Quantitative characteristics of the Feyrter cells and neuroepithelial bodies of the fetal rabbit lung in normoxia and short term chronic hypoxia

Hyperplasia of pulmonary neuroendocrine cells in infancy and childhood

Pulmonary neuroendocrine cells (PNEC) are widely distributed throughout the airway mucosa of mammalian lung as solitary cells and as distinctive innervated clusters, neuroepithelial bodies (NEB). These cells differentiate early during lung development and are more prominent in fetal/neonatal lungs compared to adults. PNEC/NEB cells produce biogenic amine (serotonin) and a variety of peptides (i.e., bombesin) involved in regulation of lung function. During the perinatal period, NEB are thought to function as airway O(2)/CO(2) sensors. Increased numbers of PNEC/NEBs have been observed in a variety of perinatal and postnatal lung disorders. Recent advances in cellular and molecular biology of these cells, as they relate to perinatal and postnatal lung disorders associated with PNEC/NEB cell hyperplasia are reviewed and their possible role in pulmonary pathobiology discussed (WC 125).

The diffuse endocrine system: from embryogenesis to carcinogenesis

In the present review we will summarise the current knowledge about the cells comprising the Diffuse Endocrine System (DES) in mammalian organs. We will describe the morphological, histochemical and functional traits of these cells in three major systems gastrointestinal, respiratory and prostatic. We will also focus on some aspects of their ontogeny and differentiation, as well as to their relevance in carcinogenesis, especially in neuroendocrine tumors. The first chapter describes the characteristics of DES cells and some of their specific biological and biochemical traits. The second chapter deals with DES in the gastrointestinal organs, with special reference to the new data on the differentiation mechanisms that leads to the appearance of endocrine cells from an undifferentiated stem cell. The third chapter is devoted to DES of the respiratory system and some aspects of its biological role, both, during development and adulthood. Neuroendocrine hyperplasia and neuroendocrine lung tumors are also addressed. Finally, the last chapter deals with the prostatic DES, discussing its probable functional role and its relevance in hormone-resistant prostatic carcinomas.

Comparative histology of pulmonary neuroendocrine cell system in mammalian lungs

It is increasingly recognized that neuroepithelial endocrine cells and organoid clusters of these cells termed neuroepithelial bodies are widely distributed in the respiratory tract of vertebrates. This review focuses on the neuroepithelial endocrine system in the airway epithelium of mammals according to observations made in a wide range of species, as it appears in light and electron microscopy by means of various visualization techniques under normal and experimental conditions. Because there are similarities but also marked differences between species, wherever possible studies in human airways are emphasized. Conventional histochemical and ultrastructural studies including microspectrofluorimetry have demonstrated the amine-handling properties and the presence of neurosecretory granules in neuroendocrine cells of the epithelium of all mammals studies so far. The neuroepithelial bodies are innervated by morphological afferent- and efferentlike synaptic specializations. These, together with the presence of reciprocal synapses, emphasize that these cells may be involved in dual functions of chemoreception and secretion. Light and electron microscopic immunohistochemistry has demonstrated that neuroepithelial endocrine cells may contain various biogenic agents, suggesting that the neuroendocrine system is highly heterogeneous. Neural elements may interact in a complex manner, and the activation of certain neural pathways may control the release of biogenic substances to influence physiological airway functions. They may be particularly relevant in pulmonary diseases. Consequently, the function of this system is complex and it is highly probable that many of its aspects are still not elucidated.

Pulmonary Neuroendocrine Cells and Lung Development

Pulmonary neuroendocrine cells produce bioactive peptides such as gastrin-releasing peptide (GRP) at high levels in developing fetal lung. The role of GRP and other peptides in promoting branching morphogenesis, cell proliferation, and cell differentiation during lung organogenesis is reviewed. Possible roles for bioactive peptides derived from these cells in the pathophysiology of perinatal lung disorders are discussed.

Pulmonary endocrine cells of Aymara Indians from the Bolivian Andes

INTRODUCTION

There is evidence to suggest that life at high altitude causes changes in the population of pulmonary endocrine cells, possibly because of exposure to chronic hypoxia. A study was made of the populations of pulmonary endocrine cells in three Aymara Indians and three Mestizos of La Paz (3600 m), Bolivia, which were compared with those in four white lowlanders.

METHODS

Pulmonary endocrine cells were immunolabelled for neurone specific enolase and their two major secretory products, gastrin releasing peptide and calcitonin, and their numbers expressed per cm2 of tissue section.

