Pulmonary Neuroendocrine Research Articles

Conditional Clara cell ablation reveals a self-renewing progenitor function of pulmonary neuroendocrine cells

The neuroepithelial body (NEB) is a highly dynamic structure that responds to chronic airway injury through hyperplasia of associated pulmonary neuroendocrine (PNE) cells. Although NEB dysplasia is correlated with preneoplastic conditions and PNE cells are thought to serve as a precursor for development of small cell lung carcinoma, mechanisms regulating expansion of the PNE cell population are not well understood. Based on studies performed in animal models, it has been suggested that NEB-associated progenitor cells that are phenotypically distinct from PNE cells contribute to PNE cell hyperplasia. We have previously used a Clara cell-specific toxicant, naphthalene, to induce airway injury in mice and have demonstrated that naphthalene-resistant Clara cells, characterized by their expression of Clara cell secretory protein (CCSP), and PNE cells contribute to airway repair and associated hyperplasia of NEBs. This study was conducted to define the contribution of NEB-associated CCSP-expressing progenitor cells to PNE cell hyperplasia after Clara cell ablation. Transgenic (CCtk) mice were generated in which herpes simplex virus thymidine kinase was expressed within all CCSP-expressing cells of the conducting airway epithelium through the use of transcriptional regulatory elements from the mouse CCSP promoter. Chronic administration of ganciclovir (GCV) to CCtk transgenic mice resulted in selective ablation of CCSP-expressing cells within conducting airways. Proliferation and hyperplasia of PNE cells occurred in the absence of detectable proliferation among any other residual airway epithelial cell populations. These results demonstrate that PNE cells function as a self-renewing progenitor population and that NEB-associated Clara cells are not necessary for PNE cell hyperplasia.

MEN1 gene mutations in sporadic neuroendocrine tumors of foregut derivation.

Foregut-derived neuroendocrine (NE) tumors occur sporadically or in association with multiple endocrine neoplasia type 1 (MEN1) syndrome. Thirty-nine sporadic NE tumors of foregut derivation (six thymic, 21 bronchial, three gastric, and nine pancreatic tumors) as well as two hindgut-derived rectal carcinoids for somatic MEN1 gene mutation were analyzed by direct sequencing analysis. Five tumors showed mutations: nonsense mutations (Q393X and R98X) in thymic and pancreatic NE tumors, respectively, a 4 b.p. deletion (357del4) in a gastric NE carcinoma, and missense mutations (D172Y and S178Y) in pancreatic NE tumors. No mutation was identified in pulmonary or rectal NE tumors. In a patient with a pancreatic NE tumor (D172Y), the corresponding germline DNA showed the same mutation, suggesting that sporadic MEN1 syndrome was masked in this case. Somatic MEN1 gene mutations and deletions may play a crucial role in the tumorigenesis of a subset of foregut-derived NE tumors. Sporadic MEN1 syndrome may occur as a sporadic NE tumor of the pancreas.

Immunohistochemical distribution of bombesin-positive pulmonary neuroendocrine cells in a congenital diaphragmatic hernia.

Morphometrical analyses of the immunohistochemical expression of bombesin, which is one of the peptides produced by pulmonary neuroendocrine (PNE) cells, were carried out on the bronchioles of human congenital diaphragmatic hernia (CDH) neonates, and the findings were then compared with those in a gestational and postnatal age-matched control group. As a result, no difference was found in the number of bombesin-positive cells between the lungs of the control group and the unaffected side lungs in the CDH group except for the ratio of the bombesin-positive cells per unit of the bronchiolar surface area (P < 0.05). However, compared with the lungs in the control group, the affected side of the lungs in the CDH group showed a significant increase in the expression of bombesin, namely, the ratio of the bombesin-positive cells per bronchiole (P < 0.05), the ratio of the bombesin-positive cells per unit perimeter of the bronchioles (P < 0.05), and the ratio of the bombesin-positive cells per unit of the bronchiolar surface area (P < 0.01). These results thus suggest that hyperplasia of the PNE-cell system in the lungs of the CDH cases, especially on the affected side, exists in human fetuses. We also further speculate that PNE cells may thus play a role in the problems associated with CDH during intrauterine life in human beings.

