Immature Secretory Granules Research Articles

Morphological changes in prolactin cells of male rats after testosterone administration.

Intact and castrated 25- and 60-day-old male rats were given 200 mug of testosterone propionate (TP) daily for 15 consecutive days. The morphology of the prolactin (PRL) cells was examined by electron microscopy and analyzed by the point counting method of Weibel and Bolender (23). The PRL cells in the controls had long cytoplasmic processes that coursed between adjacent parenchymal cells. The Golgi complex was relatively small in these cells and the area occupied by the secretory granules was, in general, less than in the TP-treated animals. After TP administration, the cells became more ovoid and the Golgi complex enlarged, displaying dilated cisternae and many immature secretory granules. In addition, the diameter of the secretory granules was greater in the animals given the steroid. When the morphology of the PRL cells in the sexually immature control rats was compared to that observed in the older, sexually mature rats, relatively few differences were observed indicating that the response to TP was essentially the same in animals of both age groups. The concentration of PRL was measured in the serum and pituitary gland by radioimmunoassay. There was a significant elevation in PRL in both the serum and pituitary glands of all animals given TP. In contrast, castration led to a fall in PRL levels. From these observations and from the morphological data it can be concluded that TP is capable of stimulating the rate of PRL synthesis and release, and that testosterone may have a regulatory role in PRL biosynthesis and turnover in the male rat.

Cations in the rat pars distalis ultrastructural localization.

Pituitary glands of female Sprague Dawley rats were fixed using the potassium pyroantimonate-osmium tetroxide technique by immersion or vascular perfusion. Both fixation procedures resulted in similar patterns of cation localization visualized as electron-dense precipitate within cells of the pars distalis. Nuclei were prominent sites of localization. Cytoplasmic precipitate occurred in association with the endoplasmic reticulum, typically within the cisternal spaces, and also was localized within the mitochondrial matrix and cristae, as well as Golgi membranes, small Golgi-associated vesicles, and multivesicular bodies. Immature secretory granules often contained precipitate between the core material of the granule and the enclosing smooth membrane. Frequently small antimonate-containing vesicles bordered the immature secretory granules. Precipitate was variable in secretory granules of more mature appearance although precipitate was apparent occasionally just within a granule's enclosing membrane. Granules closest to the plasma membrane often contained increased amounts of precipitate and small vesicles containing precipitate were observed fusing with them. Instances of granule release by emiocytosis often revealed a clustering of precipitate behind the core material away from the emiocytotic stoma, as well as at the stoma, and frequently an increased electron density of filamentous material radiating from the granules' enclosing membranes or from the adjacent plasma membrane. Exposure of section material to the chelating agents EGTA and EDTA indicate that calcium is the primary cation localized within the cytoplasm of these secretory cells. These findings are consistent with a role for calcium as a facilitator in the processes of transport and release of secretory granules.

Corticotroph cells in primary cultures of rat adenohypophysis: A light and electron microscopic immunocytochemical study

Monolayer cultures of trypsin-dispersed cells of the rat adenohypophysis were grown for 5 to 54 days. ACTH was localized by immunocytochemistry using an antiserum to synthetic ACTH1-28 prepared in rabbit and sheep anti-goat immunoglobulin coupled with peroxidase. ACTH content of the culture medium was measured by radioimmunoassay. Corttion time. The corticotrophs retained their essential morphological characteristics. Immunological staining was found in the secretory granules, some tubular or saccular structures, parts of the rough endoplasmic reticulum, and the cytoplasmic matrix. Immature secretory granules in the Golgi apparatus as well as some Golgi elements showed different degrees of immunoreactivity. In agreement with the high ACTH content of the culture medium the number, size and shape of the secretory granules, the active Golgi apparatus, the high amount of extragranular ACTH as well as pictures suggesting granule extrusion claim for a high ACTH synthesis and transport (and low ACTH storage) in the cultured corticotrophs.

