Responses of Hypothalamic-Pituitary-Adrenal axis to cold pressor stimulation

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Objective : Functional abnormalities of Hypothalamic-Pituitary-Adrenal (HPA) axis have been known implicated in chronic pain conditions (e.g., fibromyalgia). This study evaluated the changes in plasma endogenous opioid, HPA hormones concentration and trigeminal heat pain threshold upon cold pressor (CP) stimulation. Methods : In CP trials, ten healthy males (mean age : 25.3^^+__-1.3yrs) immersed their right hands for 2 minutes in 4℃ cold water. Mock trials were also done without the cold water. Whole blood samples were collected 5 minutes before, during, and 5, 15, 30, 45, 60 minutes after CP and mock stimulation for measuring Corticotropin-Releasing-Factor (CRF), Adrenocorticotropic hormone (ACTH), β-endorphine and cortisol. Whole blood was centrifuged for plasma separation, then frozen (-20℃) for later assay. Plasma CRF, ACTH, β-endorphine and cortisol concentrations were determined using radioimmunoassay techniques. Heat pain thresholds in subjects' right V2 region were simultaneous … More ly recorded 5 minutes before and 5, 30, 60 minutes after CPS using Thermal Sensory Analyzer (Medoc, Israel). Results : Mean plasma ACTH and β-endorphine levels significantly increased 5 minutes after cessation of CP stimulation and returned to the baseline in 60 minutes (p<0.01, One-way repeated measure ANOVA). Mean plasma cortisol levels also increased 30 minutes after cessation of CP stimulation (p<0.01), while no plasma CRF change was detectable (p=0.83). Mean heat pain thresholds did not show statistically significant changes during the experimental time course (p=0.41), since 4 of 10 subjects showed no obvious change in the heat pain thresholds even with the same CP stimulation schedule. Meanwhile, no variables observed in this study showed a significant change in the mock trial. Conclusions : These results suggest that CP stimulation induces progressive increase in plasma endogenous opioid and HPA hormones levels in healthy males, but this acute plasma endogenous opioid increase does not always associate to heat pain threshold responses in V2 skin region. Less