Identification of both NK1 and NK2 receptors in guinea-pig airways

Human biodistribution and radiation dosimetry of the tachykinin NK1 antagonist radioligand [18F]SPA-RQ: comparison of thin-slice, bisected, and 2-dimensional planar image analysis

(18)F-Labeled substance P antagonist-receptor quantifier ([(18)F]SPA-RQ) [2-fluoromethoxy-5-(5-trifluoromethyl-tetrazol-1-yl)-benzyl]-[(2S,3S)-2-phenyl-piperidin-3-yl)amine] is a selective radioligand for in vivo quantification of tachykinin NK(1) receptors with PET. The aims of this study were to estimate the radiation safety profile and relative risks of [(18)F]SPA-RQ with 3 different methods of image analysis.

METHODS

Whole-body PET images were acquired in 7 healthy subjects after injection of 192 +/- 7 MBq (5.2 +/- 0.2 mCi) [(18)F]SPA-RQ. Emission images were serially acquired at multiple time-points from 0 to 120 min and approximately 180-240 min after injection. Urine samples were collected after each imaging session and for 24 h after the last scan to measure excreted radioactivity. Horizontal tomographic images were compressed to varying degrees in the anteroposterior direction to create 3 datasets: thin-slice, bisected, and 2-dimensional (2D) planar images. Regions of interest were drawn around visually identifiable source organs to generate time-activity curves for each dataset. Residence times were determined from these curves, and doses to individual organs and the body as a whole were calculated using OLINDA/EXM 1.0.

RESULTS

The lungs, upper large intestine wall, small intestine, urinary bladder wall, kidneys, and thyroid had the highest radiation-absorbed doses. Biexponential fitting of mean bladder and urine activity showed that about 41% of injected activity was excreted via urine. Assuming a 2.4-h urine voiding interval, the calculated effective doses from thin-slice, bisected, and 2D planar images were 29.5, 29.3, and 32.3 microSv/MBq (109, 108, and 120 mrem/mCi), respectively.

CONCLUSION

Insofar as effective dose is an accurate measure of radiation risk, all 3 methods of analysis provided quite similar estimates of risk to human subjects. The radiation dose was moderate and would potentially allow subjects to receive multiple PET scans in a single year. Individual organ exposures varied among the 3 methods, especially for structures asymmetrically located in an anterior or posterior position. Bisected and 2D planar images almost always provided higher organ dose estimates than thin-slice images. Thus, either the bisected or 2D planar method of analysis appears acceptable for quantifying human radiation burden, at least for radioligands with a relatively broad distribution in the body and not concentrated in a small number of radiation sensitive organs.

Characterization of tachykinin NK2 receptor in the anterior pituitary gland

Tachykinins are a family of bioactive peptides that interact with three subtypes of receptors: NK1, NK2 and NK3. Substance P has greater affinity for NK1, and neurokinin A (NKA) for NK2 receptor subtype. Although only NK1 receptor has been characterized in the anterior pituitary gland, some evidence suggests the existence of NK2 receptors in this gland. Therefore, we investigated the presence of NK2 receptors in the anterior pituitary gland of male rats by radioligand binding studies using labeled SR48968, a non peptidic specific antagonist. [3H]SR48968 specific binding to cultured anterior pituitary cells was time-dependent and saturable, but with a lower affinity than previously reported values for cells expressing NK2 receptors. Unlabeled NKA inhibited only partially [(3)H]SR48968 specific binding to whole anterior pituitary cells. Since SR48968 is a non polar molecule, we performed experiments to discriminate surface from intracellular binding sites. SR48968 exhibited both surface and intracellular specific binding. Analysis of the surface-bound ligand indicated that [3H]SR48968 binds to one class of receptor with high affinity. Neurokinin A completely displaced [3H]SR48968 surface specific binding fitting to a two-site/two-state model with high and low affinity. Additionally, immunocytochemical studies showed that the NK2 receptor is expressed at least in a subset of lactotropes. These results demonstrate the presence of NK2 receptors in the anterior pituitary gland and suggest that NKA actions in this gland are mediated, at least in part, by the NK2 receptor subtype.

