Function of β₂-adrenergic receptors in chronic localized myalgia

Aims: To investigate alteration of β₂-adrenergic receptor (β₂AR) function in chronic localized myalgia subjects by evaluating levels of the β₂AR second messenger, cyclic adenosine monophosphate (cAMP), in mononuclear cells after βAR-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 × 10⁶ cells were incubated with or without stimulation of the βAR-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 × 10⁶ cells; control: 0.43 ± 0.10 pmol/5 × 10⁶ 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 β₂AR function is not different between localized myalgia subjects and healthy individuals.