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Hello everybody. I'm
Joao Paulo Fernandes,
Associate Professor at
the Federal University
of Sao Paulo, Brazil.
My talk will discuss,
about the role of histamine in
allergies and the effects that
ligands of histamine receptors
may cause on these situations.
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Undoubtedly, histamine is one of
the most pleiotropic
substances in
the human body and widely
distributed in
different tissues.
Chemically it is part of
a biogenic amine group,
and this is comprised by an
imidazoline ring linked to
an ethylene amine group very
similar to other
biogenic amines,
such as dopamine,
serotonin, and others.
Histamine was first reported
by Dale and Laidlaw as
an amine present in the tissues
as similar to its
biological precursor,
the amino acid histidine.
Biochemically, these
amino acids suffers
the decarboxylation
reaction catalyzed
by the enzyme histidine
decarboxylase,
which has vitamin
B as co-factor,
and is also a cellular marker of
the histamine activity in
experimental studies.
In physiological pH,
histamine is mainly ionized
in the primary amino group.
This characteristic is
important to activate
its receptors and
also to keep it
compartmentalized in
cellular vesicles.
When released the
main metabolic route
to eliminate histamine
activity is the oxidation by
diamino oxidase
enzyme generating
the imidazolacetic acid
and afterwards it's ribosyation.
This is the main metabolite
of histamine after
a massive release in
an allergic reaction.
However, during the years,
histamine was identified as
an important neurotransmitter in
the central nervous
system. Locally,
the main bio-transformation
route of
histamine is its methylation
in the imidazole nitrogen,
followed by oxidation of the
monoamine oxidase enzyme,
giving the major neural
metabolite
N-methyl-imidazolacetic acid.
