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  • Articles: DFG German National Licenses  (4)
  • Coleus  (2)
  • Phentolamine  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Phentolamine, a deceptive tool to investigate sympathetic nervous control of insulin release (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 337 (1988), S. 637-643 
    Details
    ISSN: 1432-1912
    Keywords: Sympathetic nervous system ; α-Adrenoceptor blockers ; Phentolamine ; Insulin secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We investigated the effects of phentolamine and another more selective α2-adrenoceptor antagonist, rauwolscine, on insulin release in vivo (in female Wistar-rats) and in vitro (in perfused rat pancreas and in isolated perifused mouse islets). Phentolamine was found to significantly increase glucose-induced insulin release. On the other hand, rauwolscine failed to do so, when applied in a concentration that effectively antagonized the inhibitory effect of clonidine. These results demonstrate that phentolamine is capable of directly stimulating insulin release. This effect is thus not mediated by α-adrenoceptors. For this reason phentolamine is not an appropriate tool to study possible inhibitory effects of the sympathetic nervous system on insulin release. An enhanced insulin response as may be observed in animals and in man in the presence of phentolamine does not furnish evidence for a tonic inhibitory control of the islet cells by the sympathetic nervous system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175789
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Fine structure, pattern of division, and course of wound phloem in Coleus blumei (1980)
    Springer
    Planta 150 (1980), S. 357-365 
    Details
    ISSN: 1432-2048
    Keywords: Cell division pattern ; Coleus ; Phloem regeneration ; Sieve elements, differentiation ; Wound sieve-elements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The wound phloem bridges which have developed six days after interrupting an internodal vascular bundle contain wound sieve-elements, companion cells, and phloem parenchyma cells. An analysis of the meristematic activity responding to the wounding clearly demonstrates that three consecutive divisions are prerequisite to the formation of phloem mother-cells. Companion cells are obligatory sister cells of wound sieve-elements, connected to the latter by specific plasmatic strands and provided with a dense protoplast. Six days after wounding most of the wound sieve-elements are still at a nucleate state of development, but already have characteristic P-protein bodies and plastids containing sieve-element starch. Their cytoplasmic differentiation corresponds to the changes recorded during maturation of ordinary sieve elements. Sieve-plate pores penetrate through preexisting parenchyma cell walls, only, and develop from primary pitfield-plasmodesmata. Wound sieve-elements do not connect to preexisting bundle sieve-elements, they open a new tier of young sieve elements produced by cambial activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00390170
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    An insulin-releasing property of imidazoline derivatives is not limited to compounds that block α-adrenoceptors (1989)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 340 (1989), S. 321-327 
    Details
    ISSN: 1432-1912
    Keywords: Sympathetic nervous system ; α-Adrenoceptor antagonists ; Phentolamine ; Imidazolines ; Insulin secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary As we have demonstrated previously phentolamine stimulates the release of additional insulin from isolated mouse islets and raises plasma insulin levels in the whole rat. This effect was independent of the well known property of phentolamine to block α-adrenoceptors. In experiments on isolated pancreatic islets from mice we now demonstrate that tolazoline and antazoline which are chemically closely related to phentolamine, share its ability to potentiate insulin release. The following results were taken as evidence that this effect does not result from an a-adrenoceptor blocking action of imidazoline compounds. More than 10 times higher concentrations of phentolamine were required to liberate additional insulin from isolated islets than were effective in counteracting the inhibitory effect of clonidine on insulin release. The newly introduced α2-adrenoceptor antagonist BDF 8933, which is an imidazoline derivative, stimulates insulin release as well, while the irreversible α-adrenoceptor blocking agent benextramine of different structure failed to do so, even when being present in concentrations blocking the α2-adrenoceptor-mediated effects of clonidine. Antazoline shared the ability of phentolamine to stimulate insulin release despite having no or only very little α-adrenoceptor blocking activity. When used under our conditions, it almost entirely failed to alleviate the inhibition of insulin release induced by clonidine. We conclude that the response of the islet cells to imidazoline derivatives is not limited to those capable of blocking α-adrenoceptors. On the other hand, α-adrenoceptor blocking agents of different chemical structure fail to induce the release of additional insulin. We take this as evidence that in our experiments the islet cells respond to imidazoline derivatives and not to α-adrenoceptor blockade.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00168517
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The development of specific sieve-element plastids in wound phloem ofColeus blumei (S-type) andPisum sativum (P-type), regenerated from amyloplast-containing parenchyma cells (1983)
    Springer
    Protoplasma 114 (1983), S. 125-132 
    Details
    ISSN: 1615-6102
    Keywords: Sieve-element plastids ; Wound phloem ; Regeneration ; Sieve-tube starch ; Coleus ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In experimentally-induced wound phloem, sieve-element plastids express their genetically determined type in depositing amylopectinrich sieve-tube starch (Coleus, S-type) and polygonal protein crystals (Pisum, P-type). Sieve-element plastids budd off from preexisting amyloplasts, pass through a short amoeboid state and develop into spherical plastids with translucent matrix. During early phases of differentiation wound sieve-elements contain two populations of plastids: typical sieve-element plastids and residual parenchyma plastids with large amylose-rich starch grains. The retardation in the break down of the latter is discussed. Sieve-tube and amyloplast starches are likewise digested by α-1,4- and α-1,6-bond cleaving glucosidases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279876
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    Paper (German National Licenses)
    Fulltext
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