Peripheral actions of tachykinins

Tachykinins mediate a variety of physiological processes in the gastrointestinal, pulmonary and genito-urinary tract mainly through the stimulation of NK1 and NK2 receptors. Preclinical evidence obtained through the use of selective tachykinin receptor antagonists indicates that endogenous tachykinins are involved in augmented smooth muscle contraction, vasodilatation, chemotaxis and activation of immune cells, mucus secretion, water absorption/secretion. Recent evidence also suggests that endogenous tachykinins released at the peripheral level may play a role in visceral inflammation, hyperreflexia and hyperalgesia. Possible mechanisms underlying the stimulation of primary afferent neurons by tachykinins may involve a direct excitation of these neurons and the release of mediators which sensitise or stimulate sensory nerves. Tachykinin receptor antagonists could have a clinical utility in several human diseases such as irritable bowel syndrome, asthma, and in micturition disturbances characterized by a hyperactive bladder.

Stimulation of airway sensory nerves by cyclosporin A and FK506 in guinea-pig isolated bronchus

We have investigated the contractile property of cyclosporin A and FK506 in guinea-pig isolated bronchus. Cyclosporin A (10 microM) failed to significantly attenuate the excitatory non-adrenergic non-cholinergic (eNANC) and cholinergic contractile response (per cent methacholine Emax) induced by electrical field stimulation (EFS). In contrast, eNANC responses were significantly attenuated by both the neurokinin (NK)-1 and (NK)-2 receptor antagonists, N-acetyl-L-tryptophan 3,5-bis (trifluoromethyl)-benzyl and SR48968, respectively. Cyclosporin A and FK506 caused a concentration-dependent contraction in guinea-pig isolated bronchus, which was significantly attenuated by NK-1 and NK-2 receptor antagonists. The capsaicin receptor antagonist, capsazepine (10 microM) significantly reduced the contractile response to cyclosporin A and capsaicin, but not to FK506. The N-type calcium channel blocker, omega-Conotoxin (omegaCTX: 10 nM), significantly reduced the contractile response to FK506 and the eNANC response following EFS. In contrast, omega-CTX failed to significantly reduce the contractile potency to capsaicin or cyclosporin A. In bronchial preparations desensitized by repeated application of capsaicin (1 microM), the contractile responses to both cyclosporin A (100 microM) and FK506 (100 microM), were significantly reduced. In contrast, the contractile responses to substance P and neurokinin A (10 microM) were not altered. Furthermore, repeated application of cyclosporin A (100 microM) significantly inhibited the contractile response to capsaicin (1 microM). The findings from this study would indicate that cyclosporin A and FK506 mediate contraction of guinea-pig isolated bronchus secondary to the release of neuropeptides from airway sensory nerves. However, the release of sensory neuropeptides appears to be mediated via different mechanisms for cyclosporin A and FK506, the former by stimulation of the vanilloid receptor and the latter via opening of N-type calcium channels.

Effects of airway inflammation on cough response in the guinea pig

We have developed a guinea pig model for cough related to allergic airway inflammation. Unanesthetized animals were exposed to capsaicin aerosols for 10 min, and cough frequency was counted during this period. The cough evaluation was performed by the following three methods: visual observation, acoustic analysis, and monitoring of pressure changes in the body chamber. These analyses clearly differentiated a cough from a sneeze. To elucidate the relationship between cough response and airway inflammation, animals were immunosensitized and multiple challenged. Sensitized guinea pigs presented no specific changes microscopically, but multiple-challenged animals showed an increased infiltration of inflammatory cells into the airway. Cough number in response to capsaicin increased significantly from 4.7 +/- 1.4 coughs/10 min in normal animals to 10.6 +/- 2.0 coughs/10 min in sensitized animals and further to 22.8 +/- 1.3 coughs/10 min in multiple-challenged animals. This augmented cough frequency was significantly inhibited by the inhalation of tachykinin-receptor antagonists and by oral ingestion, but not inhalation, of codeine phosphate. The results suggest that airway inflammation potentiates an elevation of cough sensitivity in this model.

