Release Of Secretory Products Research Articles

Biocompatibility of two different cured polyepoxy composites

Activation and release of secretory products by macrophages seem to depend upon the physical and chemical surface characteristics of the biomaterials. The authors have studied whether different levels of cure in carbon fiber reinforced epoxy resin composites were able to affect the macrophage adhesion, activation and O 2 − production. The results suggest that only macrophages cultured on partially-cured material (PCM) display the morphological characteristics of activated cells as well as the production of O 2 −.

La barrière placentaire : structure, résistance, asymétrie

The concept of placental barrier has been evaluated using recent advances in ultrastructure and in transport physiology. On a structural basis, the barrier effect is grounded by the syncytiotrophoblast continuity, and by basal and plasma membrane's electrical charges and by basement membrane porosity. The aqueous phase continuity for diffusion operates through intercellular gap, fenestrations (rat, rabbit) and transcellular channels (guinea pig). However, these connections are not apparent in the human syncytiotrophobast. For the molecular size selectivity, the hemochorial placentas with a pore radius of 10 nm appear much less selective than the epitheliochorial ones. The metabolic capacity of the placental cells (trophoblast, macrophages) participates to the barrier effect by metabolizing or by converting some substrates. Similarly, trophoblast asymmetry in the location of enzymes, carriers and receptors on outer (maternal side) and on basal (fetal side) plasma membranes, and in the release of secretory products, contributes to maintain separate fetal and maternal compartments. The functional polarity of trophoblast is expressed in metabolism (corticostéroids), nutrients (amino acids) and ions (iron) transport, and most of its secretions (hPL, hCG, SP1).

Roles of microfilaments in exocytosis: a new hypothesis.

We observed the dynamic changes in the localization of microfilaments during the exocytic secretion of rat parotid and submandibular gland acinar cells, and obtained results which led us to propose a new concept of microfilament function in exocytosis. With the electron microscopy, NBD-Phallacidin (NBD-PL) fluorescence technique and immunohistochemistry for myosin, microfilaments consisting of F-actin and myosin were localized mainly underneath the luminal plasma membrane. Microfilaments were not detectable around the secretory granules which were stored in the cytoplasm, but were clearly observed around them whose membranes were continuous with the luminal plasma membrane. When viewed with NBD-PL and myosin fluorescence, the area of fused granule membranes revealed bright fluorescence in association with the luminal border, so that the luminal membrane undergoing exocytosis appeared like a 'bunch of grapes'. When excess exocytosis was stimulated by isoproterenol (IPR), the number of individual 'grapes' increased dramatically, indicating that the secretory granules are surrounded by microfilaments after the fusion with the luminal membrane. Microfilaments thus continuously undercoat the luminal membrane during exocytosis although the exocytic process involves the dilation and subsequent reduction of the luminal membrane due to the addition and removal of secretory granule membranes. This reduction of the dilated luminal membrane following exocytosis was, however, inhibited when the microfilaments were disrupted by cytochalasin D. Following this treatment, the lumina was expanded extraordinarily and the secretory products remained in the enlarged lumina, showing that the release of secretory products is inhibited when the microfilament function is disturbed. These results indicate that 1) microfilaments are localized mainly underneath the luminal plasma membrane and act as an obstacle to exocytosis when cells are at the resting phase and 2) at the secretory phase microfilaments allow exocytosis by disorganizing their barrier system and then, by encircling the discharged secretory granule membranes, provide forces for the extrusion of secretory products through the action of the acto-myosin contractile system.

