Exogenous
prostaglandins (PG) applied in small gastroprotective doses fail to affect healing of gastro-
duodenal ulcers but accelerate the healing when used in larger gastric inhibitory doses that appear to enhance COX-2 expression and
PGE(2) generation in the
ulcer area. COX-1 and COX-inhibitors delay
ulcer healing, particularly when both COX
isoforms are suppressed such e.g. by
indomethacin.
Dexamethasone, that decreases the expression of COX-2 and mucosal generation of
PGE(2), delays
ulcer healing that can be reversed by the addition of small dose of exogenous
PGE(2).
Proton pump inhibitors (PPI) such as
omeprazole and
PGE analogs, accelerate
ulcer healing mainly due to potent inhibition of gastric acid secretion, but they also augment the COX-2 expression and
enzyme activity in the ulcerated mucosa. Endogenous PG generated at
ulcer margin appear to be involved in
ulcer healing promoted by
growth factors and gut
hormones such as
gastrin or CCK and
melatonin acting, at least in part, through increase of induction of COX-2 and local release of
PGE(2) in the
ulcer area. The
ulcer healing activity of
growth factors (e.g.
EGF,
TGF alpha, HGF) and certain gut
hormones (
gastrin, CCK) as well as
melatonin, can be attenuated by treatment with COX-1 or
COX-2 inhibitors which suppress the release of
PGE(2) but enhance the expression of COX-2. It is concluded that endogenous PG originating mainly from upregulated COX-2 at the
ulcer margin play crucial role in
ulcer healing by exogenous PG, PPI,
growth factors, gut
hormones and
melatonin, while COX-1 and
COX-2 inhibitors delay
ulcer healing by suppressing PG generation, and increasing COX-2 expression in the
ulcer area.