The effects of ruthenium tetraammine compounds on vascular smooth muscle

The time course of the relaxation effect induced by a single dose (3 × 10−6 mol/L) of trans-[Ru(NH3)4L(NO)]3+ (L = nic, 4-pic, py, imN, P(OEt)3, SO32-, NH3, and pz) species and sodium nitroprusside (4 × 10−9 mol/L) was studied in aortic rings without endothelium and pre-contracted with noradrenaline (1 × 10−6 mol/L). All the compounds induced a relaxing effect in the aortic rings, but the intensity and time of relaxation were different. Only the species where L = py, 4-pic, and P(OEt)3 were able to induce 100% (99–100%) of the relaxing effect during the assay. trans-[Ru(NH3)4(L)(NO)]3+ (L=SO32- and NH3) showed the lowest relaxing effect (36 and 37%, respectively) when compared with the other compounds. Relationship was observed between the time corresponding to half of the maximum relaxation intensity observed and, respectively, k–NO, E[Ru(NO)]3+/[Ru(NO)]2+0′ in trans-[Ru(NH3)4(L)(NO)]3+ species and ERu(III)/Ru(II)0′ in trans-[Ru(NH3)4(L)(H2O)]3+ ions. These relationships strongly suggested that the NO liberation from the reduced nitrosyl complexes was responsible for the observed relaxation.