Bone blood flow and metabolism in humans: Effect of muscular exercise and other physiological perturbations

Abstract

Human bone blood flow and metabolism during physical exercise remains poorly characterized. In the present study we measured femoral bone blood flow and glucose uptake in young healthy subjects by positron emission tomography in three separate protocols. In 6 women, blood flow was measured in femoral bone at rest and during one-leg intermittent isometric exercise with increasing exercise intensities. In 9 men, blood flow in the femur was determined at rest and during dynamic one-leg exercise and two other physiological perturbations: moderate systemic hypoxia (14 O 2 ) at rest and during exercise, and during intrafemoral infusion of high-dose adenosine. Bone glucose uptake was measured at rest and during dynamic one-leg exercise in 5 men. The results indicate that isometric exercise increased femoral bone blood flow from rest (1.8 AE 0.6 mL/100 g/min) to low intensity exercise (4.1 AE 1.5 mL/100 g/min, p ¼ 0.01), but blood flow did not increase further with increasing intensity. Resting femoral bone blood flow in men was similar to that of women and dynamic one-leg exercise increased it to 4.2 AE 1.2 mL/100 g/min, p < 0.001. Breathing of hypoxic air did not change femoral bone blood flow at rest or during exercise, but intra-arterial infusion of adenosine during resting conditions increased bone blood flow to 5.7 AE 2.4 mL/100 g/min, to the level of moderate-intensity dynamic exercise. Dynamic one-leg exercise increased femoral bone glucose uptake 4.7-fold compared to resting contralateral leg. In conclusion, resting femoral bone blood flow increases by physical exercise, but appears to level off with increasing exercise intensities. Moreover, although moderate systemic hypoxia does not change bone blood flow at rest or during exercise, intra-arterially administered adenosine during resting conditions is capable of markedly enhancing bone blood flow in humans. Finally, bone glucose uptake also increases substantially in response to exercise. ß

The Circulatory and Metabolic Responses to Hypoxia in Humans – With Special Reference to Adipose Tissue Physiology and Obesity

“…On the other hand, it is also plausible that the activation of vasoconstriction by arterial chemoreceptors predominates over a local hypoxic vasodilation in adipose tissue in humans. In this regard, adipose tissue appears to be similar to bone (39). However, increased blood flow in response to systemic hypoxia has been documented in human skin (40).…”

Inhibition of α-adrenergic tone disturbs the distribution of blood flow in the exercising human limb

“…medialis (VM) and vastus lateralis (VL)], and from the posterior hamstring muscles of the thigh. Also blood flow in adjacent bone and adipose tissue were determined as previously described (16,17,19). The data analysis was performed using standard models (24) and methods (41).…”

Dynamic Bone Imaging with99mTc-Labeled Diphosphonates and18F-NaF: Mechanisms and Applications

“…The mean vertebral blood flow (K 1 ) as measured by 15 O-H 2 O was 0.145 6 0.047 mL/(minÁcm 3 ) using a 1-tissue-compartment model. Under isometric lowintensity exercise, bone blood flow increases 2.3-fold in humans (16). At typical flow rates in bone, 15 O-H 2 O is a freely diffusible tracer; thus, its extraction into tissue approaches 100% in a single capillary passage (17).…”