R. Matran

Association between histamine-containing mast cells and sensory nerves in the skin and airways of control and capsaicin-treated pigs

SummaryThe association between mast cells (visualized by routine staining and immunohistochemistry for histamine) and capsaicin-sensitive nerves (containing calcitonin gene-related peptide (CGRP) and substance P (SP)) was studied in the pig. In the 1-ethyl-3(3-diethylaminopropyl)carbodiimide (EDCDI)-fixed skin tissue, histamine-containing mast cells and CGRP/SP-positive nerves were found in close association around blood vessels. In the EDCDI-fixed airway mucosa, only single histamine-containing mast cells were detected. However, many alcian blue-positive mast cells were found, sometimes close to the airway epithelium where CGRP/SP-containing nerve fibres were absent 2 days after systemic capsaicin pretreatment, but no changes in the number and distribution of tissue mast cells, granulocytes or lymphocytes, or the number of blood leukocytes were detected. Local injection of allergen, histamine and capsaicin into the skin of pigs actively sensitized with ascaris antigen caused a rapid light red-flare (vasodilation) reaction. Allergen and histamine, but not capsaicin, also produced plasma protein extravasation. In contrast to the absent flare, the protein extravasation response still occurred in capsaicin-treated pigs. The sensitivity to ascaris antigen was mediated by an IgE-like antibody. We conclude that a functional and morphological relationship exists between histamine-containing mast cells and capsaicin-sensitive sensory nerves in the pig skin. Mast cells and sensory nerves are also found in the airway mucosa and appear to be closely associated with the epithelium.

Inhibition of cholinergic and non-adrenergic, non-cholinergic bronchoconstriction in the guinea pig mediated by neuropeptide Y and α2-adrenoceptors and opiate receptors

The mechanisms underlying the regulatory influence of neuropeptide Y (NPY) and of alpha 2-adrenoceptor and opiate receptor activation on cholinergic and excitatory non-adrenergic, non-cholinergic (e-NANC) neurotransmission were studied in guinea pig hilus bronchi in vitro. NPY inhibited both the cholinergic and e-NANC bronchial contractions evoked by field stimulation. The NPY attenuation of the e-NANC contraction could not be antagonized by the alpha 2-antagonist, idazoxan, or naloxone. UK 14,304 a specific alpha 2-agonist, also reduced the two nervous components of bronchial contraction and this action was inhibited by idazoxan. NPY and UK 14,304 exerted a minor influence on the bronchial smooth muscle tone per se or on contractions evoked by acetylcholine or neurokinin A. This suggested that the inhibitory responses were caused by a prejunctional action reducing the release of transmitter substances from sensory and cholinergic nerve endings. Furthermore NPY (10(-7) M) seemed to be more potent to inhibit both contractile components than noradrenaline (10(-6) M) in the presence of propranolol (3 X 10(-6) M). Morphine was able to reduce the e-NANC response via a naloxone-sensitive mechanism. The capsaicin-evoked bronchoconstriction and the bronchodilator NANC effect evoked by field stimulation were, however, not influenced by UK 14,304. It is concluded that NPY, alpha 2-receptor and opiate receptor activation inhibit the release of sensory transmitters evoked by field stimulation but not by capsaicin.

Occurrence, specific binding sites and functional effects of endothelin in human cardiopulmonary tissue.

