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.

Germfree and conventional-flora Sprague-Dawley rats were fed sodium nitrate or sodium nitrite in their drinking water (1,000 ,tg/ml), and various organs, tissues, and sections of the intestinal tract were assayed for nitrate (NO3-) and nitrite (NO2-) by a spectrophotometric method. When fed NO3-, germfree rats had chemically detectable levels of NO3-(only) in the stomach, small intestine, cecum, and colon. Conventional-flora rats fed N03had both N03and NO2in the stomach, but only N03in the small intestine and colon. When fed N02-, germfree rats had both N03and N02in the entire gastrointestinal tract. Conventionalflora rats fed N02had both ions in the stomach and small intestine, but only N03in the large intestine. Conventional-flora rats fed N03or N02 had lower amounts of these ions in the gastrointestinal tract than comparably fed germfree rats. Control (non-NO3or N02-fed) germfree and conventional-flora rats had trace amounts of N03-(only) in their stomachs and bladders. These results, in

The in vivo distribution of physiological concentrations of NO3and N02 labeled with 13N was studied in germfree and conventional-flora Sprague-Dawley rats after gastric intubation (gavage), intravenous (cardiac or tail vein), or intraluminal (intestinal) injection. Some in vitro studies were performed to determine the influence of the bacterial flora on ion distribution. After gavage with 13N03-, essentially all of the label passed into the upper small intestine, where most was absorbed; however, up to 24% of the 13N could reach the ileum within 1 h. Gavage with 13N02resulted in some gastric absorption of the label, but most seemed to exit the stomach via passage into the duodenum. The exit of`3N02-from the stomach was slower, and less 13N appeared to be absorbed from the small intestine than with 13N03-. Movement of label through the gastrointestinal tract could be enhanced by inducing diarrhea. Absorbed '3N was either excreted in the urine, reentered the gastrointestinal tract at various points, or was temporarily stored in the eviscerated carcass. The bacterial flora, either by incorporation or chemical alteration, appeared to have some influence on the distribution of '3N from 13N03or 13N02-. 60 to 90 min duration were possible with '3N, and the detection of physiological concentrations of these labeled ions, and their metabolites, could be rather easily and sensitively traced in rats. MATERLALS AND METHODS 13N03and 13N02production and measurement. The tandem accelerator at the University of Wisconsin was used to produce "carrier-free" "3N as '3N03 (26). Chemical determinations showed that less than 0.1% of the '3N was in the form of '3N02or '3NH4'. About 30 mCi was made by bombarding an aerated water target for 20 min with a 3-,uA beam of 11-MeV protons (28). Passage of '3N03through regenerated spongy cadmium columns was used to make '3N02-(29). Samples were measured for radioactivity by placement inside an Nal (TI) crystal "well" detector. The carcass (i.e., the rat without the internal organs specified in the tables), however, was counted at a fixed distance from the well. Corrections to compensate for this change in counting geometry were made on these carcass values to allow comparison with other samples. All samples were counted at least twice for a 10-s interval, and values were decay-corrected to the start of '3N administration with the equation C, = Co-e"', where C, = the measured counts at various times (t) after the start of dissection, Co = the counts corrected to the start of dissection, and A = ln2/half-life of '3N. Animals. GF Sprague-Dawley rats were supplied by the University of Wisconsin Gnotobiology Labora

The nitrate balance of germfree and conventional rats was assessed to determine whether the intestinal flora produces nitrate in vivo. The results indicate that there can be excess nitrate in the urine of germfree as well as conventional rats. This nitrate is apparently of host origin, and the presence of intestinal flora decreases the output of nitrate in urine.