Effects of tramadol and buprenorphine on select immunologic factors in a cecal ligation and puncture model

Sepsis research relies on animal models. The models that most closely resemble clinical disease, such as cecal ligation and puncture, require surgery. After surgery, analgesics may not be included in experimental protocols because of concern over effects on inflammatory responses. This often generates animal welfare controversies within institutions; however, there are no scientific studies directly addressing the effects of analgesics on surgical models of sepsis. The purpose of this study was to characterize the effects of opioids on key parameters used in sepsis research.Female ICR mice were divided into four treatment groups (Ringer's lactate solution, high- or low-dose tramadol,buprenorphine) for 3-week mortality studies (n = 12 per treatment). Experimental groups were then repeated, and mice were killed at 12, 24, and 48 h postsurgery for cell counts, differentials, and cytokine levels in blood, peritoneum, and airways. Mortality studies demonstrated no significant differences between controls and any treatment group. However,significant differences were noted between buprenorphine and high-dose tramadol, revealing more and later deaths with tramadol. For comparison of immune parameters, Mann-Whitney U or Student t test was performed, emphasizing comparisons between treatment and control. Although several results were significant, comparisons between control and any treatment group yielded no differences that remained consistently apparent during the observation period. Again,differences were observed between the treatments. The results suggest that judicious and limited use of some analgesics may not dramatically affect the outcome of similarly conducted cecal ligation and puncture studies when compared with those not using analgesics. However, when different analgesics are used, comparisons between studies may be complicated.