Experimental Study on Antagonism of Intrathecal Clonidine by Naloxone in Rat

Kang, Soon Hwan; Kwon, Jae Young; Kim, Hae Kyu; Baik, Seong Wan; Kim, Inn Se; Chung, Kyoo Sub

Abstract

BACKGROUND: Clonidine depress the surge of sympathetic system outflow via central alpha 2 adrenergic effect. Still on a debate is the receptor relevant to analgesic effect of clonidine.
METHODS
Intrathecal catheter(PE-10, 10 cm in length) was inserted via the atlanto-occipital membrane and the tip of intrathecal catheter was allowed to reach at the lumbar area. At the fifth day after catheter insertion, all experimental animals were ramdomly divided to two groups. Clonidine (5 microgram) in clonidine group and morphine (45 microgram) in morphine group was administered into subarachnoid space 20 minutes before tail-clamping test. Heart rate and blood pressure changes were recorded during the experimental period. Then naloxone was given intravenously 5 minutes after the first tail-clamping test. In 2 minutes after that, the second tail clamping was done.
RESULTS
Results were as follows. First, comparing the highest blood pressure changes before and after administration of naloxone, the elevation of blood pressure was significant after administration of naloxone in morphine group(p<0.05), but not in clonidine group. Second, comparing the change of heart rate, in morphine group there was significant elevation of heart rate before and after administration of naloxone. And comparing the highest elevation of heart rate, morphine group showed significant difference before and after naloxone administration(p<0.05), but not in clonidine group.
CONCLUSIONS
From above results, we assumed that the analgesic effect of clonidine was not related to the opiate receptor.