Medicinal Plants Classification Biosynthesis and ... - Index of

Gastroprotective Triterpenoids: Pharmacological Mechanism
Figure 2. Gastroprotective mediators are divided into functional factors (mucus-alkaline secretions, the
phospholipids layer, microcirculation and motility), humoral factors (prostaglandins (PGs), nitric oxide
(NO), lipoxins (LXs) and hydrogen sulfide (H 2S)) and neuronal factors (capsaicin sensitive sensory
neurons). While there are another factors such as diverse cytokines, proteinase activated receptor
(PAR), annexin and probably resolvins that could act as protective mediators.
Mucus gel is secreted by apical expulsion from surface epithelial cells [19, 20]. The
mucus bicarbonate barrier is the only preepithelial barrier between lumen and epithelium.
The mucus gel is formed by phospholipids, and its luminal surface is coated by a film of
surfactant phospholipids with strong hydrophobic properties [19]. When the mucosal barrier
is overwhelmed or breaks down by injury, there is another mechanism that could be
performed in the mucosal defense.
3.1.2. Mucosal microcirculation
Mucosal microcirculation is essential for delivery of oxygen and nutrients and removal of
toxic substances. At the level of the muscularis mucosae, most gastric arteries branch into
capillaries which enter to lamina propia and travel upward in proximity to gastric glandular
epithelial cells. At the base of surface epithelial cells, capillaries converge into collecting
venules [21].
When acid or other irritants enter the subepithelial compartment, sensory afferent
neurons are able to trigger a rapid increase in mucosal blood flow that allows the buffering of
acid and the rapid removal of toxic substances, thus limiting their penetration into deeper
layers of the mucosa [22]. Mucosal blood flow is mediated by endogenous substances such as
PGs, NO, H2S and sensory afferent nerves [23], the role of those substances will be described
in
section 3.2.
It has been described that sildenafil, a cyclic GMP-specific phosphodiesterase inhibitor
promotes an increase in cGMP concentrations in the gastrointestinal tract; besides is well
known that cGMP mediates many of the biological actions of NO, such as promoting an
increment on gastric blood flow. Sildenafil increases mucosal defense against indomethacin-
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