Tne density of adrenergic nerves at various levels in the guinea-pig lung

Autonomic neural control of intrathoracic airways

Autonomic neural control of the intrathoracic airways aids in optimizing air flow and gas exchange. In addition, and perhaps more importantly, the autonomic nervous system contributes to host defense of the respiratory tract. These functions are accomplished by tightly regulating airway caliber, blood flow, and secretions. Although both the sympathetic and parasympathetic branches of the autonomic nervous system innervate the airways, it is the later that dominates, especially with respect to control of airway smooth muscle and secretions. Parasympathetic tone in the airways is regulated by reflex activity often initiated by activation of airway stretch receptors and polymodal nociceptors. This review discusses the preganglionic, ganglionic, and postganglionic mechanisms of airway autonomic innervation. Additionally, it provides a brief overview of how dysregulation of the airway autonomic nervous system may contribute to respiratory diseases.

Inhibition of histamine-induced bronchoconstriction in Guinea pig and Swine by pulsed electrical vagus nerve stimulation

Objective. Smooth muscle help regulate the diameter of the airways and their constriction can contribute to the pathology of acute asthma attacks. This study sought to determine if applying a specific electrical signal to the vagus nerve (VN) could minimize histamine-induced bronchoconstriction. Methods. Sixteen guinea pigs and three swine were anesthetized and had bipolar electrodes positioned on the cervical VNs. After the animals stabilized, i.v. histamine was titrated to elicit a moderate 2-4 cm H(2) O increase in pulmonary inflation pressure (Ppi). Histamine was then dosed with or without concurrent low voltage VN stimulation. Results. The peak change in Ppi following a histamine challenge was reduced in the guinea pig by VN stimulation (3.4 ± 0.4 vs. 2.1 ± 0.2 cm H(2) O, p < 0.001). The results were confirmed in a limited study in swine and indicate VN treatment is applicable to larger animals. Conclusion. This study suggests that VN stimulation can reduce bronchoconstriction and may prove useful as a rescue therapy in the treatment of acute asthma.

Atrial and ventricular rat coronary arteries are differently supplied by noradrenergic, cholinergic and nitrergic, but not sensory nerve fibres

The present immunohistochemical study set out to determine the extent of perivascular innervation in the rat heart, using markers for noradrenergic sympathetic fibres (tyrosine hydroxylase = TH), cholinergic parasympathetic fibres (vesicular acetylcholine transporter = VAChT), nitrergic fibres (neuronal NO synthase = nNOS), and peptidergic sensory fibres (calcitonin gene-related peptide = CGRP). For each of these antigens, the vascular innervation density was assessed separately in the atria, the basal and the apical parts of the ventricles, and was correlated to the inner vascular diameter. The four major findings are: (1) Each of these neurochemically defined populations shows an individual distribution pattern significantly different from the others with respect to correlation with vascular diameter and occurrence along atrial versus ventricular vessels. (2) Among autonomic efferent axons, nNOS-containing fibres are far less numerous than cholinergic and noradrenergic fibres. (3) Autonomic efferent axons (noradrenergic, cholinergic, nitrergic) are much more abundant around atrial than ventricular vessels, whereas perivascular CGRP-immunoreactive sensory nerve fibres are equally distributed in the various parts of the heart. (4) Noradrenergic and cholinergic axons preferentially innervate small-diameter vessels (negative linear correlation between index of innervation and vascular diameter), whereas the supply with CGRP-immunoreactive sensory nerve fibres does not change with vascular diameter. Collectively, the present study shows individual distribution patterns for each of the neurochemically defined populations of perivascular axons along the atrial and ventricular coronary arteries, indicating a highly differentiated nervous regulation of atrial versus ventricular, and large-diameter versus resistance vessels.

Catecholamine release from isolated guinea pig lungs during sympathetic stimulation with varied ventilation and perfusion

This study was performed to elucidate catecholamine release in the pulmonary circulation of isolated lungs due to the sympathetic nerve stimulation and to assess the experimental conditions which can modify the release, i.e., stimulus intensity, ventilation state of the lung and flow rate of perfusion. In artificially ventilated lungs, electrical stimulation of stellate ganglions evoked large noradrenaline efflux from the lung, but adrenaline efflux was below the detection limit, and dopamine was not detected in any case. In the unventilated preparations, the lung parenchyma were not bleached and the arterial pressure was significantly higher than in ventilated preparations. Noradrenaline efflux from the unventilated group was significantly lower than that from the ventilated preparations. The effect of the perfusion flow rate was investigated under pressure-operated ventilation. The pulmonary arterial pressure (Pa) was not varied at 5-10 ml min-1, but it was increased significantly at 20 ml min-1. Noradrenaline efflux was also increased significantly at 20 ml min-1. These results indicate that noradrenaline was the catecholamine exclusively released from pulmonary vasculature due to the sympathetic nerve stimulation, and that both ventilation and the perfusion flow rate could affect the release. The concomitant increase in arterial pressure indicates that noradrenaline efflux would be affected by the alteration in resistive small arteries. Circulatory change in these arteries is supposed to be one of the factors that modify noradrenaline release from the lungs. The analysis of noradrenaline should be a useful method to evaluate the sympathetic effect on the pulmonary vasculature.

