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Copyright of Acta Medica Croatica is the property of Croatian Academy of Medical Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Simple Summary: The endocrine cells of the alimentary tract (APUD) are an important component of the mucosa structure and significantly influence the stomach and intestine physiology. Prenatal development of the stomach is not limited to the qualitative and quantitative changes observed in the gastric wall, but is also reflected in APUD cell occurrence and their potential function in the development and maturation of the organ. Moreover, the perinatal period, crucial for the colostral globulin intake by the new-born animal, requires an adequately prepared gastric mucosa and its excretory function must be controlled. This study was aimed at immunohistochemical changes observed in the foetal period in equine foetuses. The changes were related to the reactivity of the endocrine cells and allowed us to better understand the developmental processes taking place both in the prenatal and perinatal period. The study consisted of the immunohistochemical analysis of fundic and pyloric mucosa in the equine stomach between the 4th and 11th month of gestation. The accessible material was classified into three age groups using the CRL method. The adult reference group was used to define potential differences between foetal and adult populations of gastric APUD cells. The samples were preserved, prepared, and stained according to the standard protocols. The immunohistochemical reaction was assessed using the semi-quantitative IRS method. The results were documented and statistically analysed. The most significant increase was seen in gastrin (G) cell activity. The activity of other endocrine cells (cholecystokinin (I) cells, somatostatin (D) cells, and somatotropin receptor (SR) cells) was less dynamic. This study proved that the development of APUD cells within the stomach mucosa undergoes quantitative and qualitative changes during stomach development. Our results correspond with the findings described in the accessible literature and prove a strong correlation between morphological changes in the stomach wall and the organ development, growth, and maturation. [ABSTRACT FROM AUTHOR]

• The NSI subepithelial glands in dromedaries had unique anatomical features. • Their ultrastructural features are typical for APUD cells. • They may have the structures required for synthesis of active peptides, amines and chemical mediators. The nasal septal island (NSI) is a sensory patch of neuroepithelium located within the soft tissue of the nasal septum in dromedaries. The island has unique anatomical features, including the specialized subepithelial glands. The aim of the present study was to describe the microscopic features and ultrastructure of these subepithelial glands and to speculate the possible functions. A total of 10 camel heads were used for the study. Unlike the serous and mucous airway glands, the NSI glands' ultrastructural features were typical for cells of the (A mine P recursor U ptake and D ecarboxylation, APUD) system. These features were included, membrane bound secretory vesicles of varying electron density, smooth endoplasmic reticulum in the form of vesicles; electron dense mitochondria, abundant rough endoplasmic reticulum and free ribosomes. Alcian-PAS identifiable mucus granules were not observed, except for few clusters of cells, located at the luminal surface. The probable functions were discussed on basis of cellular morphology and context. In a conclusion, the NSI subepithelial glands in dromedaries had unique anatomical structures, and as many other APUD cells, they had the machinery required for synthesis of a variable number of biologically active peptides, amines and chemical mediators. [ABSTRACT FROM AUTHOR]

The prevalence of gastrointestinal neuroendocrine tumors (GI-NETs) is increasing, and despite recent advances in their therapy, it remains inadequate in patients with advanced well-differentiated neuroendocrine tumors. These tumors present many challenges concerning the molecular basis and genomic profile, pathophysiology, clinicopathological features, histopathologic classification, diagnosis and treatment. There has been an ongoing debate on diagnostic criteria and clinical behavior, and various changes have been made over the last few years. Neuroendocrine carcinoma of the gastrointestinal system is a rare but highly malignant neoplasm that is genetically distinct from gastrointestinal system neuroendocrine tumors (NETs). The diagnosis and management have changed over the past decade. Emerging novel biomarkers and metabolic players in cancer cells are useful and promising new diagnostic tools. Progress in positron emission tomography-computerized tomography and scintigraphy with new radioactive agents ( 64 Cu-DOTATATE or 68 Ga-DOTATATE) replacing enough octreoscan, has improved further the current diagnostic imaging. Promising results provide targeted therapies with biological agents, new drugs, chemotherapy and immunotherapy. However, the role of surgery is important, since it is the cornerstone of management. Simultaneous resection of small bowel NETs with synchronous liver metastases is a surgical challenge. Endoscopy offers novel options not only for diagnosis but also for interventional management. The therapeutic option should be individualized based on current multidisciplinary information., Competing Interests: Conflict-of-interest statement: There is no conflict of interest associated with any of the senior author or other coauthors contributed their efforts in this manuscript., (©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.)