Endothelin (ET)-like immunoreactivity (-LI) was detected in the human cardiopulmonary system, with the highest levels being found in the left anterior descending coronary artery, followed by the lung, right atrium, pulmonary artery, bronchus, pulmonary vein and left ventricle. Chromatographic characterization showed that the ET-LI in the lung and left ventricle corresponded to synthetic ET-1. Specific, high-affinity binding sites for ET-1, with an extremely slow dissociation rate, were found in the lung, right atrium and left ventricle. Displacement studies revealed a rank order of potency of ET-1 greater than ET-2 and sarafotoxin 6b greater than ET-3 and big ET-1. Scatchard analysis indicated a single receptor population in the lung (KD 1.53 x 10(-10) M) and left ventricle (KD 3.0 x 10(-11) M). In functional experiments, ET-1 evoked concentration-dependent, long-lasting vasoconstriction of a higher potency than that evoked by ET-2 and ET-3 in epicardial coronary arteries as well as in pulmonary arteries. ET-1 and ET-2 also showed bronchoconstrictor activity at considerably lower concentrations (threshold 10(-11) M) of ET-1 than those needed to cause vasoconstriction (10(-9) M). ET-LI, mainly consisting of ET-1, occurs in human cardiopulmonary tissue. Specific, high-affinity sites with irreversible binding for ET-1 are found in both the heart and lung. ET-1 is more potent than ET-2 or ET-3 in displacing ET-1 binding and in causing vasoconstriction and bronchoconstriction. Thus, in the human heart and lung, ET-1 seems to be the most abundant and biologically active of the endothelin peptides.

Effect of endothelin-1 on regional vascular resistances in the pig.

Summary The actions of endothelin-1 (ET-1) on vascular resistances were investigated and characterized in anesthetized pigs in vivo. Intravenously administered ET-1 (2–400 pmol/kg) caused dose-dependent increases in mean arterial blood pressure accompanied by a reduction in heart rate. ET-1 also increased renal, coronary, femoral, and bronchial vascular resistances. The kidney was about 10 times more sensitive to ET-1 than the other regions. The ET-1-induced vasoconstriction in the kidney was attenuated by nifedipine (100

Innervation of lower airways and neuropeptide effects on bronchial and vascular tone in the pig

mUg/kg). The responses to ET-1 in the femoral and bronchial vascular beds were biphasic with an initial decrease followed by an increase in vascular resistance at high doses. It is concluded that ET-1 causes dose-dependent vasoconstriction in several vascular beds in vivo with the most pronounced effects in the renal circulation.

Influence of epithelium on the responsiveness of guinea‐pig isolated trachea to adenosine

SummaryThe occurrence and distribution of peptide-containing nerve fibres [substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), neuropeptide Y (NPY)] and noradrenergic nerve fibres [tyrosine hydroxylase (TH)- and dopamine beta hydroxylase (DBH)-positive] in the airways of the pig were studied by means of immunohistochemistry. SP- and CGRP-immunoreactive (-IR) nerve fibres were present close to and within the lining respiratory epithelium, around blood vessels, within the tracheobronchial smooth muscle layer and around local tracheobronchial ganglion cells. The content of CGRP- and neurokinin A (NKA)-like immunoreactivity (-LI) measured by radioimmunoassay (RIA) was twice as high in the trachea compared to that in the peripheral bronchi. SP was a more potent constrictor agent than NKA on pig bronchi in vitro. CGRP had a relaxant effect on precontracted pig bronchi. On blood vessels CGRP exerted a relaxant effect that was more pronounced on pulmonary arteries than on bronchial arteries. VIP/PHI-IR fibres were seen in association with exocrine glands and in the tracheobronchial smooth muscle layer. VIP-positive nerve fibres were abundant around blood vessels in the trachea but sparse or absent around blood vessels in the peripheral bronchi. This histological finding was supported by RIA; it was shown that the content of peptides displaying VIP-like immunoreactivity (-LI) was 18 times higher in the trachea compared to peripheral bronchi. VIP was equally potent as CGRP in relaxing precontracted pig bronchi in vitro. Both bronchial and pulmonary arteries were relaxed by VIP. NPY was colocalized with VIP in tracheal periglandular nerve fibres and in nerve fibres within the tracheobronchial smooth muscle layer. NPY was also present in noradrenergic (DBH-positive) vascular nerve fibres. The content of NPY was much higher (15-fold) in the trachea compared to small bronchi. NPY caused a contraction of both pulmonary and bronchial arteries. The bronchial smooth muscle contraction to field stimulation in vitro was purely cholinergic. A non-cholinergic relaxatory effect following field stimulation was observed after bronchial precontraction. Capsaicin had no effect on pig bronchi in vitro.

