VASCULAR ENDOTHELIAL REACTIVITY MEDIATED BY [HbO2]

PURPOSE: The effect of a sedentary lifestyle on endothelial-dependent vasodilation during exercise in young people has not been documented. METHODS: Using the thermal dilution technique we measured muscle blood flow (MBF), a surrogate measure of endothelial function, in 7 recreationally active and 7 sedentary males during submaximal single leg knee-extensor exercise in the conditions of normoxia (N) and carbon monoxide (CO) + hyperoxia. RESULTS: Oxyhemoglobin concentrations [HbO2] were similarly reduced in both groups (∼19.5 to ∼15.8 ml/dl) with the administration of CO. The sedentary subject's dose response to falling HbO2 and their increase in MBF at ∼50% of their maximum work rate was attenuated (+300 ± 98 ml/min) when compared to the active subjects (+1100 ± 494 ml/min). The decrease in [HbO2] resulted in a ∼17% increase in O2 delivery only in the active subjects. A-v HbO2 difference decreased by ∼4.1 ml/dl in the active and ∼3.5 ml/dl in the sedentary subjects during CO + hyperoxia. Leg oxygen consumption in the active and sedentary subjects was not statistically altered by the fall in [HbO2]. CONCLUSION: The compensatory increase in MBF with a decrease in [HbO2] in all subjects supports the role of O2 bound to Hb as a regulator of skeletal MBF and vasodilation during exercise. The attenuated response to this vasodilatory stimulus during exercise in the sedentary subjects documents a decreased endothelial-dependent vascular reactvity, associated with inactivity. Supported by NIH, HL 17731 and DNRF 504–14.