Medicinal Plants Classification Biosynthesis and ... - Index of

Gastroprotective Triterpenoids: Pharmacological Mechanism
is throw activation of the ERK (extracellular signal-regulated kinase) and JKN (Jun Nterminal
kinase) pathways [64].
Additionally H2S role of protecting gastric mucosa from injury, it has been related with
ulcer healing. Twice-daily treatment for a week with hydrogen sulfide donors increased
extent of healing gastric ulcers after acetic acid-induced gastric injury. L-cysteine, a precursor
of H2S, also accelerates healing of the ulcers. Taking together, these results suggest that
hydrogen sulfide is produced in the gastric mucosa response to injury and acts to promote
healing [13]. Ulcer healing may be related with the increment on VEGF (vascular endothelial
growth factor) [65].
Even though there are several reports about the anti-inflammatory and gastroprotective
effect of hydrogen sulfide, it has exhibited a paradoxical role. Hydrogen sulfide participates
as proinflammatory substance; sodium hydrosulfide (donor of H2S) in mice increased lung
and liver mieloperoxidase activity and raised TNF-α concentration, while D-Lpropargylglycine
(a CSE inhibitor) exhibited marked anti-inflammatory activity [66]. H2Sproducing
enzymes are presented on enteric neurons of humans and guinea pig; H2S evokes
ion secretion in colonic mucosa by activating TRPV1 (transient receptor potential vanilloid-
1) on extrinsic primary afferent terminals [67].
Further studies needs to be done to elucidate the mechanism for the dual role of hydrogen
sulfide acting as pro-inflammatory and anti-inflammatory molecule.
3.3. Neuronal Factors
The enteric nervous system is a collection of neurons in the gastrointestinal tract that
constitutes the "brain of the gut" and can function independently of the central nervous
system. This system controls the motility, exocrine and endocrine secretions, and
microcirculation of the gastrointestinal tract; it is also involved in regulating immune and
inflammatory processes [68].
There are two principal intramural plexuses in the gastrointestinal tract: the myenteric
plexus (Auerbach's plexus) and the submucosal plexus (Meissner's plexus) on the luminal
side of the circular muscle layer. Preganglionic and parasympatic fibers from the vagus are
connected to ganglion cells in the plexuses.
The neurons within the plexuses constitute the enteric nervous system and secrete
acetylcholine, noradrenaline (norepinephrine), 5-hydroxytryptamine, purines, nitric oxide
and a variety of pharmacologically active peptides such as gastrin-releasing peptide (GRP),
vasoactive intestinal polypeptide (VIP), pituitary adenylate cyclase-activating polypeptide
(PACAP) and substance P. The enteric plexus also contains sensory neurons, which respond
to mechanical and chemical stimuli [3, 69].
When mucosal barrier is disrupted an increment of acid in the lamina propia is the signal
key to spinal afferent neurons activates a peptide transmitter, calcitonin gen receptor peptide
(CGRP) to induce NO synthesis, finally NO increases gastric blood flow and bicarbonate
secretion [70].
Furthermore, CGRP in nerve fibers has been related with the capacity of the gastric
mucosa to defend itself against injury [71]. TRPV1 is an acid-sensitive ion channel expressed
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