A histochemical study on the correlation between secretory activity and the TCA cycle in the gland cell

Summary The activity of succinic dehydrogenase and malic dehydrogenase was observed histochemically in the gland stomach of rats, and also the relationship between the secretory activity of the gastric gland cells and the process of the TCA cycle in the cells was studied.Histochemically, enzyme activity is plainly visible in the gastric parietal cells but in the gastric chief cells and mucous neck cells.The secretory activity of the cells was promoted by the administration of food, the sub-cutaneous injection of histamine, histidine, acetylcholine or eserin.The activity of succinic dehydrogenase appears to be constant regardless of secretory activity except in a few cases. The activity of malic dehydrogenase increases as secretory activity is promoted. It seems very unlikely that one step in the cycle (the transformation of malic acid into oxalacetic acid) would be accelerated while the other step (the transformation of succinic acid into fumaric acid) is not. This inconsistency of activity may be attributed to the histochemical reaction. Thus the increase of malic dehydrogenase activity is seen as an acceleration of the whole TCA cycle. It is our conclusion, therefore, that the source of energy within the cell, i.e. the TCA cycle, is a process which parallels secretory activity.     

Size of the fibrillar centres of the nucleoli in the supraoptic nucleus of the rat taking the Swiss cheese effect into account

The size of the fibrillar centres (FC) in nucleoli was investigated taking the Swiss cheese effect into account. Electron microscopy was performed on the neurons of the rat supraoptic nucleus after the secretion of vasopressin had been fully suppressed by water load, after the secretion had been stimulated by water deprival and in normal rats with water ad libitum. When the secretory activity was suppressed from a normal level to approximately no activity, the size of the individual FC was doubled. Moreover, with increasing secretory activity the number of FC per cell increased.     

Localization of some enzymes in the main venom glands of viperid snakes

Several secretory and nonsecretory enzymes were localized histochemically in the main venom gland of 13 viperid snakes. All secretory cells show the intracellular oxidative enzymes succinate dehydrogenase and monoamine oxidase. The granular reactions obtained for both enzymes resemble mitochondria in distribution. Distinctive cells with a very high succinate dehydrogenase activity are dispersed among the secretory cells of all species except Atractaspis. Nonspecific acid phosphatase activity is found in the supranuclear region of the secretory cells in species that do not secrete this enzyme and throughout the cytoplasm in snakes that secrete the enzyme. Nonspecific alkaline phosphatase activity occurs in the secretory cells of those snakes whose venom shows this activity. Leucine amino peptidase (aryl amidase) activity is found in the venom and in the secretory cells of all the species. In Vipera palaestinae both the venom and the secretory cells of the main venom gland contain nonspecific esterase, L-amino acid oxidase and phosphodiesterase activities. The localization of phosphodiesterase and L-amino acid oxidase do not show major differences between glands at different intervals from an initial milking. Adenosine-monophosphate phosphatase activity is localized in the supranuclear region of the secretory cells in the glands of Vipera palaestinae and Aspis cerastes. Its activity is found in the venom of Aspis only.     

Ultrastructural,cyto- and biochemical observations during turnover of plasma membrane in duck salt gland

Summary The mechanism of plasma membrane turnover was investigated using the duckling salt gland as a model system. Feeding fresh water to saltstressed ducklings results in a decrease in the Na, K-ATPase in salt gland to nonstressed levels in about 7 days, as measured by ATP hydrolysis and ³H-ouabain binding. Electron micrographs reveal that this is accompanied by a decrease in plasma membrane infoldings on the basal and lateral borders of gland secretory cells. Simultaneously there is an increase in filamentous material and a rise in acid phosphatase and peptidase activities in these cells. Cytochemistry shows that the acid phosphatase activity is mostly associated with the basal or basolateral regions of secretory cells. These observations could indicate that the removal of plasma membrane components is accomplished by internalization and digestion within the secretory cells.     

