1. ¹Department of Physiology and Pharmacology, Faculty of Medicine, Federal University of Ceará, Fortaleza, CE, Brazil
2. ²Department of Organic and Inorganic Chemistry, Federal University of Ceará, Fortaleza, CE, Brazil
3. ³Institute of Biomedicine, Veterinary College, State University of Ceará, Fortaleza, CE, Brazil

Correspondence: Professor VSN Rao, Department of Physiology and Pharmacology, Faculty of Medicine, Federal University of Ceara, POB: 3157, Fortaleza, CE 60430-270, Brazil. E-mail: vietrao@ufc.br

Received 16 July 2007; Revised 26 October 2007; Accepted 1 November 2007; Published online 29 November 2007.

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 M) or K⁺ 60 mM. F_3–5 (1–300 g ml^{- 1}) relaxed the RbCC strips in a concentration-dependent and reversible manner. The relaxant effect of F_3–5 (100 g ml^{- 1}) on phenylephrine contraction was unaffected in the presence of atropine, N--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 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.