In vitro receptor binding and enzyme inhibition by an extract of Hypericum perforatum

To assess pharmacologic mechanisms of Hypericum perforatum (St. John's wort) as an antidepressant a hypericum extract and its specific constituent hypericin were tested in a battery of 39 in vitro receptor assays and 2 enzyme assays. Hypericin had affinity only for NMDA receptors while the whole extract demonstrated significant affinity for adenosine (nonspecific), GABA(A), GABA(B), benzodiazepine, inositol triphosphate receptors and monoamine oxidase (MAO) A and B. With the exception of GABA(A) and GABA(B) receptors, the concentrations of hypericum extract required for these in vitro activities are unlikely to be attained after oral administration in whole animals or humans. These data are consistent with recent pharmacologic evidence suggesting that other constituents of this plant may be of greater importance for the reported antidepressant activity