Oxaliplatin elicits mechanical and cold allodynia in rodents via TRPA1 receptor stimulation.

Platinum-based anticancer drugs cause neurotoxicity. In particular, oxaliplatin produces early-developing, painful, and cold-exacerbated paresthesias. However, the mechanism underlying these bothersome and dose-limiting adverse effects is unknown. We hypothesized that the transient receptor potential ankyrin 1 (TRPA1), a cation channel activated by oxidative stress and cold temperature, contributes to mechanical and cold hypersensitivity caused by oxaliplatin and cisplatin. Oxaliplatin and cisplatin evoked glutathione-sensitive relaxation, mediated by TRPA1 stimulation and the release of calcitonin gene-related peptide from sensory nerve terminals in isolated guinea pig pulmonary arteries. No calcium response was observed in cultured mouse dorsal root ganglion neurons or in naïve Chinese hamster ovary (CHO) cells exposed to oxaliplatin or cisplatin. However, oxaliplatin, and with lower potency, cisplatin, evoked a glutathione-sensitive calcium response in CHO cells expressing mouse TRPA1. One single administration of oxaliplatin produced mechanical and cold hyperalgesia in rats, an effect selectively abated by the TRPA1 antagonist HC-030031. Oxaliplatin administration caused mechanical and cold allodynia in mice. Both responses were absent in TRPA1-deficient mice. Administration of cisplatin evoked mechanical allodynia, an effect that was reduced in TRPA1-deficient mice. TRPA1 is therefore required for oxaliplatin-evoked mechanical and cold hypersensitivity, and contributes to cisplatin-evoked mechanical allodynia. Channel activation is most likely caused by glutathione-sensitive molecules, including reactive oxygen species and their byproducts, which are generated after tissue exposure to platinum-based drugs from cells surrounding nociceptive nerve terminals.

Montelukast inhibits inflammatory responses in small airways of the Guinea-pig.

Increased resistance in the small airways is a major contributor of airway obstruction in asthma. The role of leukotrienes (LT) in determining inflammation and obstruction of small size bronchi is not completely understood. Here, we have examined the effect of the cysteinyl-leukotriene (CysLT 1) receptor antagonist, montelukast, against the bronchoconstriction and inflammatory responses induced by exogenous leukotriene and by allergen challenge in small size (

Substance P released by TRPV1-expressing neurons produces reactive oxygen species that mediate ethanol-induced gastric injury.

Although neurokinin 1 receptor antagonists prevent ethanol (EtOH)-induced gastric lesions, the mechanisms by which EtOH releases substance P (SP) and SP damages the mucosa are unknown. We hypothesized that EtOH activates transient receptor potential vanilloid 1 (TRPV1) on sensory nerves to release SP, which stimulates epithelial neurokinin 1 receptors to generate damaging reactive oxygen species (ROS). SP release was assayed in the mouse stomach, ROS were detected using dichlorofluorescein diacetate, and neurokinin 1 receptors were localized by immunofluorescence. EtOH-induced SP release was prevented by TRPV1 antagonism. High dose EtOH caused lesions, and TRPV1 or neurokinin 1 receptor antagonism and neurokinin 1 receptor deletion inhibited lesion formation. Coadministration of low, innocuous doses of EtOH and SP caused lesions by a TRPV1-independent but neurokinin 1 receptor-dependent process. EtOH, capsaicin, and SP stimulated generation of ROS by superficial gastric epithelial cells expressing neurokinin 1 receptors by a neurokinin 1 receptor-dependent mechanism. ROS scavengers prevented lesions induced by a high EtOH dose or a low EtOH dose plus SP. Gastric lesions are caused by an initial detrimental effect of EtOH, which is damaging only if associated with TRPV1 activation, SP release from sensory nerves, stimulation of neurokinin 1 receptors on epithelial cells, and ROS generation.

Tachykinins in the respiratory tract.

