Occurrence and distribution of regulatory peptides in the respiratory tract

Role of transient receptor potential vanilloid 1 receptors in endotoxin-induced airway inflammation in the mouse

Airways are densely innervated by capsaicin-sensitive sensory neurons expressing transient receptor potential vanilloid 1 (TRPV1) receptors/ion channels, which play an important regulatory role in inflammatory processes via the release of sensory neuropeptides. The aim of the present study was to investigate the role of TRPV1 receptors in endotoxin-induced airway inflammation and consequent bronchial hyperreactivity with functional, morphological, and biochemical techniques using receptor gene-deficient mice. Inflammation was evoked by intranasal administration of Escherichia coli lipopolysaccharide (60 microl, 167 microg/ml) in TRPV1 knockout (TRPV1(-/-)) mice and their wild-type counterparts (TRPV1(+/+)) 24 h before measurement. Airway reactivity was assessed by unrestrained whole body plethysmography, and its quantitative indicator, enhanced pause (Penh), was calculated after inhalation of the bronchoconstrictor carbachol. Histological examination and spectrophotometric myeloperoxidase measurement was performed from the lung. Somatostatin concentration was measured in the lung and plasma with radioimmunoassay. Bronchial hyperreactivity, histological lesions (perivascular/peribronchial edema, neutrophil/macrophage infiltration, goblet cell hyperplasia), and myeloperoxidase activity were significantly greater in TRPV(-/-) mice. Inflammation markedly elevated lung and plasma somatostatin concentrations in TRPV1(+/+) but not TRPV1(-/-) animals. In TRPV1(-/-) mice, exogenous administration of somatostatin-14 (4 x 100 microg/kg ip) diminished inflammation and hyperreactivity. Furthermore, in wild-type mice, antagonizing somatostatin receptors by cyclo-somatostatin (4 x 250 microg/kg ip) increased these parameters. This study provides the first evidence for a novel counterregulatory mechanism during endotoxin-induced airway inflammation, which is mediated by somatostatin released from sensory nerve terminals in response to activation of TRPV1 receptors of the lung. It reaches the systemic circulation and inhibits inflammation and consequent bronchial hyperreactivity.

Effect of vasoactive intestinal polypeptide (VIP) on pulmonary ventilation-perfusion relationships and central haemodynamics in healthy subjects

Ventilation-perfusion relationships of the lung (VA/Q) and central haemodynamics were studied in nine healthy subjects before and during 30 min of vasoactive intestinal polypeptide (VIP) infusion (20 ng kg.min-1). During the infusion, arterial concentrations of VIP rose from 16.1 +/- 6.1 to 420 +/- 110 pmol l-1 and noradrenaline concentrations doubled (P < 0.01). VA/Q distributions, determined by inert gas elimination technique, were significantly shifted to lower values for VA/Q with slight increases in dispersions, but arterial oxygen tension remained unchanged. Heart rate, stroke volume and cardiac output rose 27, 44 and 80% respectively (P < 0.01). Systematic arterial pressure stabilized at a slightly lower level compared to basal (base line: 93 +/- 5 mmHg, VIP; 88 +/- 6 mmHg, P < 0.05). Right atrial and pulmonary capillary wedge pressures remained unchanged during VIP infusion, while pulmonary vascular resistance and systematic vascular resistance decreased significantly, by 25% (P < 0.03) and 53% (P < 0.01), respectively. It is concluded that VIP causes: (1) alterations in ventilation-perfusion distributions, but generates no shunt and does not cause hypoxaemia during 30 min infusion, (2) reduction of pulmonary and systemic vascular resistances and afterload reduction of the left ventricle, (3) reflex sympathoadrenal stimulation with increasing heart rate and myocardial contractility, and (4) a direct positive inotropic effect on the myocardium.

Calcitonin gene-related peptide in small cell lung carcinomas

OBJECTIVE

Calcitonin gene-related peptide (CGRP) is a regulatory peptide encoded by the calcitonin gene. CGRP is expressed in increased amounts by the cells of medullary thyroid carcinomas and has been demonstrated by immunohistochemistry to occur in neuroendocrine cells and nerve fibres of lung tissue.

MEASUREMENTS

Serum CGRP levels were measured in patients with small cell lung carcinomas before treatment (n = 74) and immediately before the second course of chemotherapy (n = 30). In-situ hybridization and immunohistochemistry were performed on tumour tissue and CGRP was extracted from two tumours and characterized by gel chromatography and high pressure liquid chromatography.

RESULTS

Serum CGRP levels were elevated in small cell lung carcinomas when compared with healthy controls of similar age and sex (median values 55.0 vs 36.6 pmol/l, P < 0.001), and 27% had levels above the upper normal range. Serum CGRP levels decreased following the initial course of chemotherapy (P < 0.05) but remained elevated when compared to the controls (P < 0.001). In-situ hybridization for CGRP mRNA was positive in three of 17 tumours and immunohistochemistry was positive in seven of 31 tumours investigated. CGRP immunoreactivity extracted from two tumours was characterized by gel chromatography and high pressure liquid chromatography. A major part of the immunoreactivity was demonstrated to represent the intact molecule.

