Phylogenetic aspects of pancreastatin- and chromogranin-like immunoreactive cells in the gastro-entero-pancreatic neuroendocrine system of vertebrates

Histopathological Chromogranin A-Positivity Is Associated with Right-Sided Colorectal Cancers and Worse Prognosis

Simple Summary

Several factors are known to affect colorectal cancer (CRC) patient survival, including elevated platelet counts (thrombocytosis) and chromogranin A-positive neuroendocrine-cell differentiation (CgA⁺). Thrombocytosis can occur due to biochemical changes caused by the tumor itself (known as paraneoplastic thrombocytosis) or due to the bleeding of the tumor (reactive thrombocytosis). Our effort was primarily focused on (1) determining if CgA⁺ and paraneoplastic thrombocytosis combined can affect CRC and (2) finding out if there is a possible connection between the two. With the help of chromogranin A immunohistochemical staining, the measurement of circulating biochemical markers of paraneoplastic thrombocytosis (interleukin-6 and thrombopoietin) and chromogranins A and -B, indication was found that CRC combined with CgA⁺ has a well-distinguishable pathophysiology, compared to CRCs without CgA⁺. A possible, new subtype of CRC is proposed, which can be identified easily with chromogranin A immunohistochemical staining. However, its impact should be further studied.

Abstract

Background: Colorectal cancer (CRC) is known to be affected by paraneoplastic thrombocytosis and chromogranin A-positive neuroendocrine-cell differentiation (CgA⁺). Their combined effect has never been previously investigated. Methods: A prospective cohort pilot study of 42 CRC patients and 42 age- and sex-matched controls was carried out. Plasma interleukin-6, thrombopoietin, and serum chromogranin A and -B were measured; furthermore, tumor tissue was immunohistochemically stained for CgA⁺. Results: Twenty-seven and 15 patients were assigned to the chromogranin A-negative (CgA⁻) and CgA⁺ groups, respectively. Within the CgA⁺ group, right-sided tumors were more frequent (18.5% vs. 53.3%), no stage I cancer was found, and patients of this group were in worse general condition. Compared to control subjects, chromogranin A level was higher in the CgA⁺ group (p = 0.0086), thrombopoietin (p = 0.0040) and chromogranin B (p = 0.0070) in the CgA⁻ group, while interleukin-6 was high in both tumor groups (p ≤ 0.0090). Survival was significantly worse in the CgA⁺ group (hazard ratio: 5.73; p = 0.0378). Conclusions: Different thrombopoietin levels indicated distinct thrombocytosis types. Within the two CRC groups, serum levels of chromogranins changed in different directions suggesting two well-distinguishable pathophysiologies. Based on these observations we propose a new subtype of CRC, which can be characterized by chromogranin A-positive neuroendocrine-cell differentiation.

Pancreatic Blood Flow with Special Emphasis on Blood Perfusion of the Islets of Langerhans

The pancreatic islets are more richly vascularized than the exocrine pancreas, and possess a 5- to 10-fold higher basal and stimulated blood flow, which is separately regulated. This is reflected in the vascular anatomy of the pancreas where islets have separate arterioles. There is also an insulo-acinar portal system, where numerous venules connect each islet to the acinar capillaries. Both islets and acini possess strong metabolic regulation of their blood perfusion. Of particular importance, especially in the islets, is adenosine and ATP/ADP. Basal and stimulated blood flow is modified by local endothelial mediators, the nervous system as well as gastrointestinal hormones. Normally the responses to the nervous system, especially the parasympathetic and sympathetic nerves, are fairly similar in endocrine and exocrine parts. The islets seem to be more sensitive to the effects of endothelial mediators, especially nitric oxide, which is a permissive factor to maintain the high basal islet blood flow. The gastrointestinal hormones with pancreatic effects mainly influence the exocrine pancreatic blood flow, whereas islets are less affected. A notable exception is incretin hormones and adipokines, which preferentially affect islet vasculature. Islet hormones can influence both exocrine and endocrine blood vessels, and these complex effects are discussed. Secondary changes in pancreatic and islet blood flow occur during several conditions. To what extent changes in blood perfusion may affect the pathogenesis of pancreatic diseases is discussed. Both type 2 diabetes mellitus and acute pancreatitis are conditions where we think there is evidence that blood flow may contribute to disease manifestations. © 2019 American Physiological Society. Compr Physiol 9:799-837, 2019.

