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Effects of the inflammatory mediator bradykinin on intestinal functions

Die Wirkung des Entzündungsmediators Bradykinin auf intestinale Funktionen

Würner, Lisa Katharina


Originalveröffentlichung: (2013) Giessen : VVB Laufersweiler
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URN: urn:nbn:de:hebis:26-opus-101430
URL: http://geb.uni-giessen.de/geb/volltexte/2013/10143/

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Universität Justus-Liebig-Universität Gießen
Institut: Institute of Veterinary Physiology and Biochemistry
Fachgebiet: Veterinärmedizin
DDC-Sachgruppe: Landwirtschaft
Dokumentart: Dissertation
Zeitschrift, Serie: Edition scientifique
ISBN / ISSN: 978-3-8359-6076-3
Sprache: Englisch
Tag der mündlichen Prüfung: 07.08.2013
Erstellungsjahr: 2013
Publikationsdatum: 12.11.2013
Kurzfassung auf Englisch: Bradykinin is a peptide, which is responsible for inflammatory processes throughout the
body. In the intestine it is assumed to be involved in the development of diarrhea by altering
gastrointestinal motility and ion secretion. My PhD‐thesis focused on these effects of
bradykinin on intestinal functions and on the question, how the different systems influenced
by the kinin, i.e. enteric nervous system, motility and secretion, interact with each other.
Therefore, I investigated the effect of bradykinin on rat myenteric neurons, rat intestinal
muscle and rat and human colonic epithelium by applying microelectrode arrays, Ca2+
imaging, immunofluorescence analysis, isometric contraction measurements as well as
standard and real time reverse transcription PCR.
Bradykinin stimulated rat myenteric neurons in a biphasic manner, which was shown on an
action potential level measured with microelectrode arrays as well as on a cytosolic Ca2+
level, as demonstrated by Ca2+ imaging experiments. This effect was mediated by both the B1
and the B2 receptor, with the B1 receptor being upregulated due to the cell culture. This
upregulation was confirmed by immunocytochemistry as well as real time PCR. The
stimulation of myenteric neurons by bradykinin was based on an influx of Ca2+ from the
extracellular space, since a removal of extracellular Ca2+ significantly reduced the bradykinininduced
peak in the fura‐2 ratio.
In the rat intestinal muscle bradykinin induced biphasic responses with a relaxation followed
by a contraction. This effect exhibited a strong segment‐dependency. Since the neurotoxin
tetrodotoxin did not alter the bradykinin‐induced effect, the enteric nervous system was
most likely not involved in the change of contractility. Tetrapentylammonium, a K+ channel
blocker preferentially inhibiting Ca2+‐activated K+ channels, reduced the relaxant component
of the response. In dissociated intestinal muscle cells bradykinin induced an increase of the
cytosolic Ca2+ level as detected in Ca2+ imaging experiments. In native tissue bradykinin acts
via B2 receptors, whereas in vitro incubation induced the expression of B1 receptors, which
then caused a purely contractile response after stimulation with a B1 agonist.
153 Summary
Immunofluorescence analysis of the colonic wall and of dissociated intestinal muscle cells, as
well as RT‐PCR confirmed this finding. The consecutive ablation of adherent layers of the
intestinal wall strongly reduced the response to bradykinin in comparison to a control
stimulus, i.e carbachol, suggesting a contribution of non‐muscle cells in the mediation of this
response.
In Ussing chamber experiments with human and rat colonic tissue I demonstrated a
bradykinin‐induced ion secretion. Measurements with rat full‐thickness preparations
showed reduced effects of bradykinin and the B2 receptor agonist on the change in shortcircuit
current compared to preparations devoid of the muscle layer. In the presence of
tetrodotoxin, the effect of bradykinin was abolished in full‐thickness preparations, whereas
in preparations devoid of the muscle layer, the response was unaltered. This demonstrates
that the reduction of the bradykinin‐response in full‐thickness preparations is not due to
inhibiting influences of the myenteric plexus, but to the muscle layer forming a diffusion
barrier for the kinin.
In human mucosa biopsies bradykinin as well as the B2 agonist (but not the B1 agonist)
induced an ion and mucus secretion. This response was reduced in ulcerative colitis patients
compared to control patients, showing that the bradykinin‐system is most likely involved in
ulcerative colitis. Tetrodotoxin partially inhibited the bradykinin‐effect on both the ion and
the mucus secretion, demonstrating a neuronal component of the bradykinin‐response in
the human mucosal biopsies.
These results demonstrate an involvement of bradykinin in the regulatory systems of the
intestine, influencing the enteric nervous system, the intestinal muscle layer, as well as the
ion and mucus secreting epithelium, which might, especially on the basis of an interaction of
these systems, lead to the beneficial as well as hazardous effects of the inflammatory
mediator bradykinin on intestinal functions.
Kurzfassung auf Englisch: Bradykinin ist wichtiger Entzündungsmediator. Es wird angenommen, dass Bradykinin an der Entstehung von Durchfällen bei entzündlichen Darmerkrankungen beteiligt ist, indem es die gastrointestinale Motilität und die epitheliale Sekretion beeinflusst. In meiner PhD-Arbeit beschäftigte ich mich mit dem Einfluss dieses Kinins auf intestinale Funktionen und mit der Frage, inwiefern die unterschiedlichen durch Bradykinin beeinflussten Systeme, d.h. das enterische Nervensytem, die Motilität und die Sekretion, miteinander interagieren.
Daher untersuchte ich die Wirkung von Bradykinin auf myenterische Neurone und die intestinale Muskulatur der Ratte sowie auf das Colonepithel von Ratte und Mensch.
Die Ergebnisse meiner PhD-Arbeit demonstrieren multiple Angriffsorte von Bradykinin in den regulatorischen Systemen des Gastrointestinaltrakts. Das Kinin beeinflusst sowohl das enterische Nervensystem als auch die intestinale Muskelschicht und das ionen- und mukussezernierende Epithel. Vor allem in Hinblick auf eine Interaktion dieser Systeme scheint der Entzündungsmediator Bradykinin eine zentrale Rolle beim Zustandekommen von Entzündungsreaktionen an diesem Organsystem zu spielen.
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