Distribution in the Macaque Pineal of Nerve Fibers Containing Immunoreactive Substance P, Vasopressin, Oxytocin, and Neurophysins

The distribution of nerve fibers containing immunoreactive substance P (SP), estrogen-stimulated neurophysin (ESN), nicotine-stimulated neurophysin (NSN), oxytocin (OT), and vasopressin (VP) was examined in the epithalamic area of adult male and female macaques. Perfused or immersion-fixed epithalamic tissues, sectioned, and mounted on glass slides were processed through the avidin-biotin immunofluorescence method. Fibers containing immunoreactive SP were observed in the pineal organ along the periphery, in the perivascular space, and dispersed between the pinealocytes. Fibers were often observed in the pineal stalk region, and the habenular nuclei had high concentration of immunoreactive SP. Immunoreactive ESN fibers were observed in the stria medullaris, in the lateral habenula, in the pineal stalk, and in the pineal organ. Within the pineal, fibers containing ESN were present in the perivascular space, often concentrated in the walls of blood vessels, but also dispersed between pineal cells. Fibers containing OT, NSN, and VP were also present in the macaque pineal, but in lower quantities compared with fibers containing ESN. These studies show that the pineal of subhuman primates contain nerve fibers (ESN, NSN, VP, OT) of possibly hypothalamic origin. It also has a rich supply of SP fibers, which might be of habenula origin, peripheral parasympathetic ganglia origin, or both. The functional significance of these peptidergic nerve fibers remains to be determined. However, there are indications that they might be involved in regulation of blood flow and release of secretory products from the pinealocytes.

Nonrandom positioning of Golgi apparatus in pancreatic B cells.

The Golgi apparatus has a polarized distribution in a variety of cell types, and in certain epithelia its intracellular position correlates with the direction of vectorial transport and release of secretory products. We have studied quantitatively the orientation of the Golgi apparatus in pancreatic islet B cells by examining its location with respect to the juxtacapillary face of the cell. This was done a) at the light microscope level on semithin sections of osmium-impregnated islets, and b) at the ultrastructural level on thin sections of intact pancreas. The data obtained with both methods show that in pancreatic B cells the Golgi apparatus is preferentially located in the position opposite to the juxtacapillary face of the cell. These results suggest a structural polarization of B cells, which may be important for the coordinate function of islets of Langerhans.

Concentration of amylase along its secretory pathway in the pancreatic acinar cell as revealed by high resolution immunocytochemistry.

The modified protein A-gold immunocytochemical technique was applied to the localization of amylase in rat pancreatic acinar cells. Due to the good ultrastructural preservation of the cellular organelles obtained on glutaraldehyde-fixed, osmium tetroxide-postfixed tissue, the labelling was detected with high resolution over the cisternae of the rough endoplasmic reticulum (RER), the Golgi apparatus, the condensing vacuoles, the immature 'pre-zymogen' granules, and the mature zymogen granules. Over the Golgi area, the labelling was present over the transitional elements of the endoplasmic reticulum, some of the smooth vesicular structures at the cis- and trans-faces and all the different Golgi cisternae. The acid phosphatase-positive rigid trans-cisternae as well as the coated vesicles were either negative or weakly labelled. Quantitative evaluations of the degree of labelling demonstrated an increasing intensity which progresses from the RER, through the Golgi, to the zymogen granules and have identified the sites where protein concentration occurs. The results obtained have thus demonstrated that amylase is processed through the conventional RER-Golgi-granule secretory pathway in the pancreatic acinar cells. In addition a concomitance has been found between some sites where protein concentration occurs: the trans-most Golgi cisternae, the condensing vacuoles, the pre- and the mature zymogen granules, and the presence of actin at the level of the limiting membranes of these same organelles as reported previously (Bendayan, 1983). This suggests that beside their possible role in transport and release of secretory products, contractile proteins may also be involved in the process of protein concentration.

8] Secretory membranes of the rat parotid gland: Preparation and comparative characterization

This chapter focuses on the secretory membranes of the rat parotid gland. The release of secretory products by exocytosis involves the specific interaction of secretion granule and apical plasma membranes, the focal rearrangement of bilayer structures in regions of contact, and eventual coalescence of the two membranes with direct extracellular deposition of secretory products. The chapter describes the preparation of a plasma membrane fraction containing the apical domain. The isolation procedure could partially preserve morphologically recognizable regions constituting the apical surface. Two important features of the procedure developed are (1) it selects for large sheets of membrane, and (2) hypoosmotic media are used at the outset, as in the case of plasma membrane purification from rat liver, so that osmotically sensitive organelles are either damaged or disrupted during homogenization. Because morphological appearance constitutes an important initial evaluation for the purity and integrity of isolated membranes containing distinct regions, aliquots of the fraction are fixed in aldehydes, postfixed in 1% osmium tetroxide, and prepared for microscopy according to standard procedures.

