Coupling of the inositol 1,4,5-trisphosphate receptor and chromogranins A and B in secretory granules

The secretory granules of neuroendocrine cells which contain large amounts of Ca(2+) and chromogranins have been demonstrated to release Ca(2+) in response to inositol 1,4,5-trisphosphate (IP(3)). Moreover, chromogranin A (CGA) has been shown to interact with several secretory granule membrane proteins, including the IP(3) receptor (IP(3)R). To determine whether the IP(3)Rs interact directly with chromogranins A and B (CGB), two major proteins of the secretory granules, we have used purified IP(3)R from bovine cerebellum in the interaction study with CGA and CGB, and have shown that chromogranins A and B directly interact with the IP(3)R at the intravesicular pH 5.5. Immunogold cytochemical study using the IP(3)R and CGA antibodies indicated that IP(3)R-labeled gold particles were localized in the periphery of the secretory granules, indicating the presence of the IP(3)Rs on the secretory granule membrane. To determine whether the IP(3)R and chromogranins A and B are physically linked in the cells, bovine type 1 IP(3)R (IP(3)R-1) and CGA or CGB are co-transfected into COS-7 cells and co-immunoprecipitation was carried out. Immunoprecipitation of the cell extracts demonstrated the presence of CGA-IP(3)R-1 and CGB-IP(3)R-1 complexes, respectively, indicating the complex formation between the IP(3)R and chromogranins A and B in native state.     

Immunocytochemical localization of surfactant protein D (SP-D) in type II cells, Clara cells, and alveolar macrophages of rat lung.

We investigated the cellular and subcellular distribution of surfactant protein D (SP-D) by immunogold labeling in lungs of adult rats that had been given bovine serum albumin coupled to 5-nm gold (BSAG) for 2 hr to visualize the endocytotic pathway. Specific gold labeling for SP-D was found in alveolar Type II cells, Clara cells, and alveolar macrophages. In Type II cells abundant labeling was observed in the endoplasmic reticulum, whereas the Golgi complex and multivesicular bodies were labeled to a limited extent only. Lamellar bodies did not seem to contain SP-D. Gold labeling in alveolar macrophages was restricted to structures containing endocytosed BSAG. In Clara cells labeling was found in the endoplasmic reticulum, the Golgi complex, and was most prominent in granules present in the apical domain of the cell. Double labeling experiments with anti-surfactant protein A (SP-A) showed that both SP-A and SP-D were present in the same granules. However, SP-A was distributed throughout the granule contents, whereas SP-D was confined to the periphery of the granule. The Clara cell granules are considered secretory granules and not lysosomes, because they were not labeled for the lysosomal markers cathepsin D and LGP120, and they did not contain endocytosed BSAG.     

Immunoreactivities for chromogranin A and B,and secretogranin II in the guinea-pig endocrine pancreas

Summary The chromogranins are acidic proteins present in various endocrine cells and organs. They consist of chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). In the pancreas, these proteins or their breakdown products are possibly involved in the regulation of pancreatic hormone secretion. The guinea-pig endocrine pancreas was now investigated immunohistochemically for the presence of the chromogranins in five endocrine cell types. CgA is a regular constituent of insulin (B-), pancreatic polypeptide (PP-) and enterochromaffin (EC-) cells. In addition, a minority of somatostatin (D-) cells were immunoreactive for CgA. CgB immunoreactivities were very faint and exclusively observed in B-cells. SgII was found in B- and PP-cells; a faint immunostaining for SgII was also seen in a few glucagon (A-) cells. Typically, the densities of CgA or SgII immunoreactivities varied among the members of a given cell population, e.g. among individual B- or PP-cells. The present findings about the heterogeneities of immunoreactivities for the chromogranins are in line with findings obtained in pancreatic endocrine cells of other species. The true reasons for these heterogeneities are enigmatic. It seems probable, however, that the corresponding immunoreactivities depend on the intracellular processing of the chromogranins which in turn might be related to the metabolic state of endocrine cells. This has to be examined in future by experimental investigations.     