RESULTS

No differences in morphology, number, content, or distribution of immunoreactive cells were found when the native highlanders were compared with the lowlanders.

CONCLUSIONS

If chronic hypoxia as such exerts an influence on human pulmonary endocrine cells it was not apparent in this morphological study. There was no increase in gastrin releasing peptide containing pulmonary endocrine cells, such as have previously been seen in patients with pulmonary hypertension characterised by plexogenic pulmonary arteriopathy. This may be due to the fact that in plexogenic pulmonary arteriopathy there is free migration of smooth muscle cells. Although three of the highlanders in this present study showed pulmonary vascular remodelling, this was in contrast only modest.

Characterization of human pulmonary endocrine cells maintained in vitro

Endocrine cells located in the epithelium of human fetal airways contain the amine, 5-hydroxytryptamine (5HT), and the peptide, bombesin (BOM), but difficulties in studying these cells experimentally have slowed progress in understanding their functional roles. This investigation describes an in vitro method to maintain pulmonary neuroendocrine cells (PNEC) in organ culture. Bronchial trees from human fetal lungs were dissected free of adherent blood vessels and lung tissue. Explants of the airways were placed in culture dishes containing defined tissue culture medium for five days. Using indirect immunofluorescence, 5HT- and BOM-like immunoreactive cells were observed both in nonincubated airways and in explants maintained for five days in organ culture. The number of 5HT-immunoreactive cells/0.1 mm2 of airway epithelium was not significantly different in the two groups, although there was a significant reduction in 5HT content measured by HPLC after the five-day culture period. The diameter of dense core vesicles and the number of dense core vesicles/micron2 of endocrine cell cytoplasm in cultures were not significantly different from non-incubated controls. Treatment of the explants with the 5HT-synthesis inhibitor p-chlorophenylalanine resulted in a significant reduction both in the number of 5HT-containing cells/0.1 mm2 of airway epithelium and in the 5HT content. These results demonstrate that both 5HT and BOM content in endocrine cells of explants from human fetal airways can be well maintained in organ culture for at least 5 days and that they are responsive to pharmacologic inhibition of 5HT synthesis.

Dynamics of the neuroendocrine cell--regulatory peptide system in the lung. Specific overview and new results

We assessed the changes in argyrophil neuroendocrine (NE) cell numbers, intensity of 5-HT fluorescence, and arterial medial thickness in the lungs of neonatal rabbits under various oxygen treatments. NE cell numbers and 5-HT fluorescence in normoxic rabbits increased from 12 hr before to 1 day after birth, and NE cells declined thereafter to the 10th day. In acute hypoxic (520 mm Hg for 2-2.5 hr) 5-day-old rabbits, 5-HT fluorescence was decreased, whereas NE cell numbers and medial thickness were unchanged. Neonates hypoxic from birth had higher NE cell numbers and increased medial thickness at 3 and 5 days, whereas 5-HT fluorescence was decreased compared with that in normoxic controls. These chronically hypoxic neonates showed a dramatic drop in argyrophil NE cell numbers to below normal when they were exposed to normoxia for 1 hr, but cell numbers and medial thickness returned to normal at 4 and 24 hr, respectively. We also tested the effect of acute and chronic hyperoxia: 100% O2 for 2-2.5 hr caused a significant drop in detectable NE cell numbers, whereas 40% O2 in N2 caused no change; chronic 40% O2 in N2 caused a fivefold increase in argyrophil NE cells by day 5, and medial thickness was below normal; 5-HT fluorescence decreased in acute 100% and chronic 40% hyperoxia and was elevated in acute 40% O2.

Development of neuroepithelial bodies in fetal rabbit lungs. I. Appearance and functional maturation as demonstrated by high-resolution light microscopy and formaldehyde-induced fluorescence

