Release Of Secretory Material Research Articles

Fine ultrastructure of chromaffin granules in rat adrenal medulla indicative of a vesicle-mediated secretory process

Observation by transmission electron microscopy, coupled with morphometric analysis and estimation procedure, revealed unique ultrastructural features in 25.94% of noradrenaline (NA)-containing granules and 16.85% of adrenaline (A)-containing granules in the rat adrenal medulla. These consisted of evaginations of the granule limiting membrane to form budding structures having different morphology and extension. In 14.8% of NA granules and 12.0% of A granules, outpouches were relatively short, looked like small blebs emerging from the granule surface and generally contained electron-dense material. A proportion of 11.2% of NA granules and 4.9% of A granules revealed the most striking ultrastructural features. These secretory organelles presented thin, elongated, tail-like or stem-like appendages, which were variably filled by chromaffin substance and terminated with spherical expansions of different electron density. A cohort of vesicles of variable size (30-150 nm in diameter) and content was found either close to them or in the intergranular cytosol. Examination of adrenal medullary cells fixed by zinc iodide-osmium tetroxide (ZIO) revealed fine electron dense precipitates in chromaffin granules, budding structures as well as cytoplasmic vesicles. These data indicate that a common constituent is revealed by the ZIO histochemical reaction in chromaffin cells. As catecholic compounds are the main tissue targets of ZIO complexes, catecholamines are good candidates to be responsible for the observed ZIO reactivity. This study adds further to the hypothesis that release of secretory material from chromaffin granules may be accomplished by a vesiclular transport mechanism typical of piecemeal degranulation.

Apocrine secretory mechanism: recent findings and unresolved problems.

Cell secretion is an important physiological process that ensures smooth metabolic activities, tissue repair and growth and immunological functions in the body. It occurs when the intracellular secretory materials are released to the exterior; these may be in the form of lipids, protein or mucous and may travel through a duct system or via blood to reach the target organ. To date three types of secretory mechanisms have been characterized, they include apocrine, holocrine and exocytosis. Apocrine secretion occurs when the release of secretory materials is accompanied with loss of part of cytoplasm. The secretory materials may be contained in the secretory vesicles or dissolved in the cytoplasm that is lost during secretion. In holocrine secretion, the entire cell is secreted into the glandular lumen, and it is presumed that the intended secretory materials are contained in the cell cytoplasm. Exocytosis is the most commonly occurring type of secretion; here the secretory materials are contained in the secretory vesicles and released without loss of cytoplasm. Apocrine secretory mechanisms have not been properly discussed; for example the biochemical and physiological pathways that regulate apocrine secretory process are not clearly known. Similarly, the plasma membrane dynamics during apocrine secretion has not been researched. In other glands morphological features during apocrine secretion have not been documented. The current paper reviews what is known about apocrine secretion, recent findings and highlights on the unresolved areas for future research.

Seasonal variation in the secretory activity of the subcommissural organ (SCO) of reptiles

Seasonal variations in the secretory activity of the subcommissural organ (SCO) of snakes and turtles was studied by immunocytochemistry, lectins, and electron microscopy. In animals sacrificed in summer, immunoreactive material, mostly devoid of sialic acid, occupied the whole cytoplasm. Cells showed many distended cisternae of rough endoplasmic reticulum and secretory granules. In animals sacrificed in winter, patches of immunoreactive sialic acid-rich material occupied the apical cytoplasm. Cells lacked distended cisternae and the secretory granules formed clusters. These results suggest a decreased synthesis and release of secretory material in the SCO of lethargic reptiles.