The Chromogranin A-derived sympathomimetic serpinin depresses myocardial performance in teleost and amphibian hearts

Chromogranin A (CgA) is an acidic protein co-stored with catecholamines, hormones and neuropeptides in the secretory granules of endocrine, neuronal and other cell types (including cardiomyocytes). Proteolytic cleavage in the C terminus of CgA generates a 2.9kDa peptide named serpinin (Serp; Ala26Leu) that can be modified at its N terminus to form a pyroglutamate residue (pGlu-Serp). In the rat heart, both peptides increase contractility and relaxation through a β-adrenergic-like action mechanism. Accordingly, Serp and pGlu-Serp were proposed as novel myocardial sympatho-adrenergic modulators in mammals. On a comparative basis, here we report the actions of Serp and pGlu-Serp on myocardial contractility in three poikilotherm vertebrate species: the eel (Anguilla anguilla), the goldfish (Carassius auratus) and the frog (Rana esculenta). Using isolated working heart preparations, we show that pGlu-Serp reduces stroke volume in all species tested, while Serp reduces contractility in the frog heart, but is uneffective in eel and goldfish hearts. In the goldfish and frog hearts, pGlu-Serp activates the Nitric Oxide/cGMP pathway involving Endothelin-1 B receptors (frog) and β₃ adrenergic receptors (goldfish). pGlu-Serp-treated hearts from goldfish and frog show increased cGMP content. Moreover, the exposure of the frog heart to pGlu-Serp is accompanied by an increased expression of activated eNOS and Akt. In conclusion, this first report showing that pGlu-Serp inhibits mechanical cardiac performance in teleost and amphibians supports an evolutionary role of the CgA system, and particularly its serpinin component, in the sympatho-adrenergic control of the vertebrate heart.

Catecholamines, cardiac natriuretic peptides and chromogranin A: evolution and physiopathology of a 'whip-brake' system of the endocrine heart

In the past 50 years, extensive evidence has shown the ability of vertebrate cardiac non-neuronal cells to synthesize and release catecholamines (CA). This formed the mindset behind the search for the intrinsic endocrine heart properties, culminating in 1981 with the discovery of the natriuretic peptides (NP). CA and NP, co-existing in the endocrine secretion granules and acting as major cardiovascular regulators in health and disease, have become of great biomedical relevance for their potent diagnostic and therapeutic use. The concept of the endocrine heart was later enriched by the identification of a growing number of cardiac hormonal substances involved in organ modulation under normal and stress-induced conditions. Recently, chromogranin A (CgA), a major constituent of the secretory granules, and its derived cardio-suppressive and antiadrenergic peptides, vasostatin-1 and catestatin, were shown as new players in this framework, functioning as cardiac counter-regulators in 'zero steady-state error' homeostasis, particularly under intense excitatory stimuli, e.g. CA-induced myocardial stress. Here, we present evidence for the hypothesis that is gaining support, particularly among human cardiologists. The actions of CA, NP and CgA, we argue, may be viewed as a hallmark of the cardiac capacity to organize 'whip-brake' connection-integration processes in spatio-temporal networks. The involvement of the nitric oxide synthase (NOS)/nitric oxide (NO) system in this configuration is discussed. The use of fish and amphibian paradigms will illustrate the ways that incipient endocrine-humoral agents have evolved as components of cardiac molecular loops and important intermediates during evolutionary transitions, or in a distinct phylogenetic lineage, or under stress challenges. This may help to grasp the old evolutionary roots of these intracardiac endocrine/paracrine networks and how they have evolved from relatively less complicated designs. The latter can also be used as an intellectual tool to disentangle the experimental complexity of the mammalian and human endocrine hearts, suggesting future investigational avenues.

Regional distribution and relative frequency of gastrointestinal endocrine cells in the ddN mice: an immunohistochemical study

