Contribution of nitric oxide and K+ channel activation to vasorelaxation of isolated rat aorta induced by procaine

The endothelium-dependent and -independent relaxant effect of procaine was examined in isolated rat aortic rings. Procaine induced relaxation of arteries precontracted with phenylephrine or with 60 mM K+ in a concentration-dependent manner (0.01-3 mM). Procaine (1 mM) inhibited the transient contraction induced by caffeine (10 mM) in Ca2+-free Krebs solution. Removal of the endothelium caused a rightward shift of the concentration-response curve for procaine. N(G)-Nitro-L-arginine (L-NNA, 10-100 microM), N(G)-nitro-L-arginine methyl ester (L-NAME, 100 microM) and methylene blue (1-10 microM) significantly attenuated the procaine-induced relaxation without affecting the maximal response. L-Arginine (1 mM) partially but significantly antagonized the effect of L-NAME (100 microM). Pretreatment of endothelium-intact aortic rings with procaine (1 mM) or with acetylcholine (10 microM) significantly elevated the tissue contents of cyclic GMP and this increase was inhibited in the presence of 100 microM L-NNA. Tetrapentylammonium ions (1-3 microM) reduced the procaine-induced relaxation in both endothelium-intact and -denuded arteries. Tetrapentylammonium ions (3 microM) did not affect the procaine-induced relaxation of 60 mM K+-contracted arteries. Tetraethylammonium ions (3 mM) inhibited the procaine-induced relaxation. In contrast, iberiotoxin (100 nM), glibenclamide (3 microM), 4-aminopyridine (3 mM) and indomethacin (10 microM) had no effect. These results indicate that the procaine-induced relaxation may be mediated through multiple mechanisms. A substantial portion of the procaine-induced relaxation in rat aorta was caused by nitric oxide but not by other endothelium-derived factors. The activation of tetrapentylammonium- and tetraethylammonium-sensitive K+ channels contributes in part to the procaine-induced vasorelaxation. Besides, procaine may directly inhibit both external Ca2+ entry and internal Ca2+ release in aortic smooth muscle cells.