Pulmonary large cell neuroendocrine carcinoma is genetically related to small cell carcinoma

Pulmonary large cell neuroendocrine carcinoma is genetically related to small cell carcinoma

Conservation of the Drosophila lateral inhibition pathway in human lung cancer: a hairy-related protein (HES-1) directly represses achaete-scute homolog-1 expression.

The achaete-scute genes encode essential transcription factors in normal Drosophila and vertebrate nervous system development. Human achaete-scute homolog-1 (hASH1) is constitutively expressed in a human lung cancer with neuroendocrine (NE) features, small cell lung cancer (SCLC), and is essential for development of the normal pulmonary NE cells that most resemble this neoplasm. Mechanisms regulating achaete-scute homolog expression outside of Drosophila are presently unclear, either in the context of the developing nervous system or in normal or neoplastic cells with NE features. We now provide evidence that the protein hairy-enhancer-of-split-1 (HES-1) acts in a similar manner as its Drosophila homolog, hairy, to transcriptionally repress achaete-scute expression. HES-1 protein is detected at abundant levels in most non-NE human lung cancer cell lines which lack hASH1 but is virtually absent in hASH1-expressing lung cancer cells. Moreover, induction of HES-1 in a SCLC cell line down-regulates endogenous hASH1 gene expression. The repressive effect of HES-1 is directly mediated by binding of the protein to a class C site in the hASH1 promoter. Thus, a key part of the process that determines neural fate in Drosophila is conserved in human lung cancer cells. Furthermore, modulation of this pathway may underlie the constitutive hASH1 expression seen in NE tumors such as SCLC, the most virulent human lung cancer.

Induction of c-fos expression following stimulation of pulmonary neuroendocrine cell proliferation by alterations in CO2/O-2 concentration

Pulmonary neuroendocrine (PNE) cells were harvested and cultivated from peripheral lung tissue of 15 day old fetal hamsters under selective growth conditions, including a 10% CO2 atmosphere. Following 24 h of serum starvation under 10% CO2, PNE cells placed in a 5% CO2 atmosphere failed to proliferate over the next 24 h, while cells kept at 10% CO2 showed a 2.7-fold increase in cell number. Addition of nicotine to the cell culture medium resulted in an additional concentration-dependent increase in cell number under a 10% CO2 atmosphere, while nicotine did not stimulate the proliferation of cells maintained at 5% CO2. The nicotinic receptor antagonist hexamethonium completely blocked the stimulatory effect of nicotine on cell growth. As a first step towards determining the molecular mechanisms regulating the mitogenic stimulation of PNE cells by alterations in CO2/O-2 and nicotine, cells that had been serum starved under a 10% CO2 atmosphere for 24 h were removed from the incubator and either left untreated or treated with 1 mu M nicotine under ambient air. The cells were then returned to either a 5% or 10% CO2 atmosphere. Removal of the cells from a 10% CO2 environment and subsequent reintroduction to a high CO2 concentration resulted in a 3- to 4-fold increase in c-Sos RNA expression within 15-30 min upon return to the cell culture incubator. c-fos RNA levels their decreased back to control values by 1 h. Reintroduction into a 5% CO2 atmosphere, which failed to stimulate cell growth in the proliferation assay, caused only a 2-fold increase in the levels of c-fos transcripts. The CO2-mediated increases in c-Sos transcripts were observed both in the presence and absence of nicotine, suggesting that the effects of nicotine were mediated through a fos-independent pathway. Neither the alterations in CO2/O-2 concentration or treatment with nicotine altered the levels of c-myc or c-jun gene transcripts. Nicotine thus acts indirectly but synergistically with high CO2 concentrations to stimulate PNE cell proliferation.

