Sympathetic vascular control of the laryngeo-tracheal, bronchial and pulmonary circulation in the pig: evidence for non-adrenergic mechanisms involving neuropeptide Y

Neuropeptide Y (NPY) and noradrenaline (NA) are co-stored in sympathetic perivascular nerves of the airway mucosa and lung. THe superior laryngeal, bronchial and pulmonary vascular responses were therefore studied in anaesthetized pigs after systemic injections of NPY and NA and after stimulation (2 or 10 Hz, 15 V, 5 ms) of the cranial and caudal portions of hte cervical sympathetic trunk or the stellate ganglia. NPY and NA increased vascular resistance, suggesting vasoconstriction in all three vascular beds. Stimulation of the cervical sympathetic trunk in the cranial direction caused clear-cut vasoconstriction and a decrease in the superficial blood flow in the laryngeal and tracheal circulation supplied by the superior laryngeal artery. This vascular response may be related to release of NA at 2 Hz and possibly also NPY at 10 Hz, since a remaining vasoconstrictor response at 10 Hz was present in reserpinized preganglionically transected pigs when tissue content of NA but not NPY was depleted. The decrease in superficial blood flow in the tracheal mucosa on sympathetic stimulation was absent after reserpine, however. Stimulation of the cervical sympathetic trunk in caudal direction provoked vasoconstriction in the bronchial and pulmonary vascular beds in control pigs. The basal tone of these two vascular beds was not influenced on electrical stimulation after reserpine pretreatment, however, suggesting involvement of NA and possibly aslo NPY, which were both depleted by reserpine. Electrical stimulation of the stellate ganglia also evoked reserpine-sensitive vasoconstriction in both the bronchial and pulmonary vascular beds. The left stellate ganglion dominated the vasomotor response in the bronchial circulation, whereas the right side mainly influenced the pulmonary circulation and the heart.

Effect of airway blood flow on airflow

Resistance to gas flow of an airway is a function of both airway smooth muscle tone and thickness of the airway wall internal to the outer ring of airway smooth muscle. Schematically, the increase in airway resistance caused by shortening of airway smooth muscle may be potentiated by a concomitant increase in airway wall thickness caused by vasodilation of the bronchial vessels and/or microvascular leakage. Conversely, bronchial vasoconstriction may limit to some extent the increase in resistance to gas flow caused by airway smooth muscle shortening and/or congestion and edema of the airway wall. Many endogenous paracrine mediators, putatively involved in asthma and bronchial hyperresponsiveness, have both bronchomotor and vascular effects. The overall effects on resistance to airflow of endogenous or exogenous agents depend not only upon pre-existing airway smooth muscle tone and pre-existing condition of bronchial vessels but also upon two factors that facilitate microvascular leakage, namely, inflammation of the airway wall and outflow pressure of the bronchial circulation, which is close to left atrial pressure.

Differential bronchial and pulmonary vascular responses to vagal stimulation in the pig

The pulmonary and bronchial vascular responses and changes in bronchial tone upon vagal stimulation (240 impulses at 2 Hz or 10 Hz) were studied in anaesthetized pigs paralyzed with pancuronium. The acetylcholine-evoked vasodilatation in the tracheobronchial circulation had the same magnitude when using pancuronium or succinylcholine as skeletal muscle relaxants. Atropine-sensitive bradycardia, hypotension and bronchoconstriction were observed upon vagal stimulation. A vasoconstrictor response in the pulmonary vascular bed and clear-cut vasodilatation in the bronchial circulation supplied by the bronchial artery also occurred upon vagal stimulation. The vagally-evoked increase in pulmonary vascular resistance was markedly reduced after atropine while the bronchial vasodilatation was unchanged. This suggests that the vagally-induced increase in bronchial blood flow was not secondary to changes in the pulmonary circulation. Furthermore, the pulmonary vasoconstrictor response caused by vagal stimulation under control conditions is probably explained by reflex sympathetic activation due to the fall in systemic blood pressure. These data indicate selective vagal non-cholinergic influence of blood flow in the bronchial vascular bed compared to the pulmonary circulation.