The response of nucleus preoticus neurosecretory cells to ovarian pressure in the frog, Rana tigrina

Intraovarian pressure (IOP) of 5, 15, and 25 mm Hg was administered in the frog, Rana tigrina, and the response of the nucleus preopticus (NPO) pars magnocellularis was investigated with aldehyde fuchsin (AF) stain and immunocytochemical method using neurophysin (NP) antisera. The 5 mm Hg IOP treatment resulted in cell and cell nuclear hypertrophy ( P < 0.001); discrete signs of de novo synthesis of AF-positive and NP-immunoreactive material in the perikarya and remarkable increases in the number and size of “Herring bodies” in the processes were observed. Stimulatory response after 15 mm Hg IOP treatment was characterized by dramatic augmentation of the AF-positive and NP-immunoreactive material in the processes; the engorged and coalescing Herring bodies totally predominated the lateral preoptic area. IOP of 25 mm Hg resulted in extensive loss of secretory material; the processes revealed the presence of vacuoles indicative of the rapid anterograde transport of the neurosecretory material. Furthermore, the application of IOP seemed to promote the transport of NP-immunoreactive material toward the anterior preoptic area and amygdala pars medialis and the release of secretory material into the cerebrospinal fluid. No changes were observed in the NPO when treatment was preceded by the transection of ipsilateral dorsal spinal nerve roots or the spinal cord. The results suggest the existence of an afferent neural pathway from the ovary capable of conducting the stretch signals to the NPO and triggering the synthesis and release of neurohypophysial hormones.

Evidence for neurosecretory control of the optic gland in terrestrial pulmonates

The optic gland in terrestrial pulmonates secretes gonadotropic hormone. The present study investigates the fine structure of the optic gland to clarify the control of secretion. Animals used were the slug, Limax marginatus, and the snail, Euhadra peliomphala. The optic gland cell has a process and the cytoplasm is filled with large granules about 750–1300 nm in diameter with a thin corfex in L. marginatus and 800–1700 nm delimited by a thick peripheral layer in E. peliomphala. These gland cells are characterized by well-developed granular endoplasmic reticulum. Granule formation was seen in the region of the Golgi apparatus. During the breeding season, the medial neurosecretory cells of the brain are active in the production and release of secretory materials. Although no neurosecretory cell bodies occur in the tentacular ganglion, neurosecretory axons penetrate into the optic gland cells. Cobalt filling reveals that axons of the medial neurosecretory cells project to the tentacular ganglion, near the optic gland. These results suggest that the optic gland is controlled by a neurohormone originating from the medial neurosecretory cells of the brain.

Ultrastructure of the secretory response of male mouse submandibular gland granular tubules.

The organization and fine structure of granular convoluted tubule cells (GCT) from male mouse submandibular glands have been examined in controls and in animals injected with adrenergic and cholinergic secretagogues. Control submandibular glands exhibited a single population of GCT cells with numerous homogeneous granules filling the apical two-thirds of the cytoplasm. A zone of transition cells, exhibiting characteristics of both GCT and striated duct cells, was found between the agranular intercalated duct and GCT segments. These transition cells possessed apical granules of variable size as well as prominent basal striations. Dramatic changes in the morphology of GCT cells followed administration of the alpha-adrenergic agent, phenylephrine. The extensive degranulation involved formation of "secretory pools" of fused granules and release of secretory material into the lumen. The appearance of numerous smooth vesicles near luminal membranes suggested extensive membrane retrieval. Intracellular membrane-limited aggregates of membrane fragments suggested that much of the retrieved membrane was destined for degradation. Rough endoplasmic reticulum was highly dilated but there was no indication of increased size or activity of the Golgi complex. Ultrastructural evidence indicated that the secretory responses to isoproterenol, a beta-adrenergic agent, and to pilocarpine, a cholinergic agent, were much more modest, but it is clear that some secretory response to these agents does occur. The other cell types of the duct and tubule system did not exhibit comparable morphological changes in response to the agents used.

Morphological and biochemical changes in mucous cells of the murine sublingual salivary gland during the carbamylcholine-induced secretory cycle

Changes in these cells have been evaluated over 6 h following cholinergic stimulation. Carbamylcholine administration resulted in the release of almost 50 per cent of secretory material within 15 min, which caused a reduction of 33 per cent in cell size. After 2 h the cells were depleted of secretory material. However, in the second hour the release of secretory material was accompanied by an enlargement of the nucleus, Golgi complexes and rough endoplasmic reticulum (RER), which suggests an elevation of biosynthetic activity. The enlargement of the RER was not the result of an increase in RNA, i.e. in the number of ribosomes, but of dilatation of its cisternal spaces. Before release took place, there was a continuous coalescence of secretory granules. After this extensive fusion, which is probably the result of an altered physiological state of the granule membrane and subsequent water uptake caused by cholinergic stimulation, the viscous mucins could be squeezed out, water transport is likely to assist in this ejection. Refilling of the mucous cells was almost complete within 6 h after stimulation.