Cell biology of pulmonary neuroepithelial bodies—validation of an in vitro model. I. Effects of hypoxia and Ca2+ ionophore on serotonin content and exocytosis of dense core vesicles

Pulmonary neuroendocrine (NE) cells including the innervated clusters of NE cells--neuroepithelial bodies (NEB)--are difficult to study because of their small numbers and diffuse distribution within the airway mucosa of the lung. We have previously reported a method for isolation and culture of NE cells from rabbit fetal using a combination of mechanical and enzymatic dissociation followed by gradient centrifugation. This method provides single cell suspension of mixed lung cells enriched in NE cells, particularly those originating from NEB. This study further validates our in vitro model by detailed morphologic characterization of cultured NEB cells using high resolution light microscopy, transmission and scanning electron microscopy, HPLC for detection of serotonin (5-HT), and molecular (Northern blot) analysis of mRNA encoding for 5-HT synthesizing enzymes, tryptophane hydroxylase, and aromatic L-amino acid decarboxylase. In addition the effects of hypoxia on NEB cells in vitro were investigated to define the role of these cells as possible airway chemoreceptors. Exposure of NEB cultures to hypoxia resulted in decreased intracellular content of 5-HT accompanied by increased exocytosis of dense core vesicles (DCV). The amount of 5-HT release correlated with the degree of hypoxia, suggesting modulation by ambient pO2 levels. The role of Ca2+ ions in exocytosis of DCV and 5-HT release from NEB cells was tested in experiments with Ca2+ ionophore (A23187). Exposure of cultures to 5 micrograms/ml of ionophore resulted in up to 40% reduction in 5-HT content of NEB cultures as well as increased exocytosis of DCV. Our overall findings are consistent with a view that NEB cells are chemosensory in nature and that Ca2+ signaling pathway is involved in stimulus-secretion coupling. Further refinements in cell separation and culture methodology are required before more detailed investigation of NEB cell membrane properties, signal transduction mechanisms, and intracellular signaling pathways can be carried out.

Localization of cholecystokinin-like peptide in neuroendocrine cells of mammalian lungs: a light and electron microscopic immunohistochemical study.

We report immunohistochemical localization of cholecystokinin (CCK)-like immunoreactivity at the light and electron microscopy (EM) level in pulmonary neuroendocrine (NE) cells of human and other mammals (monkey, rabbit, rat, hamster, pig, dog and lamb). In addition, immunolocalization of CCK-like peptide was compared with that of bombesin (predominant peptide in human lung) and serotonin (an amine found in NE cells of most species). While CCK-like and serotonin-like immunoreactivity were identified in both solitary NE cells and NE cell clusters (neuroepithelial bodies, NEB) of all species studied, bombesin-like immunoreactive NE cells were found in human and monkey lungs only. The distribution and intensity of immunostaining for CCK-like peptide varied between species with some showing relatively high levels of expression (e.g., monkey, piglet, dog and lamb), others intermediate (human, rabbit) or weak immunostaining (rat, hamster). At the EM level, CCK-like immunoreactivity was localized in dense-core vesicles (DCV), the expected site of peptide storage. Using a double immunolabeling technique, CCK and serotonin were colocalized in some, but not all DCV. The potential role of CCK in the lung (or for other pulmonary peptides) may include a variety of functions such as modulation of bronchial or vascular tone, growth factor-like and/or hormonal effects.

Chronic hyperoxia and hamster pulmonary neuroendocrine cell bombesin and calcitonin.