Characterization of the antibronchoconstrictor activity of MEN 11420, a tachykinin NK2 receptor antagonist, in guinea-pigs

We have investigated the antibronchoconstrictor activity of a novel glycosylated bicyclic peptide tachykinin NK2 receptor antagonist, MEN 11420 c¿[(beta-D-GlcNAc)Asn-Asp-Trp-Phe-Dpr-Leu]c(2beta-5beta++ +)¿, as compared to MEN 10627 c[(Met-Asp-Trp-Phe-Dpr-Leu)c(2beta-5beta)] and to the nonpeptide antagonist SR 48968 ((S)-N-methyl-N[4-acetylamino-4-phenylpiperidino-2-3,4-dichlorophenyl)bu tyl] benzamide. In the guinea-pig isolated bronchus MEN 11420 (pK(B) 8.40+/-0.07) and MEN 10627 (pK(B) 8.67+/-0.09) competitively antagonized the contraction induced by the tachykinin NK2 receptor agonist, [betaAla8]neurokinin A-(4-10). SR 48968 showed an apparent pK(B) of 9.57+/-0.2. The atropine-resistant response to electrical stimulation was reduced in a concentration-dependent manner by MEN 11420, MEN 10627 and SR 48968. In urethane-anaesthetized guinea-pigs, MEN 11420 produced a dose-dependent inhibition of bronchoconstriction induced by [betaAla8]neurokinin A-(4-10). Comparable inhibitory effects were observed after i.v. administration of SR 48968 and MEN 10627. Bilateral electrical stimulation of the vagi (20 Hz for 20 s) induced a bronchoconstriction that was dose-dependently inhibited by i.v. MEN 11420, SR 48968 and MEN 10627. MEN 11420 was also effective in inhibiting the capsaicin (20 nmol/kg i.v.)-induced bronchoconstriction. MEN 11420 (1.1 micromol/kg i.v.) showed a longer plasma half-life and a greater area under the plasma concentration-time curve value (AUC) than those of MEN 10627. These findings indicate that MEN 11420 is a potent and selective antagonist of the tachykinin NK2 receptor in guinea-pig airways with a long duration of action.

Effects of tachykinins and capsaicin on the mechanical and electrical activity of the guinea-pig isolated trachea

