Background: Pain accompanying various diseases as well as invasion and postoperative pain reduce immune activities, and affect the prognosis of diseases and recovery after surgery (metastasis and relapse). While, some anesthetics and synthetic narcotics used to reduce pain are reported to suppress immune activities depending on the kind of medication and the dosing strategy. However, it is not clear how the single use of narcotics affects the immune activity at the acute stage of severe inflammatory pain. This study is undertaken to examine the effect of a single administration of morphine on the splenic NK cell activity in the acute inflammatory pain model rats.
Methods: Rats received a 50 microl s.c. injection of 4% formaldehyde into the plantar surface of the right hindpaw. The spleen was removed 2 hours later and the splenic NK-cell activity was measured by 51Cr release assay.
Results: Acute pain significantly reduced the splenic NK cell activity, but the single administration of morphine suppressed its reduction.
Conclusions: It was indicated that the single administration of morphine could suppress the reduction of the systemic immune activity caused by acute inflammatory pain.