Topology of chromogranins in secretory granules of endocrine cells

Summary Chromogranins A and B are glycoproteins originally detected in the adrenal medulla. These proteins are also present in a variety of neuroendocrine cells. The subcellular distribution of the chromogranins, and particularly their intra-granular topology are of special interest with respect to their putative functions.Endocrine cells of the guinea pig adrenal medulla, pancreas and gastric mucosa were investigated immunoelectron microscopically for the subcellular distribution of both chromogranins. Out of 13 established endocrine cell types in all locations, only two endocrine cell types showed immunoreactivity for both chromogranin A and B, and eight endocrine cell types showed immunoreactivities only for chromogranin A. These immunoreactivities varied inter-cellularly. Three endocrine cell types were unreactive for the chromogranins. Moreover, some hormonally non-identified endocrine cells in the pancreas and the gastric mucosa also contained chromogranin A immunoreactivities.Subcellularly, chromogranin A or B were confined to secretory granules. In most endocrine cells, the secretory granules showed chromogranin immunoreactivities of varying densities. Furthermore, the intra-granular topology of chromogranin A or B in the secretory granules varied considerably: in some endocrine cell types, i.e. chromaffin-, gastrin- and enterochromaffin-like-cells, chromogranin A immunoreactivity was localized in the perigranular and/or dense core region of the secretory granules; in others, i.e. insulin-, pancreatic polypeptide-and bovine adrenal medulla dodecapeptide-cells, it was present preferentially in the electron-opaque centre of the secretory granules; chromogranin B immunoreactivity was localized preferentially in the perigranular region of the secretory granules of chromaffin cells and gastrin-cells. The inter-cellular and inter-granular variations of chromogranin A and B immunoreactivities point to differences in biosynthesis or processing of the chromogranins among endocrine cells and their secretory granules.     

Immunoreactivities for chromogranin A and B, and secretogranin II in the guinea-pig endocrine pancreas

The chromogranins are acidic proteins present in various endocrine cells and organs. They consist of chromogranin A (CgA), chromogranin B (CgB) and secretogranin II (SgII). In the pancreas, these proteins or their breakdown products are possibly involved in the regulation of pancreatic hormone secretion. The guinea-pig endocrine pancreas was now investigated immunohistochemically for the presence of the chromogranins in five endocrine cell types. CgA is a regular constituent of insulin (B-), pancreatic polypeptide (PP-) and enterochromaffin (EC-) cells. In addition, a minority of somatostatin (D-) cells were immunoreactive for CgA. CgB immunoreactivities were very faint and exclusively observed in B-cells. SgII was found in B- and PP-cells; a faint immunostaining for SgII was also seen in a few glucagon (A-) cells. Typically, the densities of CgA or SgII immunoreactivities varied among the members of a given cell population, e.g. among individual B- or PP-cells. The present findings about the heterogeneities of immunoreactivities for the chromogranins are in line with findings obtained in pancreatic endocrine cells of other species. The true reasons for these heterogeneities are enigmatic. It seems probable, however, that the corresponding immunoreactivities depend on the intracellular processing of the chromogranins which in turn might be related to the metabolic state of endocrine cells. This has to be examined in future by experimental investigations.     

Topology of chromogranins in secretory granules of endocrine cells.

Chromogranins A and B are glycoproteins originally detected in the adrenal medulla. These proteins are also present in a variety of neuroendocrine cells. The subcellular distribution of the chromogranins, and particularly their intra-granular topology are of special interest with respect to their putative functions. Endocrine cells of the guinea pig adrenal medulla, pancreas and gastric mucosa were investigated immunoelectron microscopically for the subcellular distribution of both chromogranins. Out of 13 established endocrine cell types in all locations, only two endocrine cell types showed immunoreactivity for both chromogranin A and B, and eight endocrine cell types showed immunoreactivities only for chromogranin A. These immunoreactivities varied inter-cellularly. Three endocrine cell types were unreactive for the chromogranins. Moreover, some hormonally non-identified endocrine cells in the pancreas and the gastric mucosa also contained chromogranin A immunoreactivities. Subcellularly, chromogranin A or B were confined to secretory granules. In most endocrine cells, the secretory granules showed chromogranin immunoreactivities of varying densities. Furthermore, the intra-granular topology of chromogranin A or B in the secretory granules varied considerably: in some endocrine cell types, i.e. chromaffin-, gastrin- and enterochromaffin-like-cells, chromogranin A immunoreactivity was localized in the perigranular and/or dense core region of the secretory granules; in others, i.e. insulin-, pancreatic polypeptide- and bovine adrenal medulla dodecapeptide-cells, it was present preferentially in the electron-opaque centre of the secretory granules; chromogranin B immunoreactivity was localized preferentially in the perigranular region of the secretory granules of chromaffin cells and gastrin-cells. The inter-cellular and inter-granular variations of chromogranin A and B immunoreactivities point to differences in biosynthesis or processing of the chromogranins among endocrine cells and their secretory granules.     