The distributions and frequencies of some endocrine cells in the eight portions of the gastrointestinal (GI) tract - fundus, pylorus, duodenum, jejunum, ileum, cecum, colon and rectum of the ddN mouse, were studied with immunohistochemical method using seven types of antisera against chromogranin (Cg) A serotonin, somatostatin, glucagon, gastrin, cholecystokinin (CCK)-8 and human pancreatic polypeptide (hPP). In the GI tract of ddN mice, CgA, serotonin, somatostatin, glucagon, gastrin, CCK-8 immunoreactive (IR) cells were identified with various frequencies, but hPP-IR cells were not observed in this study. Most of IR cells in the intestinal portion were generally spherical or spindle in shape (open type cell) whereas cells showing round in shape (close type cell) were found in the intestinal gland and stomach regions occasionally. They showed the highest frequency in the pylorus or colon. CgA-IR cells were observed from the pylorus to ileum. Serotonin-IR cells were detected throughout the whole GI tract except for the fundus. Somatostatin-IR cells were demonstrated throughout the whole GI tract except for the cecum and colon. Gastrin and CCK-8-IR cells were restricted to the pylorus and duodenum. In addition, a few glucagon-IR cells were restricted to the fundus and rectum. In conclusion, the general distribution patterns and relative frequency of GI endocrine cells of the ddN mouse was similar to that of other strains of mice. However, some strain and/or species-dependent unique distributions and frequencies of endocrine cells were also observed in the present study.

A Gastric Neuroendocrine Carcinoma Expressing Somatostatin in a Bearded Dragon (Pogona Vitticeps)

A metastatic gastric neuroendocrine carcinoma in a 2.5-year-old inland bearded dragon ( Pogona vitticeps) with a chronic history of anorexia, weight loss, depression, and acute melena is described. Histologic examination of the gastric mass revealed a densely cellular tumor arranged in nests and occasional rosettes of hyperchromatic cells with oval to spindle-shaped nuclei and minimal cytoplasm; the tumor was supported by a moderate fibrovascular stroma. Similar cells invaded through the gastric mucosa, and there were multiple hepatic metastases. The neoplastic cells were weakly immunopositive for neuron-specific enolase and moderately positive for somatostatin but were negative for chromogranin AB and gastrin. Ultrastructural studies revealed scattered neurosecretory granules in the neoplastic cells, confirming the diagnosis of a neuroendocrine carcinoma.

New insights into granin-derived peptides: evolution and endocrine roles

The granin protein family is composed of two chromogranin and five secretogranin members that are acidic, heat-stable proteins in secretory granules in cells of the nervous and endocrine systems. We report that there is little evidence for evolutionary relationships among the granins except for the chromogranin group. The main granin members, including chromogranin A and B, and secretogranin II are moderately conserved in the vertebrates. Several small bioactive peptides can be generated by proteolysis from those homologous domains existing within the granin precursors, reflecting the conservation of biological activities in different vertebrates. In this context, we focus on reviewing the distribution and function of the major granin-derived peptides, including vasostatin, bovine CgB(1-41) and secretoneurin in vertebrate endocrine systems, especially those associated with growth, glucose metabolism and reproduction.

The immunohistochemical localization of synaptophysin protein (p38) in the gastro-entero-pancreatic (GEP) system of reptiles

The gastro-entero-pancreatic (GEP) system of four reptilian species: turtle (Emys orbicularis), lizards (Lacerta viridis and Lacerta agilis) and snake (Natrix natrix) has been investigated immunohistochemically for the presence and topographic distribution of synaptophysin. Among the studied reptiles, only in turtles were neural, glial and neuroendocrine elements labelled for this marker protein. Semi-quantitative evaluation of the immunolabelled neural structures distributed throughout the gastroenteric wall revealed, with two exceptions, highly significant mean differences between the successive gut segments. Significant mean differences were noted also between myenteric and submucosal neurons immunolabelled in the various gastroenteric regions. Moreover, the comparison of ganglionic perikarya groups showed, at least in the stomach, significant mean differences. The amounts of immunopositive glial cells seemed to vary similarly to those of nerve fibers along the entire gastrointestinal tract. Finally, every "closed" and "open" population of immunopositive epithelial cells showed typical fluctuations along the gut. In addition to the distribution of synaptophysin in the GEP system of turtles, the above findings furnish evidence that this marker protein, which is widespread in mammals, is only occasionally expressed in reptiles and probably in most poikilothermic vertebrates.