Developing lungs of fetal rabbits aged 13 days through early postnatal stages were examined for periodic acid-Schiff (PAS)-lead hematoxylin staining, serotonin fluorescence, and argyrophilia, methods selective for small-granule (neuro) endocrine cells. Later stages were also studied by electron microscopy. These cells arise from precursors that first appear around days 18-19 in the endodermal epithelium; the latter stand out as clear cells from their undifferentiated, glycogen laden neighbors. The cells first form in the main and lobar bronchi, then continue to arise in the lining of newly laid down branches of the extending bronchial tree, tending to concentrate near points of branching. Some cells have been seen to divide, and clusters of two, four, or more soon appear. Morphologically mature neuroepithelial bodies begin to appear in larger bronchi around 23 days, although the largest examples occur in 25-day and older fetuses. After 23 days, additional bodies mature from clear-cell precursors in more recently laid down distal lung, so that by the terminal sac period (around days 28-29) all conducting airways contain them, and the clear cells and clear-cell clusters have virtually disappeared. A pinkish staining by PAS-lead hematoxylin and dense-core secretory granules, which begin to appear in the clear cells, are present in mature small-granule cells whether solitary or aggregated. Argyrophilia is less consistently demonstrable. Fluorescence for serotonin is first evident in mature neuroepithelial bodies at 23 days, increases considerably by 26 days, and reaches a prenatal peak around days 28-29, when neuroepithelial bodies and solitary small-granule cells along the whole conducting bronchial tree may participate. Fluorescence appears to decrease during days 30-31 but strengthens again after birth. Composed of these solitary small-granule cells and neuroepithelial bodies, the pulmonary APUD system of rabbits thus appears substantially functional during the final quarter of gestation.

Neuroendocrine cells of the lung. An overview of morphologic characteristics and development

The detailed morphology of pulmonary neuroendocrine (NE) cells has been defined only during the last decade. The purpose of this paper is to review the main morphologic features of the NE cells, to review the methods and techniques used for their identification, and to discuss the development and functional significance of these cells. The main emphasis is on NE cells in human lung, but where appropriate, studies in animal lungs are also included. NE cells are present in the airway epithelium of human and various animal species and occur singly as well as in clusters called neuroepithelial bodies (NEB). The general cytochemical features (common to both single NE cells and NEB) include cytoplasmic argyrophilia, fluorogenic amine content, positive staining with lead-hematoxylin, and masked metachromasia. These staining properties are similar to those found in APUD cells scattered in various tissues. More specific cell markers are immunoreactivity to peptide hormones (bombesin, calcitonin, leu-enkephalin) identified so far in NE cells of human lung, and immunoreactivity to serotonin found in both human and animal lungs. At the ultrastructural level, NE cells are characterized by the presence of cytoplasmic dense core granules (90-150 nm in diameter), which are considered the storage site of amine and peptide hormones. The distinctive feature of NEB, not found with single NE cells, is the presence of nonmyelinated nerve endings in contact with granulated cells, and positive staining for acetylcholinesterase. The single NE cells are scattered throughout the tracheobronchial epithelium, whereas NEB are found only within the intrapulmonary airways. In postnatal lungs, both the single NE cells and NEB appear concentrated in small peripheral airways. In developing human lung, the first NE cells appear at 8 weeks' gestation, when all other epithelial cells are still undifferentiated. The development and cytodifferentiation of NE cells progresses in a centrifugal direction. By the end of the glandular period, single and groups of NE cells are found along the entire length of primitive bronchial epithelium. Based on differences in the size and morphology of cytoplasmic granules, three distinct types of NE cells can be recognized. During terminal stages of development, NE cells appear in small peripheral airways and primitive saccules. The functional considerations include the possible role of NE cells as endocrine, paracrine, or receptosecretory cells involved in neurohormonal regulation of pulmonary vascular or bronchial responses, and possible function of NEB as intrapulmonary hypoxia-sensitive chemoreceptors.

Hypothesis: the bronchial Kulchitsky (K) cell as a source of humoral biologic activity

The bronchial Kulchitsky cells are scattered specific cells which lie close to the basement membrane of the bronchi and bronchioles. Electron microscopy reveals that they contain electron-dense granules similar to that seen in cells with a known endocrine function. In addition, experimentally induced degranulation of the K cell suggestive of a secretory process, and the likelihood that these cells are precursors of small cell lung carcinoma (which often elaborates humoral substances) has led to the postulate that this bronchial cell serves a humoral role of either a paracrine or endocrine nature. We have found that the bronchial K cell of man contains a calcitonin-like polypeptide which, immunologically and chemically, is not dissimilar to the hormone produced by the C cells of human thyroid. This finding may help explain the persistence of serum immunoreactive calcitonin (iCT) after total thyroidectomy, the fact that thyroidectomized man does not manifest any profound alteration of calcium metabolism, and why small cell cancer of the lung is frequently associated with hypercalcitonemia. In addition, the finding of K cell hyperplasia in chronic bronchitis and emphysema may explain the occurrence of hypercalcitonemia in patients with these diseases and some lung cancers of cell types other than the small cell variety. Further studies are needed to elucidate the role of K cell iCT, and to determine what other hormones might also be elaborated by this diffuse system of bronchial cells.