 +/- 56.5%, P < 0.001 respectively). 4. The NK1 receptor selective agonist, [Sar9]SP sulphone (10 nM) evoked a maximal facilitatory action on cholinergic responses of 334.9 +/- 63% (P < 0.01) (pD2 = 8.5 +/- 0.06) an effect which was blocked by the selective NK1-receptor antagonist, CP 96,345 (100 nM) (P < 0.05) but not by the NK2 receptor antagonist, MEN 10,376 (100 nM). The NK2 receptor selective agonist, [beta Ala8]NKA(4-10) (10 nM), produced a maximum enhancement of 278 +/- 83.5% (P < 0.01) (pD2 = 8.7 +/- 0.1) an effect which was blocked by MEN 10,376 (100 nM) (P < 0.05) and not by CP 96,345. [MePhe7]NKB, an NK3 receptor selective agonist was without effect. 5. The rank order of potency of NK2 receptor antagonists against enhancement of cholinergic responses by [Beta Ala8]NKA(4-10) was MEN 10,376> L 659,877> R 396. This pattern together with the observation of the full agonist activity of MDL 28,564 indicates that the NK2 receptors in the rabbit bronchus are similar to those which are present in the rabbit pulmonary artery.6. Neither [Sar9]SP sulphone (5 nM) nor [Beta Ala8]NKA(4- 10) (1 nM) had any effect on contractile responses to ACh (10 MicroM) suggesting a pre-junctional mechanism of action.7. By contrast, in guinea-pig bronchi only the NK1-receptor agonist [Sar9]SP sulphone (3 nM) was effective in enhancing cholinergic neurotransmission but the effect was relatively small (maximal enhancement 25.7 +/- 5.5%, P<0.01). In human bronchial rings all the selective neurokinin agonists were without effect on cholinergic neurotransmission.8. These results suggest that tachykinins may play an important role in modulating cholinergic neurotransmission in rabbit (via NK1 and NK2 receptors) and guinea-pig airways (via NK1 receptor) but have no demonstrable effect on human airways