Population Of Secretory Granules Research Articles

The USDA trypsin inhibitor study. III. Sequential development of pancreatic pathology in rats

Weanling male, Wistar rats (40 per diet) were maintained on 15 diets which provided 4 graded trypsin inhibitor (TI) levels (93, 215, 337, and 577 mg/100g diet) repeated at 3 levels of protein (10%, 20%, and 30%). Raw and heated (toasted) soy flour provided 10% protein in the diet, while casein was added to increase the protein level to 20% and 30%. Three diets containing only casein as the protein source, at 10%, 20%, and 30% were included. Histologic changes occurring in the pancreas were evaluated in approximately 5 rats from each diet at 3 month intervals, beginning at 6 months, for 22 months. Criteria for the diagnosis of the observed histologic changes in the pancreas are discussed. Ultrastructure of the endocrine cells in the gastrointestinal mucosa was also examined. Pancreatic acinar cell density, as determined morphometrically, was reduced throughout the study in rats fed the 577 mg TI/100 g diet, indicating hypertrophy at the cellular level. Nodular hyperplasia was observed in the first sacrifice group at 6 months. Incidence of the lesion was positively related to both time of exposure and level of dietary TI. Acinar adenoma was first observed at 18 months and was most prevalent in rats fed the highest concentration of TI. Endocrine cells of the duodenal mucosa which contain cholecystokinin (so-called ‘I’ cells) contained a denser population of secretory granules in animals fed the high TI diet compared with I cells from control animals, leading to the speculation that production and secretion of cytoplasmic hormones was increased in TI treated rats.

Nonconverted, amino acid analog-modified proinsulin stays in a Golgi-derived clathrin-coated membrane compartment.

The secretion of insulin by the pancreatic B-cell involves a passage of the newly synthetized (pro)insulin polypeptides across the Golgi apparatus, at the trans pole of which secretory proteins are released as a population of secretory granules characterized by a clathrinlike coat on segments of their limiting membrane. When the conversion of radiolabeled proinsulin to insulin was inhibited by replacing arginine and lysine with the aminoacid analogs, canavanine and thialysine, the nonconverted radioactive material remained associated with Golgi-derived, coated secretory granules. The coat was characterized as clathrin-containing by immunocytochemistry. Under analog treatment, the noncoated, storage secretory granules did not become markedly labeled during the pulse-chase experiment. These data are compatible with the hypothesis that in normal conditions, the maturation of the coated compartment into noncoated granules is linked to the effective conversion of the prohormone.

Immunocytochemical localization and determination of hormone-induced synthesis of the sulfated oviductal glycoproteins.

Secretory products of the oviduct provide part of the milieu for the critical events of fertilization and embryo development. Past work from this laboratory has indicated that three large sulfated glycoproteins can be isolated from rabbit oviductal fluid and are synthesized by oviductal epithelium incubated in vitro. These three glycoproteins are antigenically similar. This paper presents evidence for their localization within the oviductal tissue and their hormonal control of synthesis. Utilizing goat antiserum to these oviductal glycoproteins and the immunoglobulin-horseradish peroxidase bridge method, these macromolecules have been localized in the ampulla and isthmus of the oviduct. Ten days after ovariectomy an oviduct was removed for immunolocalization. The does were then given estradiol for the next 4 days and the second oviduct was removed. Oviducts treated with estradiol showed immunostaining of virtually all of the secretory granules within the secretory cells of the isthmus. While light level immunocytochemistry suggested the possibility of two populations of secretory granules within the ampulla because some of the granules did not show immunocytochemical staining, the more sensitive immunocytochemistry at the electron microscopic level showed staining of all granules of the ampulla and isthmus. Absorption of the antiserum with pure antigen prevented all staining. After ovariectomy and hormone withdrawal, most of the immunostaining was lost in the isthmus and virtually no staining in the ampulla was observed. Oviductal cell suspensions were made to evaluate incorporation of [35S] sulfate and [3H] leucine as a function of hormonal priming of the tissue. Estrogen-primed oviductal cells incorporated the sulfate and leucine into these specific glycoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory behavior and ultrastructural changes in mouse gallbladder principal cells after stimulation with cholinergic and adrenergic drugs: A morphometric study

Principal cells of mouse gallbladder epithelium were subjected to a quantitative electron microscope study after in vivo and in vitro exposure to pilocarpine, noradrenaline, atropine, and phenoxybenzamine. Stereologic measurements were performed on randomly selected principal cells, and special interest was paid to changes in the size of the secretory granule population of the cells. Thirty minutes after in vivo and in vitro stimulation with pilocarpine, there was a significant decrease of the volume density of the glycoprotein-containing granules in the principal cells. Thirty minutes after in vivo administration of the cholinergic antagonist atropine, a significant increase of this parameter was observed. In vitro incubation for 30 min with a combination of pilocarpine and atropine extinguished the pilocarpine-induced effect on the secretory granules. Noradrenaline and phenoxybenzamine (an α-adrenergic blocking agent) in vivo and in vitro (30 min) had no effect on the volume density of the secretory granules. The authors' findings suggest that principal cells of the mouse gallbladder epithelium exhibit an increased rate of secretion of glycoprotein granules after stimulation in vivo and in vitro with cholinergic agents, whereas adrenergic agents are without effect.

