(484) Physical activity and IL-6 related to capsaicin pain in healthy individuals

Abstract

Participation in routine physical activity is associated with reduced clinical pain in chronic pain patients and a reduction in pain sensitivity in healthy participants. Proinflammatory cytokines, such as Interleuelkin-6 (IL-6), are associated with pain sensitivity and consistent exercise has been shown to reduce IL-6 levels. We examined the association between self-reported physical activity level (over a typical week), using the Godin Leisure-Time Exercise Questionnaire, IL-6 reactivity and response to capsaicin pain under saline and naloxone conditions. Naloxone (0.1mg/kg), an opioid antagonist, was utilized to probe endogenous opioid function and examine the effect on pain processing. Twenty-six healthy individuals (13 African American and 13 Non-Hispanic White) with complete data are included in these analyses. Blood was drawn before and after application of 10% topical capsaicin to the dorsum of the non-dominant hand. A thermode maintained a constant temperature of 40°Celsius for 90 minutes and pain ratings were obtained every five minutes. Participants who reported at least 15 minutes of strenuous (e.g., jogging) exercise >3x/week were categorized as high exercisers, and compared to low exercisers (<3x/wk). Analysis of variance (ANOVA), controlling for BMI, indicated a significant effect of physical activity on IL-6 reactivity (p=0.04), such that high exercisers showed reduced inflammatory reactivity to capsaicin pain. Repeated Measures ANOVA, controlling for BMI, race and sex (all factors known to influence pain) revealed a significant drug by time by group interaction (p=0.04) on pain ratings. High exercisers reported greater pain ratings over time in the naloxone drug condition. These results suggest that healthy individuals who report regular, strenuous bouts of exercise have improved endogenous opioid function and lower IL-6 inflammatory reactivity to capsaicin pain. Future studies should explore the effects of exercise in patients with chronic pain and the extent to which this may alter inflammatory responses such as IL-6 and pain perception. Participation in routine physical activity is associated with reduced clinical pain in chronic pain patients and a reduction in pain sensitivity in healthy participants. Proinflammatory cytokines, such as Interleuelkin-6 (IL-6), are associated with pain sensitivity and consistent exercise has been shown to reduce IL-6 levels. We examined the association between self-reported physical activity level (over a typical week), using the Godin Leisure-Time Exercise Questionnaire, IL-6 reactivity and response to capsaicin pain under saline and naloxone conditions. Naloxone (0.1mg/kg), an opioid antagonist, was utilized to probe endogenous opioid function and examine the effect on pain processing. Twenty-six healthy individuals (13 African American and 13 Non-Hispanic White) with complete data are included in these analyses. Blood was drawn before and after application of 10% topical capsaicin to the dorsum of the non-dominant hand. A thermode maintained a constant temperature of 40°Celsius for 90 minutes and pain ratings were obtained every five minutes. Participants who reported at least 15 minutes of strenuous (e.g., jogging) exercise >3x/week were categorized as high exercisers, and compared to low exercisers (<3x/wk). Analysis of variance (ANOVA), controlling for BMI, indicated a significant effect of physical activity on IL-6 reactivity (p=0.04), such that high exercisers showed reduced inflammatory reactivity to capsaicin pain. Repeated Measures ANOVA, controlling for BMI, race and sex (all factors known to influence pain) revealed a significant drug by time by group interaction (p=0.04) on pain ratings. High exercisers reported greater pain ratings over time in the naloxone drug condition. These results suggest that healthy individuals who report regular, strenuous bouts of exercise have improved endogenous opioid function and lower IL-6 inflammatory reactivity to capsaicin pain. Future studies should explore the effects of exercise in patients with chronic pain and the extent to which this may alter inflammatory responses such as IL-6 and pain perception.