Role of adrenergic nervous system in cigarette smoke-induced bronchoconstriction in guinea pigs

The goal of this study was to clarify the role of the adrenergic nervous system in bronchoconstriction induced by exposure to cigarette smoke in guinea pigs. Artificially ventilated animals were exposed to 160 puffs of smoke for 8 min. Bronchoconstriction was assessed as a percentage of the baseline total pulmonary resistance (RL). The effects of pretreatment with phentolamine (0.1 mg/kg, i.v.), propranolol (1 mg/kg, i.v.), and/or atropine (1 mg/kg, i.v.) were evaluated. Exposure to cigarette smoke caused significant bronchoconstriction. Phentolamine, an alpha-adrenoceptor antagonist, significantly inhibited cigarette smoke-induced bronchoconstriction, while propranolol, a beta-adrenoceptor antagonist, significantly enhanced it. Combined use of these compounds further enhanced the bronchoconstriction. All of modulations of the bronchoconstriction by adrenoceptor antagonists were completely abolished by pretreatment with atropine. Phentolamine and/or propranolol had no effect on the bronchoconstriction induced by inhaled acetylcholine. Pretreatment with yohimbine (0.5 mg/kg, i.v.), a selective alpha2-adrenoceptor antagonist, showed modulatory effects similar to those of phentolamine on cigarette smoke-induced bronchoconstriction. These results suggest that cigarette smoke-induced bronchoconstriction is regulated by the prejunctional modulation of the cholinergic system via alpha- and beta-adrenoceptors. This mechanism may be modulated by the autoregulation of adrenergic nerves via the alpha2-autoreceptor.

Age and region-dependent contraction to alpha-adrenoceptor agonists in rat and guinea-pig isolated trachea

1. The influence of age and of region on alpha-adrenoceptor-mediated contraction to (-)-adrenaline and (-)-noradrenaline was examined in rat (4-136 weeks) and guinea-pig (2-156 weeks) isolated tracheal ring preparations with particular emphasis on the early (up to 12 weeks) maturation phase. 2. In rat tracheal rings, significant regional variation was observed with respect to maximal (-)-adrenaline-induced contraction, such that the greatest activity was seen in ring preparations from the laryngeal end of the trachea. Tracheal rings from the carinal end responded very poorly or were unresponsive to (-)-adrenaline, depending on animal age. These regional differences were seen across the age range. The potencies of (-)-adrenaline and (-)-noradrenaline remained unchanged with respect to animal age, but the maximum contractile tension that developed in response to these agonists increased with increasing animal age in all regions of the trachea. 3. In guinea-pig isolated tracheal tissue, maximum contractile responses (Emax) to (-)-adrenaline and (-)-noradrenaline remained unchanged with increasing animal age. In addition, there was no evidence for a region-dependence in the responsiveness of tracheal tissue to alpha-adrenoceptor-mediated contraction in this species. 4. In both guinea-pig and rat isolated tracheal tissue, alpha-adrenoceptor-mediated contraction appeared to involve the activation of alpha1-adrenoceptors.

Effects of five different airway smooth muscle relaxants on inhibitory neurotransmission in isolated guinea-pig trachea in vitro

Pharmacodynamic effects produced by terbutaline (10 nM), theophylline (10 microM), sodium nitroprusside (30 nM), levcromakalim (0.3 microM) or isradipine (1 nM) on frequency-dependent relaxations induced by electric field stimulation of either proximal or distal parts of isolated guinea-pig trachea were studied in vitro. Preparations were depleted for tachykinins by capsaicin, pretreated with atropine (0.1 microM) and contracted by histamine (2 microM). Drug effects were studied in preparations with combined adrenergic and inhibitory non-adrenergic non-cholinergic (NANC) innervation and in preparations with inhibitory NANC innervation either with or without additional treatment with N(G)-nitro-L-arginine methyl ester (L-NAME) (100 microM). In preparations with combined adrenergic and inhibitory NANC innervation terbutaline, sodium nitroprusside, levcromakalim and isradipine significantly reduced relaxant responses to electric field stimulation in proximal preparations, whereas distal preparations were only affected by terbutaline. In preparations with inhibitory NANC innervation without L-NAME pretreatment, terbutaline significantly enhanced relaxant responses to electric field stimulation only in distal preparations, whereas theophylline, sodium nitroprusside and levcromakalim significantly augmented responses to electric field stimulation in both proximal and distal preparations. In preparations with inhibitory NANC innervation pretreated with L-NAME, theophylline significantly inhibited relaxant responses in distal preparations, whereas sodium nitroprusside, levcromakalim and isradipine significantly augmented relaxant responses to electric field stimulation in proximal preparations. It was concluded that drugs used in the present study can modulate the effects of inhibitory autonomic and NANC neurotransmission in isolated guinea-pig trachea. Furthermore, it was shown that some variation in drug effects exists in relation to proximal and distal parts of guinea-pig trachea.

Innervation pattern of guinea pig pulmonary vasculature depends on vascular diameter

The pulmonary vasculature is supplied by various neurochemically distinct types of nerve fibers, including sensory substance P-containing and autonomic noradrenergic, nitrergic, and cholinergic axons. Pharmacological experiments have suggested that various segments of the pulmonary vascular tree respond differently to the respective neuromediators. We, therefore aimed to determine histochemically and immunohistochemically for each of these neurochemically distinct perivascular axons their quantitative distribution along the vascular tree from the extrapulmonary trunks to the smallest intraparenchymal ramifications in control guinea pigs (n = 5). Generally, arterial innervation was more developed than that of veins. Along the arterial tree, noradrenergic and substance P-containing axons were ubiquitous from the pulmonary trunk to smallest intraparenchymal vessels, whereas nitrergic axons were practically restricted to large (> 700-microns) extrapulmonary arteries. Cholinergic axons were regularly present at arteries down to 100 microns in diameter and innervated two-thirds of small arteries (50-100 microns). The results demonstrate that the noradrenergic vasoconstrictor innervation extends throughout the pulmonary vascular system whereas the innervation pattern with various types of vasodilator fibres changes with vascular diameter, parallel to known pharmacological differences in cholinergic and nitrergic vasodilator effects.

Noradrenaline-induced relaxation of rat oesophageal muscularis mucosae: mediation solely by innervated beta 3-adrenoceptors

We investigated the effects of cocaine and corticosterone on the noradrenaline-induced relaxation of rat oesophageal smooth muscle in the absence and presence of the selective beta2-antagonist, ICI 111,551. It was found that the concentration-response curve (CRC) of noradrenaline was not shifted by ICI 118,551 at 1 microM, whereas a clear shift to the right was observed at 100 microM of the antagonist. In the presence of corticosterone (10 microM), CRC's were clearly shifted to the left; with cocaine (10 microM) additionally present, a further leftward shift was observed, indicating the involvement of both neuronal and extraneuronal uptake sites. It was concluded that the relaxation of rat oesophageal muscularis mucosae by noradrenaline is solely mediated by beta3-adrenoceptors which are sympathetically innervated.