Chromogranin A, B and C immunoreactivities of mammalian endocrine cells. Distribution, distinction from costored hormones/prohormones and relationship with the argyrophil component of secretory granules

Antibodies specific for chromogranin A, B or C have been used to detect immunohistochemically these three anionic proteins. Pancreatic A, B and PP cells, gut argentaffin EC, argyrophil ECL and gastrin G cells, thyroid C cells, parathyroid cells, adrenal medullary cells, pituitary TSH, FSH and LH cells as well as some axons of visceral nerves have been found to react with chromogranin A antibodies. Pancreatic A, gut EC and G, adrenal medullary and pituitary cells as well as some gut nerve fibers showed chromogranin B immunoreactivity. Chromogranin C immunoreactivity has been detected in pancreatic A, pyloric D1, intestinal L, thyroid C, adrenal medullary and pituitary cells, as well as in some gut neurons and nerve fibers. No crossreactivity has been found in immunohistochemical tests between chromogranins A, B or C and costored monoamines or peptide hormones/prohormones, from which chromogranins can be separated by selective extraction during fixation. On both morphological and chemical grounds a relationship seems to exist between chromogranin A and Grimelius' argyrophilia. Sialooligosaccharide chains of chromogranin A and, possibly, chromogranins' phosphoserine/phosphothreonine groups, seem to interact with guanidyl, amino, and/or imidazole groups of non-chromogranin components to form silver complexing sites accounting for granules' argyrophilia, which can be removed or blocked without affecting chromogranin immunoreactivities. The abundant anionic groups of the three proteins should contribute substantially to granules' basophilia, the partly "masked" pattern of which supports the existence of a close interaction of such groups with other components of secretory granules, including monoamines and peptide hormones or prohormones. Chromogranins could play a r?le in hormone postranslational biosynthesis and intragranular packaging.     

Presence of chromogranin A, B and C in bovine endocrine and nervous tissues: a comparative immunohistochemical study

Summary Antisera against chromogranin A, B and C were used to study the distribution of these acidic proteins in bovine endocrine and nervous tissues. The three chromogranins occur together in several endocrine organs (adrenal medulla, anterior pituitary, endocrine pancreas) and in sympathetic ganglion cells. In the posterior pituitary, only chromogranin C and in the intermediate lobe only A and C are found. The parathyroid gland contains only A, and enterochromaffin cells are immunoreactive for A and B. Cells of the thyroid gland and some cells of the anterior pituitary apparently do not contain any chromogranins. It is concluded that the three chromogranins are not always stored together and that they are not present in all endocrine cells. This distinct localization of the chromogranins indicates some special, although still undiscovered, function for these proteins.     

Immunocytochemical localization of lysozyme and surfactant protein A in rat type II cells and extracellular surfactant forms.

Using immunogold labeling of fixed, cryosubstituted tissue sections, we compared the distribution of lysozyme, an oxidant-sensitive lamellar body protein, with that of surfactant protein A (SP-A) in rat Type II cells, extracellular surfactant forms, and alveolar macrophages. Morphometric analysis of gold particle distribution revealed that lysozyme and SP-A were present throughout the secretory and endosomal pathways of Type II cells, with prominent localization of lysozyme in the peripheral compartment of lamellar bodies. All extracellular surfactant forms were labeled for both proteins with preferential labeling of tubular myelin and unilamellar vesicles. Labeling of tubular myelin for SP-A was striking when compared with that of lamellar bodies and other extracellular surfactant forms. Lamellar body-like forms and multilamellar structures were uniformly labeled for lysozyme, suggesting that this protein is rapidly redistributed within these forms after secretion of lysozyme-laden lamellar bodies. By contrast, increased labeling for SP-A was observed over peripheral membranes of lamellar body-like forms and multilamellar structures, apparently reflecting progressive SP-A enrichment of these membranes during tubular myelin formation. The results indicate that lysozyme is an integral component of the lamellar body peripheral compartment and secreted surfactant membranes, and support the concept that lysozyme may participate in the structural organization of lung surfactant.     

