Acute sympathetic activation blunts the hyperemic and vasodilatory response to passive leg movement in young healthy males

Heightened muscle sympathetic nerve activity (MSNA) contributes to impaired vasodilatory capacity and vascular dysfunction associated with aging and cardiovascular disease. The contribution of elevated MSNA to the vasodilatory response during passive leg movement (PLM) is not fully understood. This study tested the hypothesis that elevated MSNA diminishes the vasodilatory response to PLM in healthy young males (n = 11, 25 ± 2 yr). Post exercise circulatory occlusion (PECO) following 2 min of isometric handgrip (HG) exercise performed at 25% (ExPECO 25%) and 40% (ExPECO 40%) maximum voluntary contraction was used to incrementally engage the metaboreceptors and augment MSNA. Control trials were performed without PECO (ExCON 25% and ExCON 40%) to account for changes due to HG exercise. PLM was performed 2 min after exercise and hemodynamics were assessed. MSNA was recorded by microneurography in the peroneal nerve (n = 8). Measures of MSNA (i.e., burst incidences) increased during ExPECO 25% (+15 ± 5 burst/100 bpm) and ExPECO 40% (+22 ± 4 burst/100 bpm) and returned to pre-HG levels during ExCON trials. Leg vascular conductance (vasodilation) during PLM was reduced by 16% and 44% during ExPECO 25% and ExPECO 40%, respectively. These findings indicate elevated MSNA attenuates the vasodilatory response to PLM and the magnitude of reduction in vasodilation during PLM is graded with the degree of sympathoexcitation.