Document Detail

Effects of ascorbic acid and thiocyanate on nitrosation of proline in the dog stomach.
MedLine Citation:
PMID:  3345579     Owner:  NLM     Status:  MEDLINE    
To elucidate the factors governing the formation of N-nitrosamines in the stomach, the formation of N-nitrosoproline (NPro) was studied under controlled conditions, using a dog equipped with a Thomas cannula. Solutions containing nitrite, proline and in some cases ascorbic acid and/or SCN-, were infused into the stomach and samples taken to determine gastric [nitrite], [NPro], [ASC], [SCN-] and pH as functions of time. (Brackets indicate molar concentrations; ascorbic acid and ascorbate ion are denoted together by ASC.) Previous work showed that the rapid decline of [nitrite] in the stomach was due primarily to absorption. Additional experiments here in which ASC, proline or NPro were infused together with a non-absorbable marker, in the absence of nitrite, demonstrated that there was negligible absorption or secretion of these substances in the stomach. Thus, changes in [ASC] and [NPro] with time could be interpreted quantitatively in terms of rates of chemical reaction and dilution of the stomach contents. A mathematical model, based on mass balance equations for the various chemical species and chemical kinetic data obtained previously from in vitro studies, was developed for this purpose. The ability of ASC to inhibit nitrosation (by reaction with nitrite) was shown to be highly dependent on initial [ASC] and on the rate of entry of O2 into the stomach from blood. The rate of NPro formation in the absence of ASC and SCN-, the inhibitory effects on nitrosation of ASC and the catalytic effects of SCN-, were all accurately predicted by the mathematical model. This suggests that similar models may prove useful in estimating rates of intragastric N-nitrosation reactions in humans, under various assumed conditions.
W R Licht; J G Fox; W M Deen
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Carcinogenesis     Volume:  9     ISSN:  0143-3334     ISO Abbreviation:  Carcinogenesis     Publication Date:  1988 Mar 
Date Detail:
Created Date:  1988-04-14     Completed Date:  1988-04-14     Revised Date:  2007-11-14    
Medline Journal Info:
Nlm Unique ID:  8008055     Medline TA:  Carcinogenesis     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  373-7     Citation Subset:  IM    
Department of Chemical Engineering, Medicine, Massachusetts Institute of Technology, Cambridge 02139.
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MeSH Terms
Ascorbic Acid / pharmacology*
Nitrites / metabolism
Nitrogen Oxides / metabolism
Nitrosamines / metabolism*
Oxygen / metabolism
Proline / metabolism*
Stomach / metabolism*
Thiocyanates / pharmacology*
Grant Support
Reg. No./Substance:
0/Nitrites; 0/Nitrogen Oxides; 0/Nitrosamines; 0/Thiocyanates; 147-85-3/Proline; 302-04-5/thiocyanate; 50-81-7/Ascorbic Acid; 7519-36-0/nitrosoproline; 7782-44-7/Oxygen

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