Chromogranin peptides in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder which primarily affects motor neurons. Eight cases of ALS and seven control cases were studied with semiquantitative immunocytochemistry for chromogranin A, chromogranin B and secretogranin II that are soluble constituents of large dense core vesicles, synaptophysin as a membrane protein of small synaptic vesicles and superoxide dismutase 1. Among the chromogranin peptides, the number and staining intensity of motor neurons was highest for chromogranin A. In ALS, the staining intensity for chromogranin peptides and synaptophysin was significantly lower in the ventral horn of ALS patients due to a loss in immunoreactive motor neurons, varicose fibers and varicosities. For all chromogranins, the remaining motor neurons displayed a characteristic staining pattern consisting of an intracellular accumulation of immunoreactivity with a high staining intensity. Confocal microscopy of motor neurons revealed that superoxide dismutase 1-immunopositive intracellular aggregates also contained chromogranin A, chromogranin B and secretogranin II. These findings indicate that there is a loss of small and large dense core vesicles in presynaptic terminals. The intracellular co-occurrence of superoxide dismutase 1 and chromogranins may suggest a functional interaction between these proteins. This study should prompt further experiments to elucidate the role of chromogranins in ALS patients.     

In situ hybridization study of chromogranin A and B mRNA in carcinoid tumors.

The distribution of the mRNAs for chromogranin A and B was analyzed by in situ hybridization with 35S-labeled oligonucleotide probes in formalin-fixed paraffin-embedded carcinoid tumor tissues. All the 15 mid-gut carcinoid tumors examined contained both mRNAs for chromogranin A and B at high level in tumor cells. Sixteen of 18 bronchial carcinoid tumors but only 2 of 5 rectal carcinoid tumors expressed one or both species of chromogranin mRNAs. The same tendency was seen with the argyrophil reaction according to Grimelius where most of the mid-gut tumor cells were uniformly stained, while considerable variation in reactivity was seen in some of the bronchial and rectal carcinoid tumor cells. The sequential sections were stained with a monoclonal antibody against chromogranin A and a polyclonal antiserum which reacts with both chromogranins. The expression of the mRNA for chromogranin A on the carcinoid tumors was almost concordant with that of chromogranin B as well as with the chromogranin A protein, whereas almost all tumors stained positively with the polyclonal antibodies. Analyses of mRNA expression of chromogranin A before and after interferon therapy on 4 patients with mid-gut carcinoids indicated an inhibition at pre-translational level. In conclusion, the mRNAs for chromogranin A and B are good markers for the carcinoid tumors, especially of mid-gut origin. Fore-gut, mid-gut and rectal carcinoid tumors are different in their endocrine properties regarding the expression of the chromogranins.     

In situ hybridization study of chromogranin A and B mRNA in carcinoid tumors

Summary The distribution of the mRNAs for chromogranin A and B was analyzed by in situ hybridization with ³⁵S-labeled oligonucleotide probes in formalin-fixed paraffin-embedded carcinoid tumor tissues. All the 15 mid-gut carcinoid tumors examined contained both mRNAs for chromogranin A and B at high level in tumor cells. Sixteen of 18 bronchial carcinoid tumors but only 2 of 5 rectal carcinoid tumors expressed one or both species of chromogranin mRNAs. The same tendency was seen with the argyrophil reaction according to Grimelius where most of the mid-gut tumor cells were uniformly stained, while considerable variation in reactivity was seen in some of the bronchial and rectal carcinoid tumor cells. The sequential sections were stained with a monoclonal antibody against chromogranin A and a polyclonal antiserum which reacts with both chromogranins. The expression of the mRNA for chromogranin A on the carcinoid tumors was almost concordant with that of chromogranin B as well as with the chromogranin A protein, whereas almost all tumors stained positively with the polyclonal antibodies. Analyses of mRNA expression of chromogranin A before and after interferon therapy on 4 patients with mid-gut carcinoids indicated an inhibition at pre-translational level. In conclusion, the mRNAs for chromogranin A and B are good markers for the carcinoid tumors, especially of mid-gut origin. Fore-gut, mid-gut and rectal carcinoid tumors are different in their endocrine properties regarding the expression of the chromogranins.     

Stimulation of rat adrenal medulla can induce differential changes in the peptide and mRNA levels of chromogranins, neuropeptides and other constituents of chromaffin granules

The levels of various components of chromaffin granules were determined in rat adrenals after treatment with several stimulants. After reserpine the levels of calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and chromogranin B but not those of chromogranin A and secretogranin II were elevated. On the other hand, the mRNA of chromogranins A, B and secretogranin II were significantly increased. Treatment with oxotremorine or nicotine (multiple injections for 2 or 3 days) induced analogous changes for peptide and mRNA levels, however, the increases were smaller and for the mRNA less consistent. A single injection of oxotremorine or nicotine raised only the levels of CGRP and NPY and of the NPY mRNA whereas those of the chromogranins and their respective mRNAs remained unaltered. Amongst the membrane proteins only the levels of dopamine beta-hydroxylase are increased after prolonged stimulation, whereas those of cytochrome b-561, carboxypeptidase H and synaptin/synaptophysin (SYN) remain unaltered. Thus, the biosynthesis of chromaffin granules can be regulated in quite sophisticated patterns.     

