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

Abstract

We described earlier that an alkaloid-rich fraction (F 3-5 ) 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 lM) or K þ 60 mM. F 3-5 (1-300 lg ml À1 ) relaxed the RbCC strips in a concentration-dependent and reversible manner. The relaxant effect of F 3-5 (100 lg ml À1 ) on phenylephrine contraction was unaffected in the presence of atropine, N-x-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 þ 60 mM as well as the maximal contraction elicited by increasing external Ca 2 þ concentrations in depolarized corpora cavernosa was inhibited by F 3-5 . We conclude that F 3-5 relaxes the RbCC smooth muscle, at least in part, through a blockade of calcium influx or its function.

Chuanxiongzine relaxes isolated corpus cavernosum strips and raises intracavernous pressure in rabbits

“…Then it was immediately immersed in an organ chamber containing fresh 4 1C Krebs solution and the corpus cavernosum tissue was carefully dissected away from the surrounding tunica. 27,28 Three to four cavernosal strips of approximately equal size (2 Â 2 Â 8 mm) were obtained from each penis and were prepared for organ bath studies separately. Each cavernosal strip was tied with silk in one organ chamber with one end fixed to a tissue holder and the other secured to a force transducer.…”

Yohimbine relaxes the human corpus cavernosum through a non-adrenergic mechanism involving the activation of K+ATP-dependent channels

“…24 The current findings offer new perspectives on the mechanisms of yohimbine-induced relaxation. In spite of its long history in the treatment of erectile dysfunction, 4 little is known about the non-adrenergic, non-cholinergic pathways involved in yohimbine-induced relaxation, and controlled studies have only been undertaken for the past few years.…”

Aspidosperma Terpenoid Alkaloids — Biosynthetic Origin, Chemical Synthesis and Importance

“…It was observed that administration of a fraction rich in alkaloids obtained from the root bark of A. ulei exerted pro-erectile effect in rats and suggested a mechanism of action via blocking presynaptic α2-adrenergic receptors, the activation of the dopaminergic system and release of nitric oxide [114]. When the same fraction was tested in corpus cavernosum penis obtained from rabbit, its ability to cause relaxation was observed and the proposed mechanism blocking the influx of calcium into the cells [115]. In assay using α-adrenergic receptors isolated from human penis, it was shown that the crude extract and four fractions obtained from the bark of A. quebracho-blanco were able to block them, and the magnitude of interaction directly proportional to the content of the alkaloid yohimbine [116].…”