Distribution of nitrogen-13 from labeled nitrate (13No3-) in humans and rats.

The body distribution of gavaged or intravenously administered nitrate labeled with nitrogen-13 was studied in humans and rats with the following results: (i) the labeled compound is not quickly absorbed from the stomach; (ii) the concentration of the label increases inside the lower intestinal tract (cercum and large intestine) when ingested or intravenously injected; and (iii) humans and rats have the capacity to store a portion of the label in their bodies. These observation indicate that depletion of body stores, the passage of nitrate down the gut, or the secretion of nitrate into the intestinal lumen may be a better explanation of the urinary, ileal, and fecal concentrations of nitrate and nitrite recently measured in humans that a bacterial nitrification reaction in the intestines, as suggested by Tannenbbaum et al.