The effects of resiniferatoxin in an experimental rat thoracotomy model.
BACKGROUND
Chronic pain after thoracotomy has been reproduced in a rat model that allows investigation of drugs that might reduce the incidence of allodynia after thoracotomy. Previous studies suggest that morphine, clonidine, neostigmine, gabapentin, and bupivacaine reduce the incidence of allodynia in the rat postthoracotomy pain model. One purpose of this study was to test whether intercostal injection of resiniferatoxin (RTX) decreased the amount of allodynia in an animal model of chronic postthoracotomy pain. We also tested whether RTX induced a transient mechanical hyperalgesic response in uninjured animals.


METHODS
Male Sprague-Dawley rats were anesthetized, and the right fourth and fifth ribs were surgically exposed. The pleura was opened, and the ribs were retracted. Intercostal RTX 0.8 or 8 microg was injected in animals that developed allodynia after surgery; a control group underwent rib retraction and received vehicle only. An additional group of uninjured animals received RTX. Rats were tested for mechanical allodynia at a predetermined area around the incision site for 3 wk.


RESULTS
Allodynia developed in 42% of the animals that underwent thoracotomy. A transient hyperalgesic response was noted in the uninjured group that underwent drug injections. Intercostal RTX did not modify the course of allodynia in injured rats.


CONCLUSIONS
The current results suggest that intercostal RTX causes a transient hyperalgesic response in uninjured animals and is ineffective in reducing the mechanical allodynia after thoracotomy.
Shin
Jin-Woo
JW
Department of Anesthesiology and Pain Medicine, College of Medicine, University of Ulsan, Asan Medical Center, Seoul, South Korea.
Pancaro
Carlo
C
Wang
Chi Fei
CF
Gerner
Peter
P
D000818:Animals; D004224:Diterpenes / Q000008:administration & dosage / Q000627:therapeutic use*; D006930:Hyperalgesia / Q000139:chemically induced; D007267:Injections; D007367:Intercostal Nerves; D008297:Male; D009407:Nerve Block; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D010149:Postoperative Pain / Q000188:drug therapy*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013908:Thoracotomy
D004224:Diterpenes; C024353:resiniferatoxin