Purpose: To investigate the active fraction of pomegranate fruit extract and screen it for analgesic activity.

Methods: The analgesic activity of pomegranate ethyl acetate fraction (EtOAc) was examined using three models of pain: writhing, hot tail flick and plantar tests. EtOAc was administered by oral gavage in doses of 100, 150 and 200 mg/kg, p.o., for all the tests and compared to aspirin (100 mg/kg, p.o.) which was used as standard drug. Phytochemical studies of EtOAc were carried out by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection and mass spectrometry (MS).

Results: In the writhing test, the index of pain inhibition (IPI) was 41 % for EtOAc (200 mg/kg, p.o.) and 56 % for aspirin. In the hot tail flick test, EtOAc (200 mg/kg, p.o.) showed analgesia reaching its peak at 60 min with maximum possible analgesia (MPA) of 30.5 %, compared with 43.8 % for aspirin. Plantar test showed that pain was reduced by EtOAc in a dose-dependent manner and compared well with aspirin at 100 mg/kg, p.o., dose. The 200 mg/kg dose showed the highest effect, prolonging withdrawal latency in the left hind paw to 11.9 ± 0.3 compared to aspirin with 13.4 ± 0.2 (p < 0.001). HPLC analysis of EtOAc revealed the presence of gallic acid, ellagic acid and punicalagins A & B. Confirmation of their structures was achieved by mass spectroscopy.

Conclusion: EtOAc has a central and peripheral analgesic effect that is most likely due to the presence of gallic acid and ellagic acid.