Anti-tumor necrosis factor alpha (TNF-alpha) treatment decreases nitric oxide (NO) synthesis and ameliorates the hyperdynamic circulation in portal hypertensive rats. We have recently demonstrated that nitric oxide synthase isoform 3 (NOS3) is overexpressed in portal hypertensive gastric mucosa and that resultant NO overproduction probably is responsible for the increased susceptibility of the mucosa to damage. In the present study, we examined whether TNF-alpha is overexpressed in portal hypertensive gastric mucosa and whether anti-TNF-alpha treatment affects gastric NOS3 messenger RNA (mRNA) and protein expression. We examined plasma concentrations of TNF-alpha and its protein expression in gastric specimens from portal hypertensive and sham-operated rats using Western blotting and immunohistochemistry. We also measured gastric mucosal blood flow, gastric expression of NOS3 mRNA and protein, and NOS3 enzyme activity in rats with and without TNF-alpha-neutralizing antibody treatment. The TNF-alpha protein levels in portal hypertensive stomachs were significantly increased by 57% compared with levels in sham-operated controls. TNF-alpha antibody treatment normalized gastric mucosal blood flow in portal hypertensive stomachs and significantly reversed overexpression of gastric NOS3 mRNA, protein, and its enzyme activity in portal hypertensive rats by 48%, 45%, and 33%, respectively. These results suggest that TNF-alpha may regulate NOS3 expression in the portal hypertensive stomach and that anti-TNF-alpha treatment may ameliorate the pathophysiological abnormalities of portal hypertensive gastric mucosa.