Differential effects of topically applied formalin and aromatic compounds on neurogenic-mediated microvascular leakage in rat skin

Various volatile organic compounds (VOCs) act as a causative agent of skin inflammation. We investigated the effect of topical application of several VOCs and formalin on microvascular leakage in rat skin. We tested capsaicin, which is a reagent that specifically causes the skin response via endogenously released tachykinins. Evans blue dye extravasation served as an index of the increase in skin vascular permeability. After shaving the abdomen, we applied formalin, m-xylene, toluene, styrene, benzene, ethylbenzene, acetone, diethyl ether, hexane, heptane, cyclohexane and capsaicin to the skin. At 40 min after application, skin samples were collected. Among all of the VOCs tested, all of the aromatic compounds significantly produced skin microvascular leakage that was similar to formalin and capsaicin. We also investigated the skin responses seen after the intravenous administration of CP-99,994 (1.5 or 5 mg/kg), which is a tachykinin NK1 receptor antagonist, ketotifen (1 or 3 mg/kg), which is a histamine H1 receptor antagonist that stabilizes the mast cells, and the topical application of capsazepine (22.5 or 50 mM), which is the transient receptor potential vanilloid 1 (TRPV1) antagonist. The response induced by formalin and capsaicin was completely inhibited by CP-99,994. On the other hand, the antagonist partially reduced the response induced by m-xylene, toluene and styrene by 39%, 50% and 46%, respectively. Capsazepine and ketotifen did not alter the response induced by formalin or any of the aromatic compounds. Like capsaicin, formalin and the aromatic compounds at least partially caused skin microvascular leakage, which was due to tachykinin NK1 receptor activation related to the release of tachykinins from the sensory nerve endings. However, it is unlikely that mast cells and TRPV1 play an important role in the skin response.     

速激肽受体拮抗剂抗豚鼠过敏性哮喘的作用

实验目的是研究速激肽与哮喘的关系,评价速激肽受体拮抗剂对哮喘的治疗作用。结果表明,ip速激肽NK-1受体拮抗剂CP-96345,NK- 2受体拮抗剂SR-48968或两药合用,均可有效减少清醒致敏豚鼠吸入抗原引起的喘息反应,降低过敏性休克死亡率。SR-48968减轻麻醉豚鼠抗原引起的气道收缩,并浓度依赖性降低抗原引起的气管和支气管平滑肌收缩幅度。CP-96345可抑制抗原诱导的支气管和肺叶伊文思蓝渗出,仅对支气管平滑肌收缩有部分抑制作用。结果提示,速激肽参与哮喘发病,速激肽受体拮抗剂可抑制抗原诱导的气道平滑肌收缩(NK-2受体)和微血管渗漏(NK-1受体)而减轻哮喘反应。     

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 immuno-reactive 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.     

The anti-emetic effects of CP-99,994 in the ferret and the dog: role of the NK1 receptor.

1. The selective NK1 receptor antagonist, CP-99,994, produced dose-related (0.1-1.0 mg kg-1, s.c.) inhibition of vomiting and retching in ferrets challenged with central (loperamide and apomorphine), peripheral (CuSO4) and mixed central and peripheral (ipecac, cisplatin) emetic stimuli. 2. Parallel studies with the enantiomer, CP-100,263 (1 mg kg-1, s.c.), which is > 1,000 fold less potent as a NK1 antagonist, indicated that it was without significant effect against CuSO4, loperamide, cisplatin and apomorphine-induced emesis. Against ipecac, it inhibited both retching and vomiting, expressing approximately 1/10th the potency of CP-99,994. 3. The 5-HT3 receptor antagonist, tropisetron (1 mg kg-1, s.c.) inhibited retching and vomiting to cisplatin and ipecac, but not CuSO4 or loperamide. 4. CP-99,994 (1 mg kg-1, i.v.) blocked retching induced by electrical stimulation of the ventral abdominal vagus without affecting the cardiovascular response, the apnoeic response to central vagal stimulation or the guarding and hypertensive response to stimulation of the greater splanchnic nerves. CP-99,994 (1 mg kg-1, i.v.) did not alter baseline cardiovascular and respiratory parameters and it failed to block the characteristic heart rate, blood pressure and respiratory rate/depth changes in response to i.v. 2-methyl-5-HT challenge (von Bezold-Jarisch reflex). 5. Using in vitro autoradiography, [3H]-substance P was shown to bind to several regions of the ferret brainstem with the density of binding in the nucleus tractus solitarius being much greater than in the area postrema. This binding was displaced by CP-99,994 in a concentration-related manner. 6. In dogs, CP-99,994 (40 micrograms kg-1 bolus and 300 micrograms kg-1 h-1, i.v.) produced statistically significant reductions in vomiting to CuSO4 and apomorphine as well as retching to CuSO4. 7. Together, these studies support the hypothesis that the NK1 receptor antagonist properties of CP-99,994 are responsible for its broad spectrum anti-emetic effects. They also suggest that CP-99,994 acts within the brainstem, most probably within the nucleus tractus solitarius although the involvement of the area postrema could not be excluded.     

