蓖麻蚕前胸腺细胞超微结构的变化与蜕皮激素分泌活动的关系

本研究叙述蓖麻蚕Philosamia cythia ricini四龄及五龄幼虫前胸腺蜕皮激素分泌活动各不同时期所显示的腺细胞超微结构变化.从幼虫蜕皮后至进入眠期之间的腺细胞结构可分为三个时期,(1)不活动期:细胞核呈圆形,核内密布染色质及核仁,细胞质内有结构完整的线粒体、粗面及滑面内质网、核糖体和高尔基氏体;细胞外围的细胞间区内有许多小囊泡及多泡囊.(2)活动期:细胞结构变化为细胞核膜出现内陷、外突,形成波浪形的核周膜;线粒体变形,出现内嵴稀疏的空心线粒体.(3)激素释放期:细胞核变形,形成若干长短不一向外伸出的指状突,有些伸达细胞边缘;其余细胞器退化,其后仅余残缺的高尔基氏体,稀疏的核糖体,线粒体的内崤逐渐消失,成为空腔扩大的及空腔内藏“膜轮”的线粒体,和一些溶解体及大形“膜轮”.     

Temporal changes in tissue glutathione in response to chemical form,dose, and duration of selenium treatment

Selenium has been reported to affect glutathione (GSH) concentrations in short-term animal-feeding experiments. Given the central role that this tripeptide plays in maintaining cellular homeostasis, it was hypothesized that perturbations in glutathione metabolism induced by selenium might account for its cancer chemopreventive activity. In the present study, four experiments were conducted in which the effect of acute, short-, or long-term exposure to selenium was assessed. Selenium was provided as either sodium selenite or D,L-selenomethionine. Selenite was observed to induce a biphasic response in total liver GSH. Injected selenium caused an acute reduction in GSH, whereas short-term feeding (up to 8 wk) increased both total GSH and oxidized glutathione (GSSH), an effect that gradually diminished in magnitude with prolonged feeding. Our data suggest that such changes are unlikely to account for the chemopreventive activity of selenium for the following reasons: Perturbations in glutathione metabolism occurred only at doses of selenite that approached toxicity. These doses are higher than what would be required for producing cancer chemoprevention. The transient nature of these changes also contrasts with the need for a continuous supplementation of selenite in suppression of tumorigenesis. Furthermore, selenomethionine was found to have little activity in altering glutathione metabolism, even though it compares favorably with selenite as a cancer chemopreventive agent. Nonetheless, these findings do not discount the possibility that sulfhydryl compounds, such as glutathione, might be used to modify the toxicity and/or enhance the cancer prophylactic activity of selenium compounds.     

Modulations of the epithelial phenotype and functional activity of cultured bovine tracheal gland cells: dependence on the culture medium and passage number.

Bovine tracheal gland (BTG) cells in culture show an epithelial-fibroblastoid transition after several passages. To investigate these BTG cell phenotype changes, we studied the effects of both the culture medium and passage number on the expression of epithelial cytoskeletal proteins and glandular serous cell markers. We also analyzed the intracellular cAMP level in the basal state and after adrenergic stimulation. Three culture media were used: 1) serum-free defined medium (SFDM); 2) medium supplemented with 2% Ultroser G; and 3) medium supplemented with 10% fetal calf serum (FCS). Using immunofluorescence microscopy, we showed that, in the first 4 passages whatever the culture conditions, BTG cells expressed immunoreactivities to cytokeratin filaments and desmoplakins I and II, whereas vimentin filaments were not detected. After four passages, BTG cells cultured in 10% FCS or 2% Ultroser G became progressively fibroblastoid and showed immunoreactivities to both vimentin and cytokeratin intermediate filaments. No immunoreactivity to vimentin filaments was observed on BTG cells cultured in a SFDM. Using biochemical analysis, we showed that basal levels of cAMP in cultured BTG cells and lysozyme secretion by these cells vary according to the culture medium and passage number. It was higher in BTG cells cultured in a SFDM compared to that recovered from cells cultured in medium supplemented with Ultroser G or FCS. Whatever the culture medium, BTG cells responded to stimulation by isoproterenol. However, the results of stimulation in a SFDM were higher than in Ultroser G or FCS supplemented medium. We conclude that the BTG epithelial cell organization and the regulation of biosynthesis of secretory proteins by these cells in culture depend on both the culture medium and passage number.(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical distribution of simple-epithelial-type keratins and other intermediate filament proteins in the developing human pituitary gland

