Function of β-adrenergic receptors on mononuclear cells in female patients with fibromyalgia

Objective. To investigate the β-adrenergic receptors (βAR) in patients with chronic fibromyalgia syndrome (FM). These receptors are present on circulating mononuclear cells, and activation of G-protein coupled receptors like βAR leads to an increase in the intracellular level of cyclic aminosine monophosphate (cAMP). Therefore, cAMP levels can be used to indirectly assess the functional status of the receptor. Methods. Eight female patients with FM and 9 matched healthy female controls participated in this study. Blood samples were drawn from subjects' anterocubital vein in the morning. Mononuclear cells were isolated from the whole blood according to Boyüm's method. Basal and stimulated intracellular cAMP levels were determined by enzyme immunoassay. Aliquots of 10⁶ cells were incubated with or without stimulation of β-agonist isoproterenol for 5 min. Two different concentrations of isoproterenol (10^-3 M and 10^-5 M) were utilized. Results. The basal cAMP levels in patients with FM (3.02 ± 0.44 pmol/10⁶ cells) were slightly more elevated (but not statistically different; p = 0.124, Mann-Whitney U test) than that of the control group (2.26 ± 0.39 pmol/10⁶ cells). Proterenol 10^-3 M stimulation significantly increased intracellular cAMP from the basal levels in both groups (FM group, p = 0.008; control group, p = 0.011). However, isoproterenol 10^-5 M did not increase mean intracellular cAMP levels in the FM group (p = 0.74), while a significant increase was observed in the control group (p = 0.012). Conclusion. These preliminary results suggest that diminished βAR function is associated with the chronic FM state.