Relaxant effects of an alkaloid-rich fraction from Aspidosperma ulei root bark on isolated rabbit corpus cavernosum

摘要

We described earlier that an alkaloid-rich fraction (F3–5) from Aspidosperma ulei (Markgr) induces penile erection-like behavioral responses in mice. This study verified a possible relaxant effect of this fraction on isolated rabbit corpus cavernosum (RbCC) strips precontracted by phenylephrine (1?μM) or K+ 60?mM. F3–5 (1–300?μg?ml?1) relaxed the RbCC strips in a concentration-dependent and reversible manner. The relaxant effect of F3–5 (100?μg?ml?1) on phenylephrine contraction was unaffected in the presence of atropine, N-ω-nitro-L-arginine methyl ester or 1H-[1,2,4]oxadiazole[4,3-a] quinoxalin-1-one and by preincubation with tetrodotoxin, glibenclamide, apamine and charybdotoxin suggesting that mechanisms other than cholinergic, nitrergic, sGC activation or potassium channel opening are probably involved. However, the phasic component of the contraction induced by K+ 60?mM as well as the maximal contraction elicited by increasing external Ca2+ concentrations in depolarized corpora cavernosa was inhibited by F3–5. We conclude that F3–5 relaxes the RbCC smooth muscle, at least in part, through a blockade of calcium influx or its function.