Fine Structure of the Pancreatic Islets in Domestic Fowl with Special Reference to the Cell Type and Secretion

The pancreatic islets of domestic fowl were investigated by electron microscope. The following results were obtained. 1. The A islet is composed of a great many A cells and a few D cells. It also contained only a few B cells which are situated mainly along capillaries. 2. On the contrary, the B islet is composed of a great many B cells and a few D cells. It also contained only a few A cells in its periphary. 3. Immature secretory granules within the Golgi complex are almost the same in size, shape and density among the three types of islet cells. Since there are quite distinct differences in these properties of mature secretory granules in the cytoplasm among the three types of islet cells, there may be a difference in the mode of maturation process among the three. 4. These granules are released from the three types of islet cells through a mechanism termed as emiocytosis.

Fine structure of Langerhans' islet cells in a marine teleost Conger japonicus Bleeker

The Langerhans' islets of a marine fish, Conger japonicus, were studied by light and electron microscopy. The islets are scattered in the exocrine tissue, which is compact (tetrapodlike). The endocrine tissue does not form principal islets (Brockmann bodies). Four kinds of islet cells are found, and they are regularly arranged in the islets. In the periphery of the islets, there are in several layers of A cells; electron microscopically, their secretory granules are spherical (500–750 nm), with an oval core of moderate density, a smooth limiting membrane, and a clear narrow halo between the two. Centrally to the A cells, there are several B-cell layers, containing scattered argyrophile D cells. Electron microscopically the β-granules (500–750 nm) consist of a smooth limiting membrane and a dense round core with a narrow halo; the δ-granules are somewhat smaller (300–400 nm), with flocculent or fine granular material of low density within a smooth limiting membrane and an indistinct halo. The fourth type of cell occupies the central part of the islets, appearing as clear cell masses under the light microscope. Ultrastructurally, its secretory granules (500–750 nm) contain flocculent material of lower density within a somewhat irregular limiting membrane. Since immature secretory granules are frequently found within the Golgi area, it is considered that this fourth cell type also has secretory activity and that it may produce a hormone different from those of the other cell types.

Zur Ultrastruktur der Hypophysenadenome beim Cushing-Syndrom nach Adrenalektomie

Four pituitary tumors of patients adrenalectomized for bilateral adrenal hyperplasia with Cushing's syndrome 4–12 years before, were classified histologically as mucoid cell adenomas. Histochemically the tumor cells reacted like normal ACTH cells. The ultrastructure showed cells with multipolar outlines tending to surround other cells, large Golgi complexes, many immature secretory granules, a lot of mature granules with perigranular membranes and 200–600mµ in diameter, scattered particles of endoplasmic reticulum, a great abundance of ribosomes, pleomorphic mitochondria, a few small accumulations of fine filaments, and moderate pleomorphism of the nuclei with distinct nucleoli and sporadically cytoplasmic invaginations. It can be assumed that these adenomas developed from hyperplasias of ACTH cells. In all cases elevated levels of ACTH had been found in the plasma.

Radioautographic analysis of the secretory process in the parotid acinar cell of the rabbit.

Intracellular transport of secretory proteins has been studied in the parotid to examine this process in an exocrine gland other than the pancreas and to explore a possible source of less degraded membranes than obtainable from the latter gland. Rabbit parotids were chosen on the basis of size (2-2.5 g per animal), ease of surgical removal, and amylase concentration. Sites of synthesis, rates of intracellular transport, and sites of packaging and storage of newly synthesized secretory proteins were determined radioautographically by using an in vitro system of dissected lobules capable of linear amino acid incorporation for 10 hr with satisfactory preservation of cellular fine structure. Adequate fixation of the tissue with minimal binding of unincorporated labeled amino acids was obtained by using 10% formaldehyde-0.175 M phosphate buffer (pH 7.2) as primary fixative. Pulse labeling with leucine-(3)H, followed by a chase incubation, showed that the label is initially located (chase: 1-6 min) over the rough endoplasmic reticulum (RER) and subsequently moves as a wave through the Golgi complex (chase: 16-36 min), condensing vacuoles (chase: 36-56 min), immature granules (chase: 56-116 min), and finally mature storage granules (chase: 116-356 min). Distinguishing features of the parotid transport apparatus are: low frequency of RER-Golgi transitional elements, close association of condensing vacuoles with the exit side of Golgi stacks, and recognizable immature secretory granules. Intracelular processing of secretory proteins is similar to that already found in the pancreas, except that the rate is slower and the storage is more prolonged.

