Effects of Saw palmetto extract in vitro on receptors and enzymes which are relevant in incontinence

Preparations of saw palmetto (Sabal serrulata Roem. & Schult., Serenoa repens (Bartn) Small.) are widely used in the treatment of benign prostate hyperplasia BPH. Clinical trials have shown that the efficacy of saw palmetto is superior to placebo and as good as 5-alpha-reductase-inhibitors and alpha-blockers. So far several mechanism of action has been postulated which lead to the decrease of symptoms of BPH. This includes inhibition of 5-alpha-reductase, cyclooxygenase, lipoxygenase and alpha₁-receptors.

One of the main symptoms connected to BPH is incontinence. At the time only scarce data is available how saw palmetto extract may affect receptors and enzymes which are known to play an important role in incontinence. Thus we investigated with radioligand binding the influence of an ethanolic saw palmetto extract (Prostasan®; DER 9–12:1; 96% V/V ethanol) on the alpha-1-adrenoreceptor, the muscarnic receptors M1, M2 and M3, the nicotinic acetylcholine receptor, and the serotonin and norepinephrine transporter.

The extract showed only a marginal binding affinity to the alpha-1-adrenoreceptor and to the muscarinic receptors M1 and M2 and almost no inhibition of the nicotinic acetylcholine receptor. Interestingly, the extract seemed to inhibit at pharmacologically relevant concentrations the muscarinic receptor M3 and had a high binding affinity to the serotonin transporter.

Further experiments are warranted to prove these findings which may contribute to a broader understanding of the mechanism of action of saw palmetto in the treatment of BPH.