速激肽受体拮抗剂对豚鼠离体气道平滑肌的作用

速激肽NK－2受体拮抗剂SR－48968（1μmol／L）能抑制抗原（OA，10mg／L）诱导的气管和支气管平滑肌收缩；NK－1受体拮抗剂CP－96345（1μmol／L）仅抑制支气管的收缩．两药均抑制辣椒素和P物质引起的支气管平滑肌收缩，对组胺和氨甲酸胆碱引起气管、支气管收缩作用无明显影响．结果证明速激肽参与抗原诱导的气道平滑肌收缩，速激肽受体拮抗剂具有抗过敏性哮喘的作用．     

Lack of a role for bradykinin in inhaled sodium metabisulphite-induced airway microvascular leakage in guinea pigs

We have investigated the role of bradykinin in airway microvascular leakage and bronchoconstriction induced by inhaled sodium metabisulphite (MBS) in guinea pigs. A selective bradykinin B2 receptor antagonist, HOE 140 (D-Arg[Hyp³, Thi⁵, D-Tic⁷, Oic⁸]-bradykinin), was used because this drug has been shown to abolish the airway responses induced by bradykinin. Lung resistance (R_L) was measured for 6 min after challenge with MBS, followed by measurement of extravasation of Evans Blue dye into airway tissues, used as an index of plasma exudation. Aerosolized MBS (40 and 80 mmol/L, 30 breaths) induced a significant increase in R_L and leakage of dye in the trachea, main bronchi and intrapulmonary airways, whereas 20 mmol/L MBS caused these responses except for the dye leakage in the trachea and main bronchi. HOE 140 (100 nmol/kg iv) had no effect against these airway responses. We conclude that bradykinin-mediated mechanisms do not play a significant role in the acute airway effects induced by inhaled MBS.     

Involvement of tachykinins in plasma extravasation induced by bradykinin and low pH medium in the guinea-pig conjunctiva.

1. The effect of bradykinin, capsaicin, substance P and low pH medium on plasma extravasation in the guinea-pig conjunctiva has been studied. Evans blue dye was measured in the conjunctiva after local instillation of the agents into the conjunctival sac. 2. Bradykinin (2-50 nmol), capsaicin (20-50 nmol) and substance P (0.5-5 nmol) caused a dose-dependent increase in plasma extravasation with the following order of potency: substance P > bradykinin = capsaicin. The effect of capsaicin (50 nmol) and substance P (5 nmol) was abolished by the tachykinin NK1 receptor antagonist, CP-99,994 (8 mumol kg-1, i.v.) (P < 0.01), whereas CP-100,263 (8 mumol kg-1, i.v.) the inactive enantiomer of CP-99,994 was without effect. CP-99,994 inhibited by 70% (P < 0.01) the effect of bradykinin. 3. The kinin B2 receptor antagonist, Hoe 140 (icatibant, 10 nmol kg-1, i.v.) abolished the response to bradykinin (50 nmol) (P < 0.01), but did not affect the responses to capsaicin (50 nmol) or substance P (5 nmol). Plasma extravasation induced by low pH medium (pH 1) was abolished by CP-99,994 (P < 0.01) and by Hoe 140 (P < 0.01). 4. The present findings suggest that: endogenous or exogenous tachykinins increase plasma extravasation in the guinea-pig conjunctiva by activation of NK1 receptors; bradykinin-induced plasma extravasation is mediated by tachykinin release from sensory nerve endings; low pH media cause plasma extravasation via release of kinins that by activation of B2 receptors release tachykinins from sensory nerve endings.     

