L-N6-(1-iminoethyl)-lysine (L-NIL) but not S-methylisothiourea sulphate (SMT) displays selectivity towards NOS-2.

Our aim was to verify potency and selectiveness of two most widely used drugs regarded as NOS-2 inhibitors: L-N6-(1-iminoethyl)-lysine (L-NIL) and S-methylisothiourea sulphate (SMT). Thioglycolate-elicited rat peritoneal macrophages and coronary endothelium of isolated guinea pig heart were used as assay systems for NOS-2 and NOS-3, respectively. A non-selective NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) was used as a reference compound. We found that L-NIL but not SMT was a selective NOS-2 inhibitor. Interestingly, L-NAME displayed selectivity towards NOS-3.