The Analgesic Effects of Intrathecal Clonidine on the Rat Postincisional Model

Kim, Hong Bum; Park, Tae Sik; Lee, Sung Ho

Abstract

BACKGROUND
Clonidine is an alpha2-adrenergic drug used for analgesic effect, reducing sympathetic stimulation and anesthetic requirement. We examined the analgesic effect of clonidine on incisional pain after its intrathecal administration using a rat postincisional model.
METHODS
After an intrathecal (IT) catheter insertion in 20 Spraw Dawley rats, they were divided into two groups; one group (Group S, n = 10) received a saline 20microl injection through an IT catheter, and another (Group C, n = 10) received clonidine 20microgram in 10microl volume followed by another 10microl of saline for washing the catheter. The measurements of the threshold of tactile allodynia (TTA) were performed at 20, 40, 60, 80, 120, 180 and 240 mins after the IT injection. Additionally, 1, 2 and 3 days after the first IT injection, IT injection and the measurements of TTA of pre- and post-injection were repeated. The measurements of TTA were performed in both areas, 5 mm (N-area) and 10 mm (R-area) away from incision by using von Frey hair and up-down method.
RESULTS
TTA (N-area) and TTA (R-area) during 4 hours after IT injection in Group C were greater than those in Group S (P< 0.05). TTA (N-area) of post-injection 2 and 3 days after the first IT injection were greater than those of pre-injection in Group C (P< 0.05), and TTA (R-area) after the IT injection 1, 2 and 3 days after the first IT injection were greater than those of pre-injection in Group C (P< 0.05).
CONCLUSIONS
A single IT injection of clonidine 20microgram had analgesic effects lasting more than 4 hours in the rat postincisional model. Additional IT clonidine could show antiallodynic effects during three days after the first IT clonidine.