Functional coupling of chromogranin with the inositol 1,4,5-trisphosphate receptor shapes calcium signaling

Chromogranins A and B are high capacity, low affinity calcium (Ca(2+)) storage proteins that bind to the inositol 1,4,5-trisphosphate-gated receptor (InsP(3) R). Although most commonly associated with secretory granules of neuroendocrine cells, chromogranins have also been found in the lumen of the endoplasmic reticulum (ER) of many cell types. To investigate the functional consequences of the interaction between the InsP(3) R and the chromogranins, we disrupted the interaction between the two proteins by adding a chromogranin fragment, which competed with chromogranin for its binding site on the InsP(3)R. Responses were monitored at the single channel level and in intact cells. When using InsP(3) R type I incorporated into planar lipid bilayers and activated by cytoplasmic InsP(3) and luminal chromogranin, the addition of the fragment reversed the enhancing effect of chromogranin. Moreover, the expression of the fragment in the ER of neuronally differentiated PC12 cells attenuated agonist-induced intracellular Ca(2+) signaling. These results show that the InsP(3)R/chromogranin interaction amplifies Ca(2+) release from the ER and that chromogranin is an essential component of this intracellular channel complex.     

Immunological characterization of chromogranins A and B and secretogranin II in the bovine pancreatic islet

Summary Antisera against chromogranin A and B and secretogranin II were used for analysing the bovine pancreas by immunoblotting and immunohistochemistry. All three antigens were found in extracts of fetal pancreas by one dimensional immunoblotting. A comparison with the soluble proteins of chromaffin granules revealed that in adrenal medulla and in pancreas antigens which migrated identically in electrophoresis were present. In immunohistochemistry, chromogranin A was found in all pancreatic endocrine cell types with the exception of most pancreatic polypeptide-(PP-) producing cells. For chromogranin B, only a faint immunostaining was obtained. For secretorgranin II, A-and B-cells were faintly positive, whereas the majority of PP-cells exhibited a strong immunostaining for this antigen. These results establish that chromogranins A and B and secretogranin II are present in the endocrine pancreas, but that they exhibit a distinct cellular localization.     

Immunological characterization of chromogranins A and B and secretogranin II in the bovine pancreatic islet

Antisera against chromogranin A and B and secretogranin II were used for analysing the bovine pancreas by immunoblotting and immunohistochemistry. All three antigens were found in extracts of fetal pancreas by one dimensional immunoblotting. A comparison with the soluble proteins of chromaffin granules revealed that in adrenal medulla and in pancreas antigens which migrated identically in electrophoresis were present. In immunohistochemistry, chromogranin A was found in all pancreatic endocrine cell types with the exception of most pancreatic polypeptide-(PP-) producing cells. For chromogranin B, only a faint immunostaining was obtained. For secretogranin II, A- and B-cells were faintly positive, whereas the majority of PP-cells exhibited a strong immunostaining for this antigen. These results establish that chromogranins A and B and secretogranin II are present in the endocrine pancreas, but that they exhibit a distinct cellular localization.     

Immunocytochemical localization of the major surfactant apoproteins in type II cells, Clara cells, and alveolar macrophages of rat lung

The adsorptive properties of phospholipids of pulmonary surfactant are markedly influenced by the presence of three related proteins (26-38 KD, reduced) found in purified surfactant. Whether these proteins are pre-assembled with lipids before secretion is uncertain but would be expected for a lipoprotein secretion. We performed indirect immunocytochemistry on frozen thin sections of rat lung to identify cells and intracellular organelles that contain these proteins. The three proteins, purified from lavaged surfactant, were used to generate antisera in rabbits. Immunoblotting of rat surfactant showed that the IgG reacted with the three proteins and a 55-60 KD band which may be a polymer of the lower MW species. Specific gold labeling occurred over alveolar type II cells, bronchiolar Clara cells, alveolar macrophages, and tubular myelin. In type II cells labeling occurred in synthetic organelles and lamellar bodies, which contain surfactant lipids. Lamellar body labeling was increased fivefold by pre-treating tissue sections with a detergent. Multivesicular bodies and some small apical vesicles in type II cells were also labeled. Secondary lysosomes of alveolar macrophages were immunoreactive. Labeling in Clara cells exceeded that of type II cells, with prominent labeling in secretory granules, Golgi apparatus, and endoplasmic reticulum. These observations clarify the organelles and pathways utilized in the elaboration of surfactant. After synthesis, the proteins move, probably via multivesicular bodies, to lamellar bodies. Both lipids and proteins are present in tubular myelin. Immunologically identical or closely similar proteins are synthesized by Clara cells and secreted from granules which appear not to contain lipid. The role of these proteins in bronchiolar function is unknown.     

