Nitric oxide-mediated vasodilation in human bone

ObjectiveRegulation of blood flow to bone is critical but poorly understood, particularly in humans. This study aims to determine whether nitric oxide (NO), a major regulator of vascular tone to other tissues, contributes also to the regulation of blood flow to bone.MethodsIn young healthy adults (n = 16, 8F, 8M), we characterized NO-mediated vasodilation in the tibia in response to sublingual nitroglycerin and contrasted it to lower leg. Blood flow responses were assessed in supine individuals by continuously measuring tibial total hemoglobin (tHb) via near-infrared spectroscopy and lower leg blood flow (LBF) as popliteal flow velocity via Doppler ultrasound in the same leg.ResultsLBF increased by Delta 9.73 +/- 0.66 cm/s and peaked 4.4 min after NO administration and declined slowly but remained elevated (Delta 3.63 +/- 0.60 cm/s) at 10 min. In contrast, time to peak response was longer and smaller in magnitude in the tibia as tHb increased Delta 2.08 +/- 0.22 mu M and peaked 5.3 min after NO administration and declined quickly but remained elevated (Delta 0.87 +/- 0.22 mu M) at 10 min (p = .01).ConclusionsIn young adults, the tibial vasculature demonstrates robust NO-mediated vasodilation, but tHb is delayed and diminishes faster compared to LBF, predominately reflective of skeletal muscle responses. Thus, NO-mediated vasodilation in bone may be characteristically different from other vascular beds.