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  • 1
    Electronic Resource
    Electronic Resource
    Somatostatin Plays a Dual, Stimulatory/Inhibitory Role in the Control of Growth Hormone Secretion by Two Somatotrope Subpopulations from Porcine Pituitary (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neuroendocrinology 9 (1997), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previous results from our laboratory demonstrated the existence of two subpopulations of porcine somatotropes of low- (LD) and high density (HD) that exhibit differences in ultrastructure and respond in an opposite manner to somatostatin (SRIF) in vitro. In LD cells, SRIF did not affect basal growth hormone (GH) release but partially blocked the stimulatory effect induced by GH-releasing factor (GRF). Conversely, SRIF paradoxically stimulated the secretory activity of HD somatotropes. Here, we have analysed in detail the basic parameters that characterize this differential response. To this end, the time- and dose-dependent effects of SRIF-14 were evaluated on separate monolayer cultures of both subpopulations. Likewise, the direct effect of the peptide on individual somatotropes from each subset was assessed by cell immunoblot assay. Finally, we compared the effects of SRIF-14 and SRIF-28 on cultures of LD and HD cells. SRIF-14 (10−7 M) induced a rapid (30 min) and sustained (4 h) 2-fold increase in GH release from HD cells, whereas it did not affect GH secretion from LD somatotropes. Surprisingly, a low dose of SRIF (10−15 M) stimulated GH release from both LD (154.1±8.2% of basal, P〈0.05) and HD (337.2±55.5% of basal, P〈0.05) subpopulations, even more effectively than higher doses of the peptide. Results from cell blotting showed that SRIF stimulatory effects were exerted directly upon individual somatotropes. Finally, SRIF-28 elicited similar responses to those observed for SRIF-14 in both somatotrope subpopulations, yet 10−15 M SRIF-28 was less potent than the same dose of SRIF-14 in stimulating GH release from HD cells. Our present findings demonstrate that SRIF can function as a true GH-releasing factor in cultures of porcine pituitary cells by acting specifically and directly upon somatotropes. Furthermore, together with previous observations, these results strongly suggest that SRIF is not merely an inhibitor of GH release in pigs, but might play a dual modulatory role. Heterogeneity of the somatotrope population contributes greatly to this divergent effect of SRIF.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.1997.00650.x
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  • 2
    Electronic Resource
    Electronic Resource
    Secretory and Morphological Heterogeneity of Porcine Somatotropes during Postnatal Development (1997)
    Oxford, UK : Blackwell Science Ltd
    Journal of neuroendocrinology 9 (1997), S. 0 
    Details
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Previous studies from our laboratory have demonstrated that porcine somatotropes can be separated into two subpopulations of low (LD) and high density (HD) by centrifugation in a Percoll gradient. The two subsets are present throughout porcine postnatal growth, although their relative proportions vary with age. In prepubertal animals, HD cells exhibit higher secretory granule content and release more GH than LD cells under basal culture conditions. In the present study, we analysed the ultrastructure of separated LD and HD cells from neonate and mature female pigs, and quantified cell size as well as the relative abundance of several subcellular organelles on immunoidentified somatotropes. Subsequently, GH release under basal conditions was assessed for cultures of unseparated cells and also for LD and HD somatotropes obtained at different stages of postnatal development. Results from the morphometric study demonstrated that LD somatotropes were significantly smaller in size, contained less secretory granules and displayed a more developed endoplasmic reticulum than their HD counterparts, regardless of the age of the pituitary donors. In terms of secretory ability, a significant age-associated decrease in GH release was observed in monolayer cultures of unseparated cells from prepubertal and mature pigs compared to neonates. A similar decline in GH-releasing ability was detected for cultures of HD cells. For LD cells, GH secretion only decreased significantly in mature animals. In spite of the divergent pattern followed by both subpopulations during growth, HD somatotropes released significantly more GH than LD somatotropes at the three ages studied. Taken together, our findings demonstrate that the population of porcine somatotropes is mainly composed of two subtypes, LD and HD, which differ in density, morphology and basal secretory activity. These differences are essentially maintained during porcine postnatal development. The progressive reduction in the secretory capacity of HD and LD somatotropes, coupled to the decrease in the relative abundance reported for the HD subpopulation, provides the cytological basis for a better understanding of the decline in GH release associated with age in pigs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2826.1997.00642.x
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  • 3
    Electronic Resource
    Electronic Resource
    Stereological study of gonadotropes in the frog, Rana pipiens, after GnRH stimulation in vitro (1990)
    Springer
    Cell & tissue research 262 (1990), S. 171-176 
    Details
    ISSN: 1432-0878
    Keywords: Immunocytochemistry ; Gonadotropes ; Morphometry ; Stereology ; Rana pipiens (Anura)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Previous physiological results have indicated the existence of two releasable pools of gonadotropins in amphibian pituitaries: an acute releasable pool that appears independent of protein synthesis, and a storage pool involved in chronic release that depends on protein synthesis. To elucidate the ultrastructural localization of these pools and the morphological changes induced in gonadotrope cells after treatment with gonadotropin-releasing hormone, we carried out a morphometric study of immuno-identified gonadotrope cells using an in vitro superfusion system. Treatment with gonadotropin-releasing hormone induced a degranulation of small (110–255 nm) and medium (236–360 nm) secretory granules as well as hypertrophy of the endoplasmic reticulum and Golgi complex. Simultaneous incubation with gonadotropin-releasing hormone and cycloheximide inhibited the release of secretory granules although the endoplasmic reticulum and Golgi complex were hypertrophied. These morphological results strongly suggest: (1) that gonadotropin-releasing hormone induces degranulation and hypertrophy of the biosynthetic machinery in gonadotrope cells; and (2) that the activation of the endoplasmic reticulum and Golgi complex by stimulation with gonadotropin-releasing hormone is independent of protein synthesis, while the release of secretory granules is protein synthesis-dependent. In addition, the second or “storage” pool of gonadotropin is associated mainly with the small and medium secretory granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00327759