1. The effects of tachykinins and capsaicin were studied by means of intracellular membrane potential and isometric tension recordings in the isolated trachea of the guinea-pig. 2. The basal membrane potential averaged -51 mV, and most preparations demonstrated spontaneous slow waves. Tetraethylammonium (TEA), a potassium channel blocker (8 x 10(-3) M), depolarized the membrane potential to -44 mV and induced a rhythmic activity. 3. In control solution, substance P (10(-8)-10(-6) M), [Nle10]-neurokinin A(4-10) (10(-8)-10(-6) M) and capsaicin (10(-7)-10(-6) M) induced concentration-dependent depolarizations which were statistically significant at the highest concentration tested (depolarization by 10(-6) M: 8, 11 and 16 mV for the NK1 agonist, the NK2 agonist and capsaicin, respectively). 4. In the presence of TEA (8 x 10(-3) M), the three substances induced depolarizations which were statistically significant at the highest concentration tested for substance P (10(-6) M) and at 10(-7) and 10(-6) M for both [Nle10]-neurokinin A(4-10) and capsaicin (depolarization by 10(-6) M: 11, 17 and 10 mV for substance P, [Nle10]neurokinin A(4-10) and capsaicin, respectively). 5. In the presence or absence of tetraethylammonium, [MePhe7]-neurokinin B (10(-8)-10(-6) M) did not induce any significant changes in membrane potential. 6. The depolarizing effects of substance P (10(-6) M) and [Nle10]-neurokinin A(4-10) (10(-6) M) were blocked only by the specific antagonists for NK1 and NK2 receptors, SR 140333 (10(-7) M) and SR 48968 (10(-7) M), respectively. The effects of capsaicin (10(-6) M) were partially inhibited by each antagonist and fully blocked by their combination. 7. Substance P (10(-9) to 10(-4) M), [Nle10]-neurokinin A(4-10) (10(-10) to 10(-5) M), [MePhe7]-neurokinin B and capsaicin (10(-7) to 10(-5) M) evoked concentration-dependent contractions. 8. The contractions to substance P were significantly inhibited by SR 140333 (10(-8) to 10(-6) M) but unaffected by SR 48968 (10(-8) to 10(-6) M). Furthermore, the response to [Nle10]-neurokinin A(4-10) was significantly inhibited by SR 48968 and unaffected by SR 140333 at the same concentrations. Although SR 48968 (10(-7) M) alone did not influence the effects of substance P, it potentiated the inhibitory effect of SR 140333 (10(-7) M). A similar synergetic effect of these two compounds was observed in the inhibition of the contractile response to [Nle10]-neurokinin A(4-10). 9. Neither SR 140333 (10(-7) M) nor SR 48968 (10(-7) M) alone influenced the contractions to [MePhe7]-neurokinin B and capsaicin. However, the combination of the two antagonists abolished the contractions to either peptide. 10. These results demonstrate that the stimulation of both NK1 and NK2 tachykinin-receptors induced contraction and depolarization of the guinea-pig tracheal smooth muscle and that both receptors were stimulated during the endogenous release of tachykinins by capsaicin. There was no evidence for a major role of NK3 receptors in the contractile and electrical activity of the guinea-pig isolated trachea.

Tachykinin receptors mediating non-cholinergic contraction of the guinea-pig isolated main bronchus in response to field stimulation

1. The primary aim of the present study was to classify the receptors activated by tachykinins released by field stimulation of intramural nerve terminals of the guinea-pig isolated main bronchus by using the novel non-peptide NK1 and NK2 receptor-selective antagonists SR 140333 and SR 48968, respectively. 2. Log concentration-response curves to substance P (SP), the NK1 receptor-selective agonist [Sar9, Met(O2)11]-SP and the NK2 receptor-selective agonist [Nle10]-neurokinin (NK) A(4-10) were constructed in the presence of indomethacin (2 mumol/L) and phosphoramidon (5 mumol/L). Substance P was the least potent of these agonists. 3. In left and right main bronchi, SR 140333 (100 nmol/L) antagonized concentration-related contractions evoked by SP yielding pKB values of 8.02 and 7.68, respectively. SR 140333 (10 nmol/L) antagonized the effects of [Sar9, Met(O2)11]-SP on the left bronchus with a pKB value of 8.04. 4. SR 48968 (100 nmol/L) antagonized the effects of SP yielding pKB estimates of 7.88 (left bronchus) and 7.31 (right bronchus). 5. [Nle10]-NKA(4-10) was more potent in the left than in the right main bronchus. SR 48968 (0.1-10 nmol/L) antagonized the effects of [Nle10]-NKA(4-10) on the left bronchus with pKB estimates of 8.26-10.25. 6. In the presence of indomethacin (2 mumol/L), phosphoramidon (5 mumol/L) and atropine (1 mumol/L), electrical field stimulation (EFS; 30 V, 1 ms, 15 s at 1, 3, 10 and 30 Hz) produced prolonged contractions. SR 48968 (0.1 mumol/L) markedly reduced responses to stimulation, whereas SR 140333 (0.3 mumol/L) caused a small but significant rightward displacement of the log frequency-response curve. In combination, these concentrations of SR 48968 and SR 140333 produced complete inhibition to field stimulation at 10 Hz. 7. These results indicate that: (i) both NK1 and NK2 receptor subtypes are present in the guinea-pig main bronchi with the left bronchus being more sensitive to an NK2 receptor agonist; and (ii) EFS of the main bronchus leads to frequency dependent contractions due to the release of tachykinin(s) that predominantly activate an NK2 receptor.

