Related Experiment Video
Updated: Aug 14, 2026

Bladder Smooth Muscle Strip Contractility as a Method to Evaluate Lower Urinary Tract Pharmacology
Published on: August 18, 2014
An extract from the bark of Aspidosperma quebracho blanco binds to human penile alpha-adrenoceptors
Herbert Sperling1, Annette Lorenz, Susanne Krege
1Department of Urology, University of Essen, Essen, Germany.
Purpose:
We determined whether an extract from the bark of the tree Aspidosperma quebracho blanco, which is used as a prescription drug to treat erectile dysfunction in some countries, can bind to human penile alpha1 and alpha2-adrenoceptors, and cloned human alpha-adrenoceptor subtypes.
Materials And Methods:
Competition binding studies were performed with alpha1 and alpha2-adrenoceptors with the extract and 4 subfractions prepared from it using [3H]prazosin (New England Nuclear, Dreieich, Germany) and [3H]RX 821002 (2-methoxy-idazoxam) (Amersham, Braunschweig, Germany) as the radioligands, respectively.
Results:
In a concentration dependent manner the extract inhibited 2-methoxy-idazoxam binding to human penile alpha2-adrenoceptors. Somewhat less potently it inhibited [3H] prazosin binding to penile alpha1-adrenoceptors. The extract also inhibited binding to cloned alpha2-adrenoceptors more potently than to alpha1-adrenoceptors but did not discriminate among subtypes. Subfraction B was more potent than the others for all cloned alpha1-adrenoceptor subtypes and much more potent at all penile and all cloned alpha2-adrenoceptor subtypes. This fraction largely contained yohimbine, whereas the other fractions were devoid of yohimbine. Based on yohimbine competition binding experiments with penile and cloned alpha1 and alpha2-adrenoceptors, it appears that the inhibitory effects of the abstract and its subfractions can largely be explained by its yohimbine content.
Conclusions:
An alpha-adrenoceptor mediated component of the pro-erectile effects of Aspidosperma quebracho blanco bark extract may predominantly be caused by its yohimbine content. The alpha-adrenoceptor independent, pro-erectile effects of the extract could not be determined from this study.
Related Concept Videos
Adrenergic Receptors: ɑ Subtype
Adrenaline ≥ Noradrenaline >> Isoprenaline
α-adrenoceptors are further divided into α1 and α2-adrenoceptors.
α1-Adrenoceptors: These receptors are located postsynaptically on the effector organs and cause constriction of smooth muscle mediated by activation of phospholipase C—inositol-1,4,5-trisphosphate...
Adrenergic Agonists: Chemistry and Structure-Activity Relationship
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...
Adrenergic Antagonists: Chemistry and Classification of ɑ-Receptor Blockers
Nonselective α-blockers: Nonselective α-blockers contain haloalkylamine or imidazoline moieties. Phenoxybenzamine, with a haloalkylamine...
Adrenergic Antagonists: Pharmacological Actions of ɑ-Receptor Blockers
α1-blockers: These drugs inhibit α1-adrenoceptors on smooth muscle cells, resulting in vasodilation. This vasodilation lowers blood pressure, making α1-blockers valuable in treating hypertension. Additionally, α1-blockers effectively address urinary obstruction...
Adrenergic Antagonists: Pharmacological Actions of β-Receptor Blockers
Antihypertensive Drugs: Vasodilators