Aging-related characteristics of the secretory response of the stomach to stimulation of its mechanoreceptors]

Age peculiarities of the gastric secretory response to the mechanical stimulation have been studied in thirty-one healthy subjects aged 60-79 and ten healthy subjects aged 20-35 (a control group). The secretory response of the gastric glands to mechanical distention of the stomach with 600 ml of water is found to decrease with aging. No changes in gastrin concentration in plasma during balloon distention have been revealed, so this confirms the hypothesis that stimulation of acid secretion by distention is mediated by reflexes without participation of the gastrin mechanism. Distention of the stomach with 800 ml of water induces significant inhibition of the acid output in subjects aged over 60. The mechanism of this reaction is not clear yet and needs further investigation.     

Golgi apparatus, GERL, and secretory granule formation within neurons of the hypothalamo-neurohypophysial system of control and hyperosmotically stressed mice

The vasopressin-producing neurons of the hypothalamo-neurohypophysial system are a particularly good model with which to consider the relationship between the Golgi apparatus nd GERL and their roles in secretory granule production because these neurons increase their synthesis and secretion of vasopressin in response to hyperosmotic stress. Enzyme cytochemical techniques for acid phosphatase (AcPase) and thiamine pyrophosphatase (TPPase) activities were used to distinguish GERL from the Golgi apparatus in cell bodies of the supraoptic nucleus from normal mice, mice hyperosmotically stressed by drinking 2% salt water, and mice allowed to recover for 5-10 d from hyperosmotic stress. In nonincubated preparations of control supraoptic perikarya, immature secretory granules at the trans face of the Golgi apparatus were frequently attached to a narrow, smooth membrane cisterna identified as GERL. Secretory granules were occasionally seen attached to Golgi saccules. TPPase activity was present in one or two of the trans Golgi saccules; AcPase activity appeared in GERL and attached immature secretory granules, rarely in the trans Golgi saccules, and in secondary lysosomes. As a result of hyperosmotic stress, the Golgi apparatus hypertrophied, and secretory granules formed from all Golgi saccules and GERL. Little or no AcPase activity could be demonstrated in GERL, whereas all Golgi saccules and GERL-like cisternae were TPPase positive. During recovery, AcPase activity in GERL returned to normal; however, the elevated TPPase activity and secretory granule formation seen in GERL-like cisternae and all Golgi saccules during hyperosmotic stress persisted. These results suggest that under normal conditions GERL is the predominant site for the secretory granule formation, but during hyperosmotic stress, the Golgi saccules assume increased importance in this function. The observed cytochemical modulations in Golgi saccules and GERL suggest that GERL is structurally and functionally related to the Golgi saccules.     

Effects of luminal osmolarity on gastric acid secretion in the little skate,Raja erinacea

Summary Isolated gastric mucosa of the skate shows marked changes in acid secretory rate (J _H ), electrical potential difference (PD), and transepithelial resistance (R) with changes in mucosal bathing solution composition and a constant serosal solution. Removal of the 350 mM urea usually present in the mucosal solution reduces acid secretory rate by 25%, while adding urea to 1 M has no significant effect. Complete removal of osmotic solutes (distilled water) inhibits secretion by 78%, isotonic urea (no salts) inhibits by 54%, while isotonic salts alone (no urea) gives control secretory rates. The changes in PD and R are consistent with acid secretory changes. Theory and experience with terrestrial organisms would not predict these changes. The most likely explanation is osmotic swelling and shrinking of the surface cells, and occlusion of the secretory tubules in the swollen condition. Since marine species never encounter hypo- or hyperosmotic conditions due to food ingestion, their surface cells may be water permeable, unlike the situation in terrestrial and fresh water animals.Abbreviations J _H acid secretory rate per square centimetre tissue area - OC oxyntic cell - PBC pit border cell - PD transepithelial electrical potential difference - R transepithelial electrical resistance per square centimetre tissue area - SEC Surface epithelial cell     

Electron microscopy and morphometry of nucleoli in rat neurosecretory cells with stimulated and suppressed secretion

The nucleoli in the neurons of the supraoptic nucleus in the rat were analyzed by electron microscopy and morphometry after the secretion of vasopressin had been fully suppressed by water load, after the secretion had been stimulated by water deprivation and in normal rats which had water ad libitum. Suppression of the secretion increased the proportion of fibrillar centres in the nucleoli 2-fold. Stimulation of the secretion increased the proportion of the granular component by 22%. The overall nucleolar organization did not change very much with the secretory activity. The results show that an increased proportion of fibrillar centres in nucleoli is an indicator of decreased secretory activity and, moreover, that an increased volume of the nucleolar fibrillar and granular components per cell indicates an increased secretory activity.     