New biological aspects of Chromogranin A-derived peptides: Focus on vasostatins

Chromogranin A (CgA), one component of the granin family, represents the major soluble protein co-stored and co-released with catecholamines, within chromaffin cells secretory granules. It is considered a diagnostic and prognostic marker of several diseases, including a variety of tumours and cardiac heart failure. It also represents a precursor of biologically active fragments, generated after proteolytic cleavage at the level of the multiple pairs of dibasic sites which enrich its sequence. CgA, and its derived fragments show an old evolutionary history being ubiquitously present throughout the animal word, from mammals to invertebrates. Their biological functions include control of hormone production, and several paracrine and autocrine actions mainly attributed to its derived peptides. Two N-terminal fragments, named vasostatins 1 (VS-1: CgA(1-76)) and vasostatin 2 (VS-2: CgA(1-113)) due to their ability to dilate pre-constricted vessels, exert a large spectrum of homeostatic actions, including antifungal and antimicrobial effect, modulation of cell adhesion, and inhibition of parathyroid hormone secretion. Recently, on isolated heart preparations from eel, frog and rat they were shown to act as negative inotropic agents able to counteract the effects of beta-adrenergic stimulation. This short note introduces the abstracts of the contributions at the "International Workshop on Vasostatins and Chromogranin A-derived peptides" (Island of Capri, Italy; September 2005). The Workshop was focused on recent findings on the role of vasostatins (VSs) in cardiovascular and gastrointestinal systems, extracellular fluids composition, and innate immunity. Particular attention has been given to the still elusive mechanism of action of these peptides.

Morphology of the pancreas of some species belonging to the genera Phelsuma and Gecko (family Gekkonidae): evidence of apoptotic process during the seasonal cycle

In this study we investigated comparative morphology of the endocrine pancreas of several species belonging to the family Gekkonidae and apoptotic processes of the pancreas which may be correlated to the seasonal cycle. The following species of the family Gekkonidae were studied: Phelsuma lineata, P. madagascariensis, P. dubia, P. abotti, Gekko gecko, G. vittatus, and Geckonia chazaliae. In all these species the pancreas consisted of large and medium islets as well as endocrine cells which were scattered throughout the acinar cells. Exocrine parenchyma consisted of tubuli-acini. Four mayor cell types were identified in the endocrine pancreas, using immunocytochemistry: glucagon-immunoreactive (A) cells, insulin-immunoreactive (B) cells, somatostatin-immunoreactive (D) cells, and pancreatic polypeptide immunoreactive (PP) cells. In the endocrine pancreas the amount of A cells and B cells was either equal or a prevalence of A cells was observed. In the wet season the pancreatic morphology presented normal features with very rare apoptotic cells. The animals belonging to the genus Phelsuma taken in the dry season (July) showed numerous vacuolated, Caspase 3, 9 and 11-immunoreactive acinar and some endocrine cells containing picnotic nuclei which were positive to tunel reaction. The animals belonging to the genus Gekko taken at the end of the dry season (October) exhibited strongly vacuolated, Caspase 3, 9 and 11-immunoreactive endocrine and some acinar cells containing nuclei which were positive to tunel reaction. These apoptosis events could be a reaction in response to stress mechanisms, such as a starvation period during the dry season.

The granin family of uniquely acidic proteins of the diffuse neuroendocrine system: comparative and functional aspects

The chromogranins A (CgA) and B (CgB) and secretogranin II (SgII) constitute the main members of a family of uniquely acidic secretory proteins in elements of the diffuse neuroendocrine system. These genetically distinct proteins, CgA, CgB, SgII and the less well known secretogranins III-VII are collectively referred to as 'granins' and characterised by numerous pairs of basic amino acids as potential cleavage sites for processing by the co-stored prohormone converting enzymes PC 1/3 and PC2. This review is directed towards comparative and functional aspects of the granins with emphasis on their phylogenetically conserved sequences. Recent developments provide ample evidence of widely different effects and targets for the intact granins and their derived peptides, intracellularly in the directed trafficking of storage components during granule maturation and extracellularly in autocrine, paracrine and endocrine interactions. Most of the effects assigned to the granin derived peptides fit into patterns of direct or indirect inhibitory modulations of major functions. So far, peptides derived from CgA (vasostatins, chromacin, pancreastatin, WE-14, catestatin and parastatin), CgB (secretolytin) and SgII (secretoneurin) are the most likely candidates for granin-derived regulatory peptides, of postulated relevance not only for homeostatic processes, but also for tissue assembly and repair, inflammatory responses and the first line of defence against invading microorganisms.

Changes of the gastric endocrine cells in the C57BL/6 mouse after implantation of murine lung carcinoma: An immunohistochemical quantitative study

AIM: The regional distributions and relative frequencies of some gastric endocrine cells of C57BL/6 mice were studied by immunohistochemical method using seven types of specific antisera against chromogranin A (CGA), serotonin, somatostatin, gastrin, cholecystokinin (CCK)-8, glucagon and human pancreatic polypeptide (HPP) after subcutaneous implantation of murine lung carcinoma (3LL) cells.

