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Role of curcumin in protection of gastric mucosa against stress-induced gastric mucosal damage. Involvement of hypoacidity, vasoactive mediators and sensory neuropeptides.

The antioxidizing properties of curcumin, a highly pleiotropic substance used for centuries in traditional medicine has been confirmed by numerous experimental and clinical studies. Curcumin exhibits anti-inflammatory, antiproliferative and anti-angiogenic actions inhibiting the development and progression of tumors but the efficacy of this compound to influence gastric acid secretion n in the stomach and to affect the gastric mucosal damage induced by non-topical ulcerogenes such as stress has been little studied. We determined the effect of curcumin on basal and pentagastrin- or histamine-stimulated gastric secretion, in rats with surgically implemented gastric fistulas and we assessed the contribution of gastric secretion, endogenous prostaglandin (PG), endogenous nitric oxide (NO), as well as sensory afferent nerves in the mechanisms underlying the potential gastroprotective effects of curcumin against stress-induced gastric mucosal lesions. Rats exposed to water immersion and restraint stress (WRS) for 3.5 h were pretreated either with: 1) vehicle (saline); 2) curcumin (2.5 - 100 mg/kg i.g.) or 3) curcumin (50 mg/kg i.g.) combined with or without indomethacin (5 mg/kg i.p.), SC-560 (5 mg/kg i.g.) or rofecoxib (10 mg/kg i.g.); 4) curcumin (50 mg/kg i.g.) co-administered with (L-NNA (20 mg/kg i.p.) with or without L-arginine (200 mg/kg i.g.), a substrate for NO-synthase; 5) curcumin (50 mg/kg i.g.) administered in rats with intact or capsaicin-induced functional ablation of sensory nerve fibers, and 6) curcumin (50 mg/kg i.g.) administered with capsazepine (5 mg/kg i.g.), the antagonist of vanilloid TRPV1 receptor. The number of gastric lesions was determined by planimetry, the gastric blood flow (GBF) was assessed by H2-gas clearance technique, the plasma gastrin concentrations were measured using the radioimmunoassay (RIA) and the expression of mRNA for tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in gastric mucosa was evaluated by reverse transcription polymerase chain reaction (RT-PCR). Curcumin dose-dependently reduced the WRS-induced gastric lesions, the dose inhibiting these lesions by 50% being about 50 mg/kg. These effects of curcumin were accompanied by an increase in GBF and the reduction in basal and histamine- or pentagastrin-stimulated gastric acid secretion. The protective and hyperemic activities of curcumin (50 mg/kg i.g.) against WRS lesions were significantly attenuated (P < 0.05) in rats pretreated with rofecoxib and SC-560 and completely reversed (P < 0.01) by indomethacin. L-NNA significantly reduced (P < 0.05) the decrease in WRS-induced lesions and the accompanying rise in GBF caused by curcumin and these effects were restored by concurrent treatment with L-arginine (200 mg/kg i.g.). The curcumin-induced decrease in the number of WRS-induced gastric lesions and accompanying increase in the GBF were significantly attenuated (P < 0.05) in capsaicin-denervated rats and in those pretreated with capsazepine. These effects of curcumin in rats with capsaicin denervation were restored by concomitant treatment with exogenous calcitonin gene related pepetide (CGRP) combined with curcumin and subsequently exposed to WRS. The expression of mRNA for TNF-α, COX-2 and iNOS was significantly increased (P < 0.05) in vehicle-pretreated control rats exposed to WRS and significantly attenuated (P < 0.05) by curcumin administered in graded dosages. We conclude that curcumin exerts gastroprotective and hyperemic activities against experimental stress-induced gastric lesions by mechanism involving endogenous prostaglandins, NO, the neuropeptides such as CGRP released from capsaicin-sensitive afferent nerves and the activation of vanilloid TRPV1 receptors located on these sensory nerve terminals.