Expression of constitutive nitric oxide synthase in rat and human gastrointestinal tract

The aim of this study was to determine the expression of constitutive NO sy ntheses (ecNOS and bNOS) at the protein level in rat and human gastrointest inal tract. We established a quantitative Western blotting method for detec tion and quantification of ecNOS and bNOS in both species. Human gastric fu ndus was further analyzed by immunohistochemistry. EcNOS expression at the protein level could be quantified in different organs of the rat gastrointe stinal tract and in human gastric mucosal biopsies. Immunohistochemistry of gastric fundus revealed that immunoreactivity for ecNOS was localized main ly in the endothelium of small vessels. In rats, expression of bNOS at the protein level was highest in esophagus. By means of immunohistochemistry of human gastric fundus, immunoreactivity was detected mainly in the plexus o f Auerbach. We conclude that isoforms of constitutive nitric oxide synthase can be identified and quantified at the protein level both in rat and huma n gastrointestinal tract. The presence of bNOS in nerve tissue supports pre vious observations that NO serves as a transmitter in non-adrenergic, non-c holinergic nerves in human esophagus and stomach. The observation that ecNO S has been found mainly in endothelial cells suggests the involvement of NO in the regulation of mucosal blood flow. (C) 1999 Elsevier Science B.V. Al l rights reserved.