Relation between pressure natriuresis and urinary excretion of nitrate/nitrite in anesthetized dogs

Alterations in intrarenal nitric oxide (NO) formation during changes in renal arterial pressure (RAP) have been suggested as a mechanism mediating pressure natriuresis. To test this hypothesis further, we examined the relation between RAP and the urinary excretion rate of nitrate/nitrite (NO3-/NO2-; NO metabolites) in anesthetized sodium-replete dogs before (n = 9) and during (n = 6) intrarenal infusion of the NO synthesis inhibitor nitro-L-arginine (NLA; 50 micrograms.kg-1.min-1). Urinary NO3-/NO2- concentrations were measured with the Griess reaction and spectrophotometry methods after enzymatic reduction of NO3- to NO2- in the samples. During control conditions, there were decreases in the urinary NO3-/NO2- excretion rate in response to reductions in RAP (150 to 75 mm Hg; slope, 0.04 +/- 0.01 nmol.min-1.g-1.mm Hg-1) in association with decreases in urinary sodium excretion (UNaV). There was a positive correlation between changes in NO3-/NO2- excretion rate and changes in RAP (r = .48; P < .005) or UNaV (r = .59; P < .001). NLA infusion resulted in decreases in NO3-/NO2- excretion rate (4.8 +/- 1.4 to 1.0 +/- 0.3 nmol.min-1.g-1) in association with reductions in UNaV (4.3 +/- 0.3 to 0.7 +/- 0.2 microL.min-1.g-1), fractional excretion of sodium (2.9 +/- 0.2% to 0.5 +/- 0.1%), and renal blood flow (4.8 +/- 0.3 to 3.3 +/- 0.2 mL.min-1.g-1), without changes in glomerular filtration rate. Furthermore, there was a marked attenuation of the NO3-/NO2- and sodium excretory responses to alterations in RAP during NO synthesis inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)