Reduction in Alpha-Adrenergic Receptor-Mediated Vascular Tone Contributes to Improved Arterial Compliance with Endurance Training

PURPOSE: Regular aerobic exercise improves large artery compliance in middleaged and older humans. However, the underlying mechanisms are unknown. We tested the hypothesis that the improved central arterial compliance with endurance training is mediated by decreased α-adrenergic tone and/or increased endothelial function. METHODS: Seven sedentary healthy adults (61±2 yr) underwent systemic α-adrenergic blockade (phentolamine) and nitric oxide synthase (NOS) inhibition using NG-monomethyl-L-arginine in sequence before and after a 3-month moderate endurance training (walk/jog, 4-5 days/week). Phentolamine was given first to isolate the contribution of nitric oxide to arterial compliance by minimizing reflex suppression of sympathetic tone resulting from systemic NOS inhibition as well as to assess the α-adrenergic receptor-mediated modulation of arterial compliance. RESULTS: Baseline arterial compliance (via simultaneous ultrasound and applanation tonometry on the carotid artery) increased 34±12% after exercise training (P<0.01). When α-adrenergic blockade was performed, arterial compliance increased 37±6% (P<0.01) before the exercise training but did not change significantly after the training. Decreases in arterial compliance from the α-adrenergic blockade to the subsequent additional NOS blockade were not different before and after exercise training. CONCLUSIONS: Our results suggest that the reduction in α-adrenergic receptormediated vascular tone contributes to the improved central arterial compliance with endurance training.