Summary An immunohistochemical study of the production of the intermediate filaments [vimentin, cytokeratin, and glial filament acidic protein (GFAP)] during development of the pituitary gland was made by use of fetal and adult human pituitary tissue. Among these intermediate filament proteins in the anterior and intermediate lobes of the pituitary, cytokeratin is the first to appear, followed by GFAP and vimentin. However, only cytokeratin is seen during the period of morphogenesis of the pituitary gland, with the type-II subfamily cytokeratin 8 being the earliest to appear. Among the simple-epithelial-type cytokeratins, cytokeratins 8 and 19 were observed within the pituitary primordium during morphogenesis. Cells immunoreactive for cytokeratins 8 and 19 showed a heterogeneous three-dimensional distribution pattern in Rathke's pouch. Both cytokeratins 8 and 19 tended to be strongly positive at sites in the pituitary primordium where cells had become more loosely arranged (i.e., areas far from the diencephalon) but were only weakly positive in areas in which the epithelial cells were densely packed (i.e., areas closely associated with the diencephalon). It is concluded that, during the period of morphogenesis, Rathke's pouch has the intermediate filaments characteristic of simple epithelium and shows different immunoreactivity for simple-epithelial-type cytokeratins from place to place according to the extent of cellular differentiation.     

Inhibin-like and gonadotropin-like immunoreactivity in pituitary cells of male monkeys (Macaca fascicularis,Macaca mulatta)

Summary Inhibin-like immunoreactivity was detected by immunocytochemistry in the pituitaries of untreated male crab-eating macaques (cynomolgus monkey) and rhesus monkeys, in rhesus monkeys actively immunized against FSH, and in one orchidectomized crab-cating macaque. Localizations were performed by the immunogold-silver staining with 5-nm colloidal gold-conjugated second or third antibodies and by the alkaline phosphatase-anti-alkaline-phosphatase technique. Two different inhibin-specific antisera, raised against the -subunit or the entire inhibin molecule, provided identical staining patterns. Positive label was confined to the pars distalis of the pituitary and occurred exclusively in the cytoplasm of morphologically different cell types throughout the pars distalis in all pituitaries. Staining was most prominent in clusters of chromophobic cells. The presence of inhibin-like activity in the pituitary of an orchidectomized monkey with undetectable serum inhibin levels suggests that inhibin is produced within the pituitary gland. Co-localization studies for the -subunits of the gonadotropic hormones revealed that on average 82% of the gonadotropes were bihormonal. Using the same protocol, co-localization of inhibin-like activity with gonadotropin-like immunoreactivity revealed only a small degree of common distribution (<15%). Inhibinpositive cells were frequently in close proximity to gonadotropic cells and, thus, paracrine effects of inhibin on gonadotropin-synthesizing cells are conceivable.     

Maturation-related changes in mass and elemental contents of secretory granules as measured by electron-microprobe

Summary The relationship between granule density, protein content, and Ca and S contents were studied in two secretory granule fractions, from parotid glands of the rat, previously shown to constitute different stages in granule maturation. The density of the lighter fraction was between 1.133 and 1.142 g/ml, while that of the heavier fraction was greater than 1.142 g/ml. The mean protein content of the denser granules was 12% greater than that of the lighter granules (P<0.03), while the dry-mass elemental concentrations in the two granule fractions were unchanged. These results indicate that protein is added to granules during the maturation process (presumably by vesicular traffic), and that the resulting increase in granule density is not driven simply by decrease in water content and/or increased concentrations of inorganic Ca or S in the granules. The elemental concentration values also indicate that the diffusible elements permeate the granule membrane during the fractionation procedures.     

