Involvement of tachykinin receptors in sensitisation to cow's milk proteins in guinea pigs.
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BACKGROUND: There is growing evidence for a pivotal role for tachykinins in gut neuroimmune interactions. AIMS: To determine whether NK1, NK2, and NK3 tachykinin receptors are involved in milk protein induced allergic sensitisation. METHODS: Eight groups of 12 Dunkin-Hartley guinea pigs (250-300 g) were used. Four groups were sensitised to milk proteins for three weeks. During this period, these animals were injected intraperitoneally each day with NK1 (SR 140333; 0.3 mg/kg), NK2 (SR 48968; 5 mg/kg), or NK3 (SR 142801; 5 mg/kg) receptor antagonist or vehicle. The fifth group had water available instead of milk and was used as a non-sensitised control. The three other groups received the NK receptor antagonists for three weeks but were not sensitised to milk proteins. RESULTS: Sensitised animals treated with NK1 and NK3 receptor antagonists had both lower IgE and IgG serum titres, evaluated by passive cutaneous anaphylaxis, and lower specific IgG serum titres, determined by enzyme linked immunosorbent assay (ELISA), than vehicle treated animals. Sensitisation induced an increase in intestinal mast cell number which was abolished by treatment with the NK1 receptor antagonist. Antigenic challenge-induced jejunal hypersecretion was also blocked by treatment with the NK1 receptor antagonist. CONCLUSION: In guinea pigs, NK1 and NK3 but not NK2 receptors are involved in sensitisation to cow's milk. However, NK1 but not NK3 receptor antagonists abolish both the hypermastocytosis induced by food allergy and the hypersecretion induced by antigenic challenge, suggesting different roles for NK1 and NK3 receptors in the mechanisms of sensitisation to beta-lactoglobulin. (+info)
Neurogenic plasma leakage in mouse airways.
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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. (+info)
Decreased vascular permeability response to substance P in airways of genetically hypertensive rats.
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1. The inbred genetically hypertensive strain (GH) of the Otago Wistar rat possesses more sensory neurons containing the neuropeptide substance P (SP) than does its genetically related control normotensive strain. 2. As SP contributes to airway inflammation by increasing microvascular permeability, we assessed the extravasation of Evans Blue dye in trachea and main bronchus of anaesthetized GH and control rats, in the presence of endogenous (capsaicin-liberated) or exogenous SP. 3. Following intravenous administration of either capsaicin (75 microg kg(-1)) or SP (3.3 nmol kg(-1)), extravasation of Evans Blue in airways from GH rats was only about 60% of that in airways of control rats. This difference was not gender-specific and responses to capsaicin were abolished by pretreatment with a selective NK1 receptor antagonist SR 140333 (360 nmol kg(-1)). 4. By contrast, the extravasation of dye caused by intravenous 5-hydroxytryptamine (0.5 micromol kg(-1)) was similar in magnitude in both GH and control strains. 5. Falls in systemic arterial blood pressure in response to exogenous SP (0.1-3 nmol kg(-1)) or acetylcholine (0.2-2 nmol kg(-1)) were also very similar between strains, but those in response to capsaicin (75 microg kg(-1)) in the GH rats were about double those in control rats. The hypotensive response to SP was abolished by SR 140333, but that to capsaicin was unaffected. 6. Our results indicate that the increased peripheral innervation density by SP-nerves in GH rats is accompanied by reduced inflammatory responses to SP. This does not involve decreased vasodilator potency of SP and is therefore probably related to altered endothelial responsiveness. (+info)
The effect of miotics on the intraocular pressure of conscious owl monkeys.
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The intraocular pressure of conscious, unsedated owl monkeys (Aotus trivirgatus) was measured with an applanation tonometer. Untreated eyes of the conscious animals were found to have higher values than those reported for owl monkeys anesthetized with pentobarbitone. Locally applied pilocarpine, carbachol, and oxotremorine gave concentration-related reduction in pressure, oxotremorine being the most potent and having longer duration of effect than the other compounds. Slight reductions were also observed with aceclidine and R. S. 86. These results are discussed in relation to the effects of miotics in man. (+info)
Effect of SR-140333, a neurokinin-1 receptor antagonist, on airway reactivity to methacholine in sedated rats.
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AIM: To study the roles of neurokinins in the airway reactivity (AR) to methacholine chloride (MC). METHODS: The effects of (S)-1-(2-[3, 4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl) piperidin-3-yl]ethyl)-4-phenyl-1-azoniabicyclo [2.2.2]octane.chloride (SR-140333), a neurokinin-1 receptor antagonist, on AR to inhaled MC in diazepam-sedated rats, and on MC-induced contraction of isolated tracheal spiral strips were observed. RESULTS: SR-140333 inhibited the increase in respiratory rate (RR) induced by MC aerosol (10-1000 mumol/m3), and the ID50 for inhibiting the response to MC aerosol (1 mmol/m3) was 4.9 micrograms.kg-1 (95% confidence limits 1.4-17.2 micrograms.kg-1). SR-140333 1 mumol.L-1 had no inhibitory effect on MC-induced tracheal contraction. Atropine blocked responses to MC both in vivo and in vitro. CONCLUSION: Endogenous neurokinins are involved in the AR to MC in rats, at least partly mediated via neurokinin-1 receptors. (+info)
Neutral endopeptidase (EC 3.4.24.11) terminates colitis by degrading substance P.