CONCLUSIONS

We found that patients with small cell lung carcinomas had elevated concentration of serum calcitonin gene-related peptide but only 27% had values above the upper normal range. Serum CGRP is therefore of limited value as a tumour marker. Intact CGRP can be extracted from tumour tissue, but in-situ hybridization and immunohistochemistry showed positive reactions in only a few of the tumours investigated. The elevated serum CGRP levels are therefore likely to be largely of extratumoral origin.

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.

Gastrin releasing peptide (GRP) binding sites in human bronchi

The autoradiographic binding site of gastrin releasing peptide (GRP), the 27 amino acid mammalian form of bombesin, were examined in human bronchial mucosa. 125I-GRP bound specifically to submucosal glands and the epithelium. There was limited binding to vessels and bronchial smooth muscle. These observations suggest that GRP or GRP immunoreactive peptides which are present in nerve fibres and pulmonary neuroendocrine cells, may act upon glandular GRP receptors to induce mucus secretion, but that GRP would probably have little effect on vascular permeability or tracheobronchial smooth muscle tone.

Neuroendocrine differentiation in lung tumours

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Calcitonin gene-related peptide and its mRNA in pulmonary neuroendocrine cells and ganglia

The occurrence of calcitonin gene-related peptide (CGRP) and it's mRNA was studied in lungs of rats and piglets using in situ hybridization with two synthetic oligonucleotide probes followed by immunocytochemistry (ICC). CGRP mRNA was present in pulmonary neuroendocrine cells (PNEC) of both the solitary type and cluster type (neuroepithelial body; NEB) at all levels of the airway epithelium from bronchi to alveoli. The distribution of labelled cells was similar to that previously described with ICC. The 44-mer probe provided stronger hybridization signal than the 34-mer and the two combined increased labelling slightly. Formalin fixation reduced labelling and tended to increase background. Labelling for CGRP mRNA was evenly distributed over the cytoplasm, whereas CGRP-like immunoreactivity (LI) usually was of highest intensity toward the base of the PNEC, suggesting basal accumulation of synthesized peptide. CGRP-LI was also observed in occasional rat ganglia and in some, but not all, piglet ganglia. These local neurons may contribute to the CGRP fibers of airways and vasculature, and could theoretically bridge their dendrites and axons between NEB and the effector organ (e.g. artery or arteriole) thus accomplishing a function similar to the postulated axon reflex.

PYY-like material and its spatial relationship with NPY, CGRP and 5-HT in the lung of the Syrian golden hamster

We investigated the presence of peptide YY, neuropeptide Y, calcitonin gene-related peptide and serotonin in the hamster lung by radioimmunoassay, high performance liquid chromatography and immunocytochemistry. Lung-tissue concentrations of peptide YY and neuropeptide Y were 1.3 +/- 0.2 and 2.5 +/- 0.2 pmol/g wet weight, respectively. These two closely related pancreatic peptides were demonstrated in separate peaks with high performance liquid chromatography. The peptide YY appeared fragmented as immunoreactive peptide YY eluted primarily late in the gradient but showed additional peaks early in the gradient. Peptide YY-like immunoreactivity (PYY-LI) was predominantly observed in one or more cells of neuroepithelial bodies in all airways peripheral to bronchioles, and in solitary neuroendocrine cells primarily located in the same peripheral areas. Neuropeptide Y-LI was seen in individual, thin nerve fibers around arteries and veins, in the airway lamina propria, and in the airway epithelium; in the latter also immunopositive nerve terminals were located. This pattern did not appear to coincide with that of calcitonin gene-related peptide-LI in epithelial nerve fibers and terminals. Peptide YY-LI, calcitonin gene-related-LI and serotonin-LI were present in cells of one and the same neuroepithelial body. However, peptide YY-LI was never found to be co-localized with calcitonin gene-related-LI or serotonin-LI, but the latter two were co-localized as previously reported.

Gastrin-releasing peptide in human nasal mucosa

Gastrin-releasing peptide (GRP), the 27 amino acid mammalian form of bombesin, was studied in human inferior turbinate nasal mucosa. The GRP content of the mucosa measured by radioimmunoassay was 0.60 +/- 0.25 pmol/g tissue (n = 9 patients; mean +/- SEM). GRP-immunoreactive nerves detected by the immunogold method of indirect immunohistochemistry were found predominantly in small muscular arteries, arterioles, venous sinusoids, and between submucosal gland acini. 125I-GRP binding sites determined by autoradiography were exclusively and specifically localized to nasal epithelium and submucosal glands. There was no binding to vessels. The effects of GRP on submucosal gland product release were studied in short-term explant culture. GRP (10 microM) significantly stimulated the release of the serous cell-specific product lactoferrin, and [3H]glucosamine-labeled glycoconjugates which are products of epithelial goblet cells and submucosal gland cells. These observations indicate that GRP released from nerve fibers probably acts on glandular GRP receptors to induce glycoconjugate release from submucosal glands and epithelium and lactoferrin release from serous cells, but that GRP would probably not affect vascular permeability.

