Extracts of Hypericum perforatum L.
(St John's wort) are now successfully competing for status as a
standard antidepressant therapy. Because of this, great effort has
been devoted to identifying the active antidepressant compounds in
the extract. From a phytochemical point of view, St John's wort is
one of the best-investigated medicinal plants. A series of
bioactive compounds has been detected in the crude material,
namely flavonol derivatives, biflavones, proanthocyanidines,
xanthones, phloroglucinols and naphthodianthrones. Although St
John's wort has been subjected to extensive scientific studies in
the last decade, there are still many open questions about its
pharmacology and mechanism of action. Initial biochemical studies
reported that St John's wort inhibits the
synaptosomal uptake of serotonin, dopamine and noradrenaline
(norepinephrine) with approximately equal affinity. However,
other in vitro binding assays carried out using St John's wort
extract demonstrated significant affinity for adenosine, GABA(A),
GABA(B) and glutamate receptors. In vivo St John's wort extract
leads to a downregulation of beta-adrenergic receptors and an
upregulation of serotonin 5-HT(2) receptors in the rat frontal
cortex and causes changes in neurotransmitter concentrations
in brain areas that are implicated in depression. In studies
using the rat forced swimming test, an animal model of depression, St John's wort
extracts induced a significant reduction of immobility. In other
experimental models of depression, including acute and chronic
forms of escape deficit induced by stressors, St John's wort
extract was shown to protect rats from the consequences of
unavoidable stress. Recent neuroendocrine studies suggest
that St John's wort is involved in the regulation of genes that
control hypothalamic-pituitary-adrenal axis function. With regard
to the antidepressant effects of St John's wort extract, many of
the pharmacological activities appear to be attributable to the
naphthodianthrone hypericin, the phloroglucinol derivative
hyperforin and several flavonoids. This review integrates
new findings of possible mechanisms that may underlie the
antidepressant action of St John's wort and its active
constituents with a large body of existing literature.
Click here to read about the most researched St. John's Wort formulation in America.
Click here to read about other natural antidepressant/emotional mood balancers
