Aim:To investigate the ultrastructural localization of atrial natriuretic peptide(ANP)-synthesizing cells and the relationship between ANP-synthesizing cellsand microvessels in rat gastric mucosa.Methods:Immunohistochemistry tech-niques and postembedding immunoelectron microscopy techniques were used tovalidate the findings regarding the expression of ANP-synthesizing cells and theultrastructural localization of ANP-synthesizing cells in the gastric mucosa.His-tochemistry techniques and the tannic acid-ferric chloride method(TA-Fe stain-ing method)were used to reveal microvessel density and the distribution of ANP-synthesizing cells in different regions of the stomach.Results:Cells expressingANP were localized and ANP-synthesizing cells were identified as enterochroma-ffin(EC)cells in the gastric mucosa.ANP-synthesizing cells existed in differentregions of the stomach.The percentage ANP-synthesizing cells in the mucosawas greatest in the fundus(46.7%e5.3%),intermediate in the antrum(40.1%±4.5%),and least in the body(21.6%±3.6%).There was a positive relationshipbetween the percentage of ANP-synthesizing cells and the density of microvesselsin the antral mucosa,but not in the fundus or body mucosa.Conclusion:ANP issynthesized by EC cells in rat gastric mucosa,and ANP-synthesizing cells aremost dense in the gastric fundus.ANP may act not only as a regional autocrineand/or paracrine regulator,but also as an endocrine regulatory peptide in thegastrointestinal tract. Aim: To investigate the ultrastructural localization of atrial natriuretic peptide (ANP) -synthesizing cells and the relationship between ANP-synthesizing cells and microvessels in rat gastric mucosa. Methods: Immunohistochemistry tech-niques and postembedding immunoelectron microscopy techniques were used to validate the findings regarding the expression of ANP-synthesizing cells and theultrastructural localization of ANP-synthesizing cells in the gastric mucosa. His-tochemistry techniques and the tannic acid-ferric chloride method (TA-Fe stain-ing method) were used to reveal microvessel density and the distribution of ANP -synthesizing cells in different regions of the stomach. Results: Cells expressing ANP were localized and ANP-synthesizing cells were identified as enterochroma-ffin (EC) cells in the gastric mucosa. ANP-synthesizing cells existed in different regions of the stomach. percentage ANP -synthesizing cells in the mucosawas greatest in the fundus (46.7% e5.3%), intermediate in the antrum (40 .1% ± 4.5%), and least in the body (21.6% ± 3.6%). There was a positive relationship between the percentage of ANP-synthesizing cells and the density of microvessels in the antral mucosa, but not in the fundus or body mucosa . Conlusion: ANP issynthesized by EC cells in rat gastric mucosa, and ANP-synthesizing cells are most dense in the gastric fundus. ANP may act not only as a regional autocrine and / or paracrine regulator, but also as an endocrine regulatory peptide in the gastrointestinal tract.