Urinary excretion of nitrite and nitrate in experimental glomerulonephritis reflects systemic immune activation and not glomerular synthesis.

In immune-induced glomerulonephritis (gn), glomeruli (gl) synthesize nitric oxide (NO), and urinary nitrite (NO2-) excretion is increased. In mammals on a low nitrate (NO3-) diet, urinary NO3- is a measure of endogenous NO3- synthesis. Excretion is increased after administration of macrophage activators, reflecting induction of NO production. To determine whether increased urinary NO2- gn is due to glomerular synthesis we studied urinary NO2-/NO3- in accelerated nephrotoxic nephritis induced by preimmunization with rabbit immunoglobulin G (IgG), followed by rabbit anti-rat nephrotoxic globulin, and in control rats similarly preimmunized with rabbit IgG, but followed by normal rabbit serum. Both urinary NO2- and NO3- were increased by i.p. preimmunization with rabbit IgG (peak 463 +/- 171 nmol NO2-/60.3 +/- 9.4 nmol NO3-/24 h, P < 0.001 for both NO2- and NO3- compared with preimmunization levels). Repeat immunization with i.v. rabbit anti-rat nephrotoxic globulin (nephritic rats) or normal rabbit globulin (control rats) again increased urinary NO2- and NO3-. There was no statistically significant difference in urinary NO2- and NO3- levels between nephritic rats where globulin had nephrotoxic activity and the control rats injected with normal rabbit globulin, despite increased NO2- synthesis in ex vivo nephritic glomeruli after nephrotoxic globulin (7.9 +/- 1.9 nmol/2000 gl/48 h; controls 3.2 +/- 1.0 nmol/2000 gl/48 h). Thus neither urinary NO2- nor NO3- levels reflect local activation of the NO pathway in glomeruli. As reported for other stimulants, we show here that systemic stimulation with foreign antigen increased NO synthesis.