RELATION BETWEEN PRESSURE NATRIURESIS AND URINARY-EXCRETION OF NITRATE NITRITE IN ANESTHETIZED DOGS/

Alterations in intrarenal nitric oxide (NO) formation during changes i n renal arterial pressure (RAP) have been suggested as a mechanism med iating pressure natriuresis. To test this hypothesis further, we exami ned the relation between RAP and the urinary excretion rate of nitrate /nitrite (NO3-/NO2-; NO metabolites) in anesthetized sodium-replete do gs before (n=9) and during (n=6) intrarenal infusion of the NO synthes is inhibitor nitro-L-arginine (NLA; 50 mu g.kg(-1).min(-1)). Urinary N O3-/NO2- concentrations were measured with the Griess reaction and spe ctrophotometry methods after enzymatic reduction of NO3- to NO2- in th e samples. During control conditions, there were decreases in the urin ary 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 associatio n with decreases in urinary sodium excretion (UNaV). There was a posit ive correlation between changes in NO3-/NO2- excretion rate and change s in RAP (r=.48; P<.005) or UNaV (r=.59; P<.001). NLA infusion resulte d in decreases in NO3-/NO2- excretion rate (4.8+/-1.4 to 1.0+/-0.3 nmo l.min(-1).g(-1)) in association with reductions in UNaV (4.3+/-0.3 to 0.7+/-0.2 mu L.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.mi n(-1).g(-1)), without changes in glomerular filtration rare. Furthermo re, there was a marked attenuation of the NO3-/NO2- and sodium excreto ry responses to alterations in RAP during NO synthesis inhibition. In another four dogs, it was observed that urinary NO3-/NO2- excretion ra te did not change during administration of thiazide and amiloride diur etics, indicating that the NO3-/NO2- excretory responses to alteration s in RAP were not simply due to changes in urine flow rate or sodium e xcretion. These findings are consistent with the hypothesis that durin g acute changes in RAP, intrarenal changes in NO production rate may b e responsible for the changes in sodium excretion.