Tachykinins as substance P and neurokinin A belong to a family of peptides, which are released from airway nerves after noxious stimulation. They influence numerous respiratory functions under both normal and pathological conditions including the regulation of airway smooth muscle tone, vascular tone, mucus secretion and immune functions. For the most part the synthesis/release of tachykinins is associated with neuronal cells; nevertheless, inflammatory and immune cells can synthesize and release tachykinins under certain physiological conditions. Moreover, this second cellular source of tachykinins may play an important role in inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD). Dual tachykinin (NK1 and NK2) receptor antagonists demonstrate a significant bronchoprotection and a possible future role in the development of novel therapeutic approaches. In addition, NK3 receptors could also possess a bronchoprotective action, however, their presence in the human respiratory tract still needs to be confirmed. The family of tachykinins has recently been extended by the discovery of a third tachykinin gene that encodes the previously unknown NK1 receptor selective tachykinins hemokinin 1, endokinin A and B. Together with other novel tachykinin peptides such as C14TKL-1 and virokinin further research is required to define their respiratory biological role in health and disease.

Protease-activated receptor-2 activation exaggerates TRPV1-mediated cough in guinea pigs.

A lowered threshold to the cough response frequently accompanies chronic airway inflammatory conditions. However, the mechanism(s) that from chronic inflammation results in a lowered cough threshold is poorly understood. Irritant agents, including capsaicin, resiniferatoxin, and citric acid, elicit cough in humans and in experimental animals through the activation of the transient receptor potential vanilloid 1 (TRPV1). Protease-activated receptor-2 (PAR2) activation plays a role in inflammation and sensitizes TRPV1 in cultured sensory neurons by a PKC-dependent pathway. Here, we have investigated whether PAR2 activation exaggerates TRPV1-dependent cough in guinea pigs and whether protein kinases are involved in the PAR2-induced cough modulation. Aerosolized PAR2 agonists (PAR2-activating peptide and trypsin) did not produce any cough per se. However, they potentiated citric acid- and resiniferatoxin-induced cough, an effect that was completely prevented by the TRPV1 receptor antagonist capsazepine. In contrast, cough induced by hypertonic saline, a stimulus that provokes cough in a TRPV1-independent manner, was not modified by aerosolized PAR2 agonists. The PKC inhibitor GF-109203X, the PKA inhibitor H-89, and the cyclooxygenase inhibitor indomethacin did not affect cough induced by TRPV1 agonists, but abated the exaggeration of this response produced by PAR2 agonists. In conclusion, PAR2 stimulation exaggerates TRPV1-dependent cough by activation of diverse mechanism(s), including PKC, PKA, and prostanoid release. PAR2 activation, by sensitizing TRPV1 in primary sensory neurons, may play a role in the exaggerated cough observed in certain airways inflammatory diseases such as asthma and chronic obstructive pulmonary disease.

Ethanol dilates coronary arteries and increases coronary flow via transient receptor potential vanilloid 1 and calcitonin gene-related peptide.

OBJECTIVES: Consumption of alcoholic beverages reduces the risk of coronary artery disease (CAD), and epidemiological studies have shown that ethanol per se is protective. However, the mechanism by which ethanol exerts protection is not fully known. Ethanol can stimulate neuropeptide-containing primary sensory neurons via the activation of transient receptor potential vanilloid 1 (TRPV1). Here, we have studied whether ethanol-mediated TRPV1 activation causes the release of calcitonin gene-related peptide (CGRP) that, via dilatation of coronary arteries and other mechanisms, may protect the heart from CAD. METHODS AND RESULTS: Ethanol caused a marked relaxation of small-sized porcine isolated coronary (0.008-2.37%, w/v) and human isolated gastro-epiploic (0.0008-2.37%, w/v) arteries in vitro, an effect that was abolished by capsaicin-desensitization, the TRPV1 antagonist capsazepine, and the CGRP receptor antagonist, CGRP(8-37). In guinea-pig isolated and perfused hearts, ethanol (0.079-0.79%, w/v) increased baseline coronary flow in a concentration-dependent manner: 0.237% ethanol doubled baseline coronary flow. This effect was also abolished by capsaicin-desensitization, capsazepine, and CGRP((8-37)). Finally, the ethanol-induced increase in CGRP release from guinea-pig isolated and perfused hearts and from slices of porcine coronary arteries was abolished by capsaicin-desensitization and by capsazepine. Similar functional and neurochemical results were obtained in all preparations with capsaicin. CONCLUSIONS: Ethanol, at low concentrations not dissimilar from those found in blood following low to moderate consumption of alcoholic beverages, releases CGRP within coronary arteries via stimulation of TRPV1 on perivascular sensory nerve terminals. Ethanol-induced release of CGRP may contribute to the reduction in the risk of CAD associated with alcohol consumption by various mechanisms, including the increase in coronary flow and arterial dilatation.