Chapter 16 Effects of Antimitotic Agents on Ultrastructure and Intracellular Transport of Protein in Pancreatic Acini

This chapter discusses the effects of antimitotic agents in the preparation of pancreatic acini and reviews the combined studies of ultrastructure, enzyme secretion, and intracellular transport of the newly synthesized protein. Pancreatic acini retain both structures and function and are exquisitely sensitive to hormones and neurotransmitters. The chapter also describes the relative importance of microtubules in intracellular transport and release of secretory materials. In the pancreas, the preformed secretory product exists as zymogen granules, and release of digestive enzymes such as amylase is not dependent on the new protein synthesis. In contrast, when the release of the newly synthesized protein is studied, intracellular transport and the final release process are measured. Thus, if an inhibitor simultaneously blocks the release of both amylase and the newly synthesized protein, the release process is affected; however, if amylase secretion is not reduced but that of the newly synthesized protein is, it can be concluded that intracellular transport is affected.

Comparison of several parameters related to the secretory activity of the subcommissural organ in European green frogs

In European green frogs the secretory activity of the subcommissural organ (SCO) was investigated and quantified measuring three parameters considered to be closely related to the cellular processes of synthesis and release of secretory material by the cells of the SCO: (1) the amount of stained secretory material in the SCO; (2) the amount of secretory material in the SCO labelled by a radioactive precursor; and (3) the growth rate of the "liquor (cerebrospinalis) fibre" (LF). A significant negative linear correlation appears to exist between the growth rate of the LF, on the one hand, and the amount of stained secretory material as well as the amount of radioactively labelled secretory material, on the other hand. A significant positive linear correlation exists between the amounts of stained material and radioactively labelled secretory material. The occurrence in the SCO of European green frogs of a larger amount of stained and/or of radioactively labelled secretory material is probably an expression of a lower (LF-producing) secretory activity. In the light of these observations the suitability of the three parameters as a measure of the secretory activity of the SCO is discussed.

Ultrastructure comparee des glandes exocrines abdominales des blattaria (Dictyoptera)

Cockroaches possess a very complex abdominal glandular exocrine system. A defensive function has been attributed to these glands by many authors. We have studied the fine structure of 5 glands: the sternal and tergal glands of Periplaneta americana, sternal glands of Eurycotis loridana, and the glands associated with the second abdominal spiracle in Diploptera punctata and Leucophaea maderae. Despite marked anatomical diversity of the glands, only a few basic types of cells are present: (1) epidermal cells that secrete the cuticular lining of the reservoir, (2) large gland cells (type 3) with a cuticular duct secreted by (3) the canal cells. The duct connects the glandular cells with the outer cuticle. The morphology is described with particular attention to the ultrastructure of the secretory cells. The probable mode of production and release of secretory material is discussed. Of these 5 glands, only 2 have a real defensive function: the sternal glands of E. floridana and the glands associated with the second abdominal spiracle of D. punctata; in the other cases, their function is unknown. This paper emphasizes the need for behavioral and biochemical studies to elucidate the biological significance of these glands.

Experimental studies of apocrine secretion in the dorsal prostate epithelium of the rat.

Rat dorsal prostate epithelium was studied in intact adult animals, in animals castrated for three days and in rats after inhibition of prolactin secretion. Thin sections, electron-microscopic autoradiographs and freeze-fracture replicas were used to analyze the process of apocrine secretion in this gland. The rough endoplasmic reticulum and the Golgi apparatus of the secretory cells are well developed, but secretory granules are absent. The only sign indicating release of secretory material is the appearance of blebs originating from the apical plasma membrane. Freeze-fracture replicas of the apical plasma membrane reveal that the blebs develop randomly from the bases of microvilli-like protrusions. In vitro pulse labeling of the proteins using 3H-leucine resulted in a labeling of the apical blebs. A post-castration period of three days was sufficient to reduce drastically the number and size of the apical blebs conhree weeks by application of lisuride, a synthetic ergot alkaloid, also induced regressive changes in the secretory cells. The apical blebs were still present, but they were shrunken and their content appeared condensed. These experimental conditions proved that the apical blebs are closely related to the functional activity of the cells and are interpreted as true apocrine secretion in the rat dorsal epithelium.

