Direct proof of nitric oxide formation from a nitrovasodilator metabolised by erythrocytes.

When 15N-isosorbide dinitrate was injected into rats, the venous blood showed a 2-line hyperfine structure in the electron spin resonance (ESR) spectra of NO hemoglobin (HbNO), proving generation of 15N-NO. When human blood was mixed with 15N-isosorbide dinitrate anaerobically, ESR spectra showed initially 14N-HbNO, which was then overwhelmed with the increased 15N-HbNO. With deoxygenation of the blood of another 4 male donors without addition of isosorbide dinitrate, two showed 14N-HbNO, but others did not, suggesting varied amount of NO-precursers, nitrosothiols, in human blood. Neither N-ethylmaleimide nor S-hexylglutathione, a glutathione-S-transferase inhibitor, inhibited the formation of UbNO in the hemolysate mixed anaerobically with isosorbide dinitrite.