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

1. The influence of nedocromil sodium on the nasal and bronchial effects induced by allergen, platelet-activating factor (PAF), capsaicin, histamine and bradykinin aerosol challenge in ascaris-sensitized and pentobarbitone-anaesthetized pigs was studied. Blood flow changes in the bronchial and nasal circulation were measured with ultrasonic flow probes around the supplying arteries, and vascular resistance was calculated. Changes in pulmonary resistance (Rpulm), dynamic compliance (Cdyn), mean arterial pressure (MAP) and heart rate (HR) were also determined. 2. Allergen and PAF aerosol challenge in the lung produced similar effects consisting of both bronchial and nasal vasodilatation, bronchoconstriction (increase in Rpulm and decrease in Cdyn) and increases in MAP and HR. Local pretreatment with nedocromil sodium (80 mg, aerosol) reduced the peak and duration of both the bronchial vasodilatation and increase in Rpulm, while only the duration of the change in Cdyn was significantly decreased. Nedocromil sodium did not alter the increases in MAP and HR. The nasal vasodilatation evoked by PAF, but not allergen, challenge in the lung was reduced by nedocromil sodium. 3. Allergen challenge in the nose induced vasodilatation of long duration which was reduced by local nedocromil sodium pretreatment (50 micrograms kg-1, intra-arterially). 4. The vasodilator response to histamine aerosol was attenuated in the nasal, but not the bronchial circulation by local nedocromil sodium pretreatment. Histamine-induced bronchoconstriction was not altered by nedocromil sodium. 5. Bradykinin aerosol-induced vasodilatation in the nasal and bronchial circulation was markedly and equally reduced by local nedocromil sodium and systemic capsaicin (50 mg kg-1, s.c. 2 days before) pretreatment. 6. In conclusion, nedocromil sodium blocks some local vascular and bronchial effects, but not increases in MAP and HR, induced by allergen and PAF aerosol in the pig. Bradykinin-induced vasodilatation in the airways, which seems to be largely dependent on capsaicin-sensitive sensory nerves, is markedly inhibited by nedocromil sodium pretreatment, whereas capsaicin-induced vasodilatation is not affected by nedocromil sodium. It may be suggested that nedocromil sodium acts by inhibiting some common process involved in the release of mediators from inflammatory cells (when stimulated by allergen and PAF) and sensory nerves (when stimulated by bradykinin and histamine, but not capsaicin).

The possible role of prostaglandin D2 in the long-lasting airways vasodilatation induced by allergen in the sensitized pig

Allergen-induced nasal and bronchial vasodilatation and bronchoconstriction were studied in ascaris-sensitized pigs with and without pretreatment with diclofenac sodium, to evaluate the contribution of prostanoids in these responses. The bronchoconstriction induced by allergen aerosol challenge was enhanced by diclofenac, whereas the duration of the bronchial vasodilatation was reduced from 80 to 30 min, without changing the maximal effect. However, both the maximal effect and the duration of the nasal vasodilatation were reduced upon nasal allergen challenge by 60% (P less than 0.01) and from 72 to 16 min (P less than 0.05), respectively. Bronchial challenge with the allergen also induced nasal vasodilatation of long duration and this response was highly sensitive to diclofenac pretreatment. I.v. injections of prostaglandins (PG) E1, E2, I2 and D2 revealed that only PGD2 induced vasodilatation of long duration in the airways without major effects on the systemic arterial blood pressure. Nebulization of PGD2 (0.7-1.4 mumol) into the pig airways also induced marked vasodilatation of long duration (greater than or equal to 40 min), especially in the nasal circulation. The vasodilatory responses to PGD2 were not changed by systemic pretreatment with capsaicin or diclofenac. Challenge in the airways with platelet-activating factor (PAF) produced bronchial and vascular responses similar to those seen with the allergen and the vasodilatory responses to PAF were partly sensitive to diclofenac. We propose that a long-lasting component of the allergen-induced vasodilatation in the pig airways, especially in the nasal mucosa, may be caused by the release of PGD2, acting independently of sensory nerves. Allergen and PAF aerosol challenge in the lung may also induce the release of a vasodilatory prostaglandin, possibly PGD2 into the systemic circulation, thereby inducing nasal vasodilatation.

