Nitroglycerin metabolism in vascular tissue: role of glutathione S-transferases and relationship between NO. and NO2- formation.
Nitroglycerin is a commonly employed pharmacological agent which produces vasodilatation by release of nitric oxide (NO.). The mechanism by which nitroglycerin releases NO. remains undefined. Recently, glutathione S-transferases have been implicated as important contributors to this process. They are known to release NO2- from nitroglycerin, but have not been shown to release NO.. The present studies were designed to examine the role of endogenous glutathione S-transferases in this metabolic process. Homogenates of dog carotid artery were incubated anaerobically with nitroglycerin, and NO. and NO2- production was determined by chemiluminescence. The role of glutathione S-transferases was studied by incubating homogenates with nitroglycerin in the presence of 1 mM GSH or 1 mM S-hexyl-glutathione, a potent inhibitor of glutathione S-transferases. Homogenates released 163 pmol of NO./h per mg of protein from nitroglycerin, and 2370 pmol of NO2-/h per mg. Adding GSH decreased NO. production by 82% and increased NO2- production by 98%. S-Hexylglutathione inhibited glutathione S-transferase activity by 96% and decreased NO2- production by 78%, but had no effect on NO. release. A linear relationship between glutathione S-transferase activity and NO2- production was observed, whereas glutathione S-transferase activity and NO. release were unrelated. Western-blot analysis demonstrated that dog carotid vascular smooth muscle contained Pi and Mu forms of glutathione S-transferases, with a predominance of the former. Purified preparations of human Pi and rat Mu isoforms metabolized nitroglycerin only to NO2- and not to NO.. On the basis of these findings, we conclude that (1) glutathione S-transferases do not contribute to the bioconversion of nitroglycerin to NO., but instead act as a degradative pathway for nitroglycerin, and (2) the release of NO. from nitroglycerin is not dependent on the formation of NO2-.
Kurz
M A
MA
Department of Internal Medicine, Emory University School of Medicine, Atlanta, GA 30322.
Boyer
T D
TD
Whalen
R
R
Peterson
T E
TE
Harrison
D G
DG
D000818:Animals; D002339:Carotid Arteries / Q000201:enzymology / Q000378:metabolism*; D004285:Dogs; D005609:Free Radicals; D005982:Glutathione Transferase / Q000302:isolation & purification / Q000378:metabolism*; D066298:In Vitro Techniques; D009566:Nitrates / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism*; D005996:Nitroglycerin / Q000378:metabolism*
D005609:Free Radicals; D009566:Nitrates; D009573:Nitrites; D005982:Glutathione Transferase; D005996:Nitroglycerin