Effects of endogenous and exogenous NO on endothelin-1 production in cultured vascular endothelial cells

Effects of NO synthase (NOS) inhibitors and spontaneous NO donors on ET-1 production were examined in cultured porcine aortic endothelial cells (ECs). NOS inhibitors such as N^G -Nitro-L-arginine, N^G -Monomethyl-L-arginine and N^G -Nitro-L-arginine methyl ester enhanced the prepro ET-1 mRNA expression, and significantly increased the ET-1 secretion in ECs. NO donors such as (±)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-3-hexanamide (NOR 2), (±)-(E)-4-ethyl-2-[(E)hydroxyimino]-5-nitro-3-hexanamide (NOR 3) and (±)-N-[(E)-4-ethyl-2[(Z)-hydroxyimino]-5-nitro-3-hexen-1-yl]-3-pyridine carboxamide (NOR 4) suppressed effectively the ET-1 release from ECs. ET-1 mRNA expression was also attenuated by these compounds. However, other NO donors such as 3-[2-hydroxy-1-(1-methylethyl)-2-nitrosohydrazino]-1-propanamine (NOC 5), 2,2-(hydroxynitrosohydrazino)bis-ethanamine (NOC 18), S-nitroso-N-acetyl-DL-penicillamine (SNAP), N-morpholino sydnonimine (SIN-1) had no effects on the ET-1 production. NO metabolites, NO_2 ^- /NO_3 ^- , in medium and intraceller cGMP level were significantly increased by all NO donors. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a selective soluble guanylyl cyclase inhibitor, unaffected NOR 3-induced decrease in ET-1 secretion, although cGMP production was completely abolished by ODQ. NOR 3 also inhibited ET-1 secretion even in the presence of 2-(4-carboxyphenyl)-4,4,5,5-tetrametylimidazole-1-oxyl 3-oxide), a NO scavenger. When NOR 3 was preincubated in phosphate-buffered saline at 37℃ for 4 hr before the experiment, no inhibitory effects of NOR 3 on ET-1 secretion were observed. These results suggest that endogenous NO plays a role as an inhibitory factor of ET-1 production in ECs. In contrast, it is unlikely that exogenous NO has an inhibitory effect on ET-1 production in ECs. NOR compounds appear to inhibit ET-1 production through NO/cGMP-independent mechanisms.