Hypericum perforatum L. Hypericaceae (St. John's wort), has been used since the time of ancient Greece
for its many medicinal properties. Modern usage is still quite diverse and includes
wound healing, kidney and lung ailments, insomnia and depression. This plant has been
known to contain a red pigment, hypericin, and similar compounds, which have been
assumed to be the primary active constituent(s) in this plant genus. A crude Hypericum extract was tested in a battery of 39 in vitro receptor assays, and two enzyme assays. A sample of pure hypericin was also tested.
Hypericin had affinity only for NMDA receptors while the crude extract had significant
receptor affinity for adenosine (nonspecific), GABAA, GABAB, benzodiazepine, inositol triphosphate, and monoamine oxidase (MAO) A and B. With
the exception of GABAA and GABAB, the concentrations of Hypericum exact 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
psychotherapeutic activity. Alternative pharmacologic mechanisms for Hypericum's antidepressant activity are critically reviewed and the possible importance of GABA
receptor binding in the pharmacology of Hypericum is highlighted. Some of these results have been previously reported (Cott, 1995; Cott, 1996; Cott and Misra, 1997).