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

¹Turku PET Centre, Departments of ²Clinical Physiology and Nuclear Medicine, ³Medicine, and ⁴Anesthesia and Intensive Care, University of Turku, Turku, Finland; ⁵IM Sechenov Institute of Evolutionary Physiology and Biochemistry, Russian Academy of Sciences, St. Petersburg, Russian Federation; ⁶Institute of Sports Medicine, Bispebjerg Hospital, Copenhagen, Denmark; ⁷Department of Exercise Science, Concordia University, Montreal, Canada; and ⁸Department of Biomedical Sciences, University of Copenhagen, Copenhagen, Denmark

Submitted 24 May 2007 ; accepted in final form 19 September 2007

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-mm³ 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.

positron emission tomography; perfusion distribution; quadriceps; theophylline