Recognition of the ectopic hormone secretion outside the primary hormone glands and tissues extends to early decades of the 20th century. Although several theories have been proposed for this entity, collection of secretory cells possessing the properties of amine precursor uptake and decarboxylation in some tissues and tumors have been the most justified proposal. As none of these theories completely provides a satisfactory explanation, roles played by more than 1 mechanism in the scenario are also probable. The ectopic production and secretion of corticotropin-releasing hormone, growth hormone-releasing hormone, gonadotropin-releasing hormone, adrenocorticotropic hormone, prolactin, growth hormone, follicle-stimulating hormone, and luteinizing hormone have all been demonstrated in the tumors, as well as in the hyperplastic and chronic inflammatory tissues outside the endocrine system. This review article focuses on the current available information on ectopic hypothalamic and pituitary hormone secreting syndromes, which may be beneficial for neurosurgeons. [ABSTRACT FROM AUTHOR]

Many disturbances in electrolyte and hormonal balance in the body induced by functional impairment of renal parenchyma may affect the activity of amine precursor uptake and decarboxylation (APUD) cells, which constitute a very important link in the regulation of homeostasis. The aim of the present study was the morphological, immunohistochemical and ultrastructural estimation of enteroendocrine cells in the stomach of uremic rats. Fragments of gastric pylorus were collected 1, 2 and 4 weeks after nephrectomy. Paraffin embedded sections were stained with H + E and by silver impregnation. For identification of neuroendocrine cells, immunohistochemical reactions were performed using specific antibodies against somatostatin, synaptophysin, neuron-specific enolase and anti-calcitonin gene related peptide. The analysis showed an increased number of APUD cells in the stomach of uremic rats compared to control rats, which may be a morphological expression of their hyperfunction in the functional impairment of renal parenchyma. These results suggest that chronic renal failure can modulate the secretory processes of APUD cells. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Changes in the frequency of endocrine cells are evidence of intestinal adaptation to germ-free (GF) status. Not only the distribution of these cells along the intestine, but also the differences in intracellular content of these regulatory peptides may be explored to explain functional and structural aspects of GF intestinal adaptation. Focusing on the endocrine L-cells, we analyzed the intracellular content of enteroglucagon (EG) and peptide YY (PYY) throughout the intestine of the 14 GF and 14 conventional (CV) mice by using immunohistochemistry and the supra-optimal dilution technique. The percentage of EG-immunoreactive cells, but not of PYY-immunoreactive cells stained at supra-optimal dilution was significantly higher in the proximal colon of GF mice than in the CV counterparts (P<0.05). Since the content of co-stored PYY did not differ between GF and CV mice, the higher content of EG was compatible with a selective cellular response. Moreover, in the cecum of GF mice, the density of EG-immunoreactive cells was significantly higher than that of PYY-immunoreactive cells (P<0.05). These results are consistent with preferential production of EG by L-cells at the expense of PYY in the proximal colon and in the enlarged cecum of GF mice. In addition, they may reflect the dynamics of the GF intestinal epithelium and/or be correlated with the higher serum levels of these peptides. The role of endocrine cells needs to be better studied in human and other experimental adaptative conditions in order to elucidate the regulatory mechanisms of intestinal functions. [ABSTRACT FROM AUTHOR]

The endocrine cells of the digestive system (entero-endocrine cells of gastro-intestinal epithelia and langerhans' islets of the pancreas) and the chemical messengers produced by them constitute a complicated and complex system. The physiological function of this system is the regulation of all processes related to digestion and resorption, and to homeostasis of carbohydrate metabolism. Using morphological and histochemical features of this cellular community, the present review deals with amines and amine metabolism, polypeptides and their immunohistochemical identification, and with the modes of action of genteric and pancreatic hormones. Special attention is paid to the significance of amine precursor uptake and decarboxvlation (APUD), to immunohistochemical methodology and the interpretation of immunohistochemical findings, and to local regulatory mechanisms, especially paracrinia. Finally, unifying concepts for the integration of these cells and similar endocrine cells of other organs into a common system are considered. [ABSTRACT FROM AUTHOR]

