Agmatine was about as potent as aminoguanidine to inhibit the activity
of the inducible form of nitric oxide synthase (iNOS) in isolated rat
aorta. Like aminoguanidine, agmatine was devoid of significant activi
ty on the constitutive form of NOS. Agmatine inhibited the conversion
of [H-3]L-arginine in [3H]L-citrulline in partially purified iNOS from
macrophages (IC50 = 262 +/- 39.9 mu M). Thus, our data suggest that a
gmatine may act as endogenous inhibitor of iNOS.