Effect of Saw Palmetto Extract on Autonomic Receptors in the Lower Urinary Tract of Rat

Hypothesis / aims of study Phytotherapeutic agents, including Saw palmetto extract (SPE), are popular in many European countries as herbal remedies represent up to 80% of all drugs prescribed for benign prostatic hyperplasia (BPH) and associated lower urinary tract symptoms (LUTS). However, the mechanism of pharmacological action of SPE is not fully elucidated. Animal experiments with SPE have demonstrated antiandrogen activity and inhibition of 5 reductase, the enzyme that converts testosterone to its active metabolite, dihydrotestosterone [1]. Recently, we have demonstrated that SPE alleviates significantly urodynamic symptoms in acetic acid-induced hyperactive rat bladders by increasing bladder capacity and subsequently prolonging the micturition interval. 1-Adrenoceptor antagonists and muscarinic cholinoceptor antagonists are commonly used in the treatment of men with voiding symptoms (urinary obstruction, pollakiuria and urinary incontinence) secondary to BPH. Thus, such improvement of voiding symptoms by SPE might be expected to result from its significant antagonism of autonomic receptors in the lower urinary tract because SPE contains many constituents. In fact, Goepel et al. [2] have shown that SPE has 1-adrenoceptor inhibitory property. Thus, we examined the binding activities of SPE and its crude fractions to several receptors ( 1-adrenoceptors, muscairnic cholinoceptors, 1,4-dihydropyridine calcium channel antagonist receptors and P2X receptors) in the prostate and bladder of rats.