The tachykinin NK1 receptor antagonist CP-99,994 attenuates cisplatin induced emesis in the ferret

The tachykinin NK₁ receptor antagonist CP-99,994 ((+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine) (0.3–3 mg/kg i.v.), but not its inactive enantiomer CP-100,263, attenuated the retching and vomiting induced by cisplatin (10 mg/kg i.v.) in the ferret. CP-99,994, 3 mg/kg i.v., prevented vomiting in all ferrets tested. Since substance P is the preferred ligand at the NK₁ receptor subtype these data support a role for the release of this peptide during the emetic response induced by cytotoxic chemotherapeutic agents.     

Pharmacological modulation of inhaled sodium metabisulphite-induced airway microvascular leakage and bronchoconstriction in the guinea-pig.

1. We have investigated the effects of chlorpheniramine, atropine and capsaicin pretreatment on inhaled sodium metabisulphite (MBS)-induced airway microvascular leakage and bronchoconstriction in anaesthetized guinea-pigs in order to clarify the mechanisms involved in these responses. The effects of frusemide and nedocromil sodium were also examined. 2. Lung resistance (RL) was measured for 6 min after inhalation of MBS (20, 40, 80 and 200 mM; 30 breaths), followed by measurement of extravasation of Evans blue dye into airway tissues, used as an index of airway microvascular leakage. MBS caused an increase in RL and leakage of dye at all airway levels in a dose-dependent manner. 3. Chlorpheniramine (10 mg kg-1, i.v.), atropine (1 mg kg-1, i.v.), their combination or inhaled nedocromil sodium (10 mg ml-1, 7 min) had no effect against the airway microvascular leakage induced by 80 mM MBS (30 breaths). Capsaicin pretreatment (50 mg kg-1, s.c.) caused a significant decrease in the leakage of dye in the main bronchi and inhaled frusemide (10 mg ml-1, 7 min) also in the main bronchi and proximal intrapulmonary airway. 4. Chlorpheniramine, atropine, their combination, capsaicin pretreatment and frusemide, but not nedocromil sodium, inhibited significantly the peak RL induced by 80 mM MBS (30 breaths) by approximately 50%. 5. We conclude that a cholinergic reflex and neuropeptides released from sensory nerve endings may participate in the mechanisms of MBS-induced airway responses. Frusemide but not nedocromil sodium may have an inhibitor effect on these neural mechanisms. The inhibitory effect of nedocromil sodium against lower doses of MBS is not excluded.     

Antinociceptive activity of the tachykinin NK1 receptor antagonist, CP-99,994, in conscious gerbils.

1. The ability of CP-99,994, and its less active enantiomer, CP-100,263, to inhibit spontaneous behaviours and hyperalgesia induced by central infusion of the NK1 receptor agonist, GR73632 or intraplantar injection of formalin was investigated in rats and gerbils. 2. GR73632 (3 pmol, i.c.v.)-induced foot tapping in gerbils was dose-dependently inhibited by CP-99,994 (0.1-1 mg kg-1, s.c.), but not by CP-100,263 (10 mg kg-1, s.c.) using pretreatment times up to 60 min. The centrally active dose-range for CP-99,994 was increased to 1-10 mg kg-1 s.c. with a higher challenge dose of GR73632 (30 pmol, i.c.v.). 3. In gerbils, intrathecal (i.t.) injection of GR73632 (30 pmol) elicited behaviours (licking, foot tapping or flinching and face washing) which closely resembled, but which was less specifically localized than, behaviours seen in animals injected with formalin (0.1-5%) into one hindpaw. 4. In rats, CP-100,263, but not CP-99,994 (up to 30 mg kg-1), inhibited the early phase response to intraplantar injection of 5% formalin (ID50 = 13.9 mg kg-1). The late phase was inhibited by both compounds (ID50 values 36.3 and 20.9 mg kg-1, respectively). In gerbils, there was marginal evidence for enantioselective inhibition of the early phase induced by formalin (2%). The ID50 values were 6.2 mg kg-1 for CP-99,994 and 13.4 mg kg-1 for CP-100,263.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of neurogenic plasma exudation in guinea-pig airways by CP-96,345, a new non-peptide NK1 receptor antagonist.

A new non-peptide tachykinin antagonist, CP-96,345, inhibited airway plasma exudation induced in guinea-pigs by i.v. substance P in a dose-dependent manner with dose-ratios in the main bronchi of 5 at 1 nmol kg-1 and 19 at 100 nmol kg-1. At 100 nmol kg-1, CP-96,345 completely inhibited plasma exudation induced by either electrical stimulation of the cervical vagus nerves or i.v. capsaicin, indicating inhibition of the effects of endogenous tachykinins, but did not inhibit the bronchoconstrictor response to neurokinin A, suggesting selectivity for NK1 receptors. CP-96,345 may be useful in examining the role of endogenous tachykinins in vivo.     

