The effects of the Brazilian herbal medicine Catuama® and each of its plant constituents (Paullinia cupana, Trichilia catigua, Zingiber officinalis and Ptychopetalum olacoides) were investigated on rabbit corpus cavernosum (RbCC) using a bioassay cascade. Catuama® caused short-lived and dose-dependent relaxations (11% ± 7%, 26% ± 5% and 82% ± 9%, at doses of 1, 3 and 10 mg, respectively). Neither the nitric oxide synthesis inhibitor Nω-nitro-L-arginine methyl ester (L-NAME; 10 μM) nor the soluble guanylate cyclase inhibitor ODQ (10 μM) significantly affected the Catuama®-induced relaxations. Similarly, the selective ATP-dependent K+ channel (KATP) blocker glibenclamide (10 μM), the muscarinic receptor antagonist atropine (1 μM) and the voltage-dependent Na+ channel blocker tetrodotoxin (1 μM) all failed to affect significantly the Catuama®-induced relaxations. These results indicate that the relaxations induced by Catuama® involve neither nitric oxide release nor KATP channel activation. The extracts of P. cupana, Z. officinalis and P. olacoides caused short-lived and dose-dependent RbCC relaxations, whereas T. catigua evoked long-lasting relaxations which were occasionally preceded by a brief contractile effect. The extract of P. cupana was the most active in relaxing RbCC strips. The relaxations induced by all extracts were not significantly affected by L-NAME (10 μM). The infusion of ODQ (10 μM) had no significant effect on the P. cupana- and Z. officinalis-induced relaxations but reduced by >50% (p < 0.05) those evoked by P. olacoides and T. catigua. Incubations of RbCC with Catuama® (10 mg/mL for 0.25 to 5 min) caused increases of cAMP levels (143% increase at 5 min of incubation). Incubations of RbCC with P. cupana extract (1mg/mL) increased the cAMP levels by 200% whereas higher doses (10 and 100 mg/mL) caused smaller increases in the nucleotide levels (150% and 89%, respectively). The extracts of Z. officinalis and P. olacoides (same doses) caused smaller increases of the cAMP levels compared with the P. cupana extract, whereas T. catigua (1-100 mg) did not increase the levels of this nucleotide above the basal values. Our results show that of the four extracts assayed, P. cupana was the most effective, indicating that it is the main extract responsible for the relaxing effect of Catuama® on rabbit cavernosal tissue. 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