Abstract
Saw palmetto extract (SPE) is approved as a medicine for benign prostatic hyperplasia (BPH) in some European countries, and is also available as a healthy food product in Japan. Numerous pharmacological actions of SPE have been proposed, including 5α-reductase inhibition, and antiandrogenic, antiproliferative, antiinflammatory and antiedema effects. Furthermore, the clinical studies have shown that irritative and obstructive symptoms of BPH are alleviated by SPE. However, none of pharmacological effects of SPE has ever convincingly been shown to be therapeutically relevant in vivo. α1-Adrenoceptor antagonists and muscarinic cholinoceptor antagonists are commonly used in the treatment of lower urinary tract symptoms in patients with BPH and overactive bladder (OAB). Thus, such improvement of voiding symptoms by SPE might be expected to arise from significant antagonism of α1-adrenoceptors and muscarinic cholinoceptors in the lower urinary tract because SPE contains many constituents. The present study was undertaken to clarify pharmacological effects of SPE on urodynamic functions and autonomic receptors in the lower urinary tract. SPE may improve urodynamic symptoms in hyperactive bladders of acetic acid-infused rats by increasing bladder capacity and prolonging the micturition interval. It is notable that hyperactive rather than normal bladder was three-fold more sensitive to SPE. SPE exerted significant binding activities of α1-adrenergic, muscarinic and 1,4-dihydropyridine (DHP) calcium channel antagonist receptors in the rat lower urinary tract. Furthermore, SPE also showed significant binding activities of prostatic α1-adrenergic and bladder muscarinic receptor in humans. Repeated oral administration of SPE showed inhibitory tendency against significant increase of number of α1-adrenergic receptor in testosterone-induced hypertrophied prostates of rats. Moreover, repeated oral administration of SPE did not influence activities of hepatic drug enzymes and blood biochemical parameters in rats. The present study may contribute significantly to the further understanding of pharmacological effects of SPE in the treatment of patients with BPH and OAB.
