Attenuation of natural killer cell activity during 2-h exercise in individuals with spinal cord injuries

DESIGN: Non-randomized study. OBJECTIVE: To determine natural killer cell cytotoxic activity (NKCA) to 2-h arm ergometer exercise in persons with spinal cord injuries (SCI) and the underlying mechanism of such response. SETTING: University of Occupational and Environmental Health, Japan. METHODS: We examined NKCA response to 2-h arm crank ergometer exercise at 60% of maximum oxygen consumption (VO(2max)) in SCI and able-bodied persons. NKCA and plasma concentrations of prostaglandin E(2) (PGE(2)), adrenaline and cortisol were measured before, during and immediately after the exercise. The study included seven subjects with SCI between Th11 and L4 and six able-bodied persons. RESULTS: NKCA in able-bodied subjects increased (P<0.05) at 60 min of exercise and immediately after the exercise, and remained elevated up to 2 h after exercise. However, NKCA in SCI decreased (P<0.05) immediately after exercise but recovered at 2 h after exercise. Plasma adrenaline in both groups increased significantly (P<0.05) immediately after exercise and returned to baseline level 2 h after the exercise. Plasma cortisol in both groups remained constant throughout the study. In SCI, PGE(2) significantly increased immediately after 2 h exercise and returned to the baseline level 2 h after exercise; however, it remained unchanged during the test in able-bodied subjects. CONCLUSION: Our results suggested that increase of PGE(2) in SCI partially contributes to NKCA.