INHIBITION OF THE RELEASE OF ENDOTHELIUM-DERIVED RELAXING FACTOR INVITRO AND INVIVO BY DIPEPTIDES CONTAINING N(G)-NITRO-L-ARGININE

1 We have shown that dipeptides containing N(G)-nitro-L-arginine (NO2Arg) inhibit the biosynthesis of endothelium-derived relaxing factor (EDRF) in vitro and in vivo. 2 In anaesthetized rats, intravenous administration at 1-30 mg kg-1 of the methyl ester of NO2Arg, NO2-Arg-L-phenylalanine (NO2Arg-Phe), L-alanyl-NO2Arg (Ala-NO2Arg) or NO2Arg-L-arginine (NO2Arg-Arg) produced dose-related increases in mean arterial blood pressure (MABP) which were unaffected by D-arginine (D-Arg; 20 mg kg-1 min-1 for 15 min), but prevented by co-infusions of L-arginine (L-Arg; 20 mg kg-1 min-1 for 15 min) or by their parent dipeptides. 3 NO2Arg methyl ester, NO2Arg-Phe methyl ester or Ala-NO2Arg methyl ester (10 mg kg-1, i.v.) also inhibited the reduction in MABP caused by the endothelium-dependent vasodilator, acetylcholine (30-mu-g kg-1 min-1 for 3 min), but not those induced by glyceryl trinitrate (20-mu-g kg-1 min-1 for 3 min) or iloprost (6-mu-g kg-1 min-1 for 3 min) which act directly on the vascular smooth muscle. 4 Moreover, NO2Arg methyl ester, NO2Arg-Phe methyl ester or NO2Arg-Arg methyl ester (100-mu-M) inhibited the acetylcholine-induced relaxation of rabbit aortic strips, and NO2Arg-Phe methyl ester (30-mu-M) blocked the stimulated (bradykinin, 30 pmol) release of EDRF from bovine aortic endothelial cells grown on microcarrier beads. 5 In endothelial cells grown in L-Arg-deficient medium, L-Arg-containing dipeptides such as L-Arg-L-Phe, L-Ala-L-Arg or L-Arg-L-Arg increased both the basal and stimulated release of EDRF. Moreover, the L-Arg containing dipeptides, but not their NO2Arg analogues, were rapidly cleaved by these cells. 6 Thus, dipeptides containing NO2Arg can directly interfere with the biosynthesis of EDRF in vitro and in vivo. Moreover, the potentiation of EDRF release from endothelial cells deprived of L-Arg by dipeptides containing L-Arg suggests that such peptides may serve as an additional or alternative substrate for the biosynthesis of EDRF.