Sensory neuropeptide involvement in animal models of airway irritation and of allergen-evoked asthma

C-fiber afferents in the airways are in close contact with mast cells and are activated both upon allergic reactions and by inhalation of irritants such as capsaicin and cigarette smoke. This evokes both protective reflexes such as cough as well as local release of tachykinins and calcitonin gene-related peptide (CGRP) with subsequent actions on blood vessels (vasodilatation and plasma protein extravasation) and bronchial smooth muscle (bronchoconstriction). After capsaicin pretreatment when peptides have been depleted from the sensory nerves, there is a marked reduction of the vasodilatatory response upon allergen challenge and the protein extravasation evoked by cigarette smoke. Conversely, chronic cigarette smoke exposure is accompanied by increased coughing to capsaicin challenge. Furthermore, aerosol immunization and chronic smoke exposure are both associated with elevated tissue levels of CGRP, suggesting upregulation of C-fiber function and peptide synthesis, which may contribute to airway hyperreactivity.

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

The 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 were abundant. The 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.

[Nervous control of bronchial circulation in pigs: application to the airway stimulation]

Vascular responses in airways were studied in an anesthetized pig model. Nervous control of bronchial mucosa blood flow was found to involve mainly the non-adrenergic, non-cholinergic (NANC) system (activation of afferent C-fibers) and the sympathetic system. Nervous control of tracheal and laryngeal vascularization involved the cholinergic and non-cholinergic parasympathetic system and the sympathetic system. Exposure of airways to irritants was followed by vasodilatation in the tracheobronchial mucosa, partly as a result of activation of afferent C-fibers. In sensitized animals, respiratory challenge with the specific allergen produced activation of the NANC system with antidromic vasodilatation in the mucosa. This response can be likened to the "axon reflex" seen in skin. Activation of airway autonomic nerves thus was found to be a central step in the genesis of inflammatory reactions in the lungs.

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

Systemic capsaicin pretreatment (total cumulative dose 50 mg/kg administered s.c. over 2h) 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 capsaicin-treated 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.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Local and central reflex mechanisms in the neural control of airway microcirculation

Sensory and parasympathetic neural mechanisms play an essential role in the control of the microcirculation in the airway mucosa in response to inhalation of irritants and in local allergic reactions. Thus extravasation of plasma proteins is evoked by local release of peptides such as substance P (SP) from capsaicin-sensitive sensory nerves upon inhalation of cigarette smoke. Calcitonin gene-related peptide (CGRP) is another vasodilator agent which is also released from airway afferent nerves by capsaicin or antidromic nerve stimulation. Parasympathetic cholinergic and noncholinergic vasodilator mechanisms dominate in the nasal mucosa and trachea whereas the bronchial circulation is influenced mainly by local mechanisms involving mediator release from capsaicin-sensitive sensory nerves. The allergen-induced vasodilatation in the airway mucosa seems to a large extent to be caused by histamine which activates capsaicin-sensitive afferent nerves and evokes peptide release.

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

1. Anesthetized 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.

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

The 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 noncholinergic relaxatory effect following field stimulation was observed after bronchial precontraction. Capsaicin had no effect on pig bronchi in vitro.

Occurrence and effects of endothelin in guinea-pig cardiopulmonary tissue

Endothelin-like immunoreactivity (-LI) was present in the guinea-pig cardiopulmonary tissues with the associated autonomic neural supply. The highest levels were found in the stellate ganglion (15 pmol g-1) followed by the vagus nerve, pulmonary artery, lung and right atrium of the guinea-pig. Endothelin I, but not endothelin III, induced an increase in contractile force and frequency followed by an atropine-resistant inhibition of right atrial contractility at higher concentrations. Exposure to endothelin I caused a pronounced, long-lasting coronary vasoconstriction as revealed by a decrease in perfusate outflow. In addition, both heart and contractile force were attenuated. Guinea-pig bronchi in vitro contracted upon exposure to endothelin I and III, but only endothelin I caused contraction of pulmonary arteries. The C-terminal hexapeptide of endothelin I did not influence right atrial, bronchial or pulmonary artery contractility. Endothelin I increased the mean arterial pressure and insufflation pressure and decreased the heart rate in the guinea-pig in vivo. In conclusion, endothelin-LI is present in the cardiovascular, respiratory and nervous tissues of the guinea-pig and endothelin induces strong coronary and pulmonary vasoconstrictor effects. The effects on atrial contractile force and frequency are concentration-dependent with stimulation at lower and inhibition at higher concentrations. Based on the diversity in response to endothelin III in the bronchi compared to atrium and pulmonary artery, it may be suggested that different receptor populations exist in bronchial and cardiovascular muscle, although the cellular localization and forms of endothelin present in guinea-pig cardiopulmonary tissue remain to be established.