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  • 4
    Electronic Resource
    Electronic Resource
    Immunocytochemical and ultrastructural study of the frog (Rana pipiens) pars distalis with special reference to folliculo-stellate cell function during in vitro superfusion (1989)
    Springer
    Cell & tissue research 256 (1989), S. 623-630 
    Details
    ISSN: 1432-0878
    Keywords: Immunocytochemistry ; Prolactin cells ; Gonadotropic cells ; ACTH cells ; Folliculo-stellate cells ; Rana pipiens (Anura)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The colloidal gold immunocytochemical technique was used to determine the ultrastructural features of the glandular cells in the pituitaries of male frogs, Rana pipiens, both in vivo and after superfusion in vitro. Specific reactions to antisera against bullfrog gonadotropins, human prolactin, and synthetic 1–39 corticotropin allowed identification of the 3 corresponding types of glandular cells. No immunoreaction was obtained with antisera against human or ovine-growth hormone, human β-thyrotropin hormone, and bovine S-100 protein. General morphological features of these immunocytochemically identified glandular cells were similar to those of equivalent cells previously described in other amphibian species. Non-glandular folliculo-stellate cells were distinctive. In freshly removed pituitaries, these folliculo-stellate cells contained lysosome-like structures, but did not show phagocytic vacuoles in the cytoplasm; they contained many mitochondria, and the Golgi complex and endoplasmic reticulum were relatively undeveloped. After 4 or 18 h of superfusion, some immunoreactive gonadotropic, prolactin, and corticotropic cells showed degeneration and destruction. In the same gland, folliculo-stellate cells retained a viable appearance, but showed phagocytic vacuoles containing secretory granule-like structures which were immunoreactive to gonadotropic, prolactin, and corticotropic antibodies. Some folliculo-stellate cells showed phagocytic vacuoles containing complete glandular cells. These results suggest that superfusion causes a destruction of some of the glandular cells, and that folliculo-stellate cells act as phagocytes when cellular debris or moribund cells are present in the intercellular space in the pituitary parenchyma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225612
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  • 5
    Electronic Resource
    Electronic Resource
    Morphometric evaluation of subcellular changes induced by in vivo TRH treatment in the pituitary gland of Rana perezi: Effects on prolactin and thyrotropic cells (1989)
    Springer
    Cell & tissue research 256 (1989), S. 391-398 
    Details
    ISSN: 1432-0878
    Keywords: Pars distalis ; Prolactin/thyrotropic cells ; TRH ; Immunocytochemistry ; Morphometry ; Rana perezi (Anura)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of synthetic thyrotropin-releasing hormone on pituitary prolactin and thyrotropic cells were investigated in adult male Rana perezi (formerly Rana ridibunda) frogs. Animals were given daily injections of synthetic thyrotropin-releasing hormone into the dorsal lymph sac. Prolactin and thyrotropic cells were identified by the colloidal-gold method, using anti-human prolactin and anti-human-β-thyrotropin hormone as primary antisera. The stereological parameters of the rough endoplasmic reticulum, Golgi complex, and secretory granules of prolactin and thyrotropic cells were evaluated by ultrastructural morphometry (point-counting method). Thyrotropin-releasing hormone caused cytological changes in both cell-types which were consistent with increased synthesis and release of both prolactin and thryrotropin. These changes were still significant after 48 h treatment in the case of thyrotropic cells, while in prolactin cells the thyrotropin-releasing hormone increased the number of secretory granules. After 6 days, the cells resembled essentially those used as controls. These results indicate that thyrotropin-releasing hormone stimulates the synthesis and release of prolactin and thyrotropin, and that the response of each cell type to this hypothalamic stimulus follows a different time-course.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00218897
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  • 6
    Electronic Resource
    Electronic Resource
    Differential morphometric values induced in Golgi apparatus of higher plant cells by aldehyde and permanganate fixation (1989)
    New York, NY : Wiley-Blackwell
    Journal of Electron Microscopy Technique 11 (1989), S. 1-8 
    Details
    ISSN: 0741-0581
    Keywords: Electron microscopy ; Fixation methods ; Golgi apparatus morphometry ; Onion roots ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Natural Sciences in General
    Notes: In order to determine the best conditions to carry out quantitative ultrastructural studies in plant specimens, five different fixation techniques, including some of the most reported electron microscopy fixatives (glutaraldehyde-paraformaldehyde, osmium tetroxide, potassium permanganate), were assayed in onion root meristems to check their ability to induce morphometric changes in Golgi apparatus ultrastructure. Although the parameters evaluated showed in all cases the same tendency, values obtained after permanganate fixation were always higher than those found after aldehyde techniques (especially aldehyde-osmium). Aldehyde followed by osmium fixation appears as the most indicated fixation method when accurate quantitative ultrastructural studies are to be developed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jemt.1060110102
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