Hypothermic effects of hops are antagonized with the competitive melatonin receptor antagonist luzindole in mice

Hops (Humulus lupulus, Cannabinaceae) has been used in traditional European medicine as a mild sedative for the treatment of anxiety, nervousness, and insomnia. However, there has been little information available about the underlying sleep inducing mechanism of hops. We have investigated the effects of a hops extract on the rectal body temperature in mice. Hops extract (250 mg kg(-1)) significantly decreased body temperature in male BL6/C57J mice (DeltaT -0.75 +/- 0.07 degrees C) 2 h after oral administration. The effects of the plant extract were comparable with melatonin (50 mg kg(-1); DeltaT -0.66 +/- 0.06 degrees C; 2 h after i.p. injection). The hypothermic effects of melatonin and hops extract were antagonized with the competitive melatonin receptor antagonist luzindole. Thus, our data suggests that the hypothermic--and therefore the sleep-inducing--effects of hops extract are possibly mediated through activation of melatonin receptors.