Neuronal control of airways smooth muscle

Sensory afferent nerves relay impulses from the airways to the central nervous system so that appropriate changes in bronchomotor tone and breathing patterns may occur. The dominant efferent control of airways smooth muscle is exerted via bronchoconstrictor parasympathetic cholinergic nerves. In some species this is opposed by bronchodilator sympathetic noradrenergic nerves. In addition, there exist both excitatory bronchoconstrictor and inhibitory bronchodilator non-adrenergic, non-cholinergic pathways. This review examines the role of the different branches of the autonomic nervous system in the control of airways smooth muscle tone with particular reference to modulation of these branches and the interactions which may exist between them.

The sensory and sympathetic innervation of guinea-pig lung and trachea as studied by retrograde neuronal tracing and double-labelling immunohistochemistry

The sympathetic and sensory innervation of guinea-pig trachea and lung were studied by means of retrograde neuronal tracing using fluorescent dyes, and double-labelling immunofluorescence. Sympathetic neurons supplying the lung were located in stellate ganglia and in thoracic sympathetic chain ganglia T2-T4; those supplying the trachea resided in the superior cervical and stellate ganglia. Retrogradely labelled sympathetic neurons were usually immunoreactive to tyrosine hydroxylase; the majority also contained neuropeptide Y immunoreactivity. However, a small number were non-catecholaminergic (i.e. tyrosine hydroxylase negative), but neuropeptide Y immunoreactive. Within the airways, tyrosine hydroxylase/neuropeptide Y-immunoreactive axons were found in the smooth muscle layer, around blood vessels including the pulmonary artery and vein, and to a lesser extent in the lamina propria. Periarterial axons contained in addition dynorphin immunoreactivity. Sensory neurons supplying the lung were located in jugular and nodose vagal ganglia as well as in upper thoracic dorsal root ganglia; those supplying the trachea were most frequently found bilaterally in the nodose ganglia and less frequently in the jugular ganglia. A spinal origin of tracheal sensory fibres could not be consistently demonstrated. With regard to their immunoreactivity to peptides, three types of sensory neurons projecting to the airways could be distinguished: (i) substance P/dynorphin immunoreactive; (ii) substance P immunoreactive but dynorphin negative; and (iii) negative to all peptides tested. Substance P-immunoreactive neurons innervating the airways invariably contained immunoreactivity to neurokinin A and calcitonin gene-related peptide. Retrogradely labelled neurons located in the nodose ganglia belonged almost exclusively (greater than or equal to 99%) to the peptide-negative group, whereas the three neuron types each represented about one-third of retrogradely labelled neurons in jugular and dorsal root ganglia. Within the airways, axons immunoreactive to substance P/neurokinin A and substance P/calcitonin gene-related peptide were distributed within the respiratory epithelium of trachea and large bronchi, in the lamina propria and smooth muscle from the trachea down to the smallest bronchioli (highest density at the bronchial level), in the alveolar walls, around systemic and pulmonary blood vessels, and within airway ganglia. Those axons also containing dynorphin immunoreactivity were restricted to the lamina propria and smooth muscle. The origin of nerve fibres immunoreactive for vasoactive intestinal polypeptide, of which a part were also neuropeptide Y immunoreactive, could not be determined by retrograde tracing experiments. Vasoactive intestinal polypeptide-immunoreactive fibres terminating within airway ganglia may be of preganglionic parasympathetic origin, whereas others (e.g. those found in smooth muscle) may arise from intrinsic ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasoactive intestinal peptide and neuropeptide Y coexist in non-noradrenergic sympathetic neurons to guinea pig trachea

Vasoactive intestinal peptide (VIP) has been suggested to be a mediator of vagal inhibition of airway tone and it has been assumed that VIP-containing nerve fibres in the airway arise from intrinsic ganglia. We have used a combination of double- and triple-labelling immunohistochemistry, retrograde axonal tracing, organotypic culture and nerve lesion studies, to identify the origin and distribution of neurons containing immunoreactivity (IR) to VIP in guinea pig airway smooth muscle. We also investigated whether immunoreactivity to other neuropeptides coexisted with VIP-IR within these neurons. We found that all VIP-IR nerve fibres in guinea pig tracheal smooth muscle also contained IR to neuropeptide Y (NPY) but not to tyrosine hydroxylase (TH), a marker for noradrenergic neurons. Both VIP-IR and NPY-IR were absent from nerve cell bodies in the tracheal plexus. After maintenance of isolated trachea in organotypic culture for 4 days, to allow degeneration of extrinsic nerve fibres, nerve fibres containing VIP-IR or NPY-IR were almost completely absent from tracheal smooth muscle. Of ganglia known to supply the trachea, coexistence of VIP-IR and NPY-IR was found only in cell bodies of the stellate ganglion. Retrograde tracing studies using the fluorescent tracer, DiI, confirmed that the stellate ganglion was the site of origin of neurons containing VIP-IR and NPY-IR supplying the airways. These neurons projected to the airways from the stellate ganglion both directly through the mediastinum, and via the cervical sympathetic trunk and vagus nerves. These results suggest that nerve fibres containing both VIP-IR and NPY-IR in the tracheal smooth muscle of the guinea pig are derived from non-noradrenergic cell bodies in the stellate ganglion. The absence of VIP-IR from vagal post-ganglionic neurons suggests that VIP cannot be a mediator of vagal inhibitory transmission in tracheal smooth muscle of this species.

