Postoperative pain management is commonly inadequate despite the availability of techniques and drugs that enable safe and effective pain control. To date, caregivers have been motivated to alleviate pain more from a sense of moral duty, than from the belief that pain itself might be harmful. The purpose of this dissertation research was to investigate whether a biological consequence could be demonstrated for inadequate postoperative pain management. Because some pain interventions have been shown to reduce the hormonal stress response to surgery, and because surgery and stress have been shown to suppress immune function, this research explored the possibility that pain intervention decreases surgery-induced immune suppression.

The MADB106 tumor is a mammary adenocarcinoma syngeneic to the inbred Fischer 344 rats used for these studies, and its metastatic development is shown here to be controlled by NK activity in vivo. This tumor was used to assess the effect of surgery on NK cytotoxicity in vitro and on metastatic development in vivo.

The findings of this research demonstrate that rats undergoing a standard abdominal surgery under halothane anesthesia exhibit a profound suppression of NK cytotoxicity and a two-fold increase in the number of pulmonary metastases compared to untreated controls or animals given halothane anesthesia only. The surgery-induced suppression of NK cell activity was associated with enhanced metastatic colonization only at times in which the growth of the MADB106 was shown in other ways (using the selective NK antibody mAb 3.2.3) to be controlled by NK cell activity. Further, this research demonstrates that analgesic doses of morphine attenuate the surgery-induced enhanced metastatic growth. This finding suggests that pain does indeed play a role in mediating surgery-induced enhanced metastasis. If similar relationships among pain, stress, and metastasis occur in humans, then pain control must be considered a vital component of postoperative care.