Effects of catecholamines on calvarial bone resorption in vitro

Many important diseases in otolaryngology manifest through abnormal bone remodeling or destruction. The mechanisms for such pathological remodeling remain poorly understood. Bone is known to be innervated by norepinephrine-containing sympathetic nerves, and sympathectomy is known to induce bone resorption. The role, however, of norepinephrine as a potential bone-modulatory substance is unknown. Using the calvarial calcium release assay, we conducted the following experiment to evaluate the bone-modulatory activity of norepinephrine, the alpha-agonist octopamine, and the beta-agonist isoproterenol. Each agent was tested at 2 concentrations with and without parathyroid hormone. Norepinephrine was found to have no effect on calcium release. In contrast, octopamine at 10^-8 mol/L exerted a significant stimulatory effect on calcium release, and isoproterenol at 10^-6 mol/L exerted a significant inhibitory effect on parathyroid hormone-induced calcium release. The investigation suggests that a bimodal, concentration-dependent, receptor-specific model for catecholamine-mediated modulation of bone resorption may operate in calvarial bone.