Effect of leukotriene C 4 on the release of secretory products by elicited populations of rat peritoneal macrophages

The experiments concerned the effect of stimulation by leukotriene C 4 (LTC 4) on secretory activity of rat peritoneal macrophage populations elicited by Freund's incomplete adjuvant (FIA.Mφ) or carrageenan (CAR.Mφ). Unstimulated FIA.Mφ produced less prostaglandin E 2 (PGE 2) and thromboxane B 2 (TxB 2), but more β-glucuronidase than CAR.Mφ. Following LTC 4 stimulation, enhancement of GUR was observed with concentrations lower than those necessary to increase PGE 2 release. PGE 2 and TxB 2 displayed opposite directional changes. LTC 4 and PGE 2 may interfere in modulating macrophage function.

The microtrabecular lattice of the adrenal medulla revealed by polyethylene glycol embedding and stereo electron microscopy

The microtrabecular lattice of the adrenal medulla revealed by polyethylene glycol embedding and stereo electron microscopy

Studies on Trifluoperazine Inhibition of Trichocyst Expansion and Secretion in Paramecium

The importance of Ca2+ ion in regulation of many cellular processes is well established, as is its role as the mediator of “stimulus-secretion coupling” in exocytic release of secretory products. However, while the Ca2+ requirement in many secretory systems is clear, its mode of action is not.To probe the site of Ca2+ action, we have employed the protozoan, Paramecium tetraurelia as a model secretory system. Secretion in Paramecium requires Ca2+ as well as specific components in both the plasma and secretory vesicle membranes that can be visualized in freeze fracture as organized intramembrane particle arrays. The fusion of plasma and secretory organelle membranes, and subsequent release of vesicle contents, is routinely elicited by exposure to picric acid, and stimulation results in synchronous release of hundreds of secretory products called trichocysts. A rise in cytoplasmic Ca2+ triggers release and expansion of the trichocysts. This is accompanied by a reordering of the trichocysts' paracrystalline matrix, transforming the 5 μm long organelle to a 20-40 μm long needle-like structure.

Identification and hormonal control of reproductive‐tract‐specific antigens present in rabbit oviductal fluid

AbstractUtilizing the intra‐abdominal flask technique to collect oviductal fluid, the presence of two or possibly three reproductive‐tract‐specific antigens have been observed in rabbit oviductal fluid. Two of these antigens may be accounted for by the two forms of uteroglobin. The other antigen has a molecular weight greater than 200,000 daltons and its concentration in oviductal fluid is under hormonal control. During pseudopregnancy (PSP), when progesterone concentrations are high, or upon progesterone administration, the concentration of this high molecular weight antigen doubles in oviductal fluid. This correlates well with the previously observed increase in release of secretory products from the oviductal epithelia.

Endocrine cells of the gastrointestinal tract: general aspects, ultrastructure and tumor pathology.

The endocrine-like cells scattered among epithelial cells of the gastrointestinal mucosa differ in several aspects from the cells concentrated in endocrine glands. In the latter, abundant sinusoidal capillaries are in close contact with endocrine cells, thus ensuring prompt and massive release of secretory products into blood; close contacts with nerve endings are also found, particularly in the islets of the dog and cat. In the gut, various amounts of connective tissue are interposed between the basal membrane of the glands or villi and blood capillaries or nerve endings. In particular, no special or preferential relationship is found between endocrine-type cells and underlying blood vessels, although some long-distance correspondance between pyloric G cells and fenestrated capillaries seems to occur. The differences of innervation and blood supply may help explain the failure of gastric A cells to respond to stimuli known to be active on pancreatic A cells.1,2

Effects of blinding on the ultrastructure of mouse pinealocytes with particular emphasis on the dense-cored vesicles.