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.

Mechanisms involved in the contractile responses induced by the hydroalcoholic extract of Phyllanthus urinaria on the guinea pig isolated trachea: evidence for participation of tachykinins and influx of extracellular Ca2+ sensitive to ruthenium red

1. The hydroalcoholic extract (HE) of stems, leaves and roots from P. urinaria (Euphorbiaceae) (1-3000 micrograms/ml), caused graded contraction in guinea pig trachea (GPT), being more effective in preparations without epithelium. 2. Response to HE was slightly affected by tetrodotoxin (0.3 microM) and nicardipine (1 microM), but was unaffected by w-conotoxin, atropine, mepyramine or staurosporine (all 1 microM). Indomethacin (3 microM) greatly inhibited HE contraction, but MK 571 (leukotriene D4 and E4 antagonist) caused partial inhibition; L-655,240 (thromboxane A2 antagonist) and WEB 2086 (PAF antagonist) (all 1 microM) were ineffective. 3. Response to HE was markedly inhibited in a Ca(2+)-free solution and was partially affected in GPT desensitized to capsaicin (10 microM). 4. Capsazepine (capsaicin antagonist, 3 microM) antagonized the contraction from capsaicin, leaving the response to HE unaffected. In contrast, ruthenium red (an ionic channel antagonist coupled to vanilloid receptors of capsaicin) (0.1-3 microM) caused graded and equipotent noncompetitive inhibition of HE- and capsaicin-induced contractions, but had no effect on carbachol- and prostaglandin E2-mediated responses. 5. FK 888 and SR 48968 (NK1 and NK2 receptor antagonists, respectively) (both 1 microM) antagonized, through a competitive mechanism, the contraction from SP and [beta-ala8]NKA (4-10) respectively, but antagonized, through a noncompetitive mechanism, HE-mediated contraction. 6. We concluded that contraction to HE in GPT is modulated by the epithelium, depends on the release of a cyclo-oxygenase metabolite, and relies largely upon an extracellular Ca2+ influx that is highly sensitive to ruthenium red, but is insensitive to L and N-type of voltage-sensitive Ca2+ channel antagonists. In addition, NK1 and NK2 tachykinins, but not vanilloid receptors, play an important role in mediating its response.

Evidence for adrenergic and tachykinin activity in venom of the stonefish (Synanceja trachynis)

The aim of the present study was to investigate previously suggested adrenergic and tachykinin activity, as well as the cardiovascular effects, of venom from the stonefish (Synanceja trachynis). Stonefish venom (60-120 micrograms/kg, i.v.) produced dose-dependent bronchoconstriction in anaesthetised guinea-pigs. This response (100 micrograms/kg, i.v.) was significantly reduced by the neurokinin 1 (NK1) receptor antagonist CP-99,994 (1 mg/kg, i.v.). Contractile responses to venom (4 micrograms/ml) of guinea-pig isolated ileum (GPI) were significantly inhibited by a combination of the sodium channel blocking drug tetrodotoxin (1 microM) and the ganglion blocking drug mecamylamine (10 microM). However, subsequent administration of CP-99,994 (0.1 microM) did not produce further inhibition. Endogenous tachykinin depletion with capsaicin (1 microM) also significantly attenuated responses to venom (4 micrograms/ml) in GPI. Venom (4 micrograms/ml) produced increases in rate and force of contraction of rat spontaneously beating isolated atria which were significantly inhibited by the beta-adrenoceptor antagonist propranolol (5 microM) but not by noradrenergic transmitter depletion with reserpine (4.5 mg/kg, i.p.). In the presence of the alpha 1-adrenoceptor antagonist prazosin (0.3 microM), venom (6 micrograms/ml) significantly inhibited electrically evoked twitches of prostatic segments of rat vas deferens. The inhibitory effect of venom was significantly reduced by the alpha 2-adrenoceptor antagonist idazoxan (1 microM) but not by propranolol (5 microM) or the neurokinin 2 (NK2) receptor antagonist SR-48,968 (0.1 microM). Venom (60-120 micrograms/kg, i.v.) produced dose-dependent increases in mean arterial blood pressure in anaesthetised rats. This pressor response (60 micrograms/kg, i.v.) was significantly reduced by prazosin (10-50 micrograms/kg, i.v.) and the leukotriene receptor antagonist SB205312 (1 mg/kg, i.v.), significantly increased by propranolol (2 mg/kg, i.v.), but not significantly affected by the cyclo-oxygenase inhibitor indomethacin (10 mg/kg, i.v.) or the thromboxane A2/prostaglandin H2 (TP) receptor antagonist GR32191B (1 mg/kg, i.v.). Pressor responses to venom (100 micrograms/kg, i.v.) were also observed in anaesthetised rabbits. These results suggest that stonefish venom contains a component capable of stimulating the release of endogenous tachykinins with subsequent activity at NK1 receptors. The venom also appears to act via stimulation of sodium channels on sensory nerves. The venom also has activity at alpha 2-adrenoceptors and a direct action at beta-adrenoceptors. The effect of venom on blood pressure of anaesthetised rats appears to include a pressor component that is mediated, in part,by alpha-adrenoceptors and leukotriene receptors, and a depressor component that is mediated by beta-adrenoceptors. However, the pressor response does not involve action at TP receptors, or require the production of cyclo-oxygenase metabolites.