The relationship between the ionic composition of the environment and the secretory activity of the endocrine cell types of stannius corpuscles in the teleost Gasterosteus aculeatus

Summary The corpuscles of Stannius of threespined sticklebacks contain two glandular cell types of presumed endocrine nature. To elucidate the function of both cell types the secretory activity of the cells was studied in fully adapted seawater and freshwater fishes and in specimens transferred from sea water to fresh water or adapted to media of various ionic composition. The secretory activity was established, in tissue sections and freeze-etch replicas, by estimating the volume of the nuclei, the density of the nuclear pores, and the frequency of exocytotic phenomena.The type-1 cells, ultrastructurally comparable to the predominant or only cell type described in many other teleosts, are more active in sea water than in fresh water. The activity of the type-2 cells, whose ultrastructural appearance is known only for salmonids and eels, is higher in fresh water. Transfer of seawater fishes to fresh water results in reduction of type-1 cells and activation of type-2 cells. The factors responsible for these changes were analyzed by exposure of fishes to solutions of various salts in fresh water and to artificial sea water with a reduced content of one of its components. The high activity of type-1 cells in sea water proved to be related to the high calcium content of this medium. These cells probably produce a substance comparable to hypocalcin, the endocrine factor isolated from the Stannius corpuscles of some other teleost species. The high activity of type-2 cells in fresh water appeared to be connected with the low sodium and potassium levels of this medium. Type-2 cells possibly produce a hitherto unknown hormone involved in the control of sodium and/or potassium metabolism.The technical assistance of Miss C. Mein and Mr. J. Zagers is gratefully acknowledged     

Secretory activity of the subcommissural organ in Rana temporaria under osmotic stimulation

The secretory activity of the subcommissural organ (SCO) in the frog Rana temporaria was studied under conditions of dehydration. After injection of a radioactive precursor the amount and concentration of radioactively labelled material in the SCO are smaller in dehydrated than in control animals. Concomitantly, the growth rate of the CSF-fibre (Reissner's fibre) increases in dehydrated animals. It follows that water deprivation enhances the secretory activity of the SCO. To investigate whether the SCO may be responsible for the secretion of an aldosteronotropic factor as suggested in the literature, brains were incubated in vitro with a radioactive precursor and with or without aldosterone. The SCO of the aldosterone-treated brains contains more radioactively labelled material than the SCO of the control brains. It is argued that this is indicative of a lower secretory activity It means that aldosterone inhibits the secretory activity of the SCO, possibly by a process of negative feed-back regulation. The results of the present experiments can be interpreted in favour of an involvement of the SCO-Reissner's fibre complex in osmoregulation.     

Number, volume and size distribution of nucleoli in rat neurosecretory cells with suppressed and stimulated secretion

The nucleoli in the neurons of the supraoptic nucleus were investigated in the rat. This was performed after the secretion of vasopressin had been suppressed by water load, after the secretion had been stimulated by water deprival and in normal rats which had water ad libitum. The cells with high secretory activity had large single nucleoli. The cells with low secretory activity had less nucleolar volume, and a substantial part of the cells contained two nucleoli.     

Enzyme modulation of the Golgi apparatus and GERL: a cytochemical study of parotid acinar cells

The distribution of thiamine pyrophosphatase (TPPase) and acid phosphatase (AcPase) has been examined in resting parotid acinar cells as well as during decreased and increased secretory granule production. In resting acinar cells, TPPase activity was restricted to the trans Golgi saccules and AcPase activity was localized in GERL and immature secretory granules. Although secretory granule production is diminished during ethionine intoxication, no significant alteration in the distribution of either TPPase or AcPase was noted. However, marked changes in enzyme localization, especially of TPPase, occurred during accelerated secretory granule production. The alterations were essentially the same for all of the conditions studied (recovery from ethionine treatment, recovery from a protein depletion diet, secretory stimulation with isoproterenol, and postnatal maturation of the parotid gland). During maximal secretory granule production, TPPase activity was localized not only in the trans Golgi saccules, but also in GERL-like cisternae and immature secretory granules. The immature secretory granules were often in continuity with the GERL-like cisternae. At the same time that the TPPase activity was increased, the AcPase activity was frequently diminished. These modulations in enzyme activity provide evidence that GERL is derived from the trans Golgi saccule.     

