Bone anabolic responses to mechanical load in vitro involve COX-2 constitutive NOS

Mechanical stimulation is essential for maintaining the homeostasis and architecture of connective tissues including bone. The purpose of our study was to test the importance of several potential signaling intermediates in the anabolic responses of bone to loads applied with a newly developed micromechanical loading device. Tibial bones excised from 7- to 8-day-old CD-1 mice were cyclically loaded at 1 Hz, 1000 μE (microstrain) at a peak load of 100 mN. DNA and protein synthesis were evaluated by measuring the incorporation of ³H-thymidine and ¹⁴C-proline, respectively. The roles of cyclooxygenase (COX) isoforms, nitric oxide synthase (NOS) isoforms, and glutamate receptor-gated Ca²⁺ channeling were examined by incubating the bones in the presence of each of their specific inhibitors. The results indicate that COX-2 and constitutive NOS are important signaling molecules in the anabolic responses of neonatal tibial bone to the micromechanical load in vitro.