The Infundibular Organ ofBranchiostoma lanceolatum

The infundibular organ of adult and larval Branchiostoma was studied by means of the electron microscope. The secretion produced by the infundibular cells is released into the ventricular fluid from secretory vacuoles, fusing with the apical plasmalemma and forming a Reissner's fiber in the ventricle. The basal cell processes reach the external limiting membrane but no basal release of secretory material has been observed. No synapses are in contact with the infundibular cells. The organ seems to function autonomously with neither nervous control from the brain tissue nor chemical regulation from the ventricular fluid.

Neuroendocrine involvement in osmoregulation in a freshwater mollusc, Lymnaea stagnalis

Physiological information on osmoregulation in molluscs has been provided for many species. However, neuroendocrine control of osmoregulation has hardly been studied and cannot, therefore, be dealt with from a comparative point of view. This is mainly due to the fragmentary nature of the histological information on the neuroendocrine system. The freshwater gastropod Lymnaea stagnalis is one of the few molluscs in which both the physiology of osmoregulation and the structure of the neuroendocrine system have been studied. This favored the study of neuroendocrine control of osmoregulation. Quantitative analysis at the ultrastructural level indicated that two types of neurosecretory cells are involved. In snails exposed to deionized water, a condition stimulating water elimination and retention and/or uptake of ions, the release of secretory material from the axons of these types was observed. In animals exposed to hypertonic saline, known to reduce water elimination and ion uptake, the release activity declines and an enhanced accumulation of secretory granules occurs. The axons of one type not only end in the main neurohemal zones around the central nervous system but also form a network around the ureter, similar to that found around water and ion transporting epithelia in insects. After evaluation of physiological data on osmoregulation it is suggested that one type activates water elimination, while the other type stimulates ion-uptake mechanisms. Possible modes of neuroendocrine engagement in osmoregulation are discussed.

Funktions- und Formwandel der Gefäßwandzellen des juxtaglomerulären Apparates der Niere beim Kaninchen

A solitary loss of blood and three subsequent orthostatical collapses in the rabbit are followed by a temporary anury and oligury. If the granular cells of the afferent arterioles are not injured too much, they answer after an initial, short depression of the juxtaglomerular granulation index with a forced de-novosynthesis. Rough-surfaced endoplasmic reticulum, golgi-complex and free ribosomes get well developed and the juxtaglomerular granulation index rises to the twofold of its normal value. Different shapes of granules represent various stages of maturity during the formation of the secret. Besides pure smooth muscle cells and granular cells there exists a further cell population in the vas afferens, which — due to functional necessity and with adequate structural differentiation — may act either more in a constringent or more in a secretory manner. The decrease of the granulation index during the state of reparation indicates the release of secretory material. The mechanism of this release ist not evident. Notable are the coagulation necroses of some strong granulated „epitheloid“ cells still 4 days after the acute injury. Ein einmaliger Blutverlust und mehrere anschliesende orthostatische Kollapse fuhren beim Kaninchen zu einer temporaren Anurie und Oligurie. Sind die granulierten epitheloiden Zellen des Vas afferens nicht zu stark geschadigt, so antworten sie nach einem initialen, kurzfristigen Absinken des juxtaglomerularen Granulationsindex mit einer forcierten de-novo-Synthese. Sie ausert sich nach einer starkeren Entfaltung des rauhen endoplasmatischen Reticulums, der Golgi-Felder und der freien Ribosomen in einem Anstieg des Granulationsindex auf das Zweifache der Norm. Unterschiede der Granulaformen sind Ausdruck der verschiedenen Reifungsstadien wahrend der Sekretbildung. Auser reinen glatten Gefasmuskelzellen und granulierten epitheloiden Zellen gibt es eine Zellpopulation, die — je nach der funktionellen Anforderung und bei entsprechender feinstruktureller Differenzierung — entweder mehr konstriktorisch oder mehr sekretorisch tatig sein kann. Der Abfall des Granulationsindex wahrend des Wiedererholungsstadiums ist Ausdruck der Sekretabgabe aus den granulierten epitheloiden Zellen. Der Mechanismus der Sekretausschleusung ist noch nicht geklart. Bemerkenswert sind Koagulationsnekrosen einzelner stark granulierter „epitheloider“ Zellen noch 4 Tage nach der akuten Schadigung.

