Περίληψη:
The concentrations of nitrite, thermo- and acetic acid-labile
TEA-responsive compounds (TACs) and N-nitroso compounds (NOCs) as a
group were measured in human gastric juice collected just before and 1,
2 and 4 h after oral ingestion of 1 g ascorbic acid (AA) or 200 mg
sodium nitrate, separately or in combination. Individual responses of
gastric [nitrite] following ingestion of AA alone varied widely, with
both decreases and increases being observed, and showed no correlation
with gastric pH. While a mixed response was also noted for [NOC] and
[TAC], substantial decreases were observed in 5/6 individuals with
initial [NOC] > 0.2-mu-M and 313 individuals with initial [TAC] >
0.2-mu-M, implying that (i) AA effectively inhibited gastric nitrosation
and (ii) a basal amount of NOCs and TACs was present in gastric juice
which could not be lowered by AA ingestion. Statistical analysis
indicated that global mean values of gastric [NOC] were significantly
reduced (P < 0.02) 1-4 h after ingestion of AA. Ingestion of 200 mg
sodium nitrate alone resulted in increases in gastric [NOC], which in
some cases were very substantial. While nitrosation appeared lower
following ingestion of the same dose of nitrate in combination with 1 g
AA, the difference from the effects of nitrate alone was not
statistically significant. In aqueous buffer, pH 2.5, and in the
presence of 1 mM AA, 50-mu-M nitrite was consumed with a t1/2 of 50 min
only if molecular oxygen had first been removed from the system. In the
presence of oxygen, no consumption of nitrite could be detected in 50
min, reflecting nitrite recycling (oxidation of nitric oxide to higher
oxides of nitrogen and hydrolysis back to nitrite). It is likely that
nitrite recycling occurring after collection of gastric juice accounted
for the inconsistent responses of gastric nitrite following ingestion of
AA. Incubation of human gastric juice, pH 2.5, in vitro in the presence
of 50-mu-M sodium nitrite for 60 min resulted in an increase of [NOC]
and [TAC] from 0.10 to 0.70 and 1.10-mu-M respectively. Nitrosation
was efficiently inhibited by AA, 2.27 mM AA resulting in 87 and 100%
inhibition respectively. Removal of oxygen from the reaction mixture did
not have any significant effect on the extent of nitrosation in the
presence or absence of AA.
Συγγραφείς:
KYRTOPOULOS, SA
PIGNATELLI, B
KARKANIAS, G
GOLEMATIS, B and
ESTEVE, J
