Hypnotic drugs are commonly used to treat sleeping disorders such as insomnia. Insomnia can be very debilitating to one's life. In fact, a survey conducted by Philippine National Statistics Office (2005) showed that among persons with disabilities, sleeping problems got the most number of respondents with severe difficulty at 4.07%.
Dioscorea hispida Dennst. has been proven to have anti-inflammatory, analgesic, antispasmodic, anti-infectious, antiphlogistic, anticontusion and hemostatic effects (Bureau of Plant and Inductry, 2011; Philippines Medicinal Plants, 2011). A preliminary study conducted by Leano et al (2012) has shown that the aqueous crude extract of nami leaf has sedative effect. This study, however, aims to evaluate and compare the hypnotic effect of aqueous leaf extract (ALE) with 70% v/v methanol leaf extract (MLE) of D. hispida. Furthermore, this study also aims to investigate the dose-dependent response for both methanolic and aqueous leaf extract.
Lastly, this study aims to semi-purify the more potent D. hispida leaf extract (methanolic or aqueous) by determining fraction with the active component for hypnotic effect through bioassay-guided fractionation using BALB/c mice.
Propofol-induced sleeping test (PPIST) was conducted to assess the hypnotic effect of MLE and ALE. PIST is the standard behavioral test for hypnotic activity as by described in the book entitiled "Drug Discovery and Evaluation: Pharmacological Assays". MLE and ALE (2000mg/kg, 1258 mg/kg, 795 mg/kg) was delivered orally then propofol (90 mg/kg) was administered intraperitoneally. The loss and regain of righting reflex was observed as an indicator of start and end of sleep, respectively. The sleep onset (in min) and sleep duration (in min) was recorded. The efficacy of MLE and ALE was compared with standard anxiolytic drug midazolan orally.
Results from One-way ANOVA and Post-Hoc show that ALE at dose 1258 mg/kg and 2000 mg/kg significantly (p<0.05) minimized onset of sleep and maximized duration of sleeping time when administered with propofol. ALE also shows a dose-dependent response in sleep duration.
Semi-purification of ALE was conducted by size-exclusion chromatography using Sephadex LH-20 in 50% v/v Methanol. Reverse-phase thin-layer chromatography profile resulted to three fractions. Propofol-induced sleeping test was conducted and showed no significant hypnotic effect among groups.
In conclusion, these results suggest that the crude aqueous leaf extracts of Dioscorea hispida possess potent hypnotic activities, which supported its therapeutic use for insomnia. However, upon semi-purification, no significant hypnotic effect was observed.