Hamsters were exposed to 60% hyperoxia for 1 week, 3 weeks, or 3 months. The exposed animals gradually failed to gain body weight as controls. The pulmonary neuroendocrine (PNE) cell peptides, mammalian bombesin (MB) and immunoreactive calcitonin (iCT), were determined in the lung and the serum. At 1 week and 3 weeks, lung MB was unchanged while the iCT levels were markedly depleted. In contrast, the lung levels of both MB and iCT were significantly elevated at 3 months. Serum levels of MB showed an initial decline at 1 week, which was followed by augmented levels at 3 weeks and at 3 months. In contrast, serum iCT showed considerable depletion at 1 week, and also at 3 weeks, followed by increased levels at 3 months. Thus, chronic exposure to hyperoxia causes profound perturbation of PNE cell peptides. In particular, the early depletion of lung and serum iCT appears to be a unique feature of the response to hyperoxia. The principal difference between the MB and the iCT responses was the lack of an initial depletion of lung MB, and the earlier rise of serum MB to supranormal levels. It seems likely that the early peptide effects of hyperoxia are related to oxygen toxicity upon the PNE cells, while the changes noted at 3 months reflect a hyperplastic accommodation of PNE cells to the prolonged oxygen exposure with resultant increases in MB and iCT. This response is distinctly different from that we have seen previously in hamsters exposed to hyperoxia combined with a nitrosamine, or a nitrosamine alone.

Cholinergic‐nicotinic control of growth and secretion of cultured pulmonary neuroendocrine cells

Dispersed newborn hamster lung cells were established in vitro in a defined, low-serum growth medium. Neuroendocrine markers (immunohistochemistry for bombesin/gastrin-releasing peptide and calcitonin) revealed a cellular predominance of pulmonary neuroendocrine (PNE) cells. While the supernatant concentration remained stable, the concentration of PNE cell immunoreactive calcitonin (iCT) gradually declined over 4 weeks. Supplementation of the medium with nicotine for 3 weeks prevented this decline in cellular iCT. Concurrently, the number of cells and [3H]thymidine incorporation were significantly increased. The stimulatory effect of chronic nicotine was reversed by the coadministration of the nicotinic antagonist hexamethonium. In another set of experiments, prior multiple transplacental nicotine pretreatments resulted in a significant increase in iCT in the lungs of newborns; when these lungs were subsequently placed in cell culture without nicotine, despite the higher concentration of iCT, there was a drop in iCT similar to that observed in the control culture. In contrast, in vivo, the lung iCT remained significantly elevated at 1 week post-parturition. Cell culture supernatants were analyzed at week 4 for the evoked release of iCT; cholinergic-nicotinic agonists promptly increased the supernatant iCT, which was blocked by nicotinic but not by muscarinic antagonists. We suggest that this in vitro system provides a useful tool to study directly the PNE cell. The acute and chronic effects of nicotine are most likely related to stimulation of cholinergic-nicotinic receptors on iCT-containing PNE cells.

Neuroendocrine Tumors of the Lung With Proposed Criteria for Large-Cell Neuroendocrine Carcinoma

Based on our review of 35 cases and the literature, we found the spectrum of pulmonary neuroendocrine (NE) tumors to be too broad to fit into the traditional three-category classification scheme of typical carcinoid (TC), atypical carcinoid (AC), and small-cell lung carcinoma (SCLC). We found that a spectrum of high- and low-grade tumors exist between TC and SCLC and that in the past many of these tumors have been called AC. We chose to adhere to Arrigoni's definition of AC, as his original criteria characterized a low-grade tumor. For the higher grade non-small-cell tumors (NSCLC), we propose a fourth category of large-cell neuroendocrine carcinoma (LCNEC), which is characterized by: (a) light microscopic NE appearance; (b) cells of large size, polygonal shape, low nuclear-cytoplasmic ratio (N:C), coarse nuclear chromatin, and frequent nucleoli; (c) high mitotic rate [greater than 10/10 high-power fields (HPF)] and frequent necrosis; and (d) NE features by immunohistochemistry (IHC) or electron microscopy (EM). Thus, after deciding that a pulmonary NE tumor is high grade, the major diagnostic issue is separation of LCNEC from SCLC. This distinction is based not only on cell size, but on a variety of morphologic features. We studied 20 TC, six AC, five LCNEC, and four SCLC and characterized the clinical, light microscopic, EM, IHC, and flow cytometric features of each type of tumor. We did not find any advantage to IHC, EM, or flow cytometry over light microscopy in the subclassification or prediction of prognosis; however, these methods were useful in characterizing these four types of pulmonary NE tumors and in demonstrating their NE properties. LCNEC must be distinguished from a fifth category pulmonary NE tumor: NSCLC with NE features in which NE differentiation is not evident by light microscopy and must be demonstrated by EM or IHC. Although the prognosis of LCNEC appears to be intermediate between AC and SCLC, larger numbers of patients will be needed to demonstrate significant differences in survival.