Heterogeneity of tachykinin receptors in the rabbit lung

The tachykinins, substance P (SP) and neurokinin A (NKA), are agonists for the NK(1) and NK(2) receptors, respectively. Tachykinins have various respiratory effects, including bronchoconstriction. This study characterizes tachykinin binding sites in the rabbit lung. We hypothesize that (2-[(125)I]iodohistidyl(1))Neurokinin A ([(125)I]NKA) interacts with NK1 and NK2 binding sites in the rabbit lung. The K d determined from saturation isotherms was 0.69 times/divided by 1.14 nM (geometric mean times/divided by SEM) and the B max was 4.15 + or - 0.22 femtomole/mg protein (arithmetic mean + or - SEM). Competitive inhibition studies with NKA, SP and various selective tachykinin agonists showed the rank order of potency; [beta-Ala(8)]-Neurokinin A 4-10 = SP >> NKA >> [Sar(9),Met(02)11]-Substance P. [beta-Ala(8)]-Neurokinin A 4-10, a selective NK(2) agonist, and SP inhibition of [(125)I]NKA binding were best described using a two-site model. Competitive inhibition studies using the selective nonpeptide NK(2) antagonist (SR 48968) and the selective nonpeptide NK(1) antagonist (CP 96,345) revealed Ki's of 5.5 nM and 8.1 nM, respectively. Our data therefore suggest that [(125)I]NKA binds to both the NK(1) and NK(2) receptors in the lung.

Autoradiographic mapping of pulmonary NK1 and NK2 tachykinin receptors and changes after repeated antigen challenge in guinea pigs

An autoradiographic technique was used to study the distribution of changes in pulmonary NK1 and NK2 receptors in guinea pig lung after repeated antigen challenge. Specific labeling of [3H]CP96345 (NK1 receptors) and [3H]SR48968 (NK2 receptors) was localized over the tracheal and bronchial smooth muscle; the density of binding increased towards smaller airways with a higher density for [3H]CP96345 binding. Bronchial epithelium and pulmonary blood vessels were also labeled densely with [3H]CP96345. No remarkable difference in the pattern of distribution of pulmonary NK1 and NK2 tachykinin receptors was observed between control, vehicle-challenged, and repeatedly antigen-challenged (weekly for three times) guinea pigs. A significant reduction in specific labeling of [3H]CP96345 (p < 0.01) and [3H]SR48968 (p < 0.05) over pulmonary structures was observed in antigen-challenged compared to control or vehicle-challenged animals. This study provides evidence that NK1 and NK2 tachykinin receptors are both localized to smooth muscle of all sizes in guinea pig airways and provides further evidence for a discrete distribution of NK1 and NK2 tachykinin receptors, consistent with their relative functional activities. In an established model of airway inflammation a decrease in the expression of NK1 and NK2 tachykinin receptors was evident on several different cell types within the lung, and this could influence airway and vascular reactivity.