Neurogenic plasma leakage in mouse airways

1. This study sought to determine whether neurogenic inflammation occurs in the airways by examining the effects of capsaicin or substance P on microvascular plasma leakage in the trachea and lungs of male pathogen-free C57BL/6 mice. 2. Single bolus intravenous injections of capsaicin (0.5 and 1 micromol kg(-1), i.v.) or substance P (1, 10 and 37 nmol kg(-10, i.v.) failed to induce significant leakage in the trachea, assessed as extravasation of Evans blue dye, but did induce leakage in the urinary bladder and skin. 3. Pretreatment with captopril (2.5 mg kg(-1), i.v.), a selective inhibitor of angiotensin converting enzyme (ACE), either alone or in combination with phosphoramidon (2.5 mg kg(-1), i.v.), a selective inhibitor of neutral endopeptidase (NEP), increased baseline leakage of Evans blue in the absence of any exogenous inflammatory mediator. The increase was reversed by the bradykinin B2 receptor antagonist Hoe 140 (0.1 mg kg(-1), i.v.). 4. After pretreatment with phosphoramidon and captopril, capsaicin increased the Evans blue leakage above the baseline in the trachea, but not in the lung. This increase was reversed by the tachykinin (NK1) receptor antagonist SR 140333 (0.7 mg kg(-1), i.v.), but not by the NK2 receptor antagonist SR 48968 (1 mg kg(-1), i.v.). 5. Experiments using Monastral blue pigment as a tracer localized the leakage to postcapillary venules in the trachea and intrapulmonary bronchi, although the labelled vessels were less numerous in mice than in comparably treated rats. Blood vessels of the pulmonary circulation were not labelled. 6. We conclude that neurogenic inflammation can occur in airways of pathogen-free mice, but only after the inhibition of enzymes that normally degrade inflammatory peptides. Neurogenic inflammation does not involve the pulmonary microvasculature.     

Effect of Hoe 140, a new bradykinin receptor antagonist, on bradykinin- and platelet-activating factor-induced bronchoconstriction and airway microvascular leakage in guinea pig.

We have investigated the effect of a new bradykinin receptor antagonist, Hoe 140 (D-Arg- Hyp3,Thi5,D-Tic7,Oic8]-bradykinin), on bradykinin- and platelet-activating factor (PAF)-induced bronchoconstriction and airway microvascular leakage in anesthetized guinea pigs. Extravasation of Evans blue dye and lung resistance were measured simultaneously. Both i.v. (15 nmol/kg) and inhaled bradykinin (1 mM, 45 breaths) caused a significant increase in lung resistance and leakage of dye at all airway levels. Hoe 140 (100 nmol/kg i.v.) almost completely inhibited these airway responses induced by bradykinin except for dye extravasation in trachea induced by inhaled bradykinin. Inhaled PAF (3 mM, 30 breaths) significantly increased lung resistance and leakage of due at all airway levels, but Hoe 140 had no effect on these responses. Bradykinin-induced bronchoconstriction and airway microvascular leakage are predominantly mediated by activation of B2 receptor, since Hoe 140 is a B2 receptor antagonist. Bradykinin receptor-mediated mechanisms do not play an important role on inhaled PAF-induced bronchoconstriction and microvascular leakage.     

Quantitative assessment of increased airway microvascular permeability to 125I-labelled plasma fibrinogen induced by platelet activating factor and bradykinin.

1. We have used 125I-labelled fibrinogen (I-FN) in experiments monitoring plasma extravasation from vessels within guinea-pig trachea and peripheral lung tissue in response to platelet activating factor (PAF) and bradykinin (BK). Retained tissue radioactivity derived from I-FN was detected by direct measurement and by autoradiography. 2. Both PAF and BK caused concentration-dependent increases in radioactivity in trachea and peripheral lung, with PAF being approximately 1000 times more potent than BK at both sites. On a wet weight basis, mean tracheal leakage responses to PAF and BK were approximately 6 times and 2 times greater respectively than those in peripheral lung. Furthermore, in trachea, the maximal response to PAF was nearly twice that to BK, although they were approximately equiactive in peripheral lung. The dipeptidyl carboxypeptidase inhibitor, enalapril (1 mg kg-1, i.v.), increased the potency of BK by approximately 40 fold. 3. In trachea, PAF (50 ng kg-1, i.v.)-induced leakage was selectively inhibited by the PAF receptor antagonist, WEB 2086 (5-50 micrograms kg-1), while responses to BK (50 micrograms kg-1, i.v.) were selectively inhibited by the BK2 receptor antagonist NPC 349 (0.5-1 mg kg-1). Neither PAF nor BK-induced leakage were significantly altered by pretreatment with the histamine H1-receptor antagonists mepyramine (10 micrograms kg-1) or ketotifen (50 micrograms kg-1) or the leukotriene receptor antagonist SKF 104353. These data indicate that both agonists caused direct, specific receptor operated increases in tracheal vascular permeability to plasma macromolecules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Enantiospecific inhibition of emesis induced by nicotine in the house musk shrew (Suncus murinus) by the neurokinin1 (NK1) receptor antagonist CP-99,994

