Distribution and metabolism of ingested NO3- and NO2- in germfree and conventional-flora rats

Abstract

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

Distribution of nitrogen-13 from labeled nitrate and nitrite in germfree and conventional-flora rats

“…If further studies confirm this assumption, it would suggest that the 13N which accumulated in the carcass of both CV and GF rats after oral or i.v. administration was also partly 13NO3-, since mammalian tissues seem unable to metabolize N03in vivo (29). More 13N was found in the carcasses than could be accounted for by blood-borne label so that the tissues generally must be considered to retain NO3.…”

“…For intragastric nitrosation to be significant, ingested NOmust not disappear too rapidly from the stomach. Since little (29) or no (15) gastric reduction of N03 seems to occur in the normal CV or GF rat, the increased retention of gavaged 13N03in full stomachs, as opposed to those empty of food, presumably reflects the contents acting mainly as a physical barrier to exit, although gastric pH changes due to the presence of food (and bacteria) may also influence 13N03exit. The situation in humans appears similar, since the time after a meal influ-APPL.…”

“…Whether 13NO3was gavaged (Table 1) or intraluminally injected (Table 3) into the ceca, GF rats absorbed and excreted the 13N faster than comparably treated CV rats. Since GF rats seem unable to metabolize N03to N02 (29), this suggests that the microbial flora of the CV rats metabolized the 13N03to chemical forms that were unable to pass the intestinal barrier as easily as NO3-. It also could indicate that the microbial flora of the CV rats was able to incorporate the 13N from 13NO3; that such incorporation does occur is indicated by the data in Table 4.…”

“…The incorporated nitrogen is then presumably excreted in the feces, although the halflife of 13N was too short to allow this to be observed. Bacterial incorporation may also explain our inability to chemically assay NO2and NO3throughout most of the intestinal tract of CV as opposed to GF rats (29 or their metabolites can move rapidly from the stomach to the lower intestines. Such passage could both increase exposure of the large intestine to carcinogens formed in the stomach as suggested by Lijinsky (11) or allow the nitrosation reactions themselves to more readily occur in the lower GI tract as suggested by Wang et al (27).…”

“…Attempts to determine the distribution of NO3and NO2in rodents colorimetrically, with a special emphasis on the lower-intestinal tract, were complicated by chemical and bacterial alteration of these ions in conventional-flora (CV) rats and by chemical conversion and the presence of assay-interfering compounds in intestinal contents of germfree (GF) rats (29). We therefore used the longest-lived radioisotope of nitrogen, 13N, to study the absorption, body distribution, and secretion of gavaged or intravenously (i.v.)…”