Abstract

Introduction: Plants are one of the most important sources of medicines and have been considered by traditional medicine researchers. Most pain medications have side effects, nowadays, and it seems essential to find new analgesics with limited side effects.

Objective: The aim of this study was to evaluate the analgesic effect of Humulus lupulus (hops) leaf on pain in rats.

Materials and Methods: In this experimental study, male NMRI rats were divided into 18 groups, 7 in each: control (saline i.p. injection), positive control (morphine 2.5 mg.kg, s.c.), and hops extract groups (10, 25, 50 & 100 mg.kg, i.p.). LD50 of hops leaf hydro-alcoholic extract was calculated. Then, Tail flick, acute and chronic phases of formalin and writhing tests (6 groups each test) were used to assess pain. The results were analyzed using one-way ANOVA, followed by post hoc Tukey test. P<0.05 was chosen as the significance level.

Results: In the tail flick test, there was no difference between hops extract groups and controls. In the formalin test, pain was reduced in both acute and chronic phases by the extract (10, 25, 50 & 100 mg.kg) significantly (P<0.001). In writhing test, the extract reduced the number of abdominal contractions in comparison with control group significantly (P<0.001). Pain was significantly reduced by morphine in all tests (P<0.001).

Conclusion: Our results showed the antinociceptive effect of hops leaf Hydro-alcoholic extract after i.p. injection.