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Neurogenic inflammation is regulated by sensory nerves and characterized by extravasation of plasma proteins and infiltration of neutrophils from post-capillary venules and arteriolar vasodilatation. Although it is well established that substance P (SP) interacts with the neurokinin 1 receptor (NK1R) to initiate neurogenic inflammation, the mechanisms that terminate inflammation are unknown. We examined whether neutral endopeptidase (NEP), a cell-surface enzyme that degrades SP in the extracellular fluid, terminates neurogenic inflammation in the colon. In NEP knockout mice, the SP concentration in the colon was approximately 2.5-fold higher than in wild-type mice, suggesting increased bioavailability of SP. The extravasation of Evans blue-labeled plasma proteins in the colon of knockout mice under basal conditions was approximately 4-fold higher than in wild-type mice. This elevated plasma leak was attenuated by recombinant NEP or the NK1R antagonist SR140333, and is thus caused by diminished degradation of SP. To determine whether deletion of NEP predisposes mice to uncontrolled inflammation, we compared dinitrobenzene sulfonic acid-induced colitis in wild-type and knockout mice. The severity of colitis, determined by macroscopic and histologic scoring and by myeloperoxidase activity, was markedly worse in knockout than wild-type mice after 3 and 7 days. The exacerbated inflammation in knockout mice was prevented by recombinant NEP and SR140333. Thus, NEP maintains low levels of SP in the extracellular fluid under basal conditions and terminates its proinflammatory effects. Because we have previously shown that intestinal inflammation results in down-regulation of NEP and diminished degradation of SP, our present results suggest that defects in NEP expression contribute to uncontrolled inflammation. (+info)
Effect of bradykinin on membrane properties of guinea pig bronchial parasympathetic ganglion neurons.
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The effect of bradykinin on membrane properties of parasympathetic ganglion neurons in isolated guinea pig bronchial tissue was studied using intracellular recording techniques. Bradykinin (1-100 nM) caused a reversible membrane potential depolarization of ganglion neurons that was not associated with a change in input resistance. The selective bradykinin B(2) receptor antagonist HOE-140 inhibited bradykinin-induced membrane depolarizations. Furthermore, the cyclooxygenase inhibitor indomethacin attenuated bradykinin-induced membrane depolarizations to a similar magnitude ( approximately 70%) as HOE-140. However, neurokinin-1 and -3 receptor antagonists did not have similar inhibitory effects. The ability of bradykinin to directly alter active properties of parasympathetic ganglion neurons was also examined. Bradykinin (100 nM) significantly reduced the duration of the afterhyperpolarization (AHP) that followed four consecutive action potentials. The inhibitory effect of bradykinin on the AHP response was reversed by HOE-140 but not by indomethacin. These results indicate that bradykinin can stimulate airway parasympathetic ganglion neurons independent of sensory nerve activation and provide an alternative mechanism for regulating airway parasympathetic tone. (+info)
Direct effects of muscarinic agents on the outflow pathways in human eyes.
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PURPOSE: Recent studies demonstrating the presence of muscarinic receptors and contractile-like cells in the trabecular meshwork tissue and/or cell cultures from human eyes suggest the possibility that there may be a direct effect of muscarinic agonists on outflow facility. The present studies were conducted to determine whether muscarinic agonists could change outflow facility in perfused human ocular anterior segments, which lack an intact ciliary muscle. METHODS: Human eyes were dissected and perfused according to previously described methods. A steady state baseline facility was established for 90 minutes, after which up to four sequential concentrations ranging from 10(-9) to 10(-3) M of pilocarpine, aceclidine, or carbachol were added to the perfusion medium. In other studies, 10(-6) M atropine was perfused alone followed by 10(-7) M carbachol with 10(-6) M atropine, whereas fellow control eyes received carbachol alone. Outflow facility was measured for 60 minutes after each drug addition. The outflow facility measurement in each eye after drug administration was compared with the baseline measurement. RESULTS: Outflow facility increased from baseline facility in eyes treated with pilocarpine, aceclidine, or carbachol at lower concentrations (10(-9) to 10(-6) M) but remained unchanged at higher concentrations (10(-4) to 10(-2) M). The effects of carbachol at 10(-7) M were completely blocked by atropine. CONCLUSIONS: Muscarinic agonists increase outflow facility in human eyes by a direct stimulation of the outflow tissues in the absence of an intact ciliary muscle. This effect is biphasic, occurring at concentrations of 10(-6) M and lower with no effect at higher concentrations. (+info)