The ultrastructure of the insunk epithelium lining the planarian pharyngeal cavity

The insunk epithelium lining the planarian pharyngeal cavity has been studied by electron microscopy. The epithelial cells consist of cell bodies sunken into the connective tissue and of outer halves forming an epithelial cytoplasmic lining. The epithelial cell is regarded as one type of apocrine gland cell which contains secretory granules of characteristic structure. The immature secretory granule of primary form is an aggregation of small dense particles which have been made up by agglutination of a substance accumulated within the Golgi cisternae. The definitive form of the granule is composed of a peripheral concentric array of filamentous crystals and of a central homogeneous area. Both parts are built up by linear linkage and by dissolution of the dense particles, respectively. The secretory granules are dissolved in the apical cytoplasm and discharged into the pharyngeal cavity as an amorphous secretory product. The possible metabolic advantage in insunk epithelia is discussed.

Electron Microscope Studies on the Gastric Mucosa of Normal Rats

The mucous membrane of the glandular stomach of rats fixed in one percent osmium tetroxide was observed with the electron microscope.1. The body chief cell can be identified by the presence of abundant endoplasmic reticulum and secretory granules and vacuoles, which are almost transparent to the electron beam. Presumable transitions may be observed, among the inclusions mentioned above. The typical GOLGI apparatus is located at the supranuclear region, and long filamentous mitchondria are numerous at the cell periphery.2. The parietal cell is characterized by the position of the cell, the presence of intracellular secretory capillaries and a multitude of large mitochondria; which are nothing but the so-called oxyntic granules, in which unusually close packing of cristae mitochondriales is recognized. No typical GOLGI apparatus is observed, and the rough surfaced endplasmic reticulum is scanty. Vesicles of the smooth surfaced endosplasmic reticulum, however, are richly contained throughout the cytoplasm. The intracellular capillary is provided with remarkable microvilli. From the free surface into lumen, extend a huge protoplasmic protrusion, which is of fine granular texture of almost homogeneous appearance and contains no mitochondrion. This figure may suggest a possibility of the presence of apocrine secretion in this cell.3. The mucous neck cell may be distinguished from other cells by the irregularity of nuclear outline and the density of secretory granules, which is higher than those of body chief cells but lower than those of surface epithelial cells. The well developed GOLGI apparatus is situated among the secretory granules, to which the apparatus is often applied closely. Sometimes small granules similar in density to secretory granules are observed within the GOLGI area, suggesting an intimate relationship between the GOLGI apparatus and the mucus production. Endplasmic reticulum of the rough surfaced type and long filamentous mitochondria are repelled to the peripheral parts of the cell.4. In the above cell types, i. e., the body chief, parietal and mucous neck cells, a peculiar behaviour of mitochondria was noted. Namely, mitochondria are often attached to the lateral plasma membrane at a thickened part shortly beneath the terminal bar.5. The argyrophile cell (basal clear cell) contains small specific granules and fat droplets. Mitochondria of this cell are extremly slender. The GOLGI apparatus and rough surfaced endoplasmic reticulum are less developed in this cell type.6. The surface epithelial cell shows a characteristic accumulation of dense secretory granules of somewhat irregular outline at the apical end of the cell. This cell always contains well developed GOLGI apparatus, within which spherical granules of various sizes considered as probable forms of immature secretory granules are contained. Small dense particles presumable to contain the ribonucleoprotein are abundant in this cell. Remarkable foldings of lateral intercelllular boundary, the interdigitations, are observed.