An indirect immunoperoxidase technique was used to investigate the site of prealbumin synthesis in the human fetus from between 8 and 43 weeks. Prealbumin staining was noted in the A cells of the fetal pancreas, both in the primary and secondary generations of the islets of Langerhans, from as early as 12 weeks gestation. Electron microscopy localized the staining to the cytoplasmic secretory granules. Prealbumin was also present in the gastrointestinal mucosa in cells which had a distribution similar to that of argentaffin cells. Positive staining was noted in the lining epithelium of the renal proximal convoluted tubules, but ultrastructural studies indicated that this was probably related to reabsorption, and not to synthesis. [ABSTRACT FROM AUTHOR]

Copyright of Klinische Wochenschrift is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Two established human small cell cancer lines (SCCL) were exposed to 5-hydroxytryptophan (5-HTP) for various time intervals. The levels of l-dopa decarboxylase (DDC), formaldehyde-induced fluorescence (FIF), number and volume density of dense-cored granules, and levels of bombesin-like immunoreactivity (BLI) and of immunoreactive calcitonin (ICT) were examined in controls and after 5-HTP treatment. The levels of DDC and BLI were not changed by 5-HTP treatment, while FIF was significantly increased in all 5-HTP treated groups. Immunoreactive calcitonin was undetectable in all groups including the controls. A quantitative increase in number and volume density of dense-cored granules was measured in one cell line after 18 h of 5-HTP and was accompanied by exocytosis of granules. The data demonstrate that while 5-HTP increased cellular activity in one of the cell lines (increase in number of densecored granules and evidence of secretion), not all of the measured parameters of APUD cells correlate under these experimental conditions. [ABSTRACT FROM AUTHOR]

A morphometric study of argyrophilic Amine Precursor Uptake and Decarboxylase (APUD) cells in airways and intestine of guinea pigs after hypothalamic lesions is reported. APUD cell densities are expressed as APUD cell number/mm of airway or gut perimeter length and as APUD cell/100 epithelial cells. The latter ratio is useful to distinguish generalized epithelial changes from specific alterations in APUD cell densities. Lesions to anterior hypothalamic areas are known to inhibit death due to anaphylactic shock in the guinea pig by a yet to be determined mechanism. It is also known that lesions placed in other hypothalamic nuclei located in the posterior hypothalamus do not interfere with lethal anaphylaxis. Recent quantitative studies of respiratory argyrophilic APUD cells have demonstrated changes in densities of these cells during sensitization and anaphylaxis in the guinea pig, suggesting that they participate in the complex events of anaphylaxis. The present study was performed to determine whether lesions in the anterior and posterior hypothalamus result in changes in APUD cell densities that would suggest a role of the neuroendocrine system in the modulation of lethal anaphylaxis in the guinea pig. The guinea pig has 0.53±2.44 APUD cells/100 nuclei in the larynx, 0.64±0.29 in the trachea, 0.39±0.18 in bronchi, 0.03±0.03 in bronchioles and 10.40±0.70 in the ileum. No significant changes were found in APUD cell densities in animals with hypothalamic lesions when compared to controls, suggesting that mechanisms other than APUD cell hyperplasia or hypoplasia are responsible for the effects of these lesions on lethal anaphylaxis in the guinea pig. [ABSTRACT FROM AUTHOR]

The amine precursor uptake and decarboxylase (APUD) cells in airways and small intestine of adult hamsters have been studied by quantitative, histochemical and immunocytochemical methods for the presence of argyrophilia, ACTH, hGH, calcitonin, bombesin and prolactin in control animals and following priming with two amine precursors: L-dopa and 5-hydroxytryptophane (5-HTP). APUD cells have been defined by the presence of intracytoplasmic argyrophilic granules. A method that related them to airway or gut perimeter length or total epithelial cell numbers has been applied. Calcitonin-like-immunoreactivity (CLIR) is present in epithelial cells in the tracheal epithelium and glands. The presence of ACTH, hGH, bombesin or prolactin is not detected. Priming with L-Dopa and 5-HTP results in up to 12 fold increases in densities of argyrophilic APUD cells in airways and ileum when ratios of APUD cells/100 nuclei are compared to those in control animals. Exposure to 5-HTP induces no significant changes in densities of cells with CLIR in the trachea but CLIR is not detected in animals exposed to L-DOPA. Ratios of APUD cells/100 epithelial cells appear to be more sensitive than those of APUD cells/mm in detecting significant changes in APUD cell densities. Priming with amine precursors is a valuable tool in quantitative studies of neuroendocrine cells. [ABSTRACT FROM AUTHOR]