Pharmacological assessment of the duration of action of glycopyrrolate vs tiotropium and ipratropium in guinea-pig and human airways.

1. Our study was aimed at investigating the duration of the bronchodilator action of the antimuscarinc drug glycopyrrolate compared to tiotropium and ipratropium. In the guinea-pig isolated trachea, the time (t1/2) necessary for a contractile response to carbachol (0.3 microM) to return to 50% recovery after washout of the antagonist was studied. The offset of the antagonist effect of glycopyrrolate, tiotropium and ipratropium (10 nM each) was t1/2 = 4.0 +/- 0.5, > 4.5 and 0.5 +/- 0.1 h, respectively. At 4.5 h from the washout of the antagonist, the recovery of the response to carbachol was 50 +/- 8, 10 +/- 4 and 70 +/- 7%, respectively. 2. In the human isolated bronchus, the offset of the bronchodilator effects of glycopyrrolate (3 nM), tiotropium (1 nM) and ipratropium (10 nM) was t1/2 = 3.7 +/- 0.2; > 6 and 3.0 +/- 0.2 h, respectively. At 6.0 h from the washout of the antagonist, the recovery of the response to carbachol (1 microM) was 101 +/- 10, 27 +/- 3 and 110 +/- 10%, respectively. 4. In anaesthetized guinea-pigs, acetylcholine-induced bronchoconstriction was markedly reduced by intratracheal instillation of glycopyrrolate (3 nmol kg(-1); 88.1 +/- 4% inhibition), tiotropium (1.3 nmol kg(-1); 86.2 +/- 5% inhibition) or ipratropium (1.45 nmol kg(-1); 88.1 +/- 10% inhibition). These inhibitory effects assessed 3 or 24 h after antagonist administration were reduced to 69.9 +/- 5 and 29.7 +/- 6%; 28.3 +/- 5 and 14.2 +/- 5% for glycopyrrolate and ipratropium, respectively, whereas they remained stable (83.5 +/- 4; 70.6 +/- 6) for tiotropium. The residual inhibitory effect of glycopyrrolate was also assessed at 16 h from administration, and proved to be as low as that found at 24 h (31.2 +/- 10 vs 29.7 +/- 6%, respectively). 5. In conclusion, glycopyrrolate-induced bronchodilation has a longer duration than that of ipratropium, but less than that of tiotropium. The efficacy of a possible glycopyrrolate-based therapy for asthma or chronic obstructive pulmonary disease given once-a-day is not guaranteed by the present investigation.

Hydrogen sulfide causes vanilloid receptor 1-mediated neurogenic inflammation in the airways.

Hydrogen sulfide (H(2)S) is described as a mediator of diverse biological effects, and is known to produce irritation and injury in the lung following inhalation. Recently, H(2)S has been found to cause contraction in the rat urinary bladder via a neurogenic mechanism. Here, we studied whether sodium hydrogen sulfide (NaHS), used as donor of H(2)S, produces responses mediated by sensory nerve activation in the guinea-pig airways. NaHS evoked an increase in neuropeptide release in the airways that was significantly attenuated by capsaicin desensitization and by the transient receptor potential vanilloid 1 (TRPV1) antagonist capsazepine. In addition, NaHS caused an atropine-resistant contraction of isolated airways, which was completely prevented by capsaicin desensitization. Furthermore, NaHS-induced contraction was reduced by TRPV1 antagonism (ruthenium red, capsazepine and SB366791), and was abolished by pretreatment with the combination of tachykinin NK(1) (SR140333) and NK(2) (SR48968) receptor antagonists. In anesthetized guinea-pigs, intratracheal instillation of NaHS increased the total lung resistance and airway plasma protein extravasation. These two effects were reduced by TRPV1 antagonism (capsazepine) and tachykinin receptors (SR140333 and SR48968) blockade. Our results provide the first pharmacological evidence that H(2)S provokes tachykinin-mediated neurogenic inflammatory responses in guinea-pig airways, and that this effect is mediated by stimulation of TRPV1 receptors on sensory nerves endings. This novel mechanism may contribute to the irritative action of H(2)S in the respiratory system.

Dopamine type 2 receptor expression and function in rodent sensory neurons projecting to the airways.