Functional control of chromogranin A and B concentrations in the body of the rat stomach.

The chromogranins are soluble, acidic, proteins which are frequently co-stored in neuroendocrine cells with biogenic amines. In the gastric mucosa chromogranin A is localized to enterochromaffin-like cells which are the main source of histamine, and which are known to be regulated by circulating gastrin. We have used radioimmunoassays selective for the extreme C-terminal regions of chromogranin A and B to examine changes in gastric extracts following modulation of the gastric luminal contents. There were decreased concentrations of the two chromogranins in tissue extracts of rats after food withdrawal (which lowered plasma gastrin concentrations); inhibition of acid secretion with the H+/K(+)-ATPase inhibitor, omeprazole (which increased plasma gastrin concentrations) raised chromogranin A and B concentrations both in fasted rats, and in rats fed ad libitum. There was no evidence for altered patterns of posttranslational cleavage of chromogranin A or B with these treatments. The data indicate that chromogranin A and B concentrations in gastric ECL cells are regulated in parallel with histamine production, and are consistent with the idea that the chromogranins play a role in the formation and stabilization of the secretory granule involved in amine storage.     

Co-localization of secretogranins/chromogranins with thyrotropin and luteinizing hormone in secretory granules of cow anterior pituitary

We investigated the co-localization in secretory granules of secretogranins/chromogranins, thyrotropin, and luteinizing hormone in ultra-thin frozen sections of cow anterior pituitary by double immunoelectron microscopy, using specific antibodies and protein A-gold particles of different sizes. The distribution of secretogranin II, chromogranin A, and chromogranin B (secretogranin I) was largely similar. In cells containing secretory granules of relatively small size (100-300 nm) and low electron density (identified as thyrotrophs and gonadotrophs by immunolabeling for the respective hormone) and in cells containing both small (170-250 nm) and large (300-500 nm) secretory granules of low electron density (also identified as gonadotrophs), all three secretogranins/chromogranins were detected in most if not all granules, being co-localized with the hormone. In cells containing both relatively large (400-550 nm), electron-dense granules and small, less electron-dense secretory granules (150-300 nm), identified as somatomammotrophs by double immunolabeling for growth hormone and prolactin, all three secretogranins/chromogranins were predominantly detected in the subpopulation of small, less electron-dense granules containing neither growth hormone nor prolactin. Interestingly, this granule subpopulation of somatomammotrophs was also immunoreactive for thyrotropin and luteinizing hormone. These data show that somatomammotrophs of cow anterior pituitary are highly multihormonal, in that the same cell can produce and store in secretory granules up to four different hormones and, in addition, the three secretogranins/chromogranins. Moreover, selective localization of the secretogranins/chromogranins together with thyrotropin and luteinizing hormone in a subpopulation of secretory granules of somatomammotrophs indicates the preferential co-packaging of the secretogranins/chromogranins and these hormones during secretory granule formation.     

Chromogranins A and B and secretogranin II in hormonally identified endocrine cells of the gut and the pancreas

Chromogranins A and B and secretogranin II have been localized in a wide spectrum of gastroenteropancreatic endocrine/paracrine cells. Chromogranin A immunoreactivity showed the widest distribution and was displayed by glucagon-, PP-, gastrin-, gastrin-CCK-, secretin-immunoreactive cells, the most intense stainings being peculiar of enterochromaffin cells. Chromogranin B immunoreactivity was detected in gastrin- and glucagon cells and in some enterochromaffin cells containing also chromogranin A. Secretogranin II was paired to chromogranin A in glucagon cells of pancreatic islets or occurred alone in glycentin/PP cells of colonic mucosa. Neither of the chromogranins nor secretogranin II have been so far detected in somatostatin-, GIP-, or motilin-immunoreactive cells. Chromogranin A but not chromogranin B or secretogranin II has been detected in the gastric argyrophilic ECL cells.