METHODS: The experimental animals were divided into two groups, one is non-implanted sham and the other is 3LL-implanted group. Samples were collected from the two regions of stomach (fundus and pylorus) at 28 d after implantation of 3LL cells (1×10⁵ cell/mouse).

RESULTS: In this study, all the seven types of immunoreactive (IR) cells were identified except for HPP. Most of these IR cells in the gastric portion were generally spherical or spindle in shape (open-type cell) while cells showing round in shape (closed-type cell) were found occasionally. The regional distributions of gastric endocrine cells in the 3LL-implanted group were similar to those of non-implanted sham. However, significant decreases of some types of IR cells were detected in 3LL-implanted group compared to those of non-implanted sham. In addition, the IR cells showing degranulation were numerously detected in 3LL-implanted group. CGA-, serotonin- and somatostatin-IR cells in the fundus and pylorus regions, and gastrin-IR cells in the pylorus regions of 3LL-implanted groups significantly decreased compared to those of non-implanted sham. However, no changes on frequencies of CCK-8- and glucagon-IR cells were demonstrated between 3LL-implanted and non-implanted groups.

CONCLUSION: Endocrine cells are the anatomical units responsible for the production of gut hormones, and the change in their density would reflect a change in the capacity of producing these hormones. Implantation of tumor cell mass (3LL) induced severe quantitative changes of gastric endocrine cell density, and the abnormality in density of gastric endocrine cells may contribute to the development of gastrointestinal symptoms such as anorexia and indigestion, frequently encountered in patients with cancer.

An Immunohistochemical Study of Gastrointestinal Endocrine Cells in the BALB/c Mouse

The distributions and frequencies of some endocrine cells in the eight portions of the gastrointestinal tract (GIT) of BALB/c mouse were studied. Endocrine cells were stained using immunohistochemical method with seven types of antisera against bovine chromogranin (BCG), serotonin, gastrin, cholecystokinin (CCK)-8, somatostatin, glucagon and human pancreatic polypeptide (HPP), and the regional distributions and their relative frequencies were observed in the eight portions of the GIT of BALB/c mice. All seven types of immunoreactive (IR) cells were identified. Most of the IR cells in the intestinal portion were generally spherical or spindle in shape (open type cell) while round-shaped cells (closed type cell) were found in the intestinal gland and stomach regions occasionally. Their relative frequencies varied according to each portion of the GIT. BCG-IR cells were observed throughout the whole GIT except for the rectum and they were most predominant in the pylorus. Serotonin-IR cells were detected throughout the whole GIT and they showed the highest frequency in the fundus. Gastrin- and CCK-IR cells were restricted to the pylorus and duodenum with a majority in the pylorus and rare or a few frequencies in the duodenum. Compared with other mammals, somatostatin-IR cells were restricted to the fundus and pylorus with a few frequencies, respectively. In addition, glucagon- and HPP-IR cells were restricted to the fundus and duodenum, respectively, with relative low frequencies. Some species-dependent unique distributions and frequencies of endocrine cells were observed in the GIT of BALB/c mouse compared with other rodents.

An immunohistochemical study on the neuropeptide-producing endocrine cells in the alimentary tract of wrinkled frog, Rana rugosa (Ranidae)

The regional distribution and relative frequency of neurohormonal peptides-producing endocrine cells were demonstrated in the alimentary tract of wrinkled frog, Rana rugosa, using eight types of specific antisera raised against mammalian regulatory peptides. The alimentary tract of frog was divided into six portions from esophagus to rectum. Most of the cells in the epithelial lining portion, between epithelial cells, were generally spherical or spindle shaped having long cytoplasmic process that was reached to the lumen (open-typed cell) while cells showing round shape (close-typed cell) were also found in the gastric, esophageal or intestinal glands occasionally. All of eight immunoreactive (IR) cells against serotonin, somatostatin, bovine Sp-1/chromogranin (BCG), gastrin, cholecystokinin (CCK)-8, bombesin, glucagon, and human pancreatic polypeptide (HPP) were observed in this study. Serotonin-IR cells were demonstrated throughout whole alimentary tract including esophagus and showed most predominant frequency in antrum. Somatostatin-IR cells were also detected throughout whole alimentary tract including esophagus and showed most predominant in pylorus and antrum. BCG-IR cells were restricted to stomach regions with relatively low frequencies. CCK-8-IR cells were observed from antrum to ileum and showed highest frequency in antrum. Gastrin-IR cells were restricted to antrum with low frequency and bombesin-IR cells were demonstrated from esophagus to antrum with various frequencies. Glucagon-IR cells were located throughout whole alimentary tract except for rectum and showed most predominant frequency at antrum. HPP-IR cells were detected from antrum to ileum with highest frequency in antrum. In conclusion, the regional distribution and relative frequency of these IR cells correspond well to the previous report in anuran species but somewhat peculiar patterns are also detected.