Modulation of pulmonary bombesin by nicotine and vagotomy

In pregnant hamsters, three transplacental injections of the ganglionic agonist nicotine resulted in a dose-dependent decrease in the concentration of mammalian bombesin (MB) in the lungs of neonatal (1 day old) animals. This decrease in neonatal MB did not occur if nicotine was given only once during gestation, or when it was given three times in conjuction with the ganglionic antagonist mecamylamine. In one week old animals born of mothers who had been exposed to three doses of nicotine during gestation, lung MB had returned to control levels. When nicotine was injected into neonatal animals, lung MB acutely increased. Right sided vagotomy to young hamsters resulted in an increase in the ratio of lung MB (right vs. left lobe) 1 week after surgery. Administration of nicotine to vagotomized animals resulted in decreased total lung MB and normalization of the MB ratio. Thus, nicotine has a potent modulatory influence on lung MB during fetal and neonatal development and maturation. This influence is also present in young animals that are subjected to partial denervation. Our hypothesis is that the innervation of pulmonary neuroendocrine (PNE) cells influences both PNE cell growth and its synthetic function. PNE MB, which is an epithelial and neoplastic growth factor, may play a role in this response.

Pulmonary Bombesin and Calcitonin in Hamsters during Exposure to Hyperoxia and Diethylnitrosamine

Combined exposure of hamsters to 60% hyperoxia and the carcinogen diethylnitrosamine for 6 wk resulted in the development of lung tumors. This was associated with progressive loss of body weight as well as increases in the pulmonary-associated peptides, mammalian bombesin (MB) and immunoreactive calcitonin (iCT). After 3 wk of exposure, multiple bronchial epithelial hyperplastic foci were noted, along with increased lung levels of MB and iCT as well as increased serum levels of MB. At this time, immunocytochemistry revealed the presence of MB and iCT within hyperplastic pulmonary neuroendocrine (PNE) cells. In addition, the localization of MB to alveolar type II cells was noted, along with the presence of lamellar bodies and secretion granules in these cells on electron microscopy. After 6 wk of exposure, distinctive microscopic pulmonary tumorlets were seen. These tumorlets were associated with a marked increase in lung and serum MB, and to a lesser extent lung and serum iCT. At this time, MB and iCT were localized exclusively to these abnormal PNE cell sites. These results, which may have relevance in humans, suggest that endogenous peptides may be important components in the process of development of neuroendocrine cancer.

Stimulation of hamster pulmonary neuroendocrine cells and associated peptides by repeated exposure to cigarette smoke.

Although the normal function of pulmonary neuroendocrine (PNE) cells containing bioactive peptides is poorly understood, various pulmonary diseases are associated with hyperplasia of these cells, and they also may be progenitors for small cell lung cancer in humans. In this study we have investigated the effects of subchronic cigarette smoke exposure in the hamster on the PNE cells and their peptide content. Daily exposure to standard research cigarette smoke for as long as 90 days led to progressively higher levels of serum calcitonin (iCT) as well as higher lung tissue iCT and the gastrin releasing-like peptides or mammalian bombesin (MB). Subsequent to a 30-day period during which there was no further exposure to smoke, serum levels returned to control levels, but the lung levels of both iCT and MB remained higher than control levels. Also, after the 90 days of exposure, immunocytochemistry revealed an increase in the number of iCT-containing PNE cells. This increase in the number of PNE cells correlated well with the increased iCT content of the lung tissue. We conclude that subchronic cigarette smoke exposure causes an increase in pulmonary levels of iCT and MB, which may be linked to the observed proliferative response of the PNE cells.