Involvement of NK1 and NK2 receptors in pulmonary responses elicited by non-adrenergic, non-cholinergic vagal stimulation in guinea-pigs

Previous studies from our laboratory using exogenously administered neurokinin (NK) agonists have shown that both NK1- and NK2-receptor subtypes are involved in plasma extravasation in the guinea-pig airways. In the present study, we have extended these observations using antidromic vagal stimulation to stimulate sensory c-fibres as a means of eliciting the release of endogenous tachykinins in propranolol- and atropine-treated guinea-pigs. Antidromic vagal stimulation (5 ms, 30 s) induced frequency-dependent (1-10 Hz) bronchoconstriction that was completely abolished by co-administration of the NK1-selective antagonist CP-99,994 ((2s-methoxy-benzyl)-(2-phenyl-piperidin-3s-yl)-amine), and the NK2-selective antagonist SR-48,968 ((S)-N-methyl-N-[4-(4-acetylamino-4-phenyl piperidino)-2-(3,4-dichlorophenyl) butyl]benzamide), each at a dose sufficient to block NK1 and NK2 receptors, respectively (each at 0.3 mg kg-1, i.v.). In contrast, SR-48,968 when given alone only partially blocked the vagal stimulation-induced bronchospasm, whereas CP-99,994 had no effect. Significant increases (2-3-fold) in plasma extravasation of [125I]fibrinogen in the trachea, main bronchi, distal airways and oesophagus following vagal stimulation (5 Hz, 5 min, 10 V, 5 ms) were observed. Pretreatment with the neutral endopeptidase inhibitor, thiorphan (1 mg kg-1, i.v.), and the angiotensin-converting enzyme inhibitor, enalapril (1 mg kg-1, i.v.), potentiated both vagal stimulation-induced bronchoconstriction and plasma leakage in all tissues examined. This potentiation was due to reduced metabolism of endogenously released tachykinins since enhanced plasma overflow of immunoreactive substance P was observed following vagal stimulation in thiorphan- and enalapril-treated guinea-pigs. CP-99,994 substantially blocked plasma leakage in all parts of the airways and in the oesophagus. In comparison, SR-48,968 had no significant effect in the trachea and the oesophagus but partially inhibited plasma leakage in the main bronchi and distal airways. Co-administration of both CP-99,994 and SR-48,968 abolished the residual plasma leakage in these two regions. These results support the hypothesis that both NK1 and NK2 receptors are involved in tachykinin-induced pulmonary responses in the airways.

Neurokinin receptors subserving bronchoconstriction

Tachykinin receptor subtypes were initially defined using agonist potency rations for the endogenous ligands substance P (SP), neurokinin (NK) A, and NKB. On this basis it was suggested that there are three tachykinin receptor subtypes. These subtypes were designated NK1, NK2, and NK3, where SP is most potent at NK1 receptors, NKA is most potent at NK2 receptors, and NKB is most potent at NK3 receptors. Recently analogs of the endogenous ligands that show greater selectivity (about 1000-fold) for the different receptor subtype have been developed. In addition selective antagonists, which are either nonpeptides or modified peptides, for the receptor subtypes have been developed. This minireview concentrates on the wealth of new knowledge concerning the tachykinin receptor subtypes subserving bronchoconstriction in several mammalian species, including man, provided by the use of these selective agonists and antagonists.