An immunohistochemical study of the gastrointestinal endocrine cells in the C57BL/6 mice

The regional distributions and relative frequencies of some gastrointestinal endocrine cells in the eight portions (fundus, pylorus, duodenum, jejunum, ileum, cecum, colon and rectum) of the gastrointestinal tract of C57BL/6 mouse was studied with immunohistochemical method using seven types of specific anti-sera against chromogranin A (CGA), serotonin, somatostatin, human pancreatic polypeptide (HPP), glucagon, gastrin and cholecystokinin (CCK)-8. In this study, all these seven types of immunoreactive (IR) cells were identified. Most of these IR cells in the intestinal portion were generally spherical or spindle in shape (open-type cell) while cells showing round in shape (closed-type cell) were found in the intestinal gland and stomach regions occasionally. Their relative frequencies were varied according to each portion of gastrointestinal tract. CGA-IR cells were demonstrated throughout the whole gastrointestinal tract and they showed most predominant in the pylorus and duodenum. Serotonin-IR cells were detected throughout whole gastrointestinal tract and they showed highest frequency in the stomach and colon. Somatostatin-IR cells were demonstrated throughout whole gastrointestinal tract except for large intestine and showed highest frequency in the fundus. HPP-IR cells were found in the fundus with rare frequency. Peculiarly, glucagon-IR cells were restricted to the fundus, ileum and colon with a few frequencies. Gastrin-IR cells were restricted to the pylorus with numerous frequency and CCK-8-IR cells were observed in the pylorus, duodenum and jejunum with numerous and/or a few frequencies, respectively. In conclusion, some peculiar distributional patterns of gastrointestinal endocrine cells were found in C57BL/6 mouse.

Expression of chromogranin A and somatostatin receptors in pancreatic AR42J cells

The exocrine pancreatic cell line AR42J is also known to display some neuroendocrine (NE) features. We have extended this fact by showing that AR42J cells express mRNA of chromogranin A (CgA), display immunoreactivity (IR) to CgA, and secrete its cleavage product pancreastatin. A sparse occurrence of typical NE secretion granules, together with only a faint IR to conventional NE markers, indicates that the NE cells are of a poorly differentiated type. CgA promoter reporter plasmid experiments showed that gastrin, epidermal growth factor, and phorbol 12-myristate 13-acetate, induce upregulation of CgA after 24 h. By RT-PCR, it was found that AR42J expresses all of the five subtypes of the somatostatin (SST) receptor (SSTR) family, except SSTR4. The existence of functional SSTRs was confirmed by showing that the SST analog octreotide could inhibit gastrin-induced proliferation. Thus, the AR42J cell line may function as a valuable experimental model to study the regulation of CgA and SSTRs in poorly differentiated NE tumor cells.

Chromogranin A-immunoreactive cells in the olfactory system of anuran amphibians

Chromogranin A (CgA) is a member of the granin family of acidic proteins that are present in the secretory granules of many endocrine and neuroendocrine cells. The specific function(s) of these proteins is not known, but they seem to be the precursors of biologically active peptides, and they may act as helper proteins in the sorting and packaging of peptide hormones and neuropeptides. Using indirect immunohistochemistry, we have found CgA immunoreactivity in the primary olfactory epithelia, the vomeronasal epithelia, the olfactory nerves, and the olfactory bulbs of tadpoles of the American toad, Bufo americanus, and the green frog, Rana clamitans. CgA immunoreactivity was present in the early stages of larval development in toads but was not detected in toad tadpoles after the hindlimb buds formed or in toadlets or adults. In green frog tadpoles, CgA-immunoreactive cells were found in pre- and prometamorphic stages but not in late climax. CgA immunoreactivity was also absent in froglets, but it was detected in the vomeronasal epithelium but not the olfactory epithelium of adult green frogs.