Amine Precursor Uptake and Decarboxylase (APUD) cells have been studied quantitatively to determine their normal distribution in the airways, ileum and cecum of adult guinea pigs utilizing tissues fixed in either Bouin's or Ito and Karnovsky's fixative. Cells were detected by four histochemical stains: Grimelius, en-block silver, lead-hematoxylin-en block silver and PAS-lead-hematoxylin. The guinea pig exhibits APUD cells in all airway segments in densities that decrease with decreasing airway size. This distribution is similar to that encountered in adult human, rat and hamster lungs and different from that in fetal or neonatal human, hamster or rabbit lungs in which these cells are more frequent in bronchioles. APUD cell densities in airways are 36-80 times lower that those in the ileum. The detection of airways APUD cells is dependent upon the histochemical stain utilized for their detection with Grimelius double impregnation providing the most sensitive stain. Fixation with the two solutions utilized does not significantly influence the results. Technical differences in staining may explain differences in quantitative studies of APUD cells performed in different laboratories and should be considered when designing future studies concerning the influence of pharmacologic, physiologic and pathologic agents on airways and intestinal APUD cells. [ABSTRACT FROM AUTHOR]

Neuroendocrine cells of the lung, occurring singly or in clusters known as neuroepithelial bodies, contain a variety of biologically active compounds, including several neuropeptides. We have investigated the localization of calcitonin and calcitonin gene-related peptide (CGRP) within single and grouped neuroendocrine cells in the respiratory epithelium of rats by an immunohistochemical double-staining technique which uses specific antisera raised in heterogeneous animal species. Calcitonin- and CGRP-immunoreactivities were nearly totally co-localized in both single neuroendocrine cells and neuroepithelial bodies. CGRP-immunoreactivity was also present in neurons in the jugular, nodose and dorsal root ganglia. The calcitonin-immunoreactivity in neuroendocrine cells, as in thyroid parafollicular (C) cells, was abolished by preincubation of the anticalcitonin serum with synthetic calcitonin. The CGRP-immunoreactivity in neuroendocrine cells and in the neuronal cells was abolished by preincubation of anti-CGRP serum with synthetic CGRP. Thus, while the calcitonin gene is expressed exclusively or predominantly as either calcitonin or CGRP in all other tissues except thyroid C-cells, our results strongly suggest that both peptides are expressed in the rat bronchopulmonary neuroendocrine cells. [ABSTRACT FROM AUTHOR]

It has been reported that only certain types of pancreatic parenchymal cells survive transplantation. This study examines whether the extent of differentiation of the pancreas at the time of transplantation affects the resulting morphology or viability of its components. Segments of chick pancreas or its primordia from stages preceding formation of dorsal bud (60 h) through hatching (day 21) were implanted in the abdominal region of three-day chick embryos. After various periods of growth, grafts were examined by light- and electron microscopy. In all transplants, individual endocrine cells (A, B, D, PP) and islet structure were identical to those of normal embryos of comparable age. The exocrine portion also appeared normal in implants from embryos younger than seven days. In grafts from older donors, however, normal acini and ducts were replaced by dilated, irregularly shaped tubules from which new islets appeared to develop. These results suggest that transplantation causes structural modification of exocrine tissue, which may reflect its initial functional capabilities. These observations are compared with similar structural alterations that occur following experimental obstruction of ducts and in human pancreatic pathology. [ABSTRACT FROM AUTHOR]

