1. In the stomach,
prostaglandins protect the gastric mucosa against
injuries. One rate-limiting step in
prostaglandin synthesis is mediated by
prostaglandin endoperoxide synthase (PGHS), the target
enzyme of non-steroidal anti-inflammatory drugs (
NSAIDs). Two
isoforms of PGHS exist: a constitutive (PGHS-1) and an inducible (PGHS-2)
enzyme. PGHS-1 is the major source of gastric
prostaglandins under physiological conditions. Inhibition of
prostaglandin synthesis by traditional
NSAIDs such as
indomethacin and
diclofenac which non-selectively inhibit both PGHS-1 and
PGHS-2, causes gastric and intestinal ulceration and delays
gastric ulcer healing in chronic models. It has been shown that selective
PGHS-2 inhibitors such as
L-745,337 (5-methanesulphonamide-6-(2,4-difluorothio-phenyl)-1-inda none) are not ulcerogenic and do not inhibit gastro-intestinal
prostaglandin synthesis. However, minimal information is available on the long-term effects of
PGHS-2 inhibitors on the healing of previously established gastric
injuries. We assessed the cellular localization and expression of PGHS-1 and
PGHS-2 during
gastric ulcer healing and assessed the effects of
L-745,337 on previously established cryoulcers in the rat gastric stomach. 2. PGHS-1 and
PGHS-2 were located and quantified by immunohistochemistry during experimental
gastric ulcer healing.
PGHS-2 immunoreactivity was only negligible in the normal gastric wall, but after gastric ulcerations, it was strongly detected in monocytes, macrophages, fibroblasts and endothelial cells below and between the regenerative glands. PGHS-1 immunoreactivity detected in normal gastric mucosa, disappeared after gastric ulceration in the mucosa adjacent to the
ulcer crater. However, it reappeared in the regenerative glands from day 5 onwards. Thus, PGHS-1 and
PGHS-2 were located at different sites and their maximal expression followed a different time-sequence. 3. We assessed the effects of
L-745,337,
indomethacin and
diclofenac on
gastric ulcer healing and histological healing parameters in rats.
L-745,337,
indomethacin and
diclofenac dose-dependently decreased the healing of
gastric ulcers.
L-745,337,
indomethacin and
diclofenac decreased epithelial cell proliferation in the
ulcer margin and microvessel density in the
ulcer bed on day 8 and increased the thickness of the granulation tissue below the
ulcer crater and the gap between both edges of the muscularis mucosae on day 15.
Indomethacin and
diclofenac, but not
L-745,337, decreased synthesis of 6-keto-PGF1alpha and
PGE2 in tissue fragments from the stomach and terminal ileum and decreased platelet
thromboxane B2 synthesis in clotting whole blood. 4. Dose-response curves for the inhibition of chronic
gastric ulcer healing by
L-745,337 (administered twice daily intragastrically) showed an ID50 value of 1.7 mg (4.3 micromol) kg(-1). Dose-response curves for the inhibition of
PGE2 synthesis in inflammatory exudates in the acute
carrageenin sponge rat model, showed ID50 values of 1.1 mg (3.1 micromol) kg(-1) and 1.3 (3.3 micromol) mg kg(-1) for
indomethacin and
L-745,337, respectively. Thus, inhibition of chronic
gastric ulcer healing by
L-745,337 occurs within a potentially therapeutic dose-range. 5. In summary,
PGHS-2 is markedly accumulated after gastric ulceration in monocytes, macrophages, fibroblasts and endothelial cells in regions of maximal repair activity. Selective inhibition of
PGHS-2 by
L-745,337 delayed
gastric ulcer healing though interference with epithelial cell proliferation, angiogenesis and maturation of granulation tissue in a potentially therapeutic dose range. PGHS-2-derived
prostaglandins seem to have an important role in
gastric ulcer healing.