Abstract
Since endogenous vasopressin has been reported to be an aggressor in the gastric mucosa and a vasoconstrictor in the gastric circulation, we investigated the gastric cytoprotective effects of OPC-21268, a newly developed, nonpeptide, orally active vasopressin-1 receptor antagonist, on ethanol-induced gastric injury in rats. The rats were treated with OPC-21268 or placebo 2 hr before ethanol administration, and the gastric mucosa was evaluated macroscopically for ulcer damage, and histologically for gastric mucosal injury. Gastric mucosal blood flow, erythrocyte volume, and erythrocyte velocity were also measured in groups given saline, ethanol alone, and ethanol after OPC-21268. To investigate the role of systemic or locally secreted vasopressin, we measured plasma and tissue (gastric mucosa) vasopressin concentrations after ethanol or vehicle administration. Prophylactic OPC-21268 treatment improved the gastric ulcer score in a dose-dependent manner, and histological examination demonstrated that the drug significantly ameliorated the gastric injury induced by ethanol. The hemodynamic values obtained in the OPC-21268-treated and ethanol-treated group were similar to those in the saline control group, but values were significantly (P < 0.05) higher for gastric mucosal blood flow and erythrocyte velocity and lower for erythrocyte volume compared to the group given ethanol alone. Plasma vasopressin concentrations were not significantly different in the control group and at 15, 30, and 60 min after administration of ethanol. However, ethanol administration caused a threefold increase in gastric tissue vasopressin level (P < 0.05) compared to the control group. These results suggested that OPC-21268 relieved congestive hyperemia in the gastric mucosa and ameliorated the mucosal injury caused by ethanol, probably as a result of inhibition of vasopressin-mediated actions on the stomach. The vasopressin involved was probably generated locally in the gastric mucosa after ethanol administration.
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