Changes in spinal iron content during remifentanil-induced hyperalgesia in a rat model of incisional pain

Abstract

Objective To evaluate the changes in the spinal iron content during remifentanil-induced hyperalgesia in a rat model of incisional pain. Methods Thirty-two pathogen-free adult male Sprague-Dawley rats, weighing 240-260 g, were randomly divided into 4 groups (n=8 each)using a random number table: control group (group C), incisional pain group (group I), remifentanil group (group R), and incisional pain + remifentanil group (group I+ R). In I and I+ R groups, a 1 cm longitudinal incision was made in the plantar surface of left hindpaw in sevoflurane-anesthetized rats.Normal saline was infused at a rate of 0.1 ml·kg-1·min-1 for 60 min via the caudal vein in C and I groups.Remifentanil was infused at a rate of 1.0 μg·kg-1·min-1 for 60 min via the caudal vein in R and I+ R groups.At 24 h before intravenous infusion and 6, 24 and 48 h after the end of infusion (T0-3), the mechanical paw withdrawal threshold (MWT)and thermal paw withdrawal latency (TWL)were measured.All the rats were sacrificed after the last measurement of pain thresholds, and the L4-6 segments of the spinal cord were removed for determination of iron content using the Perl′s iron staining and atomic absorption spectrophotometer. Results Compared with group C, the MWT was significantly decreased, and the TWL was significantly shortened at T1-3, and the iron content was significantly increased in I, R and I+ R groups (P<0.05). Compared with I and R groups, the MWT was significantly decreased, and the TWL was significantly shortened at T1-3, and the iron content was significantly increased in group I+ R (P<0.05). Conclusion The development of remifentanil-induced hyperalgesia is probably related to increased spinal iron content in a rat model of incisional pain. Key words: Piperidines; Hyperalgesia; Iron; Spinal cord