Levels of nitric oxide in the heart after experimental myocardial ischemia

The effect of myocardial ischemia on nitric oxide (NO) production is contro versial in part because of indirect NO quantification. In the present study , direct quantification of NO was investigated in an in vivo rat model of m yocardial ischemia (MI). A NO spin-trapping technique using electron spin r esonance (ESR) spectroscopy was used to study NO production in the ischemic and in the nonischemic area of the rat heart 2, 8, or 24 h after left main coronary artery ligation. The method was based on the trapping of NO by a metal-chelator complex consisting of N-methyl-D-glucamine-dithiocarbamate ( MGD) and Fe(II) to form a stable NO-FeMGD complex that gives rise to a char acteristic tripler ESR spectrum. This metal-chelator complex was administer ed half an hour before sacrifice of the rats. A large and time-dependent in crease of the ESR signal corresponding to the NO-FeMGD complex was observed 8 h (11.6 +/- 0.9 arbitrary units [AU]) and 24 h (29.7 +/- 2.9 AU) in the ischemic area after MI. On the contrary, no ESR tripler was observed in the nonischemic region of the heart and in sham-operated rats. NO blood deriva tive levels (nitrosylhemoglobin and plasma nitrites and nitrates) were unch anged compared with sham-operated rats. Previous administration of aminogua nidine, a NO synthase inhibitor, in animals subjected to a 24-h ischemia re sulted in a complete abolition in the NO-FeMGD spectrum in the ischemic are a. These findings directly demonstrated an increase of the NO-FeMGD levels during in vivo myocardial ischemia that appeared to be specifically localiz ed in the ischemic area.