Secretory activity of the subcommissural organ in Rana temporaria under osmotic stimulation

Summary The secretory activity of the subcommissural organ (SCO) in the frog Rana temporaria was studied under conditions of dehydration. After injection of a radioactive precursor the amount and concentration of radioactively labelled material in the SCO are smaller in dehydrated than in control animals. Concomitantly, the growth rate of the CSF-fibre (Reissner's fibre) increases in dehydrated animals. It follows that water deprivation enhances the secretory activity of the SCO.To investigate whether the SCO may be responsible for the secretion of an aldosteronotropic factor as suggested in the literature, brains were incubated in vitro with a radioactive precursor and with or without aldosterone. The SCO of the aldosterone-treated brains contains more radioactively labelled material than the SCO of the control brains. It is argued that this is indicative of a lower secretory activity. It means that aldosterone inhibits the secretory activity of the SCO, possibly by a process of negative feed-back regulation. The results of the present experiments can be interpreted in favour of an involvement of the SCO-Reissner's fibre complex in osmoregulation.     

Adaptive shifts in the activity of amino acid transport into mammary secretory cells in changed nutritional conditions

On the basis of analysis of published data, direct (using 13C) and indirect methods of estimating the amino acid transfer into mammary secretory cells in vivo were compared and the modified indirect method was used to determine quantitatively the shifts in transport activity in lactating cows and goats in trials with amino acid deficit or excess and in investigations that used a hyperinsulemic-euglycemic clamp. The analysis suggests that inadequacy of traditional use of extraction efficiency as a measure of tissue affinity to substrate is associated with two shortcomings: 1) if the changes in mammary blood flow are more expressed compared to transport activity, the arteriovenous difference and extraction efficiency may change in opposite direction to the shifts in transport activity; 2) due to the effect of nonlinearity, in situations characterized by small ratio of blood flow: the transport activity extraction efficiency is insensitive to shifts on activity of transport. The re-analysis of published data using the modified inbdirect method indicated that the deficit of individual amino acid caused a rise in activity of their transport and the excess decreased a net transfer into cell. The insulineuglycemic clamp treatments increased the activity of amino acid transport into the mammary cell and milk protein yield. The results obtained suggest that net transmembrane transfer of amino acid into mammary secretory cell can be controlled by the cell itself according to metabolic demand.     

Effect of chemical and pharmacological agents on the secretory activity induced by Escherichia coli heat-stable enterotoxin

The effect of aspirin (ASP), chlorpromazine (CPZ), diphenoxylate (DP), ethylene glycol tetraacetate (EGTA), hydrocortisone (HC), loperamide (LPA), methylprednisolone (MP), phenotolamine mesylate (PTM), propranolol (PR), and trifluoperazine (TPZ) on the secretory activity induced by Escherichia coli heat-stable (ST) enterotoxin in infant mice was studied. LPA and DP, which are used therapeutically for diarrhea, did not inhibit the effect of ST enterotoxin; MP and HC, known inhibitors of cholera enterotoxin, and two adrenergic agents (PR and PTM) had no effect on ST-induced secretory activity. TPZ, EGTA, ASP, and CPZ caused a significant (P less than 0.05) decrease in the secretory activity induced by ST enterotoxin, CPZ, EGTA, and TPZ inhibited secretory activity induced by 8-bromoguanosine 3'5'-cyclic monophosphoric acid (8-BrcGMP), a cGMP analog.     

Restoration of the secretory activity of the digestive glands under high physical load

The time course of the restoration reactions of the secretory functions of the gastric glands were studied in patients differing in the level and specificity of daily physical activity. Dependence was found between the level and specificity of daily physical activity and reactivity of the secretory apparatus of the gastric glands during the recovery period after physical load. A high reactivity of the digestive gland activity is typical of subjects with a high daily physical load. Differences in the functional stability of the secretory mechanisms of various components of the gastric juice were found in different states: at rest, under physical load, and in the recovery period. The maximal stability of the secretory mechanisms of the digestive gland was marked in athletes trained to develop endurance (skiers). Heterochronism of the restoration reactions of the gastric secretion after physical loads was found. At the beginning, secretion of enzyme is restored, followed by acid composition of the digestive juices. An inverse relationship was found between the content of the blood levels of the digestive enzymes pepsinogen-1 and -2 and the concentration of proteolytic enzymes in gastric contents in subjects with various adaptation degrees to the physical load.     