Evidence that blood vessels in guinea-pig lung are supplied by both noradrenergic and dopaminergic axons

Assay of catecholamines in guinea-pig lung showed that the amount of dopamine in this tissue is 3-4 times greater than that predicted to be associated only with noradrenergic nerves, and is depleted by animal treatment with 6-hydroxydopamine. Fluorescence microscopy after formaldehyde condensation did not reveal any non-neuronal stores of catecholamines within the lung. The pulmonary and bronchial arterial vessels are accompanied by numerous fine nerve fibres that exhibit immunoreactivity for tyrosine hydroxylase, and are therefore presumed to be catecholaminergic. A small proportion of these fibres are also immunoreactive for DOPA decarboxylase. The results are consistent with innervation of pulmonary and bronchial resistance vessels by dopaminergic as well as noradrenergic sympathetic axons.

Effects of noradrenaline on the isolated human bronchus. Comparison with the isolated guinea pig trachea

The pharmacodynamic activity of noradrenaline was evaluated comparatively in vitro on isolated human bronchi and on guinea pig tracheal spirals. Noradrenaline exerted a contractile effect on both preparations under resting tone and in the presence of propranolol 10(-6) M; maximal noradrenaline-induced contraction was 15-20% of maximal acetylcholine (ACh)-induced contraction. Without propranolol, the contractile effect of noradrenaline was negligible when the preparations were under resting tone and absent when they were precontracted with ACh. In contrast, noradrenaline exerted a strongly relaxant effect on both human bronchi (-log ED50 5.24 +/- 0.17; N = 5) and guinea pig tracheae (-log ED50 6.15 +/- 0.29; N = 8). With maximal contraction induced by ACh 3.10(-3) M the -log ED50 of both preparations were shifted to the right by functional antagonism and became 4.72 +/- 0.17 and 5.31 +/- 0.11, respectively. The pKD values of noradrenaline, calculated according to Furchgott and Bursztyn (1967), were 4.79 +/- 0.04 in human bronchi (N = 5) and 4.77 +/- 0.16 in guinea-pig tracheae (N = 8). In the presence of cocaine plus phenoxybenzamine these values were not significantly modified in human bronchi and only slightly modified in guinea pig tracheae. It is concluded that noradrenaline induces a strong beta-adrenergic response and a negligible alpha-adrenergic response from both human bronchi and guinea pig tracheae in vitro.

Innervation of airway smooth muscle. Efferent mechanisms

The classical view, with one excitatory (cholinergic) and one inhibitory (noradrenergic) component, of the innervation of airway smooth muscle is incomplete and at least two other, possibly peptidergic, types of innervation must be included when the innervation of airways is considered. A summary of these neuronal components is given in Fig. 1 and their possible origin is outlined. Besides the inhibitory noradrenergic innervation of the airways observed in some species, an inhibitory NANC (i-NANC) innervation has been demonstrated. The polypeptide, VIP, seems to be the most likely candidate for the neurotransmitter in the i-NANC innervation of the airways. The excitatory cholinergic innervation is present in the airways from the trachea down to the peripheral bronchi. In the guinea-pig bronchi an excitatory NANC (e-NANC) innervation has been demonstrated as well. The e-NANC nerves may correspond to chemosensitive primary afferent nerves with substance P or a related tachykinin as transmitter. When the innervation of airway smooth muscle of different mammalian species is compared it is evident that all nerve components except the cholinergic, show a considerable variability among species. The cholinergic innervation seems to be present in all mammalian species whereas the other components may be completely absent from some species. Distinct regional variations in the innervation of the airways may occur, which is exemplified by the distribution of the autonomic innervation in the guinea-pig tracheo-bronchial tree. Cholinergic neurotransmission in for example the guinea-pig and human airways can be modulated by NA via prejunctional inhibitory alpha 2-adrenoceptors. Furthermore, the e-NANC neurotransmission in the guinea-pig airways may be modulated by NA or by selective alpha 2-adrenoceptor agonists, acting via prejunctional inhibitory alpha 2-adrenoceptors. The clinical importance of the NANC innervation in relation to asthma is discussed. The i-NANC nerves may exert a modulating effect on bronchoconstriction, and a functional defect would presumably lead to an exaggerated response to constrictor stimuli. The e-NANC nerves in the airways may also be clinically relevant since the transmitter (tachykinins) from these nerves can produce bronchoconstriction and promote inflammation of the airway epithelium, either by direct mechanisms or indirectly by activation of mast cells, and thus contribute to the features of asthma.(ABSTRACT TRUNCATED AT 400 WORDS)

Determination of extrinsic pathways of adrenergic nerves to the guinea-pig trachealis muscle using surgical denervation and organ-bath pharmacology

Intraluminal pressure changes were recorded in an isolated tracheal tube during electrical stimulation of the recurrent laryngeal nerve or transmural stimulation of the extra-thoracic trachealis muscle. The recurrent laryngeal nerve contained adrenergic nerve fibres running both anteriorly and posteriorly along this nerve and they caused an adrenergic inhibitory response of the trachealis muscle. The superior cervical ganglion was the source of the majority of the adrenergic fibres running both anteriorly and posteriorly within the recurrent laryngeal nerve. The antero-posterior adrenergic fibres reached the recurrent laryngeal nerve via an anastomosis with the superior cervical ganglion. The postero-anterior adrenergic fibres reached the recurrent laryngeal nerve via the vagus nerve, as ipsilateral vagotomy markedly reduced the inhibitory response of the trachealis muscle which had been due to the postero-anterior adrenergic fibres. Superior cervical ganglionectomy caused a significant reduction in the adrenergic response as a percentage of the total inhibitory response of the extra-thoracic trachealis muscle following transmural stimulation. The remaining response was due to stimulation of non-adrenergic non-cholinergic fibres and adrenergic fibres from another source.