Agonists of the dopamine receptors have been demonstrated to have bronchodilatory properties in pathologically constricted airways. The mechanism by which these agonists induce bronchodilatation is thought to involve airway sensory nerves. In this study, the expression and function of dopamine D(2) receptor were examined in sensory ganglia supplying the airways. Neuronal dopamine D(2) receptor mRNA expression was demonstrated by single-cell RT-PCR following laser-assisted microdissection. The projection of the neurons to the airways was confirmed by retrograde neuronal labeling. In functional studies, dopamine D(2) receptor agonists (AR-C65116AB and ropinirole) inhibited intraneuronal calcium mobilization in rat capsaicin-sensitive primary sensory neurons and capsaicin-induced plasma extravasation in the rat trachea. Our results provide support to the hypothesis that dopamine D(2) receptor activation inhibits neurogenic inflammation and proinflammatory reflex responses.

Effects of alpha calcitonin gene-related peptide in human bronchial smooth muscle and pulmonary artery.

Although airway and pulmonary vessel tone are regulated predominantly by cholinergic and adrenergic impulses, biologically active peptides such as calcitonin gene-related peptide (CGRP) may significantly influence human smooth muscle tone in normal and pathophysiological states. In the present study, the expression of CGRP and its receptor CGRPR-1 and the biological effect of the peptide were investigated in human airways and pulmonary arteries. Immunohistochemistry revealed the presence of CGRP in human airway nerves and neuro-epithelial cells, whereas the receptor was found in epithelial cells and smooth muscle myocytes of the bronchi and in pulmonary artery endothelium. On precontracted bronchi (3-4 mm in diameter) alpha-CGRP (0.01-10 nM) caused a concentration-dependent contraction on epithelium-denuded bronchi, whereas no significant effect was recorded in bronchi with intact epithelium. In pulmonary arteries (2-6 mm in diameter), alpha-CGRP caused a concentration-dependent relaxation of endothelium intact and denuded vessels. Pre-treatment with indomethacin, but not with l-NAME, prevented the relaxation induced by alpha-CGRP in pulmonary arteries suggesting that prostaglandins but not nitric oxide (NO) are involved in the intracellular signal transduction pathway. The effects induced by alpha-CGRP in bronchi and vessels were prevented by application of the antagonist CGRP((8-37)). In summary, the present studies examined the biological function of CGRP in human airways and demonstrated a constrictory effect of CGRP only in epithelium-denuded airway smooth muscle indicating an alteration of CGRP airway effects in respiratory tract pathological states with damaged epithelium such as chronic obstructive pulmonary disease or bronchial asthma.

Ethanol causes inflammation in the airways by a neurogenic and TRPV1-dependent mechanism.

Ethanol (EtOH) stimulates peptidergic primary sensory neurons via the activation of the transient receptor potential vanilloid-1 (TRPV1). EtOH is also known to trigger attacks of asthma in susceptible individuals. Our aim was to investigate whether EtOH produces airway inflammation via a TRPV1-dependent mechanism and to verify whether this effect is produced via a mechanism distinct from that of acetaldehyde (AcH). EtOH caused a Ca(2+)-dependent release of neuropeptides from guinea pigs airways, an effect that was inhibited by both capsaicin pretreatment and the TRPV1 antagonist capsazepine (CPZ). Furthermore, EtOH contracted isolated guinea pig bronchi, showing efficacy similar to that of carbachol: this effect of EtOH was sensitive to capsaicin pretreatment, tachykinin receptor blockade, and TRPV1 antagonism. The EtOH metabolite AcH also contracted isolated guinea pig bronchi, but this action was not affected by capsaicin pretreatment, tachykinin receptor, or TRPV1 antagonism. EtOH by intravenous or intragastric route of administration caused bronchoconstriction and increased plasma extravasation in the guinea pig airways, effects that were abolished selectively by CPZ. In conclusion, we have demonstrated that EtOH stimulates peptidergic primary sensory neurons in the guinea pig airways by TRPV1 activation. This excitatory effect of EtOH, distinct from that of AcH, results in neurogenic inflammatory responses that may contribute to the mechanism of EtOH-induced asthma.

Capsaicin-like effects of N-arachidonoyl-dopamine in the isolated guinea pig bronchi and urinary bladder.