Capsaicin-induced local effector responses, autonomic reflexes and sensory neuropeptide depletion in the pig

1 The influence of epithelium removal on the effects of adenosine on airway contractility was investigated on the guinea‐pig isolated trachea. 2 In preparations under resting tone or precontracted with histamine 10−5 m, removal of the tracheal epithelium resulted in similar shifts to the left of the adenosine concentration‐response curves (0.61 ± 0.18 (P < 0.05) and 0.80 ± 0.09 (P < 0.001) log units; n = 5), corresponding to 4.07 and 6.31 fold potentiations of the relaxant effect of adenosine. 3 In the presence of dipyridamole 10−5 M the relaxant effects of adenosine were potentiated 85.1 fold on tracheae with epithelium; removal of the epithelium did not produce a significant additional shift to the left of the adenosine concentration‐response curves (0.07 ± 0.03 log units; n = 5; NS). 4 In the absence of dipyridamole, the theophylline‐adenosine antagonism was not of the competitive type, irrespective of whether the tracheae were with or without epithelium. 5 In the presence of dipyridamole, this antagonism was likely to be of the competitive type and its characteristics were the same when the epithelium was present or absent. Regression slope and pA2 values were 0.84 and 5.07, respectively, in the presence of epithelium and 0.76 and 4.89, respectively, in its absence. 6 It is suggested that, at least in the guinea‐pig isolated trachea model, the airway epithelium seems to be involved only in the uptake and metabolism of adenosine.

Cigarette smoke, nicotine and capsaicin aerosol-induced vasodilatation in pig respiratory mucosa

SummarySystemic capsaicin pretreatment (total cumulative dose 50 mg/kg administered s.c. over 2 h) was performed in pigs under pentobarbitone anaesthesia and the effects on sensory and sympatho-adrenal mechanisms were examined acutely and 2 days after treatment. During pretreatment with capsaicin, pronounced sensory and sympatho-adrenal activation were noticed. This resulted in a several-fold increase in the systemic arterial plasma levels of calcitonin gene-related peptide (CGRP), neurokinin A (NKA), noradrenaline (NA), adrenaline (Adr) and neuropeptide Y (NPY), and a slight increase (39%) in plasma cortisol. Simultaneously, there was marked tachycardia, an increase in blood pressure, total skin erythema and some bronchoconstriction, all lasting for about 30 min. Upon repeated injections tachyphylaxis was observed. 2 days after capsaicin pretreatment, basal plasma levels of the neuropeptides, catecholamines and cortisol as well as basal cardiovascular and pulmonary parameters were similar in control and capsaicin-treated pigs.The tissue content of CGRP and NKA was reduced by 50–65% in the airways and by 80–90% in the skin 2 days after capsaicin pretreatment. In contrast, the CGRP content was unchanged or increased (by 195%) in the nodose and spinal ganglia, respectively. The corresponding tissue levels of vasoactive intestinal polypeptide (VIP) and NPY were basically unchanged in capsaicintreated pigs. A bolus injection of capsaicin (1 mg/kg i.v.) in control animals resulted in a marked increase in plasma catecholamines and NPY, concomitant with elevation in blood pressure and heart rate. These effects were preceded by an initial bradycardia and decrease in blood pressure. Moreover, capsaicin i.v. produced a clear-cut increase in plasma CGRP and NKA levels together with vasodilatation in the nasal, laryngeal, bronchial and skin circulations and a slight fall in dynamic lung compliance. In capsaicin-treated pigs there was no release of catecholamines, NPY, CGRP or NKA upon i.v. capsaicin challenge. Furthermore, the increase in blood pressure and heart rate and the vasodilatation in the bronchial and skin circulation were markedly reduced. However, the initial bradycardia and the vasodilatation in the nasal and laryngeal circulations after capsaicin i.v. injection persisted in capsaicin-treated animals, and the fall in dynamic compliance was inverted to an increase together with a fall in pulmonary resistance. Local capsaicin aerosol (10 mg) challenge in the airways of control pigs induced a marked vasodilatation, and this response was reduced by 55–85% at all three levels of the airways in capsaicin-treated pigs. Local skin injections with capsaicin (50μg) in control pigs produced a marked vasodilatation, but no plasma protein (Evans blue) extravasation. This vasodilatory response was abolished by capsaicin pretreatment.We conclude that systemic capsaicin pretreatment of the anaesthetized pig may be used as a model to show depletion of the content of sensory neuropeptides in peripheral sensory nerve endings of large animals. Furthermore, the functional importance of capsaicin-sensitive sensory nerves in local axon reflexes and sympathoadrenal activation may be studied using this model, although capsaicin-induced effects presumably of parasympathetic origin persist.

