Study on the hypnotic effect of rare protopanaxadiol-type and protopanaxatriol-type ginsenosides†
Ginsenosides, as major active components of ginseng, possess various pharmacological activities, including anti-tumor, anti-diabetic and hypotensive effects. However, the sedative and hypnotic effect of ginsenosides and the involved mechanism remain unclear. In the present study, the hypnotic effect of rare protopanaxadiol-type (PD) ginsenosides, consisting of Rg3, Rk1, Rg5, and protopanaxatriol-type (PT) ginsenosides, consisting of Rh1, Rk3, Rh4, was investigated and compared in rodent models through behavioral pharmacology methods. Both rare PD and PT ginsenosides decreased spontaneous locomotion activity in normal mice and reduced sleep latency, and extended sleep duration in pentobarbital-treated mice. Moreover, PD and PT ginsenosides attenuated the insomnia induced by caffeine in mice. These hypnotic effects of PD and PT ginsenosides were potentiated by 5-hydroxytryptophan (5-HTP), a precursor of serotonin, and inhibited by p-chlorophenylalanine (PCPA), a 5-HT synthesis inhibitor. Flumazenil (FLU, a specific gamma aminobutyric acid (GABA) antagonist) also impaired the hypnotic effect of both PD and PT ginsenosides. The aforementioned results indicated that PD and PT ginsenosides exhibit sedative and hypnotic activity, and PT ginsenosides show higher activity than PD ginsenosides at high doses (96 mg kg−1). Furthermore, the bioactivity of these two types of ginsenosides might be mediated via the serotonergic and GABAergic systems.