The New Nitric Oxide Donor, FOR 911B, Induces Relaxation in Isolated Rat Aorta Involving the NO/sGC/cGMP Pathway and K+ Channels

Background: Nitric oxide (NO) is a gaseous molecule considered to be a protagonist in the dilation of blood vessels, and its property and/or bioavailability are reduced in pathophysiological conditions such as cardiovascular diseases. Therefore, its exogenous administration becomes attractive, and new classes of compounds able to induce NO release have emerged to minimize the adverse effects found by existing NO donor drugs. Objective: Our aim was to investigate the vasorelaxant effect and mechanism of action induced by the ruthenium complex, which contains nitric oxide in its structure, [Ru(phen)2(TU)NO](PF6)3 (FOR 911B), in isolated rat aorta. Methods: The animals were euthanized, and the aorta artery was identified, removed, and immediately placed in modified Krebs–Henseleit solution. To verify tissue viability, a contraction was obtained with phenylephrine (Phe) (0.1 μM), and to assess endothelial integrity, acetylcholine (ACh) (1 μM) was added. Results: In the present study, we demonstrated, for the first time, that FOR 911B promotes vasorelaxation in a concentration-dependent manner in isolated rat aortic artery rings. After the removal of the vascular endothelium, the potency and efficacy of the relaxation were not altered. With pre-incubation with hydroxocobalamin, the relaxing response was abolished, and with the use of ODQ, the main NO receptor blocker, the vasorelaxant effect was attenuated with a shift of the curve to the right. To investigate the participation of K+ channels, the solution concentration was changed to KCl (20 and 60 mM), and it was pre-incubated with the non-selective K+ channels blocker (TEA). Under these conditions, relaxation was altered, demonstrating that K+ channels are activated by FOR 911B. By selectively blocking the different subtypes of K+ channels with specific blockers, we demonstrated that the subtypes KV, KIR, SKCa, and BKCa are involved in the vasodilator effect induced by FOR 911B. Conclusions: The results obtained demonstrated that FOR 911B promotes vascular relaxation in aortic artery rings in a concentration-dependent manner and independent of the vascular endothelium through the participation of the NO/sGC/cGMP pathway, as well as with the involvement of different K+ channels.