Capsaicin and histamine antagonist-sensitive mechanisms in the immediate allergic reaction of pig airways

The airway vascular and bronchial responses were studied in pigs sensitized with Ascaris suum. Ascaris, histamine (H) and capsaicin aerosol all induced a clear-cut increase in blood flow in the nasal, laryngeal and bronchial circulation with a decrease in vascular resistance of 20-40%. When delivered to the lung both ascaris and histamine, but not capsaicin, caused pulmonary airflow obstruction with increase in resistance and a fall in dynamic compliance of 40-70%. After pretreatment of pigs with a combination of the H1- and H2-receptor antagonists terfenadine and cimetidine, the vascular and bronchial responses were strongly reduced to both histamine (by greater than 77%) and ascaris (by greater than 58%), but not to capsaicin aerosol. The bronchoconstriction to histamine was found to be mediated by H1-receptors only, while both H1- and H2-antagonists were necessary to block the vasodilatory response, with H2-receptors being more important in the bronchial circulation and H1-receptors being more important in the laryngeal and nasal circulation. Furthermore, when pigs were pretreated with capsaicin systemically 2 days before the experiment, the vasodilation was decreased upon capsaicin (by 80%), ascaris (by greater than 40%) and histamine (by greater than 50%) aerosol challenge. When histamine was administered intravenously the desensitizing effect of capsaicin pretreatment was much less pronounced. The effect of capsaicin desensitization on the pulmonary obstruction upon ascaris and histamine challenge was limited to a 60% reduction of the fall in dynamic compliance and a delayed peak in resistance upon ascaris challenge. We conclude that histamine is one of the main vasodilatory mediators released upon allergen challenge at three different levels of the pig airways. A considerable part of the histamine effect is indirect and probably due to activation of capsaicin-sensitive sensory nerves.

Endothelin-1 increases airway mucosa blood flow in the pig

The vascular effects of bolus intravenous injections (4.5, 45 and 450 pmol.kg-1) of porcine endothelin-1 on the bronchial and nasal circulations were investigated in ten anesthetized pigs. Endothelin-1 produced a dose-dependent and long-lasting increase in bronchial blood flow with a concomitant rise in systemic arterial pressure suggesting vasodilatation. The highest doses of endothelin-1 also caused a slight decrease in the nasal vascular resistance. Furthermore, the vascular responses to endothelin-1 were not modified in systemically capsaicin pretreated animals or after pretreatment with a cyclocoxygenase inhibitor, diclofenac. Our results suggest that endothelin-1 has a potent and regional vasodiator effect of the bronchial circulation.

Bronchial hyperresponsiveness to methacholine in patients with impaired left ventricular function

To elucidate the pathogenesis of bronchospasm in congestive heart failure, we studied 23 patients with chronic impairment of left ventricular function due to coronary artery disease or dilated cardiomyopathy. In 21 of them we found marked bronchial hyperresponsiveness to methacholine. The mean dose (+/- SD) of methacholine that elicited a 20 percent decrease in the forced expiratory volume in one second (FEV1) was 421 +/- 298 micrograms, nearly the same as in patients with symptomatic asthma. In contrast, there was no bronchial response to methacholine in 9 of 10 patients who had coronary artery disease but normal left ventricular function. Administration of the bronchodilator albuterol led to a partial (43 percent) reversal of the methacholine-induced bronchial obstruction. In 12 patients, pretreatment with the alpha-adrenergic agonist methoxamine (10 mg by inhalation), a potent vasoconstrictor, fully prevented the methacholine-induced decrease in FEV1. The protective effect of methoxamine was blocked by the alpha-adrenergic antagonist phentolamine in all six patients who received this agent. We conclude that bronchial hyperresponsiveness to cholinergic agonists is frequent in patients with impaired left ventricular function and may contribute to the wheezy dyspnea commonly observed in such patients. The bronchoconstriction may be mediated at least in part by dilatation of the bronchial vessels.

