Surgery stress has been shown to be associated in rat with decreased natural killer (NK) cell activity and enhancement of
tumor metastasis. We have previously shown that the
analgesic drug tramadol stimulates NK activity both in the rodent and in the human. In the present study, we analyze, in the rat,
tramadol ability to prevent the effect of experimental surgery on NK activity and on the enhancement of metastatic diffusion to the lung of the NK sensitive
tumor model MADB106. The administration of
tramadol (20 and 40 mg/kg) before and after laparatomy significantly blocked the enhancement of lung
metastasis induced by surgery. In contrast, the administration of 10 mg/kg of
morphine was not able to modify this enhancement. The modulation of NK activity seemed to play a central role in the effect of
tramadol on MADB106 cells. In fact, both doses of
tramadol were able to prevent surgery-induced NK activity suppression, while the
drug significantly increased NK activity in normal non-operated animals.
Morphine, that in normal rats significantly decreased NK cytotoxicity, did not prevent surgery-induced immunosuppression. The good
analgesic efficacy of
tramadol combined with its intrinsic immunostimulatory properties suggests that this
analgesic drug can be particularly indicated in the control of peri-operative
pain in
cancer patients.