Endogenous opioid tone in patients with rheumatoid arthritis

We have previously shown that there is deficient hypothalamic-pituitary-adrenal (HPA) responsiveness in rheumatoid arthritis (RA) patients. The basis for this deficient response is not known. The purpose of the project was to investigate whether the defective HPA response in RA patients is the result of increased endogenous opioid tone secondary to chronic pain which can suppress corticotrophin-releasing hormone (CRH) production. We conducted a double-blind placebo-controlled cross-over trial to study the effect of the opiate antagonist, naloxone, on psychometric function together with plasma adrenocorticotrophic hormone (ACTH), cortisol and prolactin. Seven RA patients with active and established disease and eight healthy controls were studied. Each received either a bolus i.v. infusion of 20 mg naloxone or normal saline. After at least 72 h, they received naloxone if they had previously received normal saline or vice versa. The pain score was statistically significantly higher at baseline in the RA group compared with controls (5.7 +/- 3.25 vs 0.35 +/- 0.21, P < 0.001). No difference was found in the other psychometric assessments throughout the study. Patients receiving normal saline did not show any significant change in cortisol or ACTH. Cortisol and ACTH showed a sharp and significant rise after naloxone treatment in both RA and normal subjects (P < 0.001 and P < 0.01), but no difference was observed between the two groups. The mean prolactin level showed no significant change in both groups after any treatment. We conclude that endogenous opioid tone does not appear to be a major contributor to the HPA defect in RA. However, the number of patients studied was small and this result will require confirmation from larger trials.