Vagal vasodilatory mechanisms in the pig bronchial circulation preferentially involves sensory nerves.

1 Anaesthetized pigs were used to study vascular responses in the sphenopalatine artery (SPA), superior laryngeal artery (SLA) and bronchial artery (BA) upon exposure to cigarette smoke or aerosol of nicotine and capsaicin. Direct blood flow recordings were made with ultrasonic probes around the vessels. 2 Smoke from one cigarette was administered as inhalation for 2 min with or without a Cambridge filter which removes the particulate matter including nicotine from the smoke. Aerosols of nicotine (2.5 mg) or capsaicin (10 mg) were administered to the nose or the lower airways for 3 min. 3 Cigarette smoke exposure caused a reproducible reduction of the vascular resistance (VR) suggesting vasodilatation in the SPA, SLA, and especially the BA. The vasodilatation was not modified by the Cambridge filter, suggesting that it was caused by vapour phase components rather than nicotine. 4 The smoke effect was not changed after pretreatment with the cyclo‐oxygenase inhibitor, diclofenac, or with atropine, guanethidine, H1 or H2‐histamine receptor antagonists, nedocromil, or by vagotomy. The smoke‐evoked decrease in VR was not modified by the nicotinic receptor antagonist chlorisondamine in the SLA or BA. 5 In pigs pretreated with increasing doses of capsaicin two days earlier, the decrease in VR upon smoke exposure in both the BA and SLA was unaffected while the change in VR was attenuated in the SPA. 6 Nicotine aerosol had no effect on VR in the peripheral airways supplied by the BA while a decrease in VR was observed in the SLA and SPA. The nicotine response was reduced after capsaicin pretreatment in the nasal and upper tracheal circulation. 7 Capsaicin aerosol reduced VR in the vascular beds supplied by the SPA, SLA and BA and this response was markedly reduced after capsaicin pretreatment. 8 The mechanisms underlying vasodilatation upon cigarette smoke exposure in the bronchial mucosa are at the moment unclear while both non‐cholinergic parasympathetic and sensory components may be involved in the nose. Capsaicin induced a vasodilatation at all levels via sensory mechanisms, whereas nicotine‐evoked vasodilatation is restricted to the upper airway mucosa and is at least partly dependent on parasympathetic reflexes involving capsaicin‐sensitive sensory nerves.

Effect of nedocromil sodium on allergen-, PAF-, histamine- and bradykinin-induced airways vasodilatation and pulmonary obstruction in the pig.

The present study shows that in contrast to the upper trachea, where the parasympathetic vasodilatory components of both cholinergic and non-cholinergic nature are dominating, the vagal blood flow regulation in the peripheral airways of the pig supplied by the bronchial artery is entirely carried out by local release of vasodilatory mediators from capsaicin-sensitive sensory nerves. Also inhalation of the vapour phase from the major airway irritant cigarette smoke was associated with a marked increase in bronchial blood flow possibly via local axon reflexes. Capsaicin, substance P (SP) and calcitonin gene-related peptide (CGRP) caused vasodilatation in both the trachea and bronchi while vasoactive intestinal polypeptide (VIP) was most active in the trachea. These functional data were supported by immunohistochemical studies showing the presence of SP- and CGRP-containing nerves of presumably sensory origin around bronchial blood vessels while VIP-positive perivascular fibres of local parasympathetic origin were found mainly in the trachea.