Role of adenosine in regulating the heterogeneity of skeletal muscle blood flow during exercise in humans

Abstract

Evidence from both animal and human studies suggests that adenosine plays a role in the regulation of exercise hyperemia in skeletal muscle. We tested whether adenosine also plays a role in the regulation of blood flow (BF) distribution and heterogeneity among and within quadriceps femoris (QF) muscles during exercise, measured using positron emission tomography. In six healthy young women, BF was measured at rest and then during three incremental low and moderate intermittent isometric one-legged knee-extension exercise intensities without and with theophylline-induced nonselective adenosine receptor blockade. BF heterogeneity within muscles was calculated from 16-mm(3) voxels in BF images and heterogeneity among the muscles from the mean values of the four QF compartments. Mean BF in the whole QF and its four parts increased, and heterogeneity decreased with workload both without and with theophylline (P < 0.001). Adenosine receptor blockade did not have any effect on mean bulk BF or BF heterogeneity among the QF muscles, yet blockade increased within-muscle BF heterogeneity in all four QF muscles (P = 0.03). Taken together, these results show that BF becomes less heterogeneous with increasing exercise intensity in the QF muscle group. Adenosine seems to play a role in muscle BF heterogeneity even in the absence of changes in bulk BF at low and moderate one-leg intermittent isometric exercise intensities.

The Spatial Distribution of Absolute Skeletal Muscle Deoxygenation During Ramp-Incremental Exercise Is Not Influenced by Hypoxia

“…However, whether hypoxia decreases or increases NO remains controversial [3,5]. Exercise intensity is also known to alter blood flow spatial distribution in quadriceps muscles [6], with higher compared to lower power output associated with a more heterogeneous response. This may be related to an altered contribution of various vasoregulatory metabolites at different exercise intensities or in different fibre types, and/or an increased distribution of blood flow towards newly recruited muscle fibres [6].…”

“…Exercise intensity is also known to alter blood flow spatial distribution in quadriceps muscles [6], with higher compared to lower power output associated with a more heterogeneous response. This may be related to an altered contribution of various vasoregulatory metabolites at different exercise intensities or in different fibre types, and/or an increased distribution of blood flow towards newly recruited muscle fibres [6]. This may also help explain why we found no reduction in the spatial heterogeneity of [HHb] during RI exercise: The expected reduction in [HHb] heterogeneity (based on findings from moderate intensity cycling [2]) were offset by an increased heterogeneity during high intensity exercise recruiting poorly perfused muscle regions [6].…”

“…This may be related to an altered contribution of various vasoregulatory metabolites at different exercise intensities or in different fibre types, and/or an increased distribution of blood flow towards newly recruited muscle fibres [6]. This may also help explain why we found no reduction in the spatial heterogeneity of [HHb] during RI exercise: The expected reduction in [HHb] heterogeneity (based on findings from moderate intensity cycling [2]) were offset by an increased heterogeneity during high intensity exercise recruiting poorly perfused muscle regions [6]. Although the CV for [HHb] was not different between FIO2 conditions, it is estimated that, with 7 subjects, we had power to detect an ~3% difference in regional deoxygenation CV.…”

Local heating, but not indirect whole body heating, increases human skeletal muscle blood flow

“…Scanning began simultaneously with the bolus infusion of the tracer and scanning consisted of the following frames; 6 ϫ 5 s, 12 ϫ 10 s and 7 ϫ 30 s. Arterial blood radioactivity was also sampled continuously with a detector during imaging for blood flow quantification. The data analysis was performed using standard models (14) and methods (11)(12)(13)32). Blood flow was analyzed from calf musculature, with specific regions of interest including the soleus and gastrocnemius muscles, but avoided all apparent blood vessels and bone structures ( Fig.…”

Skeletal muscle blood flow and oxygen uptake at rest and during exercise in humans: a pet study with nitric oxide and cyclooxygenase inhibition

“…The data analysis was performed using the standard models (16) and methods (29). Heterogeneity of blood flow (relative dispersion) was calculated as coefficient of variation (SD divided by mean blood flow) of voxel blood flow values within the region of interest as described earlier (14).…”