Inhibition of cholinergic and non-adrenergic, non-cholinergic bronchoconstriction in the guinea pig mediated by neuropeptide Y and alpha 2-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.

In vitro desensitization of beta-adrenoceptors in guinea pig trachea: interactions between beta-adrenoceptor agonists and influence of adenosine and other drugs

The aim of this study was to investigate quantitatively the action of and the interaction between beta-adrenergic receptor agonists in desensitizing guinea pig isolated trachea. It was also to evaluate the influence of substances whose effects on desensitization are either disputed (theophylline, indomethacin, ketotifen, hydrocortisone) or unknown (nicardipine, Bay K 8644, fenspiride, adenosine). Tracheal strips were contracted with histamine (5 x 10(-5) M) or acetylcholine (5.10(-5) M) and concentration-response (C/R) curves for various beta-adrenoceptor agonists were determined before and after incubation (20 min to 4 h) with the same beta-adrenoceptor agonist (autodesensitization), with other beta-adrenoceptor agonists (cross-desensitization), or with a beta-adrenoceptor agonist and another substance. Our results show that the autodesensitization induced by isoprenaline is concentration dependent and that concentration dependence is more pronounced with salbutamol and fenoterol than with isoprenaline and adrenaline with respect to autodesensitization: shifts (log unit) of the C/R curves were 0.59 +/- 0.06 (N = 5) for salbutamol (10(-5) M), 0.78 +/- 0.09 (N = 5) for fenoterol (10(-6) M), 0.30 +/- 0.04 (N = 9) for isoprenaline (10(-5) M), and 0.33 +/- 0.05 (N = 5) for adrenaline (10(-5) M). Our studies of cross-desensitization (desensitization to isoprenaline, adrenaline, salbutamol, and fenoterol induced by incubation with isoprenaline 10(-5) M) showed a significantly greater shift in the C/R curves for fenoterol (0.56 +/- 0.08, N = 5) and salbutamol (0.62 +/- 0.05, N = 5) than for adrenaline (0.35 +/- 0.07, N = 5) and isoprenaline itself (0.30 +/- 0.05, N = 9). Of the substances we studied, none modified the desensitization induced by isoprenaline except hydrocortisone and adenosine. Hydrocortisone (10(-8) M) reduced it significantly, although to a negligible extent. Adenosine (3 x 10(-4) M) did not shift the C/R curve to isoprenaline by itself, but incubation of tracheal strips with adenosine and isoprenaline caused a significantly greater shift of C/R curves to isoprenaline (0.30 +/- 0.04) than incubation with isoprenaline alone (0.20 +/- 0.04) (P less than 0.05, N = 5). These experiments suggest that adenosine may have increased the uncoupling and/or down-regulation phenomena induced by isoprenaline, or modified adenylate cyclase-cAMP activity.

Effects of neuropeptides and capsaicin on tracheobronchial blood flow of the pig

Blood flow changes upon systemic i.v. injections in the pig of various neuropeptides, capsaicin, bradykinin and histamine were directly monitored by a Transonic blood flowmeter in the superior laryngeal, bronchial and femoral arteries and indirectly in the larynx and skin using laser Doppler flowmetry. To minimize influence of compensatory reflexes and indirect effects, the pigs were pre-treated with atropine, guanethidine, chlorisondamine and capsaicin. Substance P (SP), vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), calcitonin gene-related peptide (CGRP), capsaicin, bradykinin and histamine all decreased vascular resistance, suggesting vasodilation in the superior laryngeal and bronchial arteries. All peptides and histamine when given i.v. exerted vasodilatory effects independent of autonomic motor nerves and capsaicin-sensitive afferents. SP was the most potent vasodilator agent tested in both tracheal and bronchial circulation, being about 1000-fold more active than histamine. VIP was about 10-fold more potent than PHI in decreasing vascular resistance and had a preferential action on the SLA compared to CGRP. In the femoral artery capsaicin and also SP in the highest dose increased vascular resistance. Capsaicin increased the laser Doppler signal in both laryngeal mucosa and skin, while i.v. peptides caused variable effects. In conclusion, SP and CGRP mimicked capsaicin-induced vasodilation in the tracheobronchial circulation while VIP had a preferential effect on the tracheal circulation.