Pulmonary actions of the neurokinin1-specific agonist [Sar9,Met(O2)11]-substance P

We examined the relationship between airway obstruction and plasma extravasation produced by the intravenous administration of the selective NK1 receptor agonist [Sar9, Met(O2)11]-substance P(SP). Conscious guinea-pigs were injected with Evans' blue dye followed by intravenous [Sar9,Met(O2)11]-SP. Animals were killed 3 min later and airway obstruction, determined via excised lung gas volumes, and plasma extravasation in the trachea, mainstem bronchi and intrapulmonary airways quantitated. Maximal plasma protein extravasation occurred at a dose about 30 times less than that required to elicit airway obstruction. Neither the neutral endopeptidase (NEP) inhibitor, thiorphan, or the angiotensin-converting enzyme (ACE) inhibitor, captopril, altered the extravasation response to [Sar9,Met(O2)11]-SP. However, thiorphan alone or combined with captopril produced a small but significant potentiation of the airway obstructive response. The marked difference between pulmonary gas trapping and Evans' blue extravasation responses suggest that [Sar9,Met(O2)11]-SP-induced airway obstruction is not secondary to increased pulmonary edema.

Tachykinins contract trachea from Fischer 344 rats by interaction with a tachykinin NK1 receptor

The contractile effect of substance P, neurokinin A, carbachol and serotonin (5-HT) on isolated Fischer 344 rat trachea was studied. Contractions of two distal tracheal rings were measured isometrically in a 2-ml organ bath. Cumulative concentration-response curves were obtained for carbachol (EC50 ring 1: 1.6 x 10(-7) M and ring 2: 2.2 x 10(-7) M) and for 5-HT (EC50 ring 1: 10.2 x 10(-7) M and ring 2: 10.5 x 10(-7) M). Non-cumulative administration of substance P and neurokinin A (10(-8) to 10(-5) M) caused a concentration-dependent contraction with an EC50 (x 10(-7) M) of 1.10 +/- 0.27 and 1.97 +/- 0.45 respectively. The maximal contraction was 32.6 +/- 2.5% (substance P) and 32.6 +/- 1.5% (neurokinin A) of the maximal contraction with carbachol. In contrast, neither substance P nor neurokinin A caused contraction of trachea from BDE rats. The tachykinin NK1 receptor agonist, Ac[Arg6, Sar9, Met(O2)11] substance P-(6-11), caused a concentration-dependent contraction with an EC50 (x 10-(-9) M) of 1.38 +/- 0.09 and a maximal effect of 25.5 +/- 2.1% of the maximal contraction with carbachol. The tachykinin NK2 receptor agonist, [beta-Ala8]neurokinin A-(4-10), had a small contractile effect at 10(-6) M (8.4 +/- 0.8% of the maximal contraction with carbachol) while the tachykinin NK3 receptor agonist, senktide, had no effect up to 3.3 x 10(-6) M.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of neurokinin A receptor cDNAs from guinea-pig lung and rabbit pulmonary artery

cDNA clones for NK-2 receptors (NK-2R) were isolated from guinea-pig lung (GPl) and rabbit pulmonary artery (Rpa) using a polymerase chain reaction based methodology. The GPl NK-2R consists of 402 amino acids and encodes a protein with a relative molecular mass of 45,097. The Rpa NK-2R consists of 384 amino acids and encodes a protein with a relative molecular mass of 43,169. The GPl and Rpa NK-2Rs share significant amino acid sequence homology amongst themselves (90.1%), as well as with human, bovine, hamster and rat NK-2 receptors. The two receptors were stably transfected into mouse erythroleukemia cells, high-speed membranes were prepared from induced cells and their pharmacological properties examined utilizing [3H]-NKA in a receptor-binding assay. [3H]NKA bound to both NK-2Rs with high affinity (KD = 2-7 nM) and saturable (Bmax = 633-9000 fmol/mg protein) manner which was inhibited by GTP analogs. Competition experiments with agonists demonstrated identical order of potency in both NK-2Rs; NKA > [Nle10]NKA(4-10) > [beta-Ala8]NKA(4-10) > > Substance P > > > Senktide. Similarly, an identical profile for both receptors was observed with selective NK-2 antagonists: SR48,968 > MEN10,376 > > R396. The rank order of antagonist affinity is consistent with that in cloned human NK-2R and the observations of NK-2 receptor pharmacology in native human, guinea pig and rabbit tissues.