Immunohistochemical Evaluation of Neuroendocrine Cells and Neoplasms of the Lung

The dispersed neuroendocrine (NE) system is represented in the bronchopulmonary tract by submucosal nerves and ganglion cells and, in the mucosal lining by solitary NE cells and neuroepithalial bodies (NEB's). The latter two components variably express pan-NE markers including NSE, chromogranin (s) and, notably, synaptophysin. The expression of serotonin, bombesin, calcitonin and leu-enkephalin has been well established; additional eutopic materials include somatostatin and calcitonin gene-related peptide. Solitary NE cells and NEB's are epithelial structures as defined by their consistent cytokeratin expression. Hyperplasia and dysplasia of NE cells may be found in association with various forms of chronic injury; they have been noted in chronic bronchiectasis and in the vicinity of neoplasms of various types. Hyperplastic and dysplastic pulmonary NE cells frequently express ectopic materials particularly ACTH. NE neoplasms of the bronchopulmonary tract comprice a spectrum that includes a) carcinoids, b) well differentiated NE carcinomas, c) intermediate cell NE carcinomas and d) small cell NE carcinomas. The precise pathologic criteria defining these entities are discussed in detail as are their clinical implications. The entire spectrum of lung NE neoplasms express NE markers demonstrable by immunocytochemistry; these include pan-NE markers, serotonin and numerous neuropeptides. The expression of multiple hormonal materials is frequent. Within any given tumor, some variation in expression may be noted in different sites and in different periods of the "normal" or therapeutically modified lifespan of the tumor. The entire spectrum of lung NE neoplasms is epithelial for they express cytokeratin polypeptides and desmoplakin; subsets of the tumors coexpress cytokeratins and neurofilament proteins. Also, subsets of these NE neoplasms may be immunostained with monoclonal antibodies to antigens related to exocrine phenotype suggesting focal amphicrine features.

Evidence for cigarette smoke-induced calcitonin secretion from lungs of man and hamster

In hamsters, acute cigarette smoke inhalation increased serum levels of the hormone calcitonin; and, in humans, smoking of two high-nicotine content cigarettes increased serum and urine levels of this hormone. The source of this immunoreactive calcitonin (iCT) does not appear to be the thyroid gland, since previously thyroidectomized patients demonstrated a similar response. In the hamster, the increased serum iCT levels were accompanied by a decreased lung tissue iCT content and hypocalcemia. It is suggested that the source of the cigarette smoke-induced hypercalcitonemia is the lung, possibly from the iCT-containing pulmonary neuroendocrine (PNE) cells. Moreover, this response appears to be dependent on the nicotine content of the cigarettes.

Association of changes in bombesin immunoreactive neuroendocrine cells in lungs of newborn infants with persistent fetal circulation and brainstem damage due to birth asphyxia.

The pulmonary neuroendocrine (NE) cells, from 16 term infants dying at 1-4 days of age from birth asphyxia, were immuno stained for bombesin-like immunoreactivity by the immunoperoxidase method. The distribution and frequency of bombesin-immunoreactive NE cells were quantified morphometrically and correlated with the presence or absence of brainstem function and persistent fetal circulation (PFC). In infants with loss of brainstem function, the frequency of bombesin immunoreactive NE cells was significantly increased compared to infants with intact brainstem function, i.e. meconium aspiration with PFC. Infants with brainstem injury, with one exception, failed to develop PFC. Pathological changes in the tegmentum of the brainstem, i.e. containing the respiratory center, correlated in nine of 10 cases with loss of brainstem function. These data suggest an inverse relationship between brainstem function, release of bombesin-like peptide from the pulmonary NE cells and the functional state of the pulmonary vasculature. Intact brainstem function appears to be essential for both the release of bombesin-like peptide from the NE cells and for pulmonary vasoconstriction leading to PFC; absence of brainstem function is, on the other hand, associated with failure to release bombesin-like peptide and loss of PFC type reactivity in the pulmonary vasculature. However, it appears unlikely that bombesin itself is a direct mediator of pulmonary vasoconstriction.

