Correlation between body weight changes and postoperative pain in rats treated with meloxicam or buprenorphine

Abstract

It is essential to identify objective and efficient methods of evaluating postoperative pain in rodents. The authors investigated whether postoperative changes in rates of body weight gain could serve as a measure of the efficacy of meloxicam or buprenorphine analgesia in growing rats. Young adult male Lewis rats underwent general endotracheal anesthesia and thoracotomy and were treated postoperatively for 3 d with saline (no analgesia), buprenorphine (six doses of 0.1 mg per kg) or meloxicam (three doses of 1 mg per kg). The authors evaluated rats' daily growth rates for 5 d after surgery and compared them with baseline (preoperative) growth rates. To discriminate between the effects of postoperative pain and other concurrent physiologic effects associated with anesthesia, thoracotomy or analgesia, the authors evaluated weight changes in multiple control groups. Treatment with buprenorphine in the absence of any other procedure or with anesthesia alone significantly affected rats' body weight. Notably, growth rate was maintained at near normal levels in rats treated postoperatively with meloxicam. These findings suggest that growth rate might serve as an efficient index of postoperative pain after major surgical procedures in young adult rats treated with meloxicam but not in rats treated with buprenorphine.

FIGURE 1

Growth rates over 24-h periods in young adult rats that underwent various manipulations associated with a thoracotomy. For groups D–I, GETA and thoracotomy were carried out on day 0. On days 0 (post-procedure for groups D–I), 1 and 2, rats received injections of saline, buprenorphine or meloxicam. Error bars indicate s.e.m. Horizontal lines indicate a significant difference within a single group when comparing growth rates on two study days (P < 0.05; ANOVA with Bonferroni correction). (a) Rats that did not undergo anesthesia or surgery (groups A, B and C). (b) Rats that underwent GETA with no surgery (groups D, E and F). (c) Rats that underwent GETA and thoracotomy (groups G, H and I).