(181) Ethnic differences in endogenous pain regulatory function

Abstract

Ethnic differences in the prevalence, severity and impact of a number of clinical pain conditions have been well documented. These differences are mirrored by similar differences in the laboratory, with Black participants reporting enhanced sensitivity to a variety of quantitative sensory testing methods when compared to non-Hispanic Whites. One theory potentially explaining these disparities could be differential functioning of endogenous pain-regulatory systems between groups. We examined the association between self-reported ethnicity and response to capsaicin pain under both saline and naloxone conditions. Naloxone (0.1mg/kg), an opioid antagonist, was employed to probe endogenous opioid function and examine its effect on pain report. Forty healthy, young individuals (20 Black and 20 non-Hispanic White; average age, M=25.4, SD=5.2) participated. A 10% topical capsaicin cream was applied to the dorsum of the non-dominant hand and a thermode was applied, maintaining a constant temperature of 40°Celsius for 90 minutes. Pain ratings were obtained every five minutes, using a 0-100 scale. Capsaicin pain typically increases over approximately 20 to 25 minutes and then plateaus for over one hour. Analyses focused on ratings provided to stimuli between minutes 30 and 90. There were no demographic differences between ethnic groups, and no differences in psychological characteristics (i.e., pain catastrophizing, reactivity and depression; p’s < 0.05). A main effect of drug emerged (p = 0.007), with responses during the naloxone session generally being rated as less intense when compared to the saline session. A drug by ethnicity interaction was also observed (p = 0.03), with Black participants reporting a significant pain reduction in the naloxone condition when compared to non-Hispanic Whites. The findings of this study suggest differences in endogenous pain regulatory function between Black and non-Hispanic Whites. Potential mechanisms for these somewhat counterintuitive findings warrant further investigation. Ethnic differences in the prevalence, severity and impact of a number of clinical pain conditions have been well documented. These differences are mirrored by similar differences in the laboratory, with Black participants reporting enhanced sensitivity to a variety of quantitative sensory testing methods when compared to non-Hispanic Whites. One theory potentially explaining these disparities could be differential functioning of endogenous pain-regulatory systems between groups. We examined the association between self-reported ethnicity and response to capsaicin pain under both saline and naloxone conditions. Naloxone (0.1mg/kg), an opioid antagonist, was employed to probe endogenous opioid function and examine its effect on pain report. Forty healthy, young individuals (20 Black and 20 non-Hispanic White; average age, M=25.4, SD=5.2) participated. A 10% topical capsaicin cream was applied to the dorsum of the non-dominant hand and a thermode was applied, maintaining a constant temperature of 40°Celsius for 90 minutes. Pain ratings were obtained every five minutes, using a 0-100 scale. Capsaicin pain typically increases over approximately 20 to 25 minutes and then plateaus for over one hour. Analyses focused on ratings provided to stimuli between minutes 30 and 90. There were no demographic differences between ethnic groups, and no differences in psychological characteristics (i.e., pain catastrophizing, reactivity and depression; p’s < 0.05). A main effect of drug emerged (p = 0.007), with responses during the naloxone session generally being rated as less intense when compared to the saline session. A drug by ethnicity interaction was also observed (p = 0.03), with Black participants reporting a significant pain reduction in the naloxone condition when compared to non-Hispanic Whites. The findings of this study suggest differences in endogenous pain regulatory function between Black and non-Hispanic Whites. Potential mechanisms for these somewhat counterintuitive findings warrant further investigation.