Characterization of pancreatic endocrine cells of the European common frog Rana temporaria

To characterize the endocrine cell types of the pancreas of Rana temporaria, conventional staining, silver impregnation, and immunocytochemical methods for light and electron microscopy have been applied to paraffin, thin and semithin sections, many of them serial pairs. Quantitative data on the frequency and distribution (insular, extrainsular among the exocrine cells, or within the pancreatic ducts) of each endocrine cell type are also reported. Four distinct endocrine cell types have been identified: insulin (B) cells, which are also immunoreactive for [Met]enkephalin; glucagon/PP (A/PP) cells, also immunoreactive for GLP1; somatostatin (D) cells; and a fourth endocrine-like cell type (X cells) of unknown content and function. X cells display characteristic ultrastructure and tinctorial traits but are nonimmunoreactive for all of the 37 antisera tested. The presence of [Met]enkephalin in amphibian pancreatic endocrine cells is now reported for the first time. Almost half (44.9 +/- 7.9) of the total endocrine cell population lies outside the islets, mainly spread among the exocrine cells. Approximately 37.2 +/- 4.6% of the total endocrine cell population was immunoreactive for insulin, 48.8 +/- 6.9% was immunoreactive for glucagon/PP, and 14.0 +/- 4.9% was immunoreactive for somatostatin; 79.2 +/- 6.4% of glucagon/PP cells are found within the exocrine parenchyma, representing the majority (86.4 +/- 4.3%) of extrainsular endocrine component. On the contrary, most B cells (94.2 +/- 2.1%) are located within the islets; 30.8 +/- 12.9% of D cells are found outside the islets.

Granin proteins (chromogranin A and secretogranin II C23-3 and C26-3) in the endocrine pancreas of reptiles

The endocrine pancreas of four reptile species belonging to the turtles, lizards and snakes was investigated immunohistochemically for the occurrence and cellular distribution of chromogranin A (CgA) and of two synthetic secretonin II (SgII)-peptides (C23-3 and C26-3). CgA-immunoreactivity was found only in the turtle pancreas, whereas that for SGIIC23-3 appeared both in the turtle and snake. None of the species studied displayed immunoreactivity for SgIIC26-3. The two detected granins showed different distributions in relation to the endocrine cell types. Conspicuous variations of the immunostaining density for either granin in the same endocrine cell population and even complete lack of the immunoreaction were recorded. The findings suggest that, despite the restricted presence in the endocrine pancreas of the reptiles investigated, the granins are relatively well conserved during phylogeny; they do not confirm, however, the previously accepted usefulness of the granin protein family as common markers of neuroendocrine cells.

Granin proteins (chromogranin A and secretogranin II C23-3 and C26-3) in the intestine of amphibians

The occurrence, distribution and possible cellular colocalizations of chromogranin A (CgA) and of two synthetic secretogranin II peptides (SgIIC23-3 and SgIIC26-3) with serotonin, somatostatin, neurotensin, pancreatic polypeptide and bombesin have been investigated immunohistochemically in the amphibian gut. CgA or SgIIC26-3-immunostained enterocytes were found throughout along the frog intestine, while no immunoreaction for any of the tested antisera against granins was seen in the same organ of newts. Variable amounts of serotonin-immunoreactive cells co-storing CgA or SgIIC26-3, but never both granins, were encountered in all intestinal segments of the frogs investigated. In addition, CgA was co-localized with somatostatin in a few endocrine cells of the frog (genus Rana) duodenum and small intestine. In the duodenum of another frog (genus Xenopus) several enterocytes co-stored SgIIC26-3 and neurotensin. Pancreatic polypeptide- and bombesin-immunoreactive cells, the latter detected only in the duodenum of Xenopus, did not contain and granin. The results suggest that, in spite of their relatively restricted occurrence in the intestine of frogs and even of their absence in that of newts, the granins are well conserved during phylogeny. On the other hand, the heterogeneous distributions of these anionic glycoproteins, related to the entero-endocrine cell types, make their previously assigned usefulness as markers of all neuro-endocrine cells unlikely.