We recorded serotonin-emission intensity using formalin induced fluorescence and counted the number of neuroendocrine cells (NEC's) and neuroepithelial bodies (NEB's) containing argyrophil granules. Comparison of serotonin-emission intensity in NEB's of acutely hypoxic neonates (520 mmHg for 2-21/2 h) and normoxic controls showed significantly lower fluorescence in hypoxic animals. Neuroendocrine cell numbers as shown with Grimelius silver-nitrate stain did not change. This suggests either that the Grimelius stain reacts with compounds other than serotonin, or that the decrease in serotonin in acutely hypoxic rabbits is not sufficient to alter argyrophil stainability. [ABSTRACT FROM AUTHOR]

For the first time the hormonal activity of a glomus jugulare tumour, clinically manifest by intermitting hypertension, could be demonstrated by catecholamine level determination in blood. Endocrinological and diagnostic aspects concerned to the differential diagnosis of the hypertension in these patients are discussed. [ABSTRACT FROM AUTHOR]

Matrix metalloproteinases (MMPs) are involved in remodeling processes and have been immunocytochemically localized in some endocrine glands and their tumors. Using anterior pituitary gland and pituitary adenomas, immunocytochemical localization of MMP-2 (gelatinase-A),-9 (gelatinase-B), tissue inhibitor of metalloproteinase (TIMP)-1 and-2 was performed. Normal anterior-pituitary cells all contain MMPs and lesser amount of TIMPs, whereas far fewer MMPs and TIMPs are identified in anterior pituitary adenomas. There is no correlation between pituitary hormone and MMPs-TIMPs localization, thus MMP-TIMP homeostasis may not be involved in hormone synthesis and secretion of anterior pituitary cells and their adenomas. Because MMPs and TIMPs are more abundantly and specifically localized in pituitary cells and their adenomas, MMPs and TIMPs may be included as markers for endocrine cells, including anterior-pituitary cells. [ABSTRACT FROM AUTHOR]

Argyrophilia and argentaffinity, as basic properties of APUD cells, were investigated in 50 normal and hyperplastic prostates, which included both autopsy and surgical specimens from patients of various ages. Normal prostates (including glands from 3 foetuses) had 62% of argyrophil-positive granules in the glandular epithelia, while only 44% of the hyperplastic glands were positive. Argentaffin-positive cells were found in 12% of the surgical hyperplastic cases. Both argyrophil and argentaffin cells were distributed in zones, often in lobule-like shapes, lying along the basal membrane. On the basis of these findings, there is a discussion on the possible roles played by the so-called APUD cells in hyperplastic and neoplastic growths of the prostate, such as carcinoid tumours (apudomas) or endocrine-associated syndromes in the course of prostatic cancer. [ABSTRACT FROM AUTHOR]

The neuroepithelial bodies (NEB's) of the lung of 29-day-old fetuses and 1-day-old rabbits, under the conditions of this study, neither take up H-thymidine nor undergo mitosis. Also the NEB's are not derived at these times from proliferations of other kinds of epithelial cells in the intrapulmonary airways. It is, therefore, suggested that the difference in numbers of NEB's previously observed by us, between the 29-day fetus and the 1-day-old rabbit, is due either to regranulation or acquisition of argyrophilic material by the NEB's or differentiation of other epithelial types. It is concluded that the NEB's are composed of well differentiated cells, which have a greatly reduced capacity to undergo mitosis. [ABSTRACT FROM AUTHOR]

The immunocytochemical localisation of motilin in endocrine cells of the mammalian gut has been investigated by the use of a range of regionspecific antisera to both the C- and N-terminal parts of the peptide molecule. The possibility of motilin being co-stored with serotonin (5-HT) in a subpopulation of enterochromaffin cells was also studied by the use of specific antibodies to 5-HT. Motilin-like immunoreactivity was found exclusively in the mucosal APUD cells of the small intestine in all species investigated. Further characterisation of these cells indicated that antibodies reacting with both the C- and N-terminals immunostain a population of nonargentaffin (argyrophil) cells. In addition, a minor subpopulation of EC cells was immunostained with N-terminal directed antibodies only. In view of these results it is possible that the non-enterochromaffin cells detected by antibodies directed against both the N- and C-terminals of the motilin molecule are the source of the 22 amino acid motilin originally described. In contrast, the subpopulation of enterochromaffin cells detected only by N-terminal directed antibodies may be the source of a related peptide, yet to be identified. However, the possibility cannot be ruled out that the antigenic site on the peptide molecule may be altered when motilin is costored with variable quantities serotonin. [ABSTRACT FROM AUTHOR]

