Assessing nitrate metabolism in the intestinal tract by measuring breath nitric oxide and nitrous oxide, and its clinical significance.
BACKGROUND
The toxicity of dietary nitrate (NO3-) is controversial. One reason is nitrate metabolism in the intestine is so complicated that it is far from fully understood. There is no study measuring breath nitric oxide (NO) and nitrous oxide (N2O) after ingesting vegetables and high-nitrate food at the same time.


METHODS
Breath samples from 10 healthy young and 10 healthy old subjects were collected at 15-min intervals for 5 h after ingestion of 100 g of lettuce and during fasting (control). Breath NO and N2O were analyzed by a chemiluminescence and an IR-PAS analyzer respectively.


RESULTS
N2O maximum concentration and excretions increased significantly after ingesting lettuce in each group [303 (30) vs. 750 (81) ppb, 771 (72) vs. 1668 (146) microg in young; 442 (52) vs. 1092 (109) ppb, 1088 (125) vs. 2100 (183) microg in old subjects; mean (SE), P<0.01], while NO did not. In addition, breath NO was strongly influenced by ambient NO, which varied greatly. N2O maximum level in old subjects after ingesting lettuce was higher than that of young subjects (750 vs. 1092 ppb, P<0.05), and significantly higher N2O concentration levels were seen at 30, 45, 60, and 105 min in old subjects.


CONCLUSIONS
A large amount of N2O produced in the intestine and normal nitrate intake do not influence the breath NO concentration, probably due to its relatively small production. Higher maximum N2O concentration after ingesting lettuce in old subject is probably because more bacteria, which rapidly reduce dietary nitrate in the upper intestinal tract, inhabit the gut in old age. Our results suggested that breath N2O is a useful noninvasive maker to estimate dietary nitrate reduction in the intestinal tract.
Mitsui
Takahiro
T
Research Center of Health, Physical Fitness and Sports, Nagoya University, Furocho, Chikusaku, 464-8601, Japan. mitsui@hotai1.htc.nagoya-u.ac.jp
Kondo
Takaharu
T
D000328:Adult; D000368:Aged; D001944:Breath Tests / Q000379:methods*; D005260:Female; D005508:Food Deprivation; D005767:Gastrointestinal Diseases / Q000175:diagnosis; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D018545:Lactuca / Q000378:metabolism; D008297:Male; D009566:Nitrates / Q000378:metabolism*; D009569:Nitric Oxide / Q000032:analysis / Q000378:metabolism*; D009609:Nitrous Oxide / Q000032:analysis / Q000378:metabolism*; D013997:Time Factors
D009566:Nitrates; D009569:Nitric Oxide; D009609:Nitrous Oxide