A capsaicin-like endogenous ligand of vanilloid (VR1) receptors, N-arachidonoyl-dopamine, was recently identified in bovine and rat nervous tissue, and found to be almost as potent as capsaicin, and 5-10-fold more potent than anandamide, on these receptors, both in isolated cells and in vivo. Here we have investigated if N-arachidonoyl-dopamine also exerts other capsaicin-like effects at VR1 receptors in some isolated organ preparations. N-arachidonoyl-dopamine exerted a potent contractile response of guinea pig isolated bronchi (EC50=12.6 +/- 1.7 microM, Emax=69.2 +/- 2.4% of carbachol Emax), which was blocked by pre-treatment with capsaicin or with the VR1 antagonist capsazepine, as well as by a combination of tachykinin NK1 and NK2 receptor antagonists. In this assay, N-arachidonoyl-dopamine was less and more potent and/or efficacious than capsaicin (EC50=40.0 nM; Emax=93.5%) and anandamide (EC50=15.2 microM, Emax=38.0%), respectively. Unlike capsaicin and anandamide, forskolin or ethanol did not enhance N-arachidonoyl-dopamine effect in this preparation, whereas epithelial denudation resulted in a 2.5-fold increase in potency without affecting the efficacy. N-arachidonoyl-dopamine also contracted the isolated guinea pig urinary bladder, although in this preparation, as well as in the isolated rat urinary bladder, the potency (EC50=3.7 +/- 0.3 and 19.9 +/- 0.1 microM) and/or efficacy (Emax=12.0 +/- 0.1% and 20.7 +/- 0.7% of carbachol Emax) of the compound were significantly lower than those of both capsaicin and anandamide. These data suggest that the extent to which exogenous N-arachidonoyl-dopamine activates VR1 receptor in isolated organs is largely dependent on pharmacodynamics and bioavailability.

Halogenation of a capsaicin analogue leads to novel vanilloid TRPV1 receptor antagonists.

1. The C-5 halogenation of the vanillyl moiety of resiniferatoxin, an ultrapotent agonist of vanilloid TRPV1 receptors, results in a potent antagonist for these receptors. Here, we have synthesized a series of halogenated derivatives of 'synthetic capsaicin' (nonanoyl vanillamide=nordihydrocapsaicin) differing for the nature (iodine, bromine-chlorine) and the regiochemistry (C-5, C-6) of the halogenation. 2. The activity of these compounds was investigated on recombinant human TRPV1 receptors overexpressed in HEK-293 cells. None of the six compounds exerted any significant agonist activity, as assessed by measuring their effect on TRPV1-mediated calcium mobilization. Instead, all compounds antagonized, to various extents, the effect of capsaicin in this assay. 3. All 6-halo-nordihydrocapsaicins behaved as competitive antagonists against human TRPV1 according to the corresponding Schild's plots, and were more potent than the corresponding 5-halogenated analogues. The iodo-derivatives were more potent than the bromo- and chloro-derivatives. 4. Using human recombinant TRPV1, 6-iodo-nordihydrocapsaicin (IC(50)=10 nM against 100 nM capsaicin) was about four times more potent than the prototypical TRPV1 antagonist, capsazepine, and was tested against capsaicin also on native TRPV1 in: (i) rat dorsal root ganglion neurons in culture; (ii) guinea-pig urinary bladder; and (iii) guinea-pig bronchi. In all cases, except for the guinea-pig bronchi, the compound was significantly more potent than capsazepine as a TRPV1 antagonist. 5. In conclusion, 6-iodo-nordihydrocapsaicin, a stable and easily prepared compound, is a potent TRPV1 antagonist and a convenient replacement for capsazepine in most of the in vitro preparations currently used to assess the activity of putative vanilloid receptor agonists.

Bradykinin B2 receptors mediate contraction in the normal and inflamed human gallbladder in vitro.

