The role of oral nitrate in the nitrosation of [14C]proline by conventional microflora and germ-free rats.

The urinary excretion of N-nitroso-L-[U-14C]proline by conventional microflora and germ free rats was used to assess the role of the gut bacteria and oral nitrate in the endogenous formation of N-nitroso compounds. The formation of nitrosoproline was qualitatively similar in conventional and germfree rats (equivalent to nitrosation of approximately 0.01-0.05% of the initial dose of [U-14C]proline) suggesting no involvement of the intestinal flora in this reaction. Furthermore, nitrosamino acid production was similar following the administration of nitrate and [U-14C]proline or [U-14C]proline alone, demonstrating no involvement of exogenous nitrate under the conditions of the experiment. Dietary contamination with nitrate/nitrite was negligible. The results are consistent with the suggestion that nitrate/nitrite reserves in the body are important in the formation of nitrosoproline in vivo.