Role of calcium in the preparation and secretory activity of cells isolated from the gastric mucosa of rabbits

The role of calcium in the preparation and the acid secretory activity of parietal cells was studied using cells isolated from rabbit gastric mucosa. The preparation of isolated cells was performed by enzymatic dissociation (collagenase) in the presence of EDTA; without EDTA, only isolated gastric glands were obtained. The acid secretory activity of parietal cells was determined by the 14C-aminopyrine accumulation method; the stimulation induced by histamine or isobutylmethylxanthine (IBMX) was not significantly affected by a reduction of extracellular Ca2+ level (20% diminution in a Ca2+-free medium). The carbachol induced stimulation was highly dependent upon the concentration of extracellular Ca2+: incubation of parietal cells in a Ca2+-free medium reduced the response to 100 microM carbachol by about 60%.     

The hypothalamo-hypophyseal system of Rana temporaria under osmotic stimulation with special reference to the hypothalamo-median eminence-distal lobe axis

The secretory activity of the hypothalamo-hypophyseal system in the frog Rana temporaria under conditions of dehydration has been studied histologically using two parameters, the amount of stained neurosecretory material and the amount of neurosecretory material labelled by a radioactive precursor. The results are indicative of an increased secretory activity of the hypothalamo-neural lobe system as a result of water deprivation. In addition the involvement of the preoptic nucleus-median eminence axis in osmoregulation is confirmed. The pattern of distribution of autoradiographic silver grains over the median eminence together with data from literature support the idea that mesotocine is involved in the regulation of the activity of the adenohypophysis.     

The effect of plant hormones on the components of the secretory pathway in human normal and tumor cells

Plant hormones play a key role in plant growth and differentiation. Certain plant hormones are known to be potential antitumor agents, affect the secretory activity of animal cells, and are produced by mammalian cells as proinflammatory cytokines. The goal of this research was to study the effect of abscisic and gibberellic acids on the secretory system of human epidermoid A431 carcinoma cells and HaCaT keratinocytes. Immunocytochemical and morphometric analysis showed that a subtoxic concentration of abscisic and gibberellic acids induced extension of the ER network and increased the size of the Golgi complex. Electron-microscope studies confirmed the hypertrophic changes of the Golgi complex: swelling of cisternae in the trans-Golgi compartment after exposure to abscisic acid and swelling of cis- and trans-compartments after exposure to gibberellic acid. The Click-iT technique revealed elevation of total protein synthesis only in A431 cells exposed to abscisic acid. Our data suggest that the hypertrophy of Golgi may reflect enhanced secretory activity in A431 cells exposed to abscisic acid. In other experiments, Golgi hypertrophy was not accompanied with increased protein synthesis that suggested the stress-related changes of ER and Golgi complex. Our results demonstrate that morphologically similar reaction manifested in hypertrophy of Golgi complex, in response to plant hormones, is the result of different functional activities, and that molecular mechanisms underlying induced changes need further investigations.     

Regulation of secretory processes in parietal cells in the different stomach pathologies

This review deals with the analysis of the modern literature concerning molecular mechanisms of secretory activity of gastric mucosa cells and their importance during development of different pathologies. Gastric acid secretion is regulated by paracrine, endocrine and neural systems. The result of these systems functioning at the molecular level is signal transduction pathways activation by histamine, acetylcholine, gastrin and other mediators. Coupling of these agents with specific receptors located on the basolateral plasma membrane of parietal cells modulates acid secretion. It was shown that protein phosphorylation enzymes play the significant role in realization of functional and proliferative activity of the stomach secretory cells in physiological and pathological states. The key role of tyrosine protein kinases associated with growth factors is considered, which take part in regulation of acid secretion, have trophic influence on mucosa cells, protect it from acute injuries, stimulate cell proliferation and accelerate ulcer healing.