Dopaminergic characteristics of isolated parietal cells from rats

Recently we have identified a dopamine-producing system in the gastric mucosa of rats. All the available morphological data suggest that parietal cells synthesize dopamine. In the present study we investigated the dopaminergic characteristics of isolated parietal cells by different methods. Mixed gastric mucosal cells were isolated and size-fractionated by elutriation. The proportion of neurons, parietal and endocrine cells in the fractions were determined by immunocytochemistry (ICC) using antibodies to neurofilament, proton pump and chromogranin A, respectively. No neurons were found in any of the cell preparations, while 56% parietal cell and 0.0% endocrine cell were achieved in the parietally enriched fraction. By Western blot, a tyrosine hydroxylase (TH, the rate-limiting enzyme of the catecholamine synthesis) immunoreactive protein species was demonstrated in isolated mucosal cells, comigrating with the TH immunoreactivity from PC12 cells. The TH immunoreactivity was colocalized to parietal cells by ICC. Dopamine transporter (DAT), a regulator of extracellular/intracellular dopamine balance in the nervous system, was also demonstrated in parietal cells. A significant amount of dopamine and DOPA were measured by HPLC (13.4 and 9.57 pg/10(6) cell, respectively) in parietally enriched cell fraction. Since this enriched cell fraction was virtually clear of both neurons and endocrine cells, demonstration of TH enzyme, DAT and dopamine in this fraction confirms that the parietal cell population might be a major source of dopamine in the rat stomach, supporting our previous results achieved using whole tissue samples.

Immunohistochemical localization of chromogranin A and B in the endocrine cells of the alimentary tract of the green frog, Rana esculenta

Novel monoclonal antibodies to human chromogranin A (CgA) and chromogranin B (CgB) were used to investigate the presence of immunoreactive (-IR) elements in the alimentary tract of the green frog Rana esculenta. Numerous CgA-IR and a few CgB-IR endocrine cells were found within the gut mucosa, from the oesophagus to the cloaca, with some local differences in density. Co-localization studies demonstrated that they were co-stored in almost all the serotonin-IR, the amylin-IR or islet amyloid polypeptide-IR cells and in the peptide tyrosine tyrosine-IR cells located proximal to the pylorus, but not in those located in more caudal tracts. No other co-localization was demonstrated; substances investigated included somatostatin, substance P, gastrin/cholecystokinin, glucagon, glycentin, bombesin, secretin and neurotensin. CgA-IR and CgB-IR cells nearly always displayed argyrophilia with the Grimelius silver method.

Immunohistochemical localization of insulin-like growth factor 1 and 2 in the endocrine pancreas of rat, dog, and man, and their coexistence with classical islet hormones

Immunohistochemical techniques were used to study the occurrence and distribution of insulin-like growth factor 1 (IGF-1) and IGF-2 in the pancreas of man, dog, and rat and their possible coexistence with insulin (INS), glucagon (GLUC), somatostatin (SOM) and pancreatic polypeptide (PP). All control experiments, including pre-absorption of the antisera with synthetic peptide hormones, indicated the specificity of the immunoreactions obtained. In all species investigated, IGF-2-immunoreactivity occurred exclusively in INS-immunoreactive cells as was found by the use of consecutive sections and double immunofluorescence on identical sections. In contrast, IGF-1-immunoreactivity co-existed with GLUC-immunoreactivity. In man, singular SOM-immunoreactive cells also contained IGF-1-immunoreactivity. Thus, IGF-1 and IGF-2 can be localized by means of immunohistochemistry in the mammalian pancreas, and can be shown to occur in different islet cell populations. It is presumed that IGF-1 derived from A-cells and/or D-cells acts on the B-cells in a paracrine manner. The co-existence of IGF-2-immunoreactivity and INS-immunoreactivity in the human, rat, and dog endocrine pancreas indicates that mammalian IGF-2 and INS genes are regulated simultaneously.

The primary structure of TE-6: a novel neuropeptide from the nematode Ascaris suum

Extensive immunoreactivity (IR) towards a hexapeptide (sequence KGQELE), which flanks the C-terminus of the pancreastatin sequence in rat chromogranin A (CGA), is found throughout the nervous system of the nematode parasite Ascaris suum. The peptide IR was purified from the gonoduct of the parasite and found to have the sequence TKQELE. This peptide, designated TE-6, has some C-terminal homology with several regions of the CGA molecule. However, TE-6 was the only peptide isolated suggesting that either the nematode does not possess CGA, or that the -ELE regions of parasite CGA-like peptides which would be larger than TE-6 are not accessible to the antiserum in RIA, or are not being successfully extracted from the parasite. The N-terminus of TE-6 has little homology with any of the sequences preceding -ELE regions in CGA. This, and the fact that the tissue from which TE-6 was isolated does not contain IR towards another, highly conserved, region of the CGA molecule (WE-14) suggests that TE-6 may belong to a new class of regulatory peptide unrelated to CGA.