Muscarinic and alpha 1-adrenergic receptor binding characteristics of saw palmetto extract in rat lower urinary tract.
OBJECTIVE
To elucidate the in vitro and ex vivo effects of saw palmetto extract (SPE) on autonomic receptors in the rat lower urinary tract.


METHODS
The in vitro binding affinities for alpha 1-adrenergic, muscarinic, and purinergic receptors in the rat prostate and bladder were measured by radioligand binding assays. Rats received vehicle or SPE (0.6 to 60 mg/kg/day) orally for 4 weeks, and alpha 1-adrenergic and muscarinic receptor binding in tissues of these rats were measured.


RESULTS
Saw palmetto extract inhibited specific binding of [3H]prazosin and [N-methyl-3H]scopolamine methyl chloride (NMS) but not alpha, beta-methylene adenosine triphosphate [2,8-(3)H]tetrasodium salt in the rat prostate and bladder. The binding activity of SPE for muscarinic receptors was four times greater than that for alpha 1-adrenergic receptors. Scatchard analysis revealed that SPE significantly reduced the maximal number of binding sites (Bmax) for each radioligand in the prostate and bladder under in vitro condition. Repeated oral administration of SPE to rats brought about significant alteration in Bmax for prostatic [3H]prazosin binding and for bladder [3H]NMS binding. Such alteration by SPE was selective to the receptors in the lower urinary tract.


CONCLUSIONS
Saw palmetto extract exerts significant binding activity on autonomic receptors in the lower urinary tract under in vitro and in vivo conditions.
Suzuki
Mayumi
M
Department of Pharmacokinetics and Pharmacodynamics, School of Pharmaceutical Sciences, University of Shizuoka, Shizuoka, Japan.
Oki
Tomomi
T
Sugiyama
Tomomi
T
Umegaki
Keizo
K
Uchida
Shinya
S
Yamada
Shizuo
S
D000726:Androgen Antagonists / Q000494:pharmacology; D000818:Animals; D066298:In Vitro Techniques; D008297:Male; D023421:Models, Animal; D010936:Plant Extracts / Q000494:pharmacology*; D011467:Prostate / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000187:drug effects*; D011983:Receptors, Purinergic / Q000187:drug effects*; D028024:Serenoa; D001743:Urinary Bladder / Q000187:drug effects*
D000726:Androgen Antagonists; D010936:Plant Extracts; D018340:Receptors, Adrenergic, alpha-1; D011976:Receptors, Muscarinic; D011983:Receptors, Purinergic; C040972:saw palmetto extract