A physiological basis for subclassifying beta-adrenoceptors examined by chemical sympathectomy of guinea-pigs

Chemical sympathectomy of guinea-pigs was induced by chronic pretreatment with 6-hydroxydopamine over a 20 day period. Control animals were sham injected with vehicle at the same times. Isolated tissues were removed from the animals and beta-adrenoceptor sensitivity assessed from cumulative concentration-response curves for isoprenaline, followed after wash-out by a partial agonist (salbutamol, ritodrine or prenalterol). The following responses were measured: increases in force and rate of contraction of left and right atria respectively, inhibition of carbachol-induced ileal contractions, relaxation of intrinsic tone of lung strips and tracheal spirals, inhibition of contractions of vas deferens and soleus muscle induced by field stimulation. Left and right atria and ileum from 6-hydroxydopamine-pretreated guinea-pigs exhibited supersensitivity to beta-adrenoceptor stimulation. This was measured as a leftwards shift of the concentration-response curve for isoprenaline and as an elevation of the partial agonist maximum response (relative to isoprenaline), when compared with tissues from sham-injected controls. The supersensitivity was assumed to be due to the loss of endogenous neurotransmitter release by chemical sympathectomy and specific for the beta-adrenoceptor. In contrast, lung strips, vas deferens and soleus muscle were not supersensitive. The responses of these tissues are thought to be mediated via beta 2-adrenoceptors whereas cardiac and ileal responses are beta 1-adrenoceptor mediated. The latter receptor subtype would therefore appear to be under the influence of sympathetic innervation, but since no supersensitivity occurred at beta 2-adrenoceptors these were presumed to be non-innervated but stimulated by circulating adrenaline. These results obtained by use of chemical sympathectomy with 6-hydroxydopamine support the contention that the physiological basis of beta-adrenoceptor subclassification is that the beta 1-subtype are innervated whereas the beta 2-subtype are non-innervated.

The adrenergic innervation of pulmonary vasculature in the normal and pulmonary hypertensive rat

It would appear that susceptibility to chronic proliferative pulmonary hypertension in response to chronic alveolar hypoxia is most severe in species in which adrenergic innervation of pulmonary arteries is reduced or lacking. Intrapulmonary arteries of the rat have been reported to lack adrenergic innervation by some workers but not others. Since the rat develops severe proliferative pulmonary hypertension in response to prolonged alveolar hypoxia, the different divisions of the lung vasculature of Sprague-Dawley rats were thoroughly examined to determine the presence or absence of an adrenergic innervation. The degree of innervation in normal rats was compared with that of rats developing pulmonary hypertension. Both in normal and experimental pulmonary hypertensive rats the pulmonary arteries, all their branches and the small pulmonary veins with a smooth muscle media were found to be devoid of adrenergic innervation. In contrast, the cardiac-like muscle in the media of large pulmonary veins, the bronchial arteries and the vasa vasorum of larger vessels were richly innervated by adrenergic nerves. Thus the increase in medial smooth muscle which occurs in pulmonary arteries during chronic alveolar hypoxia is independent of a pre-existing adrenergic innervation or of such an innervation newly derived from that of adjacent vessels or structures. This is in contrast to systemic vessels where it has been suggested that increased adrenergic activity and density of innervation may augment hypertrophy of the media in hypertensive animals. Adrenergic nerves are suggested to have a protective action on pulmonary vessels.

Extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle

Origins and extrinsic pathways of the adrenergic innervation of the guinea-pig trachealis muscle were studied using fluorescence histochemical techniques. Bilateral superior cervical ganglionectomy caused a marked reduction in the adrenergic innervation of the extra-thoracic region, which suggests that these ganglia are a major source of adrenergic innervation to this muscle. Combined anterior and posterior transection of the recurrent laryngeal nerves also caused a marked reduction in the density of adrenergic fibres in the extra-thoracic trachealis muscle. Crushing of these nerves revealed adrenergic fibres running both anteriorly and posteriorly. The majority of these adrenergic nerves were lost after superior cervical ganglionectomy and thus the fibres running in both directions originate in the superior cervical ganglion. Antero-posteriorly directed fibres entered the recurrent laryngeal nerve from the superior cervical ganglion via an anastomosis at the level of the cricoid cartilage, while those running postero-anteriorly entered the recurrent laryngeal nerve posteriorly from the vagus nerve and these adrenergic fibres were lost after cervical vagotomy.

Beta-adrenoceptor heterogeneity in guinea-pig airways: comparison of functional and receptor labelling studies

The distribution of beta-adrenoceptor subtypes in guinea-pig airways has been studied by radioligand binding assays and analysis of mechanical responses. Binding studies with the ligands [3H]-dihydroalprenolol and [125I]-cyanopindolol, revealed that beta-adrenoceptors were unevenly distributed throughout the airways with the highest density located in the parenchyma and the lowest density in the trachea. The relative proportion of beta 1:beta 2-adrenoceptor binding sites was assessed by computer-assisted analysis of the inhibition curves generated by selective agents. It was virtually identical in each region and in the order of 15:85%. beta-Adrenoceptor agonists caused concentration-dependent relaxations of both tracheal spirals and parenchymal lung strips. This response appeared to be mediated by both beta 1- and beta 2-adrenoceptors in tracheal spirals as the pA2 value for the beta 1-selective antagonist, atenolol, varied depending upon which agonist was used, and, in the presence of the beta 2-adrenoceptor antagonist ICI 118,551, noradrenaline and isoprenaline produced biphasic concentration-effect curves. In parenchymal lung strips only the one subtype was involved as antagonist pA2 values were not dependent on the agonist used and the properties were consistent with those expected for a beta 2-adrenoceptor.

