Pharmacologists unravel the mechanism of action of St. John’s Wort
In the treatment of patients with mild to moderate depression the herbal antidepressant St. John’s Wort displays a therapeutic effect equivalent to that of synthetic psychotropic drugs. This fact has been confirmed beyond doubt in a large number of comparative clinical studies. But how does this effect come about? A team of Swiss pharmacologists at the University of Berne has conducted experiments at the cellular level in a bid to answer this question.
From the development of chemical antidepressants it is known that these act on the sites of transmission of the neuronal messenger substances noradrenaline, serotonin and dopamine. Depending on the substance in question, they increase the release of these neurotransmitters, or they inhibit the breakdown or reuptake of messenger substances in the nerve cell receptors.
Professor Dr. Ulrich Honegger and his team compared the effects of various St. John’s Wort extracts with the biochemical effects of tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs) on isolated brain cells from rats. The effect on messenger substance transport was measured using radiolabelled biogenic amines and quantified by fluorescence microscopy.
The results of the experiments were presented in Munich by Professor Honegger. They demonstrate that St. John’s Wort extracts also produce biochemical changes that are pharmacologically comparable with those attributable to classic synthetic antidepressants of the TCA and SSRI type:
- They inhibit the transport mechanisms of noradrenaline and serotonin in the nerve cells;
- They reduce the density of the beta-adrenoreceptors;
- This effect is displayed only by extracts and not by the isolated pure ingredients of the medicinal plant.
Professor Honegger’s conclusion: “The effective antidepressant principle is the extract as a whole. Its effect is comparable with that of synthetic antidepressants.“
CRNM 15/2005 – 20 December 2005
