Localization of nitric oxide synthases and increased enterochromaffin-like cells in rat stomach under hypergastrinemia induced by omeprazole

Enterochromaffin-like (ECL) cell, one of the neuroendocrine cells in stomach, has been considered to play roles in the regulation of gastric mucosal blood flow and in the acid secretion by histamine release. We have reported the NO synthesizing activity of ECL cells during the healing process of rat gastric ulcers. Thus, the present study was undertaken to examine the relation between ECL cell and NO synthesis under hypergastrinemia induced by omeprazole (OPZ) as a model of ECL cell hyperplasia. Wistar strain male rats weighing 200 to 250 g were given omeprazole (80 μg/kg/day, through oral intubation) for 14 days before the experiments. ECL cells in the fundic mucosa were detected using anti-chromogranin A immunoreactivity and by electron microscopic observations. NADPH diaphorase histochemistry and immunohistochemistry using antiserum of NO synthase (NOS) isoforms were performed on the cryostat sections of the fixed stomach and observed by light and electron microscopies. In the in vivo method for autoradiography, after the intraaortic infusion of ³H-L-arginine (³H-L-Arg; 10 nmol/hr/100 g) alone or with the blockers, the uptake sites of ³H-L-Arg were observed by light and electron microscopies. NOS activities were measured by the formation of L-[U-¹⁴C] citrulline from L-[U-¹⁴C] arginine. In addition, NOS mRNA expression in the mucosa was detected by RT-PCR method. As a result, after OPZ administration, hypergastrinemia was evoked and the number of ECL cells increased in the mucosa of OPZ-treated rats. NADPH diaphorase activity was significantly enhanced on some of the epithelial cells and these cells were coincided with ECL cells by electron microscopic observations. Immunoreactivity of inducible NOS (iNOS) in the OPZ-treated mucosa was observed in the epithelial cells corresponding to the chromogranin A-containing cells. Uptake of ³H-L-Arg significantly increased in the treated mucosa and the uptake sites were mainly located on ECL cells as well as endothelial cells. iNOS activity was significantly increased and iNOS mRNA expression was observed in the treated mucosa. In conclusion, iNOS was expressed in ECL cells under OPZ-induced hypergastrinemia. This study suggests that ECL cells produce NO under chronic gastrin stimulation.