Effects of the NK₁ receptor antagonist CP-99,994 on nicotine-induced emesis were examined in Suncus murinus. CP-99,994 (3 and 10 mg/kg i.p.) attenuated emesis to (−)nicotine (4 mg/kg s.c.). CP-100,263 (3 and 10 mg/kg i.p.), the enantiomer of CP-99,994 with 1000 fold lower affinity for the NKj receptor was without effect and RP67580 reduced emesis only at a dose of 30 mg/kg i.p. Responses to NK₁ antagonists were ranked according to their affinities for the Suncus murinus NK₁ receptor.     

The effect of the NK1 receptor antagonist CP-99,994 on emesis and c-fos protein induction by loperamide in the ferret

The site of the anti-emetic action of the neurokinin1 receptor antagonist CP-99,994 was studied in the ferret using the centrally acting opiate receptor agonist loperamide at a dose (0.5 mg/kg s.c.) which induced emesis in all animals tested. CP-99,994 (1 mg/kg, s.c.x2) abolished the emetic response (retching and vomiting) and the behaviours (licking, wet dog shakes, mouth scratching and gagging) induced by loperamide over a 2-h observation period. The enantiomer of this compound CP-100,263 (1 mg/kg, s.c.x2) did not have any significant effect on emesis or related behaviours. Loperamide (0.5 mg/kg s.c.) administration (but not its vehicle) resulted in dense fos-like immunoreactivity (FLI) mainly throughout the rostro-caudal extent of the nucleus tractus solitarius but not the area postrema. Although CP-99,994 (1 mg/kgx2) abolished the loperamide-induced emesis, it did not have any statistically significant effect on FLI in the brainstem. In loperamide and CP-100,263 (1 mg/kg, s.c.x2) treated animals FLI was comparable to that in animals treated with loperamide and CP-99,994. The results from this study taken together with those from previous studies indicate that loperamide exerts its emetic effect via nucleus tractus solitarius dendrites projecting into the area postrema. The lack of significant effect of CP-99,994 on the FLI induced by loperamide in this nucleus suggests that it is acting at a site "deep" in the nucleus tractus solitarius or elsewhere. The marked reduction in behaviours associated with loperamide administration by CP-99,994 provides a preliminary indication that NK1 receptor antagonist (as represented by CP-99,994) may in the clinic have effects on behaviours induced by emetic agents in addition to their previously described effects on retching and vomiting.     

Bradykinin-induced plasma exudation in guinea-pig airways: involvement of platelet activating factor.

1. We studied the effect of bradykinin on plasma exudation in the airways of the anaesthetized guinea-pig in vivo. Tissue content of extravasated Evans blue dye was used as an index of protein exudation in the larynx, trachea, main bronchi and intrapulmonary airways (i.p.a.). 2. Bradykinin increased the content of Evans blue in all tissues studied in a dose-related manner. The response was greatest in the main bronchi and i.p.a., less in the trachea and least in the larynx. A dose of 47 nmol kg-1 was the lowest tested which caused significant (P less than 0.001) plasma exudation with increases in leakage above control values of 256% in the larynx, 405% in the trachea, 394% in the main bronchi and 485% in intrapulmonary airways. 3. Leakage was significantly (P less than 0.05) increased above control values by 1 min after bradykinin (47 nmol kg-1) in the main bronchi and intrapulmonary airways and was maximal in all airways 5 min after bradykinin. Although reduced by 15 min, the tissue content of dye was still significantly (P less than 0.05) increased 2 h after bradykinin. 4. The prolonged tissue dye retention was due to a later phase of slow and maintained exudation preventing full clearance of dye after the initial response. 5. The initial phase of leakage was partially attenuated by the platelet activating factor (PAF) receptor antagonists WEB 2086 or BN 52021, by indomethacin or by inhibiting sensory nerve activation by opioid anaesthesia: it was not affected by mepyramine and cimetidine nor by the sulphidopeptide leukotriene receptor antagonists FPL 55712 or ICI 198,615.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alteration in airway microvascular leakage induced by sensorineural stimulation in rats exposed to inhaled formaldehyde

