Distribution, Secretion and Metabolism of Nitrate in the Rat Lower Digestive Tract

Abstract

The metabolic fate of nitrate in the lower digestive tract was investigated using Wistar male rats. Little or no nitrate or nitrite was detected in the contents of the digestive tract except that 1232±208ppm of nitrate was found in the stomach contents when rats were fed on a diet containing 5000ppm of nitrate for a week. The secretion of blood nitrate into the lower digestive tract was clearly observed by replacement of the contents with saline in ligated sections of the tract; no nitrate was detected in any ligated sections with contents, but the lower small intestine, cecum and large intestine filled with saline contained 23±13, 35±6 and 46±12ppm of nitrate, respectively, at 15min after the injection of 5mg of nitrate into the abdominal vein.Nitrate injected into the lower digestive tract was rapidly reduced to nitrite by the contents. Upon simultaneous injection of 250μg each of nitrate and dimethylamine into ligated sections with contents, the formation of N-nitrosodimethylamine was observed at the level of 10-51ppb. Rapid absorption of N-nitrosodimethylamine from the sections was also observed.