Nitric oxide and another potent vasodilator are formed from NG-hydroxy-L-arginine by cultured endothelial cells.
The hypothesis was investigated that NG-hydroxy-L-arginine (L-HOArg) is an intermediate in the biosynthesis of nitric oxide (.NO) from L-arginine (L-Arg) by the constitutive .NO synthase (NOS) present in endothelial cells (ECs). When infused through a column of bovine aortic ECs on beads, either L-HOArg or D-HOArg (1-10 microM) substantially potentiated relaxations of the bioassay tissues to .NO released from the cells by ADP or bradykinin, and this effect was abolished by coinfusions of NG-nitro-L-arginine (L-NO2Arg) methyl ester (10 microM) or NG-monomethyl-L-arginine (L-MeArg; 30 microM). Both L-HOArg and D-HOArg, irrespective of the presence of ECs, also potentiated relaxations induced by authentic .NO, but not glyceryl trinitrate. This was due to a rapid chemical reaction of either isomer with .NO, resulting in the formation of a potent and more stable vasodilator. When infusions of L-HOArg (3 microM) were consequently made in the presence of D-HOArg (10 microM), the L-isomer no longer had any effect on relaxations induced by authentic .NO, but significantly increased the stimulated release of .NO from the column of ECs. The conclusion that L-HOArg is a substrate for the constitutive NOS in cultured ECs was strongly supported by the L-NO2Arg-sensitive conversion of L-HOArg, but not D-HOArg, to .NO by NOS preparations from these cells. Interestingly, cultured ECs produced from L-HOArg (greater than or equal to 3 microM), but not D-HOArg, a stable vasodilator, the effects of which were inhibited by oxyhemoglobin (0.3-3 microM). However, the formation of this substance was not prevented by L-NO2Arg methyl ester (10 microM) or L-MeArg (10-100 microM), suggesting an enzymatic pathway different from NOS.
Zembowicz
A
A
William Harvey Research Institute, St. Bartholomew's Hospital Medical College, London.
Hecker
M
M
Macarthur
H
H
Sessa
W C
WC
Vane
J R
JR
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D001120:Arginine / Q000031:analogs & derivatives* / Q000378:metabolism; D001681:Biological Assay; D002417:Cattle; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology; D011817:Rabbits; D013347:Subcellular Fractions / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014664:Vasodilation / Q000187:drug effects; D014665:Vasodilator Agents / Q000378:metabolism* / Q000494:pharmacology
D014665:Vasodilator Agents; D013481:Superoxides; D009569:Nitric Oxide; C068309:N(omega)-hydroxyarginine; D001120:Arginine