PROLONGED EFFECT OF A NOVEL S-NITROSATED GLYCOAMINO-ACID IN ENDOTHELIUM-DENUDED RAT FEMORAL ARTERIES - POTENTIAL AS A SLOW-RELEASE NITRIC-OXIDE DONOR DRUG

1 The vasodilator properties of a novel S-nitrosated glyco-amino acid (RIG200) were investigated in isolated rat femoral arteries and compar ed with those of the parent S-nitrosothiol compound, S-nitroso-N-acety lpenicillamine (SNAP). 2 Spectrophotometric analysis revealed that 2.5 mM solutions of RIG200 decomposed more slowly (half-life (t(1/2))=216 .2+/-26.7 min) than SNAP (t(1/2)=37.2+/-13.8 min) in Krebs buffer at 2 4 degrees C. Furthermore, the rate of decomposition of SNAP, but not o f RIG200, was significantly reduced by the Cu(I) chelator, neocuproine . We concluded that the relative stability of RIG200 is due, at least in part, to its resistance to trace CuO(I)-catalyzed decomposition. Ni tric oxide (NO) generation from SNAP and RIG200 was confirmed by use o f an NO electrode. 3 Experiments to investigate the vasodilator effect s of RIG200 were carried out on isolated femoral arteries taken from a dult male Wistar rats (400-550 g). Lengths of artery (7-8 mm long) wer e cannulated, dissected free and perfused at constant flow rate (0.6 m l min(-1)) with Krebs buffer. Vessels were precontracted with phenylep hrine (10.2+/-0.3 mu M) and developed pressures of 91.8+/-4 mmHg, dete cted upstream by a differential pressure transducer. 4 Concentration-d ependent vasodilator responses to bolus injections of SNAP or RIG200 ( 10 mu l; 10(-8)-10(-3) M) made into the perfusate of endothelium-intac t vessels were transient, recovering the preinjection pressure in <20 min. 5 Responses to equivalent bolus injections of SNAP in endothelium -denuded vessels were also transient but those in response to concentr ations of RIG200 >10(-5) M were sustained. Responses to 10(-3) M RIG20 0 were sustained for periods >4 h. Sustained vasodilatation was revers ed by the NO scavenger, ferrohaemoglobin (10 mu M) but was unaffected by the NO synthase inhibitor, N-omega-nitro-L-arginine methyl ester (2 00 mu M), indicating involvement of NO from a source other than NO syn thase. 6 We suggest that a possible explanation for the prolonged effe ct of RIG200 is retention of the compound by the vascular wall, facili tated by endothelial denudation. Slow decomposition of RIG200 in situ would release sufficient NO to maintain a 'vasodilator tone' which per sists for more than 4 h. Selective retention by damaged vessels could have important therapeutic implications with regard to targeted delive ry of NO, restoring protection to areas deprived of endogenous NO, whi lst avoiding unwanted hypotension.