Involvement of NO in the Endothelium-Independent Relaxing Effects ofN^ω-Hydroxy-l-arginine and Other Compounds Bearing a C=NOH Function in the Rat Aorta

Abstract

The mechanisms of vasorelaxation elicited by N -hydroxy-Larginine (L-NOHA) and other compounds bearing a CϭNOH function and the structural determinants governing this effect were investigated in rat aorta. L-NOHA, formamidoxime, five aromatic monosubstituted amidoximes, and one aromatic monosubstituted ketoxime elicited relaxation in endothelium-denuded rings. N-Hydroxyguanidine and substituted N-hydroxyguanidines were markedly less active. Relaxations induced by L-NOHA and by the most active studied compound, 4-chlorobenzamidoxime (ClBZA), were unmodified by the presence of endothelium. In endothelium-denuded rings, they were blunted by the NO scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (300 M) and by the inhibitor of guanylylcyclase activation 1H[1,2,4,]oxadiazolo[4,3-a]quinoxalin-1-one (1 M). In addition, L-NOHA-and ClBZA both caused cGMP accumulation. L-Arginine, but not D-arginine (1 mM), antagonized the effect of L-NOHA but not ClBZA. Both L-NOHA-and ClBZA-induced relaxations were inhibited by the NAD(P)H-dependent enzymes inhibitor diphenyliodonium (30 M) and the NAD(P)H-dependent reductases inhibitor 7-ethoxyresorufin (10 M), but they were unmodified by the cytochrome P450 (P450) inhibitor proadifen (10 M) and by the NO synthase inhibitor N -nitro-L-arginine methyl ester (L-NAME, 300 M). These results show that L-NOHA and other compounds with a CϭNOH function can cause endothelium-independent relaxation in the rat aorta. They suggest that activation of guanylyl cyclase and NO formation is implicated in relaxation and that a 7-ethoxyresorufin-sensitive NAD(P)H-dependent pathway is involved. On one hand, L-NOHA and amidoximes may be useful tools for characterizing this pathway in blood vessels and, on the other, may offer a novel approach for treating vascular diseases with impaired endothelial NO activity.

Vasorelaxation Induced by a New Naphthoquinone-Oxime is Mediated by NO-sGC-cGMP Pathway

“…It has been reported that non-amino acid compounds sharing the R 2 C=NOH group can produce nitric oxide synthase-independent relaxation in endothelium-denuded aortic rings of rats [10,[14][15][16]. In addition, the mechanisms underlying the effects of exogenous nitrovasodilators are predominantly mediated by cyclic guanosine monophosphate (cGMP), as a result of the activation of soluble guanylyl cyclase [17,18].…”

“…Administration of Oxime S1 (10,15,20 and 30 mg/Kg, i.v., randomly) induced dose-dependent hypotension (−10 ± 3, −18 ± 4, −22 ± 3 and −32 ± 6 mmHg, respectively) associated to increase in the heart rate (8 ± 3, 15 ± 3, 21 ± 4 and 25 ± 4 bpm) (Figure 2). …”

“…This biotransformation process results in nitric oxide (NO) or NO-related vasorelaxant species formation in blood vessels that are independent of nitric oxide synthase activity [7][8][9]. Among the compounds containing the structural group (R=NOH) are the oximes, N-hydroxyguanidines, amidoximes and ketoximes [10][11][12].…”

“…In the present study, the cardiovascular effects of the new oxime 3-hydroxy-4-(hydroxyimino)-2-(3-methylbut-2-enylnaphtalen-1(4H)-one (Oxime S1) derived from lapachol were evaluated. In normotensive rats, administration of Oxime S1 (10,15, 20 and 30 mg/Kg, i.v.) produced dose-dependent reduction in blood pressure.…”

Endothelium-Derived Nitric Oxide Contributes to the Vasorelaxant Response Induced by Mesoionic 2-(4-Chlorophenyl)-3-methyl-4-(4-methoxyphenyl)-1;3-thiazolium-5-thyolate (CMMTT) in Rats

“…It is well reported in the literature that L-NOHA (48) and other NO-donors can also induce NOS-independent relaxation in endothelium-denuded arteries and that this relaxation involves the NO-cGMP pathway (48,49). Since both, NO formation (measured as NO x levels) as well as the vasorelaxant response induced by the compound were almost completely attenuated in rings in which the vascular endothelium was mechanically removed, endothelium-derived NO seems to be involved in CMMTT action and allowed us to discard a possible NO-donating effect induced by the compound.…”