Acute pain induces an instant increase in natural killer cell cytotoxicityin humans and this response is abolished by local anaesthesia

We have investigated the effect of pain without tissue injury on natural ki ller (NK) cell activity in peripheral blood in humans and the effect of loc al anaesthesia on the response. Ten subjects were investigated during two s essions. First, self-controlled painful electric stimulation was applied to abdominal skin for 30 min to an intensity of 8 on a visual analogue scale (0-10). Next, the electric intensity profile was reproduced during local an aesthesia (mepivacaine 10 mg ml(-1) s.c. to a total dose of 2.5 mg kg(-1)). NK cell cytotoxicity was measured using a 4-h Cr-51- release assay against K562 target cells. NK cell activity increased from mean 22 (SEM 4)% (basel ine) to 35 (6)% and 36 (5)% after 15 and 30 min of painful stimulation, res pectively (P<0.02). A simultaneous increase in the number of CD56+ cells in peripheral blood during pain was found. Stimulation after local anaesthesi a did not change either NK cell activity or number. Parallel and significan t increases in concentrations of plasma epinephrine and serum cortisol were observed. These changes were abolished by local anaesthesia. We conclude t hat acute severe pain without tissue injury markedly increased NK cell cyto toxicity. Local anaesthesia completely abolished this immunological and hor monal response.