Ultrastructural visualization of exocytosis in the pig pineal gland

Summary The pinealocytes of the pig contain conspicuous dense bodies, the nature and role of which are not yet fully elucidated. The aim of this study was to demonstrate whether or not these structures are involved in the secretion process. The tannic acid-Ringer incubation (TARI)-method, which allows a clear-cut ultrastructural study of secretory discharge by exocytosis, has been used. The results indicate that pig pinealocytes release the content of the dense bodies with an amorphous inner structure into the extracellular space via exocytosis and that this secretion is quantitatively important. The secreted material is proteinaceous in nature; this indicates that polypeptides are released by the pineal.     

Ultrastructure of the frontal organ in Convoluta and Macrostomum spp.: significance for models of the turbellarian archetype

Present models of turbellarian evolution depict the organism with a frontal organ — a complex of glands whose necks emerge at the anterior tip of the body — and therefore imply that this organ is homologous throughout the Turbellaria. However, comparisons of representatives of the Acoela and Macrostomida, two putatively primitive orders of the Turbellaria, show that frontal organs in these two are not similar in ultrastructure or histochemistry. The acoel Convoluta pulchra had a prominent cluster of frontal mucous glands whose necks emerged together in a frontal pore at the exact apical pole of the organism, and an array of smaller glands of at least five other types opened at the anterior end, separately from and ventral to this pore. The frontal organs (Stirndrüsen) of two species of Macrostomum on the other hand, comprised an array of discretely emerging necks of at least two gland types including one with rhabdiform (rhammite) and one with globular mucous secretion granules neither of which emerge at the apical pole. In neither species did the organ appear to be sensory. Our findings indicate a low probability of homology between the frontal glands of the Acoela and Macrostomida.     

Pathophysiologic alterations in Biomphalaria glabrata infected with Angiostrongylus costaricensis

Hemolymph glucose, alkaline phosphatase, lactic dehydrogenase, and creatine phosphokinase in Biomphalaria glabrata infected with Angiostrongylus costaricensis were significantly higher on day 27 postinfection (PI) than in uninfected snails. Hemolymph total calcium from infected snails was less on days 6, 12, and 27 PI than that from controls. Total hemolymph protein was similar for controls and infected animals during the entire study. Throughout the study the mean number of amoebocytes/mm³ hemolymph from infected snails was significantly less than that for controls. Mean total wet weights of digestive gland and foot muscle from infected and uninfected snails was similar throughout the study. Mean μg glycogen/mg wet weight of digestive gland from infected snails was significantly greater on days 24, 27, and 28 PI than that from controls. Mean μg glycogen/mg wet weight of foot muscle from infected snails was significantly reduced between days 12 and 28 PI from that of uninfected snails. It is suggested that hemolymph glucose and digestive gland glycogen in infected snails are augmented by glycogen breakdown in the foot muscle of parasitized animals. Elevations in hemolymph enzymes are due to tissue destruction by larvae emerging from the foot muscle of infected snails. Parasite-induced derangements in shell metabolism underlie observed changes in hemolymph calcium in infected snails.     

Effect of Acute Hypoxia on Ascorbate Content of Plasma, Cerebral Cortex, and Adrenal Gland

Levels of ascorbic acid (AA) in the plasma, brain, and adrenal gland of rats were determined after 15 min of hypoxia (PaO2 less than 25 mm Hg) and following asphyxia. In rabbits, AA plasma levels were followed up to 75 min of reoxygenation following 15 min of hypoxia of the same severity. A significant increase (approximately 70%) in AA levels was found in plasma of rats and rabbits after hypoxia and asphyxia. This increase was found to be transient, with a return to normal levels within 1 h after resumption of normal oxygenation. Pretreatment with dexamethasone reduced the increase in AA level in both rabbits and rats. Adrenalectomy in rats, performed 24 h before the experiment, abolished the response to hypoxia. Ascorbate levels in the cerebral cortex, hypothalamus, and adrenal gland of awake rats subjected to hypoxia or asphyxia were found to be the same as in normoxic rats. Our results suggest that the observed changes in plasma AA levels are probably mediated through adrenocorticotropic hormone and that the adrenal gland is the major source of ascorbate efflux into the circulation during oxygen deprivation.