Beta 2-adrenoceptor blockade is the basis of guinea-pig bronchial hyper-responsiveness to leukotriene C4 and other agonists

Four beta-adrenoceptor antagonists, namely (-)-propranolol, (+)-propranolol, ICI-118551 and (+/-)-practolol, were investigated for their effects on leukotriene C4 (LTC4)-induced bronchoconstriction in the anesthetized guinea-pig. (-)-Propranolol was also investigated for its effects on acetylcholine and histamine bronchospasm in the anaesthetized guinea-pig, and on LTC4-induced contractions of guinea-pig isolated trachea and lung parenchyma. The various beta-adrenoceptor antagonists potentiated, dose-dependently, the bronchoconstriction induced by threshold doses of LTC4 and the intensity of the potentiation correlated with the beta 2-blocking capacity possessed by the drugs. (-)-Propranolol potentiated the bronchospasm induced by threshold doses of acetylcholine and histamine but to a lesser degree than the LTC4-induced bronchospasm. The airway hyper-responsiveness induced by (-)-propranolol was unaffected by pretreatment with mepyramine, cyproheptadine, phenoxybenzamine, atropine or indomethacin. The airway hyper-responsiveness induced by (-)-propranolol persisted even in adrenalectomized or reserpine-treated guinea-pigs, although adrenalectomy induced some increase in airway responsiveness. (-)-Propranolol had no effect on LTC4, histamine and acetylcholine-induced contractions of isolated trachea and lung parenchyma. The results show that the airway hyper-responsiveness induced by beta-adrenoceptor antagonists generally correlates with their beta 2-blocking activity. The possibility remains that some other unknown mechanism(s) may also be implicated.

Physiological and pharmacological aspects of adrenergic receptor classification

The questions raised are: what is the physiological or pharmacological basis for the differentiation into beta 1- and beta 2-, and alpha 1- and alpha 2-adrenergic receptors?; and do the neurotransmitter norepinephrine and the hormone epinephrine differ in their receptors? On the basis of a preference of beta 2- and alpha 2-adrenergic receptors for epinephrine, the hormone, and of beta 1-and alpha 1-receptors for norepinephrine, the neurotransmitter, it was postulated that the alpha 2- and beta 2-receptors are predominantly epinephrinergic in nature and located extrajunctionally and presynaptically whereas the alpha 1- and beta 1-receptors are predominantly norepinephrinergic in nature and located postsynaptically in the sympathetic terminal junction. The alpha 2- and beta 2-character of the presynaptic receptors matches that of the corresponding extrajunctional receptors. This indicates that a circulating catecholamine, namely epinephrine, is involved in the regulation of adrenergic transmitter release.

Neurone-specific enolase and S-100: new markers for delineating the innervation of the respiratory tract in man and other mammals

Lung innervation has been studied in the past by methylene blue staining and silver impregnation and more recently by histochemical methods. These techniques give only a partial picture of the total innervation. We have delineated the innervation of the lung in man and three other mammalian species by immunostaining with antibodies to two new markers of nervous tissue. These markers are neurone-specific enolase (NSE), an enzyme present in nerve cells in both the central and the peripheral nervous systems, and S-100, a protein found in glial cells. Throughout the respiratory tract NSE was localised in ganglion cells and nerve fibres in all species examined, while S-100 was found in the supporting glial cells of ganglia and in Schwann cells of peripheral nerves. The distribution of NSE immunoreactivity in serial sections was compared with that of acetylcholinesterase-containing, noradrenergic, and peptide-containing nerves. In all areas NSE was found to be a specific marker for all three types of nerves. Thus these two antibodies provide an effective histological means of examining both the neuronal and the non-neuronal components of the lung innervation and should be of value in investigating this system in lung disease.

Comparison of functional beta-adrenoceptor heterogeneity in central and peripheral airway smooth muscle of guinea pig and man

The nature of the beta-adrenoceptor population(s) mediating the relaxation of guinea pig and human airway smooth muscle was investigated. On the basis of a preferential blockade by beta 1- and beta 2-selective antagonists of the relaxation induced by beta 1- and beta 2-selective agonists, guinea pig tracheal strip relaxation was found to be mediated both by beta 1- and beta 2-adrenoceptors, the relative participation of which depending on the relative affinities of the agonist towards these two receptors. With highly selective antagonists the noradrenaline (NA)-induced relaxation could be split up biphasically into a beta 1- and a beta 2-component. In contrast, no such differential blockade was observed with the guinea pig lung parenchyma strip relaxation which is mediated by a homogenous beta 2-adrenoceptor population. On comparison of the tracheal, the spirally cut main bronchus- and intrapulmonary airway smooth muscle strips it could be shown that both the sensitivity of NA for neuronal uptake and the apparent affinity of the relaxation by NA decreased in the direction of the lung periphery. Using the same techniques it was ascertained that the relaxation of human tracheal smooth muscle (autopsy, obtained within 6 hours after death), main bronchus and intrapulmonary smooth muscle (operation) are mediated by homogenous beta 2-adrenoceptor populations. In addition, neuronal and extraneuronal uptake sites were not operative in these preparations, whether obtained from operation or from autopsy.

A possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity

To investigate a possible role of a nonadrenergic inhibitory nervous system in airway hyperreactivity, we measured changes in RL and CL caused by electrical stimulation of cervical vagus nerve during the infusion of 5-HT, after treatment with atropine and propranolol in 18 cats. RL decreased to 56 +/- 3% (mean +/- SE) and CL increased to 186 +/- 13% of the prestimulated values, respectively, after stimulation. Hexamethonium diminished these responses significantly. Airway reactivity to 5-HT was reduced by continuous electrical stimulation of cervical vagus nerve in cats pretreated with atropine and propranolol. Hexamethonium potentiated airway reactivity to 5-HT. These results suggest that a nonadrenergic inhibitory nervous system could play an important role in the control of the bronchomotor tone and contribute to airway hyperreactivity.

Modulation of bronchoconstrictor responses to histamine in pithed guinea-pigs by sympathetic nerve stimulation

1 Electrical stimulation (40V, 0.5-8 Hz, pulse width 0.5 ms) of the thoracic spinal outflow for between 10 and 120 s inhibited histamine-induced bronchoconstriction in pithed guinea-pigs. 2 The degree of this bronchodilatation varied with the position of the stimulating electrode within the spinal canal. Two maxima were identified. The first, at the level of the 9th and 10th thoracic vertebrae, was abolished by adrenalectomy. The second, at the level of the 3rd and 4th thoracic vertebrae, was associated with tachycardia and was unchanged by adrenalectomy. 3 The magnitude of this second bronchodilator effect varied with the frequency of stimulation. It was abolished by pretreatment with reserpine (5 mg/kg i.p. 48 and 24 h beforehand) and was competitively blocked by propranolol (0.01-1.0 mg/kg). 4 These observations are consistent with the view that bronchodilator tone is derived from neuronally-released noradrenaline within the lung. The noradrenaline probably overflows from well-innervated vasculature adjacent to sparsely innervated airways.