Interaction of vinblastine with the secretagogue action of db-cAMP in the rat exocrine pancreas

It has been shown that vinblastine (VB) potentiates the secretagogue action of dibutyryl cyclic adenosine-3′,5′-monophosphate (db-cAMP) in the rat exocrine pancreas. The present work determined the step of the secretory process involved in this potentiation. To this effect, rat pancreatic fragments were pulse-labelled with l-[U- 14C]leucine, then transferred to a chase medium. Intracellular transport of synthesized proteins from ribosomes into zymogen granules was followed by determining the specific radioactivity of proteins in subcellular fractions. Discharge of exportable proteins was studied either during the migration of proteins or after the initially synthesized proteins had reached the secretory granule population. These studies indicated that VB (5 × 10 −5 M) diminished the rate of transport of new synthesized proteins, but stimulated the db-cAMP (2 mM)-induced enzyme release by initiating the preferential discharge of old unlabelled proteins located around the acinar lumen.

Endocrine cells in the human fetal small intestine.

In this report we describe the time of appearance and ultrastructural features of enteroendocrine (EECs) in the human fetal small intestine (SB) between 9 and 22 weeks gestation. Thirteen distinctive EECs were identified in fetal SB. Two of these, not found in normal adult SB, appeared within the stratified epithelium of the proximal SB at 9--10 weeks. They were arbitrarily termed "primitive" and "precursor" cells. As in all fetal EECs, the pale cytoplasm of the "primitive" cell contains a distinctive population of secretory granules (SGs). Primitive cell SGs average 200-330 nm; some have dense cores with lucent halos while others are filled with a homogeneous dense or flocculent material. The SGs of the "precursor" cells are larger, averaging up to 1 micron in diameter and their contents vary in electron density. A third group of cells not described in normal adult SB was arbitrarily termed "transitional" cells. These have two populations of SGs; one resembles the SGs of the "precursor" cells, and the other resembles the SGs of some of the specific adult type EECs. Transitional EC, S, I and G cells are seen. In addition, mature appearing EC, S, G, I, L, D, and D1 cells were identified by 12 weeks of gestation. The "primitive", "precursor", and "transitional" cells may represent sequential developmental precursors of adult type EECs.

Human Fetal Pituitary in Culture: Hormone Secretion and Response to Somatostatin, Luteinizing Hormone Releasing Factor, Thyrotropin Releasing Factor and Dibutyryl Cyclic AMP

Human fetal pituitaries, 10 to 19 weeks gestation, were kept in organ or monolayer culture for up to 6 weeks. Light and electron microscopic investigation provided evidence that the morphology of the tissue was well maintained and that at least four epithelial cell types could be distinguished based on their secretory granule population. The levels of GH, LH, FSH, TSH, and PRL released into the media were determined by radioimmunoassay as a function of time in culture and gestational age. In general, the older the fetal pituitary the greater the trophic hormone secretion and the longer the release was sustained in vitro. The exception was TSH which reached undetectable levels within two weeks after initiation of the cultures regardless of the age of the fetus. Corticotrophic activity was detectable by bioassay from 11 weeks gestation. From 10 to 13 weeks gestation on, somatostatin (2 × 10−5 to 10−9M) inhibited GH secretion 14 to 78%, luteinizing hormone releasing factor (10−6 to 10−8M) stimulated LH and FSH secretion 2 to 4-fold and thyrotropin releasing factor (10−8M) increased TSH release 2 to 5-fold. DBcAMP (1 IDM) enhanced GH secretion at 13 weeks gestation and LH, FSH and PRL release by 15 weeks. The data suggest that the early gestation human fetal pituitary is capable of synthesizing, storing and secreting trophic hormones and that by 10 to 13 weeks gestation the gland is responsive to hypothalamic releasing and inhibitory factors as well.

The mucigenous glandular mucosa in the complex stomach of two new‐world camelids, the llama and guanaco

AbstractIn contrast to the so‐called true ruminants, the compartmentalized stomach of these camelids contained an extensive mucigenous glandular mucosa. This mucosal epithelium was studied with the light and electron microscope. Surface, foveolar, isthmic, and end‐piece regions were identified. Undifferentiated cells with many free ribosomes and few mucigen granules were found in the gland isthmus. More fully differentiated mucigenous cells with fewer free ribosomes, an extensive Golgi complex and a large heterogeneous population of secretory granules were observed in the subjacent end‐piece. These cells were compared with cardiac and other gastric glandular epithelia. The cells in the foveola contained a more extensive granular reticulum, a prominent Golgi complex, and large numbers of mucigen granules and mitochondria. In the upper foveolar cells, large supranuclear and narrow apical accumulations of mucigen granules were separated by an intervening mitochondrial mass. In the tall surface cells there was a diminution in the number of mucigen granules and a concomitant supranuclear massing of mitochondria. Basally, these cells were often separated by prominent intercellular spaces. Effete surface cells were also noted. These lacked desmosomal attachments and sometimes appeared partially extruded. These findings suggested that cells derived from the undifferentiated isthmic cells moved up the foveola and onto the luminal surface. During this migration, these cells appeared to undergo sequential cytologic differentiation. The possible functional significance of these differentiations was considered.