The mammalian pineal is thought to produce an antigonadotropic principle under conditions of reduced photoperiod, constant darkness or blinding by optic enucleation. A number of previous studies on mammalina pineals have suggested that the dense-corde vesicles present in pinealocytes may represent morphological evidence of secretory activity. In the present study the ultrastructure of pinealocytes was studied in adult Charles River CD-1 mice blinded by optical enucleation. By one month following optic enucleation the mean number of dense-corde vesicles in the cytoplasm of pinealocytes adjacent to pericapillary spaces had significantly decreased by 55% when compared with intact controls, and remained at this low level at two months and six months. A relative increase in the proportion of large agranular vesicles and an increased number of large, irregular vacuoles was observed also in the pinealocytic polar processes of blinded mice. When compared to control mice the pinealocytic Golgi regions appeared to be hypertrophied in blinded mice. The apparent stimulation of pinealocytic organelles coupled with the observed decrease in dense-corde vesicles suggest an increased synthesis and release of secretory product.

Effects of isolation and transplantation of the corpus cardiacum on hormone release from its glandular cells after flight in Locusta migratoria. A quantitative electron microscopical study.

The glandular lobe of the corpus cardiacum (CC) of Locusta migratoria contains secretory cells and axon terminals. It is generally accepted that the glandular cells produce an adipokinetic hormone which stimulates the release of diglycerides from the fat body. The axon terminals are supposed to be involved in the regulation of the secretory activity of these cells. CC were transplanted into locust hosts. The secretory activity of the glandular cells and axons was studied in the transplants as well as the intact host CC. Quantitative electron microscopical examination of the glandular cells of the CC in animals both at rest and after flight shows that only in the host CC the secretory activity of the glandular cells is stimulated by flight, as indicated by an increase in the activity of the Golgi zones and in the number of exocytotic pits. In the axon terminals release of secretory products, indicated by synaptic vesicles and membrane indentations, is reduced as a result of the transplantation. It is concluded that the glandular cells need excitatory input from outside the CC for stimulation of their secretory activity. Furthermore, it is proposed that the transplanted glandular cells decrease the level of activity of the intact host cells by way of a negative feedback mechanism.

Biochemical observations on the formation of small noradrenergic vesicles in the splenic nerve of the dog

Splenic nerve terminals contain noradrenergic vesicles which can be classified as small and large on the basis of both morphological and biochemical experiments. The origin of the large vesicles is likely to be the cell body and they are probably supplied to the nerve terminals by axonal transport. The origin of the small noradrenergic vesicles is still obscure so we have tested, using centrifugation techniques, the hypothesis that they are formed from the large noradrenergic vesicles during secretory activity in the nerve endings. Normally the small noradrenergic vesicles in resting splenic nerve terminals contain very little dopamine β-hydroxylase activity, as distinct from the large vesicles. However, after stimulation in vitro of the perfused spleen there is an appreciable amount of the enzyme associated with the small particles. These newly formed small vesicles are able to concentrate exogenous noradrenaline and their formation is dependent upon release of secretory products from the large vesicles as shown by their absence if the splenic nerve of a spleen perfused with a Ca 2+ -free solution is stimulated. A balance sheet has been drawn up which suggests that membrane-bound dopamine β-hydroxylase lost from the large noradrenergic vesicles upon stimulation is almost quantitatively recovered in the small noradrenergic vesicles. It is suggested that at least three types of noradrenaline storage particles exist in splenic nerve terminals (i) large vesicles which contain noradrenaline and dopamine β-hydroxylase and that can give rise to (ii) small vesicles which also contain both constituents and, (iii) vesicles which are virtually devoid of dopamine β-hydroxylase activity but which can store noradrenaline and have an origin quite different from those of the other two types.

Incorporation of radioactive precursors into the membrane and contents of the neurosecretory granules of the rat neurohypophysis as a method of studying their fate.

