The role of the seven crude drug components in the sleep-promoting effect of Yokukansan.

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan is a traditional Japanese "Kampo" medicine derived from Yi-Gan San in traditional Chinese medicine. Many studies have been published on its effects and mechanisms. In this study, we focused on the sleep-promoting effects of Yokukansan.

AIM OF THE STUDY

Yokukansan composes of seven crude drugs: Uncaria Hook, Bupleurm Root, Cnidium Rhizome, Japanese Angelica Root, Poria Sclerotium, Atractylodes Lancea Rhizome, and Glycyrrhiza. Although each has distinctive effects in isolation, they combine to work as a sleep aid in the Yokukansan formula. We examined the roles of the seven crude drug components in the sleep-promoting effect of Yokukansan.

MATERIAL AND METHODS

In this study, we used an easy in vivo assay method which we developed previously to screen sleeping substances using thermography. This assay method focuses on the decrease in skin temperature of mice during sleep inducement.

RESULTS

By administering the crude drug components of Yokukansan one at a time, it was possible to separate them into two groups: those that caused a decrease in body temperature (Uncaria Hook, Bupleurm Root, Cnidium rhizome, and Japanese Angelica root) and those that did not (Poria Sclerotium, Atractylodes Lancea Rhizome, and Glycyrrhiza). Accordingly, it was thought that the crude drugs causing a drop in body temperature were responsible for promoting sleep, while those in the other group would have no such effect in isolation. To investigate whether the crude drugs that did not cause a decrease in body temperature might be unnecessary for the sleep-promoting effect of Yokukansan, a number of decoctions were prepared using only six of the seven crude drug components, excluding a different crude drug in each case. Results showed that when any of the three components (Poria Sclerotium, Atractylodes Lancea Rhizome, or Glycyrrhiza) of Yokukansan that had no effect on body temperature in isolation were removed from Yokukansan, the resulting extract no longer had any of Yokukansan's sleep-promoting effects. This result suggested that these three crude drug components were involved indirectly in the activity of Yokukansan, by supporting other crude drugs. The interactions of the three supporting crude drugs were then examined further. As a result, a combination of Poria Sclerotium, Atractylodes Lancea Rhizome, and Glycyrrhiza was found to cause a decrease in body temperature, even though none of the three crude drugs had this effect in isolation. When an extract prepared by infusing the three crude drugs together was tested alongside extracts made by infusing the three crude drugs separately, the latter showed no effect and there were differences between the two in constituent analysis by HPLC. These results indicate that some reactions may occur during extraction.

CONCLUSIONS

Results of this study show that all crude drug components of Yokukansan contribute to its sleep-promoting effects. This is the first report to show the role of the seven clude drug components in the sleep-inducing effects of Yokukansan.