BACKGROUND & AIMS: The components of the kinin system, including kinongens, kininogenases, and B(2) and B(1) receptors, are expressed and activated during inflammation. Here, we investigated the expression of the kinin B(2) receptor messenger RNA, kininogen and kallikrein immunoreactivity, and the ability of kinins to contract control and inflamed gallbladders in vitro. METHODS: Human gallbladders, obtained from patients undergoing cholecystectomy either for acute cholecystitis secondary to gallstone disease or during elective gastro-entero-pancreatic surgery (controls), were processed for reverse-transcription polymerase chain reaction analysis, kallikrein and kininogen immunohistochemistry, binding studies, and in vitro contractility studies. RESULTS: Tissue expression of B(2) receptor messenger RNA and specific binding of [(3)H]-bradykinin increased significantly in acute cholecystitis compared to controls. Kallikrein immunoreactivity was detected in the epithelium and infiltrating leukocytes, whereas kininogen immunoreactivity in the lumen of blood vessels and interstitial space. Bradykinin contracted isolated strips of control and acute cholecystitis gallbladders. In acute cholecystitis tissue, efficacy of bradykinin was higher than that of control gallbladders and similar to that of cholecystokinin. The contraction induced by bradykinin was significantly attenuated by B(2) receptor antagonism but not by cyclooxygenase inhibition and B(1), muscarinic, or tachykinin receptor antagonism. CONCLUSIONS: All the components of the kinin system are expressed in the human gallbladder. Bradykinin is a powerful spasmogen via B(2) receptor activation in the normal and, especially, in the inflamed human gallbladder.

Proteinase-activated receptor-1 (PAR-1) activation contracts the isolated human renal artery in vitro.

1. The in vitro motor function of protease-activated recepter-1 (PAR-1), PAR-2 and PAR-4 and the presence by immunohistochemistry of PAR-1 in the human renal artery have been investigated. 2. Thrombin and the human PAR-1 (SFLLRN-NH(2)) activating peptide, but not the PAR-1 reverse peptide (NRLLFS-NH(2)), contracted both endothelial-intact and endothelial-denuded human renal artery strips, whereas no relaxation was observed either in strips non-precontracted or precontracted with phenylephrine. Maximum contraction by thrombin or SFLLRN-NH(2) was about 60% of phenylephrine. However, thrombin was approximately 1000-fold more potent than SFLLRN-NH(2). 3. PAR-1 desensitisation, using repeated applications of SFLLRN-NH(2), almost completely blocked the response to thrombin. The contractile effect produced by thrombin and SFLLRN-NH(2) was not affected by nitric oxide synthase inhibition, but was significantly reduced by cyclooxygenase blockade. 4. Trypsin, the PAR-2 (SLIGKV-NH(2) and SLIGRL-NH(2)) and PAR-4 (GYPGQV-NH(2) and AYPGKF-NH(2)) activating peptides did not produce any significant contraction or relaxation. 5. In agreement with the motor function data immunohistochemistry showed specific staining patterns for PAR-1 in the human renal artery. 6. Combined, these studies would suggest a possible role for PAR-1 in renal vascular homeostasis.

Neurogenic responses mediated by vanilloid receptor-1 (TRPV1) are blocked by the high affinity antagonist, iodo-resiniferatoxin.

(1) Stimulation of the vanilloid receptor-1 (TRPV1) results in the activation of nociceptive and neurogenic inflammatory responses. Poor specificity and potency of TRPV1 antagonists has, however, limited the clarification of the physiological role of TRPV1. (2) Recently, iodo-resiniferatoxin (I-RTX) has been reported to bind as a high affinity antagonist at the native and heterologously expressed rat TRPV1. Here we have studied the ability of I-RTX to block a series of TRPV1 mediated nociceptive and neurogenic inflammatory responses in different species (including transfected human TRPV1). (3) We have demonstrated that I-RTX inhibited capsaicin-induced mobilization of intracellular Ca(2+) in rat trigeminal neurons (IC(50) 0.87 nM) and in HEK293 cells transfected with the human TRPV1 (IC(50) 0.071 nM). (4) Furthermore, I-RTX significantly inhibited both capsaicin-induced CGRP release from slices of rat dorsal spinal cord (IC(50) 0.27 nM) and contraction of isolated guinea-pig and rat urinary bladder (pK(B) of 10.68 and 9.63, respectively), whilst I-RTX failed to alter the response to high KCl or SP. (5) Finally, in vivo I-RTX significantly inhibited acetic acid-induced writhing in mice (ED(50) 0.42 micro mol kg(-1)) and plasma extravasation in mouse urinary bladder (ED(50) 0.41 micro mol kg(-1)). (6) In in vitro and in vivo TRPV1 activated responses I-RTX was approximately 3 log units and approximately 20 times more potent than capsazepine, respectively. This high affinity antagonist, I-RTX, may be an important tool for future studies in pain and neurogenic inflammatory models.