Rat neural lobes have been separated into subcellular fractions by differential centrifugation at various times after an intracisternal injection of [35S]cysteine or [3H]choline. Both isotopes led to a rise and fall in the radioactivity of neurosecretory granules (NSG) which paralleled that found previously for the neurohypophysial hormones and the neurophysins. While the radioactivity of the NSGs resulting from [35S]cysteine injection was predominantly associated with granular contents, [3H]choline injections led to a preferential labelling of the granular membrane. There was no indication of a sequential movement of radioactivity from the NSG-membrane fraction into the microsomal fraction (containing the so-called small vesicles) which might be expected if granular membrane were recaptured as small vesicles after release of secretory product by exocytosis. When release was stimulated in injected animals by giving them 2% NaCl solution to drink, 35S diappeared from the gland as expected, but 3H was retained and, moreover, appeared in the NSG-membrane fraction; results compatible with membrane conservation occurring by recapture of large vesicles. There was an indication that some of the neurophysin in the NSG was membrane-bound and that this too was retained after release of the granular contents.

The release of secretory products from the corticotrophic cells of Salmo gairdneri in vitro.

During organ culture of the pituitary of Salmo gairdneri, the secretory granules of the ACTH cell migrate to the distal pole of the cell where they persist even over prolonged periods of culture. Electron microscope studies suggest that the granule contents are released from the cell and that the accumulated material is extracellular. Immunofluorescent studies demonstrate immunoreactive ACTH within the cell cytoplasm but none or little associated with the accumulated extracellular material. A dissociation between ACTH and the granule “matrix” at about the time of granule release is proposed.

Secretory surface phenomena in freeze-etched preparations of the adenohypophysial cells and neurosecretory fibers.

The freeze-etching technique was used in studies of cell surface phenomena during the release of secretory products from the adenohypophysis and from neurosecretory terminals of rats in which exocytosis had been stimulated by the administration of hypothalamic extracts (somatotrophs, thyrotrophs, gonadotrophs and mammotrophs) or severe hemorrhage (neurohypophysis). The observations suggest that secretory granules are extruded through an opening at the tip of a protrusion of the cellular surface. The protrusions seem to result from the abutting of secretory granules on the inner surface of the plasma membrane. These structural details revealed in freeze-etched preparations have not been seen previously in conventional micrographs of ultrathin sections and may provide a clue to the mechanism of secretion.

Effects of 5-Fluorouracil on Exocrine Glands I. Gland Weights in Mice Receiving Synthetic Polynucleotides

SummaryBody weights and weights of major salivary glands and pancreas of mice given sublethal doses of 5-FUR were studied after pilocarpine or poly A:U injection. Body weights showed a significant decrease during the first 5 days after 5-FUR alone, while in the same period the glandular weights increased in all 4 organs. Injections of pilocarpine prior to sacrifice abolished the increase in glandular weights in salivary glands, but the pancreas failed to respond. This increase in organ weight was thought to be due to the inability of the organs to release synthesized secretory products. An injection of poly A:U 24 hr prior to sacrifice produced a uniform release of secretory products during the recovery phase in all of the organs studied. Such effect was notably absent on day 5 when the 5-FUR effect was at a maxium. It is concluded that the introduction of synthetic poly A:U might improve the recovery processes following nucleotide insult, as well as trigger release mechanisms in a manner which is differe...

MORPHOLOGIC OBSERVATIONS CONCERNING THE RELEASE AND TRANSPORT OF SECRETORY PRODUCTS IN THE ADENOHYPOPHYSIS

The processes involved in the release of secretory products from the parenchymal cells and the movement of these products into the circulating blood were studied by electron microscopic observations on the adenohypophyses of virgin estrous rabbits. The released secretory products were found in the form of discrete granules, with or without a perigranular membrane, in intercellular spaces, between the plasma membrane and the parenchymal basement membrane, in the perivascular space, in the endothelial cytoplasm, and in the lumen of capillaries. Vesicles containing material which resembled that in the perivascular space were observed in endothelial cells. Interpretation of these observations has led to the proposal of the theory that secretory products of the adenohypophysis may be liberated from parenchymal cells in the following way: by fusion of the perigranular membrane with the plasma membrane (merocrine) or by the detachment of small processes containing secretory granules (“microapocrine”). It is further believed that the discharged products may be transported into circulation in three different manners: by diffusion of dissolved material through the fenestrated endothelium, by active transport of dissolved secretory products by the endothelial cells, or by active transport of intact secretory granules through the endothelial cytoplasm.