CONSTITUTIVE NOS ISOFORMS ACCOUNT FOR GASTRIC-MUCOSAL NO OVERPRODUCTION IN UREMIC RATS

To study whether renal failure enhances gastric mucosal nitric oxide ( NO) formation in the rat, we measured 1) in vivo NO concentration and 2) NO synthase (NOS) activity, content, and mRNA expression in gastric mucosal homogenates of uremic and sham-operated anesthetized rats. Ga stric mucosal NO release was measured by an electrochemical technique. NOS content was analyzed by Western immunoblots, using specific monoc lonal antibodies. Constitutive (Ca2+ dependent; cNOS) and inducible (C a2+ independent; iNOS) NOS activities were assayed by following the co nversion of L-[U-C-14]arginine to [U-C-14]citrulline. mRNA expression for the constitutive neuronal (ncNOS), endothelial (ecNOS), and iNOS i soforms was determined by reverse transcription-polymerase chain react ion. Under basal conditions, gastric mucosal NO concentration was sign ificantly greater in uremic compared with control rats. This was accom panied by significantly greater gastric mucosal cNOS activity in uremi c rats than in control rats, whereas no differences were observed in i NOS activity between both groups of animals. Moreover, total enzyme co ntent and the levels of gastric mucosal mRNA expression for ncNOS, ecN OS, and iNOS showed no significant differences between uremic and sham -operated rats. These data confirm that, in uremic rats, enhanced Ca2-dependent NOS activity is responsible for gastric mucosal NO overprod uction and suggest that the main regulatory mechanism is not transcrip tional but translational and/or posttranslational in nature.