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Saw palmetto extracts potently and noncompetitively inhibit human α 1 ‐adrenoceptors in vitro
Author(s) -
Goepel Mark,
Hecker Ulrich,
Krege Susanne,
Rübben Herbert,
Michel Martin C.
Publication year - 1999
Publication title -
the prostate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.295
H-Index - 123
eISSN - 1097-0045
pISSN - 0270-4137
DOI - 10.1002/(sici)1097-0045(19990215)38:3<208::aid-pros5>3.0.co;2-4
Subject(s) - prazosin , pharmacology , antagonism , in vitro , phenylephrine , receptor , inositol phosphate , chemistry , agonist , bioavailability , medicine , endocrinology , inositol , antagonist , biochemistry , blood pressure
BACKGROUND We wanted to test whether phytotherapeutic agents used in the treatment of lower urinary tract symptoms have α 1 ‐adrenoceptor antagonistic properties in vitro. METHODS Preparations of β‐sitosterol and extracts of stinging nettle, medicinal pumpkin, and saw palmetto were obtained from several pharmaceutical companies. They were tested for their ability to inhibit [ 3 H]tamsulosin binding to human prostatic α 1 ‐adrenoceptors and [ 3 H]prazosin binding to cloned human α 1A ‐ and α 1B ‐adrenoceptors. Inhibition of phenylephrine‐stimulated [ 3 H]inositol phosphate formation by cloned receptors was also investigated. RESULTS Up to the highest concentration which could be tested, preparations of β‐sitosterol, stinging nettle, and medicinal pumpkin were without consistent inhibitory effect in all assays. In contrast, all tested saw palmetto extracts inhibited radioligand binding to human α 1 ‐adrenoceptors and agonist‐induced [ 3 H]inositol phosphate formation. Saturation binding experiments in the presence of a single saw palmetto extract concentration indicated a noncompetitive antagonism. The relationship between active concentrations in vitro and recommended therapeutic doses for the saw palmetto extracts was slightly lower than that for several chemically defined α 1 ‐adrenoceptor antagonists. CONCLUSIONS Saw palmetto extracts have α 1 ‐adrenoceptor‐inhibitory properties. If bioavailability and other pharmacokinetic properties of these ingredients are similar to those of the chemically defined α 1 ‐adrenoceptor antagonists, α 1 ‐adrenoceptor antagonism might be involved in the therapeutic effects of these extracts in patients with lower urinary tract symptoms suggestive of benign prostatic obstruction. Prostate 38:208–215, 1999. © 1999 Wiley‐Liss, Inc.