Inhibition by sulfhydryl compounds of vascular relaxation induced by nitric oxide and endothelium-derived relaxing factor.

On rings of rabbit thoracic aorta precontracted with phenylephrine, L-cysteine (Cys) and dithiothreitol (DTT) (1-100 microM), but not glutathione (GSH), produced dose-dependent augmentation of contraction in endothelium-intact, but not in endothelium-denuded rings. The augmentation appeared to be due to inhibition of basally released endothelium-derived relaxing factor (EDRF), and was abolished by pretreatment with superoxide dismutase (SOD, 15 U/ml). At a high dose (1 mM), Cys and GSH produced transient, and DTT produced sustained endothelium-independent relaxation, not influenced by SOD. Cys and DTT (10 microM), but not GSH, produced a small but significant inhibition of acetylcholine-induced endothelium-dependent relaxation, and this inhibition was prevented by SOD. In a perfusion-bioassay system in which EDRF was released by acetylcholine from endothelium of a perfused segment of rabbit aorta, Cys and DTT (20 microM), but not GSH, infused into the perfusate between the segment and an endothelium-denuded bioassay ring, partially inhibited relaxation by the EDRF, but not when SOD was present. In organ chamber experiments, the large transient relaxation of endothelium-denuded rings produced by 75 nM nitric oxide (NO) was partially inhibited in a concentration-dependent manner by Cys, DTT and GSH (0.1-100 microM). Moderate relaxation by 15 nM NO was almost completely inhibited by each compound at 10 microM. The order of potency was Cys > DTT > GSH. Cystine, glutathione disulfide and alanine did not inhibit. Inhibition of NO-induced relaxation was largely attenuated by SOD.(ABSTRACT TRUNCATED AT 250 WORDS)