Quantitative histological and immunocytochemical studies have been carried out on the endocrine cells of the gastrointestinal tract in genetically obese mice and their heterozygous (lean) litter mates. In the ob/ob mice hyperplasia of most of the endocrine (APUD) cells of the gut was found, a condition which can be described as apudosis. Quantitative histology of silver-stained preparations, using a method which demonstrates the majority of endocrine cells, showed a significant degree of hyperplasia in all regions of the gastrointestinal tract, with statistically significant differences in the upper intestine ( p = < 0.001). Quantitative immunocytochemical studies by image analysis showed a difference in both number and hormone content of Gastric Inhibitory Peptide (GIP) ( p= < 0.001) and Enteroglucagon (EG) cells in obese as compared to lean mice. Differences in the case of Secretin (S), Gastrin (G) and Vasoactive Intestinal Peptide (VIP) cells were not great but in the obese mice both S and G cells were present in larger numbers in the lower intestine whereas in the lean, and in normal mice, they are predominant in the upper intestine. Whether these complex gut endocrine changes are primary, or secondary to the metabolic abnormalities seen in the ob/ob mouse, cannot presently be determined. [ABSTRACT FROM AUTHOR]

Electron microscopic investigations of the pulmonary epithelium of human foetuses reveal the occurrence of cells exhibiting fine-structural characteristics of polypeptide hormone producing APUD cells. Three types of cells were identified mainly on basis of the morphology of their secretory granules. Cells of type 1 have the appearance of monoamine storing cells and the dense core of vesiculated granules of these cells are reactive to argentaffine reaction performed directly on ultra-thin sections. Cells of type 2 contain granules of uniform shape and size and of rather homogeneous appearance. Besides in larger bronchial tubules these cells are localized in the epithelium of developing alveoli. Cells of type 3 with large osmiophilic granules tightly bound by a membrane are few and scattered. These cells are observed in larger bronchial tubuli only. [ABSTRACT FROM AUTHOR]

An electron microscopic investigation of the extrapulmonary respiratory tract of embryos and chick of the domestic fowl ( Gallus domesticus) has demonstrated for the first time in birds the presence here of a small number of epithelial cells characterised by an aminecontaining type of granule. These granular cells were scattered singly throughout the trachea, syrinx and primary bronchi and seemed more numerous in the caudal part of the airway. In favourable planes of section a small part of the cell was in contact with the luminal surface of the epithelium. The characteristic granular vesicles (approximate diameter 140 nm) appeared to be randomly distributed in the cytoplasm and there was no concentration of vesicles close to the plasma membrane. One of the cells was closely associated with an intraepithelial axon. By fluorescence microscopy, a small number of cells with a similar shape and distribution to the granular cells was observed after administration of 3,4-dihydroxyphenylalanine which may indicate the presence of an amine handlign mechanism in these cells. It is suggested that the granular cells belong to the APUD system of endocrine cells and that they may be modulated by the concentration of gas in the airways. [ABSTRACT FROM AUTHOR]

Endocrine cells in the bronchial epithelium in the glandular and beginning of the canalicular period of lung development, of rabbits, mice and guinea-pigs were searched for by use of the formaldehyde-fluorescence technique, by silver stains, staining of endocrine cell granules and by electron microscopy. One type was observed but differences between various animal species were noted. In rabbit foetuses numerous argyrophil cells in the bronchial epithelium were shown to contain amine and to have the capacity to take up and store further amounts of amine upon administration in vivo and in vitro of amine precursors. This capacity to produce and store amine under experimental conditions was shown by a smaller number of cells in the bronchial epithelium of mouse foetuses and by few scattered cells in the bronchial epithelium of guinea pig foetuses. By electron microscopic examination cells characterized by cytoplasmic secretory granules were observed, similar in number and distribution to those demonstrated by fluorescence microscopy. Differences were noted with respect to the texture, electron-density and size of the granules as well as in the contact of the cells to the lumen of the bronchi. [ABSTRACT FROM AUTHOR]