Function of ß2-Adrenergic Receptors in Chronic Localized Myalgia

Aims: To investigate alteration of ß2-adrenergic receptor (ß2AR) function in chronic localized myalgia subjects by evaluating levels of the ß2AR second messenger, cyclic adenosine monophosphate (cAMP), in mononuclear cells after ßAR-agonist stimulation. Methods: Eleven chronic localized myalgia subjects and 21 matched healthy controls participated in this study. Peripheral blood (30 cc) was drawn from the subjects' anterocubital vein. Mononuclear cells were isolated from the total blood by using the Ficoll-Hypaque gradient technique. Basal and stimulated intracellular cAMP levels were determined by enzyme immunoassay using a commercially available kit. Aliquots of 5 x 10 6 cells were incubated with or without stimulation of the ßAR-agonist isoproterenol for 5 minutes. Five different concentrations of isoproterenol (10-3M to 10-7M) were utilized. cAMP levels in both groups were tested statistically by a 2-way repeated-measures ANOVA with 2 predictors, group difference and isoproterenol concentration difference. As with isoproterenol stimulation, the cAMP responses to forskolin, which activates adenylyl cyclase directly and produces cAMP, bypassing the cell surface receptors were also measured. Results: The basal cAMP levels in both groups (myalgia: 0.33 ± 0.02 pmol/5 x 10 6 cells; control: 0.43 ± 0.10 pmol/5 x 10 6 cells) were almost identical, and isoproterenol-produced cAMP levels increased dose-dependently in both groups. No significant differences in the mean cAMP levels were observed between the groups (P = .909). Significant increases were observed according to the isoproterenol concentration increase (P .0001). The cAMP responses to forskolin stimulation also showed no significant group difference (P = .971). Conclusion: These results suggest that ß2AR function is not different between localized myalgia subjects and healthy individuals. Keywords: localized myalgia, ß2-adrenergic receptor, cAMP, mononuclear cell, isoproterenol