Osmotically Induced Changes in the Activity of Neurosecretory Cells Located in the Pleural Ganglia of the Fresh Water Snail Lymnaea Stagnalis (L.), Studied By Quantitative Electron Microscopy

The neurosecretory cells present in the pleural ganglia of the fresh water snail Lymnaea stagnalis, the Dark Green Cells, were studied to establish whether these neurones are engaged in osmoregulation. Groups of 5 snails were exposed to conditions which induce changes in the diuretic activity (de-ionized water or a 0.1 M sodium chloride solution) for 1, 8, and 15 days, respectively. Animals kept in tap water were used as controls. The cell bodies as well as the axon terminals of the Dark Green Cells were studied quantitatively at the ultrastructural level. To estimate the rate of secretory activity of the neurones changes in the relative extent of the granular endoplasmic reticulum (determined by lineal analysis) and in the number of active Golgi zones were used as parameters. Lineal analysis was also used to determine the fractional volume of the mitochondria and of the cytosomes. Variations in the amount of secretory material in the cell bodies were determined by counting the number of elementary granules per surface unit. Accumulation and release of the secretory material in cross sections of the main neurohaemal area (the right pleuro-parietal connective) were determined by counting the total number of granule-containing axon profiles, and the number of these axons showing release phenomena, respectively. Exposure to de-ionized water, presumably leading to enhanced diuresis, showed a statistically significant increase (a duplication in 15 days) of the extent of the granular endoplasmic reticulum and of the number of active Golgi zones per surface unit (2000 μ 2 ). Moreover, a twofold increase of the volume of the cytoplasm per cell body was noted. In the axon terminals located in the right parieto-pleural connective an enhanced release of secretory material was observed. These trends, which were statistically significant, point to an activation of the Dark Green Cells when the animals are exposed to de-ionized water. During exposure of the snails to 0.1 M sodium chloride, a solution, which is hypertonic to the blood and known to reduce the rate of urine formation, the secretory activity of the DGC was markedly reduced. The observed decrease of the extent of the granular endoplasmic reticulum and of the number of active Golgi zones per surface area was statistically significant. At day 8 the occurrence of cellular atrophy was indicated by the presence of large numbers of newly formed lysosomes of autophagous nature. After two weeks the cytoplasmic volume per cell body was reduced to at least half the control value. In the axon terminals release of secretory material was hardly observed. The secretory material in the axon terminals, rapidly accumulated during the first hours of exposure, gradually diminished during the experiment which was partly due to release, and partly to lysosomal breakdown. The changes observed in both experiments were reversible: the quantitative data obtained from snails kept in tap water for one week after a stay of 15 days in the experimental solutions was within the control range. The results are in line with the hypothesis that the Dark Green Cells synthesize a substance which acts in diuresis. Additional physiological evidence is, however, needed to define more accurately the function of these neurones in the maintenance of the water balance.

Failure of scopolamine, pilocarpine or phenoxybenzamine to influence the rate of oviduct secretion in the rabbit.

