MAR-99

In this study, we determined the role of mucosal mast cell (MMC) activation in the pathogenesis of intestinal ischaemia-reperfusion (I/R) injury by immunohistochemical analysis using anti-RMCP II antibody. In addition, we investigated the role of free-radical generation in the activation of MMCs in this model.

In the first experiment, rats were divided into four groups: (1) sham operated; (2) I/R + saline; (3) I/R + the mast cell stabilizer, MAR-99 (30 mg/kg); and (4) I/R + MAR-99 (100 mg/kg). Treatment with MAR-99 was started 1 h before the occlusion of the superior mesenteric artery (SMA). In the second experiment, rats were divided into five groups: (1) sham operated; (2) I/R + saline; (3) I/R + superoxide dismutase (SOD; 50,000 U/ml); (4) I/R + catalase (90,000 U/ml); and (5) I/R + allopurinol (50 mg/kg/day). Intravenous administration of SOD and catalase was performed 1 h before SMA occlusion. Oral administration of allopurinol was started 2 days before I/R surgery. We measured several parameters of intestinal mucosal injury and evaluated the degranulation of MMCs by using an immunohistochemical technique.

The number of resting MMCs, detected by anti-RMCP II antibody, was significantly decreased in the I/R-treated rats. The I/R treatment induced a decrease in the mucosal histamine content and an increase in plasma histamine levels. Mucosal permeability in the small intestine was significantly enhanced by I/R treatment. However, these changes were significantly prevented by pretreatment with the MMC stabilizer, MAR-99. Furthermore, administration of several free-radicals scavengers (SOD, catalase, and allopurinol) also blocked the I/R-induced degranulation of MMCs.

These data indicate that activation of MMCs was involved in the pathogenesis of I/R-induced intestinal mucosal injury. In addition, some parts of the I/R-induced MMC activation pathway were mediated by free-radical generation.

To clarify the anti-gastric acid secretory mechanism of 1,6-dihydro-2-[2-(2-methylpropoxy)anilino]-6-oxo-5-pyrimidinecarbo xylic acid (CAS 98772-05-5, MAR-99), the relationship between gastric acid secretion and gastric mucosal mast cell (MMC) was studied and the effect of this compound on these parameters was examined and compared with anti-allergic drugs (mast cell stabilizers) and anti-ulcer drugs. The release of histamine from MMC cultured from bone marrow and connective tissue mast cell (CTMC) isolated from peritoneal cavity was found to be induced by the addition of ethanol (final conc. 17.5%), and the inhibitory effect on histamine release from MMC is closely associated with the anti-gastric secretory effect. That is to say, MAR-99 (10(-9)-10(-7) mol/l) inhibited histamine release from MMC induced by ethanol in a concentration-dependent manner. The action of MAR-99 on MMC was more sensitive than that of CTMC. In addition, MAR-99 (100 mg/kg i.d.) suppressed gastric acid secretion. On the other hand, anti-allergic drugs (mast cell stabilizers), such as DSCG and tranilast (both 10(-7) mol/l), markedly inhibited histamine release from CTMC induced by ethanol, but these drugs (10(-8)-10(-7) mol/l) showed only a tendency to prevent the release of histamine from MMC. Furthermore these drugs (both 100 mg/ kg i.d.) had no effects on gastric acid secretion. Equally anti-ulcer drugs, such as cetraxate, teprenone and sofalcone, had no effects on histamine release from mast cells of two types and gastric acid secretion. From these results, it was suggested that MMC is closely correlated with gastric acid secretion, and the anti-gastric secretory effect of MAR-99 may mainly contribute to prevent the degranulation of MMC.