L-NG-NITRO ARGININE P-NITROANILIDE (L-NAPNA) IS ANTINOCICEPTIVE IN THE MOUSE

L-N(G)-NITRo arginine p-nitroanilide (L-NAPNA), L-N(G) nitro arginine methyl ester (L-NAME) and L-N(G)-monomethyl arginine (L-NMMA) inhibit rat cerebellar nitric oxide synthase (NOS) with IC50s of 1.4 +/- 0.1 muM, 0.81 +/-0.16 muM and 5.1 +/- 0.07 muM respectively. L-NAPNA inhibits the late phase of formalin-induced hindpaw licking (ED50, 57.2 mg kg-1) and acetic acid induced abdominal constrictions (ED50 25 mg kg-1) in the mouse. L-NAPNA is approximately 65 times less active than L-NAME as an inhibitor of endothelium-dependent relaxation in the rabbit aorta and about 10 fold less potent as a vasopressor in the anaesthetized mouse. LNAPNA shows some degree of selectivity for the central NOS isoform and may be of clinical interest for the treatment of pain.