Fate of Ingested 15 N‐Labelled Nitrate and Nitrite in the Rat

ABSTRACT The fate of ingested nitrate and nitrite was investigated in rats by carrying out single and multiple dose feeding studies with 15 N‐labelled nitrate and nitrite. By 72 hr after discontinuation of administration of the 15 N‐labelled compounds, about 60–70% of the dose was excreted in the urine, and 10–20% was eliminated in the feces. Residual 15 N remaining in the bbody carcass was about 10% following single dose experiments and 3–4% following continuous feeding trials. One‐half or more of the excreted 15 N was not analyzable chemically as nitrate or nitrite. On the basis of chemical analysis, about 30% of the dose was excreted in urine as nitrate plus nitrite; excretion in the feces was low. Negligible amounts of nitrate‐N or nitrite‐N were found in blood and organs of the animals. Most of the nonnitrate‐ 15 N and nonnitrite‐ 15 N was excreted, like nitrate‐N and nitrite‐N, rather rapidly from the body.