Catecholamine transport in isolated lung parenchyma of pig

1 Lung parenchyma strips of the pig incubated at 37 degrees C with [(3)H]-(-)-noradrenaline ([(3)H]-NA) or [(3)H]-(+/-)-isoprenaline ([(3)H]-Iso), accumulated radioactivity via saturable, high affinity uptake processes. Apparent saturation constants (K(m)) for [(3)H]-NA and [(3)H]-Iso were 1.34 x 10(-6) M and 1.63 x 10(-6) M respectively, while apparent transport maxima (V(max)) were 4.86 and 1.63 x 10(-9) mol min(-1) g(-1) respectively.2 Cellular accumulation of radioactivity from radiolabelled catecholamines was greatly reduced by lowering the temperature to 7 degrees C, pretreatment with ouabain (100 muM), phentolamine (15 muM) or phenoxybenzamine (80 muM). However, accumulation of radioactivity derived from ((3)H]-NA was inhibited selectively by cocaine (10 muM) and desipramine (1 muM), while normetanephrine (80 muM) and 3-O-methylisoprenaline (50 muM) caused much greater reductions in cellular radioactivity from [(3)H]-Iso than from ((3)H]-NA. Taken together with information from kinetic studies, the results indicate that these amines are transported by separate uptake processes.3 Cocaine (50 muM) which selectively reduced [(3)H]-NA transport, had no significant effect on the sensitivity (EC(50)) of isolated parenchyma lung strips of the pig to the contractile effects of cumulative concentrations of NA. The catechol-O-methyl transferase (COMT) inhibitor, U-0521 (60 muM), also failed to alter the potency of NA, while normetanephrine (80 muM) caused a 2 fold decrease in potency.4 Phentolamine (15 muM), which reduced the cellular accumulation of radioactivity derived from [(3)H]-Iso by 64%, caused a small potentiation of Iso-induced relaxations of porcine lung strips. Normetanephrine (80 muM) and 3-O-methylisoprenaline (50 muM), which also depressed the accumulation of cellular radioactivity from [(3)H]-Iso by > 50%, caused rightward shifts in Iso concentration-effect curves as a result of beta-adrenoceptor blockade. In sharp contrast, cortisol (80 muM) and U-0521 (60 muM), which caused smaller reductions in the cellular accumulation of radioactivity derived from [(3)H]-Iso, both caused an approximately 9 fold potentiation of responses to Iso in isolated lung strips.5 The results indicate that the major sites of uptake and metabolism of NA in porcine parenchyma strip are remote from alpha-adrenoceptors mediating NA-induced contraction. Similarly, some major sites of uptake of Iso are remote from beta-adrenoceptors mediating Iso-induced relaxation. However, beta-adrenoceptors are apparently in close proximity to a compartment containing COMT activity.

Adrenergic and non-adrenergic inhibitory nerves in mammalian airways

A study of the actions of adrenergic and non-adrenergic nerves which affect mammalian airways was carried out. The preparations studied included strips of lung from guinea-pig, rat, rabbit, monkey and human, tracheal strips from the first 4 animals and bronchial strips from the last 3. Relaxations to field stimulation of sympathetic nerves were found in the guinea-pig trachea only. Functional nonadrenergic inhibitory nerves were found in the larger airways of all species except rat. Lung strips from all the mammals failed to respond to sympathetic or nonadrenergic inhibitory nerve stimulation suggesting a lack of functional inhibitory nerves of either type in the fine airways. Studies on the distribution of adrenergic nerves showed that primary target of the nerves in all species appeared to be the vasculature, especially in lung. Occasional fibres were seen entering the smooth muscle of the fine airways in guinea-pig, rabbit, and rat, but not in monkey or human lung or in monkey trachea or bronchus or human bronchus. Guinea-pig and rabbit trachealis muscles received a significant innervation but only the guinea-pig tissue responded to sympathetic stimulation. Inhibitory beta-adrenoceptors were demonstrated in the proximal airways of all species except rabbit. The fine airways of rat, monkey and human contained a mixed population of alpha-excitatory and beta-inhibitory adrenoceptors only were found in guinea-pig lung and alpha-adrenoceptors only in rabbit lung.

Haemophilus influenzae induced loss of lung beta-adrenoceptor binding sites and modulation by changes in peripheral catecholaminergic input

Vaccination of guinea pigs with killed suspensions of Haemophilus influenzae, a bacterium often found in the deeper respiratory airways of asthmatic bronchitics, results in a number of effects suggesting an impairment of beta-adrenoceptor function. A [3H]dihydroalprenolol binding assay was used to determine the number of beta-adrenoceptors (Bmax) following H. influenzae vaccination. The Bmax declined significantly by 29% from 1240 +/- 80 to 880 +/- 70 fmol/mg protein, while the binding affinity of the sites was not changed. Specific binding in the presence of 1.8 nM [3H]DHA to tracheal longitudinal smooth muscle was also significantly lower in H. influenzae-vaccinated animals as compared to controls. Furthermore modulation of peripheral sympathetic input to lung beta-adrenoceptors was evaluated in our model. Pretreatment with Ro4-4602, an inhibitor of dopa-decarboxylase, increased the number of beta-adrenoceptors and prevented the H. influenzae-induced loss of beta-adrenoceptors. On the other hand repeated doses of the antidepressant desipramine mimicked the effect of H. influenzae vaccination i.e. a loss of beta-adrenoceptors. Desipramine and H. influenzae vaccination were not synergistic in their effects. The effects of H. influenzae and modulation of catecholaminergic input on guinea pig lung beta-adrenoceptors were compared with tracheal strip relaxation by isoproterenol, following similar treatments assessed in a superfusion model. Changes in lung beta-adrenoceptor number were almost identical with changes in tracheal strip relaxation. These results suggest that compensatory regulation adapts the number of respiratory beta-adrenoceptors to changes in sympathetic input. A similar mechanism may underlie the loss of beta-adrenoceptors following H. influenzae vaccination.

