THE EFFECTS OF PEROXYNITRITE ON RAT AORTA - INTERACTION WITH GLUCOSE AND RELATED SUBSTANCES

Peroxynitrite (1-100 mu M) induced a concentration-dependent relaxatio n of rat aortic rings; the log EC50 and maximum relaxation on endothel ium-denuded rings were -5.31+/-0.03 and 105+/-5%, n = 6, respectively. The presence of the endothelium significantly impaired this relaxatio n (log EC50, -4.41+/-0.04; maximum relaxation, 71+/-4%; n = 6); an eff ect which was reversed by the inhibitor of nitric oxide synthase, N-G- nitro-L-arginine methyl ester (L-NAME; 100 mu M). Incubation with a hi gh concentration of peroxynitrite (1 mM, 10 min followed by washout) h ad no effect on subsequent relaxation to acetylcholine (0.01-1 mu M) I t did, however, significantly depress subsequent contraction to phenyl ephrine (1-300 nM). This depression was dependent upon the presence of D-glucose in the Krebs solution, could be reversed by the inhibitor o f soluble guanylate cyclase, methylene blue (10 mu M) and reversed spo ntaneously after 2 h. When peroxynitrite (1 mM) was mixed with D-gluco se (11 mM) and subsequently neutralised to remove unreacted peroxynitr ite, a new more potent relaxant was formed. Despite this, the ability of peroxynitrite (1-100 mu M) to produce relaxation of endothelium-den uded rings was similar in normal and glucose-free Krebs. Glycerol (22 mM), which like D-glucose is membrane permeant, also reacted with pero xynitrite (1 mM) to form a new more potent relaxant. L-cysteine (1 mM) had no effect by itself on the tone of aortic rings and when present in the tissue bath had no effect on the ability of peroxynitrite or ne utralised peroxynitrite (1-100 mu M) to produce relaxation. It did, ho wever, potentiate the relaxant actions of the products formed from the reaction of peroxynitrite with D-glucose or glycerol. The membrane im permeant sugars, mannitol and sorbitol (each 11 mM) also reacted with peroxynitrite (1 mM), but expression of the vasorelaxant properties of their respective derivatives was seen only in the presence of L-cyste ine (1 mM). Membrane permeance cannot, however, explain why peroxynitr ite reacts with D-glucose and glycerol, but not mannitol or sorbitol t o form products with intrinsic relaxant activity, as the product forme d from the impermeant sugar, L-glucose (11 mM), also has intrinsic act ivity. The relaxant potency of this product was equipotent to that for med from D-glucose and was also potentiated by L-cysteine (1 mM). Thes e result confirm that peroxynitrite can react with glucose and other c ompounds with alcohol functional groups to form vasorelaxant species. The relaxation induced when peroxynitrite is added to rat aortic rings is not, however, dependent upon this reaction since it occurs in gluc ose-free Krebs. (C) 1997 Elsevier Science B.V.