Inhaled formaldehyde can rapidly produce microvascular leakage in the airway through stimulation of tachykinin NK1 receptors by tachykinins released from sensory nerves. Tachykinin NK1 receptors are known to be internalized in the cytoplasm after being stimulated, thus leading to transient attenuation of their action. We investigated time changes in airway microvascular leakage during formaldehyde inhalation for 45 min, and whether pre-inhalation of formaldehyde (5 ppm, 30 min) decreases the responses induced by subsequent inhaled formaldehyde (5 ppm, 15 min), intravenous capsaicin (75 μg/kg) and intravenous substance P (10 μg/kg) in rat airway. Evans blue dye content extravasated into the tissues was measured as an index of plasma leakage. Formaldehyde rapidly produced dye leakage in the airway, a response that ended within 15 min after the start of formaldehyde inhalation. Pre-inhalation of formaldehyde markedly decreased the responses induced by formaldehyde and capsaicin, but not substance P. However, dye leakage induced by formaldehyde was significantly enhanced by formaldehyde inhalation 20 h earlier. Our results suggest that tachyphylaxis in neurogenic airway microvascular leakage seen after formaldehyde inhalation may be due to impairment of tachykinin release from sensory nerves or decreases in tachykinins within sensory nerves. However, desensitization of tachykinin NK1 receptors was unlikely to be important in the tachyphylactic response.     

Role of tachykinins in airway narrowing induced by cigarette smoke in guinea pigs

To investigate the mechanism of the airway narrowing induced by cigarette smoke, anaesthetized guinea pigs were exposed to 200 puffs of smoke for 10 min. Airway narrowing was assessed by monitoring the total pulmonary resistance (R_L). Plasma extravasation was determined by measuring the amount of Evans blue dye extravasated into the trachea and main bronchi. Exposure to cigarette smoke caused a marked airway narrowing and plasma extravasation. Pretreatment with the dual NK₁ and NK₂ receptor antagonist, FK224, abolished such airway narrowing and significantly inhibited the extravasation. While the NK₁ receptor antagonist, FK888, inhibited the extravasation, it had no effect on airway narrowing. Atropine partially inhibited airway narrowing without affecting extravasation. Results suggest that the airway narrowing induced by cigarette smoke is caused by tachykinins, and that a cholinergic pathway is involved. Thickening of the airway walls induced by NK₁ receptor-mediated extravasation may not be involved in such airway narrowing.     

Attenuation of tachykinin-induced airflow obstruction and microvascular leakage in immature airways.

1. To study the effect of maturation on substance P (SP)- and neurokinin A (NKA)-induced airflow obstruction and airway microvascular leakage (MVL), we have measured changes in both lung resistance (RL) and extravasation of Evans blue dye in anaesthetized immature (aged 14 +/- 1 days) and adult guinea-pigs (aged 80 +/- 3 days). 2. RL and its recovery after hyperinflation at 5 min were measured for 6 min after i.v. SP (0.2, 1 and 30 nmol kg-1), NKA (1 and 10 nmol kg-1) or vehicle (0.9% NaCl). After measurement of RL, MVL in trachea, main bronchi and intrapulmonary airways was also examined. 3. The order of potency in inducing airflow obstruction did not change with age (NKA > SP) but immature animals required a larger dose of SP or NKA than adults to cause a significant increase in RL. 4. The order of potency in inducing airway microvascular leakage was SP > NKA in both immature and adult animals. The amount of extravasated dye after SP was significantly less in immature airways, especially in central airways. 5. Phosphoramidon (2.5 mg kg-1), a neutral endopeptidase (NEP) inhibitor, significantly increased RL after 0.2 nmol kg-1 SP only in adult airways. Phosphoramidon enhanced the dye extravasation after 0.2 nmol kg-1 SP in both immature and adult airways with a significantly greater amount of dye in adult animals, suggesting that mechanisms other than changes in NEP activity may be responsible for this age-related difference.(ABSTRACT TRUNCATED AT 250 WORDS)