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African Americans Show Alterations in Endogenous Pain Regulatory Mechanisms and Reduced Pain Tolerance to Experimental Pain Procedures

From the Departments of Psychiatry (M.B.M., K.C.L., J.M.F., S.S.G.), Psychology (M.B.M.), and Dentistry (W.M.), University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.

Address correspondence and reprint requests to Susan S. Girdler, PhD, University of North Carolina at Chapel Hill, CB #7175, Medical Research Building A, Chapel Hill, NC 27599-7175. E-mail: susan_girdler{at}med.unc.edu

Objectives: To examine ethnic differences in pain sensitivity and relationship of pain tolerance to blood pressure and neuroendocrine factors.

Methods: Fifty-one African Americans (24 men, 27 women) and 55 people from other ethnic groups (primarily Caucasian; 26 men, 29 women) were tested twice for pain sensitivity to tourniquet ischemia, thermal heat, and cold pressor tests, once following mental stress and once following rest control. Resting and stress-induced blood pressure (BP), plasma norepinephrine (NE), and cortisol were assessed.

Results: In response to all three pain tests, African Americans had lower pain tolerance relative to Caucasian/Others after both rest and stress. Only the non–African American group showed the expected inverse relationship between BP and pain sensitivity. African Americans had lower cortisol concentrations at rest and stress and showed blunted NE and systolic BP responses to stress. Only in Caucasians/Others was the relationship seen between higher stress-induced BP, cortisol, and NE levels and greater pain tolerance.

Conclusions: The results suggest that there are alterations in endogenous pain regulatory mechanisms involving BP, cortisol, and NE in African Americans. Such dysregulation may contribute to the greater rate of clinical pain symptoms they experience. It is hypothesized that greater chronic stress in African Americans may be a contributing factor to the alterations in pain regulation.

Key Words: African Americans • pain sensitivity • blood pressure • norepinephrine • cortisol

Abbreviations: ANOVA = analysis of variance; BP = blood pressure; NE = norepinephrine; SBP = systolic blood pressure; SIA = stress-induced analgesia; TSST = Trier Social Stress Test; LC = locus coeruleus.