Endothelium-independent vasorelaxant effect of sodium ferulate on rat thoracic aorta

This study was designed to investigate the effects of sodium ferulate (SF) on rat isolated thoracic aortas and the possible mechanisms.

Isometric tension was recorded in response to drugs in organ bath. Cytosolic free Ca(2+) concentration ([Ca(2+)](i)) was measured using Fluo-3 in cultured rat aortic smooth muscle cells (RASMC).

SF (0.1-30 mM) relaxed the isolated aortic rings precontracted with phenylephrine (PE) and high-K(+) in a concentration-dependent manner with respective pD(2) of 2.7+/-0.02 and 2.6+/-0.06. Mechanical removal of endothelium did not significantly modify the SF-induced relaxation. In Ca(2+)-free solution, SF noticeably inhibited extracellular Ca(2+)-induced contraction in high-K(+) and PE pre-challenged rings, and suppressed the transient contraction induced by PE and caffeine. The vasorelaxant effect of SF was unaffected by various K(+) channel blockers such as tetraethylammonium, glibenclamide, 4-aminopyridine, and barium chloride. In addition, SF concentration-dependently reduced the contraction induced by phorbol-12-myristate-13-acetate, an activator of protein kinase C (PKC), in the absence of extracellular Ca(2+), with the pD(2) of 2.9+/-0.03. In RASMC, SF had no effect on PE- or KCl-induced [Ca(2+)](i) increase either in the presence or in the absence of external Ca(2+).

These results indicate that SF acts directly as a non-selective relaxant to vascular smooth muscle. The direct inhibition of the common pathway after [Ca(2+)](i) increase may account for the SF-induced relaxation in Ca(2+)-dependent contraction, while the blockage of the PKC-mediated contractile mechanism is likely responsible for the SF-induced relaxation in Ca(2+)-independent contraction.