The present study examined the interaction between neutrophils and gastric mucosal nitric oxide (NO) synthesis in the regulation of gastric mucosal integrity in the rat. Male Sprague-Dawley rats were made neutropenic by intraperitoneal injections of methotrexate (MT; 2.5 mg/kg) or antineutrophil serum (ANS; 100 microliters). Control rats were treated with saline. Neutropenia was confirmed by circulating neutrophil counts and tissue myeloperoxidase activity. Neutropenic or control rats were given 2 ml of ethanol (EtOH; 40% w/v intragastrically). Neutropenic rats were less susceptible to EtOH-induced mucosal damage when compared to control rats. Mucosal NO synthesis was increased in neutropenic rats. EtOH instillation reduced NO synthase in control rats. However, in MT-treated rats the reduced NO synthase activity was not different from that observed in untreated control rats.
Conclusions: (1) EtOH-mediated gastric mucosal injury appears to be a neutrophil-mediated process. (2) Neutropenia results in an increase in mucosal NO synthesis. (3) MT treatment augments the degree of mucosal integrity. The increase in integrity is associated with a reduction in mucosal neutrophil infiltration as well as maintenance of NO synthase activity. ANS appears to influence mucosal integrity primarily by a reduction in circulating neutrophils.