Evaluation of analgesic effects of intrathecal eugenol in male rats

Eugenol, the most important substance of clove plant (Eugenia caryophyllata) extract, has been widely used as a local relief for pain and inflammation in dentistry. To our knowledge, the beginning time and duration time of intrathecal injection of eugenol were not determined. Thus the purpose of this study was to investigate the analyesic effects of intrathecal injection of eugenol regarding the beginning and duration time, using thermal pain method (water: 52ºC) in male rats.

In this experimental study, 51 male Wistar rats, were divided into three groups of eugenol (5, 10 and 15 µl) and three groups of normal saline (5, 10 and 15 µl). Lumbar intrathecal catheters were implanted under anesthesia. Five days later, different volumes of eugenol and normal saline (5, 10 and 15 µl /rat) were administrated intrathecally and the withdrawal tail responses to high temperature (51º C) water (tail immersion) at different times intervals (pre-catheterization, pre-administration, 10, 30, 180, 360, 720, 1440 minutes after eugenol administrations) were evaluated. Data were analyzed using one and two way ANOVA and LSD post hoc tests.

Eugenol induced analgesia dose-dependently. Furthermore, eugenol at higher doses induced longer analgesic effect (P<0.05). Higher doses of eugenol caused long term paralysis and immobility. The beginning time of analgesia was 10 minutes after injection of eugenol and maximum analgesia was seen after 30 minutes (P<0.05(.

The observed analgesic effect of intrathecal eugenol can be helpful in the clinical use at the future.