An extract from the bark of Aspidosperma quebracho blanco binds to human penile alpha-adrenoceptors.
OBJECTIVE
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.


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.
Sperling
Herbert
H
Department of Urology, University of Essen, Essen, Germany.
Lorenz
Annette
A
Krege
Susanne
S
Arndt
Rainer
R
Michel
Martin C
MC
D030009:Aspidosperma; D001667:Binding, Competitive; D046508:Culture Techniques; D004305:Dose-Response Relationship, Drug; D006801:Humans; D008297:Male; D010413:Penis / Q000378:metabolism*; D008517:Phytotherapy; D010936:Plant Extracts / Q000493:pharmacokinetics*; D011869:Radioligand Assay; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D015016:Yohimbine / Q000493:pharmacokinetics
D010936:Plant Extracts; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine