Nitric oxide inhibitor L-NAME suppresses mechanically induced bone formation in rats.

We hypothesized that nitric oxide may act as an intermediary in the transduction of mechanical loading of bone into a bone formation response. In the present study, 48 rats were divided into the following three treatment groups: control, treatment with N omega-nitro-L-arginine methyl ester (L-NAME; an inhibitor of nitric oxide synthase), and treatment with D-NAME (the less active enantiomer of L-NAME). The rats were subdivided into groups subjected to four-point bending or sham loading of their right tibiae. Bone formation was measured at the midshaft of the loaded and nonloaded (left) tibiae of each rat using histomorphometric methods. The application of four-point bending, but not sham loading, resulted in new bone formation. Treatment with L-NAME reduced the rate of mechanically induced bone formation by 66% compared with the control group. Bone formation rates in nonloaded or sham-loaded limbs were not affected by L-NAME treatment. The results suggest that nitric oxide may play a role in the transduction of a mechanical stimulus into a biological response in bone.