An array of clinical studies have demonstrated the effectiveness of valerian as a sedative [15,51,52].
However, despite extensive study and its use for about 2000 years, the basis for this pharmacological ac-
tivity is less clear [42]. Although it had been thought that the sedative activity of valerian was associated
with the valeopotriates, more recent studies have suggested that the sesquiterpenes may play an impor-
tant role [15,19,51]. Valerone and valerenic acid have been shown to block degradation and synaptic re-
uptake of the neurotransmitter GABA, thus increasing its level in the synapse [51,53]. In addition, there
is some evidence that sesquiterpenes may bind to benzodiazepine receptors and potentially exert effects
similar to those of these drugs [e.g., diazepam (Valium)] [12,51]. Nevertheless, the role of sesquiterpenes
in the action of valerian has been questioned because of the relative level of these components in typical
extracts [42].
V. PHYTOMEDICINAL CHEMICAL PRODUCTION IN THE CONTEXT OF
PLANT CHEMICAL ECOLOGYGiven that many phytochemicals that have pharmaceutical effects can play a defensive role in the plants
from which they are produced, it is worthwhile to consider briefly plant secondary product metabolism
in the context of chemical ecology. This has been an area of strong interest over the past 35 years, es-
pecially as it relates to plant-herbivore interactions (Ref. 54 and references therein). Of primary inter-
est would be identifying the factors that could potentially determine the levels and patterns of phy-
tomedicinal chemical production in plants. In this respect, several models have been developed to
rationalize relationships between environmental factors (biotic and abiotic) and plant secondary prod-
uct production.
In models related to “optimal defense theory,” a central concept is that plant defense chemistry (sec-
ondary product metabolism) is expensive from a biochemical standpoint and diverts resources that would
otherwise be utilized for growth and development [55–59]. Hence, plants will utilize chemical defenses
to protect the regions of the plant that will provide the greatest return from an ecological standpoint
[55,58]. This would certainly include reproductive structures as well as storage root structures in peren-
nial plants that are indispensible for plant survival. On the other hand, less critical regions of the plant that
could be more easily replaced would receive less defensive chemistry. In addition, some models associ-
ated with optimal defense theory also consider plant chemical defense to be dependent on the vulnerabil-
ity of particular plants to herbivory over ecological time frames [56]. That is, plants that are more susep-
tible to herbivore attack will have a greater extent of defensive chemistry.
496 BRISKINFigure 8 The sesquiterpenes and iridoids present in root extracts of valerian (Valeriana officinalis).
(Adapted from Ref. 19.)