title: Nitrate reduction, gastro-intestinal pH and N-nitrosation in gnotobiotic and conventional rats.
abstract: The reduction of nitrate in germ-free, gnotobiotic and conventional rats was investigated using blood methaemoglobin values as indicative of nitrite formation. Nitrate reduction was found to occur in the absence of a microbial flora, and throughout the experiment the blood content of methaemoglobin was higher in germ-free than in conventional rats. In vitro incubations of the gastric and small-intestinal mucosae of germ-free rats confirmed the presence of a heat-labile nitrate-reducing system. Measurement of the gastro-intestinal pH of germ-free and conventional rats revealed a generally higher pH value throughout the germ-free gastro-intestinal tract, with highly significant differences in the luminal pH of the forestomach, jejunum/ileum and caecum and a significant difference in the pH of the glandular stomach. Although some formation of N-nitrosoproline from proline and nitrate occurred in germ-free and gnotobiotic rats, nitrosation proceeded more readily in conventional rats. This effect may have been due to the lower gastric pH in the conventional rats although a more direct role for the flora cannot be discounted.
mesh_terms: D000818:Animals; D055598:Chemical Phenomena; D002621:Chemistry; D004064:Digestive System / Q000378:metabolism* / Q000382:microbiology; D004755:Enterobacteriaceae / Q000378:metabolism*; D005260:Female; D005856:Germ-Free Life; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008297:Male; D008706:Methemoglobin / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D009602:Nitrosamines / Q000378:metabolism; D009603:Nitroso Compounds / Q000096:biosynthesis*; D010084:Oxidation-Reduction; D051381:Rats; D013997:Time Factors
chemical_list: D009566:Nitrates; D009602:Nitrosamines; D009603:Nitroso Compounds; D008706:Methemoglobin; C010259:nitrosoproline