Elevated serum levels of calcitonin gene-related peptide (CGRP) but no evidence for CGRP gene expression in non-small cell lung carcinomas

Calcitonin gene-related peptide (CGRP) is a hormone formed by alternative post-transcriptional processing of the calcitonin gene. It is a neuropeptide localized to discrete regions of the central nervous system (CNS) and in nerve fibres associated with blood vessels. It is also expressed in medullary carcinomas of the thyroid and lung carcinoma cell lines. The latter finding suggests a possible value for CGRP as tumour marker in lung carcinomas. In this investigation of 22 patients undergoing operation for lung tumours, pre and post-operative levels of serum CGRP were measured. Preoperative as well as postoperative serum CGRP levels were significantly elevated when compared to age-matched normals. However, no evidence could be found for CGRP gene expression in tumour tissue from the same patients as judged by immunocytochemistry or in-situ hybridization using CGRP cRNA probes. CGRP has been localized to nerve fibres in relation to pulmonary blood vessels and has been shown to be a potent vasodilator. These findings, and the absence of evidence for synthesis in tumours, as opposed to cell lines derived from lung carcinomas, suggests that the lack of post-operative normalization of serum CGRP concentrations may be related to physiological changes in cardiovascular haemodynamics following surgery. Elevated pre-operative serum CGRP levels may also reflect a consequence of the lung carcinoma leading to increased release of CGRP from sites in the vasculature yet to be determined, but does not indicate synthesis de novo and secretion of CGRP by the tumours.

Effects of neuropeptides and capsaicin on the canine tracheal vasculature in vivo

1. The nonadrenergic, noncholinergic nervous system may control the airway vasculature via various neuropeptides. We have perfused the cranial tracheal arteries of the anaesthetized dog and investigated the effects of neuropeptides and capsaicin (which is supposed to release neuropeptides from sensory nerve endings) on the tracheal vasculature by injecting them locally into the perfusion system. 2. Neurokinin A (NKA, 0.02-20 pmol), calcitonin gene-related peptide (CGRP, 2-200 pmol) and peptide histidine isoleucine (PHI, 0.02-2 nmol) dose-dependently decreased tracheal vascular resistance (Rtv). NKA was 10 and 100 times more potent than CGRP and PHI, respectively. The duration of the response to CGRP was greatly prolonged with larger doses. Galanin (0.2-2 nmol) had no appreciable effect on Rtv. 3. Neuropeptide Y (NPY 0.02-2 nmol) and bombesin (0.02-10 nmol) dose-dependently increased Rtv. However, the dose-response curve for bombesin was bell-shaped suggesting the development of tachyphylaxis with larger doses. In smaller doses, bombesin was twice as potent as NPY. The duration of the response to NPY was prolonged with larger doses. 4. With the exception of PHI no neuropeptide altered tracheal smooth muscle tone; PHI (1 and 2 nmol) caused small dilatations of the trachea. 5. The effects of capsaicin (2-100 nmol) were complex. Usually, the vascular response had two dose-dependent phases: a rapid vasoconstriction followed by a small, longer-lasting vasodilatation. The tracheal smooth muscle response was usually biphasic, a contraction followed by a relaxation. 6. According to previous and present data, the order of potency of the neuropeptides on the canine tracheal vasculature is for the vasodilators : NKA > vasoactive intestinal peptide (VIP) > CGRP > substance P > PHI, and for the vasoconstrictors: bombesin > NPY. The longer-acting neuropeptides (VIP, CGRP and NPY) may be more important than the shorter-acting neuropeptides (substance P, NKA, PHI and bombesin) as regulators of the airway wall blood flow.

Calcitonin gene-related peptide in hamster lung and its coexistence with serotonin: a chemical and immunocytochemical study

The mammalian lung may have an important endocrine function besides being involved in gas exchange mechanisms. A number of peptide hormones have been localized to neurons and endocrine cells in the lung where they may contribute to the regulation of local pulmonary functions. We have investigated the presence of calcitonin gene-related peptide (CGRP), in the hamster lung by radioimmunoassay and by immunocytochemistry. Measurable quantities of CGRP were detected in lung tissue. Females had higher lung tissue levels of CGRP-like immunoreactivity (IR) than males. This was not reflected in an observable increase in the intensity or distribution of CGRP-like reactivity with immunocytochemistry. Distinct CGRP-like IR was recorded in clustered (NEB) and solitary (NEC) neuroendocrine cells in neonates, weanlings and adults, including all airways from trachea (NEC only) to bronchi, bronchioles, and alveolar ducts to the level of alveoli (NEC and NEB). In adult hamsters, there seemed to be fewer immunoreactive cells, although intensity was unchanged. In addition some NEB contained serotonin-like IR, and colocalization of the peptide and the amine was noted within some cells. Intra-epithelial beaded nerve fibers, subepithelial fibers, and large-caliber nerves in the hilus region and tracheal wall were also CGRP-IR, and immunoreactive nerves were occasionally found in close association with NEB at the basal pole. Positive nerve fibers were not observed in vessels within the lung, and were sparse in the adventitia of tracheal arteries.