Cytoskeletal differences between human neuroendocrine tumors: A cytoskeletal protein of molecular weight 46,000 distinguishes cutaneous from pulmonary neuroendocrine neoplasms

The cytoskeletons of various human neuroendocrine (NE) tumors were analyzed immunohistochemically using antibodies against intermediate-filament (IF) proteins as well as by two-dimensional gel electrophoresis of proteins from microdissected tissue samples. All of the tumors studied were found to contain cytokeratin filaments and are therefore referred to as ‘NE tumors of the epithelial type’. In addition, neurofilaments were found in most cutaneous and some pulmonary NE tumors, as well as in medullary carcinomas of the thyroid and in pancreatic islet cell tumors. The neurofilament staining was frequently concentrated in cytoplasmic IF aggregates. Gel-electrophoretic analyses showed that all NE tumors examined synthesize ‘simple epithelium-type’ cytokeratin polypeptides, cytokeratins nos. 8 and 18 being the most prominent ones, whereas cytokeratin no. 19 was found in variable and usually minor amounts. A new cytoskeletal protein, designated IT protein, with a relative molecular weight of 46,000 and an isoelectric pH value of approximately 6.1 (in 9.5 M urea) was detected in all 9 cases of cutaneous NE tumors (‘Merkel-cell carcinomas’), including 2 lymph-node metastases, but was not found in any of the 17 cases of pulmonary NE tumors. In addition, 2 medullary carcinomas of the thyroid, 2 islet cell tumors of the pancreas, and 1 intestinal carcinoid tumor also seemed to lack this protein. A protein indistinguishable from IT protein by electrophoresis and tryptic peptide mapping was found in cytoskeletal preparations of mucosal cells of human intestine and in cultured human colon carcinoma cells of line HT-29. A possible relationship between IT protein and the type-I subfamily of cytokeratin polypeptides is discussed. Our study shows that the co-expression of cytokeratin filaments and neurofilaments may provide a criterion which is useful for the recognition of some NE tumors but which does not distinguish between NE tumors of different types and origins. In contrast, IT protein seems to be present specifically in cutaneous NE tumors, but absent in pulmonary NE tumors. The implications of these findings for the elucidation of the histogenesis of cutaneous NE tumors and for the histopathological differential diagnosis of NE tumors of cutaneous and pulmonary origin are discussed.

Hypoxia and the neonatal rabbit lung: neuroendocrine cell numbers, 5-HT fluorescence intensity, and the relationship to arterial thickness.

We assessed the dynamics of neuroendocrine (NE) cell numbers, the intensity of specific 5-HT fluorescence, and the arterial medial thickness in the lungs of neonatal rabbits in normoxia and acute and chronic hypoxia. Hypoxic neonates had significantly higher NE cell numbers and medial thickness of the pulmonary arteries at 5 days of age than did normoxic controls; 1- and 3-day-old young that died in hypoxia also had significantly higher cell numbers and medial thickness than did hypoxic survivors. A decline in these cell numbers was noted between 1 and 5 days of age among normoxic young, whereas there was no significant change among hypoxic young. Medial thickness was unchanged among normoxic young but increased between 1 and 5 days of age among hypoxic survivors. A 1-day exposure to normoxia of hypoxic young four days postpartum caused a decrease in NE cell numbers and medial thickness to more normal values. Serotonin (5-HT) fluorescence intensity levels of groups of NE cells or neuroepithelial bodies (NEBs) in this group were equal to those of normal controls although these levels were decreased in early chronic hypoxia. Medial thickness and NE cell numbers were inversely correlated with serotonin levels, suggesting that serotonin may be associated with medial hypertrophy and presence of argyrophil material. Medial thickness was positively correlated with NE cell numbers. The above findings led to the following summary: pulmonary NE cells respond to changes in airway oxygen levels; hypoxia or decreased oxygen is associated with decreased cellular 5-HT content and an increase in NE cell numbers by argyrophil stain and medial thickness of pulmonary artery walls. The change to normoxia from hypoxia results in higher cellular 5-HT content and decreased NE argyrophil cell numbers along with reduced pulmonary artery wall medial thickness.