Adrenergic and cholinergic induced contractions of tracheal smooth muscle in the rabbit as demonstrated by a new in vivo method

An in vivo tracheal muscle preparation in the rabbit was developed which enabled us to measure changes in the isometric tension of the trachealis muscle in response to electrical stimulation of autonomic nerves and to i.v. administration of autonomic agonists and antagonists. The preparation was very sensitive to injections of carbachol, and showed graded contractions to stimulation of the caudal end of the cut cervical vagus as frequency and strength of stimulation were increased. Stimulation of the rostral end of the cut cervical sympathetic nerve fibers produced contractions in all preparations. This effect was mimicked by the alpha-adrenoceptor agonist, phenylephrine. The effects of both sympathetic stimulation and phenylephrine were blocked by phentolamine and not inhibited by pretreatment with atropine or propranolol. Sympathetic stimulation produced contractions of the trachealis muscle whether the initial tone was normal or actively increased by carbachol, while adrenaline produced relaxation when the initial tone was high. Using this new in vivo trachealis muscle preparation in the rabbit, we could show that sympathetic stimulation produced contractions of the trachealis muscle. This effect is consistent with the existence of smooth muscle activating alpha adrenoceptors.

Pharmacological characterization of the autonomous innervation of the guinea pig tracheobronchial smooth muscle

From the trachea, main bronchi and hilus bronchi of guinea pigs, preparations were isolated for registration of mechanical tension on electrical field stimulation and drugs. The trachea contracted on short trains of electrical stimulation. Usually these contractions were followed by a relaxant response. The contractions were abolished while the relaxations were potentiated by atropine. In the main bronchi field stimulation induced a contractile response which was abolished by atropine. In the latter preparation relaxant responses were never observed, even not after atropine. In the trachea and main bronchi neither the alpha 1 blocker prazosin nor the alpha2 blocker yohimbine affected the contractile or relaxant responses when used in alpha-blocking concentrations. The relaxant response in trachea was neither affected by the "P1 blocker" theophylline nor by the "P2 blocker" quinidine but it was partially inhibited by guanethidine or beta-blocking agents. The hilus bronchi contracted on field stimulation as well as histamine. The contractile response on electrical stimulation was only slightly inhibited by atropine or guanethidine. In all three preparations responses on field stimulation were abolished by tetrodotoxin. It is suggested that in both trachea and main bronchi excitatory cholinergic innervation is present. Further, the trachea but not the main bronchi is innervated by both adrenergic and nonadrenergic inhibitory nerves. The hilus bronchi contains a non-adrenergic non-cholinergic excitatory nervous system.

Contribution of vascular smooth muscle to contractile responses of guinea-pig isolated lung parenchymal strips

Parenchymal strips, isolated from the guinea-pig lung, were stimulated transmurally at different electrical frequencies in vitro. Frequency-response analyses for contraction were obtained on paired strips in the absence or presence of antagonists. Tetrodotoxin was shown to block the effects of electrical stimulation, demonstrating that the contractile response was due to activation of efferent neurons in the tissue. Phentolamine, 10(-5) M, and atropine, 10(-6) M, antagonists demonstrated to be selective for blocking alpha-adrenergic and muscarinic receptors, respectively, produced inhibition of the contractile effects of electrical stimulation. When analyzed at the level of the frequency required to produce a contraction equal to 10% of the maximum produced by histamine, the EF10, the frequency-response curves were shifted 3- to 4-fold to the right by each receptor antagonist. Combination of the two receptor antagonists produced a greater degree of blockade than either alone and, at the maximum frequency utilized (32 Hz), the contractile response did not reach the EF10 in al tissues. Propranolol, 10(-6) M, did not alter the effects of electrical stimulation, but increased the magnitude of contraction produced by exogenously applied norepinephrine. In tissues taken from reserpine-pretreated animals, phentolamine did not produce a statistically significant change in EF10 for electrical stimulation. The data provide evidence that both vascular and airway smooth muscles are present and contribute to contractile responses in the guinea-pig lung parenchymal strip.

Some characteristics of the purinergic nervous system in normal and sensitized airway smooth muscle

Supramaximal electrical field stimulation was employed to produce biphasic response in segments of cervical and thoracic tracheas and in first generation of bronchi isolated from guinea pigs. This response consists of contraction (as measured by maximal active tension, ATmax) followed by relaxation (as measured by maximal active relaxation, ARmax). First, the effect of electrical stimulation was studied in relation to frequency and duration of impulse. Highest degree of relaxation (ARmax) was achieved with a frequency of stimulus of 40 pulses per sec for segments of trachea, and 60 pulses per sec for first generation bronchi, and with duration of pulse of 1.0 msec for segments of trachea, and 2.0-2.5 msec for bronchi, and with duration of pulse of 1.0 msec for segments of trachea, and 2.0-2.5 msec for bronchi. Secondly, mean length-tension relationship was determined. It was found that maximal relaxation (ARmax) occurred at 160 +/- 5% of Lmax in case of tracheal segments and 160 +/- 2% of Lmax for bronchial preparations. Using propranolol pretreatment (10(-4) M), which inhibited participation of adrenergic receptors in relaxation, it was determined that approximately 50% relaxation of airway smooth muscle of the normal guinea pig is mediated through the purinergic nervous system. Both tracheas and bronchi isolated from sensitized guinea pigs, chronically exposed to antigen, showed a significant decrease in overall relaxation (P less than 0.01). However, the per cent decrease in relaxation after propranolol was not different in sensitized animals than that found in controls. The data suggest that relaxation of segments of airways isolated from animals chronically exposed to antigen is decreased in consequence of alterations in both purinergic and adrenergic nervous systems.