Effect of sodium nitrate loading on electrolyte transport by the renal tubule

In dogs effects of sodium nitrate were compared with sodium chloride loading on transport of electrolytes by the nephron. Maximal levels of free water clearance/glomerular filtration rate (CH0/GFR) averaged 8.4% with nitrate loading and 14.4% with saline loading. Since ethacrynic acid and chlorothiazide exert their major natriuretic effect in the distal nephron, the increment in Na and Cl excretion produced by these agents was utilized as an index of Na and Cl reabsorbed beyond the proximal tubule. The administration of these agents resulted in an increase in fractional sodium excretion (CNa/GFR) of 21.1%, urinary sodium excretion (UNaV) of 1,126 μeq/min, and urinary chloride excretion (UCLV) of 848 μeq/min during nitrate loading compared with an increase in CNa/GFR of 37.6%, UNaV of 2,362 μeq/min, and UCLV of 2,397 μeq/min during saline loading. The smaller diuretic induced increment in Na and Cl excretion in the nitrate studies suggests, as do the hydrated studies, that less Cl and Na are reabsorbed in the distal nephron during nitrate than saline loading. At every level of UNaV, fractional bicarbonate reabsorption was higher, urine pH was lower, and urinary potassium excretion (UKV) was higher in the nitrate studies. Thus, compared with saline loading, sodium nitrate decreases chloride and sodium reabsorption in the distal nephron. The higher hydrogen and potassium secretion in the nitrate studies may be consequent to the decreased ability of the distal nephron to reabsorb chloride.