The innervation of the oviduct is primarily adrenergic although parasympathetic fibres may also be present (see Brundin (1965) for a review of the literature). While the neural control of the oviduct musculature has received much attention, little is known of the effect of the nervous system on the rate of formation or composition of oviduct fluid. Bishop (1956) reported that pilocarpine injections increased both the rate of oviduct fluid secretion and secretory pressure. He concluded from his experiments that pilocarpine stimulated fluid production by way of the cholinergic innervation of the oviduct. He further concluded that pilocarpine caused the release of secretory materials from the oviduct epithelium since oviduct fluid after pilocarpine was cloudy and contained cellular d\l=e'\bris. The aim of this experiment was to determine whether the rate of oviduct fluid production could be altered by injections of pharmacological agents known to affect the sympathetic and parasympathetic nervous system. Eight adult, New Zealand rabbits (about 3 kg) were prepared for continuous collection of oviduct secretions by the method described by Clewe & Mastroianni (1960). The collection device was slightly modified by encasing the glass collecting coil in an aluminium cassette provided with a removable cover. Approximately 1 1/2weeks was allowed between surgery and the beginning of the study. During this time, oviduct fluid was withdrawn from the collection device each morning and evening and the volume of secretion recorded. The experimental period for each drug was 5 days. Each day during the 5-day experimental period, four observations on secretion rate were made at 2-hr intervals. The drug to be studied was given only on the 3rd day, 2 days being allowed between experimental periods. The drugs used (in the order of their use) were scopolamine, pilocarpine and phenoxybenzamine. All drugs were dissolved in 0-9% sterile sodium chloride solution immediately before use and injected subcutaneously. Scopolamine (100 mg/ml) was administered at the rate of 120 mg per animal every 2 hr to give a total dose of 480 mg. One injection of pilocarpine (1-0 mg in 1-0 ml

Fine structural organization of the spermatheca in the cockroach, Periplaneta americana

The detailed structure of the cockroach spermatheca is described and discussed firstly as an example of an insect integumentary gland, and secondly, from the standpoint of its role in reproduction. The gland comprises a cortical rank of separate secretory units, each associated with an epithelial duct cell responsible for receiving secreted materials and transporting them through the cuticular intima lining the reproductive tract. Secretory activity is cyclic, and the probable mode of elaboration and release of secretory material is described, together with the fine structure of the markedly differing intimas associated respectively with the glandular and conducting units.

Similar structural bases for the storage and release of secretory material in adreno-medullary and beta-pancreatic cells.

Both in normal pancreatic β cells and in the adrenal medulla discontinuities have frequently been observed in the individual membranes surrounding secretion granules. In the β cells the edges of these hiatuses are characteristically inverted in the manner of a scroll. It is suggested that intracytoplasmic release of secretory material may occur through these membrane perforations.

Electron microscopy of neurohypophysis in normal, adrenaline-treated and pilocarpinetreated rabbits.

1. The fine structure of the neurohypophysis in normal, adrenaline-treated and pilocarpine-treated rabbits has been studied, using the electron microscope. The normal structure of the nerve terminal and pericapillary region is quite similar to that of the rat as described by Palay (1957) and Hartmann (1958). 2. Pituicytes are significantly different, however, and are classified into three types. The first one (Type A) is identical with the astrocyte of Farquhar and Hartmann (1957) and of Schultz, Maynard and Pease (1958). This type cell has a round or oval nucleus of low electron density and abundant watery cytoplasm with few formed elements. 3. The second type (Type B) is considered to be an atypical astrocyte. This type cell has a nucleus closely resembling that of Type A, but with abundant cytoplasm containing relatively numerous formed elements. The inverse relationship between relative numbers of Type A and Type B cells in a given gland suggests the possibility of one type being readily transformed into the other under normal conditions. The last type (Type C) has a dark, irregular nucleus and dense cytoplasm with many cell organelles. This cell is structurally identical with the microglia of Farquhar and Hartmann, and of Schultz, Maynard and Pease. A typical oligodendrocyte is not found. No secretory granules are present in pituicytes. The pituicytes are in contact with nerve fibers with a double membrane intervening, and sometimes enclose nerve fibers in invaginations of their cytoplasm. The cell bodies of the pituicytes are located in the parenchymatous region far from blood capillaries, and their processes, along with the nerve terminals, reach to the outer basement membrane of the pericapillary space. 4. During 1–2 hours after injection of adrenaline there was found to be a statistically significant increase in number and size of secretory granules, as well as structural changes of mitochondria in the nerve terminals, enlargement of the pericapillary space and endothelial alterations. These phenomena are considered to reflect a blocking of the release of secretory material after injection of adrenaline. 5. After injection of pilocarpine, a statistically significant decrease in number and size of neurosecretory granules, plus the appearance of many optically empty granules, structural changes of mitochondria and attenuation of the pericapillary space were observed. These phenomena are considered to be related to an acceleration of the release of secretory granules after injection of pilocarpine.