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Perfusion to exercising skeletal muscle is regulated to match O2 delivery to the O2 demand, but this regulation might be compromised during or approaching maximal whole-body exercise as muscle blood flow for a given work rate is blunted. Whether muscle perfusion is restricted when there is an extreme metabolic stimulus to vasodilate during supramaximal exercise remains unknown. To examine the regulatory limits of systemic and muscle perfusion in exercising humans, we measured systemic and leg haemodynamics, O2 transport, and , and estimated non-locomotor tissue perfusion during constant load supramaximal cycling (498 ± 16 W; 110% of peak power; mean ±s.e.m.) in addition to both incremental cycling and knee-extensor exercise to exhaustion in 13 trained males. During supramaximal cycling, cardiac output ( ), leg blood flow (LBF), and systemic and leg O2 delivery and reached peak values after 60–90 s and thereafter levelled off at values similar to or ∼6% ( P < 0.05) below maximal cycling, while upper body blood flow remained unchanged (∼5.5 l min−1). In contrast, and LBF increased linearly until exhaustion during one-legged knee-extensor exercise accompanying increases in non-locomotor tissue blood flow to ∼12 l min−1. At exhaustion during cycling compared to knee-extensor exercise, , LBF, leg vascular conductance, leg O2 delivery and leg for a given power were reduced by 32–47% ( P < 0.05). In conclusion, locomotor skeletal muscle perfusion is restricted during maximal and supramaximal whole–body exercise in association with a plateau in and limb vascular conductance. These observations suggest that limits of cardiac function and muscle vasoconstriction underlie the inability of the circulatory system to meet the increasing metabolic demand of skeletal muscles and other tissues during whole-body exercise. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of injected darbepoetin [novel erythropoietin stimulating protein (NESP)] on the density of three erythrocyte membrane transport proteins: the lactate-H+ cotransporter (monocarboxylate transporter 1), the chloride/bicarbonate exchanger 1 (anion exchanger 1), and the water channel aquaporin 1. Thirteen subjects were injected with NESP once a week for 4 wk. Blood samples were obtained before, during, and after the injection period, and the erythrocyte transport proteins were determined by Western blotting. The NESP injections induced a transient increase in hematocrit, red cell volume, and reticulocyte fraction. The density of aquaporin 1 protein was higher (maximal increase +59%) (P < 0.01) during the injection period compared with the preinjection value and lower (P < 0.01) after the injection period. The density of anion exchanger 1 protein was higher (maximal increase + 15%) (P < 0.05) during the injection period compared with the preinjection value and tended (P 0.06) to be lower after the injection period than before the injection period. The density of the erythrocyte monocarboxylate transporter 1 protein was higher (maximal increase +43%) (P < 0.05) during the injection period than in the preinjection period. Age separation experiments using self-creating Percoll gradients demonstrated a higher density of membrane transport proteins in young red blood cells. These data suggest that the NESP-induced increase in membrane transport proteins is caused by a higher fraction of newly formed erythrocytes (and reticulocytes), which have a higher density of membrane transport proteins. However, increased incorporation of membrane proteins during erythrocyte formation may also be involved. We suggest that NESP improves the quality of erythrocyte membrane transport through these mechanisms. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Testing for Recombinant Human Erythropoietin in Urine: Problems Associated With Current Anti-Doping Testing."

A letter to the editor is presented in response to the article "Testing for recombinant human erythropoietin (rHuEpo)," by J. R. Delanghe and M. J. Joyner in the June 26, 2008 issue.

Introduction: Marked changes in different blood variables, e.g. hemoglobin concentration ([Hb]) and hematocrit (Hct), are indications of blood manipulation. Blood sampling and the development of individual, longitudinal blood profiles have therefore been implemented in doping control in different sports federations., Materials and Methods: During the Tour de France 2007, 7 riders were randomly tested on 3 different occasions; the day before the prologue, and 12 and 19 days after the prologue. Blood was drawn into 3 mL EDTA covered tubes and kept at 4 degrees Celsius. They were analyzed within 24 hours on a Sysmex R-500., Results: [Hb] and Hct were significantly lower on day 12 (p = 0.005) and day 19 (p < 0.001) compared to baseline. All 7 riders had lower [Hb] and Hct on day 19 compared to baseline, while this was the case in 6 out of 7 riders already on day 12. The [Hb] and Hct were 11.5% and 12.1% lower on day 19 compared to baseline., Conclusion: We observed significant decreases in [Hb] and Hct in 7 riders during Tour de France 2007. Whether or not this is due to decrease in hemoglobin mass or hemodilution, or the latter solely, increases in [Hb] and Hct during prolonged stage racing seem unphysiological and should therefore lead to further examination of the rider.